Hydration kinetics of clinoptilolite zeolite blended ternary cementitious materials with fly ash and metakaolin

Abstract

The typical characteristics of hydration kinetics for the natural zeolite blended cementitious system may be impacted due to the varied sources and compositions of the zeolite particles. Previous research reported that the substitution of portland cement with natural clinoptilolite zeolite substantially minimized the tricalcium aluminate (C3A) peak heat of hydration apart from the regular matrix of the hydration kinetics, an indication of the potential interaction of zeolite particles in the blended system. Therefore, the present study investigated the suitable reasons for minimizing C3A peak heat of hydration in the blended system replacing the portland cement with clinoptilolite zeolite up to 20% by mass. Similarly, class C fly ash and metakaolin were utilized up to 20% by mass to observe the hydration kinetics of the zeolite blended ternary cementitious system. Additional 5% gypsum replaced the portland cement in the zeolite mixed system to verify the undersulfation. The heat of hydration was observed via isothermal conduction calorimetry. Phase identification of hydration products was done by x-ray diffraction (XRD) analysis at an early age of 3 days. Results revealed that the minimized C3A peak heat of hydration was not due to the undersulfation. Results also revealed that the zeolite blended ternary samples (i.e., cement-zeolite-class C fly ash, and cement-zeolite-metakaolin) obtained a relatively higher C3A peak heat flow and an increased duration for the monosulfate formation compared to the binary (i.e., cement-zeolite) samples. Likely, zeolite particles had a relatively slow chemical dissolution compared to the class C fly ash and metakaolin particles which supplied comparatively reduced amounts of alumina in the system in the early ages. The XRD results indicate the potential formation of a new hydration product (calcium-aluminum–silicate-hydrate), which likely consumed a reasonable amount of aluminate leading to a minimized C3A peak heat of hydration in the clinoptilolite zeolite blended system.