Ceramics-Silikáty 65, (3) 247 - 254 (2021)

The application of natural zeolite clinoptilolite (Si/Al = 5.8) for substituting up to 20 vol% of the cement (in mortars) was studied. The effect of the natural zeolite on the consistency and compressive strength at 7, 28 and 90 days was tested at different dosages of clinoptilolite in the mixture. The optimal content (15 % by volume) of the active mineral addition was selected according to the achieved strength results of the mixture and the effect of natural zeolite on the early and late cement hydration was studied. The results of Chapelle test for pozzolanic activity, the initial and final setting times of the paste, thermogravimetric analysis and X-ray diffraction analysis of hardened cement paste showed that natural zeolite clinoptilolite accelerates early and late hydration of cement. No significant differences in calcium hydroxide (CH) content between the specimens modified with clinoptilolite and the specimens containing only ordinary Portland cement (OPC) were observed, despite the high pozzolanic activity of the zeolite.