Durability studies on conventional concrete and slag-based geopolymer concrete in aggressive sulphate environment

As a potential substitute to conventional concrete, slag-based geopolymer concrete can be a promising material towards green and low carbon building approach. However, the lack of understanding of its performance subjected to sulphate environment can prohibit its use to some extent. This study examines the properties of conventional concrete exposed to a severe sulphate environment in comparison with slag-based geopolymer (SGPC). Plain cement concrete (PCC) also known as conventional concrete was cast using ordinary Portland Cement (OPC) as a binder. The durability of both types of concrete was examined by immersing test specimens in sulphate solutions (for varied salt concentrations of 2 and 4 g/l) for different curing ages up to a year. The performance of both types of concrete was studied for both mechanical and durability properties. Mechanical properties included compressive, tensile and flexural strengths (FS), while durability consisted of sorptivity, chloride diffusion, corrosion, EDS and SEM studies. The outcomes of this study revealed that the compressive (CS) and split tensile strengths (STS) of both OPC and SGPC decreased with the increase in magnesium sulphate salt concentrations and curing age. After being exposed to a 4% sulphate solution for 365 days, a decrease in the compressive strength was observed by 36.53% in SGPC and 55.97% in OPC, and a similar trend was found for the FS and STS. Rapid chloride permeability (RCPT) and sorptivity test results showed an increased diffusion with age and thus supported the findings of the compressive strength. Micro-structural properties were also studied, and observations showed that the formation of Sodium alumino-silicate hydrate (N-A-S-H) and Calcium alumino-silicate hydrate (C-A-S-H) was more obvious with the curing age in SGPC. At the same time, C-S-H gel formation decreased in conventional concrete with an increase in sulphate salt concentration. The cumulative effect of all these factors led to a much higher corrosion rate of rebars embedded in conventional concrete than in SGPC. Therefore, slag-based geopolymer concrete performed better than conventional concrete in an aggressive sulphate environment for all curing periods.