The effects of silica fume and fly ash on reducing the risk of concrete damage due to alkali-silica reaction are presented in this thesis. One silica fume and twenty fly ashes of a wide range of chemical composition were investigated. The effect of the selected materials on expansion when used with high-alkali Portland cement and a siliceous limestone reactive aggregate (Spratt) was evaluated using the concrete prism and the accelerated mortar bar tests. Portland cement pastes and lime/pozzolan blends were prepared using similar combinations of materials used in the expansion tests. These samples were used to study the effects of fly ash and silica fume on the pore solution alkalinity and composition of hydration products. The study showed that the efficiency of fly ash in limiting the risk of deleterious expansion is linked to its efficiency in lowering the pore solution alkalinity. High-calcium and high-alkali fly ashes are generally less effective in this respect compared to low-calcium ash. Silica fume was found to be effective in reducing the pore solution alkalinity at early ages; however, the alkalinity was found to increase at ages later than 28 days. Combinations of moderate levels of silica fume (5%) and high-calcium fly ash (20-30%) were found to be effective in limiting the expansion even after three years. This was attributable to the high capacity of such combinations to achieve and maintain low pore solution alkalinity. The silica fume reduces the pore solution alkalinity at early ages and the fly ash maintained the low alkalinity at later ages. The study showed that, for low and moderate-alkali fly ash, the 14-day expansion in the accelerated mortar bar test could be used to predict the 2-year expansion of concrete prisms. The results from the lime/pozzolan blends confirmed that the hydration products of pozzolan play the dominant role in reducing the pore solution alkalinity of cementitious systems containing pozzolans. The two-year expansion of concrete prisms containing fly ash could be correlated reliably to the alkalis available from the ash as determined by leaching mature paste samples in leaching solution of alkali ion concentration of 0.25 moles per litre.

This book reviews the fundamental causes and spectrum effects of ASR. It considers he advances that have been made in our understanding of this problem throughout the world.

Concretes with equal water/cement ratios and equal paste volumes of various combinations of cement, fly ash, and silica fume were tested to establish parameters for strength and chloride permeability. Comparative specimens with Type II and Type III cement were tested. The effects of temperature and moisture availability during curing were also evaluated. In general, the laboratory tests showed that, when adequate curing in the 73°F to 100 °F temperature range is provided, concretes with satisfactory early and 28-day strengths and good resistance to chloride ion penetration can be obtained with either type of cement and various combinations of fly ash and silica fume. The cementitious material can be in the range of 30 to 35 percent fly ash and 5 percent silica fume, based on the weight of the cementitious material. Similar specimens cured at 43°F generally did not develop an adequate early strength, and the chloride permeability was high. Combinations of the pozzolans with Type III cement yielded higher strengths and a lower chloride permeability than did similar combinations with Type II cement.