Mississippi Department of Transportation
Admixtures; Bridge decks; Chloride content; Permeability; Portland cement concrete; Test procedures
Mississippi Department of Transportation (MDOT) is now requiring waterproofing (permeability reducing) admixtures in bridge deck overlays in an effort to improve the long-term performance of bridges. These admixtures reportedly reduce permeability of concrete by plugging pores and capillaries throughout the entire mass of concrete. These admixtures react with water and cement hydration by-products to either formulate coalescing polymer globules or crystalline structures that seal pores, capillary tracts and micro cracks in hardened concrete. This makes hardened concrete less permeable to water and chemicals that corrode the reinforcing steel and create costly repairs. While some manufacturers note that these chemicals exceed performance requirements of industry standards such as ASTM C494 Type S, limited data is provided to document their performance in a bridge deck. Bridge structures create a restrained system for concrete shrinkage and many Mississippi bridges are exposed to chloride ions when salt is broadcast on the decks in winter months. This laboratory study will use testing equipment and chloride ion exposure to simulate these field conditions. Data compiled from this study will provide MDOT Engineers with information needed to verify that ordinary portland cement (OPC) or portland limestone cement (PLC) combined with these admixtures will reduce the permeability of portland cement concrete (PCC) in bridges.