Improving the strength and reliability of mortar composites with zeolite substitution

Clinoptilolite zeolite, a naturally occurring pozzolan, is a viable supplemental cementitious material (SCM) for reducing the carbon footprint generated by the cement industry. While previous literature has explored the use of natural zeolite as an SCM for cement composites, this investigation advances understanding on the effectiveness of natural zeolites as an SCM in three phases. In Phase I, two distinct forms of zeolite (Z1 and Z2) in relative mineralogical compositions and particle sizes were incorporated into mortar composites to replace ordinary Portland cement (OPC) at concentrations up to 20 wt% and characterized over a period of 28 days. Based on the superior performance of the higher clinoptilolite content zeolite (Z2), it was used in Phase 2 to evaluate the effect of zeolite substitution. In Phase 3, the reliability of the resultant composites prepared with Z2 were assessed using Weibull statistics. The inclusion of Z2 type zeolite at #200 mesh size and 10 % concentration yielded compressive strength and reliability comparable to the OPC control mortar at day 7, but significantly greater strength and reliability from day 14 onward. Porosity detailed by microCT suggests that increasing zeolite content to 15 % and greater results in unreacted zeolite that is detrimental to strength. The findings further establish the merits of natural zeolite as an SCM material and distinguish what is necessary for further improvements in mechanical properties of zeolite cement composites.