2004

At its 2004 Annual Meeting, the AASHTO Subcommittee on Bridges and Structures approved revisions to the AASHTO LRFD Bridge Design Specifications for the 2005 edition to permit the use of several articles with concrete compressive strengths up to 15.0 ksi (103 MPa). The following is a summary of the approved revisions, which do not become official until they are published by AASHTO.

5.4.2.3 Shrinkage and Creep

The equations for calculating shrinkage and creep of concrete are revised based on the results of NCHRP Project 18-07 and published in NCHRP Report No. 496. The new equations provide approximately the same results as the current equations for conventional strength concrete and provide more accurate results for high-strength concrete.

5.4.2.4 Modulus of Elasticity

A new factor is added to the equation for calculating the modulus of elasticity. This factor allows for an adjustment based on the aggregate used in the concrete.

5.4.2.6 Modulus of Rupture

An upper bound value for the modulus of rupture of normal weight concrete is added. This value is to be used in calculating the cracking moment for determination of minimum reinforcement.

5.7.1 Assumptions for Service and Fatigue Limit States.

The limit of 6.0 for modular ratio is removed.

5.9.5 Loss of Prestress

Articles 5.9.5.1 through 5.9.5.4 are revised based on the results of NCHRP Project 18-07 and published in NCHRP Report No. 496. The new articles result in a more accurate prediction of prestress losses and camber for high-strength concrete members.

2003

At its June 2003 Annual Meeting, the AASHTO Subcommittee on Bridges and Structures approved a number of revisions to the AASHTO LRFD Bridge Design and Construction Specifications for the 2004 Editions to facilitate the implementation of high performance concrete. Please note that the following is only a summary of the approved revisions.

DESIGN SPECIFICATIONS

• Recognize that concrete unit weight increases as concrete compressive strength increases (Table 3.5.1-1)
• Extend some provisions to concrete compressive strengths greater than 10.0 KSI (Articles 5.1 and 5.4.2.1)
• Allow concrete compressive strengths to be specified at ages other than 28 days (Article 5.3)
• Allow the use of ground granulated blast-furnace slag (Article C5.4.1)
• Allow higher cementitious materials content for high strength concrete (Article 5.4.2.1)

CONSTRUCTION SPECIFICATIONS

• Introduce two new classes of high performance concrete (Articles 8.2, 8.3.1, 8.4.1, 8.4.4, 8.6.6, 8.6.7, and 8.11.1)
• Allow the use of ASTM 1157 Blended Hydraulic Cement (Article 8.3.1)
• Allow a combined aggregate grading (Article 8.3.5 and a new Appendix)
• Allow the use of ground granulated blast-furnace slag (Articles 8.3.7, 8.4.4, and 8.6.4.1)
• Allow higher cementitious materials content for high strength concrete (Article 8.4.3)
• Recognize the use of 4x8-in. cylinders (Article 8.5.7.1)
• Allow concrete compressive strengths to be specified at ages other than 28 days (Articles 8.5.7.3 and 8.5.7.5)
• Require the use of match-cured cylinders for high strength precast concrete (Article 8.5.7.5)
• Ensure proper curing of high performance concrete (Articles 8.6.4.1, 8.11.1, 8.11.3.5, 8.11.4, and 8.13.4)