The influence of multiple combined chemical attack on cast-in-situ concrete: Deformation, mechanical development and mechanisms

Abstract

In this paper, a laboratory program was performed to investigate the influence of combined internal chloride and external sulfate/magnesium simulated exposure on cast-in-situ OPC concrete samples. Specimens of cylinder shape were prepared and then stored in distilled water or aggressive solutions, which were sulfate or sulfate-magnesium solutions. The specimen parameters, such as diameter increments, mass increments, unconfined compression strength together with sulfate concentration, were determined continuously during the immersion. Mineral and microstructural changes of tested samples were analyzed to determine the attack products after 12-months immersion. Results illustrate that the development of concrete strength was limited by sulfate, chloride, magnesium, or multiple combined chemical attack at the early stage and resulted in a low strength in the long-term. Internal chlorides accelerated the degradation induced by external sulfate attack, subsequently enhancing the accumulation rate of sulfates in concrete in both sulfate and sulfate-magnesium solutions. Coexisting magnesium helps to restrain the degradation and decrease the diffusion speed of sulfates. Magnesium weakens the acceleration effect of internal chlorides on the degradation induced by sulfate attack. While the internal chlorides restrains the protection effect on internal concrete by Magnesium. Degradation layer-by-layer is the proposed mechanism when concrete subjected to magnesium involved chemical attack.