Effects of chloride ions on the durability and mechanical properties of sea sand concrete incorporating supplementary cementitious materials under an accelerated carbonation condition

Abstract

The aim of this study is to investigate the effects of chloride ions on the durability and mechanical properties of non-desalted sea sand (NSS) concrete containing fly ash (FA) or ground granulated blast furnace slag (BFS) under accelerated carbonation. Six mixtures were prepared using a constant water-to-cementitious materials ratio of 0.50. The cementitious materials consisted of primarily ordinary Portland cement with a portion replaced by a supplementary material, either FA (15% by mass) or BFS (45% by mass). After being cured with a sealed condition of 20 °C for 28 days, half of the concrete specimens remained sealed while the other half were exposed to an accelerated carbonation chamber for 182 days. The accelerated carbonation chamber consisted of a 5% CO2 concentration with 60% relative humidity. The durability and mechanical properties of the concrete were investigated, including carbonation resistance, sorptivity, compressive strength, and the modulus of elasticity. The chloride binding capacity was also evaluated. Porosity, crack evaluation, and scanning electron microscopy tests were implemented to better understand the macro- and microscopic structures of the different concrete compositions. The results showed that the presence of chloride ions in NSS could improve the carbonation resistance of concrete. Carbonation shrinkage generated cracks which led to a significant increase in sorptivity for the FA and BFS concretes under accelerated carbonation. However, this increase was restricted by the chloride ions in NSS. In general, the presence of chloride ions enhanced the mechanical properties of the concrete, regardless of curing ages, FA or BFS replacement, or exposure conditions. Even considering the effects of carbonation, NSS is found to be potentially viable material for use in concrete production.