The use of high-strength concrete (HSC) for pretensioned concrete bridge girders has become common - place among state highway agencies because of its economic and durability benefits. This paper summarizes part of the research work performed under the National Cooperative Highway Research Program (NCHRP) project 18-07, Prestress Losses in Pretensioned High-Strength Concrete Bridge Girders, which is fully documented in NCHRP report no. 496. The researchers were assigned the task of extending the American Association of State and Highway Transportation Officials�? (AASHTO’s) AASHTO LRFD Bridge Design Specifications provisions for estimatingprestress losses to cover concrete strengths up to 15 ksi (104 MPa). This paper summarizes the portion of that work onconcrete properties that have an impact on design for long-term effects: modulus of elasticity, shrinkage,and creep. These research findings were adopted into the 2005 and 2006 interim provisions of the AASHTO LRFD specifications. The experimental component of the research includes testing of specimens produced from raw materials and mixture proportions provided by four participating states (Nebraska, New Hampshire, Texas, and Washington) to encompass the regional diversity of materials throughout the country. The theoretical component of the research addresses the background of prior prediction formulas and the development of the new formulas that have now been adopted.
