Acid-Resistance Behaviors of Natural Aggregates

In this study, the acid resistance characteristics of commercial aggregates that are commonly employed in concrete construction, were investigated. The aggregates studied were of three categories, namely: (1) the siliceous group consisting of reef-quartzite, metaquartzite, and granite, (2) the siliceous-calcareous group consisting of dolerite and amphibolite, and (3) dolomite of the calcareous group. Samples of the aggregates were oven-dried, immersed in 20% by weight concentration of hydrochloric or sulphuric acid maintained at 60°C for 24 h, and then their mass loss values were measured. Mineralogical compositions and phase reaction changes in the aggregates were examined using X-ray fluorescence, Rietveld quantitative X-ray diffraction analysis, petrography, and scanning electron microscopy coupled with energy dispersive spectroscopy. A strong, nonlinear inverse correlation was found between quartz content and mass loss, for which aggregates that had SiO2≥70% exhibited very low or negligible mass loss. Metaquartzite and granite aggregates of the siliceous group showed the most superior resistance responses to acid attack, owing to their high levels of quartz content. Reef-quartzite, dolerite, and amphibolite all showed a partial or moderate level of acid resistance. Dolomite exhibited high susceptibility to acid attack, forming gypsum as a reaction product upon exposure to sulphuric acid.