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Publication Number: FHWA-HRT-05-056
Date: October 2006

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Chapter 3. COMPILATION OF INFORMATION AND SPECIFICATIONS FROM HPC BRIDGES

 

INTRODUCTION

This chapter contains the results of the task B review of the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing, theAASHTO Standard Specifications for Highway Bridges, the AASHTO LRFD Bridge Design Specifications, and the AASHTO LRFD Bridge Construction Specifications to identify provisions that directly impact the use of HPC.

For each provision that is listed, an action item is included to indicate that a proposed revision is included, a research problem statement is proposed, or no action was indicated. Details of the proposed revisions are included in appendixes A through E. Research problem statements are included in appendix F. No action was taken on some provisions because the change would not have a significant impact on the use of HPC.

Methodology

The compilation of the information from the AASHTO Specifications was accomplished by identifying provisions that impact the use of HPC. For those sections of the specifications that relate to structural design, the biggest impact comes from the use of high-strength concrete (HSC). For those sections that relate to materials, the impact is from the use of HPC as a durable concrete, HSC, or a combination of both. Consequently, when a provision impacts the use of high-strength concrete only, the abbreviation HSC is used. When a provision impacts a broader range of performance, the abbreviation HPC is used.

Units

The AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing contains some specifications and tests written with metric units as the primary measurement and others with English units as the primary measurement. The AASHTO Standard Specifications for Highway Bridges uses only English units. The AASHTO LRFD Bridge Design Specifications has two separate versions. One uses only English units. The other uses only metric units. The AASHTO LRFD Bridge Construction Specifications uses metric units.

In this compilation, any quotations from a document use the units as they appear in the original document. Subsequent discussion uses metric units first, followed by English units in parentheses.

AASHTO STANDARD SPECIFICATIONS FOR TRANSPORTATION MATERIALS AND METHODS OF SAMPLING AND TESTING, PART I: SPECIFICATIONS

The compilation in this section is based on the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing, 21st edition, 2001, PartI: Specifications.(1) All specifications listed in the table of contents under the headings of Aggregates; Concrete, Curing Materials, and Admixtures; and Hydraulic Cement were reviewed. For each specification, the title and scope of the specification are shown in italics followed by specific comments about potential changes for use with HPC. References in the comments to specific sections or tables refer to the document being reviewed and not the sections or tables in this report. If no change appears to be needed, this is stated. The end result of the project is stated under the action item. Proposed revisions are included in appendix A. Research problem statements are included in appendix F.

Aggregates

M 6 Fine Aggregate for Portland Cement Concrete

This specification covers the quality and grading of fine aggregate for portland cement concrete used in pavements or bases, highway bridges, and incidental structures.

Section 5.3 has limits on percent passing any sieve and retained on the next consecutive sieve as well as limits for the fineness modulus of the fine aggregate. For HPC, the grading and fineness of all combined materials are important. A preferred approach for HPC is to provide limits on the grading of fine and coarse aggregate combined. In prescriptive specifications, narrower limits on the aggregate size retained on each sieve would be appropriate for HPC. However, the goal is to move toward performance-based specifications where the emphasis is on desired concrete properties.

Section 5.4 provides an exception for aggregate failing to meet the sieve analysis and fineness modulus based on the track record of concrete made using the aggregate. For HPC, the track record is unlikely to exist. Alternative wording to allow exceptions for HPC needs to be considered.

Supplementary requirement S1.1 has an upper limit of 0.60 percent for alkalies in cement when reactive aggregate is a concern. The limit of 0.60 percent has not provided satisfactory performance in all cases. A lower limit such as 0.40 percent, a limit on total alkalies in the concrete, or a limit on expansion using AASHTO T 303 could be used for HPC and should be evaluated.

ACTION: A new specification for combined aggregates is proposed. Revisions to the title and requirements for reactive aggregates are proposed.

M 43 Sizes of Aggregates for Road and Bridge Construction (ASTM Designation: D448)

This specification defines aggregate size designations and ranges in mechanical analyses for standard sizes of coarse aggregate and screenings for use in the construction and maintenance of various types of highways and bridges.

The percentages for each sieve size given in table 1 have a wide range. In prescriptive specifications, a narrower limit on the aggregate retained on each sieve size would be appropriate for HPC. Improved gradings enable the use of less water, which is very important for both HSC and durable concrete. For HPC, the grading and fineness of all combined materials are important. A combined aggregate grading that includes both the fine and coarse aggregates is preferred for HPC and should be considered. However, the goal is to move toward performance-based specifications where the emphasis is on the desired concrete properties.

ACTION: A new specification for combined aggregates is proposed.

M 80 Coarse Aggregate for Portland Cement Concrete

This specification covers coarse aggregate, other than lightweight aggregate, for use in concrete. Several classes and gradings of coarse aggregate are described.

Section 5 refers to specification M 43. The percentages for each sieve given in table 1 of M 43 have a wide range. In prescriptive specifications, narrower limits on the aggregate size retained on each sieve size would be appropriate for HPC. However, the goal is to move toward performance-based specifications where the emphasis is on the desired concrete properties.

Section 6.2 has an upper limit of 0.60 percent for alkalies in cement when reactive aggregate is a concern. The limit of 0.60 percent has not provided satisfactory performance in all cases. A lower limit such as 0.40 percent, a limit on total alkalies in the concrete, or a limit on expansion using AASHTO T 303 could be used and should be evaluated.

The appendix describes methods for evaluating potential reactivity of an aggregate. This appendix needs updating to incorporate more recent information. Reference to AASHTO T303 and ASTM C 1293 would provide current information.

ACTION: A new specification for combined aggregates is proposed. Revisions to the title and requirements for reactive aggregates are proposed.

M 195 Lightweight Aggregates for Structural Concrete (ASTM Designation: C 330)

This specification covers lightweight aggregates intended for use in structural concrete in which the prime consideration is reducing the density while maintaining the compressive strength of the concrete. Procedures covered in this specification are not intended for job control of concrete.

Table 1 provides grading requirements for lightweight aggregates. The percentages have a wide range. In prescriptive specifications, narrower limits on the aggregate size retained on each sieve size would be appropriate for HPC. Also, a combined grading that includes both the fine and coarse aggregates is preferred for HPC and should be considered. However, the goal is to move toward performance-based specifications where the emphasis is on the desired concrete properties.

ACTION: Revisions to include references to the new combined aggregate specifications are proposed.

Concrete, Curing Materials, and Admixtures

M 148 Liquid Membrane-Forming Compounds for Curing Concrete (ASTM Designation: C309)

This specification covers liquid membrane-forming compounds suitable for application to concrete surfaces to reduce the loss of water during the early-hardening period. White-pigmented, membrane-forming compounds serve the additional purpose of reducing the temperature rise in concrete exposed to radiation from the sun. The membrane-forming compounds covered by this specification are suitable for use as curing media for fresh concrete, and may also be used for further curing of concrete after removal of forms or after initial moist curing.

Many States use water curing of bridge decks for improved performance. However, some States still use curing compounds. Section 6 restricts loss of water to 0.55 kilograms per square meter (kg/m2) (0.11 lb/ft2) in 72h. Loss of water during hydration is critical for any concrete, especially for HPC. The loss of water limits the hydration reaction and causes volumetric changes that can result in cracking. Therefore, a stricter requirement for loss of water is essential for HPC. For example: the Virginia Department of Transportation (VDOT) specifications require no more than 0.116 kg/m2 (0.024 lb/ft2) moisture loss at 24h and no more than 0.232 kg/m2 (0.048 lb/ft2) at 72 h when tested using Virginia's test methods. However, there are some differences in the procedures that would need to be addressed. Even with a stricter requirement, the use of curing compounds may not be appropriate for HPC with a very low water-cementitious materials ratio. The adequacy of curing compounds for HPC with different water-cementitious materials ratios needs to be evaluated.

Temperature management is important for hydration and volume changes in HPC. Section 7 limits reflectance to not less than 60 percent. This may need to be higher for HPC. For different classifications of HPC, loss of moisture and reflectance limits may need to be different.

ACTION: A research problem statement is proposed to address the effectiveness of curing compounds.

M 154 Air-Entraining Admixtures for Concrete (ASTM Designation: C 260)

This specification covers materials proposed for use as air-entraining admixtures to be added to concrete mixtures in the field.

Section 6.1 lists requirements for bleeding, time of setting, compressive strength, flexural strength, shrinkage, and relative durability. In prescriptive specifications, narrower limits on the properties of test concretes containing the admixture would be appropriate for HPC. However, the goal is to move toward performance-based specifications where the emphasis is on the desired concrete properties.

In section 6.1.1, the dynamic modulus of elasticity at the end of the test calculated as a percentage of the dynamic modulus of elasticity at zero cycles is required to be 60 or greater. The value 60 should be increased to a higher value for HPC. In addition, a relative durability factor of 80 is allowed for an admixture under test compared to the referenced admixture. A higher value should be considered for HPC to ensure satisfactory durability. The selected value will depend on the variability of the test procedure.

Section 6.1.2 lists requirements for length change on the drying of concrete for 14 days. Some HPC appears to dry more slowly than conventional concrete. The provisions of this specification need to be reviewed for use with HPC.

Section 8.1 references ASTM designation C 233 for test methods and recommends that tests be made using the cement proposed for the specific work. Most HPC contains pozzolanic material. Consequently, cementitious material containing the proposed pozzolans should be used in the test.

ACTION: Revisions to section 8.1 and the addition of an optional test age of 56 days are proposed. A research problem statement is proposed to address performance requirements.

M 157 Ready-Mixed Concrete

This specification covers ready-mixed concrete manufactured and delivered to a purchaser in a freshly mixed and unhardened state as hereinafter specified. Requirements for the quality of the concrete shall be either as hereinafter specified or as specified by the purchaser. In any case, where the requirements of the purchaser differ from those in this specification, the purchaser's specification shall govern. This specification does not cover the placement, consolidation, curing, or protection of the concrete after delivery to the purchaser.

In section 3.1, the definition of ready-mixed concrete needs to include all hydraulic cements.

Section 4.1.1 on cement needs to include cement conforming to ASTM C 1157.

Section 4.1.2 mentions only fly ash. It needs to include other pozzolans and ground granulated blast-furnace slag.

Section 4.1.4.1 allows the use of wash water when approved by the purchaser. Since wash water can vary greatly, its use in HPC needs to be assessed carefully.

Section 5.1 allows the engineer to specify the mix design. Mixture proportions for HPC should only be specified by those familiar with the material. However, the option of allowing the engineer to specify the mix design may not be appropriate for HPC.

Sections 5.1.1 through 5.1.6 and 5.2 are based on prescriptive concrete. For HPC, performance criteria need to be specified, followed by trial batches and then approval by the purchaser. Prescriptive specifications do not allow for the innovation required for HPC.

Section 6 discusses tolerances in slump. The entire issue of specifying slump for HPC needs to be reviewed.

In section 7.2, the point of discharge needs to be defined: ready-mix truck or discharge end of pump line. Concrete should be tested at the point nearest to its final location. Where it is not practical to test at this point, correlations between the properties measured at the end point and the nearest practical location should be established.

In table 5, slumps higher than 152 millimeters (mm) (6 inches) are not mentioned. Slumps higher than 152mm (6inches) are common for HPC and need to be included. A difference of 7.5 percent is allowed for variation in compressive strength for two samples from the same truck.

This variance may be too large for HPC.

Section 11.3.1 gives the acceptable mixing time as 1 minute for capacities of 0.76 m3 (1yd3) or less and, for greater capacities, the minimum is increased by 15 seconds (s) for each additional cubic yard. HPC requires thorough mixing. The speed of the mixers and the number of revolutions should be revisited.

Section 11.5 gives the minimum and maximum revolutions as 70 and 100, respectively, for truck-mixed concrete. These may not be sufficient for HPC with a stiff consistency.

Section 15 requires slump and air content to be measured. Since M 157 applies to concrete made with lightweight aggregate, unit weight should be a required test and should be included in this section.

ACTION: Revisions to sections 2.1, 3.1, 4.1.1, 4.1.2, 4.1.3, 5.1, 5.1.1, 5.1.3, 7.2, 11.3.1, and 15.2 and the addition of a new section 5.3 are proposed. A research problem statement is proposed to address the use of wash water.

M 171 Sheet Materials for Curing Concrete (ASTM Designation: C171)

This specification covers materials in sheet form used for covering the surfaces of hydraulic cement concrete to inhibit moisture loss during the curing period and, in the case of white reflective-type materials, to also reduce temperature rise in concrete exposed to radiation from the sun.

Section 6 lists performance requirements. The moisture loss is limited to a maximum of 0.55kg/m2 (0.11 lb/ft2) in 72 h when tested according to ASTM C 156. The daylight reflectance of white curing paper is limited to a minimum of 50 percent when measured by ASTM E 1347. These limits need to be assessed for use with HPC.

ACTION: A research problem statement is proposed to assess the limits.

M 182 Burlap Cloth Made From Jute or Kenaf

This specification covers requirements for burlap made from jute or kenaf for use in curing concrete.

Either this specification should include cotton mats that are used in several States or another specification needs to be developed.

ACTION: Revisions to include cotton mats are proposed.

M 194 Chemical Admixtures for Concrete (ASTM Designation: C494)

This specification covers materials for use as chemical admixtures to be added to portland cement concrete mixtures in the field for the purpose or purposes indicated for the seven types.

The scope should be extended to hydraulic cement concrete rather than portland cement concrete.

Note 1 refers to ASTM C 1017, “Specification for Chemical Admixtures for Use in Producing Flowing Concrete.” AASHTO should consider adopting ASTM C 1017 or a similar specification.

Table 1 lists physical requirements, including compressive and flexural strengths. The test ages should include 56 days, since this test age is frequently used for HPC.

For air-entrained concrete that may be exposed to freezing and thawing while wet, table1 states that the relative durability factor shall be at least 80. A higher value should be considered for HPC to ensure satisfactory durability. For shrinkage, a length change of concrete containing an admixture is allowed to be 135 percent of a control concrete without the admixture. The appropriateness of this number needs to be assessed for HPC.

ACTION: Revisions to include hydraulic cement concrete and a test age of 56 days are proposed. A research problem statement is proposed to address the durability factor.

M 205 Molds for Forming Concrete Test Cylinders Vertically (ASTM Designation: C470)

This specification covers molds for use in forming cylindrical concrete specimens. The provisions of this specification include the requirements for both reusable and single-use molds.

Section 5.1 includes the use of paper as a mold material. Several test programs have shown that the dimensional stability of molds is an important factor that can influence compressive strength test results for HSC. The suitability of paper products for cylindrical molds needs to be assessed. ACI Committee 363 reports that even high-quality cardboard molds produced concrete strengths 13 percent lower than when steel molds are used.(15) The committee has also recommended that plastic molds with a wall thickness of less than 6 mm (0.25 inch) should have a cap to maintain a circular shape and that the cap should be domed to provide clearance to the concrete surface.(16) This specification needs to be revised for the above items.

ACTION: A revision to section 5.1 to eliminate paper products and a requirement for top caps are proposed.

M 210 Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete (ASTM Designation: C 490)

This practice covers the requirements for the apparatus and equipment used to prepare specimens for the determination of length change in hardened cement paste, mortar, and concrete; the apparatus and equipment used for the determination of these length changes; and the procedures for its use.

This practice does not require any modification for use with HPC.

ACTION: None.

M 224 Use of Protective Sealers for Portland Cement Concrete

This guide includes the selection factors for and the use of protective sealers for highway purposes to be applied to hardened concrete for the purpose of protecting new concrete or prolonging the life of sound, in-service concrete. Information in this guide is not applicable to the repair of badly deteriorated concrete.

This guide does not require any modification for use with HPC. However, penetrating sealers may not penetrate as much with HPC because of the lower permeability.

ACTION: None.

M 233 Boiled Linseed Oil Mixture for Treatment of Portland Cement Concrete

This specification covers the boiled linseed oil-petroleum spirits mixture to be applied to hardened portland cement concrete as a protection against damage by deicing chemicals.

This specification does not require any modification for use with HPC.

ACTION: None.

M 241 Concrete Made by Volumetric Batching and Continuous Mixing (ASTM Designation: C 685)

This specification covers concrete made from materials continuously batched by volume, mixed in a continuous mixer, and delivered to the purchaser in a freshly mixed and unhardened state. Tests and criteria for batching accuracy and mixing efficiency are specified herein.

Cement conforming to ASTM C 1157 needs to be added to section 5.1.1.

Optional chemical limits for wash water need to be tightened for HPC applications.

Silica fume needs to be included in section 5, Materials.

In section 6.1.2, point of delivery needs to be defined: ready-mix truck or discharge end of pump line. Concrete should be tested at the point nearest to its final location. Where it is not practical to test at this point, correlations of properties measured at the end point and the nearest practical location should be established.

Section 6.3 defines ordering information when the purchaser assumes responsibility for the proportioning of the concrete mixture. This option may not be appropriate for HPC.

Notes 7 and 8 need to include reference to ACI 211.4 for HSC with fly ash.(17)

Section 10.1 should require that the fresh unit weight of concrete be measured when lightweight concrete is used.

Section 10.3 lists tolerances in slump. These should be reviewed for appropriateness with HPC.

The overdesign requirements in table 4 need to be reviewed for use with HSC. ACI 318 has revised its overdesign requirements.(18)

Section 11.3 specifies two standard-size cylinders for each strength test. Since M 241 refers to ASTM C 31 for the procedure to be used, standard-size cylinder may be interpreted to mean 152 by 305 mm (6by 12inches). ACI 363 recommends three cylinders for HSC and allows the use of 102- by 203-mm (4‑ by 8‑inch) cylinders.(16) The effect of a different number of specimens and specimen sizes need to be evaluated.

ACTION: Revisions to sections 2, 5.1.1, 5.1.6, 6.1.3, 6.1.5, 11.2, 11.3, and 11.5.2; notes 7 and 8; and tables 5 and 6 are proposed. A research problem statement is proposed to address the limits for wash water.

M 295 Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete (ASTM Designation: C 618)

This specification covers coal fly ash and raw or calcined natural pozzolan for use as a mineral admixture in concrete where cementitious or pozzolanic action, or both, is desired, or where other properties normally attributed to finely divided mineral admixtures may be desired or where both objectives are to be achieved.

In table 3, the strength activity index should include a test age of 56 days because it is more appropriate for HSC.

Table 4 on optional physical requirements should include tests for sulfate resistance. Tests have shown that concretes with some fly ashes will deteriorate when exposed to sulfates in soils or water.(19)

Table 4 allows an increase of 0.03 percent in drying shrinkage of mortar bars when fly ash is used. This may not be appropriate for HPC.

ACTION: Revisions to eliminate table 2, Supplementary Optional Chemical Requirements, and to add 56 days in table 3 are proposed. Research problem statements are proposed to address drying shrinkage limits and sulfate resistance.

M 302 Ground Granulated Blast-Furnace Slag for Use in Concrete and Mortars (ASTM Designation: C 989)

This specification covers three strength grades of finely ground granulated blast-furnace slag for use as a cementitious material in concrete and mortar.

In table 1, the slag activity index should include a test age of 56 days because it is more appropriate for HSC.

In appendix A3, Effectiveness of Slag in Preventing Excessive Expansion of Concrete Due to Alkali-Aggregate Reaction, a high-alkali content is assumed to be 0.60 percent. A lower limit such as 0.40 percent, a limit on total alkalies in concrete, or a limit on expansion using AASHTO T303 would be preferred for HPC.

This specification does not include a requirement on shrinkage similar to that in M 295 for fly ash and pozzolans and M 307 for silica fume.

ACTION: Revisions to table 1, section A3.2, and appendix A4 are proposed. A research problem statement is proposed to address the shrinkage requirement.

Hydraulic Cement

M 85 Portland Cement (ASTM Designation: C 150)

This specification covers eight types of portland cement.

In table 2, Optimal Chemical Requirement, alkali content should be lower than 0.60percent for HPC. A lower limit such as 0.40 percent, a limit on total alkalies in concrete, or a limit on expansion using AASHTO T 303 would be preferred.

In tables 3 and 4 on physical requirements, an age of 56 days should be included for compressive strength tests because 56 days is more appropriate for HSC.

ACTION: A footnote to table 2 about the alkali content is proposed.

M 240 Blended Hydraulic Cement (ASTM Designation: C 595)

This specification pertains to five classes of blended hydraulic cements for both general use and special applications, using slag or pozzolan, or both, with portland cement or portland cement clinker or slag with lime.

In section 10.1.12, mortar expansion using ASTM C 227 is mentioned. ASTM C 227 covers the determination of the susceptibility of cement-aggregate combinations to expansive reactions involving hydroxyl ions associated with the alkalies. The test takes a long time, with measurements up to 12 months, and, if necessary, every 6 months thereafter. ASTM C 441 includes pozzolans or slag. It determines the effectiveness of mineral admixtures or slag in preventing excessive expansion of concrete because of alkali-silica reactivity. It is much faster because of the use of highly reactive Pyrex® glass for aggregate and should be included in M240.

In table 2, Physical Requirements, an age of 56 days should be included for strength tests because 56 days is more appropriate for HSC.

In table 3, the slag and pozzolan activity index should include a test age of 56 days because 56days is more appropriate for HSC.

ACTION: Revisions to tables 2 and 3 are proposed.

M 307 Microsilica for Use in Concrete and Mortar

This specification covers microsilica for use as a mineral admixture in portland cement concrete and mortar to fill small voids and/or where pozzolanic action is desired. Microsilica is a product with a particle size typically two orders of magnitude smaller than portland cement. It is a material often marketed as an aqueous suspension with a typical 50 percent solids content. This specification details requirements and tests to be performed on the dry material before being processed into either the dry compacted form (densified powder) or a slurry.

This specification is listed under Hydraulic Cement Concrete in the table of contents. It should be listed under Concrete, Curing Materials, and Admixtures. The specification uses the term “microsilica.” Silica fume is the more generic term. The provisions of M307 should be compared with ASTM C 1240 for differences that may be appropriate for HPC.

Section 1.1 states that the material is often marketed as an aqueous suspension. For transportation structures, the description may not be appropriate since the dry form is often used.

In table 3, Physical Requirements, the strength activity index is required at 28 days. A test age of 56days may be more appropriate for HSC and should be evaluated.

In table 4, Optional Physical Requirements, the reduction of mortar expansion with cement alkalies is limited to 80 percent. For HPC, it should be increased from 80 to 100percent.

Section 8.2.4 refers to ASTM C 311. ASTM C 311 requires that water be added to the test mixture to achieve a flow comparable to that of the control mixture. Use of a constant water/cementitious materials ratio is being considered by ASTM and is more appropriate for concrete containing silica fume.

ACTION: Revisions to the title, sections 1.1, 3.2, 8.2.4, and tables 2, 3, and 4 are proposed. A research problem statement is proposed to address the reduction in mortar expansion.

AASHTO STANDARD SPECIFICATIONS FOR TRANSPORTATION MATERIALS AND METHODS OF SAMPLING AND TESTING, PART II: TESTS

The compilation in this section is based on the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing, 21st edition, 2001, Part II: Tests.(1) All tests listed in the tables of contents of these document under the headings of Aggregates; Concrete, Curing Materials, and Admixtures; and Hydraulic Cement were reviewed. For each test, the title and scope of the test is shown in italics, followed by specific comments about potential changes for use with HPC. Reference in the comments to specific sections or tables refer to the document being reviewed and not the sections or tables in this report. If no changes appear to be needed, this is stated. The end result of the project is stated under the action item. Proposed revisions are included in appendixB. Research problem statements are included in appendix F.

Aggregates

With the exception of methods T 96 and T 304, none of the aggregate tests listed in this section require any modification for use with HPC.

ACTION: No action needed on any of the test methods for aggregates.

T 2 Sampling of Aggregates

This practice covers sampling of coarse and fine aggregates.

T 11 Materials Finer Than 75-mm (No. 200) Sieve in Mineral Aggregates by Washing (ASTM Designation: C 117)

This test method covers determination of the amount of material finer than 75-mm (No.200) sieve in aggregates by washing.

T 19 Bulk Density (“Unit Weight”) and Voids in Aggregate (ASTM Designation: C 29)

This test method covers determination of the bulk density (“unit weight”) of aggregate in a compacted or loose condition, and calculated voids in fine, coarse, or mixed aggregates based on the same determination. This test method is applicable to aggregates not exceeding 125 mm (5 inches) in nominal maximum size.

T 21 Organic Impurities in Fine Aggregates for Concrete (ASTM Designation: C 40)

This test method covers the procedure for an approximate determination of the presence of injurious organic compounds in fine aggregates that are to be used in cement mortar or concrete.

T 27 Sieve Analysis of Fine and Coarse Aggregates (ASTM Designation: C 136)

This method covers the determination of the particle size distribution of fine and coarse aggregates by sieving.

This method provides separate analysis for fine and coarse aggregate. For HPC, a test that provides a combined grading for fine and coarse aggregate is needed.

T 30 Mechanical Analysis of Extracted Aggregate

This method of test covers a procedure for the determination of the particle size distribution of fine and coarse aggregates extracted from bituminous mixtures, using sieves with square openings.

T 37 Sieve Analysis of Mineral Filler for Road and Paving Materials (ASTM Designation: D546)

This method of test covers the sieve analysis of mineral fillers used in bituminous paving materials.

T 71 Effect of Organic Impurities in Fine Aggregate on Strength of Mortar (ASTM Designation: C 87)

This test method covers determination of the effect on mortar strength of the organic impurities in fine aggregate, whose presence is indicated by tests with T 21. Comparison is made between compressive strengths of mortar made with washed and unwashed fine aggregate.

T 84 Specific Gravity and Absorption of Fine Aggregate (ASTM Designation: C128)

This method covers determination of bulk and apparent specific gravity, 23/23 °C (73.4/73.4 °F), and absorption of fine aggregate.

T 85 SPECIFIC GRAVITY AND ABSORPTION OF COARSE AGGREGATE (ASTM DESIGNATION: C127)

This method covers the determination of specific gravity and absorption of coarse aggregate. The specific gravity may be expressed as bulk specific gravity, bulk specific gravity (saturated-surface-dry (SSD)), or apparent specific gravity. The bulk specific gravity (SSD) and absorption are based on aggregate after 15 hours soaking in water. This method is not intended to be used with lightweight aggregates.

T 96 Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine (ASTM Designation: C 131)

This test method covers a procedure for testing sizes of coarse aggregate smaller than 37.5 mm (1½ inches) for resistance to degradation using the Los Angeles testing machine.

The applicability of this test to lightweight aggregate should be evaluated.

T 103 Soundness of Aggregates by Freezing and Thawing

This method describes three procedures to be followed in testing aggregates to determine their resistance to disintegration by freezing and thawing. It furnishes information helpful in judging the soundness of aggregates subjected to weathering, particularly when adequate information is not available from service records of the behavior of the aggregate.

T 104 Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate

This method covers the procedures to be followed in testing aggregates to determine their resistance to disintegration by saturated solutions of sodium sulfate or magnesium sulfate.

T 112 Clay Lumps and Friable Particles in Aggregate (ASTM Designation: C 142)

This method covers the approximate determination of clay lumps and friable particles in natural aggregates.

T 113 Lightweight Pieces in Aggregate (ASTM Designation: C 123)

This method covers the determination of the percentage of lightweight pieces in aggregate by means of sink-float separation in a heavy liquid of suitable specific gravity.

T 210 Aggregate Durability Index (ASTM Designation: D 3744)

This method describes the procedure for determining the durability of aggregates. The durability index is a value indicating the relative resistance of an aggregate to produce detrimental claylike fines when subjected to the prescribed mechanical methods of degradation.

T 248 Reducing Samples of Aggregate to Testing Size (ASTM Designation: C 702)

These methods cover the reduction of large samples of aggregate to the appropriate size for testing, employing techniques that are intended to minimize variations in measured characteristics between the test samples so selected and the large sample.

T 255 Total Evaporable Moisture Content of Aggregate by Drying (ASTM Designation: C566)

This method covers determination of the percentage of evaporable moisture in a sample of aggregate by drying both surface moisture and moisture in the pores of the aggregate.

T 279 Accelerated Polishing of Aggregates Using the British Wheel (ASTM Designation: D3319)

This method covers a laboratory procedure by which an estimate may be made of the extent to which different coarse aggregates may polish.

T 304 Uncompacted Void Content of Fine Aggregate

This method describes the determination of the loose uncompacted void content of a sample of fine aggregate.

This test indirectly addresses aggregate shape and texture. However, a more direct test measuring particle shape would be beneficial (e.g., the videograder).(20)

Concrete, Curing Materials, and Admixtures

T 22 Compressive Strength of Cylindrical Concrete Specimens (ASTM Designation: C 39)

This method covers determination of compressive strength of cylindrical concrete specimens such as molded cylinders and drilled cores. It is limited to concrete having a unit weight in excess of 800 kg/m3 (50 lb/ft3).

Section 7.3 lists permissible time tolerances for different ages, including 28 and 90 days. A tolerance for 56 days needs to be added since 56 days is frequently used with HSC. Section 7.5 provides a rate of loading of 20 to 50 psi/s (0.14 to 0.34 MPa/s). In HSC, such a rate may take a long time. Loading rate should be evaluated for use with HSC.

A precision statement does not exist. When available, it should include HSC and compare 102- by 203-mm (4- by 8-inch) cylinders with the 152- by 305-mm (6- by 12-inch) cylinders. Comparisons of averages for different sizes and variability for each size are needed. The appendix to this test method describes the procedure for determining the compressive strength of cylindrical concrete specimens using neoprene caps. The scope is limited to the testing of 152- by 305-mm (6- by 12-inch) cylinders. Because of the limited capacity of the testing machines, 102- by 203-mm (4- by 8-inch) cylinders are frequently used for testing HSC. The appendix needs to be revised to include 102- by 203-mm (4- by 8-inch) cylinders.

In A 12.3.1, verification of cap systems is limited to 41.4 MPa (6000 psi). Higher strengths should be included. ASTM C 1231 permits the use of cap systems up to a cylinder compressive strength of 85 MPa (12,000 psi).

ACTION: Revisions to sections 6.2, 7.3, 7.5.1, 10.1, and the appendix are proposed. A research problem statement is proposedto address other issues.

T 23 Making and Curing Concrete Test Specimens in the Field (ASTM Designation: C31)

This method covers procedures for making and curing cylindrical and prismatic specimens using job concrete that can be consolidated by rodding or vibration as described herein.

Section 5.2 requires that beams made in the field shall not have a width or depth less than 152mm (6 inches). The test method should consider using flexural strength beams that are smaller in cross section rather than 152 by 152 mm (6 by 6 inches) when the maximum size aggregate is 25 mm (1inch) or less. It is more convenient to use smaller specimens. However, the effect of specimen size on measured flexural strength will need to be evaluated.

Section 8.3.1 requires consolidation either by rodding or vibration, depending on the slump value. This test should consider self-consolidating concretes and flowing concretes, which require less consolidation effort. HPC with high workability, as in self-consolidating concrete, has been successfully used in Japan, Canada, and Europe.

Section 9.2.1 requires that, after molding, the specimens shall be stored between 16 and 27degrees Celsius ( °C) (60 and 80 °F). A stricter requirement for HPC is needed.

ACTION: Revisions to sections 8.3.1, 8.3.3.1, 9.2.1, and table 1 are proposed. A research problem statement is proposed to address the use of smaller specimens.

T 24 Obtaining and Testing Drilled Cores and Sawed Beams of Concrete (ASTM Designation: C 42)

This method covers obtaining, preparing, and testing: (1) cores drilled from concrete for length or compressive or splitting tensile strength determinations, and (2) beams sawed from concrete for flexural strength determinations.

Section 6.4 requires capping of drilled cores in accordance with AASHTO T 231, Capping Cylindrical Concrete Specimens. Test method T 231 specifies high-strength gypsum plaster or sulfur mortar. Test method T 24 should include testing with pads in steel extrusion controllers since it is a very convenient test procedure and is used with HSC. Testing with lapped ends should also be included.

In section 6.9, the precision statement is limited to compressive strengths less than 48.3MPa (7000 psi). Higher strengths should be included.

ACTION: Revisions to sections 6.2.2, 6.4, and 6.7.2 are proposed.

T 26 Quality of Water to be Used in Concrete

The acidity or alkalinity shall be determined by one of the following methods, A or B.

Section 3.4 mentions other AASHTO tests that may need changes to accommodate HPC. These are addressed in other sections of this compilation.

ACTION: None.

T 97 Flexural Strength of Concrete (Using Simple Beam With Third-Point Loading) (ASTM Designation: C 78)

This method covers determinationof the flexural strength of concrete by use of a simple beam with third-point loading.

Section 5.2 states that the load is to be applied continuously at a rate that constantly increases the extreme fiber stress within a range of 861 to 1207 kilopascals per minute (kPa/min) (125 to 175psi/min). For HSC, the test may take too long and the possibility of a faster loading rate should be considered.

ACTION: None.

T 119 Slump of Hydraulic Cement Concrete (ASTM Designation: C 143)

This method covers the determination of slump of concrete, both in the laboratory and in the field.

After lifting the slump cone, slump is determined by the vertical difference between the top of the mold and the displaced original center of the top surface of the specimen. HPC concretes can have very high slump values limited by the height of the maximum-size aggregate. Slump spread may be a better measure. However, slump or slump spread alone does not address workability. Measurement of rheological properties, including viscosity, filling capacity, or flow time, may provide better understanding of workability, pumpability, and placeability.(21)

ACTION: A new specification for slump flow is proposed.

T 121 Mass per Cubic Meter (Cubic Foot), Yield, and Air Content (Gravimetric) of Concrete (ASTM Designation: C 138)

This method covers determination of the mass per cubic meter (or cubic foot) of freshly mixed concrete and gives formulas for calculating the yield, cement content, and the air content of the concrete.

The samples are to be consolidated by either rodding or internal vibration. External vibration should also be allowed. Also, in the case of self-consolidating HPC, no vibration should be permitted.

ACTION: None.

T 126 Making and Curing Concrete Test Specimens in the Laboratory (ASTM Designation: C192)

This method covers procedures for making and curing test specimens of concrete in the laboratory under accurate control of materials and test conditions using concrete that can be consolidated by rodding or vibration as described herein.

Section 7.4.1 requires consolidation either by rodding or vibration, depending on the slump value. This test should consider self-consolidating concretes and flowing concretes, which require less consolidation effort.

The precision statement presents the standard deviation for 7-day compressive strengths. A longer test age should be included for HPC. The precision statement is for laboratory trial batches that contain prescribed quantities of materials with a prescribed water-cementitious materials ratio. It is stated that values should be used with caution for air-entrained concrete and concrete with a slump of less than 50 mm (2 inches) or more than 150 mm (6 inches). The limitations are not suitable for HPC and need to be broadened.

ACTION: A revision to section 7.4.1 is proposed. A research problem statement to include the measurement of precision is proposed.

T 140 Compressive Strength of Concrete Using Portions of Beams Broken in Flexure (ASTM Designation: C 116)

This method covers the determination of compressive strength of concrete, using portions of beams broken in flexure for test specimens.

This method was withdrawn in February 1999 by ASTM because it was not updated by the end of the eighth year.

In section 6.3, the rate of loading is given as 0.05 inch/min. This rate may be too time-consuming for HSC.

ACTION: None.

T 141 Sampling Freshly Mixed Concrete (ASTM Designation: C 172)

This method covers the procedures for obtaining representative samples of fresh concrete as delivered to the project site and on which tests are to be performed to determine compliance with the quality requirements of the specifications under which the concrete is furnished.

This test method requires the sampling of two or more portions of the batch and combining them into a composite sample. The use of a single sample should be evaluated.

ACTION: None.

T 148 Measuring Length of Drilled Cores (ASTM Designation: C 174)

This test method covers determination of the length of a core drilled from a concrete pavement or structure.

This test method does not require any modification for use with HPC.

ACTION: None.

T 152 Air Content of Freshly Mixed Concrete by the Pressure Method (ASTM Designation: C231)

This method covers determination of the air content of freshly mixed concrete from observation of the change in volume of concrete with a change in pressure.

This method does not require any modification for use with HPC.

ACTION: None.

T 155 Water Retention by Concrete Curing Materials (ASTM Designation: C 156)

This test method covers laboratory determination of the efficiency of liquid membrane-forming compounds and sheet materials for curing concrete, as measured by their ability to reduce moisture loss during the early hardening period.

This test method does not require any modification for use with HPC. However, section 17 states that “efforts to establish a more meaningful measure of the precision of this test method continue.” This test is known to have high variability and improvements are needed.

ACTION: None.

T 157 Air-Entraining Admixtures for Concrete (ASTM Designation: C 233)

This test method covers the testing of materials proposed for use as air-entraining admixtures in the field.

This test method may require modification for use with HPC. Currently, it does not indicate the behavior of air-entraining admixtures in the presence of other admixtures and when higher consistency mixtures are prepared. Section 4.4 needs to be revised to include the various constituent materials used in HPC.

ACTION: Revisions to sections 4.1, 4.4, 10.1.1, and 13.1.6 to include other materials and a test age of 56 days are proposed.

T 158 Bleeding of Concrete (ASTM Designation: C 232)

These test methods cover the determination of the relative quantity of mixing water that will bleed from a sample of freshly mixed concrete. Two test methods that differ primarily in the degree of vibration to which the concrete sample is subjected are included.

These test methods do not require any modification for use with HPC. There is a typographical error in section 5.1. Line 1 mentions T 120, which should be T 126.

ACTION: A revision to section 5.1 is proposed.

T 159 Comparing Concrete on the Basis of the Bond Developed With Reinforcing Steel (ASTMDesignation: C 234)

This test method covers comparison of concretes on the basis of the bond developed with reinforcing steel.

Note 4 recommends internal vibration with low-slump concrete. External vibration should also be permissible. For self-consolidating concretes, no vibration should be permitted.

ACTION: None.

T 160 Length Change of Hardened Hydraulic Cement Mortar and Concrete (ASTMDesignation: C 157)

This test method covers determination of the length changes of hardened hydraulic cement mortar and concrete due to causes other than externally applied forces and temperature changes.

This test method does not require any modification for use with HPC.

ACTION: None.

T 161 Resistance of Concrete to Rapid Freezing and Thawing (ASTM Designation: C 666)

This method covers the determination of the resistance of concrete specimens to rapidly repeated cycles of freezing and thawing in the laboratory by two different procedures.

Section 8.1 indicates that unless some other age is specified, specimens are cured in lime-saturated water for 14 days. For HPC, a longer curing period, or a drying period before testing, should be included unless the elements are in contact with water continuously after placement. Subjecting saturated specimens to rapid freezing and thawing after 14 days of moist curing is a very severe environment and may not correlate well with field experience. In many applications, longer curing times are specified for HPC.

Section 8.3 states continuation of the test for 300 cycles or until a relative dynamic modulus of elasticity (RDM) of 60 is reached. In HPC, more cycles and higher RDM are desirable.

ACTION: A revision to section 8.3 for HPC is proposed. A research problem statement to evaluate the test method is proposed.

T 177 Flexural Strength of Concrete (Using Simple Beam With Center-Point Loading) (ASTM Designation: C 293)

This method covers the determination of the flexural strength of small-sized concrete specimens by the use of a simple beam with center-point loading.

Section 5.2 indicates that loads will be applied at a rate to increase the extreme fiber stress within a range of 0.86 to 1.21 MPa/min (125 to 175 psi/min). HSC may have high flexural strength and such a rate may take a long time. The possibility of using a faster loading rate should be considered.

ACTION: None.

T 178 Cement Content of Hardened Portland Cement Concrete (ASTM Designation: C1084)

This method of test for determining the cement content of concrete is applicable to hardened portland cement concretes except those containing certain aggregates or combinations of aggregates or admixtures that yield significant amounts of dissolved calcium oxide (CaO) and dissolved silica (SiO2) under conditions of the test.

This method only addresses portland cement concrete. Pozzolans and ground granulated blast-furnace slag are widely used in HPC. There is a need to know the amount of cementitious materials (including portland cement) used in hydraulic cement concrete. This test method may need to be modified or a new one developed.

ACTION: A research problem statement is proposed.

T 196 Air Content of Freshly Mixed Concrete by the Volumetric Method (ASTM Designation: C173)

This test method covers determination of the air content of freshly mixed concrete containing any type of aggregate, whether it be dense, cellular, or lightweight.

This method does not require any modification for use with HPC.

ACTION: None.

T 197 Time of Setting of Concrete Mixtures by Penetration Resistance (ASTM Designation: C1084)

This test method covers the determination of the time of setting of concrete, with slump greater than zero, by means of penetration resistance measurements on mortar sieved from the concrete mixture.

This test method does not require any modification for use with HPC.

ACTION: None.

T 198 Splitting Tensile Strength of Cylindrical Concrete Specimens (ASTM Designation: C496)

This method covers the determination of the splitting tensile strength of cylindrical concrete specimens such as molded cylinders and drilled cores.

Section 6.5 specifies a constant rate of loading that increases the splitting tensile stress from 689to 1380 kPa/min (100 to 200 psi/min). HSC may have a high splitting tensile strength and such a rate may take a long time. The possibility of providing a faster loading rate should be considered.

ACTION: None.

T 199 Air Content of Freshly Mixed Concrete by the Chace Indicator

This method of test covers the determination of the air content of freshly mixed concrete by displacing the air with alcohol and observing the change in level of the liquid in a tube.

This method does not require any modification for use with HPC.

ACTION: None.

T 231 Capping Cylindrical Concrete Specimens (ASTM Designation: C 617)

This method covers apparatus, materials, and procedures for capping freshly molded concrete cylinders with neat cement and hardened cylinders and drilled concrete cores with high-strength gypsum plaster or sulfur mortar.

This test procedure specifies capping with neat cement for freshly molded specimens and high-strength gypsum plaster or sulfur mortar for hardened specimens. Note 6 states that type I neat cement caps require 6 days to develop acceptable strength, and section 5.2.2 states that sulfur mortar may be used if allowed 2 h to harden. Section 6.2.1 states that caps should be about 3mm (0.125 inch) thick and in no instance shall any part of a cap be more than 8 mm (0.3125 inch) thick.

National Ready Mixed Concrete Association (NRMCA) Technical Memo 5 recommends that when sulfur mortar is used, cylinders with a compressive strength of 34 MPa (5000 psi) and higher strengths should be capped at least 1day and preferably 7 days prior to testing.(22) Furthermore, it is stated that cylinder ends should be sawed to ensure that the thickness of the cap is 3 mm (0.125 inch) or less, and preferably 1.5mm (0.0625 inch). NRMCA also recommends that when the strength of concrete exceeds 69MPa (10,000 psi), neat cement paste be used to cap the ends. Cylinders should be capped 7 days prior to testing and the cap thickness should be less than 3 mm (0.125 inch). Thus, type and strength of capping material, thickness of caps, and the time to cap prior to testing need to be considered and appropriate changes made to T231.

ACTION: Revisions to sections 5.1 through 5.2.2 to make AASHTO T 231 consistent with ASTM C 617 are proposed. A research problem statement is proposed to address other issues related to capping.

T 259 Resistance of Concrete to Chloride Ion Penetration

This method covers the determination of the resistance of concrete specimens to the penetration of chloride ion.

Section 3.1 specifies abrading the surface if the surface is exposed to vehicular traffic. However, since in most applications where a comparison between different concretes is sought, the surface abrasion can be deleted.

Sections 3.4 and 3.5 specify ponding for 90 days. This time period is not long enough to discern differences between concretes, especially HPC. A longer ponding period should be included for HPC.(23) A specified ponding period of 90 days or an even shorter period may be used if thinner sections than 13 mm (0.5 inch) are prepared for the chloride profile. For example, Nordtest NT Build 443 requires an exposure of at least 35 days and 1- to 2-mm- (0.04- to 0.08-inch-) thick layers for determination of chloride are common.(24)

Section 3.6 requires the determination of the chloride content at two depths, each approximately 13 mm (0.5 inch) thick. A 13-mm (0.5-inch) increment does not provide enough data points over the depth. Chloride values at different depths are used to determine the diffusion coefficients. Diffusion coefficients are desirable since they can be incorporated into service-life prediction models. To determine diffusion coefficients, at least four (or even six) chloride values from different layers are needed. Consequently, the thickness of the sampled layer needs to be much less and should be chosen to enable the collection of 10 grams (0.4 ounces) of representative material as required by AASHTO T 260. Thicknesses as thin as 1 mm (0.04 inch) have been used.(25)

ACTION: Revisions to sections 2.1 and 3.4 are proposed. A research problem statement is proposed to address other issues.

T 260 Sampling and Testing for Chloride Ion in Concrete and Concrete Raw Materials

This method covers procedures for the determination of the acid-soluble chloride ion content or the water-soluble chloride ion content of aggregates, portland cement, mortar or concrete.

This method does not require any modification for use with HPC.

ACTION: None.

T 271 Density of Plastic and Hardened Portland Cement Concrete In-Place by Nuclear Methods

These methods cover the determination of the density of plastic and hardened concrete in place by gamma radiation.

This method does not require any modification for use with HPC.

ACTION: None.

T 276 Developing Early-Age Compression Test Values and Projecting Later-Age Strengths (ASTM Designation: C 918)

This test method covers a procedure for making, curing, and testing specimens of concrete stored under conditions intended to measure the maturity as it relates to strength gain in the concrete.

Section 4.1 states that the test method uses conventional curing. ASTM C 1074 and AASHTO TP52 provide a procedure for the estimation of strength using other temperature histories.

Section 9.1 has the latest test age at 28 days, but requires a later test age if the age for which the projected strength is to be achieved exceeds 28 days. HPC often requires a later age. Ages of 56and 90 days should be specifically listed.

The use of this test method to predict high early strengths should be evaluated.

ACTION: A research problem statement is proposed.

T 277 Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration (ASTM Designation: C 1202)

This test method covers the determination of the electrical conductance of concrete to provide a rapid indication of its resistance to penetration of chloride ions.

The curing procedure and test age are not given in the test method. They are important variables and should be included. Concrete with pozzolans and ground granulated blast-furnace slag usually take a longer time to exhibit reduced permeability. (Silica fume concrete may be an exception.) Accelerated curing at higher temperatures or extended curing ages are needed to observe the benefits of these supplementary cementitious materials. The curing procedure and test age need to be addressed in this method.

ACTION: A revision to section 8.1 to define test age and the option of rapid curing is proposed.

T 285 Bend Test for Bars for Concrete Reinforcement

This method covers a bend test for evaluating the ductility of bars used for concrete reinforcement.

This method does not require any modification for use with HPC. However, this test should be listed under Metallic Materials for Bridges in the table of contents.

ACTION: A relocation in the index is proposed.

T 299 Rapid Identification of Alkali-Silica Reaction Products in Concrete

This test covers the rapid visual detection of the products of alkali-silica reaction in portland cement concrete.

This method does not require any modification for use with HPC.

ACTION: None.

T 303 Accelerated Detection of Potentially Deleterious Expansion of Mortar Bars Due to Alkali-Silica Reaction

This test method allows detection within 16 days of the potential for deleterious expansion of mortar bars due to alkali-silica reaction.

This method does not require any modification for use with HPC.

ACTION: None.

Hydraulic Cement

Hydraulic cement tests are applicable to cementitious material used in HPC. However, in many of these test methods, the word “cement” is used and generally addresses only portland cement. In HPC, pozzolans and ground granulated blast-furnace slag are widely used. Precision statements should be based on cements with pozzolans or slag.

T 98 Fineness of Portland Cement by the Turbidimeter (ASTM Designation: C 115)

This test method covers determination of the fineness of portland cement as represented by a calculated measure of specific surface, expressed as square centimeters of total surface area per gram, or square meters of total surface area per kilogram, of cement, using the Wagner Turbidimeter.

This test method does not require any modification for use with HPC.

ACTION: None.

T 105 Chemical Analysis of Hydraulic Cement (ASTM Designation: C 114)

These test methods cover the chemical analyses of hydraulic cements.

These test methods do not require any modification for use with HPC.

ACTION: None.

T 106 Compressive Strength of Hydraulic Cement Mortar (Using 50-mm or 2-inch Cube Specimens) (ASTM Designation: C 109)

This test method covers determination of the compressive strength of hydraulic cement mortar, using 50-mm (or 2-inch) cube specimens.

In section 10.6, Determination of Compressive Strength, an age of 56 days should be included since it is more appropriate for use with HSC.

ACTION: Revisions to tables 3 and 4 to include 56 days are proposed.

T 107 Autoclave Expansion of Portland Cement (ASTM Designation: C 151)

This test method covers determination of the autoclave expansion of portland cement by means of a test on a neat cement specimen.

This test method does not require any modification for use with HPC.

ACTION: None.

T 127 Sampling and Amount of Testing of Hydraulic Cement (ASTM Designation: C 183)

This practice covers procedures for sampling and for the amount of testing of hydraulic cement after it has been manufactured and is ready to be offered for sale.

This test method does not require any modification for use with HPC.

ACTION: None.

T 128 Fineness of Hydraulic Cement by the 150-mm (No. 100) and 75-mm (No. 200) Sieves (ASTM Designation: C 184)

This test method covers determination of the fineness of hydraulic cement by the 150-mm (No.100) and 75-mm (No. 200) sieves.

This test method does not require any modification for use with HPC.

ACTION: None.

T 129 Normal Consistency of Hydraulic Cement (ASTM Designation: C 187)

This method covers determination of the normal consistency of hydraulic cement.

This method does not require any modification for use with HPC.

ACTION: None.

T 131 Time of Setting of Hydraulic Cement by Vicat Needle (ASTM Designation: C191)

This method covers determination of the time of setting of hydraulic cement by means of the Vicat needle.

This method does not require any modification for use with HPC.

ACTION: None.

T 132 Tensile Strength of Hydraulic Cement Mortars

This method covers determinationof the tensile strength of hydraulic cement mortars employing the briquet specimen. It is primarily for use by those interested in research on methods for determining tensile strength of hydraulic cement.

The oldest test age listed for this test is 28 days. Since HPC is tested at later ages, tests at 56days need to be included.

The precision and bias statements in section 11 are only applicable to portland cement mortars. They need to be extended to include blended cement mortars.

ACTION: Revisions to include supplementary cementing materials and a test age of 56 days are proposed. A research problem statement is proposed to address precision and bias statements.

T 133 Density of Hydraulic Cement (ASTM Designation: C188)

This method covers determination of the density of hydraulic cement.

This method does not require any modification for use with HPC.

ACTION: None.

T 137 Air Content of Hydraulic Cement Mortar (ASTM Designation: C185)

This test method covers determination of the air content of hydraulic cement mortar under the conditions hereinafter specified.

This test method does not require any modification for use with HPC.

ACTION: None.

T 153 Fineness of Hydraulic Cement by Air Permeability Apparatus (ASTM Designation: C204)

This test method covers determination of the fineness of hydraulic cement, using the Blaine air permeability apparatus, in terms of the specific surface expressed as total surface area in square centimeters per gram, or square meters per kilogram of cement.

This test method does not require any modification for use with HPC.

ACTION: None.

T 154 Time of Setting of Hydraulic Cement by Gillmore Needles (ASTM Designation: C266)

This test method covers determination of the time of setting of hydraulic-cement paste by means of the Gillmore needles.

This test method does not require any modification for use with HPC.

ACTION: None.

T 162 Mechanical Mixing of Hydraulic Cement Pastes and Mortar of Plastic Consistency (ASTM Designation: C305)

This method covers the mechanical mixing of hydraulic cement pastes and mortars of plastic consistency.

Sections 7 and 8 provide procedures for mixing pastes and mortars, respectively. Pastes and mortars are mixed at low and medium speeds for specified durations. HPC pastes and mortars may be more cohesive than conventional pastes and mortars. Consequently, longer mixing times or higher speeds may be needed.

ACTION: None.

T 185 Early Stiffening of Portland Cement (Mortar Method) (ASTM Designation: C359)

This method covers the determination of early stiffening in portland cement mortar.

Section 10 describes the procedure and requires mixing dry and wet materials at specified speeds for specified durations. HPC mortars may be more cohesive than conventional mortars and may require longer mixing times or higher speeds.

ACTION: None.

T 186 Early Stiffening of Hydraulic Cement (Paste Method) (ASTM Designation: C451)

This test method covers the determination of early stiffening in hydraulic cement paste.

Section 10 describes the procedure and requires mixing materials at specified speeds for specified durations. HPC mortars may be more cohesive than conventional mortars and may require longer mixing times or higher speeds.

ACTION: None.

T 188 Evaluation by Freezing and Thawing of Air-Entraining Additions to Portland Cement

This method is intended for use in determining the ability of cement containing an air-entraining agent to produce frost-resistant concrete when tested in accordance with the procedures described below.

This method only indicates the performance of an air-entrained addition in a concrete with a fixed cement content, fixed slump, and optimum ratio of fine aggregate to total aggregate. As such, it does not indicate the behavior of air-entraining agents in the presence of other admixtures or when higher consistency mixes are used. Modifications may be needed for HPC.

ACTION: Revisions to the title and a requirement for including other admixtures are proposed.

T 192 Fineness of Hydraulic Cement by the 45-mm (No. 325) Sieve (ASTM Designation: C430)

This test method covers determination of the fineness of hydraulic cement by means of the 45-mm (No. 325) sieve.

This test method does not require any modification for use with HPC.

ACTION: None.

AASHTO STANDARD SPECIFICATIONS FOR HIGHWAY BRIDGES

The compilation in this section is based on the AASHTO Standard Specifications for Highway Bridges, Sixteenth Edition, 1996, and the 1997, 1998, 1999, and 2000 interim revisions. See references 2 through 6. This section only lists articles affected by HPC. For each listed article, the portion affected by HPC is shown in italics, followed by specific comments in regular font. For long articles, only a synopsis, followed by comments, is included. References in the comments to specific sections, articles, or tables refer to the document being reviewed and not the sections, articles, or tables in this report. The end result of the project is stated under the action item. Proposed revisions are included in appendix C. Research problem statements are included in appendix F.

Division I: Design

Section 3: LOADS

3.3 DEAD LOAD

3.3.6 The following weights are to be used in computing the dead load:
Concrete, plain, or reinforced....................................................................... 150 pcf

HPC may be somewhat denser than conventional concrete. A slightly higher unit weight may be justified and needed.

ACTION: A revision to 3.3.6 is proposed.

Section 8: REINFORCED CONCRETE

8.3 REINFORCEMENT

8.3.3 Designs shall not use a yield strength, fy, in excess of 60,000 psi.

The use of higher yield strengths should be allowed with concretes of all strengths.

ACTION: A revision to 8.3.3 is proposed.

8.5 EXPANSION AND CONTRACTION

8.5.3 The coefficient of thermal expansion and contraction for normal-weight concrete may be taken as 0.000006 per deg F.

ACI Committee 363, High-Strength Concrete, reports that the coefficient of thermal expansion and contraction for HSC is approximately the same as that for conventional strength concrete, but cites only two studies.(15) An attempt should be made to find more information on the coefficient of thermal expansion and contraction, and to verify the coefficient of thermal expansion for HPC.

ACTION: A revision and a research problem statement are proposed.

8.5.4 The coefficient of shrinkage for normal-weight concrete may be taken as 0.0002.

Data on HPC show a wide variation in measured shrinkage strains. There is no consistent comparison with conventional concrete; some HPC shows less shrinkage, some HPC shows more, and some the same. A single value of shrinkage may not be valid for HPC. The use of 0.0002 for shrinkage of HPC needs to be verified. In addition, the condition under which a shrinkage strain of 0.0002 is valid needs to be defined.

ACTION: Revisions to 8.5.4 and 8.5.5 are proposed.

8.7 MODULUS OF ELASTICITY AND POISSON'S RATIO

8.7.1 The modulus of elasticity, Ec, for concrete may be taken as The graphical element reads w subscript c to the power of 1.5 times 33 times the square root of f prime subscript c. in psi for values of wc between 90 and 155 pounds per cubic foot. For normal-weight concrete (wc = 145 pcf), Ec may be considered as 57,000 the square root f prime, subscript c.

The ACI Committee 363 report shows data indicating that the formula given in this article may not be appropriate for HSC.(15) Other data suggest that the Ec for HSC may be influenced by aggregate stiffness.(26) Furthermore, some HSCs have a unit weight greater than 2.48megagrams per cubic meter (Mg/m3) (155lb/ft3). Thus, the formula for Ec in this article needs to be evaluated using recent data for HPC from many locations.

ACTION: A revision based on NCHRP project 18-07 is proposed.

8.7.3 Poisson's ratio may be assumed as 0.2.

The ACI Committee 363 report shows data that indicate that the statement in this article is valid for HPC.(15) A check of the literature should be made to see if there are any recent data that might contradict the cited report.

ACTION: None.

8.13 COMPUTATION OF DEFLECTIONS

8.13.4 Unless values are obtained by a more comprehensive analysis, the long-time deflection for both normal-weight and lightweight concrete flexural members shall be the immediate deflection caused by the sustained load considered, computed in accordance with Article 8.13.3, multiplied by one of the following factors:

  1. (a) Where the immediate deflection has been based on Ig, the multiplication factor for the long-time deflection shall be taken as 4.
  2. (b) Where the immediate deflection has been based on Ie, the multiplication factor for the long-time deflection shall be taken as 3 – 1.2(As'/As) > 1.6.

HSC usually has lower creep than conventional strength concrete, so long-time deflection multipliers may be less. Long-time deflection may need to be verified for use with HSC. Consideration should also be given to using the factors in the ACI Building Code.(18)

ACTION: A research problem statement is proposed.

8.15 SERVICE LOAD DESIGN METHOD (ALLOWABLE STRESS DESIGN)

8.15.2 Allowable Stresses

8.15.2.1 Concrete

Stresses in concrete shall not exceed the following:

8.15.2.1.1 Flexure

Extreme fiber stress in compression, fc.......................................................... 0.40 f prime, subscript c

Extreme fiber stress in tension for plain concrete, ft ...................................... 0.21 fr

Modulus of rupture, fr, from tests, or, if data are not available:

Normal-weight concrete ............................................................................. 7.5 the square root f prime, subscript c

Sand-lightweight concrete .......................................................................... 6.3 the square root f prime, subscript c

All-lightweight concrete.............................................................................. 5.5 the square root f prime, subscript c

The modulus of rupture for normal-weight HSC is higher than given in this article. The multipliers need to be evaluated for use with HSC.

ACTION: A revision for normal-weight concrete is proposed. A research problem statement
is proposed for other weights of concrete.

8.15.2.1.2 Shear

For detailed summary of allowable shear stress, vc, see Article 8.15.5.2.

See comments on article 8.15.5.2.

ACTION: None. Further research is being conducted under NCHRP project 12-56.

8.15.2.1.3 Bearing Stress

The bearing stress, fb, on loaded area shall not exceed 0.30 f prime, subscript c.

When the supporting surface is wider on all sides than the loaded area, the allowable bearing stress on the loaded area may be multiplied by The graphical element reads the square root of A subscript 2 divided by A subscript 1., but not by more than 2.

When the supporting surface is sloped or stepped, A2 may be taken as the area of the lower base of the largest frustrum of the right pyramid or cone contained wholly within the support and having for its upper base the loaded area, and having side slopes of 1 vertical to 2 horizontal.

When the loaded area is subjected to high-edge stresses due to deflection or eccentric loading, the allowable bearing stress on the loaded area, including any increase due to the supporting surface being larger than the loaded area, shall be multiplied by a factor of 0.75.

The upper limit for the bearing stress, fb, needs to be verified for HSC.

ACTION: A research problem statement is proposed.

8.15.5 Shear
8.15.5.2 Shear Stress Carried by Concrete

8.15.5.2.1 Shear in Beams and One-Way Slabs and Footings

For members subject to shear and flexure only, the allowable shear stress carried by the concrete, vc, may be taken as 0.95 the square root f prime, subscript c. A more detailed calculation of the allowable shear stress can be made using :

Equation 1.  The equation reads v subscript c equals .9 times the square root of f prime subscript c plus 1,100 times rho subscript w, open parentheses V times d divided by M close parentheses, equal to or less than 1.6 times the square root f prime, subscript c.
(8-4) [Equation 1]



Note:

(a) M is the design moment occurring simultaneously with V at the section being considered.

(b) The quantity Vd/M shall not be taken greater than 1.0.

Test results have indicated that the shear stress carried by the concrete can be proportionally lower for HSC because of the smoother crack surfaces.(15) Consequently, the constants in this article need to be verified for HSC.

ACTION: None. Further research is being conducted under NCHRP project 12-56.

8.15.5.2.2 Shear in Compression Members

For members subject to axial compression, the allowable shear stress carried by the concrete, vc, may be taken as 0.95 the square root of f prime, subscript c. A more detailed calculation can be made using:

Equation 2.  The equation reads v subscript c equals .9 times open parentheses 1 plus .0006 times N divided by A superscript g close parentheses, times the square root of f prime subscript c.
(8-5) [Equation 2]

The quantity N/Ag shall be expressed in pounds per square inch.

The constants in this article need to be verified for HSC.

ACTION: A research problem statement is proposed.

8.15.5.2.3 Shear in Tension Members

For members subject to axial tension, shear reinforcement shall be designed to carry total shear, unless a more detailed calculation is made using:

Equation 3.  The equation reads v subscript c equals .9 times open parentheses 1 plus .004 times N divided by A subscript g close parentheses, times the square root of f prime subscript c.
(8-6) [Equation 3]

Note:

(a) N is negative for tension.

(b) The quantity N/Ag shall be expressed in pounds per square inch.

The constants in this article need to be verified for HSC.

ACTION: A research problem statement is proposed.

8.15.5.2.4 Shear in Lightweight Concrete

The provisions for shear stress, vc, carried by the concrete, apply to normal-weight concrete. When lightweight aggregate concretes are used, one of the following modifications shall apply:

(a) When fct is specified, the shear stress, vc, shall be modified by substituting fct /6.7 for , but the value of fct /6.7 used shall not exceed the square root f prime, subscript c.

(b) When fct is not specified, the shear stress, vc, shall be multiplied by 0.75 for all-lightweight concrete, and 0.85 for sand-lightweight concrete. Linear interpolation may be used when partial sand replacement is used.

HPC can be made with lightweight aggregate. Consequently, the constants need to be verified for use with lightweight HPC.

ACTION: A research problem statement is proposed.

8.15.5.3 Shear Stress Carried by Shear Reinforcement

8.15.5.3.2 When shear reinforcement perpendicular to the axis of the member is used:

Equation 4.  The equation reads A subscript v equals open parentheses v minus v subscript c close parentheses, times b subscript w times s all divided by f subscript s.
(8-7) [Equation 4]

8.15.5.3.3 When inclined stirrups are used:

Equation 5.  The equation reads A subscript v equals open parentheses v minus v subscript c close parentheses, times b subscript w times s that total divided by f subscript s times open parentheses the sine of alpha plus the cosine of alpha close parentheses.
(8-8) [Equation 5]

8.15.5.3.4 When shear reinforcement consists of a single bar or a single group of parallel bars all bent up at the same distance from the support:

Equation 6.  The equation reads A subscript v equals open parentheses v minus v subscript c close parentheses, times b subscript w times d that total divided by f subscript s times the sine of alpha.
(8-9) [Equation 6]

where (v - vc) shall not exceed 1.5 .

Limited test results have indicated that shear stress carried by the reinforcement is apparently higher with HSC. Therefore, the limit on (v – vc) needs to be verified for HSC.

ACTION: None. Further research is being conducted under NCHRP project 12-56.

8.15.5.3.8 When (v - vc) exceeds 2 , the maximum spacings given in Article 8.19 shall be reduced by one-half.

The limit on (v – vc) needs to be verified for HSC.

ACTION: None. Further research is being conducted under NCHRP project 12-56.

8.15.5.3.9 The value of (vvc) shall not exceed 4.

The upper limit on (v – vc) needs to be verified for HPC.

ACTION:None. Further research is being conducted under NCHRP project 12-56.

8.15.5.4 Shear Friction

8.15.5.4.3 Shear-Friction Design Method

(a) When shear-friction reinforcement is perpendicular to shear plane, the area of shear-friction reinforcement, Avf , shall be computed by:

Equation 7.  The equation reads A subscript vf equals V divided by f subscript s times mu.
(8-10) [Equation 7]

where m is the coefficient of friction in accordance with Art. 8.15.5.4.3(c).

(b) When shear-friction reinforcement is inclined to the shear plane such that the shear force produces tension in shear-friction reinforcement, the area of shear-friction reinforcement, Avf , shall be computed by:

Equation 8.  The equation reads A subscript vf equals V divided by f subscript s open parentheses mu times the sine of alpha subscript f plus the cosine of alpha subscript f close parentheses.
(8-11) [Equation 8]

where a f is the angle between the shear-friction reinforcement and the shear plane.

Coefficient of friction m in Eq. (8-10) and Eq. (8-11) shall be:

concrete placed monolithically..................................................................... 1.4l

concrete placed against hardened concrete with surface intentionally roughened as specified in Art. 8.15.5.4.7................................................................................................................ 1.0l

concrete placed against hardened concrete not intentionally roughened.... 0.6l

concrete anchored to as-rolled structural steel by headed studs or by reinforcing bars (see Art. 8.15.5.4.8) 0.7l

where l = 1.0 for normal-weight concrete, 0.85 for sand-lightweight concrete, and 0.75 for all-lightweight concrete. Linear interpolation may be applied when partial sand replacement is used.

Tests have indicated that a smoother crack plane occurs with HSC.(15) Consequently, the values of µ and l need to be verified for HSC.

ACTION: A research problem statement is proposed.

8.15.5.4.4 Shear stress, v, shall not exceed 0.09f prime, subscript c nor 360 psi.

This article imposes a limit of 28 MPa (4000 psi) on the compressive strength of concrete that can be used in design and is a barrier to the effective use of HSC. This limit needs to be evaluated based on recent test data.

ACTION: A research problem statement is proposed.

8.15.5.5 Horizontal Shear Design for Composite Concrete Flexural Members

8.15.5.5.3 Design horizontal shear stress vdh at any cross section may be computed by:

Equation 9.  The equation reads v subscript dh equals V divided by b subscript v time d.
(8-11A) [Equation 9]

where V is the design shear force at the section considered and d is for the entire composite section. Horizontal shear vdh shall not exceed permissible horizontal shear vh in accordance with the following:

(a) When contact surface is clean, free of laitance, and intentionally roughened, shear stress vh shall not exceed 36 psi.

(b) When minimum ties are provided in accordance with paragraph 8.15.5.5.5, and the contact surface is clean and free of laitance, but not intentionally roughened, shear stress vh shall not exceed 36 psi.

(c) When minimum ties are provided in accordance with paragraph 8.15.5.5.5, and the contact surface is clean, free of laitance, and intentionally roughened to a full magnitude of approximately ¼ inch, shear stress vh shall not exceed 160 psi.

(d) For each percent of tie reinforcement crossing the contact surface in excess of the minimum required by 8.15.5.5.5, permissible vh may be increased by 72fy /40,000 psi.

The horizontal shear values, vdh, need to be evaluated for HPC.

ACTION: A research problem statement is proposed.

8.15.5.6 Special Provisions for Slabs and Footings

8.15.5.6.3 Design shear stress, v, shall not exceed vc given by Equation (8-13) unless shear reinforcement is provided in accordance with Article 8.15.5.6.4.

Equation 10.  The equation reads v subscript c equals open parentheses .8 plus 2 divided by beta subscript c close parentheses times the square root of f prime subscript c less than or equal to 1.8 times the square root of f prime subscript c.
(8-13) [Equation 10]

bc is the ratio of long side to short side of concentrated load or reaction area.

The constants used in equation 8-13 need to be verified for HSC.

ACTION: A research problem statement is proposed.

8.15.5.6.4 Shear reinforcement consisting of bars or wires may be used in slabs and footings in accordance with the following provisions:

(a) Shear stresses computed by Equation (8-12) shall be investigated at the critical section defined in 8.15.5.6.1(b) and at successive sections more distant from the support.

(b) Shear stress vc at any section shall not exceed 0.9the square root of f prime, subscript c and v shall not exceed 3the square root of f prime, subscript c .

(c) Where v exceeds 0.9 the square root of f prime, subscript c, shear reinforcement shall be provided in accordance with Article 8.15.5.3.

The limiting values of v and vc need to be verified for HSC.

ACTION: A research problem statement is proposed.

8.15.5.7 Special Provisions for Slabs of Box Culverts

For slabs of box culverts under 2 feet or more fill, shear stress vc may be computed by:

Equation 11.  The equation reads v subscript c equals the square root of f prime subscript c plus 2,200 times rho times open parentheses V times d divided by M close parentheses.
(8-14) [Equation 11]

but vc shall not exceed 1.8the square root of f prime, subscript c. For single cell box culverts only, vc for slabs monolithic with walls need not be taken less than 1.4the square root of f prime, subscript c, and vc for slabs simply supported need not be taken less than 1.2the square root of f prime, subscript c. The quantity Vd/M shall not be taken greater than 1.0 where M is the moment occurring simultaneously with V at the section considered. For slabs of box culverts under less than 2 feet of fill, applicable provisions of Articles 3.24 and 6.4 should be used.

Although HSC may not be used in slabs of box culverts, the constants in equation 8-14 and limiting values of vc should be verified.

ACTION: A research problem statement is proposed.

8.15.5.8 Special Provisions for Brackets and Corbels*

8.15.5.8.3 The section at the face of support shall be designed to resist simultaneously a shear V, a moment [Vav + Nc(h – d)], and a horizontal tensile force Nc. Distance h shall be measured at the face of support.

(a) Design of shear-friction reinforcement, Avf, , to resist shear, V, shall be in accordance with Article 8.15.5.4. For normal-weight concrete, shear stress v shall not exceed 0.09f prime, subscript c nor 360 psi. For all-lightweight or sand-lightweight concrete, shear stress v shall not exceed (0.09 – 0.03av /d) nor (360 – 126av /d) psi.

(b) Reinforcement Af to resist moment [Vav + Nc(h – d)] shall be computed in accordance with Articles 8.15.2 and 8.15.3.

(c) Reinforcement An to resist tensile force Nc shall be computed by An = Nc/fs. Tensile force Nc shall not be taken less than 0.2V unless special provisions are made to avoid tensile forces.

(d) Area of primary tension reinforcement, As, shall be made equal to the greater of (Af +An) or (2Avf /3 + An).

*These provisions do not apply to beam ledges. The PCA publication, “Notes on ACI 318-83, ” contains an example design of beam ledges, Part 16, example 16-3.

Article (a) imposes a limit of 28 MPa (4000 psi) on the compressive strength on concrete that can be used in design and is a barrier to the effective use of HSC. The limits and factors need to be evaluated.

ACTION: A research problem statement is proposed.

8.15.5.8.5 Ratio rhor = As /bd shall not be taken less than 0.04(f prime, subscript c/fy).

Since the minimum value ofrhoincreases as concrete strength increases, values of r can be high with HSC. It needs to be determined if this minimum applies to HSC.

ACTION: A research problem statement is proposed.

8.16 STRENGTH DESIGN METHOD (LOAD FACTOR DESIGN)

8.16.1 Strength Requirements

8.16.1.1 Required Strength

The required strength of a section is the strength necessary to resist the factored loads and forces applied to the structure in the combinations stipulated in Article 3.22. All sections of structures and structural member shall have design strengths at least equal to the required strength.

8.16.1.2 Design Strength

8.16.1.2.1 The design strength provided by a member or cross section in terms of load, moment, shear, or stress shall be the nominal strength calculated in accordance with the requirements and assumptions of the strength-design method, multiplied by a strength-reduction factor phi.* The strength-reduction factors, phi, shall be as follows:

(a) Flexure............................................................................................. phi = 0.90

(b) Shear................................................................................................ phi = 0.85

(c) Axial compression with:
Spirals.............................................................................................. phi = 0.75
Ties................................................................................................... phi = 0.70

(d) Bearing on concrete......................................................................... phi = 0.70

The value of phi may be increased linearly from the value for compression members to the value for flexure as the design axial load strength, phiPn, decreases from 0.10 f prime, subscript cAg or phiPb, whichever is smaller, to zero.

* The coefficient phi provides for the possibility that small adverse variations in material strengths, workmanship, and dimensions, while individually within acceptable tolerances and limits of good practice, may combine to result in understrength.

HPC tends to be very sensitive to water content and constitutive materials. The chance of understrength concrete may increase, especially at very high compressive-strength levels. On the other hand, HPC is produced with stricter quality control and a lower coefficient of variation than conventional concrete. Also, HSC has less lateral expansion than conventional strength concrete, so the effect of confinement is less. This affects column behavior. There is, therefore, a need to verify the suitability of the given strength-reduction factors for HPC, especially HSC.

ACTION: A research problem statement is proposed to address strength-reduction factors.

8.16.2 Design Assumptions

8.16.2.7 A compressive stress/strain distribution, which assumes a concrete stress of 0.85 f prime, subscript c uniformly distributed over an equivalent compression zone bounded by the edges of the cross section and a line parallel to the neutral axis at a distance a = beta1c from the fiber of maximum compressive strain, may be considered to satisfy the requirements of Article 8.16.2.6. The distance c from the fiber of maximum strain to the neutral axis shall be measured in a direction perpendicular to that axis. The factor b1 shall be taken as 0.85 for concrete strengths, , up to and including 4,000 psi. For strengths above 4,000 psi, beta1 shall be reduced continuously at a rate of 0.05 for each 1,000 psi of strength in excess of 4,000 psi, but beta1 shall not be taken less than 0.65.

The stress/strain curve for HSC is more linear than for conventional strength concrete. However, the stress block factors are generally considered to be still valid for members where flexure predominates. For members where axial compression predominates, the concrete stress of 0.85f prime, subscript c may need to be reduced as concrete strength increases.(27) In the Canadian Standard for Design of Concrete Structures, the 0.85 factor is replaced by (0.85–0.0015 f prime, subscript c) greater than or equal to 0.67, in which f prime, subscript c is in megapascals.(28) A review is needed to determine if the rectangular stress block and factors are valid with HSC.

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