Effect of geopolymer cement on microstructure, compressive strength and sulphuric acid resistance of concrete

Abstract

The effect of geopolymer cement on the compressive strength and resistance to sulphuric acid of concrete made with type 10 and type 50E cements was studied. Hydration products and microstructure of various concrete mixtures incorporating geopolymer cement were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmitted light microscopy in order to identify the mechanisms underlying the effects of the geopolymer cement on concrete properties. Experimental results indicate that using geopolymer cement as partial replacement for ordinary Portland cement (OPC) effectively improved both the compressive strength and resistance to sulphuric acid. Replacement of 50% OPC by geopolymer cement increased the 28-day compressive strength by about 50% and reduced the mass loss of concrete specimens subjected to eight weeks of immersion in sulphuric acid solutions with pH of 0·3 and 0·6 by 42% and 30%, respectively. The effect of geopolymer cement on the compressive strength and sulphuric acid resistance of concrete made with type 50E cement was less significant than that for concrete made with type 10 cement. Results of XRD, SEM and light microscopy indicate that improvements in compressive strength and sulphuric acid resistance of the geopolymer modified concrete can be mainly attributed to the formation of new hydration products such as calcium–magnesium–aluminium-oxide silicates. A direct relationship between the ability of geopolymer modified concrete specimens to resist sulphuric acid and their normal 28-day compressive strength was found, but varied with the binder used.