Revised Curing Practices for NDOT Bridge Decks to Minimize Restrained Shrinkage Cracks

Due to their high cement content and low water-to-cement ratio, cast-in-place concrete bridge decks are particularly susceptible to early-age cracking. This is often exacerbated by the shrinkage of the concrete when constrained by supporting girders. Such cracks can lead to significant issues, such as rebar corrosion and delamination, posing a primary concern for the Nebraska Department of Transportation (NDOT). Recognizing this challenge, recent and ongoing research initiatives at NDOT, including projects SPR-FY22(001)1 and SPR-P1 (19) M0832, as well as ongoing studies at NDOT Materials & Research (M&R), have identified promising strategies to mitigate this issue. These strategies include internal curing, reduction in cementitious material content, and the use of innovative admixtures (e.g., E5® Internal Cure admixture), all aimed at reducing shrinkage-related cracking in bridge decks. The previous projects exemplifies a successful approach for reducing free and restrained shrinkage strains in concrete bridge decks by reducing cementitious material content by 50, 100, and 150 lbs per cubic yard and optimizing aggregate gradation. This approach is expected to significantly lower the likelihood of shrinkage cracking in concrete bridge decks. Despite the progress in reducing concrete shrinkage, there remains a gap in understanding regarding the feasibility of shortened curing durations when using lower-shrinkage mixtures.