Deck Reinforcement Detailing and Concrete Mix Additives to Reduce Bridge Deck Cracking

Abstract

Despite recent changes to MnDOT mix designs, transverse cracking has still been observed shortly after the bridge deck is poured. The goal of this research was to determine the causes of this cracking and to propose deck reinforcement or mix design practices that efficiently mitigate the problem. Initial investigations focused on synthesizing existing research relating to crack mitigation in concrete bridge decks, and how these practices aligned with current Minnesota Department of Transportation (MnDOT) design and construction practices. This was followed by laboratory testing of high-performance bridge deck mixes to test alterations to the accepted mix specifications, and computational modeling to determine the most critical bridge deck demands and effects of altered deck reinforcement. Computational results indicated that minimizing shrinkage and the temperature difference between the placed deck concrete on the girders are the most effective means to reduce tensile demands on the bridge deck. Introducing shrinkage reducing admixtures into the mix effectively reduced strain due to unrestrained shrinkage by approximately 25% and forces due to restrained shrinkage by approximately 50%. Changing deck reinforcement has no effect on crack initiation but may control crack width once it forms. Thus, recommendations include a combination of reduced shrinkage and increased top longitudinal reinforcement in the bridge deck.