ASR-Induced Damage Detected by Site Air-Permeability Tests

Gas-permeability has been proved useful to monitor the evolution of damage in concrete specimens subjected to mechanical loads. This paper describes the use of air-permeability to monitor and evaluate the damage caused by Alkali-Silica Reaction (ASR), in Argentina and Switzerland. In both cases, a standard NDT to measure the coefficient of air-permeability kT ‘in situ’ was applied. The data originated in Argentina correspond to observations conducted on laboratory specimens stored under controlled conditions and of large concrete blocks, some plain, some fiber-reinforced, made with reactive aggregates and containing 2.8 and 4.0 kg/m3 of Na2Oeq. The blocks were exposed outdoors to a mild climate and monitored for a period of 3.5 years, measuring kT, expansion and cracks width and density. The data originated in Switzerland were the result of condition assessment of real structures affected by ASR-related damage. The results indicate that measuring kT is useful to anticipate the formation of cracks, as the Argentine results showed that the increase in permeability happened before cracks became noticeable, probably detecting incipient micro-cracking. On the contrary, once the structure becomes visibly cracked, the vacuum-based test method either could not be applied or did not prove particularly useful, due to the resulting heterogeneity.