Hydration kinetics of cation exchanged clinoptilolite zeolite based cementitious materials

Abstract

This paper provides information on the global reaction path and hydration kinetics of a natural clinoptilolite-Ca zeolite blended portland cementitious system. The replacement of up to 20% as-received clinoptilolite-Ca zeolite with portland cement substantially minimized the tricalcium aluminate (C3A) peak heat of hydration as observed using isothermal calorimetry. Inductively coupled plasma-optical emission spectrometry results showed that the zeolite-blended samples had a higher initial chemical dissolution of calcium and aluminate; but subsequently, the consumption of both was higher compared to the neat cement control sample, likely due to the formation of new hydration reaction products, indicating an interaction between cement and clinoptilolite-Ca zeolite. Clinoptilolite-Ca zeolite transformed into clinoptilolite-Na zeolite using NaOH and NaCl solutions showed a distinct aluminate (C3A) peak heat flow, indicating a different reaction path compared to clinoptilolite-Ca zeolite. Micro-chemical analysis using energy dispersive spectroscopy suggests a different hydration reaction mechanism for both calcium and sodium-based zeolite, along with the possibility of reduction in the formation of C–S–H, ettringite, and monosulfate due to the formation of new hydration products. The clinoptilolite-Ca zeolite consumed significantly higher aluminate contents leading to the formation of amorphous calcium-aluminum-silicate-hydrate (C-A-S-H) gels, which consequently reduced the aluminate-related reaction (C3A) heat flow in the system. In contrast, the clinoptilolite-Na zeolite released sodium ions through cation exchange to produce sodium aluminosilicate hydrate (N-A-S-H) in the blended system, which did not interfere with the C3A peak heat flow during the hydration process.