Durability performance of alkali-activated concretes exposed to sulfuric acid attack

In this research, chemical durability performances of the alkali-activated slag (AAS), 50% ground granulated blast furnace slag and 50% fly ash (AFS), ordinary Portland cement (OPC), and geopolymer (GPC) concretes were investigated thoroughly under 5% sulfuric acid attack. All alkali-activated concrete specimens were produced considering the minimum binder content of 360 kg/m3 and the maximum alkali activator to binder ratio of 0.45 according to the XA3 environment given in EN 206-1 standard for OPC concrete. The visual inspection, weight change and compressive strength tests were performed to understand the influence of sulfuric acid attack on the resulting performances. Also, scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS) analyses were performed to examine the morphological variations in micro-scale. The mechanical performances and durability of alkali-activated concretes were also compared to the OPC concrete for structural utilization. The results revealed that AFS specimens showed the best durability, while GPC specimens exhibited the poorest durability. SEM/EDS results pointed out that AFS specimens exhibited denser and less porous microstructure, and the reductions in Al/Si and Ca/Si atomic ratios were observed under 5% sulfuric acid attack. In contrast, GPC specimens showed less dense and porous microstructure, and high aluminum leaching was observed. In addition, the wider interconnected macro cracks and high calcium leaching were observed in the AAS samples under 5% sulfuric acid attack. Finally, the AAS and AFS specimens can be utilized in structural applications, while GPC specimens should not be used with a minimum binder content proposed by EN 206-1 standard.