Effect of zinc oxide on the hydration, microstructure and compressive strength of ternary mixtures

The use of supplementary cementitious materials as partial Portland cement substitutes in concrete is one of the best strategies for reducing carbon dioxide (CO₂) emissions in the cement industry, and also improves the properties of concrete. When highly reactive calcined pozzolans such as metakaolin are used, the setting time of concrete is reduced, and the use of retardants is necessary. The effect of zinc oxide (ZnO) as a cement hydration retarder has already been investigated; however, the influence of zinc oxide on ternary mixtures is unknown and needs study. In this research, the effect of adding zinc oxide on the hydration, microstructure and compressive strength of ternary mixtures is studied using setting time and compressive strength tests, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis with differential scanning calorimetry and scanning electron microscopy. The results show that the hydration process of ternary pastes is delayed or even inhibited when the amount of zinc oxide in the paste is increased. With the addition of 0.5 wt.% zinc oxide, the initial setting time and compressive strength of ternary mixtures after 3 days of curing are similar to those of the cement paste without the addition of pozzolans and zinc oxide.