Effect of heat treatment on reactivity-strength of alkali-activated natural pozzolans

Natural pozzolans can be activated and condensed with sodium silicate in an alkaline environment to synthesize high performance cementitious construction materials with low environmental impact. The nature of the starting materials including mineral composition, chemical composition and crystal structure groups affects the formation of the geopolymer gel phase. In this paper, the pozzolanic activities of five natural pozzolans are studied. From XRD and XRF results, most of the raw materials contain zeolite clay minerals and have a high loss on ignition. Therefore, before use, samples were calcined at 700, 800 and 900 °C, respectively. The improvement in pozzolanic properties was studied following heat treatment including calcinations and/or elevated curing temperature by using alkali solubility and compressive strength tests. The results show that pozzolan containing sodium zeolite clinoptilolite can be used to prepare a moderate to high strength binder by heat treatment and calcinations can impart disorder hornblende as a constituent of pozzolan with no amorphous phase to prepare a moderate strength binder.

► Natural and calcined pozzolans can be activated to prepare a high performance construction material.
► It is the properties of the main mineral phases which govern the behaviour of the pozzolans.
► Pozzolan containing sodium clinoptilolite can prepare up to high strength binder by heat treatment.
► Calcinations can impart disorder a constituent of pozzolan with no amorphous phase to prepare a binder.
► The highest reactivity obtained for pozzolan with minimum L.O.I. and highest soluble calcium.