Early-Age Cracking Tendency and Ultimate Degree of Hydration of Internally Cured Concrete

Abstract

Early-age cracking in bridge decks is a severe problem that may reduce functional life of the structure. The effect of lightweight fine aggregate on the cracking tendency of bridge deck concrete was evaluated using cracking-frame testing techniques. Water for internal curing is provided by incorporating prewetted absorptive lightweight aggregate (LWA) into the mixture during batching. The absorbed water within the LWA is desorbed at early ages as hydration progresses. The release of the internal curing water increases cementing material hydration and reduces capillary stress caused by self-desiccation. Cracking frames measure the development of stresses due to thermal and autogenous shrinkage effects from setting until the onset of cracking. Restrained concrete specimens were tested under temperature conditions that match those of an in-place bridge deck and under isothermal curing conditions to determine the stress development due to autogenous shrinkage. Internal curing from LWA increased the time to initial cracking, reduced autogenous shrinkage stress development, and increased the degree of hydration in bridge deck concretes.