| Summary: | The present study investigates the influence of zinc oxide nanoparticles, gypsum, and combinations of them on hydration properties of white cement clinker. Gypsum optimization for the clinker was detected using highly purified gypsum. Compressive strength, setting time, and soundness of all mixes were examined. The results showed that the setting time of pure clinker (C) and clinker with ZnO (CZ) mixes yields flash set after few minutes from the preparation time. While the clinker with gypsum (CG) and clinker with combination from gypsum and ZnO (CGZ) mixes yields a recordable value for setting time. The optimum compressive strength of the (CZ) mix obtained from the mix with content (100% clinker + 0.7% ZnO) reaches 41.9, 55.8, and 63.9 MPa at 3, 7, and 28 days, respectively. The optimum compressive strength of (CGZ) mix achieved from the mix with content (97% clinker + 3% gypsum + 0.7% ZnO) reaches 53.0, 68.9, and 75 MPa at 3, 7, and 28 days, respectively. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectrometry (FTIR) of mortars showed that the absence of gypsum in the mixes retarded the hydration of C3S phase due to the rapid formation of calcium aluminate hydrate C-A-H. The optimum combination of gypsum and ZnO accelerates the hydration process of the C3S phase, reduces the formation of C-A-H and improves the strength.
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