Combined Action of Mechanical Pre-Cracks and ASR Strain in Concrete

An experimental study was undertaken to investigate aspects of durability of reinforced concrete elements subjected to the combined action of mechanical pre-cracking and alkali-silica reaction (ASR). Concrete beams with a high alkali content were pre-cracked in cyclic loading and subsequently submerged partially in water, or exposed to high humidity according to ASTM C1293-07 conditions (long-term method). Aggregates of relatively high, and aggregates of low reactivity were used. Reference beams with both reactive and less reactive aggregate were placed in the ASR chambers to compare the responses of specimens exposed to the combined action and specimens subjected to the ASR action only. The crack widths were monitored in pre-cracked specimens under both conditions (humidity, partially submerged). The test results indicate that the expansion due to the combined action at the middle of samples (mechanical crack zone) was significantly different in specimens exposed only to a high alkaline environment. The micro and macro cracks, induced by cyclic load, form ingress paths leading to increased ASR rate, while the macro-mechanical cracks provide regions of relatively free expansion, as deduced from decreasing crack widths.