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

Abstract

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.

Alkali–silica reaction: Current understanding of the reaction mechanisms and the knowledge gaps

“…This aggregate has been the subject of numerous ASR studies [105][106][107], particularly when rapid and severe expansion from ASR is desired. Pulverized samples of the aggregate subjected to hot-water extraction with a soak time of 24 h released an average Na 2 O eq of 0.24 kg/m 3 (by mass of concrete), assuming the aggregate would constitute 30% by mass of concrete.…”

Effect of Multiaxial Stresses on Alkali-Silica Reaction Damage of Concrete

“…Surface cracks have been mapped to assess the ASR damage experienced by concrete structures, sometimes in terms of a "cracking index". 6,7 However, the cracking index method involves monitoring cracks along the four sides and two diagonals of a square area on a concrete surface, and does not differentiate the cracks by their orientation, which can be influenced by the stress state of concrete. 8 Another method to assess the damage due to ASR by monitoring cracking is the damage rating index (DRI).…”

Ultra-accelerated alkali-silica reaction testing using autoclaving methods

“…Aggregates HR1, HR6, and VHR4 produced expansions in excess of 0.50% in the autoclave test. All three aggregates are welldocumented for being reactive in field structures and the laboratory (Ideker et al 2004;Giannini et al 2014;Tremblay et al 2012). Nevertheless, the other two aggregates classified as very highly reactive in ASTM C1260, VHR1 and VHR3, were indistinguishable from moderately reactive aggregates in the autoclave test.…”