Examination of Cement and Aggregate Type on the Crack-Resistance of Colorado's Bridge Deck Concretes

摘要

In 2003, the Colorado Department of Transportation (CDOT) revised their StandardSpecifications for Road and Bridge Construction to include two new classes of structuralconcrete. Class H and HT concrete was included into the standard specifications as acrack-resistant concrete. These concretes are currently used in the construction ofbridges and other concrete structures in Colorado. Recently, the CDOT has discovered anumber of bridge decks throughout the state constructed with Class H and HT concretethat exhibit cracking. It is suspected that the rate of strength gain for these concretemixtures may in part be a contributing factor to this cracking. Several bridge decks haveobtained the 56-day compressive strength within three days. This paper examines theeffect of using coarse-ground cement and lightweight aggregate to decrease crackingpotential. Hardened concrete properties tests included compressive strength, freeze/thawdurability, permeability, and restrained shrinkage. The coarse-ground cement loweredthe ultimate shrinkage strain; however, cracked at earlier ages when compared tomixtures containing Type Ⅱ cement. Internal curing using lightweight aggregate waseffective in reducing ultimate shrinkage strain. All mixtures exhibited low permeabilityat 56 days of age and satisfactory freeze/thaw resistance. Reduced strain developmentminimizes drying shrinkage cracking, thereby reducing maintenance costs over the life ofthe structure.