Determination of Concrete Shrinkage Initiation in Internally Cured and Conventional Concrete Decks

The extended performance of the concrete bridge deck depends on the concrete's ability to resist early-age cracks, which are primarily induced by self-desiccation shrinkage. Several stud-ies have been conducted to study the effect of shrinkage on the development of early-age cracks. When concrete shrinkage occurs, its magnitude may account for tensile stresses devel-oping in the concrete deck over time. Therefore, determining when shrinkage stress initiates in concrete is critical to precisely predict and analyze early-age cracking. The main objective of this research was to determine the appropriate time at which shrinkage initiates at early age for various concrete mixtures under field conditions. To achieve this objective, two adjacent bridge decks, one with internally cured concrete (ICC) and one with conventional concrete, were con-structed and instrumented to measure concrete strains and the temperature in both bridge decks during the first 30 h after concrete placement. The results of the field study were also compared with previous studies. Besides, a new approach to determine shrinkage initiation at early age depending on the strains of the free and restrained shrinkage was used in this re-search. The results showed that the time of concrete shrinkage initiation in both concrete decks was identical. For each deck, this time was approximately 5 h after concrete casting. The results showed that the time of the shrinkage development initiation in the ICC was consistent with the initial setting time.