Cracking due to alkali-silica reaction and its effect on durability properties of concrete

Around the world, many structures built during the last few decades have suffered from damage due to alkali-silica reaction (ASR). Some of these structures were considered structurally inadequate and have been replaced or repaired. Most of the others are structurally safe but the concrete might have failed as a protective barrier to the reinforcement. ASR causes microcracks in concrete which may lead to inserviceability of structures by providing easy access for other deterioration processes to take place.This thesis work investigates the effect of ASR-induced microcracks on the durability of concrete. Specifically, mass transfer properties and freeze-thaw resistance of damaged, non-air-entrained concrete were assessed.Due to the hydrophilic natural of the alkali-silica gel, it was found that the role it plays in concrete durability is significant. Microcracks caused by ASR increased the rate of diffusion of chloride and gas permeability through concrete. However, it reduced water permeability. The gel exists in the pores and microcracks may mitigate the detrimental effect of cracks on mass transfer. Nevertheless, the net effect is unfavourable to the durability of concrete. The expansion due to ASR had an adverse effect on the freeze-thaw resistance of concrete. The relative dynamic modulus of samples with expansion levels of 0.092%, 0.122% and 0.205% dropped below 60% in less than 50 cycles. Other samples with lower level of expansion lasted about 150 cycles before 60% of relative dynamic modulus was reached.Further research using samples with higher expansion in mass transfer tests and air-entrained concrete in freeze-thaw test is recommended by the author.