Evaluation of Early-Age Cracking Sensitivity in Bridge Deck Concrete

Abstract

Early-age cracking is a problem in bridge deck concrete as it can have several detrimental effects on long-term behavior and durability. The primary objective of this project was to evaluate the early-age cracking tendency of bridge deck concrete.The research presented in this thesis involved testing of a rigid cracking frame and a free shrinkage frame, under match-cured and isothermal conditions, to explore early-age cracking mechanisms of bridge deck concrete. The rigid cracking frame was used to evaluate the development of restrained stresses due to thermal and autogenous deformations. The free shrinkage frame was used to evaluate the thermal and autogenous deformations under zero-stress conditions. The laboratory testing program was designed to evaluate the effects of placement temperature, ambient temperature, aggregate type and supplementary cementing materials on the cracking sensitivity of bridge deck concrete mixtures. The laboratory testing program revealed that the heat generated during hydration greatly affects the restrained stress development of concrete. The temperature, at which the cracking occurred, decreased and time of cracking was delayed, when the control mixtures were placed in cold weather conditions. Use of supplementary cementing materials (SCMs) was found to be very effective in reducing the heat generation in bridge deck concrete and in reducing the restraint stresses, which significantly delayed the time of cracking. The behavior of concrete under isothermal conditions was also investigated. The rigid cracking frame was held at a constant temperature for the duration of the test. Use of SCMs was found to reduce the magnitude of shrinkage stress and development associated with autogenous shrinkage. The use of SCMs during hot weather conditions significantly reduced the cracking tendency of bridge deck concrete.