High Performance Concrete 1991

This guide is a complete revision of the committee document "Guide to Durable Concrete," ACI 201.2R - 77 (Reapproved 1982), which appears in Part 1 of the ACI Manual of Concrete Practice. This new document represents major revisions in a number of areas, which reflect an increase in the knowledge of the numerous factors influencing concrete durability since 1977. In general, separate chapters are devoted to specific types of concrete deterioration. Each chapter contains a discussion of the mechanisms involved and the recommended requirements for individual components of the concrete, quality considerations for concrete mixtures, construction procedures, and influences of the exposure environment, all important considerations to assure concrete durability. Some guidance as to repair techniques is also provided.

3219
Ahmad, S. H. and Barker, R.
"FLEXURAL BEHAVIOR OF REINFORCED HIGH-STRENGTH LIGHTWEIGHT CONCRETE BEAMS"
ACI Structural Journal, Jan-Feb 1991, Vol. 88, No. 1, pp 69-77.

Flexural tests were conducted on six singly reinforced beams. The variables were strength of concrete and the ratio of tensile steel content r as a ratio of the balanced steel content. No compression or lateral reinforcement was used in this study. Test results are presented in terms of load-deformation behavior, ductility indexes, and cracking patterns. It is concluded that to achieve a ductility index of 3, / b should not exceed 0.40 for beams with concrete strengths of 8000 psi or 0.20 for beams with concrete strength of 11,000 psi. The flexural design provisions of the ACI Building Code are found to be adequate to predict the strength of reinforced high-strength concrete beams.

3220
Ahmad, S. H. and Batts, J.
"FLEXURAL BEHAVIOR OF DOUBLY REINFORCED HIGH-STRENGTH LIGHTWEIGHT CONCRETE BEAMS WITH WEB REINFORCEMENT"
ACI Structural Journal, May-Jun 1991, Vol. 88, No. 3, pp 351-358.

This paper develops limited experimental data on the flexural behavior of doubly reinforced high strength lightweight concrete beams with web reinforcement. Flexural tests were conducted on six doubly reinforced beams. The test results are presented in terms of load-deformation behavior, cracking, and ductility indexes. The experimentally obtained load-deflection curves are compared to those predicted analytically, and good comparisons are obtained. Conclusions drawn from the study results are discussed.

3221
Alameddine, F. and Ehsani, M. R.
"HIGH-STRENGTH RC CONNECTIONS SUBJECTED TO INELASTIC CYCLIC LOADING"
Journal of Structural Engineering, Mar 1991, Vol. 117, No. 3, pp 829-850.

This study investigates the influence of key variables on the behavior of corner high-strength reinforced concrete beam-column connections subjected to inelastic cyclic loading. The study investigated the current code requirements for connection design in order to establish whether a revision of these requirements is needed. It is noted that when properly designed, high-strength reinforced concrete connections exhibit ductile hysteretic response. The test results indicate that the joint performance, including strength and ductility, appears to be more influenced by the joint shear stress and the joint confinement level than the level of the concrete compressive strength. These and other study findings are discussed.

3222
Baalbaki, W., Benmokrane, B., Chaallal, O., and Aitcin, P-C.
"INFLUENCE OF COARSE AGGREGATE ON ELASTIC PROPERTIES OF HIGH-PERFORMANCE CONCRETE"
ACI Materials Journal, Sep-Oct 1991, Vol. 88, No. 5, pp 499-503.

The paper reports tests carried out on high-strength concrete made with different types of crushed rocks. These tests highlight the role played by coarse-aggregate through the elastic properties of the parent rock. The results obtained open an opportunity to review the present formulas relating Ec to Fc recommended by some codes.

3223
Bentur, A. and Jaegermann, C.
"EFFECT OF CURING AND COMPOSITION ON THE PROPERTIES OF THE OUTER SKIN OF CONCRETE"
Journal of Materials in Civil Engineering, Nov 1991, Vol. 3, No. 4, pp 252-262.

Work is reported in which the properties and performance of concrete skin were evaluated by means of capillary absorption and carbonation (natural and accelerated) test. The data obtained in three years of exposure tests are described. It is noted that inadequate curing in a hot, dry environment may have only a small detrimental effect on strength but a marked negative influence on the performance of the skin as estimated by carbonation tests. Concrete strength, is therefore an inadequate parameter to evaluate the properties of the skin, and it may even be misleading when used to specify or to provide a measure for quality control when durability is an issue.

3224
Bentz, D. P. and Garboczi, E. J.
"SIMULATION STUDIES OF THE EFFECTS OF MINERAL ADMIXTURES ON THE CEMENT PASTE-AGGREGATE INTERFACIAL ZONE"
ACI Materials Journal, Sep-Oct 1991, Vol. 88, No. 5, pp 518-529.

In concrete, the interfacial zone between cement paste and aggregate plays a critical role in determining mechanical performance. In recent years, high-performance concretes have been produced based on a low water-cement ratio cement paste containing a superplasticizer and silica fume. One of the key benefits of silica fume is its ability to improve the integrity of the interfacial zone in concrete. This paper presents a three-dimensional microstructural model for simulating the interfacial zone in concrete, including the incorporation of inert and pozzolanic mineral admixtures. The model is used to obtain the cementitious-material phase distributions as a function of distance from the aggregate surface to quantitatively characterize the interfacial zone. Pozzolanic admixtures, such as silica fume and fly ash, are found to increase the homogeneity of the interfacial region, with the most important enhancement proposed to be the improved homogeneity of the calcium-silicate-hydrate phase. The effects of mineral admixture particle size and reactivity are also computed via simulations. Simulation results are compared to conventional experimental measurements, such as compressive strength, and scanning electron micrographic investigations of the microstructure of actual cement-based materials.

3225
Berke, N. S.
"CORROSION INHIBITORS IN CONCRETE"
Concrete International, July 1991, Vol. 13, No. 7, pp. 24-27.

Steel-reinforced concrete is one of the most widely used construction materials throughout the world, but corrosion of the reinforcing steel is causing the early failure of structures in environments where concrete is subjected to an ingress of chlorides. Calcium nitrite is a corrosion inhibitor used commercially on a wide scale in the United States, Japan, and Europe. This paper summarizes the results of several recent corrosion studies using calcium nitrite as corrosion inhibitor. The results show that calcium nitrite performs well even in cracked concretes. It is recommended that to prevent steel corrosion in concrete, more should be done than just adding an inhibitor. ACI 201 states that low water-cement ratio and good concrete cover should be employed when chloride exposures are moderate to severe. Calcium nitrite becomes more effective as concrete quality improves.

3226
Bickley, J. A., Ryell, J., Rogers, C., and Hooton, R. D.
"SOME CHARACTERISTICS OF HIGH-STRENGTH STRUCTURAL CONCRETE"
Canadian Journal of Civil Engineering, Oct 1991, Vol. 18, No. 5, pp 885-889.

The 68-story Scotia Plaza tower in Toronto is an outstanding example of the use of concrete technology to achieve high-performance high-strength concrete. Cementitious hydraulic slag, silica fume, and a superplasticizer were combined with CSA type-10 portland cement and high-quality aggregates to produce very workable high-strength concrete. During the course of construction, data were published suggesting the possibility of the strength regression of some silica fume concretes after long exposure to low humidity, the determinations being made on standard test cylinders. Tests were therefore made at ages of 1 year and 2 years on specimens drilled from columns in the structure. This technical note gives details of the laboratory examination and testing of these specimens.

3227
Bijen, J. and van Selst, R.
"EFFECTS OF FLY ASH ON CARBONATION OF CONCRETE WITH PORTLAND BLAST-FURNACE SLAG CEMENT"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 1001-1030. (ACI SP-126)

An investigation has been carried out into the effects of cement replacement by fly ash on the carbonation rate of concrete. The research was mainly devoted to portland blast-furnace slag cement because this cement has a major market share in the Netherlands. It has been concluded that in the case of portland blast-furnace slag cement, replacement up to 25 percent by mass results in a substantially higher carbonation rate while for a similar portland-cement concrete, the difference between concrete with and without replacement is relatively small. A useful relation exists between the carbonation depth after one or two years and compressive strength after 28 days and, even better, after 7 days for each type of cement. This relation might cover all types of cements when the lime content of the binder is involved.

3228
Bilodeau, A., Carette, G. G., Malhotra, V. M., and Langley, W. S.
"INFLUENCE OF CURING AND DRYING ON SALT SCALING RESISTANCE OF FLY ASH CONCRETE"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 201-228. (ACI SP-126)

This paper gives the results of an investigation undertaken to determine the scaling resistance of concrete incorporating fly ash, and discusses factors affecting that resistance. In this investigation a total of 21 air-entrained concrete mixtures were made. Water-to-(cement + fly ash) ratios of 0.35, 0.45, and 0.55 were used, and reference concrete (without fly ash) and concrete incorporating 20 and 30 percent fly ash as replacement by mass for cement were made. Two aggregate types were used in the investigation. Results show that concrete incorporating up to 30 percent fly ash performed satisfactorily under the scaling test with minor exceptions. Extended moist-curing or drying periods did not affect significantly the performance of the reference and fly ash concretes in the scaling test, at least within the periods investigated.

3229
Bulgakova, M. G. and Kaprielov, S. S.
"HIGH STRENGTH SILICA FUME CONTAINING GUNITE FOR REINFORCED CONCRETE STRUCTURES AND PROTECTIVE RECONSTRUCTION COATINGS"
Papers presented at the International Conference on Blended Cements in Construction, held Sep 9-12, 1991 at the University of Sheffield, UK; Ed. by R. N. Swamy; Elsevier Applied Science, London, 1991, pp 492-506.

This paper presents the results of an extensive study on the use of high strength gunite containing silica fume which can be used as a protective or reconstructed layer for reinforced concrete structures. The gunite was made from a mixture of natural silica sand, ordinary portland cement and silica fume. A superplasticizer C-3, based on sulphonated naphthalene formaldehyde compound, was used as a water reducing agent. Up to 20% of the fine grain cement was replaced by silica fume. Tests of short term properties indicated that the silica fume gunite attained a strength of 22.0 MPa after 3 days and continued to increase in strength with time. After 250 days strength had increased to 78 MPa. Other properties assessed included both cube and prism strength; elastic modulus; linear deformation and volume change; transverse strain differential coefficient; upper limit of crack formation; shrinkage; and creep flow. The coefficient of linear thermal expansion and frost resistance were also measured.

3230
Burnett, I.
"SILICA FUME CONCRETE IN MELBOURNE, AUSTRALIA"
Concrete International, Aug 1991, Vol. 13, No. 8, pp 18-24.

Silica fume cannot simply be added to ordinary concrete: to do so is inadequate and in many cases can be quite dangerous. Mixes must be redesigned, and the proportions of stone, sand, and admixtures varied to produce SFC with required performance characteristics. Work to date in Melbourne has clearly demonstrated the excellent performance characteristics of silica fume concrete. The need and market for SFC in Australia is strong. The many possible applications will provide: reduced construction costs; faster construction; different construction methods; production of very high strength concrete; improved resistance to attack by chemicals and aggressive water; reduced reinforcing steel corrosion; improved durability, and improved permeability.

3231
Cabrera, J. G. and Claisse, P. A.
"THE EFFECT OF CURING CONDITIONS ON THE PROPERTIES OF SILICA FUME CONCRETE"
Papers presented at the International Conference on Blended Cements in Construction, held Sep 9-12, 1991 at the University of Sheffield, UK; Ed. by R. N. Swamy; Elsevier Applied Science, London, 1991, pp 293-301.

Two concrete mixes with 20% silica fume and water/cementitious ratios of 0.3 and 0.46 were compared with corresponding ordinary portland cement concrete mixes. The effect of both cold and dry curing on the major engineering properties and the progress of the pozzolanic reaction was measured at ages up to 90 days. The engineering properties measured at 3, 28 and 90 days were as follows: a) the compressive strength of 100mm cubes after curing; b) compressive strength of 100mm cubes after curing and subsequent storage for 1 year; c) modules of rupture in flexure; d) tensile splitting strength of 150mm diameter cylinders; e) static modulus and f1 dynamic modulus by acoustic resonance. The long term effect was evaluated with further measurements after a year. The paper shows that silica fume (SF) which is a highly reactive pozzolanic material is very sensitive to low temperature curing and drying out during curing. This effect is taken into account when designing silica fume concrete for durability and performance.

3232
Chi, W. K.
"NCSU CONCRETE MATERIALS DATABASE"
Department of Civil Engineering, North Carolina State University, Raleigh, NC, 1991, 49 pp. (SHRP-C-UWP-91-501; PB91-153494)

The NCSU Concrete Materials Database Program was designed to collect and organize research data on the mechanical properties of high performance concrete. The program is based on the relational model and was developed using commercial software. It contains a menu system and other user interfaces that guide users with little database knowledge to extract desired data for data analysis. The development of the NCSU Database program represents the first attempt to collect research data in the concrete area. It also demonstrates the feasibility of establishing a general database that encompasses all aspects of concrete properties.

3233
Chi, W. K.
"NCSU CONCRETE MATERIALS DATABASE PROGRAM: USER MANUAL"
Department of Civil Engineering, North Carolina State University, Raleigh, NC, 1991, 81 pp. (SHRP-C/UWP-91-502; PB92-127927)

The NCSU Concrete Materials Database Program organizes research data on the mechanical properties of high performance concrete. The database is based on the relational model and was developed using commercial software. This guide consists of two parts: I - User Manual; II - Reference. The User Manual explains how to query the database and describes how to input and update data. The Reference section provides information concerning separate operations and fields.

3234
Chitla, S. R., Zollinger, D. G., and Macha, R. K.
"EFFECTS OF AIR ENTRAINMENT ON PORTLAND CEMENT CONCRETE"
Research Report No. FHWA/TX-92/1254-1, Texas Transportation Institute, College Station, TX, 1991, 194 pp. (TTI-2-5-91-1254; RR-1254-1; PB93-120855)

Experience in Texas suggests problems may occur in stabilizing the air content of entrained concrete during and after pumping operations. In one instance, normal air entraining dosage rates were significantly exceeded in an effort to maintain the desired amount of air content in the concrete immediately after discharge. It was determined subsequently from hardened samples that the lost air was fully recovered and actually was 50% greater than the desired levels. Several factors have been noted in the literature to affect the level of entrained air in concrete. Factors such as cement content and fineness, coarse aggregate size, amount of fine aggregate, slump, type of admixture, etc., have been identified as factors affecting entrained air content. Preliminary test results indicate an apparent loss of air occurs immediately after discharge from the pump and tends to return after a period of time. This noted variation of air follows a dissolution process suggesting a shifting of the air-void system from smaller bubbles to larger bubbles. A test program is suggested to identify significant factors in this process.

3235
de Almeida, I. R.
"RESISTANCE OF HIGH STRENGTH CONCRETE TO SULFATE ATTACK: SOAKING AND DRYING TEST."
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 1073-1092. (ACI SP-126)

The sulfate resistance of concretes with compressive strengths between 60 and 110 MPa was evaluated. The test comprises several soaking/drying cycles of samples in a Na2SO4. 10H2 O solution, followed by measurement of mass variation and residual compressive strength. Visual inspection and sulfate recovery by distilled water immersion increased the accuracy of test results. Results reveal significant differences compared to the test normally used, involving prolonged immersion. The resistance to sulfate attack depends on concrete porosity and capillary absorption, and not on permeability, because pozzolanic reactions seem to interrupt pore continuity. The reduced w/c ratio obtained with the aid of the super-plasticizer was much more effective than the chemical characteristics related to the presence of mineral admixtures in concrete, as regards its resistance to sulfates.

3236
Detwiler, R. J., Kjellsen, K. O., and Gjorv, O. E.
"RESISTANCE TO CHLORIDE INTRUSION OF CONCRETE CURED AT DIFFERENT TEMPERATURES"
ACI Materials Journal, Jan-Feb 1991, Vol. 88, No. 1, pp 19-24.

This paper describes a preliminary investigation of the ability of concrete to protect against the corrosion of reinforcing steel. Two types of tests measured the rate of chloride diffusion and then an accelerated corrosion test compared the ability of the concrete to protect against the corrosion of reinforcing steel. Both test methods are described. The results of both tests indicate that at a given water-cement ratio, elevated curing temperatures reduce the ability of portland cement concrete to protect against chloride diffusion and the consequent depassivation of reinforcement. This effect is more pronounced at lower water-cement ratios. These findings should be taken into account in the construction of concrete structures for which durability is a concern.

3237
Dhir, R. K., Hewlett, P. C., and Chan, Y. N.
"ASSESSMENT OF CONCRETE DURABILITY BY INTRINSIC PERMEABILITY"
Durability of Building Materials and Components, Proceedings of the Fifth International Conference, held Nov 7-9, 1990, Brighton, UK; Ed. by J. M. Baker, P. J. Nixon, A. J. Majumdar, and H. Davies; E & FN Spon, London, 1991, pp 503-513.

The measurement of the intrinsic permeability of concrete is described. The tests developed are rapid and reliable. It is shown that the intrinsic permeability of concrete can be characterised using the air permeability test. Hydraulic permeability data can also be derived if required. The permeability of concrete in the surface layer (that comprising the cover to reinforcement) is greatly affected by both the water/cement ratio and curing. Concrete quality should not be estimated from strength data alone. The link between measured insitu permeability and estimated durability is the subject of current research.

3238 Dunster, A. M., Kawano, H., and Nixon, P. J.
"THE EFFECT OF SILICA FUME TO REDUCE EXPANSION DUE TO ALKALI-SILICA REACTION IN CONCRETE"
in Durability of Building Materials and Components, Proceedings of the Fifth International Conference, held Nov 7-9, 1990, Brighton, UK; Ed. by J. M. Baker, P. J. Nixon, A. J. Majumdar, and H. Davies; E & FN Spon, London, 1991, pp 193-199.

Concrete prism specimens containing calcined flint were stored in humid conditions at 20 deg C and the influence of silica fume content, proportion of calcined flint, and alkali level on alkali silica reaction (ASR) expansion were investigated. The addition of silica fume reduced both the rate and total amount of expansion due to ASR, and delayed the onset of expansion. Increasing the calcined flint and/or alkali level of otherwise equivalent specimens had the reverse effect.

3239
Durning, T. A. and Hicks, M. C.
"USING MICROSILICA TO INCREASE CONCRETE'S RESISTANCE TO AGGRESSIVE CHEMICALS"
Concrete International, Mar 1991, Vol. 13, No. 3, pp 42-48.

Microsilica, also called silica fume or condensed silica fume, is a material added to concrete to reduce the rate of deterioration of concrete by chemical attack. This article presents the results of a 2-year study of the increase in chemical resistance provided by adding microsilica to concrete. Since acidic solutions and sulfate solutions account for the major portion of the chemical degradation of concrete currently in use, chemical environments of these types were chosen for study. The experimental evidence shows that adding microsilica can increase the resistance of quality concrete to chemical attack by several aggressive chemical environments. The results of the study are presented and discussed.

3240
Ehsani, M. R. and Alameddine, F.
"DESIGN RECOMMENDATIONS FOR TYPE 2 HIGH-STRENGTH REINFORCED CONCRETE CONNECTIONS"
ACI Structural Journal, May-Jun 1991, Vol. 88, No. 3, pp 277-291.

The present recommendations of ACI-ASCE Committee 352 for the design of ductile moment-resistant beam-column connections limit the joint-shear stress to a gamma factor relationship, where the gamma factor is a function of the type of joint and loading condition. Test results of corner connections subjected to inelastic cyclic loading show that when a frame is constructed with high-strength concrete with compressive strength between 8,000 and 14,000 psi, the equation becomes unconservative. In addition, the current recommendations for joint confinement, which were developed for normal strength concrete, cannot be satisfied for high-strength concrete frames. Based on the test results, new requirements for allowable joint-shear stress as well as joint confinement are presented to insure ductile behavior of frames.

3241
Ellis, W. E., Jr., Riggs, E. H., and Butler, W. B.
"COMPARATIVE RESULTS OF UTILIZATION OF FLY ASH, SILICA FUME AND GGBFS IN REDUCING THE CHLORIDE PERMEABILITY OF CONCRETE"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 443-458. (ACI SP-126)

This research project was undertaken to determine the effect on the chloride permeability of concretes of increasing amounts of fly ash in low water/cementitious material ratio concrete, as compared with comparable high quality concretes containing combinations of portland cement, silica fume and ground granulated blast furnace slag. The test method utilized was the Rapid Determination of the Chloride Permeability of Concrete (AASHTO T-277). Fifteen superplasticized concrete mixtures were evaluated for compressive strength at ages of 28 and 56 days, and for chloride permeability at 56 days. The inclusion of fly ash, silica fume, and ground granulated blast furnace slag all significantly reduced the chloride permeability of concrete, as compared with concrete containing portland cement only. Increasing amounts of fly ash generally showed decreased permeability in the tests conducted.

3242
"EVALUATION AND REHABILITATION OF CONCRETE STRUCTURES AND INNOVATIONS IN DESIGN"
Proceedings of ACI International Conference, held Dec 2-6, 1991, Hong Kong; Ed. by V. M. Malhotra, American Concrete Institute, Detroit, MI, 1991, 2 vols. (ACI SP-128)

This 2-volume set of proceedings contains 90 selected papers presented at the conference covering a wide variety of topics addressing evaluation and rehabilitation of concrete structures and design innovations. The topics include: coating materials and technology, non-destructive testings, corrosion protection materials and techniques, applications of shotcrete and fiber reinforced concrete, injection materials and techniques, design code considerations for steel fiber reinforced concrete structures, and many case studies on repair and rehabilitation of deteriorated and/or damaged reinforced concrete structures.

3243
Ezeldin, A. S. and Aitcin, P-C.
"EFFECT OF COARSE AGGREGATE ON THE BEHAVIOR OF NORMAL AND HIGH-STRENGTH CONCRETES"
Cement, Concrete and Aggregates, Winter 1991, Vol. 13, No. 2, pp 121-124.

The results are presented of the experimental investigation to study the effect of 4 coarse aggregates with different characteristics on the compressive strength, flexural strength, and flexural strength/compressive strength ratio of normal- and high-strength concretes. The study investigates the possibility of obtaining a relatively high flexural strength/compressive strength ratio at high compressive strength by using different aggregate types.

3244
Fang, I-K., Horng, M-T., and Poung, S-C.
"SHEAR STRENGTH OF HIGH STRENGTH CONCRETE BEAMS"
IABSE Reports, 1991, Vol. 64, pp 384-385.

This brief article investigates the shear strength of high strength concrete beams with and without stirrups. Thirty three beams, (of which 12 were without stirrups), having compressive strength in the range of 64 to 90 MPa were tested. The following variables were considered: concrete strength; shear span to effective depth ratio (a/d); and the amount of stirrups (Pvfy). The beams were tested by two point loadings symmetric about midspan. The a/d ratio used were 2.0, 2.5, 3.0 and 3.5 respectively. The amount of stirrups designed were 0.5, 0.75 and 1.0 times the estimated inclined shear strength (Vcr). In the analytical study the effectiveness factors of high strength concrete beams were calculated using analyses based on the theory derived by Neilson. Two mix proportions of high strength concrete were used. The first mix had a cement content of 600 kg per cubic metre, providing a compressive strength of up to 70 MPa. In the second mix, 5% of cement by weight was replaced by silica fume to improve the strength. The volumetric ratio of fine to total aggregate was 0.37. The strains of stirrups and longitudinal steels, deflections at midspan and quarter span were monitored throughout the test. The results showed that most of the beams without stirrups failed in shear tension while those with stirrups failed in shear compression. Other results are also presented briefly.

3245
Feldman, R. F. and Beaudoin, J. J.
"PRETREATMENT OF HARDENED HYDRATED CEMENT PASTES FOR MERCURY INTRUSION MEASUREMENTS"
Cement and Concrete Research, Mar-May 1991, Vol. 21, No. 2-3, pp 297-308.

Porosity is one of the major factors controlling durability and strength of hydrated cement products. A measure of pore size distribution of these materials is more definitive and can lead to a basic understanding of many phenomena occurring within the material. An accurate measurement of this is, however, difficult to obtain. Hg intrusion porosimetry to 414 MPa was used in this work to measure the pore size distribution of cement pastes prepared at water/cement ratio of 0.8, 0.6 and 0.45. Specimens were predried before intrusion measurements by several techniques including solvent replacement with methanol or isopropanol, evacuation and/or heating for various periods and conditioning at 11% RH. Second Hg intrusions were also performed to investigate the effects of first intrusion. It was concluded that it is not possible to obtain an actual pore size distribution of cement paste by Hg intrusion because of its sensitivity to stress.

3246
Fu, H. C., Erki, M. A., and Seckin, M.
"REVIEW OF EFFECTS OF LOADING RATE ON CONCRETE IN COMPRESSION"
Journal of Structural Engineering, Dec 1991, Vol. 117, No. 12, pp 3645-3659.

This paper surveys and summarizes the research in the behavior of concrete subjected to dynamic compressive loading. General conclusions on the effects of strain rate on some mechanical properties of concrete under compression are presented. It was found that both compressive strength and stiffness increase with increasing strain rates, and that increasing of the rate of strain has not resulted in consistent increase or decrease in ultimate strain and strain at maximum stress. Higher strain rates appear to have a more profound effect on low to moderate strength concrete than on high-strength concrete. Wet concrete is relatively more sensitive to a change in loading rate than dry concrete. These and other findings are discussed.

3247
Gagne, R., Pigeon, M., and Aitcin, P-C.
"DEICER SALT SCALING RESISTANCE OF HIGH STRENGTH CONCRETES MADE WITH DIFFERENT CEMENTS"
in Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 185-199. (ACI SP-126)

Seventeen concrete mixtures were prepared to evaluate the deicer salt scaling resistance of some high strength concretes with a 28 days strength in the 60-90 MPa range. A 0.30 water/(cement + silica fume) ratio was used for most of the mixtures and 3 additional mixtures were prepared with a 0.26 water/(cement + silica fume) ratio. In the 0.30 mixtures, two types of cements and a silica fume were used (Type III, Type III + 6 percent silica fume, Type I + 6 percent silica fume), and in the 0.26 mixes, only Type I + 6 percent silica fume. All specimens were submitted to 150 daily cycles freezing and thawing in accordance with ASTM C672, using sodium chloride as a deicer. For all concretes, the weight loss after 50 cycles was lower than 0.75 kg/m (squared) and under 2 kg/m (squared) after 150 cycles, and no clear relationship was found between the scaling resistance and the spacing factor. Based upon results in this study, and in others, it seems that the use of a water/(cement + silica fume) ratio of 0.30, a good quality coarse aggregate and a portland cement with silica fume generally allows the production of non-air-entrained concretes with a good deicer salt scaling resistance, even after only 24 hours of curing. It is also possible, with certain Type III cements, to produce deicer salt scaling resistant non-air-entrained concretes without using silica fume.

3248
Galeota, D., Giammatteo, M. M., Marino, R., and Volta, V.
"FREEZING AND THAWING RESISTANCE OF NON AIR-ENTRAINED AND AIR-ENTRAINED CONCRETES CONTAINING A HIGH PERCENTAGE OF CONDENSED SILICA FUME"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 249-261. (ACI SP-126)

This research examines the resistance to repeated freezing and thawing cycles of non air-entrained and air-entrained concrete containing a high dosage of condensed silica fume. Testing was carried out on a total of seventy-six air-entrained and non air-entrained cylindrical specimens. The compressive strength and the complete stress-strain curves of the specimens under uniaxial compression were determined from different freezing and thawing cycles. The influence of the treatment on the shape of the stress-strain curves was investigated. In addition, the dynamic modulus under the same cyclic conditions was determined. In order to investigate both the spacing factor and the specific surface, the air void and pore structure characteristics of hardened specimens were studied.

3249
Galligo, J. M. and Rodriguez, F.
"STUDY ON THE INFLUENCE OF SOME PARAMETERS OF MIX DESIGN ON THE PERMEABILITY OF HARDENED CONCRETE"
Durability of Building Materials and Components, Proceedings of the Fifth International Conference, held Nov 7-9, 1990, Brighton, UK; Ed. by J. M. Baker, P. J. Nixon, A. J. Majumdar, and H. Davies; E & FN Spon, London, 1991, pp 341-346.

A study on the different available techniques to test concrete permeability has been carried out by the Laboratorio Central de Estructuras y Materiales. This research programme includes several test methods on laboratory specimens and for in-situ measurements, including the water penetration method. Some operational problems can appear when the test is carried out according to ISO 7031: 1.983. Some modifications were developed to solve them in order to develop the Spanish Standard UNE 83.309, which deals with this method. The research work also includes a test programme to assess the influence of some parameters of the dosage in the permeability of concrete. The water/cement ratio, the maximum size of aggregate and the curing duration are taken into account. Five test methods are used in the experimental work: water penetration method, initial surface absorption test, the Figg methods to evaluate the air and water permeability of concrete and the Hansen, Ottosen and Petersen's method for permeability of concrete to gases under low pressures. About one hundred and fifty specimens with ten different dosages were tested. The first experimental results obtained with the two first methods mentioned above are presented in this work.

3250
Gamble, W. L. and Klinar, J. D.
"TESTS OF HIGH-STRENGTH CONCRETE COLUMNS WITH INTERVENING FLOOR SLABS"
Journal of Structural Engineering, May 1991, Vol. 117, No. 5, pp 1462-76.

The results of 12 recent tests of column-slab-column specimens, in which very high-strength reinforced concrete columns are separated by ordinary strength reinforced concrete slabs, has shown that the provisions of the current ACI code for the interior column cases are not necessarily conservative. The new tests greatly extend both the range of strengths and the concrete used in the columns, and the range of the ratio of column concrete strength to slab concrete strength. Details of the study are described and the conclusions drawn from the results are presented.

3251
Geiker, M., Thaulow, N., and Andersen, P. J.
"ASSESSMENT OF RAPID CHLORIDE PERMEABILITY TEST OF CONCRETE WITH AND WITHOUT MINERAL ADMIXTURES"
Durability of Building Materials and Components, Proceedings of the Fifth International Conference, held Nov 7-9, 1990, Brighton, UK; Ed. by J. M. Baker, P. J. Nixon, A. J. Majumdar, and H. Davies; E & FN Spon, London, 1991, pp 493-502.

A study of permeability by means of the AASHTO T 277-83 I, Rapid Determination of the Chloride Permeability of Concrete, was made on ten concrete mixes differing in cementitious material (w/c from 0.31 to 0.36, 16.5 weeks and 36 weeks old). The mixes included one, two and three powder mixtures of either low alkali sulphate resistant portland cement or rapid hardening portland cement with and without silica fume and fly ash. The repeatability, expressed as the coefficient of variation within specimens from the same mix varied from 5% to 18%. For unblended cements a linear correlation between electrical charge passed (coulomb) and porosity was found. For blended cements with either fly ash, silica fume or both much lower values of coulomb without a similar change in the amount of porosity were obtained. The measurements of electrical charge passed correlate well with resistivity measurements, especially for dense concretes. The increase in electrical current passed during the six hour long test period experienced for porous concretes tested according to the AASHTO T 277-83 I method is a temperature effect.

3252
Glover, P.
"THE USE OF CHEMICAL ADMIXTURES TO PRODUCE DURABLE CONCRETE"
New Zealand Concrete Construction, 1991, No. 35, pp 2-5.

This paper discusses admixtures to counter the corrosion of concrete by chlorides. These admixtures have two types: (1) admixtures resistant to chloride penetration, including superplasticisers and silica fume; (2) corrosion inhibitors, including calcium nitrite. Quality concrete is the first line of defence against chloride-induced corrosion; it is properly proportioned, has a water/cement ratio of 0.4 at most, is placed and consolidated in a manner avoiding segregation, is fully cured, and has adequate cover for its reinforcing. The use of these admixtures does not ensure protection unless applied to quality concrete. Superplasticisers allow the production and use of low water/cement ratio concrete that maintains a high degree of workability. Condensed silica fume is a microsilica containing a silica content of at least 85%. Research shows that microsilica has a considerable effect on chloride ion permeability; some typical test results are tabulated. After sufficient time, chlorine ions will penetrate concrete treated with superplasticisers or microsilica or any other material designed to densify, block or coat the concrete's pore structure. Further protection can be obtained by using a chemical corrosion inhibitor. Some test results are given for the use of calcium nitrite. The rate of chloride diffusion determines the quantity and type of admixture required.

3253
Haque, M. N., Gopalan, M. K., and Ho, D. W. S.
"ESTIMATION OF INSITU STRENGTH OF CONCRETE"
Cement and Concrete Research, Nov 1991, Vol. 21, No. 6, pp 1103-1110.

Twelve concretes of low, medium and high strength, with and without a fly ash and with and without a proprietary superplasticizer were designed. From each concrete 375 x 375 x 150 mm slabs and 100 x 200 mm cylinders were cast. The slabs were stored in out-door exposure conditions and 75 x 150 mm cores were extracted after 28, 91 days and 6 months duration. The moulded cylinders were cured in a fog room, control room maintained at 45% RH (relative humidity) and placed alongside the slabs. The concrete strength is known to be highly variable and depends on a great many factors. Nonetheless, the results suggest that the insitu strength can be estimated by dividing the strength of the fog cured cylinders by a factor of 1.25. Similarly, for most concretes it can also be assumed that the core strength is equal to the strength of the field-cured cylinders. In spring/summer- like ambient conditions, the core strength is 80% of the strength of the standard cured cylinders instead of 85% required by some codes of practice.

3254
Hatanaka, S., Hattori, H., Kondo, Y., and Tanigawa, Y.
"EFFECTIVE LATERAL STRESS AND STRESS-STRAIN RELATION OF LATERALLY CONFINED HIGH-STRENGTH CONCRETE"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 141-148.

This paper studies the confining lateral pressure by hoops applied to normal and high-strength concretes. First, the compressive deformation behavior of confined normal and high-strength concrete with circular or square hoops is examined and then the lateral pressure due to hoops is evaluated by using a stress-strain model proposed by the authors. Based on the evaluation of the equivalent lateral pressure, the influence of the pitch and shape of the hoops on their efficiency as confinement is discussed quantitatively.

3255
Hatanaka, S., Hattori, H., Kondo, Y., and Tanigawa, Y.
"STRESS-STRAIN MODEL FOR NORMAL AND HIGH STRENGTH CONCRETE UNDER TRIAXIAL COMPRESSION"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 125-132.

A series of triaxial compression tests of high strength concrete were carried out by using a steel ring confinement. Based on the test results, the earlier proposed stress-strain model for concrete under triaxial compression was extended so that it would be applicable to the concrete of higher compressive strength up to 1000 kgf/cm2 and under higher confining pressure up to 50 kgf/cm2. Further, quantitative discussion was carried out on how much lateral confining pressure was required to keep concrete ductile based on the proposed stress-strain model.

3256
Hibi, J., Mihara, Y., Otani, S., and Aoyama, H.
"BEHAVIOR OF REINFORCED CONCRETE COLUMNS USING HIGH STRENGTH CONCRETE AFTER FLEXURAL YIELDING"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp. 395-402.

Shear behavior after flexural yielding was investigated experimentally for reinforced concrete columns using high-strength concrete of approximately 1,000 kgf/cm2 compressive strength. Ductile flexural behavior was observed in specimens subjected to an axial stress of 0.3 times concrete strength, but specimens subjected to higher axial stress eventually failed in shear with lateral dilation.

3257
Hoff, G. C.
"DURABILITY OF OFFSHORE AND MARINE CONCRETE STRUCTURES"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 33-64. (ACI SP-126)

The durability of concrete is generally regarded as its ability to resist the effects and influences of the environment while performing its desired function. In an offshore or marine environment, the concrete can be subjected to the influences of wetting and drying, freezing and thawing, abrasion by ice and other debris, chemical attack or mineral depletion by water it is in, salt accumulations, and attack by marine organisms. The paper reviews these deteriorating mechanisms and also reviews the recent trends in strength development for concretes made with modern materials. Chloride ion penetration into concrete information from 33-year old Gulf of Mexico offshore concrete platforms is presented. The advantages of supplementary cementing materials in offshore and marine concretes are discussed along with recommendations for producing durable marine concretes.

3258
Hognestad, E.
"DESIGN CONSIDERATIONS FOR SERVICE LIFE"
Concrete International, Mar 1991, Vol. 13, No. 3, pp. 57-60.

It is noted that concrete structures designed for service life are proportioned and built to serve their intended functions in a specified environment over a required number of years. Design for service life calls for sharply increased emphasis on the construction process and planned maintenance. The article discusses the concept of service life. Construction of North Sea structures is discussed, as well as hot climate structures. Environmental exposure is discussed with particular reference to design codes, and special exposures. Resistance to exposures is covered in relation to concrete constituents, concrete cover, compaction, curing and corrosion reinforcement.

3259
Holm, T. A. and Bremner, T. W.
"THE DURABILITY OF STRUCTURAL LIGHTWEIGHT CONCRETE." Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 1119-1133. (ACI SP-126)

Long-term durability of structural lightweight concrete used in bridges, ships, and buildings is reviewed. Particular attention is given to mature structures located throughout the world that have been subjected to severe weather conditions. Ongoing testing programs carried out on structures subjected to several decades of exposure are reported. The nature of both the vesicular lightweight aggregate itself as well as the interfacial contact zone between aggregate and cement paste matrix are analyzed as the microstructure of lightweight concrete reveals factors that contribute to long-term durability. The information gained on the microlevel is used to explain observed performance, and provides a basis for predicting behavior. To facilitate the practical design of durable structures, long-term field exposure studies of normal weight and lightweight concretes are being conducted to assess their relative performance in a severe environment. The results obtained from ongoing testing programs conducted by the Canadian Concrete Technology Section of CANMET at the U.S. Corps of Engineers Treat Island Severe Weather Exposure Station are discussed in relation to the design process.

3260
Hwang, C-L. and Shen, D-H.
"EFFECTS OF BLAST-FURNACE SLAG AND FLY ASH ON THE HYDRATION OF PORTLAND CEMENT"
Cement and Concrete Research, Jul 1991, Vol. 21, No. 4, pp 410-425.

In this study, a calorimeter, an ultrasonic tester, an optical microscope, and other pieces of conventional laboratory equipment, such as a Vicat needle, were employed in the investigation of the effect of blast-furnace slag and fly ash on the hydration of fresh cement paste. Test results indicate that a strong relationship exists among the calorimetric curve, the ultrasonic pulse velocity curve, and the penetrative resistance strength curve. A transition zone appearing in the ultrasonic pulse velocity curve corresponds to the period between the end of the dormant period and the deceleration period in the calorimetric curve. In the calorimetric curve during the end of the dormant period, the ultrasonic pulse velocity curve rises rapidly and the penetrative resistance strength curve begins to develop simultaneously. From optical microscopy observations, it is found that CH crystals develop rapidly and contribute to the early strength development of cement paste in the plastic state. The end of the dormant period and the second peak in the calorimetric curve are similar to both the initial and final setting times as measured by the Vicat needle. Although the transition zone of hydration introduced by the blast-furnace slag and fly ash differ slightly, they both appear somewhat later in comparison to that of ordinary portland cement.

3261
Idorn, G. M.
"CONCRETE DURABILITY & RESOURCE ECONOMY"
Concrete International, July 1991, Vol. 13, No. 7, pp. 18-23.

It is noted that concrete of certified, long term durability, tailored to its performance requirements, will become a basic element in the development of resource economy policies worldwide. The article discusses concrete materials and concrete processing and testing, and points out the need for innovation in the development of modern instrumentation and test methods for site monitoring of effective compaction. Quality control should be based on physico-chemical science-based monitoring methods. It is expected that during the next decade, on-site monitoring of the processing of fresh concrete and of early curing will completely replace conventional quality control by means of sample testing. Comments are made on research sponsored by litigation and forensic engineering. The Strategic Highway Research Program is noted as having created more cooperation and effectiveness in the planning and management of research in concretes than ever before.

3262
Kabeyasawa, T., Shen, F-H., Kuramoto, H., and Rubiano, N. R.
"EXPERIMENTAL STUDY ON BEHAVIORS OF ULTRA-HIGH-STRENGTH REINFORCED CONCRETE COLUMNS UNDER TRI-AXIAL FORCES"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 279-286.

This paper presents experimental and analytical investigations on the behavior of ultra-high-strength reinforced concrete columns under biaxial moment reversals and axial load. Two column specimens of one-third scale were tested, for which concrete of 700 kgf/cm2 grade and reinforcing bars of 6,200 kgf/cm2 and 10,000 kgf/cm2 grades were used. The variable investigated was the axial load level, either high constant load or varying axial load. The experimental result showed that the axial load level had a significant effect on the deformability of the columns. The result was also confirmed by the analysis considering triaxial cyclic loads.

3263
Keck, R. and Casey, K.
"A TOWER OF STRENGTH"
Concrete International, Mar 1991, Vol. 13, No. 3, pp 23-25.

The construction is described of a high-rise structure in Atlanta, Georgia, using 12,000 psi concrete. Field performance to date shows that the use of high strength concrete on this project has been a success due to the careful attention to material selection and jobsite practices, as well as to cooperation between the designer, the contractor, and the ready mixed concrete producer. After taking into account various considerations, it was found that the combined concrete frame and shearwall bracing scheme using 12,000 lb/sq inch concrete was the most economical. The admixtures are described. The development of the mix proportions began with the optimization of aggregates. The selection of the coarse aggregate is described as well as the silica fume. The admixture selection provides for water-reduction and maintenance. Fly ash added to the workability and pumpability of plastic concrete. Quality control was implemented to insure that the mix conforms to the design.

3264
Khayat, K. H.
"DETERIORATION OF LIGHTWEIGHT FLY ASH CONCRETE DUE TO GRADUAL CRYOGENIC FROST CYCLES"
ACI Materials Journal, May-Jun 1991, Vol. 88, No. 3, pp 233-239.

Although the mechanical properties of a high strength lightweight concrete containing fly ash were shown to improve at cryogenic temperatures, its susceptibility to repetitive cryogenic frost cycles still must be evaluated. Longitudinal thermal strains of water-saturated and air-dried concretes were monitored between 65o and -250o F. Cumulative drops in compressive and splitting tensile strengths were measured after each of 5 gradual freeze-thaw cycles ranging from a high of 65o F to two low temperatures of -40o and -100o F. This was done to evaluate the concrete's frost durability at liquified petroleum and natural gas temperatures, respectively. As expected, moist concrete exhibits larger dilation and residual strains than air-dried concrete. The study results are discussed, particularly with regard to the coefficients of thermal length changes, compressive strengths, and the splitting tensile strength.

3265
Kitayama, K., Fukuoka, M., Eto, K., and Fujita, T.
"BASIC TESTS ON BOND ALONG HIGH-STRENGTH BEAM LONGITUDINAL BARS THROUGH HIGH-STRENGTH R/C BEAM-COLUMN JOINT"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 619-624.

High-strength concrete panels reinforced by high-strength longitudinal bars were tested by a simple method developed herein to study the bond characteristics along the beam reinforcement within an interior beam-column joint. The bond stress reached the maximum value for panels constructed with the high-strength materials when a diagonal shear crack occurred across the beam bar, and the bond transfer subsequently decayed with the beam bar yielding. On the contrary, the bond deterioration for panels made of the ordinary-strength materials was caused by the yielding of the beam reinforcement.

3266
Koike, S. and Hatanaka, S.
"EFFECT OF SIZE AND SLENDERNESS RATIO OF SPECIMEN ON STRESS-STRAIN BEHAVIOR OF CONFINED HIGH STRENGTH CONCRETE"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 133-140.

A series of uniaxial compression tests of confined concretes were carried out to examine the size effects on their compressive behavior. The strength of concrete was varied from about 300 to 700 kgf/cm2. The relationships between concrete strength and the size effects on the compressive strength, strain at the peak stress, and stress-strain curve of confined concrete were discussed based on the test results.

3267
Korhonen, C. J. and Cortez, E. R.
"ANTIFREEZE ADMIXTURES FOR COLD WEATHER CONCRETING"
Concrete International, Mar. 1991, Vol. 13, No. 3, pp. 38-41.

Antifreeze concrete can be cured at temperatures significantly below 0o C (32o F) without harming its performance compared to that of normal concrete cured at room temperature. Of the antifreeze concrete mixes tested, those containing sodium nitrite/calcium nitrite and sodium nitrite/potassium carbonate performed the best - they were essentially unaffected by the 5o and 10o C (23o and 14o F) temperatures used in the study. Even for those concretes whose strength lagged behind that of the control mix, the prognosis is that they will eventually recover full strength when thawed. The effects of these admixtures on durability, corrosiveness, workability, ice formation, and the economics of their use in portland cement concrete, need to be investigated further. Laboratory tests suppported by field demonstrations are needed to develop this technology for the U. S. construction industry.

3268
Kukko, H. and Matala, S.
"EFFECT OF COMPOSITION AND AGING ON THE FROST RESISTANCE OF HIGH-STRENGTH CONCRETE." Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 229-248. (ACI SP-126)

The use of high-strength concrete with compressive strengths between 60 and 100 MPa has been studied in Finland since the early 1980s. In this study, it was stated that the frost resistance and salt-frost resistance of the non-air-entrained, high-strength concrete is generally high. The best results were achieved with rapid hardening portland cement with or without silica fume. Blended slag cement and slow hardening portland cement did not show as good resistance, and especially after aging, resistance was decreased.

3269
Lahoud, A. E.
"SLENDERNESS EFFECTS IN HIGH-STRENGTH CONCRETE COLUMNS"
Canadian Journal of Civil Engineering, Oct 1991, Vol. 18, No. 5, pp 765-771.

High-strength concretes are being increasingly used in the columns of high-rise buildings. Analytical studies of the slenderness effects in these columns have been very limited. The behavior of slender columns with normal- and high-strength concretes is studied using a finite element program. Differences and similarities in long-term and short-term behaviors between high-strength and normal-strength slender concrete columns are noted and discussed.

3270
Laplante, P., Aitcin, P-C., and Vezina, D.
"ABRASION RESISTANCE OF CONCRETE"
Journal of Materials in Civil Engineering, Feb 1991, Vol. 3, No. 1, pp 19-28.

An experimental program is described which explored the extent to which abrasion resistance can be increased through new technology using silica fume addition, water/cementitious ratio, and coarse aggregate type as variables. The details of the experiments are described, and the results are discussed. The findings show that coarse aggregate is the most important factor affecting concrete abrasion resistance measured by ASTM C-779-82. Water/cementitious ratio ranks second in importance. The abrasion resistance of concrete is strongly influenced by the relative abrasion resistance of its constituent coarse aggregate and mortar. However, when the coarse aggregate and mortar have nearly the same abrasion resistance, the concrete can present serious skidding or slipping problems when wet due to fairly uniform surface wear. Also, very low W/C can make the concrete nearly as abrasion resistant as high-performance rocks.

3271
Lee, S., Fujita, T., Kitayama, K., and Otani, S.
"ANCHORAGE OF BEAM REINFORCEMENT IN HIGH-STRENGTH REINFORCED CONCRETE INTERIOR BEAM-COLUMN JOINTS"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 625-632.

Two interior beam-column subassemblages were tested under load reversals to investigate the bond strength of beam reinforcement within high-strength reinforced concrete joint. The variable was the diameter of beam longitudinal reinforcement. The experimental results were compared with the previous results obtained from specimens using ordinary-strength reinforced concrete. "Bond index" proposed in the paper was found to express bond strength of beam reinforcement within the joint even for the high-strength reinforced concrete.

3272
Lees, T. P. and Berke, N. S.
"INFLUENCE OF SUPERPLASTICISERS ON THE DURABILITY OF CONCRETES CONTAINING FLY ASH, SILICA FUME AND CALCIUM NITRITE"
Papers Presented at the International Conference on Blended Cements in Construction, held Sep 9-12, 1991 at the University of Sheffield, UK; Ed. by R. N. Swamy; Elsevier Applied Science, London, 1991, pp 389-400.

Superplasticisers allow the production of high workability, placeable concrete with low water/cement ratios and long term studies show that such concretes have improved resistance to corrosion and chloride ingress. Further studies show that the use of superplasticisers in conjunction with the use of fly ash or silica fume and/or calcium nitrite corrosion inhibitor leads to concrete of exceptionally high durability. Mechanical properties such as compressive strength are also improved and with the additional use of air entraining agents freeze- thaw resistance is enhanced. This paper reviews work carried out over a number of years and is currently in progress in the authors' laboratories.

3273
Luciano, J. J., Nmai, C. K., and DelGado, J. R.
"A NOVEL APPROACH TO DEVELOPING HIGH-STRENGTH CONCRETE"
Concrete International, May 1991, Vol. 13, No. 5, pp 25-29.

This paper describes the approach to identify suitable mix proportions in a project in Cleveland, Ohio, where the specifications for a project under construction required the production of concrete with a 28-day compressive strength of 12,000 psi. A statistical approach was employed to minimize the time required to obtain meaningful data. The process involved setting up an experimental program to facilitate understanding of the interrelationship between raw materials, admixtures, and specified concrete performance criteria. Statistical models were developed from the data collected and an optimization program built. The program then iterated through thousands of potential concrete mix proportions until combinations with optimal cost-performance ratios were obtained. The details of the experimental program are described. The findings are presented and the conclusions drawn from the study are discussed.

3274
Malhotra, V. M., Carette, G. G., Bilodeau, A., and Sivasundaram, V.
"SOME ASPECTS OF DURABILITY OF HIGH-VOLUME ASTM CLASS F (LOW-CALCIUM) FLY ASH CONCRETE"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 65-82. (ACI SP-126)

Low-calcium fly ash, ASTM Class F, is being increasingly incorporated into portland cement concrete as a partial replacement for cement. The replacements commonly used are 15 to 25 percent by weight of cement. This paper presents data on several aspects of durability of this new type of concrete. The aspects discussed include freezing and thawing cycling, resistance to chloride ion diffusion, deicing salt scaling resistance, carbonation, and volume stability. Data on the role of high volumes of fly ash to control alkali-silica reaction in concrete are also presented. It is concluded that, in general, high-volume fly ash concrete has excellent durability characteristics. The only exception is the deicing salt scaling tests, in which the above concrete performs poorly.

3275
Malier, Y.
"THE FRENCH APPROACH TO USING HPC"
Concrete International, July 1991, Vol. 13, No. 7, pp 28-32.

This article notes that high performance means more than high strength, and describes how many of the methods for obtaining high-strength concrete also improve such qualities as durability, workability, shear strength, and abrasion and impact resistance. Research to obtain high performance concrete (HPC) has focused on deflocculation using organic products, and extending the grain size range by addition of extremely fine elements to fill the microvoids. Approaches to obtaining high strengths are discussed. Characteristics of HPC are reviewed including microstructure, placing, mechanical behavior, and durability. New approaches to structural design demanded by the new material are also discussed.

3276
Malier, Y., Brazillier, D., and Roi, S.
"THE BRIDGE OF JOIGNY"
Concrete International, May 1991, Vol. 13, No. 5, pp 40-42.

The design and construction of a bridge across the River Yvonne in Joigny, France are described. The bridge demonstrated the feasibility of building a typical prestressed bridge with high-strength concrete, using unsophisticated means and materials that could be found throughout France. The 28-day strength of the concrete was 60 MPa (8700 psi). The details are described of the prestressing, design stress, high-strength vs ordinary concrete, fresh concrete, concrete design, compressive strength, tensile strength, and concrete placement. Monitoring instruments were built into the bridge to verify the assumptions in the calculations. Thermal evolution was measured, as well as prestressing forces and deformations, creep and shrinkage. The bridge was successfully completed in 1989, and the use of 60 MPa concrete will be extended to the construction of most bridges in the future in France.

3277
Marzouk, H. and Hussein, A.
"EXPERIMENTAL INVESTIGATION ON THE BEHAVIOR OF HIGH-STRENGTH CONCRETE SLABS"
ACI Structural Journal, Nov-Dec 1991, Vol. 88, No. 6, pp 701-713.

Seventeen reinforced concrete slabs were tested to investigate the deformation and strength characteristics of punching shear failure of high-strength concrete slabs. The tested specimens had different slab depths and reinforcement ratios varying between 0.49 and 2.33 percent. Test results revealed that high-strength concrete slabs exhibit a more brittle failure than normal strength concrete. Experimental results indicated that as the level of reinforcement is increased the punching strength of the slabs also increased. It was found that using the cubic root of the concrete compressive strength to predict the punching resistances of the concrete slabs generally yields better results than the square root expression used in North American codes.

3278
Marzouk, H. and Hussein, A.
"PUNCHING SHEAR ANALYSIS OF REINFORCED HIGH-STRENGTH CONCRETE SLABS"
Canadian Journal of Civil Engineering, Dec 1991, Vol. 18, No. 6, pp 954-963.

An experimental investigation was conducted at the structural laboratory at Memorial University of Newfoundland to examine the behavior of high-strength concrete two-way slabs. It was evident that a new mechanical model is required to predict the punching shear capacity of such slabs. The experimental results of the tested slabs with regard to deformations, strains, ultimate capacity, and modes of failure were examined. Based on the test results, a mechanical model was adopted and developed for high-strength concrete slab applications. The formulation takes into account the actual behavior of the high-strength concrete and steel. The proposed model gives a fairly good agreement between the predicted and experimental punching loads.

3279
McDonald, J. E.
"PROPERTIES OF SILICA-FUME CONCRETE. REPAIR, EVALUATION, MAINTENANCE, AND REHABILITATION RESEARCH PROGRAM"
Final Report; Structures Laboratory, Waterways Experiment Station, U.S. Army Corps of Engineers, Vicksburg, MS, 1991, 47 pp. (WES/TR/SL-REMR-CS-32; AD-A235-369)

Two major applications of silica-fume concrete within the Corps of Engineers were to repair abrasion-erosion damage in the stilling basin at Kinzua Dam and in the concrete lining of the low-flow channel, Los Angeles River. In each case, concrete cracking occurred during the repair. Apparently, this cracking has not significantly affected the performance of the concrete in resisting abrasion-erosion damage. However, such cracking could limit the use of silica-fume concrete in other repair and rehabilitation applications. This study was conducted to determine those properties of silica-fume concrete which might affect cracking and to develop guidance for minimizing cracking problems associated with the use of such concrete in future repair projects. Tests included compressive and tensile splitting strengths, modulus of elasticity, Poisson's ratio, ultimate strain capacity, uniaxial creep, shrinkage, coefficient of thermal expansion, adiabatic temperature rise, and abrasion erosion. None of the material properties of silica-fume concrete reported herein, with the possible exception of autogenous shrinkage, indicate that this material should be significantly more susceptible to cracking as a result of restrained contraction than conventional concrete. In fact, some material properties, particularly ultimate tensile strain capacity, would indicate that silica-fume concrete should have a reduced potential for cracking. Silica fume offers potential for improving many properties of concrete. The very high compressive strength and resulting increase in abrasion-erosion resistance are particularly beneficial in repair of hydraulic structures. These concretes should be considered in repair of abrasion-erosion susceptible locations, particularly in those areas where locally available aggregate might not otherwise be acceptable.

3280
Mehta, P. K.
"DURABILITY OF CONCRETE--FIFTY YEARS OF PROGRESS?" in Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 1-31. (ACI SP-126)

This paper reviews the proceedings of the cement chemistry congresses as well as other symposia held during the last 50 years by ACI, ASTM, and RILEM. What is presented is a state-of-the-art report from the author's perspective. In order of decreasing importance, the major causes of concrete deterioration today are: corrosion of reinforcing steel, frost action in cold climates, and physico-chemical effects in aggressive environments. There is a general agreement that the permeability of concrete, rather than normal variations in the composition of portland cement, is the key to all durability problems. A rise in chemical aggressivity of the environment through the increasing use of de-icer salts, and an increase in land, water, and air pollution, has also contributed to concrete durability problems.

3281
Meininger, R. C. and Nelson, N. R.
"CONCRETE MIXTURE EVALUATION AND ACCEPTANCE FOR AIR FIELD PAVEMENTS"
Proceedings of the Conference on Aircraft/Pavement Interaction: An Integrated System, held Sep 4-6, 1991 at Kansas City, MO, Sponsored by ASCE with Others; Ed. by P. T. Foxworthy; ASCE, New York, 1991, pp 199-224.

Evaluation of the strength of portland cement concrete using flexural strength and compressive strength tests is examined. Problems with the use of flexural testing in the field are discussed and alternative specification approaches to minimize testing problems and to provide an organized way of troubleshooting and settling low strength problems are covered. Data collected by the concrete industry and by a consultant for FAA projects show standard deviations for flexural strength from paving projects ranging from about 40 psi to 150 psi (coefficient of variation from 6 to 20 percent) with an average standard deviation of 75 psi. Specifications for concrete for air field pavements should recognize that an adequate strength overdesign as well as good testing practices are necessary to assure that a very high percentage of strength tests will meet requirements. Data are presented from case studies which show the effect of different specification strategies. Also included are suggested quality control and trouble shooting protocols which should be included in specifications to improve data and information available and to handle low strength tests. It will help determine whether the concrete, as-placed, is truly substandard; whether the low strength is simply due to poor curing, handling, and testing; or whether it is due to an occasional low test from normal statistical variation. The procedure includes evaluation of the project data, the proper use of non-destructive tests, and testing of cores when necessary. Specifications and testing can be improved to minimize on-the-job strength problems, and provide an organized way of investigating strength problems so that job delay and strength problems due to poor testing can be rapidly identified and minimized.

3282
Millard, S. G. and Gowers, K. R.
"THE INFLUENCE OF SURFACE LAYERS UPON THE MEASUREMENT OF CONCRETE RESISTIVITY"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 1197-1220. (ACI SP-126)

The measurement of the electrical resistivity of concrete is a non-destructive technique that is rapidly gaining acceptance as a means of evaluating the severity of reinforcement corrosion, when used in conjunction with potential mapping methods. The concrete resistivity can be determined in situ from placing four equi-spaced surface electrodes in contact with the structure and passing a current between the outer electrodes. A measurement of the voltage between the inner electrodes leads to an assessment of the resistivity of the concrete. One practical difficulty in interpreting resistivity measurements is allowing for the error caused by a surface layer with a resistivity lower or higher than that of the underlying concrete. This could be due to recent wetting or carbonation of the surface zone. This effect is discussed and practical correction curves permitting a true assessment of the resistivity of the underlying concrete are given. A very dramatic error in resistivity measurement can occur with two surface layers with resistivities one lower and one higher than the underlying concrete. Reasons for this effect are discussed and practical guidance for in situ resistivity measurement is given.

3283
Millard, S. G., Harrison, J. A., and Gowers, K. R.
"PRACTICAL MEASUREMENT OF CONCRETE RESISTIVITY"
British Journal of Non-Destructive Testing, Feb 1991, Vol. 33, No. 2, pp 59-63.

A recent paper by the authors discussed the development of a new device for measuring the electrical resistivity of concrete. This device was designed to assess the corrosion durability risk of in situ reinforced concrete structures, where a survey of a large number of spot resistivity measurements needs to be taken quickly and stored for later inspection. A subsequent paper discusses several possible advantages of alternative instrumentation that has been independently developed. The authors welcome the opportunity to compare and to discuss the merits of the different approaches. It is the authors' opinion that both instruments can be used successfully to measure the resistivity of concrete with a high accuracy, but that they each have different operational functions that may suit the specific needs of the user to a greater or lesser degree.

3284
Miller, B.
"MICROSILICA MODIFIED CONCRETE FOR BRIDGE DECK OVERLAYS"
First Year Interim Report; Materials and Research Section, Highway Division, Oregon Department of Transportation, Salem, OR, 1991, iv, 27 pp. (OR 90-03/Interim-2)

The study objective was to see if microsilica concrete (MC) is a viable alternative to the latex modified concrete (LMC) usually used on bridge deck overlays in Oregon. The study addresses MC overlays placed in 1989 on 7 portland cement concrete (PCC) bridge decks. This report covers the performance of the overlays during the first year of use. After one year, the only distresses on these overlays were cracking and delamination. There was cracking on all of the overlays. In most cases, the cracking was hairline and random. In heavily cracked areas, the cracks connected to form a map pattern. This cracking may be due to drying shrinkage. Similar problems are seen on Oregon State Highway Division (OSHD) LMC overlays. In addition, there were delaminations on 5 of the 7 overlays. This distress was not extensive, as the worst deck had only 2.5% of its surface delaminated. In most cases, the delaminations were small, scattered throughout the deck, and covered by uncracked MC. The exceptions were two large delaminations that were under sections of the overlay with severe map cracking, and numerous delaminations adjacent to construction and expansion joints. The delaminations that were repaired were almost always between the overlay and the old deck. The cause of these delaminations is not known. Similar distress is often seen on OSHD LMC overlays. The wheel-to-pavement friction numbers of these overlays were similar to typical state highway pavements and LMC bridge decks in Oregon. The only maintenance and repair cost to the OSHD was the sealing of cracks on one deck with methacrylate and sand, at a cost of $4,000. This sealant was effective. The overlays met 2 of their 3 design objectives after one year's use. They were still adding strength to the deck and providing a smooth and durable wearing surface. However, as they were cracked, it is surmised that they were no longer sealing the underlying deck from the intrusion of chlorides. Experience with a recently placed MC overlay is discussed and recommendations are made.

3285
Mintoff, L. A.
"THE PERFORMANCE OF UNDERFIRED FLY ASH IN HIGH STRENGTH CONCRETE"
Paper presented at the International Conference on Blended Cements in Construction, held Sep 9-12, 1991 at the University of Sheffield, UK; Ed. by R. N. Swamy; Elsevier Applied Science, London, 1991, pp 236-247.

This paper is intended to study the feasibility of utilising ungraded fly ash for high early strength concrete and of using fly ash as a fourth ingredient. Short term tests are described in which two different ungraded fly ashes derived from boilers in Malta were added in different proportions to a mix. For direct comparison, similar mixes using British graded pfa (pulverised fly ash) and a normal ordinary portland cement concrete mix designed to have similar wet and hardened properties were tested. Various tests were made to measure the workability, air-content and compressive strength of the samples. A full chemical and physical analysis was made on all the fly ashes and portland cement used. It was concluded that all the types of fly ash can be utilised in high strength concrete but with varying limitations on their use. A very important criterion is the water requirement and that the lower this value is, the easier it is to achieve concrete of the desired specifications.

3286
Mizoguchi, M., Arakawa, T., and Arai, Y.
"STRENGTH BEHAVIOR OF HIGH STRENGTH R/C COLUMNS UNDER BIAXIAL BENDING-SHEAR AND VARYING AXIAL LOAD"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 387-394.

Twelve short square R/C columns using high-strength concrete were tested to examine the effects of biaxial bending-shear force and varying axial load on the shear and flexural strength behavior. The columns were cyclically deflected either along their transverse principal axis to produce uniaxial bending-shear or along their diagonal to produce biaxial bending-shear. For columns failing in flexure, the experimental results were found to be in close agreement with the computed values given by the AIJ Code, regardless of the differences of concrete strength, biaxial bending-shear and varying axial load. For short columns subjected to low compressive or tensile axial stress, the computed ultimate shear strengths by the 1988 AIJ design equation overestimated the test results. The shear test results were in best agreement with the computed values by the "Kuramoto-Minami's Ultimate Shear Design Equation" proposed in 1990.

3287
Muszynski, L. C.
"CORROSION PROTECTION OF REINFORCING STEEL USING PYRAMENT BLENDED CEMENT CONCRETE"
Papers presented at the International Conference on Blended Cements in Construction, held Sep 9-12, 1991 at the University of Sheffield, UK; Ed. by R. N. Swamy; Elsevier Applied Science, London, 1991, pp 442-454.

Pyrament cement is a high performance Type IP blended hydraulic cement that meets the requirements of ASTM C-595. The cement has been modified with proprietary interground functional additions that meet the requirements of ASTM C-688. Concrete made of Pyrament cement exhibits high early strength, resistance to freeze/thaw conditions and deicer scaling without the aid of air entraining admixtures. Durability testing was performed to evaluate the resistance of concrete made with Pyrament blended cement and Florida limestone aggregate to chloride-ion penetration and subsequent corrosion of the steel reinforcement. Both Rapid Chloride Ion Permeability testing (AASHTO T277) and Florida Time- To-Corrosion tests were carried out. The results clearly indicate that concrete made with Pyrament blended cement has unusually high resistance to chloride-ion permeability and time-to-corrosion. Concrete made with Pyrament blended cement and recycled concrete as aggregate also exhibit this high resistance to chloride-ion penetration and time-to-corrosion.

3288
Nagataki, S., Ohga, H., and Inoue, T.
"EVALUATION OF FLY ASH FOR CONTROLLING ALKALI-AGGREGATE REACTION." Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 955-972. (ACI SP-126)

Mortar using Pyrex as an aggregate was made using water-binder ratio of 50 percent, replacement ratio of fly ash from 0 to 30 percent by weight and an alkali content of 1.2 percent per weight of cement. Eight fly ashes were used as supplementary cementing materials. These mortars were cured at a temperature of 40 degrees Centigrade and a relative humidity more than 95 percent, and the expansion of these mortars was measured. The concentration of soluble alkali ion in fly ash immersed in the solution containing sodium hydroxide and calcium hydroxide was also determined. By studying effects of physical properties, chemical and amorphous silicon dioxide in fly ash, a method to evaluate the expansion of mortar containing fly ash was proposed based on amorphous silicon dioxide, the replacement ratio and particle diameter of fly ash.

3289
Nagataki, S. and Ujike, I.
"INFLUENCE OF MICRO CRACKING ON AIR PERMEABILITY OF CONCRETE"
Durability of Building Materials and Components, Proceedings of the Fifth International Conference, held Nov 7-9, 1990, Brighton, UK; Ed. by J. M. Baker, P. J. Nixon, A. J. Majumdar, and H. Davies; E & FN Spon, London, 1991, pp 235-240.

This study deals with the air permeability of concrete with microcrackings. Mircocrackings chosen in this study are crackings induced by the differences of thermal expansion coefficients between aggregate and mortar or between aggregate and cement paste under elevated temperature as well as internal crackings formed around deformed tension bar. The air permeability coefficient of concrete under elevated temperature above 100 deg C becomes more than scores of times compared with that of concrete at normal temperature. The increasing rate of air permeability coefficient of concrete by heating corresponds to the amount of microcrackings. In the case of reinforced concrete specimen subjected to sustained tensile loading, the air permeability coefficient of specimen averaged through cover has the large value compared with the specimen without tensile force. And, as the tensile stress and the diameter of steel bar become larger, the air permeability coefficient of specimen increases.

3290
Naik, T. R. and Singh, S. S.
"SUPERPLASTICIZED HIGH-VOLUME FLY ASH STRUCTURAL CONCRETE"
in Energy in the 90's, Proceedings of the ASCE Energy Division Specialty Conference on Energy, held Mar 10-13, 1991, Pittsburgh, PA; Ed. by B. F. Hobbs; ASCE, New York, 1991, pp. 339-343.

This research was carried out to develop structural grade concrete containing high-volumes of ASTM Class C fly ash. A portland cement concrete, proportioned to have 28-day compressive strength of 6000 psi (41 MPa) was used in this study. Concrete mixes were also proportioned to have various levels of cement replacement by fly ash ranging from 40-70% by weight. Properties of concrete, namely, compressive strength, splitting tensile strength, and modulus of elasticity were measured as a function of fly ash amounts and age. Analysis of results showed that ASTM Class C fly ash could be substituted for cement replacement up to 70% for high strength structural grade concretes without sacrificing its performance significantly.

3291
Nakamura, N., Sakai, M., and Swamy, R. N.
"EFFECT OF SLAG FINENESS ON THE ENGINEERING PROPERTIES OF HIGH STRENGTH CONCRETE"
Papers presented at the International Conference on Blended Cements in Construction, held Sep 9-12, 1991 at the University of Sheffield, UK; Ed. by R. N. Swamy; Elsevier Applied Science, London, 1991, pp 302-316.

This paper presents extensive test data on the use of finely ground granulated blastfurnace slag as partial replacement of cement for the development of high strength concrete of 60 to 120 MPa cylinder compressive strength at 28 days. The slag used in these tests was obtained by pulverising and classifying ordinary ground slag of 453 per cubic metre/kg Blaine. Two series of tests were performed. In the first series, slag of 453 per cubic metre/kg fineness was used to replace 30, 50 and 70% of portland cement. Water-binder materials ratios were confined to 0.35 to 0.45, and together with a high range water reducer, slumps of 150 to 200mm were designed. The compressive strength, tensile strength, and the elastic modulus properties of these concretes are reported. In the second series, slags of 453, 786 and 1160 per cubic metre/kg Blaine fineness were used at a substitution rate of 50%. The water-binder ratio was varied from 0.30 to 0.40, and slumps of 150 to 200mm were designed using the same water reducer. The strength and elasticity properties of these concrete mixtures and the importance of water curing are also reported. In both series the effects of slag addition on bleeding and setting were studied. The data presented in the paper show that slag concrete with high workability and high early strength development compared to ordinary portland cement concrete can be produced.

3292
Nam, C. H., Gasiorowski, J. G., and Tatum, C. B.
"MICROLEVEL STUDY OF INTEGRATION IN HIGH-STRENGTH CONCRETE INNOVATION"
Journal of Construction Engineering and Management, Jun 1991, Vol. 117, No. 2, pp 294-309.

The development of high strength concretes is reviewed, and the paper describes the background of the Two Union Square project in Seattle, Washington, in which 19,000 psi concrete was successfully field placed in 10 ft diameter steel tubes to construct columns for a 58 story building. The paper describes the process of innovation in the project: the commitment of each party, interaction among parties, and the reconciliation of dissimilar goals and organizational cultures. The paper describes lessons extracted from the study, and gives recommendations for increasing the rate of innovation in construction.

3293
Nawy, E. G.
"FLEXURAL CRACKING IN CONCRETE STRUCTURES," Transportation Research Record, 1991, No. 1301, pp 22-32.

The state-of-the-art in the evaluation of the flexural crack width development and crack control of macrocracks is described. It is based on extensive research over the past 50 years in the United States and overseas in the area of macrocracking in reinforced and prestressed concrete beams and two-way-action slabs and plates. Control of cracking has become essential to maintain the integrity and aesthetics of concrete structures. The trends are stronger than ever -- toward better use of concrete strength, use of higher-strength concretes including superstrength concretes of over 20,000 psi compressive strength, use of more prestressed concretes, and increased use of limit failure theories -- all requiring closer control of serviceability requirements of cracking and deflection behavior. Common expressions are discussed for the control of cracking in reinforced concrete beams and thick one-way slabs; prestressed, pretensioned, and posttensioned flanged beams; and reinforced concrete, two-way-action, structural floor slabs and plates. In addition, recommendations are given for the maximum tolerable flexural crack widths in concrete elements.

3294
Norberg, P.
"MONITORING OF SURFACE MOISTURE BY MINIATURE MOISTURE SENSORS"
Durability of Building Materials and Components, Proceedings of the Fifth International Conference, held Nov 7-9, 1990, Brighton, UK; Ed. by J. M. Baker, P. J. Nixon, A. J. Majumdar, and H. Davies; E & FN Spon, London, 1991, pp 539-550.

A new electrolytic cell with resistance grids of Au has been developed and tried out according to the NILU WETCORR method in a climatic chamber. A commercial dew sensor, Murata HOS103, was also included in the evaluation programme. Several specimens of each sensor have been tested under varying temperature and relative humidity while mounted on a substrate of coil coated sheet metal. Although quite different in character, both sensors have shown acceptable properties in terms of individual variability, sensitivity, reproducibility and long-term stability. Regression analysis has provided an empirical relationship between on one side the current through the Au/Au-sensor, and on the other side the ambient relative humidity and the surface temperature. The equation works well for temperatures from 0 to 30 deg C and relative humidity (RH) values in the range of 50 to 100%. The dew sensor, HOS103, was found to react drastically to moisture loads exceeding 90 to 95% RH. Surface moisture measurements using the two types of sensors evaluated can give valuable information about the microclimate on and near surfaces of buildings. Such knowledge is important when describing the interaction between the microclimate and the degradation of the materials.

3295
Paulson, K. A., Nilson, A. H., and Hover, K. C.
"LONG-TERM DEFLECTION OF HIGH-STRENGTH CONCRETE BEAMS"
ACI Materials Journal, Mar-Apr 1991, Vol. 88, No. 2, pp 197-206.

A large body of experimental evidence is available confirming that the creep coefficient of high-strength concrete under sustained axial compression is significantly less than that of ordinary concrete. Thus, the ratio of time-dependent deflection to immediate elastic deflection of high-strength concrete beams under sustained loads should likewise be lower. However, long-term deflection multipliers of the 1989 ACI Building Code do not account for concrete strength as a variable. Experimental results are reported for 9 beams with nominal concrete compressive strengths over a range to 13,000 psi, loaded over a 12 month period. These tests confirm the significant differences between beams using high-strength and normal strength concrete. Based on these and other tests, modifications to the present ACI Building Code method for predicting long-term deflections are suggested.

3296
Petersson, P. E
"FROST RESISTANCE OF BUILDING MATERIALS"
Proceedings from a Nordic Seminar, held Oct 29-30, 1991 in Boras, Sweden; Statens Provningsanstalt, Boras, 1991, 59 pp. (SP-RAPP-1991:32; PB92-219286).

The 23 contributions to the conference were documented in "extended" abstracts which are presented in this report. The report ought to be valuable as a platform for the intended coordination of the Nordic frost resistance research in the field of building technology. The papers presented were as follows: Hypotheses for frost resistance (Hjorslev Hansen, M); Frost resistance and service life of concrete (Vesikari, E); Frost resistance of building materials (de Place, E J); Effect of deicing salts on the critical degree of saturation and the water uptake of concrete (Fagerlund, G); Freezing in porous materials (Pueringer, J); Frost resistance of concrete with and without silica fume. Effects of curing conditions -part 1 (Ljungkrants, C); Frost resistance of concrete with and without silica fume. Effects of curing conditions - part 2 (Roenning, T); Ice formation and frost-salt scaling of concrete. Effect of curing temperature and condensed silica fume on normal and high strength concrete (Sellevold, E J, Jacobsen, S); Frost resistance of clay bricks (Sandstroem, M); Freeze-thaw test of concrete using different test methods (Chandra, S, Aavik, J); Can the frost resistance of porous materials be evaluated after only one freeze-thaw cycle? (Kalmar, G, Norberg, P); Use of NMR in the study of ice formation in concrete (Gran, H C); Analysis of air pore distribution in concrete (Damgaard Jensen, A); Measurement of the air void distribution in fresh concrete (Joensson, U); Can the WETCORR-method be used for studies of frost damage under in service conditions? (Norberg, P; Kalmar, G); Comparing frost-salt scaling of field exposed concrete with laboratory testing according to SS 137244 (Farstad, T); Frost resistance of concrete - field exposure tests (Malmstroem, K); Strength of frost degradated concrete (Krus, J); Effect of delayed addition of air entraining admixtures to concrete (Okkenhaug, K, Gjoerv, O E); Frost damage and frost resistance of light weight aggregate concrete (Hammer, T A); Frost damage and frost resistance of masonry (Ylae-Mattila, R); Frost-salt resistance of polypropylene fibre mortars (Saravanta, L, Jaervelae, E); Determination of frost resistance of shotcrete (Andalen, A).

3297
Philipose, K. E., Beaudoin, J. J., and Feldman, R. F.
"DURABILITY PREDICTIONS FROM RATE OF DIFFUSION TESTING OF NORMAL PORTLAND CEMENT, FLY ASH, AND SLAG CONCRETE"
Chalk River Laboratories, Chalk River, Ontario, Canada, 1991, 24 pp. (AECL-10489; MIC-94-05511)

A waste repository for the below ground disposal of low-level radioactive waste, labelled IRUS (Intrusion Resistant Underground Structure), is planned at the Chalk River Laboratories. It relies greatly on the durability of concrete for a minimum of 500 years of service life. A research program based on laboratory testing to design a durable concrete and predict its useful engineered service life is in progress. The durability of concrete depends on its resistance to deterioration from both internal and external causes. Since the rate of degradation depends to a major extent on the rate of ingress of aggressive ions into concrete, laboratory testing is in progress to establish the diffusion rates of chlorides and sulphate ions. A total of 1000 concrete specimens and 500 paste specimens are being exposed at 22 degree and 45 degree C to twenty five different combinations of corrosive agents, including CO2. Procedures to measure the ionic penetration profile and to determine the factors controlling diffusion of ions in the various concretes have been developed. The paper presents the initial results from the research program and the longevity predictions to quality concretes for the IRUS waste repository, based on 16 months of diffusion testing on laboratory specimens.

3298
Pigeon, M., Gagne, R., Aitcin, P-C., and Banthia, N.
"FREEZING AND THAWING TESTS OF HIGH-STRENGTH CONCRETES"
Cement and Concrete Research, Sep 1991, Vol. 21, No. 5, pp 844-852.

Seventeen high-strength concretes were made using portland cement (with and without silica fume) and tested for frost resistance (using the procedure 'A' (freezing and thawing in water) of ASTM Standard C 666) to analyze the influence of various parameters on the limiting value of the water to binder ratio below which air entrainment is no longer required for good freezing and thawing cycle durability. The parameters included the type of cement, the type of aggregate and the length of the curing period. The results of these tests, as well as previously published data, indicate that this value can be higher than 0,30 in certain cases, but equal to or lower than 0,25 in others, depending particularly on the characteristics of the cement. More research is needed before these values can be used as guidelines, since field exposure conditions differ from laboratory testing conditions, and because the air void spacing factor of non-air-entrained field concretes could be significantly higher than that of laboratory made concretes.

3299
Ramakrishnan, V., Shafai, H. F., and Wu, G.
"CYCLIC HEATING AND COOLING EFFECTS ON CONCRETE DURABILITY"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 1285-1303. (ACI SP-126)

The main objective of this investigation was to determine the effects of cyclic heating on the strength of portland cement concrete subjected to high temperature, and to compare the effects of cyclic heating on concrete contaminated with hydraulic fluid and jet fuel with non-contaminated concrete. Five different concrete mixtures were investigated. Twenty one prisms and twenty one cylinders were made from each mixture and were tested for compressive strength, flexural strength, pulse velocity and dry unit weight. Within each group, three specimens were tested after each of the following heating/cooling cycles: 0, 15, 30, 60, 120, 240, and 400. Each cycle consisted of 60 minutes at 400 degrees F followed by 30 minutes at room temperature. After every 15 heating/cooling cycles, the contaminated specimens were soaked in jet fuel or hydraulic fluid for overnight before the next heating/cooling cycles. Test results indicate that jet fuel contamination is more detrimental than hydraulic fluid contamination. Compressive strength, flexural strength, and pulse velocity are adversely affected by the cyclic heating.

3300
Rangan, B. V.
"STRENGTH OF HIGH-STRENGTH CONCRETE COLUMNS," Transactions of the Institution of Engineers, Australia: Civil Engineering, Dec 1991, Vol. CE 33, No. 4, pp 293-298.

The paper presents a brief state-of-the-art report on the behaviour and the strength of high-strength concrete columns. Tentative procedures for the calculation of failure loads of stocky and slender columns are given. The need for a comprehensive experimental program is emphasized.

3301
Rasoulian, M.
"FLY ASH IN CONCRETE"
Final Report No. FHWA/LA-91/221; Louisiana Transportation Research Center, Baton Rouge, LA, 1991, 128 pp. (RR-221; PB92-185099)

This study was initiated to develop information regarding the use of fly ash in portland cement concrete for state construction projects. Concrete mixes containing 10%, 20%, 30%, 40%, and 60% fly ash were evaluated in the laboratory in combination with various cement contents. Type C fly ash was selected from three local sources which had been approved by the department for concrete mixes. Also, specifications were developed for using fly ash in a paving project. In general, fly ash when used at replacement below 40% by weight of cement was found to be satisfactory in concrete. In areas that the maximum possible strength loss cannot exceed 10% of control, replacement rate of less than 25% is recommended. Increasing amounts of fly ash caused a reduction in compressive strength, especially when air-entraining agents were used or when the concrete was less than 28 days old. Retardation in the set times was also noticed with increasing amounts of fly ash. However, strength gains of up to 10% were noticed in some mixes after extended curing periods. There were no adverse effects observed on the plastic properties, freeze and thaw durability, modulus of elasticity, length change, abrasion resistance, or absorption characteristics of fly ash concrete at the replacement rates evaluated. Based on the overall results of this study, no changes are recommended to the current fly ash concrete specifications developed earlier in this project.

3302
Rostasy, F. S.
"POTENTIALS AND DEVELOPMENTS OF MATERIALS FOR STRUCTURAL CONCRETE"
IABSE Reports Vol. 64, 1991, pp 325-330.

The structural materials concrete, reinforcing and prestressing steel as well as the post-tensioning systems in general reflect a high technical standard. Certainly, there exist regional differences in view of economic and other factors and due to different resources. Improvement will continue, new materials will advance. Dominant factor of materials development will be their suitability to satisfy the performance requirements of structures. Brief details of the advances in high strength concrete, on prestressing steel, and improvements in corrosion protection of various anchorage types of post tensioning systems are provided. These include the development of mono-strand which is encapsulated in polyethylene sheeting and protected by grease. Fibre reinforced plastics are also discussed briefly.

3303
Sabir, B. B. and Kouyiali, K.
"FREEZE-THAW DURABILITY OF AIR-ENTRAINED CSF CONCRETE"
Cement and Concrete Composites, 1991, Vol. 13, No. 3, pp 203-208.

This paper reports the results of a laboratory investigation to determine the strength and freeze and thaw durability of concrete incorporating various amounts of CSF (condensed silica fume). A total of five concrete mixes were made incorporating 0-12% CSF as partial replacement by mass of cement. All mixes were air entrained and had a constant water to cementitious materials ratio, W/(C+CSF), of 0.4. CSF improved the compressive strength of 7-days and 28-days concrete. The flexural strength after 35 cycles of freezing and thawing was also increased with increasing CSF content. All the CSF concretes performed satisfactorily when subjected to freezing and thawing, even though the performance was somewhat inferior to that of the reference mix. There were no noticeable differences in the physical appearances of the concrete prisms after the 35 cycles of freezing and thawing.

3304
Sakai, E., Kosuge, K., Teramura, S., and Nakagawa, K.
"CARBONATION OF EXPANSIVE CONCRETE AND CHANGE OF HYDRATION PRODUCTS"
in Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 989-999. (ACI SP-126)

Microstructure and mechanical properties of concrete with expansive additive are reported compared with ordinary concrete. Samples of long-term concrete (22 years) were collected from an actual building built in 1967 with calcium sulfoaluminate (CSA) used as expansive additive. Hydration products were separated from these samples by using heavy media and analyzed by means of DSC, XRD and FT-IR. The morphology of the mortar portion was observed by SEM. No differences were detected on the carbonation depth and the compressive strength between CSA concrete and ordinary concrete. Qualitative analysis shows that following carbonation of concretes, C-S-H was changed to silica gel or to C-S-H with low Ca/Si ratio and decomposed to CaCO3, whereas ettringite (AFt), present in CSA concrete, was decomposed to CaCO3, Al (OH)3 gel and gypsum. Quantitatively, hydration products in carbonated CSA concrete are larger than in carbonated ordinary concrete. Therefore, decomposition rate of AFt by carbonation is slower than that of C-S-H.

3305
Sakai, K., Watanabe, H., Nomachi, H., and Hamabe, K.
"ANTIFREEZE ADMIXTURE DEVELOPED IN JAPAN"
Concrete International, Mar 1991, Vol. 13, No. 3, pp 26-30.

An antifreeze admixture that is both non-chloride and non-alkaline has been developed in Japan. This admixture contains polyglycolester derivatives and calcium nitrite-nitrate. In the usual dosage of this admixture there are approximately 10g/cu m of alkali and less than 10g/cu m of chloride ions. The article describes the laboratory tests on the freezing temperature of pore water, heat evolution, strength development and freeze-thaw resistance. The alkali-aggregate reaction is also discussed. Details of field tests are given. The test results show that the admixture lowered the freezing point of pore water and promoted strength development and is an excellent anti-freezing admixture for cold weather concreting.

3306
Sakamoto, J., Matsuoka, Y., Shindoh, T., and Tangtermsirikul, S.
"AN APPLICATION OF SUPER WORKABLE CONCRETE TO CONSTRUCTION OF ACTUAL STRUCTURES"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 41-48.

This paper describes test results of mixing and placing a super workable concrete, of which the performance is excellent in fresh state due to its superior deformability and segregation resistance. The stability of concrete properties after mixing, easiness of placing, and qualities after hardening were investigated. The results of the investigation confirmed that it was possible to produce the super workable concrete in an actual concrete mixing plant, and to construct the concrete structure without applying vibration.

3307
Sarkar, S. L., Baalbaki, M., and Aitcin, P-C.
"MICROSTRUCTURAL DEVELOPMENT IN A HIGH-STRENGTH CONCRETE CONTAINING A TERNARY CEMENTITIOUS SYSTEM"
Cement, Concrete and Aggregates, Winter 1991, Vol. 13, No. 2, pp 81-87.

The cause of the sudden upsurge of mechanical strength at 12 h in a silica fume/fly ash high-strength concrete is investigated and the microstructural characteristics are determined. The concrete was subject to progressive hydration from 1 to 91 days. It is noted that the early increase in compressive strength in a silica fume/fly ash concrete might be explained by the dissolution of a certain quantity of K2O from the surface of a substantial number of fly ash particles in very early hydration. In contrast, silica fume concrete with identical cement, aggregates, and W/C fails to develop such high strength though this trend was reversed from age one day. This and other findings are discussed.

3308
Saucier, F., Bastien, J., Pigeon, M., and Fafard, M.
"COMBINED SHEAR-COMPRESSION DEVICE TO MEASURE CONCRETE-TO-CONCRETE BONDING," Experimental Techniques, Sep-Oct 1991, Vol. 15, No. 5, pp 50-55.

In many instances, deteriorated concrete structures could be economically repaired if a thin concrete overlay could be used. However, experience has shown that debonding often occurs, sometimes after only few months of service. In fact, the actual knowledge of the new-to-old concrete bonding mechanism is very limited and needs to be improved before durable repairs can be obtained in every case. To study the bonding mechanism, the first task is to choose a testing procedure to evaluate the mechanical strength of a concrete-to-concrete joint. Many procedures have already been proposed, but it was considered necessary, for research purposes, to develop a new testing device working with small concrete specimens and designed to minimize the influence of stress concentrations. Because our research program on the durability of bonding involved a large number of specimens, special attention was given to obtaining an overall testing time (fabricating and preparing specimens, testing and cleaning) as short as possible. The procedure and the device developed to fit these needs are described in this paper following a discussion of some of the classical methods of testing concrete-to-concrete bonding.

3309
Saucier, F., Pigeon, M., and Cameron, G.
"AIR-VOID STABILITY, PART V. TEMPERATURE, GENERAL ANALYSIS, AND PERFORMANCE INDEX"
ACI Materials Journal, Jan-Feb 1991, Vol. 88, No. 1, pp 25-36.

An important research project on air-void stability was carried out over a period of 2 years. Different series of concrete mixes were prepared and the results discussed in four preceding papers. A final series on the influence of temperature is now presented. The complete project has produced a very large database on air-void characteristics covering a wide range of air-void systems (334 measurements of air-void characteristics are reported). This database is used to investigate the general relationships among the different parameters of the air-void system, as well as some mix characteristics. To help in the rapid assessment of the overall quality of any air-void system, a performance index is proposed. A summary of the principal conclusions and recommendations terminates the series.

3310
Senbetta, E. and Bury, M. A.
"CONTROL OF PLASTIC SHRINKAGE CRACKING IN COLD WEATHER"
Concrete International, Mar. 1991, Vol. 13, No. 3, pp. 49-53.

The addition of the freezing weather admixture (FWA) protected the mortar specimens from freezing. Conversely, plain mortar specimens froze after 24 hours in a 30o F (-1oC) environment. The specimens containing the FWA had less evaporation of water from their surfaces than the plain mortar specimens at both 40o and 65oF (4o and 18o C) mix temperatures. Also, the rate of evaporation was significantly greater for the 65o F (18o C) mix than for the 40o F (4o C) mixes. The FWA mortar specimens showed no signs of plastic shrinkage cracking whereas the plain mortar specimens had significant plastic shrinkage cracking.

3311
Shilstone, J. M., Sr.
"PERFORMANCE SPECIFICATIONS FOR CONCRETE PAVEMENTS"
Concrete International, 1991, Vol. 13, No. 12, pp 28-34.

The paper discusses the question of what characteristics of the portland cement concrete portion of a pavement will provide a 30 to 40 year durability under a certain E18 use when cast on a sound, engineered subgrade and base and that has properly installed joints. It is pointed out that the answer must be in the form of a detailed, technical description of the concrete composite. The description should include objectives for the paste, including entrained air, spacing factor, and the amount of trapped air; aggregate size and qualities including geological types with shape and texture limitations and particle distribution; in-place strength (after at least 90 days) in both flexural and compressible terms; relative density; permeability; and surface conditions. The need for research into the nature of the mixture is indicated. The performance contract and two alternative contract arrangements are described. The need for defining the difference between good and poorly performing pavements is emphasized.

3312
Shimada, H., Sakai, K., and Litvan, G. G.
"ACOUSTIC EMISSIONS OF MORTAR SUBJECTED TO FREEZING AND THAWING"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 263-278. (ACI SP-126)

To determine the characteristics of deterioration of concrete under freezing and thawing, acoustic emissions (AE) of mortar were measured and analyzed. Acoustic emissions of ice formation were examined to establish test conditions. In addition, propagation properties of acoustic emissions such as wave velocity and amplitude were examined with an AE pulser.

3313
Smadi, M. and Migdady, E.
"PROPERTIES OF HIGH STRENGTH TUFF LIGHTWEIGHT AGGREGATE CONCRETE"
Cement & Concrete Composites, 1991, Vol. 13, No. 2, pp 129-135.

The potential use of naturally occurring tuff aggregates available in northeastern Jordan to produce high strength lightweight concrete has been studied. As a result of various concrete mixes, and using normal techniques, it was possible to obtain high quality lightweight concrete which is suitable for application in reinforced and prestressed concrete structures, with a compressive strength as high as 60 MPa at 90 days. In order to investigate the mechanical short term properties of this type of high strength concrete, a large number of specimens of different shapes and sizes were tested at different ages. The properties obtained include unit weight, Poisson's ratio, static modulus of elasticity, specimen size and shape effect, and the development with age of compressive strength, splitting tensile strength and modulus of rupture under different curing conditions.

3314
Soongswang, P., Tia, M., and Bloomquist, D.
"FACTORS AFFECTING THE STRENGTH AND PERMEABILITY OF CONCRETE MADE WITH POROUS LIMESTONE"
ACI Materials Journal, Jul-Aug 1991, Vol. 88, No. 4, pp 400-406.

An extensive laboratory study was performed to investigate the differences between the properties of concretes made with a porous limestone and those made with a siliceous river gravel and with a dense limestone. The effects of maximum aggregate size, cement type, water-cement ratio, and curing duration were also studied. The results of the study indicate that the concretes made with porous limestone are not significantly different from those made with river gravel. The concretes made with dense limestone show higher strengths and lower permeability than those made with porous limestone or river gravel. Concretes with high strength and low permeability can be produced using porous limestone if the concrete mixture is properly designed.

3315
Sprinkel, M. M.
"APPLICATIONS OF HIGH PERFORMANCE CONCRETES," Proceedings of a Specialty Conference Sponsored by the Highway Division of the American Society of Civil Engineers and the Federal Highway Administration, held Apr 8-10, 1991, Denver, CO; Ed. by B. T. Harder; ASCE, New York, 1991, pp 6-8.

The two principal applications in transportation of high performance concretes are the rapid repair of structures and the construction of structures with a longer service life than is now obtained with conventional concretes. Specific applications of such concretes for the rapid repair of structures include the installation of overlays, patching, and the replacement of sections of bridge decks and pavements. Parapets, median barriers, beams, and piers can also be repaired rapidly. The use is described of high performance ready mix concrete containing 10 bags/cubic yd of a special blended cement. The use of high performance ready mix concrete containing 8 to 9 bags/cubic yd of type III cement is also described. The requirements for increasing the use of high performance concretes in repair operations are discussed.

3316
Stark, D.
"THE MOISTURE CONDITION OF FIELD CONCRETE EXHIBITING ALKALI-SILICA REACTIVITY"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 973-987. (ACI SP-126)

The moisture condition of field concretes exhibiting evidence of alkali-silica reactivity was investigated utilizing relative humidity (RH) measurements. Prior determinations were made on laboratory mortar specimens to determine the threshold level required to sustain expansive reactivity. Results indicated that RH values greater than 80 percent, referenced to 21 degrees to 24 degrees Centigrade, are required to support expansive alkali-silica reactivity. Field measurements revealed that most of the concrete in highways and dams in desert areas are sufficiently damp to sustain expansive ASR.

3317
Strand, G. W.
"HIGH-PERFORMANCE CONCRETE IN ALL-WEATHER DECK POURS"
Proceedings of the Sixth International Cold Regions Engineering Specialty Conference, held Feb 26-28, 1991, West Lebanon, NH; Sponsored by the New Hampshire Section of ASCE and Others; Ed. by D. S. Sodhl; ASCE, New York, 1991, pp 210-229.

A high performance concrete mix enhanced with a combination of microsilica, superplasticizer, and high dosages of a corrosion-inhibiting, accelerating admixture (calcium nitrite); proved to be advantageous for pouring exposed parking decks during both very hot and very cold conditions in Minneapolis. This was the first major project in the United States to utilize both microsilica and calcium nitrite corrosion inhibitor for improved durability and resistance to road salt-induced corrosion. Both the unique mix design and carefully planned construction procedures allowed a concrete that might have otherwise been assumed to be difficult, to be quickly placed and post-tensioned in conditions with air temperatures as low as minus 5 degree F ( minus 21 degree C). The workability and all-weather adaptability of this high performance concrete mix, along with the successful techniques of the construction team, in a wide variety of temperature conditions may unshackle concrete from many of its limitations as a construction material in cold regions.

3318
"STRATEGIC HIGHWAY RESEARCH PROGRAM PRODUCTS"
Proceedings of a Specialty Conference sponsored by the Highway Division of the American Society of Civil Engineers and the Federal Highway Administration, held Apr 8-10, 1991, Denver, CO; Ed. by B. T. Harder; ASCE, New York, 1991, 96 pp.

This conference introduced the products of the first three years of the Strategic Highway Research Program to the highway engineering and construction organizations, and to governmental agencies. The papers were presented in two major categories: paving materials products; and roadway maintenance and management tools. Thirty nine papers were presented in ten sessions as well as the opening and closing plenary sessions. The sessions covered the following: performance based specifications; workzone safety devices; high performance concretes; materials handling; alkali-silica reactivity; automated deflection testing; freeze-thaw problems; pavement distress surveys; asphalt-aggregate mixture analysis system; corrosion of highway bridges; improving concrete mixes and curing; crack-filling robot; fiber-optic air meter; traffic monitoring - class and weight; laboratory tests; improved winter weather forecasting & communications; innovative test methods for binders; evaluation of deicing chemicals; innovative test measures for mixtures; improved snow fences and snowplows.

3319
Taerwe, L.
"HIGH STRENGTH CONCRETE FOR PRESTRESSED CONCRETE GIRDERS"
IABSE Reports, 1991, Vol. 64, pp 355-60.

This paper illustrates that the use of high strength concrete allows increasing the span of prestressed girders with a given cross section. It is also indicated that for a given span length, girder spacing can be significantly increased. These benefits are demonstrated by means of numerical examples, which give formulae to calculate the maximum span lengths that can be achieved for both post tensioned girders and precast prestressed girders.

3320
Tamura, K. and Tazawa, E.
"IMPROVEMENT ON RESISTANCE OF HIGH-STRENGTH LIGHT-WEIGHT CONCRETE TO FREEZING AND THAWING BY NEW SEPARATE MIXING"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 219-230.

A new mixing procedure for improving resistance to freezing and thawing as well as workability by coating the light-weight coarse aggregate with cement paste is proposed in this paper. The new mixing procedure was tested and compared with the conventional procedure on consistency, compressive strength and resistance to freezing and thawing (as per ASTM C666 A(1)) of high-strength light-weight concretes having the same mix proportion but mixed by the two different procedures.

3321
Tamura, K., Teramoto, H., and Tagaya, K.
"RESISTANCE OF STEEL/HIGH STRENGTH LIGHT-WEIGHT CONCRETE HYBRID STRUCTURES TO FREEZING AND THAWING"
in Offshore and Arctic Operations, 1991: Papers presented at the Fourteenth Annual Energy-Sources Technology Conference and Exhibition, Jan 20-23, 1991, Houston, TX; Sponsored by the Petroleum Division ASME; Ed. by R. G. Urqhart and A. S. Tawfik; ASME, New York, 1991, PD-Vol. 38, pp 91-99.

This paper describes the resistance to freezing and thawing of sandwich-type hybrid structure consisting of steel and high strength light weight concrete for operation in arctic regions. In this study, the following tests were performed: a freezing and thawing test of high strength light weight concrete in the atmosphere; compressive strength and punching shear tests with respect to the bond strength between steel and concrete; and a loading test of the sandwich-type hybrid beam after freezing and thawing - temperature cycles. A new separate mixing method in which 2 parts of water and cement are mixed was tested as the mixing method of high strength light weight concrete. This method improved the resistance to freezing and thawing of high strength light weight concrete.

3322
Tanigawa, Y., Nakamura, M., Shibata, T., and Odaka S.
"EFFECT OF COARSE AGGREGATE ON COMPRESSIVE FAILURE OF HIGH-STRENGTH CONCRETE," Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 61-68.

A series of experiments were carried out to examine the effect of coarse aggregate on the compressive failure of high-strength concrete. The method for estimating the apparent compressive strength of coarse aggregate in concrete proposed earlier by the authors was applied to high-strength concrete, and the compressive fracture process of the concrete was discussed by examining the occurrence and growth of microcracks in concrete.

3323
Thomas, M. D. A., Nixon, P. J., and Pettifer, K.
"THE EFFECT OF PULVERISED-FUEL ASH WITH A HIGH TOTAL ALKALI CONTENT ON ALKALI SILICA REACTION IN CONCRETE CONTAINING NATURAL UK AGGREGATE"
in Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 919-940. (ACI SP-126)

A number of seven-year old, externally-stored 500 x 100 x 100 mm concrete beams, some of which had suffered severe cracking due to alkali silica reaction, have been examined. The concretes were produced using pfa at a range of addition levels and contained a fixed proportion of a known reactive sand. Following seven years exposure, severe cracking was observed in the specimens without pfa or with 5 percent pfa. Surface crack widths were often in excess of 1 mm and examination of sawn surfaces indicated that the depth of visible cracks was up to 20 mm. Specimens containing 20 percent or more pfa did not exhibit any visible cracking. The lower quantity of available calcium in pfa concrete and the increased absorption of potassium by its hydrates are discussed with respect to their possible contributions to the suppression of damaging alkali silica reaction.

3324
Torii, K. and Kawamura, M.
"PORE STRUCTURE AND CHLORIDE PERMEABILITY OF SURFACE LAYERS OF CONCRETE"
Transactions of the Japan Concrete Institute, 1991, Vol. 13, pp 195-202.

This paper presents the data on the effects of mix proportions and curing conditions on the pore structure and chloride permeability of surface layers of concretes with and without a mineral admixture. Large-sized concrete specimens were initially cured in water for 7 days and 28 days, and then exposed to three environments for 1 year: in water at 20 degrees C, in a room at 20 degrees C, 60% R.H. and outdoors. From the results, it was found that at the surface of concretes with a mineral admixture the hydration of portland cement was considerably depressed and coarse pores were developed when concretes with a mineral admixture were stored in a dry condition for a long time, while at the depth of 5 cm from the surface of concrete specimen there was little change both in the degree of hydration and the pore structure. AASHTO T 277-83 data showed that both surface layers and interior concretes with a mineral admixture were much less permeable to chloride irons than those of the corresponding ordinary portland cement concretes independent of curing and environmental conditions.

3325
Torii, K., Kawamura, M., Asano, T., and Mihara, M.
"CHLORIDE PERMEABILITY AND CORROSION OF REINFORCEMENT IN CONCRETE CONTAINING SILICA FUME"
Journal of the Society of Materials Science, Japan/Zairyo, Sep 1991, Vol. 40, No. 456, pp 1164-1170.

Condensed silica fume (CSF) is an ultra-fine and high reactive pozzolan. Some properties of fresh and hardened concretes can be significantly improved by the use of CSF. CSF has been used in concrete to make a high strength and durable concrete. This study aims at showing the influence of CSF on the chloride permeability of concrete and the chloride corrosion of steel bars embedded in concrete. From the experimental results, it was confirmed that the use of small amounts of CSF could effectively reduce the chloride permeability of concrete and improve the protective function of concrete against the chloride corrosion of steel bars. With respect to the strength development of concrete and the protection against the chloride corrosion of steel bars in concrete, the most favorable replacement ratio of cement by silica fume was approximately 10%. In Japanese.

3326
Torrent, R. J. and Jornet, A.
"THE QUALITY OF THE 'COVERCRETE' OF LOW-, MEDIUM- AND HIGH-STRENGTH CONCRETES"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 1147-1161. (ACI SP-126)

A comprehensive research program was carried out to evaluate the quality of the outer layer of concrete (the 'covercrete'), in terms of its durability and protective value to the underlying reinforcing bars. Parts of the results of that investigation are presented in this paper, namely those dealing with the influence of the concrete grade and cement type on the permeability to oxygen and water absorption properties of the 'covercrete' of concrete specimens subjected to 7 days moist + 21 days dry curing. The results obtained show that the permeability to oxygen is reduced 40 times when the concrete strength is raised from 25 to 85 MPa, whilst the rate of water absorption is reduced by a factor of 4. In addition, the cement type (including portland and blended cements) seems to play only a secondary role in the quality of the 'covercrete' of concretes of the same grade, especially above 25 MPa.

3327
Tuthill, L. H.
"LONG SERVICE LIFE OF CONCRETE"
Concrete International, July 1991, Vol. 13, No. 7, pp. 15-17.

The length of concrete service life depends on the correct choice and use of materials. Problems such as alkali-silica reaction (ASR) and the prospect of sulfate attack and corrosion need to be identified early and properly. These conditions must be controlled with resistant materials. An often overlooked requirement for long concrete life is preventing or minimizing thermal cracking of the massive structural concrete found in power plants, bridge piers, foundation elements, and thick linings of large tunnels. The long service life of concrete can be assured with the current technology advances and good engineering practices.

3328
Urpani, D., Mak, S. L., and Attard, M. M.
"CURING OF HIGH STRENGTH CONCRETE CYLINDERS"
Department of Civil Engineering, Monash University, Clayton, Victoria, Australia, Civil Engineering Research Report, No. 1/1991, 24 pp.

The development of new, higher strength concretes requires a re-examination of the relationship between cylinder compressive strength and in-situ values. High strength concretes (HSC) are concretes with compressive strengths between 50 MPa and 80 MPa, while very high strength concretes (VHSC) refer to even higher strengths. Normal strength concretes (NSC) are concretes with strengths between 20 MPA and 50 MPa, and include 50 MPa. This study aims to look at the effects of moist curing and cylinder size on the compressive strength of a range of concretes. Six concrete mixes varying from normal strength to HSC and VHSC are studied. Three sizes of cylinders ranging from a small 75 mm diameter, a medium 100 mm diameter to a large 150 mm diameter were used to study size effects on cylinder strength. All cylinders have a height to diameter ratio of two. Different moisture conditions (at a constant temperature) were investigated by the use of four moist curing regimes. These were air cured (AC), wrapped in plastic (PW), water bath cured (WB) and set-in- water (SW).

3329
Vruno, D. M., Downs, M. B., and Smith, S. S.
"LIGNITE FLY ASH CONCRETE HIGHWAY PAVEMENT - A 15-YEAR PERFORMANCE HISTORY"
Transportation Research Record, 1991, No. 1301, pp 155-159.

A research study was conducted at Twin City Testing Corporation in 1973, in cooperation with the North Dakota State Highway Department and the FHWA. The purpose of the study was to determine the effect on properties and performance of paving concrete with lignite fly ash substituted for various percentages of portland cement. The test program included both laboratory and field evaluations of compressive and flexural strength and freeze-thaw durability. The good performance of this concrete after 15 years of field exposure supports the original laboratory findings. The fly ashes used in this study do not conform to certain chemical and physical requirements of the current version of ASTM C618, the national consensus specification generally used as guidance for fly ash procurement; however, the nonspecification fly ash was used in pavement construction only after laboratory testing indicated its potential for providing satisfactory performance.

3330
Wakeley, L. D., Husbands, T. B., and White, C. L.
"EVALUATION OF RAPID-SETTING CONCRETES FOR AIRFIELD SPALL REPAIR"
Final Report; Structures Laboratory, Waterways Experiment Station, U. S. Corps of Engineers, Vicksburg, MS, 1991, 1 vol. (various pagings) (WES/TR/SL-91-4; AD-A237046)

Three commercially available, off-the-shelf, rapid-setting materials were evaluated for their potential as spall-repair concretes for Rapid Runway Repair (RRR). The three were a methyl methacrylate binder (Silikal R17AF), a magnesium phosphate mortar mix (Set-45), and a high-performance blended cement mortar mix (Pyrament 505). Each was extended 50 percent by mass with coarse aggregate for these tests. Test methods were chosen, or developed as required, to evaluate the performance of these three rapid-setting concretes in cold and wet conditions as well as at room temperature. None of the materials performed ideally under all conditions. Silikal R17AF gives very high strengths in cold, dry conditions. But it bonds poorly to wet surfaces and loses much of its strength when mixed with wet aggregate. Pyrament 505 gains strength more slowly, especially at temperatures below 20 F, but it bonds consistently well under all conditions tested. The Set-45 product evaluated could not be tested at temperatures below 40 F, due to insufficient strength even for removing specimens from the molds. Compressive strength may not be the most important factor to consider when choosing a spall repair material. Flexural strength, early thermal history, and bond to existing concrete may be more critical for a shallow patch such as a spall repair. Further analyses are recommended for the material that is least expensive, relatively nontoxic, and appears to be most versatile among these three, i.e., Pyrament 505.

3331
Walters, G. V. and Jones, T. R.
"EFFECT OF METAKAOLIN ON ALKALI - SILICA REACTION (ASR) IN CONCRETE MANUFACTURED WITH REACTIVE AGGREGATE"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 2, pp 941-953. (ACI SP-126)

This study is on the effectiveness of metakaolin in preventing ASR (alkali-silica reaction). Samples of metakaolin were prepared by calcining china clay (relatively pure kaolin) and several ball clays, all collected from South West England. Compression cube strength tests were carried out in which part of the cement content of a 1:6 mixture of aggregate and ordinary portland cement (OPC) was replaced by calcined clay. Results showed that some of the mixtures containing calcined clay exhibited no reduction in the 28 day compressive strength even when 25 percent of the OPC was replaced. Tests for ASR were conducted using prisms produced in accordance with the Draft British Standard 812, Part 123, containing highly reactive natural aggregates which gave an expansion of 0.450 percent at twelve months. It is concluded that expansion due to ASR is completely suppressed when sufficient metakaolin is added to thee concrete formulation. Metakaolin does not reduce the ultimate compressive strength of the concrete, provided that the feed clay is relatively free of impurity minerals.

3332
Whiting, D. and Burg, R. G.
"FREEZING AND THAWING DURABILITY OF HIGH-STRENGTH LIGHTWEIGHT CONCRETES"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 83-100. (ACI SP-126)

Concretes having strengths ranging from 54 to 73 MPA and densities ranging from 1920 to 2080 kg/m3 were produced from two lightweight aggregate sources. Supplementary cementitious materials (including silica fume, fly ash, and ground granulated blast furnace slag) were used in the mixtures. Test specimens were subjected to a variety of freezing and thawing test procedures and conditioning methods. The high strength lightweight concretes exhibited outstanding performance, with virtually no degradation during standard freezing and thawing testing. Prolonged exposure was needed to cause significant damage under simulated arctic offshore conditions. Durability was found to be a strong function of cumulative freezing and thawing cycles and moisture content, with saturation of aggregates prior to test leading to premature failure.

3333
Yamato, T., Emoto, Y., and Soeda, M.
"FREEZING AND THAWING RESISTANCE OF ANTI-WASHOUT CONCRETE UNDER WATER"
Durability of Concrete; Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, 1991, Vol. 1, pp 169-183. (ACI SP-126)

This paper presents the results of laboratory studies conducted to determine freezing-and-thawing resistance of anti-washout concretes under water. Three anti-washout admixtures were used in these studies. The water-to-cement ratio was 0.45, and the sand-coarse aggregate ratio was 0.67. A number of test cylinder were made for testing in compression at 7 and 28 days, and test prisms were cast for determining their resistance to freezing-and-thawing cycles in accordance with ASTM C-666, Procedure A. The air-void parameters of the hardened concrete were determined on sawn sections. The pore size distributions of the hardened concrete was measured by a mercury porosimeter. The test results indicated that the anti-washout concrete having the same water-to-cement ratio and the same air content as the control concrete showed poorer resistance to freezing-and-thawing than the control concrete without the anti-washout admixture.

3334
Yeginobali, A. and Mujahed, F. S.
"DURABILITY OF CONCRETES MIXED WITH SEA WATER"
Durability of Building Materials and Components, Proceedings of the Fifth International Conference, held Nov 7-9, 1990, Brighton, UK; Ed. by J. M. Baker, P. J. Nixon, A. J. Majumdar, and H. Davies; E & FN Spon, London, 1991, pp 53-63.

Series of mortar and concrete mixes were prepared to have combinations of three types of cement: ordinary, pozzolanic and sulfate-resisting; three types of mixing water: tap, Red Sea and its 50% diluted version. From each mix cubic specimens were cast, each containing pairs of steel bars having different covers. The specimens were divided into groups and were subjected to different exposure conditions. At the age of one year they were tested for compressive strength and weight losses in steel bars. According to the results mixing with sea water increased the strengths of the specimens stored in dry air while causing slight reductions in most of the other specimens. In general ordinary portland cement performed better. Smaller cover, mixing with sea water, leaner mix and wetting-drying in sea water were corrosion increasing factors. Diluting the sea water for mixing could reduce corrosion to half or even less. The use of pozzolanic portland or pozzolan replacement of cement generally was not helpful in reducing steel corrosion.

3335
Yoshino, A., Nishibayashi, S., and Inoue, S.
"STUDY ON SUPERPLASTICIZED CONCRETE CONTAINING BLAST FURNACE SLAG"
Journal of the Society of Materials Science, Japan/Zairyo, Sep 1991, Vol. 40, No. 456, pp1143-1149.

Recently, the deterioration of concrete due to alkali-aggregate reaction or salt attack has become a serious matter. In order to improve the durability of concrete, it has been recommended that blast furnace slag be incorporated into concrete. On the other hand, it can be expected that the use of superplasticizer is effective to improve the workability of this type of concrete. This study was conducted for the purpose of establishing appropriate mix designs for superplasticized concrete incorporating blast furnace slag, as well as gaining and understanding of properties of fresh and hardened concretes. A superplasticizer and two types of high range water reducing agent (AE type) were used in this study. The slag contents were 0, 50 and 70%, respectively. The effects of these factors were measured by slump test, rheological test, segregation test, strength test, etc. The results showed that the flowability of cement paste increased with an increase in slag content at a constant dosage of admixture. This effect of slag was influenced by the type and addition method of admixture. Also, the slump loss of superplasticized concrete increased with an increase in slag. In Japanese.

3336
Yuan, R. L., Ragab, M., Hill, R. E., and Cook, J. E.
"EVALUATION OF CORE STRENGTH IN HIGH-STRENGTH CONCRETE"
Concrete International, May 1991, Vol. 13, No. 5, pp 30-34.

Research is reported that attempted to correlate high strength concrete core strength to the strength of standard moist-air cured and field-cured cylinders. The details of the experimental program and results are described. The results showed that the in-situ strength as determined using drilled cores is less than that of moist-air cured and field-cured cylinders tested at the same age. At any given age, core strength is about 75 % of moist-air cured cylinder strength, and about 85 % of field-cured cylinder strength. The data shows that for a column of concrete with a large cross-section area, coring location has little or no effect on core strength. The temperature at the center of a column with a large cross-sectional area is significantly higher than near the surface. For a concrete column with a large cross-sectional area, the core strength at the center is significantly lower than that near the surface. It is noted that strength tests done on standard, moist-air cured cylinders are useful for quality control purposes and for checking the acceptability of the concrete as it is produced.

3337
Zayed, A. M.
"EFFECT OF FLY ASH QUALITY ON THE DURABILITY AND SERVICE LIFE OF CONCRETE"
Final Report, College of Engineering, University of South Florida, Tampa, FL, 1991, 62 leaves.

This investigation addresses the effect of variable loading in power stations on the material properties and quality of the produced Class F Fly Ash. In addition, the effect of varying fly ash quality on the properties and durability of concrete was investigated. The properties of the as-received ash that were quantified include: oxides composition, oil content, carbon content, LOI, glass content, particle size distribution, fineness, mortar cube strength and reacted fly ash fraction. It was found that variation in loading conditions affected the pozzolanic activity of the ashes. The pozzolanic activity was found to be a function of the fly ash glass content, fineness and oil content. Properties of fresh concrete, namely, air content and slump were found to be affected by the quality of the as-received ash, specifically its carbon content. The strength of concrete mixes incorporating different quality fly ashes was found to be a function of the as-received ash properties.

3338
Zhang, M-H. and Gjorv, O. E.
"CHARACTERISTICS OF LIGHTWEIGHT AGGREGATES FOR HIGH-STRENGTH CONCRETE"
ACI Materials Journal, Mar-Apr 1991, Vol. 88, No. 2, pp 150-158.

The paper reports on some high-strength lightweight aggregates available on the European market. For the various aggregates, the particle shape, surface texture, and pore structure varied within wide limits. In all the aggregates, there were some relatively large voids and fissures, which made the aggregate weak and friable. Some of the aggregates had a distinct dense outer shell. The particle density varied from 1.07 to 1.54 g/cm3. This variation was related to characteristic differences in macroscopic and microscopic pore structure. After the first 30 min, the water absorption varied from 8 to 13 % by weight, but most of the water absorption took place within the first 2 min. Within the first 30 min, more than half of the 24 hr water absorption was observed. For cut particles of those aggregates that had dense surface layers, the water absorption within the first 30 min was approximately 30% higher than that of whole particles of the same specific surface.

3339
Zhang, M-H. and Gjorv, O. E.
"EFFECT OF SILICA FUME ON PORE STRUCTURE AND CHLORIDE DIFFUSIVITY OF LOW POROSITY CEMENT PASTES"
Cement and Concrete Research, Nov 1991, Vol. 21, No. 6, pp 1006-1014.

This paper presents the results of an experimental investigation on the effect of silica fume on pore structure and diffusivity of low porosity cement pastes. For cement pastes with w/c (water/cement) ratios in the range of 0.20 to 0.30, a 10% replacement of the cement with silica fume only reduced the total porosity to a small extent. However, a refinement of the pore size distribution took place in such a way that the content of larger pores was reduced for decreasing w/c ratio. For pure portland cement pastes the effect of a certain constant change of w/c ratio on the chloride diffusivity was substantially higher at high w/c ratios than at low w/c ratios. A 10% replacement with silica fume reduced the chloride diffusivity for all w/c ratios so much that the effect of w/c ratio became less important.

3340
Zhang, M-H. and Gjorv, O. E.
"MECHANICAL PROPERTIES OF HIGH-STRENGTH LIGHTWEIGHT CONCRETE"
ACI Materials Journal, May-Jun 1991, Vol. 88, No. 3, pp 240-247.

Information is presented on the mechanical properties of high-strength lightweight concrete up to 100 MPa with a corresponding density of 1865 kg/ sq m. Five different types of lightweight aggregates were investigated and the strength of the aggregate appears to be the primary factor controlling the strength of the high strength lightweight concrete. The tensile/compressive strength ratio appears to be lower for high strength lightweight concrete than that for high strength normal weight concrete, and the elastic modulus, which varied from 17.8 to 25.9 GPa, is much lower than that of normal weight concrete. For the high strength lightweight concrete, the shape of the ascending part of the stress-strain curve was more linear than that of lightweight concrete with low to medium strength.

3341
Zhang, M-H. and Gjorv, O. E.
"PERMEABILITY OF HIGH-STRENGTH LIGHTWEIGHT CONCRETE"
ACI Materials Journal, Sep-Oct 1991, Vol. 88, No. 5, pp 463-469.

Information on the resistance of high strength lightweight concrete 50 to 100 MPa to water penetration and accelerated chloride penetration is presented. Testing techniques are also discussed. The permeability of high strength-lightweight concrete appears to be very low, but it may be higher than that of normal weight concrete at a similar strength level. The permeability of high strength lightweight concrete appears to be more dependent on the porosity of the mortar matrix than the porosity of the lightweight aggregate. There appears to be an optimum cement content for permeability. A too high cement content may increase the permeability. No direct relationship between water permeability and electrical conductivity was observed, but a direct relationship between water permeability and accelerated rate of chloride penetration was observed. Hence, accelerated testing of chloride penetration appears to be a more valuable way to test the permeability than testing the electrical conductivity.

3342
Zia, P., Ahmad, S. H., and Leming, M. L.
"MECHANICAL BEHAVIOR OF HIGH PERFORMANCE CONCRETES"
Proceedings of a Specialty Conference Sponsored by the Highway Division of the American Society of Civil Engineers and the Federal Highway Administration, held Apr 8-10, 1991, Denver, CO; Ed. by B. T. Harder; ASCE, New York, 1991, pp 3-5.

The objectives of this 4-year research project are: to obtain needed information which fills gaps in the present knowledge, and to synthesize this information in a form that is directly useful to highway engineers; and to develop new significantly improved engineering criteria for the mechanical properties and behavior of high performance concretes, and to provide recommendations and guidelines for using these concretes in highway applications according to the intended use, required properties, environment, and service. The research program consists of 4 major tasks: evaluation and interrelationship of the mechanical properties of concrete; use of high performance concrete; effects of field conditions; and recommendations and guidelines. The primary focus of the first years work was the first task, the goal of which was to conduct a critical literature review relative to the properties and behavior of high performance concrete, to identify any significant gaps in the knowledge base, and to use the findings to develop a work plan for the second task. The products of Task I are noted.

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Zia, P., Ahmad, S. H., and Leming, M. L.
"MECHANICAL PROPERTIES OF HIGH PERFORMANCE CONCRETE"
Proceedings of the Second Canadian Symposium on Cement and Concrete, held July 24-26, 1991, Vancouver, B. C., Canada; Ed. by Sidney Mindess, University of British Columbia, Vancouver, Canada, 1991, pp. 130-139. (Also in ACI SP-128)

This paper presents a discussion of the objectives, scope, and progress of a 4-year research project on the mechanical properties of high performance concretes with particular reference to highway applications. High performance concrete is defined by certain requirements of strength and durability.

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Zia, P., Leming, M. L., and Ahmad, S. H. "HIGH PERFORMANCE CONCRETES. A STATE-OF-THE-ART REPORT"
Strategic Highway Research Program, National Research Council, Washington, D. C., 1991, 251 pp. (SHRP-C/FR-91-103; PB92-130087)

This state-of-the art report summarizes the results of an extensive search and review of available literature on the mechanical properties of concrete, with particular reference to high performance concrete for highway applications. Included in the review and discussion are the behavior of plastic concrete as well as the strength and deformation characteristics of hardened concrete. Both short-term and long-term effects are considered. Based on the review of the available information, research needs are identified. It is concluded that much research is needed to develop data on the strength and durability properties of concrete that develops high strength, particularly very early strength.