Building Materials Exam 2 Practice

Alkali-silica reaction expands concrete when moisture allows alkalis from cement to attack reactive silica in aggregates. A proven way to curb this is to add supplementary cementitious materials that react with the alkaline pore solution, reducing its availability and slowing the reaction. Fly ash is a pozzolanic material; its reactive silica and alumina react with calcium hydroxide from cement hydration to form additional cementitious products. This consumes the caustic components, refines the pore structure, and lowers diffusion of alkalis to the reactive silica, so the ASR gel forms less and swells less. Because of this mechanism, fly ash is commonly used to mitigate ASR. Other options don’t provide the same reliable pozzolanic activity: limestone mostly acts as filler, granite is inert, and bentonite’s effects are less consistent for ASR control.