Determination of the effect of sodium salts on hydration kinetics, hydration degree and mechanical properties of zinc oxide blended Portland cement

conference proceedings

English

Retarded hydration of ordinary Portland cement (OPC) based binder presents a significant problem in the application of these materials, mainly by long setting time and reduced mechanical properties. One of the contaminants that cause cement hydration retardation are zinc compounds. Based on the current understanding of the mechanism behind this effect, zinc forms a layer of semipermeable Ca(Zn(OH)3)2·2 H2O on the surface of cement silicate phases and depletes Ca2+ ions from the pore solution. Various additives in the form of soluble salts are employed to accelerate hydration and negate the effect of metal ions on the hydration mechanism. Isoperibolic calorimetry is a simple method for measuring changes in temperature of samples that give information about materials' real environment behaviour. On the other hand, isothermal calorimetry is commonly used to study changes in the mechanism of hydration. Hydration degree is an indicator used to determine the effect of additives on the hydration mechanism that can be measured using differential thermal analysis (DTA). Changes in phase composition can be identified by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Sodium nitrate and carbonate seem to be effective at accelerating the setting of zinc oxide containing cement system but at the expense of mechanical properties at high doses. The addition of sodium chloride, on the other hand, was detrimental to both the setting and mechanical properties.

Thermal analysis, hydration degree, Cement, Zinc oxide, Hydration retardation

MATĚJKA, L.; ŠILER, P.; NOVOTNÝ, R.; MÁSILKO, J.; ŠVEC, J.

21. 10. 2022

Palermo