Development of Specifications for a Crack Resistant Bridge Deck Concrete

Within the past five years, the Colorado Department of Transportation (CDOT) has experienced a continued problem with bridge deck cracking. In 2003, CDOT implemented the concrete mixture design Class H into the CDOT Standard Specification for Road and Bridge Construction. Class H was developed to provide crack resistant concrete structures and was intended to be used in the construction of concrete bridge decks that would not receive a waterproofing membrane and asphalt overlay. Recently, the CDOT has noticed cracking in several bridge decks using this concrete specification. This paper includes the design and testing of eleven concrete mixtures in an effort to create a more crack resistant concrete and improve the current specification. The concrete mixtures were designed with water-to-cementitious material’s ratio amounts and cement content both above and below the current specifications. The design approach was intended to investigate the effect of individual and multiple supplemental cementitious materials replacement levels and aggregate and cement type on the concrete properties: restrained shrinkage strain, compressive strength, rate of strength gain, freeze/thaw durability, and permeability. A national state Department of Transportation (DOT) survey was conducted to determine other DOT’s current and past research involving crack resistant concrete as well as comments regarding their own specifications currently used for bridge decks. A more crack resistant concrete mixture was developed through this study. The primary recommendations from this research were: increase the maximum allowable w/cm, decrease the cementitious content, increase the percent of allowable fly ash, and include a shrinkage reducing admixture.