Thermal Expansion of Concretes: Case Study in Iowa

To control the effect of concrete expansion or contraction on the integrity of concrete bridge structures, the thermal coefficient of expansion of concrete is often incorporated into design equations. Current practice is to use the value recommended by the Association of American State Highway and Transportation Officials of 11 parts per million per °C (6 parts per million per °F) change. Historically this has been used without considering the effect of local material properties on the overall expansion of concrete. This paper summarizes research findings on the thermal behavior of structural bridge concretes in Iowa. The thermal coefficient of expansion of limestone aggregates, gravel aggregates, mortar, corresponding limestone aggregate concretes, and gravel aggregate concretes were determined in the laboratory. Laboratory results were compared to actual bridge expansion data from field studies and the results from an empirical equation for determining concrete expansion. Results of the laboratory study compared very favorably to field data and results from the empirical equation. Results also indicated that the coefficients of expansion obtained in this study were lower than the Association of American State Highway and Transportation Officials suggested design value. These lower values of thermal coefficient of expansion affect the design length of integral abutment bridges in Iowa.