Fiber Reinforced Concrete 1989

The long term durability of pva (polyvinyl alcohol) fibres used as reinforcement in cement-based products has been assessed after exposure of the products to natural weathering and an accelerated aging process. The pva fibres were extracted, then characterised by x-ray diffraction techniques. The mechanical properties of the extracted fibres were compared with the mechanical properties of the composite. In general an increase in composite strength and stiffness was evident; this may in part be associated with carbonation of the matrix and increase in the pva fibre-matrix interfacial bond. X-ray diffraction studies on the extracted pva fibres indicated in some cases a loss of crystalline order with age (natural weathering) related to a disordering of the hydrogen-bonded sheets. The possible changes are minor and have no influence on the tensile properties of the pva fibres or the aging properties of the composites. It is suggested that pva fibres which participate in the reinforcement of the cement matrix are durable over a period of at least 7 years, and there is every reason to believe that these fibres will continue to be durable for extended periods.

4002
Banthia, N. and Foy, C.
"MARINE CURING OF STEEL FIBER COMPOSITES," Journal of Materials in Civil Engineering, May 1989, Vol. 1, No. 2, pp 86-96.

A study is reported which compared the effects of normal and sea water curing on the long term pull-out behavior of steel fibers embedded in cementitious matrices. The effects of silica fume addition and temperature of curing on the durability of a single fiber unit were also studied. It was found, based on a limited number of tests, that the marine curing of steel fiber concrete appears to be acceptable only at very low (less than 2 deg C) ambient temperatures. High temperatures promote early corrosion and lead to strength reductions. The silica fume does not appear to enhance corrosion. Preferential anodic pitting is possible at the deformed locations in the fibers, perhaps due to residual stresses. This finding is relevant in the manufacture of fibers for marine applications.

4003
Bayasi, Z. and Soroushian, P.
"OPTIMUM USE OF POZZOLANIC MATERIALS IN STEEL FIBER REINFORCED CONCRETE"
Transportation Research Record, 1989, No. 1226, pp 25-30.

The effects on fresh and hardened material properties for fly ash caused by substituting cement with fly ash and silica fume in steel fiber reinforced concrete were studied experimentally. The percentage substitution of cement ranged from 0 to 40% and from 0 to 20% for silica fume. The workability of fresh fibrous mixtures was characterized by measuring the inverted slump cone time. The hardened material was tested at 28 days under compression and flexural loads. The development of compressive strength with time was also assessed in steel fiber reinforced concrete incorporating fly ash. The generated test data were used to decide the optimum ranges of cement substitution with fly ash or silica fume in steel fiber reinforced concrete for achieving desirable fresh mix and hardened material characteristics.

4004
Benaiche, F. and Barr, B.
"FRACTURE CHARACTERISTICS OF HIGH STRENGTH CONCRETE AND FRC MATERIALS"
Fibre Reinforced Cements and Concretes: Recent Developments, Papers presented at the International Conference held September 18-20 1989 at the School of Engineering, University of Wales College of Cardiff, UK; Ed. by R. N. Swamy and B. Barr; Elsevier Applied Science, London, 1989, pp 411-419.

The main objective of the work reported was to investigate the fracture characteristics of high strength fibre reinforced concrete. The various fracture parameters studied were the modulus of rupture and fracture toughness (in Mode I loading), the shear strength (in Mode II loading), the tensile strength and their respective toughness indices. The high strength was provided by reducing the water-cement ratio, by the use of admixtures and by the use of microsilica. Two types of fibres were used in the study - steel and polypropylene fibres. Increasing the compressive strength resulted in increased modulus-of-rupture and fracture toughness together with a significant enhancement of the shear strength. Increased compressive strength due to a reduced water-cement ratio had only a marginal effect on the tensile strength, whereas much larger increases in tensile strength were observed by the use of admixtures and, in particular, by the use of microsilica. The post-cracking toughness (measured by means of a toughness index) increased with increasing fibre concentrations. The greatest enhancement of toughness was observed in the Mode I tests. The post-cracking toughness in shear and tension is significantly less than that observed in the Mode I tests.

4005
Bentur, A.
"SILICA FUME TREATMENTS AS MEANS FOR IMPROVING DURABILITY OF GLASS FIBER REINFORCED CEMENTS"
Journal of Materials in Civil Engineering, Aug 1989, Vol. 1, No. 3, pp 167-183.

A study is reported which found that treatment of alkali resistant glass fibers with silica fume was effective in improving durability performance of alkali resistant glass fiber reinforced cement composites (GFRC), to retain more than 50% of the composite toughness over accelerated aging periods of 5 to 9 months. Findings regarding silica fume replacement in the matrix and durability performance are also discussed. It is suggested that fiber treatment eliminates the aging induced by microstructural effects, while the matrix modification reduces the influence of chemical attack.

4006
Bentur, A., Mindess, S., and Skalny, J.
"REINFORCEMENT OF NORMAL AND HIGH STRENGTH CONCRETES WITH FIBRILLATED POLYPROPYLENE FIBRES"
Fibre Reinforced Cements and Concretes: Recent Developments, Papers presented at the International Conference held September 18-20, 1989 at the School of Engineering, University of Wales College of Cardiff, UK; Ed. by R. N. Swamy and B. Barr; Elsevier Applied Science, London, 1989, pp 229-239.

The present study deals with an investigation of the effects of low volumes of fibrillated polypropylene fibre reinforcement on the properties of concrete, in particular, on impact resistance. The main conclusions are: (1) The various types of commercial polypropylene fibres evaluated in the present study exhibited good bond with the matrix. However, in spite of the favourable bond, a low content of polypropylene fibre reinforcement (0.1 to 0.5%) had only a small positive influence on the impact resistance of both normal and high strength concretes; (2) In static loading, a low content of polypropylene reinforcement led to a marked improvement in fracture energy, suggesting that from a practical point of view its potential use is for control of cracks induced by static loading, and not in enhancing resistance to dynamic loading; and (3) Some potential advantages of a low volume content of polypropylene fibres may be found in enhancing the impact resistance of conventionally reinforced concrete.

4007
Chanvillard, G., Aitcin, P-C., and Lupien, C.
"FIELD EVALUATION OF STEEL FIBER REINFORCED CONCRETE OVERLAY WITH VARIOUS BONDING MECHANISMS"
Transportation Research Record, 1989, No. 1226, pp 48-56.

An experimental rehabilitation project was conducted on the Transcanadian Highway where old concrete pavement was recovered with a thin, steel fiber reinforced concrete overlay. In this project, 18 different construction conditions were investigated. The surface of the old pavement was either sandblasted or scarified. Three different types of steel fibers were used, and all the overlay was bonded with a thin cement grout. In addition, two lanes were repaired with some mechanical bonding provided by 37.5-mm (1.5-in.) steel nails. The most significant results obtained during the construction period as well as all data recorded over the succeeding two winters are reported and analyzed in this paper.

4008
Ezeldin, A. S. and Balaguru, P. N.
"BOND BEHAVIOR OF NORMAL AND HIGH-STRENGTH FIBER REINFORCED CONCRETE"
ACI Materials Journal, Sep-Oct 1989, Vol. 86, No. 5, pp 515-524.

Experimental results on the bond behavior of normal and high-strength concrete made with and without fibers are reported. A total of 18 mix proportions were investigated. The fiber lengths and reinforcement bar sizes were 30, 50, and 60 mm and #3, 5, 6, and 8 (9, 16, 19 and 25 mm) respectively. The bond tests were conducted using a modified pullout test in which the concrete surrounding the bar was in uniform tension. Addition of silica fume results in higher bond strength but causes brittle bond failure. Fibers can be used to improve the ductility to a considerable extent. The slip (relative movement between the bar and the concrete) at maximum bond load increases with increase in fiber content. Postpeak behavior is improved substantially by the fibers.

4009
Fahmy, M. F. and Lovata, N. L.
"CHEMICAL TREATMENTS OF POLYPROPYLENE FIBER SURFACES USED IN FIBER REINFORCED CONCRETES"
Transportation Research Record, 1989, No. 1226, pp. 31-35.

This paper reports the results of an experimental investigation to determine the effects of chemical treatment of polypropylene fibers (PPF) used in reinforced concretes. The control group concrete was designed at 4,000 psi. The chemical solution used to treat the fiber surfaces was a basic solution of linear alcohol alkoxylates. The investigation included comparison of some static strength as well as the interfacial bond characteristics of unreinforced, plain fiber reinforced, and chemically treated fiber reinforced concretes that were cured for two different periods of 28 and 45 days. Three separate methods of testing were conducted to ascertain the mechanical measures of the concrete samples: compression testing (ASTM 4.02, C-39), flexural strength tests (ASTM 4.02, C-78), and splitting tensile tests (ASTM 4.02,C-496). A random sampling of the failed PPF specimens was prepared and observed using scanning electron microscopy (SEM) technique. The interfacial features of the fiber surfaces were evaluated to determine the bonding characteristics between the fiber and the concrete matrix. A correlation between the chemical surface treatment of the PPF and the mechanical measures was statistically analyzed.

4010
Fan, C. and Zhu, L.
"STUDY OF THE MIX PROPORTION OF THE NO SLUMP CONCRETE [WITH] MELT-EXTRACTED CARBON STEEL FIBER"
Transportation Research Record, 1989, No. 1226, pp 98-104.

This paper reports an investigation of the mix proportion of melt-extracted carbon steel fiber reinforced no slump concrete. The optimum sand ratio, water content, and cement content, which are relevant to the fiber volume, were determined by a series of tests. Based on this investigation, a formula was derived for calculating the consistency. This formula is useful for such applications as the pavement of roads.

4011
Ibukiyama, S., Kokubun, S., and Ishikawa, K.
"INTRODUCTION OF RECENT THIN BONDED CONCRETE OVERLAY CONSTRUCTION AND EVALUATION OF THOSE PERFORMANCES IN JAPAN"
Proceedings of the 4th International Conference on Concrete Pavement Design and Rehabilitation, April 18-20 1989, Purdue University, West Lafayette, IN, 1989, pp 193-203.

This paper presents a recent example of the application of thin bonded concrete overlay (TBCO) onto jointed portland cement concrete pavement (PCCP) and continuously reinforced concrete pavement (CRCP) in Japan and reports on the results obtained. Conclusions are summarized as follows: (1) Some tests were performed to secure the bond of TBCO. In these tests, there was no obvious difference in crack occurrence. The method that should be selected differs according to what is economical and practical. (2) The cracks occurring on TBCO are tiny at the present phase (0.6 mm or less) and have no influence on serviceability. (3) As a preventive repair method, the use of steel fiber reinforced concrete (SFRC) is effective. In particular, replacement is more effective in locations suffering from severe damage. (4) When TBCO is applied to CRCP, many existing cracks did not reflect onto the TBCO, since SFRC, which is resistant to cracks, was used. (5) In developed regions in Japan, old roads naturally require repair work under various restrictions. In such circumstances, TBCO is one of the most promising methods.

4012
"INTERNATIONAL SYMPOSIUM ON RECENT DEVELOPMENTS IN CONCRETE FIBER COMPOSITES"
Transportation Research Record, 1989, No. 1226, 114 pp.

The 14 papers in this report deal with the following areas: Current Research and Applications of Fiber Reinforced Concrete Composites in India; Fiber Reinforced Concrete and Shotcrete for Repair and Restoration of Highway Bridges in Alberta; Flexural Fatigue Strength, Endurance Limit, and Impact Strength of Fiber Reinforced Concretes; Optimum Use of Pozzolanic Materials in Steel Fiber Reinforced Concrete; Chemical Treatments of Polypropylene Fiber Surfaces Used in Fiber Reinforced Concretes; Fatigue Strength of Fibrillated Polypropylene Fiber Reinforced Concretes; Field Evaluation of Steel Fiber Reinforced Concrete Overlay With Various Bonding Mechanisms; Natural Fiber Reinforced Concrete; Properties and Design of Fiber Reinforced Roller Compacted Concrete; Flexural Behavior and Toughness of Fiber Reinforced Concretes; A Comparative Evaluation of Plain, Polypropylene Fiber, Steel Fiber, and Wire Mesh Reinforced Concrete; Analysis of Fiber Reinforced Concrete Beams Under Combined Loadings; Study of the Mix Proportion of the No-Slump Concrete Melt-Extracted Carbon Steel Fiber.

4013
Johnston, C. D. and Carter, P. D.
"FIBER REINFORCED CONCRETE AND SHOTCRETE FOR REPAIR AND RESTORATION OF HIGHWAY BRIDGES IN ALBERTA"
Transportation Research Record, 1989, No. 1226, pp 7-16.

Under contract with the Research and Development Branch of the Alberta Transportation Department, the University of Calgary began work to assess the first-crack strength and toughness parameters of concrete and shotcrete to which steel and polypropylene fibers had been added. Laboratory tests used concrete typical of that normally specified for bridge deck overlays and shotcrete typical of that used for repairing deteriorated portions of supporting bridge structures. To these mixtures were added various types and sizes of steel and polypropylene fibers; silica fume was also included in a few fiber-matrix combinations. Laboratory results showed first-crack strengths from 5.0 to 6.4 MPa for matrixes without silica fume and from 7.9 to 8.6 MPa for those with silica fume. Longer high-aspect-ratio fibers suitable for conventionally mixed overlays produced material with elastic-plastic performance and toughness index (I sub 10) about 10, residual strength factor (R sub 5,10) about 100. Combinations with other high-aspect-ratio fibers yielded lower levels of performance, as did those with the shorter low-aspect-ratio fibers needed for shotcrete. Based on these laboratory findings, 26 bridge decks were restored with steel fiber reinforced concrete overlays and structural repairs were made to the beams, piers, or abutments of 19 bridges using steel fiber reinforced, dry-process shotcrete.

4014
Li, V. C., Backer, S., Wang, Y., Ward, R., and Green, E.
"TOUGHENED BEHAVIOR AND MECHANISMS OF SYNTHETIC FIBER REINFORCED NORMAL STRENGTH AND HIGH STRENGTH CONCRETE"
in Fibre Reinforced Cements and Concretes: Recent Developments, Papers presented at the International Conference held September 18-20 1989 at the School of Engineering, University of Wales College of Cardiff, UK; Ed. by R. N. Swamy and B. Barr; Elsevier Applied Science, London, 1989, pp 420-433.

This paper broadly reviews some of the improvements in toughness and ductility of normal and high strength concrete due to synthetic fiber reinforcement. Examples of improvements in the ultimate shear strength of longitudinally reinforced beams without shear stirrups and the flexural strength and energy capacity of unreinforced beams, which are a direct result of synthetic fiber reinforcement, are mentioned. Some preliminary results relating to the ability of synthetic fibers to reduce the brittleness of high strength mortar and concrete are presented. Finally some of the mechanisms which lead to the improved performance of synthetic fibre reinforced concrete (FRC) are reviewed.

4015
Marks, V. J.
"A FIFTEEN YEAR PERFORMANCE SUMMARY OF FIBROUS PC CONCRETE OVERLAY RESEARCH IN GREENE COUNTY, IOWA"
Highway Division, Iowa Department of Transportation, 1989, 20 p.

The Greene County, Iowa, overlay project, completed in October 1973, was evaluated in October 1978 after five years, in October 1983 after ten years, and most recently in October 1988 after fifteen years of service. The 33 fibrous concrete sections, four CRCP sections, two mesh reinforced and two plain concrete sections with doweled reinforcement were rated relative to each other on a scale of 0 to 100. The rating was conducted by original members of the Project Planning Committee, Iowa DOT, Iowa County, Federal Highway Administration and industry representatives. In all, there were 23, 25, and 17 representatives who rated the project in 1978, 1983, and 1988, respectively. The 23, 25, or 17 values were then averaged to provide a final rating number for each section or variable. All experimental overlay sections had performed quite well in the period from five through fifteen years, experiencing only limited additional deterioration. The 4-in.-thick nonfibrous mesh reinforced continuous reinforced concrete pavement overlay sections provided the best performance in this research project. Another nonfibrous 5-in.-thick bar reinforced overlay section performed second best. The best performance of a fibrous reinforced concrete section was obtained with 160 lbs of fiber per cu yd. The use of 750 lbs of cement per cu yd in the fibrous concrete overlays provided no benefit over the use of 600 lbs of cement per cu yd. There was no significant difference in the performance of the 2.5-in.-long and 1-in.-long fibers. The 3-in.-thick fibrous concrete overlays yielded substantially better performance than the 2-in. fibrous overlays. Substantial bonding was not achieved on any of the fibrous concrete overlay sections and, therefore, no conclusion can be reached in regard to the type of bonding. In general, the thicker, nonfibrous pavement overlay sections performed better than the fibrous reinforced concrete overlays. The additional cost of the fibrous concrete overlays cannot be justified based upon the comparative performance of the fibrous and thicker nonfibrous overlay sections.

4016
Morgan, D. R., McAskill, N., Richardson, B. W., and Zellers, R. C.
"A COMPARATIVE EVALUATION OF PLAIN, POLYPROPYLENE FIBER, STEEL FIBER, AND WIRE MESH REINFORCED SHOTCRETES"
Transportation Research Record, 1989, No. 1226, pp. 78-87.

Since the early 1970s, steel fiber reinfoced shotcrete has been increasingly used for such applications as support in tunnels, mines, excavations, and rock slopes. Previous studies have shown that steel fiber reinforced shotcrete, at fiber addition rates now commonly used, can provide equivalent or even superior performance than that provided by standard wire mesh reinforcement, when properties such as residual load-carrying capacity after first crack are compared. This paper presents the results of recent studies comparing the performance of common wire mesh reinforced shotcretes with that of shotcretes reinforced with high-volume concentrations of a collated fibrillated polypropylene (CFP) fiber. The tests were conducted using wet mix shotcrete applied to large panels, which were anchored and loaded to destruction with continuous monitoring of the crack formation and load vs deflection characteristics of the panels. The panels were tested in the same manner as tests previously conducted on plain, wire mesh, and steel fiber reinforced shotcretes; thus, the performance characteristics of the various shotcrete mixtures can be compared. It is shown that at certain addition rates of CFP fiber, similar residual load-carrying capacity after first crack can be obtained compared with shotcrete reinforced with wire mesh and shotcrete reinforced with steel fiber. Testing of standard flexural test beams to ASTM C1018 provided further verification of the equivalence of performance between shotcretes with these levels of addition of steel and CFP fiber with respect to parameters such as toughness index. The incorporation of high-volume concentrations of CFP fiber in wet-mix shotcrete presents opportunities for a wide range of applications where a tough, ductile, corrosion-resistant material is required.

4017
Naaman, A. E., Namur, G., Najm, H., and Alwan, J.
"BOND MECHANISMS IN FIBER REINFORCED CEMENT-BASED COMPOSITES"
Final Report, Department of Civil Engineering, University of Michigan, Ann Arbor, MI, 1989, 253 pp. (AD-A213637)

This report presents a comprehensive investigation of the mechanism of bond in steel fiber reinforced cement based composites. Following a state-of-the-art review on bond in reinforced and prestressed concrete as well as fiber reinforced concrete, the results of an experimental and an analytical program are described. The experimental program focuses primarily on the behavior of fibers under pull-out conditions. Pull-out load versus end slip behavior and bond shear stress versus slip relationship are studied extensively.

4018
Nagabhushanam, M., Ramakrishnan, V., and Vondran, G.
"FATIGUE STRENGTH OF FIBRILLATED POLYPROPYLENE FIBER REINFORCED CONCRETES," Transportation Research Record, 1989, No. 1226, pp. 36-47.

This paper presents the results of an experimental investigation to determine the flexural fatigue strength of concrete reinforced with three different concentrations of fibrillated polypropylene fibers. The properties and performance of fresh and hardened concretes with and without fibers are compared. The test program included the evaluation of 1) flexural fatigue strength and endurance limit; 2) hardened concrete properties, such as compressive strength, static modulus, pulse velocity, modulus of rupture, and toughness indexes; and 3) fresh concrete properties, including slump, vebe time, inverted cone time, air content, and concrete temperature. The test results indicated an appreciable increase in post-crack energy absorption capacity and ductility due to the addition of fibers. When compared with corresponding plain concrete, the flexural fatigue strength and the endurance limit (for 2 million cycles) significantly increased. The static flexural strength increased after being subjected to fatigue loading.

4019
Nakagawa, H., Akihama, S., and Suenaga, T.
"MECHANICAL PROPERTIES OF VARIOUS TYPES OF FIBRE REINFORCED CONCRETES"
in Fibre Reinforced Cements and Concretes: Recent Developments, Papers presented at the International Conference held September 18-20 1989 at the School of Engineering, University of Wales College of Cardiff, UK; Ed. by R. N. Swamy and B. Barr; Elsevier Applied Science, London, 1989, pp 523-532.

This paper reports on the mechanical properties of concrete reinforced with carbon fibres, Aramid fibres, and high-strength Vinylon fibres. Compressive, tensile, and flexural tests were conducted to prove that the strength of short-fibre FRC and its reinforcing efficiency depend on the material and volume ratio of the fibre. Flexural tests on fibre reinforced concrete (FRC) with continuous fibres using a three-dimensional fabric, and on a hybrid-type FRC with a three-dimensional fabric filled with short-fibre FRC, have clarified that the flexural characteristics generally depend upon the matrix at the initial stage of loading and upon the characteristics of the fibre used in the three-dimensional fabric at later stages.

4020
Nanni, A.
"PROPERTIES AND DESIGN OF FIBER REINFORCED ROLLER COMPACTED CONCRETE"
Transportation Research Record, 1989, No. 1226, pp 61-68.

Extensive experimentation in pavement construction was conducted using steel fiber reinforced concrete (SFRC). Although SFRC has demonstrated outstanding mechanical properties, its commercial application has been limited because of high cost. Cost savings could be realized for paving projects constructed with the emerging roller compacted concrete (RCC) technology. In particular, pavement thickness reduction due to the inclusion of fibers in RCC can allow single-lift construction where two lifts of unreinforced concrete would be required. Alternatively, for two or more lifts, SFRC can be confined to the most stressed layer(s). This paper presents compression and split tension results of laboratory cylinders and field cores reinforced with different types of steel fiber in various percentages. The concrete matrix contained fly ash, either Class F (used as a filler) or Class C (used as a binder). Fiber inclusion disturbed the consolidation of laboratory specimens, whereas field cores did not indicate any loss of density or compressive strength. Post-cracking characteristics were greatly enhanced by fibers with ultimate strength and toughness indexes derived from stress-strain curves for split tension. Sample design calculations compare the preliminary pavement thickness of unreinforced and fiber reinforced RCC with cost estimates for each.

4021
Nanni, A. and Johari, A.
"RCC PAVEMENT REINFORCED WITH STEEL FIBERS," Concrete International: Design & Construction, Mar 1989, Vol. 11, No. 3, pp 64-69.

A study is reported which observed the effect of fibers in RCC (roller compacted concrete) from a construction standpoint (i.e. mixing, placing, and attainable density). An experimental roller compacted concrete pavement strip reinforced with two types of steel fibers was successfully constructed. Laboratory test results obtained from site collected samples are presented. The improvement in strength and pseudo-ductility characteristics are discussed. The study indicates that addition of steel fibers in RCC does not affect preparation or placement of the mix. Test results showed that the mechanical properties improve with the addition of fibers. Composite properties are improved in terms of strength and pseudo-ductility.

4022
Paillere, A. M., Buil, M., and Serrano, J. J.
"EFFECT OF FIBER ADDITION ON THE AUTOGENOUS SHRINKAGE OF SILICA FUME CONCRETE"
ACI Materials Journal, Mar-Apr 1989, Vol. 86, No. 2, pp 139-144.

It has been found experimentally that very high strength silica fume concretes undergo early cracking when deformation is restrained. This phenomenon, which occurs even when the concrete is protected against any evaporation, is attributed to autogenous shrinkage, because of its exceptionally low water-cement ratio (0.26). An attempt was made to correct this weakness of the material by adding steel fibers. Two types of hooked fibers with ratios of length (in mm to diameter in hundredths of mm) of 30/60 and 50/50 were tested at a content of 0.8 percent by volume. For each type of fiber, the optimum sand-aggregate ratio giving maximum slump was determined together with the bending, compressive, and tensile strengths of the material. The fiber concretes have an autogenous shrinkage lower than the reference concrete and undergo cracking at a later age under restrained deformation.

4023
Ramakrishnan, V., Wu, G. Y., and Hosalli, G.
"FLEXURAL FATIGUE STRENGTH, ENDURANCE LIMIT, AND IMPACT STRENGTH OF FIBER REINFORCED CONCRETES"
Transportation Research Record, 1989, No. 1226, pp 17-24.

In many applications, particularly in pavements, bridge deck overlays, and offshore structures, the flexural fatigue strength and endurance limit are important design parameters because these structures are designed on the basis of fatigue load cycles. This paper presents the results of an extensive experimental investigation to determine the behavior and performance characteristics of the most commonly used fiber reinforced concretes (FRC) subjected to fatigue loading. A comparative evaluation of fatigue properties is presented for concretes with and without four types of fibers (hooked-end steel, straight steel, corrugated steel, and polypropylene) at two different quantities (0.5 and 1.0% by volume), using the same basic mix proportions for all concretes. The test program involved the determination of fresh concrete properties, including slump, vebe time, inverted cone time, air content, unit weight, and concrete temperature; and the determination of hardened concrete properties, including flexural fatigue strength, endurance limit, and impact strength. The addition of the four types of fibers caused a considerable increase in the flexural fatigue strength and the endurance limit for 4 million cycles, with the hooked-end steel fiber providing the highest improvement (143%) and the straight steel and polypropylene fibers providing the least. The impact strength was increased substantially by the addition of all four types of fibers, with straight steel fiber producing the lowest increase.

4024
Ramakrishnan, V., Wu, G. Y., and Hosalli, G.
"FLEXURAL BEHAVIOR AND TOUGHNESS OF FIBER REINFORCED CONCRETES"
Transportation Research Record, 1989, No. 1226, pp 69-77.

This paper presents the results of an extensive investigation to determine the behavior and performance characteristics of the most commonly used fiber reinforced concretes (FRC) for potential airfield pavements and overlay applications. A comparative evaluation of static flexural strength is presented for concretes with and without four different types of fibers: hooked-end steel, straight steel, corrugated steel, and polypropylene. These fibers were tested in four different quantities (0.5, 1.0, 1.5, and 2.0 percent by volume), and the same basic mix proportions were used for all concretes. The test program included (a) fresh concrete properties, including slump, vebe time, inverted cone time, air content, unit weight and concrete temperature, and hardened concrete properties; (b) static flexural strength, including load-deflection curves, first crack strength and toughness, toughness indexes, and post-crack load drop; and (c) pulse velocity. In general, placing and finishing concretes with less than 1 percent by volume for all fibers using laboratory-prepared specimens was not difficult. However, the maximum quantity of hooked-end fibers that could be added without causing balling was limited to 1 percent by volume. Corrugated steel fibers (Type C) performed the best in fresh concrete; even at higher fiber contents (2 percent by volume), there was no balling, bleeding, or segregation. Higher quantities (2 percent by volume) of straight steel fibers caused balling, and higher quantities of polypropylene fibers (2 percent by volume) entrapped a considerable amount of air. Compared with plain concrete, the addition of fibers increased the first crack strength (15 percent to 90 percent), static flexural strength (15 percent to 129 percent), toughness index, post-crack load-carrying capacity, and energy absorption capacity. Compared with an equal 1 percent by volume basis, the hooked-end steel fiber contributed to the highest increase, and the straight steel fiber provided the least (but appreciable) increase in the above-mentioned properties.

4025
Rollings, R. S.
"DEVELOPMENTS IN THE CORPS OF ENGINEERS RIGID AIRFIELD DESIGN PROCEDURES"
Proceedings of the 4th International Conference on Concrete Pavement Design and Rehabilitation, April 18-20 1989, Purdue University, West Lafayette, IN, 1989, pp 405-418.

In 1979 the U.S. Army Corps of Engineers introduced an airfield design manual that included design procedures for plain, reinforced, continuously reinforced, steel fiber reinforced, and prestressed concrete airfield pavements. In the intervening ten years additional work has led to changes in some of these procedures and to preparation of two updated design manuals published in 1988. This paper reviews the basis for these changes. Some of the topics covered include revised fatigue relationships for plain and steel fiber reinforced concrete pavements, acceptance of layered elastic design procedures as an alternative to Westergaard procedures, changes to thickness design for continuously reinforced concrete pavements, and revisions to the jointing criteria for steel fiber reinforced concrete pavements. Some work that has not progressed to the point to allow its inclusion in the 1988 manuals and the current status of changes to prestressed and overlay pavement design are presented.

4026
Swamy, R. N. and Barr, B.,(Eds.)
"FIBRE REINFORCED CEMENTS AND CONCRETES: RECENT DEVELOPMENTS"
Proceedings of an International Conference held Sep 18-20 1989 at the University of Wales College of Cardiff, School of Engineering, UK; Elsevier Applied Science, London, 1989, 700 pp.

Fibre reinforced cements and concretes are widely used as construction materials. The papers contained in this book give the state-of-the-art reports in a number of areas of research and applications. A number of papers deal with new fibres and matrices and optimizing composition. Durability testing and sheet materials are discussed. Recent studies on testing and mechanical performance, including toughness and impact resistance are covered. The range of new applications where these materials are being used is discussed. Also, several papers present the use of fibre reinforced concrete beams, columns, slabs and pavements.

4027
Taylor, M. A.
"CRACKING BEHAVIOR COMPARISONS BETWEEN NORMAL AND FIBER-CONCRETES"
in Structural Materials, Proceedings of the Sessions at the ASCE Structures Congress '89, May 1-5, 1989, San Francisco, CA; Ed. by James F. Orofino; ASCE, New York, 1989, pp 12-20.

A comparative study of the cracking behavior of plain- and polypropylene fiber concrete was performed. Both high- and low-strength concretes were studied. Maximum and average crack widths are reported and compared with ACI committee suggestions. Also reported are crack spacings and the height to which cracks spread toward the compressive face of the beams. Fibers appear to reduce all crack characteristics noted.

4028
Verhoeven, K.
"THIN OVERLAYS OF STEEL FIBER REINFORCED CONCRETE AND CONTINUOUSLY REINFORCED CONCRETE: STATE OF THE ART IN BELGIUM"
Proceedings of the 4th International Conference on Concrete Pavement Design and Rehabilitation, April 18-20 1989, Purdue University, West Lafayette, IN, 1989, pp 205-219.

Resurfacing of existing roads with cement concrete has been in use in Belgium for the last 10 years. With renewed interest in steel fiber reinforced concrete (SFRC), created by better incorporation possibilities and subsequent lower fiber content, new uses in thin resurfacings (less than 15 cm) were considered. Together with SFRC, alternatives were examined such as thin continuously reinforced concrete (TCRCP) with a thickness between 12 and 16 cm. Since 1982, experimental sections of thin overlays have been constructed in Belgium; eight are made of SFRC and four are of thin continuously reinforced concrete (TCRC). In spite of the fact that most of the presented test sections are still relatively young, this report attempts to formulate some interim conclusions that should lead to practical guidelines for their use.

4029
Zhao, J., Xu, P., and Fan, C.
"AN INVESTIGATION OF THE TOUGHNESS AND COMPRESSIVE TOUGHNESS INDEX OF STEEL FIBER REINFORCED CONCRETE"
Transportation Research Record, 1989, No. 1226, pp. 88-93.

In this paper, various methods for determining the toughness of steel fiber reinforced concrete (SFRC) are compared and evaluated using five criteria. The ASTM C1018-85 method mostly conforms to these criteria and, hence, is accepted as the foundation for China's standard test method of compressive toughness of SFRC. It is proposed that the critical-load point should replace the first-crack point in defining the compressive toughness index based on an analysis of the onset and propagation of cracks in concrete under uniaxial compressive loading. A transient coefficient for load-carrying capacity (Kn) is also introduced to indicate the variational characteristics of toughness. Experiments were carried out to verify the validity of the recommended index.

4030
Zheng, Q. and Chung, D. D. L.
"CARBON FIBER REINFORCED CEMENT COMPOSITES IMPROVED BY USING CHEMICAL AGENTS"
Cement and Concrete Research, Jan 1989, Vol. 19, No. 1, pp 25-41.

Carbon fibers are inert, medically safe, as strong as steel fibers and more chemically stable than glass fibers in an alkaline environment. By using short pitch-based carbon fibers together with a water reducing agent and an accelerating admixture, the compressive, tensile and flexural strengths of the carbon fiber reinforced cement mortar were found to increase by about 18-31%, 113-164% and 89-112%, respectively, compared to the corresponding plain cement values. The ductility was also much improved. In addition, the electrical resistivity decreased to 0.1% of the plain cement value.