Tests were conducted to quantify the effect of alkali-silica reaction on the properties of concrete. Two reactive aggregates, Beltane opal and an amorphous fused silica, were used to simulate the reaction in the laboratory. At 0.1% expansion, concrete containing 5.2 kg/m³ equivalent sodium oxide showed a loss of 12% compressive strength but 50% tensile strength. The compressive strength was not found to be a good indicator of alkali-silica reaction, but the modulus of rupture test proved to be a sensitive and reliable test to identify the progress of the reaction. Dynamic modulus and pulse velocity also appear to be good indicators of alkali-silica reaction. The tests suggest that fused silica is an ideal reactive aggregate to simulate expansion due to alkali-silica reaction, and that it provides an effective means of determining the deterioration in concrete properties and in evaluating mineral admixtures to control expansion.