Abstract
Materials made by hydrating the natural zeolite clinoptilolite with calcium hydroxide (Ca(OH)2) have been characterised and compared to other alkali-activated waste-derived and naturally occurring pozzolana. Compressive strength is dependent on the Ca(OH)2 content, clinoptilolite particle size, and curing conditions. Optimising each of these factors has produced compacted materials containing 20 wt.% Ca(OH)2 with average compressive strengths of 38.7 MPa. Capillary rise tests have been used to determine sorptivity coefficients of dry samples that range from 0.027 to 0.087 cm min−1/2 depending on the alkali addition and the clinoptilolite particle size. Sorptivity depends on the Ca(OH)2 content and reducing the clinoptilolite particle size reduces sorptivity but increases the level of water accessible porosity. X-ray diffraction (XRD) confirms that Ca(OH)2 is consumed during curing and that it is not present in high strength, fully cured materials. Scanning electron microscopy combined with energy dispersive X-ray (SEM–EDX) analysis indicates the formation of hydration products with Ca/Si ratio in the range 0.8–1.2 and that a significant amount of unreacted clinoptilolite remains in optimised materials.
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