Elasticity modulus, shrinkage, and creep of high-strength concrete as adopted by AASHTO

Abstract

This paper covers the experimental and theoretical components of National Cooperative Highway Research Program (NCHRP) research project Number 18-07, which is discussed in NCHRP Report 496. The components are related to modulus of elasticity, shrinkage, and creep of concrete. An experimental program was conducted at various bridge sites and at the University of Nebraska-Lincoln for specimens produced from raw materials and mixture proportions provided by 4 participating states: Nebraska, New Hampshire, Texas, and Washington. Previously reported measurements of material properties are also included. The experimental program was used to extend the pre-2005 AASHTO-LRFD specification prediction formulas to concrete with compressive strengths up to 15 ksi (104 MPa). For each material property, a summary of the experimental values is presented followed by a comparison with the values obtained from the pre-2005 AASHTO-LRFD specifications and the American Concrete Institute 209 committee report. The proposed formulas provide designers of prestressed concrete girders with more realistic estimates of long-term material properties, including effects of aggregate type and other significant factors. The use of these formulas with high-strength concrete (HSC) should result in more realistic camber predictions and lower prestress loss estimates. The background and recommendations for prediction of the modulus of elasticity, shrinkage, and creep of HSC are provided. To help with clarity, the notation and units employed in the pre-2005 AASHTO-LRFD specifications are adopted as much as possible. Stresses are expressed in units of ksi (MPa) rather than psi.