Evaluation of the phase composition, microstructure, mechanical performance, and resistance to acid attack of blended cement paste composed of binary trass-cement system

Abstract

This study comprehensively investigated the viability of binary blended trass-cement system for being used as a competitive alternative to cement or other traditional blended cements. Concerning the phase composition, the trass blended sample had not only higher gel contents, but also faster rates of gel formation, which were 1.5 and 1.2 times greater than those of the plain cement sample during the periods of 7–28 and 28–90 days, respectively. Regardless of the samples types, the increase rate of ultrasonic pulse velocity was highest within the interval of 3–7 days, then decreased during the period of 7–28 days, and almost approached zero at 28–90 days. This indicated the minor change of the samples microstructure at prolonged ages compared to those earlier ones. Due to the pozzolanic effect of trass, the pore size distribution significantly shifted toward smaller pore diameters and also became more uniform. Furthermore, the filler effect of trass reduced the total intruded volume and total porosity by 11.7% and 9.2%, respectively. In the case of mechanical performance, the blended sample showed higher compressive strengths, whereas slightly lower flexural ones in comparison to its plain counterpart, which could be owing to the changes in phase composition and microstructure induced by blending cement with trass. Lastly, it was revealed that the nitric acid attack, by progressively decalcifying the exposed samples, gradually transformed them into soft, cracked, and highly porous materials with new microstructural morphology and mineralogical composition. This way, substantial losses in their performance and integrity happened over immersion time.