Strain Gradients in Concrete Affected by Alkali–Silica Reaction: A Laboratory Simulation

Alkali–silica reaction (ASR) is a significant durability issue that has resulted in expansion and cracking of numerous concrete structures. Expansion is often not uniform in a given structure, leading to the development of strain gradients and manifested in macrocracking patterns on the surface. Techniques developed to mitigate ASR in existing structures involving surface treatments, such as lithium impregnation or silanes, can cause strain gradients to develop by suppressing expansion in the near-surface region, while expansion in the center of the concrete continues uninhibited. A set of plain concrete slabs consisting of a layer of ASR-resistant concrete with lithium nitrate admixture cast over a layer of ASR-susceptible concrete were monitored for expansion and crack development. The study found that a layer of ASR-resistant concrete of at least 50 mm (2.0 in.) deep was necessary to significantly suppress expansion and cracking at the top surface. However, in all layered specimens, the bottom layer continued to expand and a significant strain gradient developed between the top and bottom surfaces.