High Dosage Type-C Fly Ash and Limestone in Sand-Gravel Concrete

Alkali-silica reactions are a major cause of concrete deterioration. The reactions can lead to severe damage that may ultimately endanger the performance and safety of concrete structures. The use of fly ash as partial replacement of Portland cement and the use of some limestone in concrete mixtures were considered as two potential approaches to minimize the severity of the problem. Sand-gravel concrete mixtures were prepared by replacing 15, 25, and 35 percent, by weight of Portland cement, with an equal weight of ASTM Type C fly ash. In those mixtures, either 30 percent or 50 percent of the total aggregate was limestone. Concrete beams were prepared and the wetting-and-drying test was performed in accordance with Kansas Department of Transportation (KDOT) specifications. Also, freeze-and-thaw testing of concrete beams were performed on some selected mixtures. Results indicate that most of the fly ash concrete mixtures with 30 percent limestone do not fulfill the requirements of the KDOT specifications. The fly ash mixtures with 50 percent limestone yield better results; most of them meet the specifications. Results also show that increasing the fly ash dosage does not seem as effective as introducing limestone for alleviating alkali-silica reaction problems.