Effect of alkali-bearing aggregates on alkali-silica reaction

The effect of two kinds of alkali-bearing aggregates, nepheline syenite and alaskite on alkali-silica reaction (ASR) were studied using a new accelated test method, by which specimens were cured in steam at 80°C. Additionally, through curing specimens in different alkalion solutions at 150°C, the mechanism of alkali releasing from alkali-bearing aggregate was analyzed. The results show that the effect of nepheline syenite on ASR is remarkably influenced by the change of alkali content in cement, ASR expansion can be enhanced by nepheline syenite and alaskite in mortar using low alkali cement, while it is reduced in mortar using high alkali cement due to the decrease of alkali release of nepheline syenite and alaskite; Nepheline mineral is stable in saturation Ca(OH)₂ solution, but decomposes with the alkali content increasing in saturation Ca(OH)₂ solution. Feldspar minerals are stable in alkaline solution, only little dissolution can be found in the crystal interface. It is concluded that alkali releases from feldspar minerals in concrete mainly depend on ion change between surface layer of minerals and Ca²⁺ ion in solution.