Effect of trass calcination on properties of geopolymer mixtures

Abstract

Cement production causes serious environmental problems and requires large amounts of energy. Studies have proven that the use of geopolymers can significantly reduce carbon dioxide emission and energy consumption arisen from cement production. Although there are many studies on the geopolymers, the number of studies dealing with geopolymers containing natural pozzolans other than metakaolin is very limited. In this study, the compressive strength and pore structure of geopolymers produced with trass (a type of natural pozzolan) were investigated. The mineralogical composition of trass, morphology of trass, and microstructure of geopolymer paste as well as the weight loss of the paste were determined using XRD, SEM, and TGA examinations, respectively. Moreover, the pore size distribution of the paste mixtures was obtained with Micro-CT analysis. The trass was used both in the natural form and after calcining at 550 °C for 6 h. The strength of geopolymer mortars produced with calcined trass, cured at 90 °C for 24 and 96 h, was found to be 86.7% and 81.6% higher than that of their counterparts containing natural trass. In addition, calcination of the trass resulted in 12.8–22.9% reduction in the porosity of geopolymer paste, compared to that of the paste containing natural trass. In XRD and TGA investigations, it was determined that the trass calcination performed at 550 °C did not make a significant change in the paste crystal structure and the weight loss-temperature graphs. SEM images proved that the reactivity of trass in geopolymerization increased with calcination and the matrix structure became denser and more homogeneous.