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Appendix F-Research Problem Statements

I. PROBLEM NUMBER

1

II. PROBLEM TITLE

Performance Requirements for High-Performance Concrete

III. RESEARCH PROBLEM STATEMENT

High-performance concrete (HPC) is expected to have performance characteristics exceeding those of conventional concretes. The desired characteristics may be related to mechanical properties (strength, elasticity, shrinkage, or creep) and to durability characteristics (resistance to freezing and thawing, scaling, abrasion, penetration of chlorides, sulfate attack, or alkali-silica reaction) or a combination of these.⁽¹⁾ An important performance criteria for bridge decks is the elimination of cracking.

In specifications for admixtures, where the properties of concrete containing the admixture are compared with the properties of a similar reference concrete, the performance requirements for the concrete containing the admixture are less than 100 percent for strength or higher than 100 percent for shrinkage. For example, in AASHTO M 154, strengths of 90 percent and shrinkages of 120 percent of the reference concrete are allowed. In M 154 and M 194, the relative durability factor is 80. In table 1 of M 194, it is stated that the values include allowances for normal variation in test results. This was also mentioned in the paper by Newlon and Mitchell.⁽²⁾ In HPC, tighter control and different values may be needed.

In table 4 of AASHTO M 295 and M 307, the maximum difference in drying shrinkage of mortar bars at 28 days over the control mortar is given as 0.03 percent. In AASHTO M 302 for slag, there are no criteria for shrinkage. These values should be evaluated. Also, the applicability of the mortar test for concrete should be determined.

This project should also evaluate if additional tests, such as sulfate resistance for fly ash concrete, are needed.

The age at which standard tests are made should be considered since HPC properties may develop more slowly than for conventional concretes. The FHWA definition of HPC has adopted a test age of 56 days.⁽¹⁾

Each test method should encompass the materials used in HPC and have complete precision and bias statements. For example, AASHTO T 132 includes only portland cement in its statement; T 106 lists values for portland cements and blended cements; and T 97 does not have precision or bias values.

AASHTO T 160 is used to measure the shrinkage of unrestrained concrete. However, no generally accepted test method is available to assess the cracking potential of concrete as used in bridge decks. Development of a test will allow the development of a performance criteria related to cracking.

IV. RESEARCH OBJECTIVE(S)

The main objective of the proposed research is to develop performance criteria for HPC. For HPC, tighter control and improved performance requirements are needed. Precision and bias statements of test methods should be complete and include hydraulic cement concretes.

To accomplish the objective, the following tasks will be performed:

Task 1. Review performance criteria used in different AASHTO and ASTM specifications and test methods for HPC to identify where further research is needed. The review shall include the following standards as a minimum:

Task 2. Develop a detailed work plan and test program to obtain the necessary data. Describe how the work plan will provide the necessary data. It is anticipated that the following specimens will be included:

Task 3. Perform the work plan.

Task 4. Develop specific proposed revisions to AASHTO and ASTM specifications and test methods.

Task 5. Submit a final report documenting the entire work effort including recommended revisions to the specifications and test methods.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $250,000

Research Period: 3 years

VI. URGENCY/PRIORITY

The current performance limits are too lenient for HPC. To fully benefit from HPC, new limits should be established. As the industry moves towards the greater use of high-performance concrete, the need to revise the performance limits becomes more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Highway Subcommittee on Materials and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Material Specifications and the AASHTO Test Methods.

Effectiveness

The benefits of this research include improved and more consistent concrete.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications and test methods for high-performance materials, performance based specifications, high-performance concrete, and performance based acceptance criteria.

VII. REFERENCES

1. Goodspeed, C. H., Vanikar, S., and Cook, R., "High Performance Concrete Defined for Highway Structures," Concrete International, Vol. 18, No. 2, February 1996, pp. 62-67.
2. Newlon, H. and Mitchell, T. M., "Freezing and Thawing," Significance of Tests and Properties of Concrete and Concrete-Making Material, STP 169C, American Society for Testing and Materials, 1994, pp. 153-163.

I. PROBLEM NUMBER

2

II. PROBLEM TITLE

Use of Wash Water in High-Performance Concrete

III. RESEARCH PROBLEM STATEMENT

Many State agencies restrict the use of wash water in hydraulic cement concrete. The chemicals in wash water can affect the setting characteristics of fresh concrete and may have adverse effects on the strength and durability of the concrete. AASHTO T 26, Test Method for Quality of Water to Be Used in Concrete and AASHTO M 157, Standard Specification for Ready-Mixed Concrete, address the chemicals and solids in water. AASHTO M 157 and M 241 provide limits for chlorides, sulfates, alkalies, and solids, which are under scrutiny. Meeting the total solids requirement is considered to be difficult. AASHTO M 157 refers to the testing of mortar specimens for acceptance of questionable water supplies. However, the interest is in the performance of concrete and not mortar. Concerns are raised about the use of wash water in regular concrete. These concerns are more critical with high-performance concrete (HPC). Currently, there is reluctance to using wash water in concrete for transportation facilities and the resistance will grow with the introduction of HPC.

On the other hand, environmental regulations restrict the disposal of wash water from the concrete plants. Ready-mixed concrete plants will have to recycle water and use it in concrete or discharge it to the environment after proper treatment. State DOTs and public agencies will have to find ways of using wash water to help the plants meet the environmental regulations.

IV. RESEARCH OBJECTIVE(S)

The main objective of the proposed research is to develop guidelines and specifications for the use of wash water in concrete. The chemicals and solids in water affect the performance of concrete. Test procedures are needed to predict the performance of concretes.

To accomplish the objective, the following tasks will be performed:

Task 1. Review the literature and identify the chemicals and amount of solids that affect the properties of HPC. The review shall include the following standards:

Task 2. Develop a detailed work plan and test program to obtain the necessary data. Describe the test program in detail and show how the work plan will provide the necessary data. For questionable water supplies use AASHTO T 22 to test concrete cylinders (rather than the mortar bars required). Also check the time of setting using AASHTO T 197 (ASTM C 403).

Task 3. Perform the work plan and develop draft guidelines and specifications.

Task 4. Verify the guidelines and specifications in field applications.

Task 5. Develop specific proposed revisions to AASHTO and ASTM material specifications and test methods.

Task 6. Submit a final report documenting the entire work effort including recommended revisions to the specifications and test methods. Chemical limits on wash water shall include chloride, sulfate, and alkali contents, and total solids.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $250,000

Research Period: 3 years

VI. URGENCY/PRIORITY

The lack of proper AASHTO specifications causes barriers to the use of wash water in high-performance concrete and high-strength concrete. However, the environmental regulations make it necessary to consider the use of wash water in all concrete, including HPC, for economic reasons. As the industry moves towards the greater use of high-performance concrete and high-strength concrete, the need to consider using wash water becomes more urgent. Implementation of these guidelines and specifications will indicate if and when wash water can be used in making HPC.

User Community

Results of the research will be directly applicable to the AASHTO Highway Subcommittee on Materials and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Material Specifications and the AASHTO Test Methods.

Effectiveness

The benefits of this research include maintaining high standards for HPC but at the same time addressing the environmental concerns.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications and test methods for high-performance materials, performance based specifications, high-performance concrete, and performance based acceptance criteria.

I. PROBLEM NUMBER

3

II. PROBLEM TITLE

Air-Void Requirements and Freeze-Thaw Testing Requirements for Durability of High-Performance Concrete

III. RESEARCH PROBLEM STATEMENT

For a uniform product, proper consolidation of concrete is needed. High-performance concrete (HPC) with a low water-cementitious materials ratio is expected to have a stiff consistency and is difficult to consolidate unless water-reducing admixtures or high-range water-reducing admixtures (HRWRA) are used. HRWRA may adversely affect the air-void system by stabilizing large voids. Furthermore, with high frequency vibration recommended by ACI 309 for consolidation, there are concerns that paving concretes lose many of the entrained voids that are essential for resistance to freezing and thawing during this process.⁽¹⁾ Such concretes were oversanded, which may also be the case with concrete for bridge structures. Thus the air-void system may be adversely affected, thereby influencing the resistance to freezing and thawing.

In HPC, improved workability is highly desirable. Self-consolidating concretes (SCC) that do not need any mechanical vibration but consolidate under their own mass are available. These concretes have high amounts of HRWRA and have very high flow. Maintaining the proper air-void system in these concretes should be evaluated.

The ACI Building Code permits a 1 percent reduction in the total air content if the compressive strength of the concrete exceeds 34 MPa (5000 psi). This is related to the low permeability of high-strength concrete. A decrease in air content requirement makes it easier to achieve the high strengths since an increase in air content reduces the strength. A change in total air content is expected to affect the air-void system. The relationship between strength, permeability, and air-void system for different exposure conditions is needed.

AASHTO Test Method T 161 (ASTM C 666) covers the determination of resistance of concrete specimens to rapidly repeated cycles of freezing and thawing in the laboratory. Unless specified otherwise, specimens are cured in lime saturated water for 14 days and then subjected to freezing and thawing. This is a severe test and may not correlate with field experience, especially for HPC. The test also requires 300 cycles of freezing and thawing or until the relative dynamic modulus of elasticity is 60 percent. These limits are not appropriate for HPC and need to be assessed.

IV. RESEARCH OBJECTIVE(S)

The objectives of the proposed research are to establish the required air-void system including the total air content for HPC that is consolidated mechanically or is SCC and to develop revised procedures, if appropriate, for AASHTO T 161.

To accomplish the objectives, the following tasks will be performed:

Task 1. Perform a literature survey to identify the effect of consolidation and admixtures on the air void systems of HPC and on freezing and thawing test procedures for HPC. The review shall include the following guides and standards:

Task 2. Develop a detailed work plan and test program to obtain the necessary data. Describe how the work plan will provide the necessary data. It is anticipated that the following specimens will be tested:

Task 3. Compare laboratory results with field experiences.

Task 4. Prepare specifications for establishing limits on air-void parameters for different permeabilities.

Task 5. Prepare revised specifications for freeze-thaw testing of concrete.

Task 6. Submit a final report documenting the entire work effort including recommended revisions to the test methods and specifications.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $350,000

Research Period: 3 years

VI. URGENCY/PRIORITY

The current air content requirements and freeze-thaw test method contain barriers to the greater use of high-performance concrete and high-strength concrete. These barriers restrict the application of existing and new technology to bridges. As the industry moves towards the greater use of high-performance concrete, the need to revise the limits for air content and the test procedure for freeze-thaw resistance become more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Highway Subcommittee on Materials and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Material Specifications and the AASHTO Test Methods.

Effectiveness

The benefits of this research include concrete with high resistance to degradation from freezing and thawing.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications and test methods for high-performance materials, performance based specifications, high-performance concrete, and performance based acceptance criteria.

VII. REFERENCES

1. Steffes, R. and Tymkowicz, S., "Vibrator Trails in Slipformed Pavements," Concrete Construction, April 1977, pp. 361-368.

I. PROBLEM NUMBER

4

II. PROBLEM TITLE

Penetrability Criteria for High-Performance Concrete

III. RESEARCH PROBLEM STATEMENT

One of the most important characteristics of high-performance concrete (HPC) is low permeability. However, tests and acceptance values to determine permeability have been controversial. The FHWA HPC definition⁽¹⁾ uses a very convenient electrical test, AASHTO T 277, which indicates the penetrability of concrete. This test has been criticized for not always correlating adequately with measured chloride ion penetration. AASHTO T 277 is also affected by interferences such as the presence of calcium nitrite. A recent migration test is similar to the AASHTO T 277 test except that the depth of chloride penetration rather than the charge is measured.⁽²⁾ This test is not affected by the presence of calcium nitrite and is being developed as an AASHTO provisional standard.

The 90-day ponding test, AASHTO T 259, has generated less criticism but takes a long time to run. In addition, 90 days is not sufficient time to discern differences between concretes when chlorides are measured using 13‑mm (0.5-in) thick layers. Longer ponding times or thinner layers are needed. The benefit of the ponding test is the possibility of generating diffusion coefficients that can be used in service-life prediction models.

In a series of HPC showcase bridges sponsored by the FHWA, specified values for permeability for bridge deck concrete ranged from 1000 to 2500 coulombs measured using AASHTO T 277. For precast girders, the values ranged from 1000 to 3000 coulombs.⁽³⁾ These values were based on the lowest values that could be reasonably achieved in each location. For reducing chloride penetration, a lower value of permeability is better. However, achieving these lower values can adversely affect other performance criteria such as deck cracking. Guidance is needed to identify optimum values for overall improved bridge deck, girder, and substructure performance in different environments.

Permeability of the field concretes should also be evaluated and compared with the laboratory findings.

IV. RESEARCH OBJECTIVE(S)

The objectives of the proposed research are to improve existing test procedures and to establish acceptable ranges for the penetrability of HPC.

To accomplish the objectives, the following tasks will be performed:

Task 1. Review the literature and identify the permeability methods for HPC. The review shall include the following tests:

Task 2. Develop a detailed work plan and test program to obtain the necessary data. Describe how the work plan will provide the necessary data. It is anticipated that the following specimens will be tested:

Task 3. Conduct a laboratory investigation of the variables.

Task 4. Correlate laboratory results with field experience and exposure conditions.

Task 5. Develop limits on penetrability, chloride content, and diffusion coefficients for the range of exposure conditions in the United States.

Task 6. Submit a final report documenting the entire work effort including recommended revisions to the specifications and test methods.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $300,000

Research Period: 4 years

VI. URGENCY/PRIORITY

The current permeability requirements based on AASHTO T 277 are controversial. Some agencies set very low limits. A better understanding of the relationship between longevity and coulomb numbers is needed. Chloride contents and diffusion coefficients should also be related to field performance. Permeability is an essential property when durability is a concern and a better understanding of values and performance is justified. As the industry moves towards the greater use of high-performance concrete, the need to establish limits for permeability or penetrability becomes more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Highway Subcommittee on Materials and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Material Specifications and the AASHTO Test Methods.

Effectiveness

The benefits of this research include a better understanding of the permeability or penetrability of concrete. This is essential for longevity of concrete bridges.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications for high-performance materials, performance based specifications, high-performance concrete, and performance based acceptance criteria.

VII. REFERENCES

1. Goodspeed, C. H., Vanikar, S., and Cook, R., "High Performance Concrete Defined for Highway Structures," Concrete International, Vol. 18, No. 2, February 1996, pp. 62-67.
2. Hooton, R. D., Thomas, M. D. A., and Stanish, K., "Prediction of Chloride Penetration in Concrete," FHWA, U.S. Department of Transportation, Report No. FHWA-RD-00-142, Washington, DC, 2001, 412 pp.
3. "High Performance Concrete," Compact Disc, Federal Highway Administration, Washington, DC, August 2001.

I. PROBLEM NUMBER

5

II. PROBLEM TITLE

Curing of High-Performance Concrete

III. RESEARCH PROBLEM STATEMENT

The three curing methods for concrete bridge decks are water curing, curing compound, or the waterproof cover method. Curing is necessary to maintain favorable moisture and temperature conditions in the concrete.

Water curing is favored especially when the water-cementitious materials ratio (w/cm) is below 0.40. In these concretes, autogenous curing is considered to cause shrinkage, which is additive to other shrinkage factors that may lead to cracking of the concrete. Whether water curing prevents autogenous shrinkage is not clear from the research. In water curing, it is not clear how long water supplied to the concrete can penetrate the material to help with autogenous shrinkage or further curing. This is particularly true for high-performance concrete (HPC).

AASHTO M 148 for liquid membrane-forming compounds requires a moisture loss of no more than 0.55 kg/m² (0.11 lb/ft²) in 72 hours and a daylight reflectance of not less than 60 percent. In summer months, these compounds contain white pigments to reflect solar energy and minimize heating of the concrete.

AASHTO M 171 for sheet materials requires moisture loss of no more than 0.55 kg/m² (0.11 lb/ft²) in 72 hours and a daylight reflectance of at least 50 percent for white curing paper and 70 percent for white polyethylene film.

All three curing methods need to be evaluated for HPC used in bridge decks. In addition to testing laboratory specimens, cores shall be taken from the field projects to determine the effectiveness of the curing methods.

IV. RESEARCH OBJECTIVE(S)

The objective of the proposed research is to establish effective curing methods for HPC. It will evaluate if a curing compound or waterproof covers with certain reflectance and moisture retention can be successfully used in HPC with different cementitious materials and w/cms, and if water curing reduces drying and autogenous shrinkage.

To accomplish the objectives, the following tasks will be performed:

Task 1. Review the literature and identify the curing methods for HPC. The review shall include the following documents:

Task 2. Develop a detailed work plan and test program to obtain the necessary data. Describe how the work plan will provide the necessary data. It is anticipated that water curing using burlap, cotton mats, ponding, fogging, or soaker hoses; curing compounds: and various sheet materials including curing paper, polyethylene film, and burlap-polyethylene sheet will be evaluated for moisture retention and temperature control. Concretes cured with these materials will be tested to determine the effectiveness of curing. Laboratory specimens and cores with varying dimensions shall be tested. A statistical analysis shall be conducted to determine the variability of each test and the differences in the methods used.

Task 3. Conduct field tests under a variety of typical outdoor environments.

Task 4. Prepare specifications for curing compounds, waterproof covers, and water curing for concrete with different strengths and permeabilities.

Task 5. Submit a final report documenting the entire work effort including recommended revisions to the specifications and test methods.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $250,000

Research Period: 3 years

VI. URGENCY/PRIORITY

The current curing requirements of the AASHTO specifications may not be appropriate for HPC. Improper curing results in poor quality concrete with undesirable cracking. As the industry moves towards the greater use of high-performance concrete, the need to revise the curing methods becomes more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Highway Subcommittees on Materials and Bridges and Structures and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Material Specifications, the AASHTO Test Methods, and the AASHTO LRFD Bridge Construction Specifications.

Effectiveness

The benefits of this research include more effective curing methods and will result in longer lasting concretes requiring less maintenance.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications for high-performance materials, performance based specifications, high-performance concrete, and performance based acceptance criteria.

I. PROBLEM NUMBER

6

II. PROBLEM TITLE

Procedures for Measuring Compressive and Flexural Strengths of High-Strength Concrete

III. RESEARCH PROBLEM STATEMENT

The AASHTO and ASTM test methods for measuring the compressive strength of concrete cylinders and cores were developed for the testing of concrete with compressive strengths up to about 40 MPa (6000 psi). Revisions have been made to some sections of the test methods to extend their applicability to concrete with compressive strengths up to 83 MPa (12,000 psi). With the greater use of high-strength concretes, particularly in transportation structures, there is a need to review the test methods for their applicability to high-strength concretes and to provide test methods for concrete with compressive strengths greater than 83 MPa (12,000 psi).

Some of the topics that need to be addressed are specimen size for different maximum aggregate sizes, consolidation procedures for cylinders, tolerances on test specimens, capping materials and procedures, qualification procedure for capping systems, testing machine characteristics including spherical head design, machine stiffness and loading rate, correction factors for different length to diameter ratios, and precision statements.

The AASHTO and ASTM test methods for measuring flexural strength require the use of a beam with a cross section of 152x152 mm (6x6 in) when the maximum size of coarse aggregate is up to 50 mm (2 in). These are large and heavy beams and a smaller size is desirable and may be appropriate with the smaller sizes of aggregate used in high-strength concrete. For the flexural strength tests, the size of specimen, curing conditions prior to test, and loading rate need to be evaluated.

IV. RESEARCH OBJECTIVE(S)

The objective of the proposed research is to refine existing test methods and procedures for measuring compressive strengths of concrete cylinders and cores and flexural strengths of concrete beams so that they are applicable for compressive strengths up to 140 MPa (20,000 psi).

It is anticipated that the research will include the following tasks as a minimum:

Task 1. Review of existing test methods and specifications for provisions that need to be evaluated for use with high-strength concrete. This review shall include the following standards:

Task 2. Identification of existing data that can be used to evaluate the existing provisions.

Task 3. Development of a work plan and test program to obtain the necessary data. Describe how the work plan will provide the necessary data.

Task 4. Submit an interim report within 6 months of the contract start date to document the results of tasks 1 through 3.

Task 5. Perform the work plan developed in task 3.

Task 6. Develop specific proposed revisions for the AASHTO and ASTM test methods and specifications.

Task 7. Submit a final report documenting the entire work effort including recommended revisions to the test methods and specifications.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $150,000

Research Period: 24 months

VI. URGENCY/PRIORITY

The current test methods for measuring the compressive and flexural strengths of concrete contain barriers to the greater use of high-strength concrete. These barriers restrict the application of existing and new technology to bridges. As the industry moves towards the greater use of high-strength concrete, the need to revise the test methods becomes more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Test Methods and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Test Methods.

Effectiveness

The benefits of this research include more reliable and consistent test methods for measuring the compressive and flexural strengths of high-strength concrete.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications for high-performance materials, performance-based specifications, high-performance concrete, and performance-based acceptance criteria.

I. PROBLEM NUMBER

7

II. PROBLEM TITLE

Application of Bridge Design Specifications to High-Strength Concrete Structural Members: Material Properties

III. RESEARCH PROBLEM STATEMENT

As part of FHWA Project No. DTFH61-00-C-00009 titled "Compilation and Evaluation of Results from High Performance Concrete Bridge Projects," a review of the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications was made to identify provision impacted by the use of high-performance concrete (HPC). Most of the identified provisions related to the use of high-strength concrete and indicated a need for additional research in order to extend the provisions to concrete compressive strengths greater than 70 MPa (10,000 psi). This research problem statement encompasses the provisions that are structural but involve a strong component of material behavior.

IV. RESEARCH OBJECTIVE(S)

The objective of the proposed research is to develop recommended revisions to the AASHTO specifications to extend the applicability of the provisions to compressive strengths of normal weight concrete greater that 70 MPa (10,000 psi). The scope of the project includes the following provisions:

Standard Specifications for Highway Bridges

8.5.3 Coefficient of thermal expansion and contraction

8.13.4 Computation of deflections

8.15.2 Allowable concrete stresses for modulus of rupture in sand lightweight and lightweight concrete and bearing stresses

8.16.7 Bearing strength

9.5.2.3 Cracking stress

9.15.2.4 Anchorage bearing stress

9.18.2.2 Minimum steel

9.21 Post-tensioned anchorage zone design

LRFD Bridge Design Specifications

5.4.2.6 Modulus of rupture

5.4.2.7 Tensile strength

5.7.3.6.2 Deflection and camber

5.7.5 Bearing

5.14.1.2.5 Concrete strength

5.14.2.3.3 Construction load combinations-tensile stress limits

5.14.2.4.7b Segment reinforcement-tensile stress

Standard Specifications for Transportation Materials and Methods of Sampling and Testing Part 2 - Tests

T 276 Developing Early-Age Compression Test Values and Projecting Later-Age Strengths

Accomplishment of the project objective will require the following tasks as a minimum:

Task 1. Identify the basis for the existing provisions.

Task 2. Identify testing and analysis required to extend the provisions to concrete compressive strengths greater than 70 MPa (10,000 psi).

Task 3. Develop a detailed work plan for experimental and analytical work. The work plan should include all testing needed to provide information that will permit extending the application of the specifications to high-strength concrete and should include estimates of the cost and time to complete each testing and analysis component.

Task 4. Submit an interim report to document tasks 1 through 3. A project panel will prioritize and select those portions of the plan that can be accomplished with the available funds.

Task 5. Perform the work approved by the panel. The test program shall include concrete with compressive strengths as high as 124 MPa (18,000 psi) although strengths as high as 140 MPa (20,000 psi) are desirable.

Task 6. Submit a final report documenting the entire research project. Any proposed revisions to the AASHTO specifications shall be included in the report.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $250,000

Research Period: 2 years

VI. URGENCY/PRIORITY

The current AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications contain barriers to the greater use of high-strength concrete. These barriers restrict the application of existing and new technology to bridges. As the industry moves towards the greater use of high-strength concrete, the need to revise the specifications becomes more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications.

Effectiveness

The benefits of this research include extension of the existing design previsions to concrete compressive strengths greater than 70 MPa (10,000 psi). The use of high-strength concrete in the right applications can result in more economical, aesthetic, and functional bridges.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications for high-performance materials, performance-based specifications, high-performance concrete, and performance-based acceptance criteria.

I. PROBLEM NUMBER

8

II. PROBLEM TITLE

Application of Bridge Design Specifications to High-Strength Concrete Structural Members: Shear Provisions Except Prestressed Concrete Beams

III. RESEARCH PROBLEM STATEMENT

The objective of NCHRP Project 12-56, titled "Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions," is to develop recommended revisions to the AASHTO LRFD Bridge Design Specifications to extend the applicability of shear design provisions for reinforced and prestressed concrete structures to concrete compressive strengths greater than 70 MPa (10,000 psi). The first part of the project required the development of an expanded work plan for experimental and analytical work based on a review of design and construction practices, identification of barriers to the use of high-performance concrete, and identification of research needs. The work was performed in cooperation with FHWA Project No. DTFH61-00-C-00009 titled "Compilation and Evaluation of Results from High Performance Concrete Bridge Projects."

Since the primary application of extended LRFD shear design specifications will be for the design of long-span and/or slender girders, the experimental program of NCHRP 12-56 will focus on testing large bulb-tee bridge girders. Analysis will initially focus on use of the sectional design model followed by the strut-and-tie model. Consequently, the project will only address shear in prestressed concrete beams. Other aspects of shear that need to be investigated include compression members, tension members, lightweight concrete, shear-friction, horizontal shear, slabs and footings, culverts, brackets, corbels, and ledges.

IV. RESEARCH OBJECTIVE(S)

The objective of the proposed research is to develop recommended revisions to the AASHTO LRFD Bridge Design Specifications and the AASHTO Standard Specifications for Highway Bridges to extend the applicability of the shear design provisions for reinforced and prestressed concrete structures to compressive strengths of normal weight concrete greater than 70 MPa (10,000 psi). The scope of work does not include prestressed concrete beams.

Accomplishment of the project objective will require the following tasks as a minimum:

Task 1. Review existing data that address shear in high-strength concrete members.

Task 2. Identify design provisions for which additional research is needed.

Task 3. Develop an expanded work plan for experimental and analytical work. The work plan should include all testing needed to provide information that will permit extending the application of the specifications to high-strength concrete and should include estimates of the cost and time to complete each testing component.

Task 4. Submit an interim report to document tasks 1 through 3. A project panel will prioritize and select those portions of the plan that can be accomplished with the available funds.

Task 5. Perform the work approved by the panel. It is anticipated that the majority of the work will consist of proof tests of large-scale concrete members to verify that the existing provisions are applicable for concrete compressive strengths up to about 140 MPa (20,000 psi). Test specimens are expected to represent compression members, tension members, slabs, footings, culverts, brackets, corbels, and ledges. Where existing provisions are found to require modifications, modified provisions will be developed and verified by additional tests, if needed. The scope of the project does not include the development of new design approaches.

Task 6. Submit a final report documenting the entire research project. Any proposed revisions to the AASHTO specifications shall be included in the report.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $700,000

Research Period: 4 years

VI. URGENCY/PRIORITY

The current AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specificationscontain barriers to the greater use of high-strength concrete. These barriers restrict the application of existing and new technology to bridges. As the industry moves towards the greater use of high-strength concrete, the need to revise the specifications becomes more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications.

Effectiveness

The benefits of this research include extension of the existing design previsions to concrete compressive strengths greater than 70 MPa (10,000 psi). The use of high-strength concrete in the right applications can result in more economical, aesthetic, and functional bridges.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications for high-performance materials, performance-based specifications, high-performance concrete, and performance-based acceptance criteria.

I. PROBLEM NUMBER

9

II. PROBLEM TITLE

Verification of Stress Limits and Resistance Factors for High-Performance Concrete

III. RESEARCH PROBLEM STATEMENT

Concrete has material properties that vary from batch to batch. Evaluation of these properties is based on a statistical method that examines random samples. In general, concrete material properties are determined from a sample of about 0.03 cu m taken from every 75 to 100 cu m (1 cu ft per 100 to 150 cu yd). The possibility exists that some of the unsampled concrete might have insufficient strength. Also, the acceptance criteria for concrete allows for a statistically small number of samples to be understrength. Resistance factors are placed in the AASHTO LRFD Bridge Design Specifications to allow for the possibility that a small amount of understrength concrete might exist in the structure. (These factors are called strength reduction factors in the AASHTO Standard Specifications for Highway Bridges). These factors also attempt to compensate for imperfect knowledge of the actual state of stress in the structure. The resistance factor is higher for bending, where the stress distributions are well understood, but lower for cases like bearing, where the stress distribution is less certain. The resistance factors are reduced if the failure mode is brittle such as shear or if failure of the element is likely to be catastrophic such as columns.

The properties of high-performance concrete (HPC), and high-strength concrete (HSC) in particular, are known to be more sensitive to the amount of added water, aggregate type and moisture condition, brand and type of cement, and admixtures used than conventional concrete. As a result, there may be a higher incidence of understrength concrete in structures using high-performance concrete. There is also evidence that high-strength concrete may be more brittle, exhibit less aggregate interlock, and less lateral expansion (causing confinement to be less effective) than conventional concrete. As a result, the resistance factors might not provide the anticipated level of safety for high-performance concrete.

In certain cases, such as prestressed concrete under service load conditions, the AASHTO LRFD Specifications and the AASHTO Standard Specifications also limit the service load concrete stress. However, these stress limits were developed for conventional strength concrete and their applicability to high-strength concrete may not be valid.

IV. RESEARCH OBJECTIVE(S)

The research objectives of this project are as follows:

1. Collect data on resistance factors and stress limits from previous research. Determine if the data are sufficient to evaluate the resistance factors and stress limits.
2. Where the data are insufficient to evaluate the resistance factors and stress limits, conduct experiments to generate the data needed.
3. Using the data from objectives 1 and 2, verify the resistance factors and stress limits in the AASHTO LRFD Specifications. Propose changes as needed. This same data should be used to evaluate the strength reduction factors and allowable stresses in the AASHTO Standard Specifications.

The objectives can be accomplished with the following tasks:

Task 1. Conduct an extensive literature search for experimental data on the strength properties of structures and/or elements made with HPC.

Task 2. Determine from the data found in task 1 where significant gaps in the data exist.

Task 3. Where there are sufficient data from task 1, evaluate the resistance factors and stress limits. Propose changes as needed.

Task 4. Where task 2 suggests significant gaps in the data, propose experiments to provide the needed data. Where structural tests are needed, they should be full scale. Unless data are available from other sources, the experiments should be designed to generate the following results:

1. Field verification of the actual incidence of understrength HSC/HPC.
2. Verification that the statistical nominal strength of HSC/HPC structural members, after being reduced by the resistance factor, still exceeds strength design moments.
3. An evaluation of the performance of HSC/HPC under service loads for cases where stress limits are specified in the AASHTO LRFD Specifications.

Task 5. Prepare an interim report summarizing the results of tasks 1-4.

Task 6. After approval of the interim report, conduct the experiments as approved.

Task 7. Verify the resistance factors and stress limits in the AASHTO LRFD Specifications. Propose changes, as needed, to the resistance factors and stress limits. Also verify or propose changes to the strength reduction factors and allowable stresses in the AASHTO Standard Specifications.

Task 8. Submit a final report.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $500,000

Research Period: 36 months - Approximately 10 months to complete tasks 1-5, 2 months to review the interim report, 21 months to complete tasks 6-8, and 3 months to review the final report.

VI. URGENCY/PRIORITY

The current specifications contain barriers to the greater use of high-performance concrete and high-strength concrete. These barriers restrict the application of existing and new technology to bridges. As the industry moves towards the greater use of high-performance concrete and high-strength concrete, the need to revise the resistance factors and stress limits becomes more urgent since the current factors may not provide the anticipated level of safety.

User Community

Results of the research will be directly applicable to the AASHTO LRFD Bridge Design Specifications and the AASHTO Standard Specifications for Highway Bridges and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO LRFD Bridge Design Specifications and the AASHTO Standard Specifications for Highway Bridges.

Effectiveness

The benefits of this research include a more realistic evaluation of the actual safety factors as related to high strength/high-performance concrete.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications for high-performance materials, high-performance concrete, and performance-based acceptance criteria.

I. PROBLEM NUMBER

10

II. PROBLEM TITLE

Confinement of High-Strength Concrete Columns for Seismic and Nonseismic Regions

III. RESEARCH PROBLEM STATEMENT

The American Concrete Institute State-of-the-Art Report on High-Strength Concrete Columns (ACI 441R-3) states that the presence of transverse (confining) reinforcement increases the strength of concrete columns but, for a given amount of transverse reinforcement, the effect is less pronounced with high-strength concrete (HSC) than with conventional strength concrete. This is often attributed to HSC having less expansion of the core under high axial load. The ACI report summarizes the results of approximately 15 different studies on concentrically loaded HSC columns. The results suggest that:

1. Columns with similar values of (D_s f_yt / f_c') have similar axial ductilities. Note that if the transverse steel yield strength, f_yt, is constant, a larger transverse reinforcing ratio (D_s) is required for higher strength concrete.
2. For HSC columns to achieve the minimum axial load capacity calculated by the procedures of ACI 318, (D_s f_yt / f_c') needs to be greater than 30 percent.

However, this report has some shortcomings. Some of the tests were made using confined cylinders, not columns. While the data suggesting that (D_s f_yt / f_c') needs to be greater than 30 percent are based on nine sets of tests, only two sets have (D_s f_yt / f_c') greater than 30 percent. The report says that HPC will have acceptable levels of ductility if "certain minimum limitations are met for the volumetric ratio and spacing of transverse reinforcing," but neither the report nor the cited reference indicates the actual limitations. Finally, the presented data do not differentiate between spiral reinforced columns and tied columns.

Thus, there needs to be some consistent data generated for spiral and tied columns with similar transverse reinforcing ratios and using HSC. The tests should address the minimum value of (D_s f_yt / f_c') needed to achieve acceptable strength and ductility in both seismic and nonseismic regions. The tests should also address the question of minimum bar size and spacing.

IV. RESEARCH OBJECTIVE(S)

Task 1. Complete a literature search for data on HSC columns. Divide the data into groups for spiral and tied columns for both monotonic and cyclic loading. Also consider concentric and eccentric loadings. This search should include column like structures, such as piles. Do an analysis of the data to determine where gaps exist in the data or where there are insufficient data to draw a firm conclusion. The analysis should consider concrete with compressive strengths up to 140 MPa (20,000 psi).

Task 2. Submit an interim report that summarizes the literature search. Propose full-size specimens, which can be tested to fill in the data pool, as identified in task 1.

Task 3. After approval of the interim report and testing plan, test full-size specimens to determine the amount, type, arrangement, and spacing of transverse reinforcement needed to assure strength and ductility in HSC columns in both seismic and nonseismic regions. This testing program should consider concrete with compressive strengths up to 140 MPa (20,000 psi). Tied and spiral columns must be included. The effects of eccentric loading should also be tested.

Task 4. Prepare draft specifications for the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications. The draft specifications should address the amount, type, arrangement, and spacing of transverse reinforcement needed to ensure strength and ductility in HSC columns under both eccentric and concentric loads.

Task 5. Prepare a final report.

V. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $500,000

Research Period: 36 months

VI. URGENCY/PRIORITY

The current AASHTO specifications contain barriers to the greater use of high-strength concrete. These barriers restrict the application of existing and new technology to bridges. As the industry moves towards the greater use of high-strength concrete, the need to revise the AASHTO Standard Specifications and the AASHTO LRFD Specifications becomes more urgent.

User Community

Results of the research will be directly applicable to the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications and will benefit the whole bridge community.

Implementation

Research results will be implemented with proposed revisions to the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications.

Effectiveness

The benefits of this research include:

1. Use of HSC in columns allows for the use of smaller columns, which are generally more economical. Small columns might improve the hydraulic characteristics of underflowing waterways or provide more clearance for underpassing roadways.
2. HSC columns may be more resistant to vehicle or debris impacts.
3. HSC columns will usually be more durable than conventional strength columns.

Thrust Areas/Business Needs

The proposed research addresses the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) thrust areas of Enhanced Specifications for Improved Structural Performance and/or Enhanced Materials, Structural Systems, and Technologies.

The associated building blocks are specifications for high-performance materials, performance-based specifications, high-performance concrete, and performance-based acceptance criteria

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FHWA-HRT-05-057