Experimental study and classification of natural zeolite pozzolan for cement in South Africa

The present study investigated the performance of South African natural zeolite for potential use as a cement extender. To the best knowledge of the authors, the natural zeolite studied has not been employed before as pozzolan in the cement industry, and its proposed use would be new in concrete construction. In the investigation, mortar mixtures were prepared using ordinary Portland cement CEM I 52,5N blended with 0, 10, 20 and 30% natural zeolite. The effectiveness of natural zeolite was also compared with performance results of mixtures containing 30% fly ash. The tests conducted were workability, compressive strength, pozzolanic activity with lime, drying shrinkage, alkali-silica reaction, and sulphate resistance. Analytical studies were done using X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. It was found that, while incorporation of natural zeolite in cement reduces workability, its effects on mechanical properties and on durability characteristics were superior to those of fly ash, as the former effectively enhanced long-term strength and mitigated drying shrinkage, alkali-silica reaction and sulphate attack. Incorporation of 20% natural zeolite in cement gave an effective overall performance, meeting the ASTM C618 (2015) criteria for Class N pozzolan. Based on EN 197-1 (2000) / SANS 50197-1 (2013), the blend of natural zeolite and ordinary Portland cement met the criteria for its classification as CEM II/A-P 32.5N,R cement type.