Laboratory and field investigations of the influence of sodium chloride on alkali–silica reactivity

Concrete cylinders, 255 mm in diameter, were made with high- and low-alkali cements, a highly alkali–silica-reactive coarse aggregate, and subjected to various conditions at 38 °C: (1) immersion in 3% NaCl solution; (2) immersion in 6% NaCl solution; (3) humid air at 100% RH, and (4) 14-day cycles including 12 days in humid air, 2 days of drying, and 3 h in 6% NaCl solution. After 1 year, a number of cylinders were drilled to obtain dry powder samples from different depths, which were analyzed for total and soluble chloride and for soluble sodium and potassium. Concrete cores were also taken in a number of parapets and abutments, either exposed to deicing salts or not, on which chemical analyses were also performed on slices taken at different depths from the exposed surface. The results obtained suggest that making concrete with a low-alkali content is an effective way to prevent expansion due to alkali–silica reaction even for concretes exposed to seawater or deicing salts; this is attributed to the fact that the OH ⁻ ion concentration in the pore solution, and then the pH, is decreased in the near-surface layers of concrete exposed to sodium chloride, which does not penetrate at depth in concrete.