Abstract Shrinkage cracking is reducing the service life of concrete bridge decks in South Dakota due to premature deterioration. In this study, the effects of varying concrete mix design parameters on autogenous and drying shrinkage was observed. Tested mix design changes include aggregate type (limestone and quartzite) and gradations (ASTM C33, Tarantula Curve, and 0.45 Power Curve), supplementary cementitious materials (fly ash), cementitious content, water-to-cementitious ratio, internal curing using saturated lightweight aggregates (expanded shale), and shrinkage reducing admixtures. These changes were evaluated for their effect on the shrinkage of paste, mortar, and concrete as measured by ASTM C1698 (autogenous shrinkage) and ASTM C157 (drying shrinkage). Fresh property tests, compressive strength, and electrical resistivity measurements were performed on each mix as well. A survey of state Department of Transportations revealed the current state-of-the-art practices on shrinkage reduction in bridge decks, including the use of admixtures, internal curing agents, and external curing methods.

Early-age shrinkage cracking has been observed in many concrete bridge decks in Washington State and elsewhere around the U.S. The cracking increases the effects of freeze-thaw damage, spalling, and corrosion of steel reinforcement, thus resulting in premature deterioration and structural deficiency of the bridges. In this study, the main causes of the early-age cracking in the decks are identified, and concrete mix designs as a strategy to prevent or minimize the shrinkage cracking are evaluated. Different sources (eastern and western Washington) and sizes of aggregates are considered, and the effects of paste content, cementitious materials (cement, fly ash, silica fume, slag), and shrinkage reducing admixture (SRA) are evaluated. A series of fresh, mechanical and shrinkage property tests were performed for each concrete mix. The outcomes of this study identify optimum concrete mix designs as appropriate mitigation strategies to reduce or eliminate early-age shrinkage cracking and thus help minimize shrinkage cracking in the concrete bridge decks, potentially leading to longer service life.

Early-age shrinkage cracking has been observed in many concrete bridge decks in Washington State and elsewhere around the U.S. The cracking increases the effects of freeze-thaw damage, spalling, and corrosion of steel reinforcement, thus resulting in premature deterioration and structural deficiency of the bridges. In this study, the main causes of the early-age cracking in the decks are identified, and concrete mix designs as a strategy to prevent or minimize the shrinkage cracking are evaluated. Different sources (eastern and western Washington) and sizes of aggregates are considered, and the effects of paste content, cementitious materials (cement, fly ash, silica fume, slag), and shrinkage reducing admixture (SRA) are evaluated. A series of fresh, mechanical and shrinkage property tests were performed for each concrete mix. The outcomes of this study identify optimum concrete mix designs as appropriate mitigation strategies to reduce or eliminate early-age shrinkage cracking and thus help minimize shrinkage cracking in the concrete bridge decks, potentially leading to longer service life.

Restrained shrinkage cracking of concrete bridge decks creates a significant durability problem. Major admixture suppliers in the United States have introduced a new category of chemical admixtures called shrinkage reducing admixtures (SRAs). SRAs work by reducing the surface tension of pore water and thereby decreasing the capillary stress and shrinkage induced by drying. Several studies have reported that using SRAs in concrete mixtures is one of the most effective ways of reducing shrinkage cracking. The purpose of this study was to investigate the effectiveness of SRAs in reducing drying shrinkage in Virginia Department of Transportation (VDOT) concrete mixtures and thus reducing cracks in bridge decks. Nine bridges located in VDOT's Northern Virginia, Staunton, and Fredericksburg districts were selected for study. Three different SRA products were used. With the exception of one mixture, the maximum cementitious content was limited to 600 lb/yd3. Fresh and hardened concrete properties were determined for each mixture, and field placement details were documented. The results showed that low cementitious concrete with SRA was effective in minimizing bridge deck cracking. The study showed that bridges with fewer and narrower cracks or no cracks can be constructed and that proper construction practices are needed to reduce bridge deck cracking. The study recommends the use of SRA with a lower cementitious content in VDOT bridge deck concrete mixtures. A VDOT special provision was developed for the future use of SRA in concrete mixtures.