Effect of Low Shrinkage Mix Designs to Reduce Early Cracking of Bridge Decks

South Dakota Department of Transportation (SDDOT) bridge inspectors are noticing concrete bridge decks cracking early in their life unlike decks 40-50 years ago. Early cracking is often apparent when the forms are removed from newly constructed decks. Concrete bridge decks are typically designed with a 20-year service life with the option to then overlay or repair. However, many concrete bridge decks require earlier maintenance and need an overlay after 10 years. Shrinkage may be the leading cause of early concrete bridge deck cracking. Drying shrinkage and plastic shrinkage may occur prior to the concrete hardening. Hardened concrete can also experience volumetric reductions from thermal contraction, autogenous shrinkage, and carbonation shrinkage. (Construction practices, structural design, and curing of the concrete may also contribute to early deck cracking but are not the focus of this project.) The SDDOT would like to investigate mix designs to evaluate their drying and autogenous shrinkage, strength, and workability for South Dakota’s bridge deck applications. The department needs to identify test methods to best predict drying and autogenous shrinkage. Laboratory testing and evaluation of the mix designs using conventional mixes, lightweight aggregate, and shrinkage reducing admixtures will give the SDDOT a better understanding of how alternative structural concrete mix designs could be formulated and how they may perform. The objectives of this research are to: (1) evaluate and determine the best test methods to predict concrete shrinkage and (2) identify effective methods to reduce bridge deck shrinkage cracking by evaluating structural concrete mix designs.