Abstract
Previous studies have shown that the partial replacement of portland cement with natural zeolite can improve the strength and durability of cementitious systems. However, the hydration of clinoptilolite zeolite cementitious materials at an early age as well as microstructural development has not been fully understood. In this study, natural clinoptilolite zeolite replaced portland cement at 0, 5, 10, 15, and 20 % by mass as a supplementary cementitious material. Particle size distribution and mineral phase identification of zeolite particles were done by laser diffraction particle size analysis and x-ray diffraction (XRD), respectively. Workability, setting time, chemical shrinkage, heat of hydration via isothermal calorimetry, compressive strength, and degree of hydration were used to assess the effects of zeolite addition on early age properties. Furthermore, pozzolanic activity via thermal gravimetric analysis, chemical and microstructural characterization were accomplished by XRD as well as scanning electron microscopy. Results revealed that the addition of zeolite lowered the heat of hydration and minimized or shifted the tricalcium aluminate (C3A) peak in the heat of hydration curve. Results also indicated that the addition of zeolite likely produced calcium aluminate silicate hydrate (C-A-S-H) at an early age, due to the initial dissolution of aluminate concentration in the alkaline solution. Furthermore, the addition of zeolite can accelerate the early age of hydration by reducing the initial and final setting time of pastes. As zeolite dosage rate increased, compressive strength decreased because of the slow pozzolanic reactivity as well as the lower degree of hydration. Results also showed that zeolite led to the formation of elongated needle-shaped and fibrous hydration products.