Bridge Decks: Mitigation of Cracking and Increased Durability—Phase III

Early-age cracking in concrete decks significantly reduces the service life of bridges. This report discusses the application of various concrete mixtures that include potential early mitigation ingredients. Large-scale (7 ft × 10 ft) experimental bridge prototypes with similar restraint conditions found in actual bridges were poured with different concrete mixtures to investigate mitigation techniques. Portland cement (control), expansive Type K cement, internally cured lightweight aggregate (LWA), shrinkage-reducing admixture (SRA), and gypsum mineral were investigated as mitigating ingredients. Seven concrete mixtures were prepared by using individual ingredients as well as a combination of different ingredients. The idea behind combining different mitigating techniques was to accumulate the combined benefit from individual mitigating materials. The combined Type K cement and LWA mixture showed higher concrete expansion compared with mixtures containing Portland cement, Type K cement, LWA, and SRA in the large-scale experimental deck. Extra water provided by LWA significantly enhanced the performance of Type K cement’s initial expansion as well as caused larger total shrinkage over the drying period. A combination of Type K cement and gypsum mineral showed insignificantly higher expansion compared with the individual Type K mixture. Overall, the experimental deck containing SRA showed the least total shrinkage compared with other mixtures. Finite-element modeling was performed to evaluate and predict concrete stress-strain behavior due to shrinkage in typical bridges. A parametric study using finite-element analysis was conducted by altering the structure of the experimental deck. More restraint from internal reinforcement, less girder spacing, larger girder flange width, and more restrictive support conditions increased the concrete tensile stress and led to potential cracking in the concrete deck.