Investigations of the Influence of Nano-Admixtures on Early Hydration and Selected Properties of Calcium Aluminate Cement Paste

Abstract

In this work, the hydration of calcium aluminate cement (CAC, Al2O3 ≥ 70%) paste with nano admixtures (0, 0.05%, 0.1% and 0.2%) of nano-silica (NS) and carbon nano-cones (NC) when W/CAC = 0.35 was investigated. The methods of calorimetry, thermal analysis, X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM) were used. In addition, the physical and mechanical properties of hardened cement pastes were determined after 3 days of hardening. NS was found to shorten the induction period of CAC hydration and accelerate the time of the secondary heat release effect, especially in the specimens with the highest NS content. The incorporation of NC (up to 0.2%) slows down the hydration process. After 3 days of hydration, the formation of hydration products, such as C2AH8, CAH10, C3AH6 and AH3 hydrates, was observed in CAC pastes, however, the quantitative compositions were different depending on the kind of nano admixture and its amount. SEM results obtained show differences in the effect of NS and NC on the formation of the structure of cement paste during its hardening. Significant changes in CAC paste microstructure were caused by the addition of NS and NC admixtures. Compressive strength was found to increase with the increase of NS and the optimal NS content was found to be 0.10 wt.%. The modification of the cement paste with an NS admixture results in a higher amount of hydrates, lower total porosity, and a higher amount of the smallest pores in the microstructure of the sample. NS and NC influence the hydration behaviour of CAC in different ways, which causes characteristic changes in the microstructure and properties of hardened samples.

Effects of Fly Ash Composition to Mitigate Conversion of Calcium Aluminate Cement Composites

“…The strength first rises rapidly to a high early strength (corresponding to CAH 10 and C 2 AH 8 ), then gradually drops to a minimum (during the transformation to C 3 AH 6 and AH 3 ) before rising once more from prolonged hydration. Boris et al [6] investigated the conversion process, especially in the presence of nanomaterials. These nanomaterials vary in chemical composition and grain size, and their effects on CAC depend on their type and quantity.…”

“…Nano-silica was found to accelerate the CAC hydration process, shortening the induction period and intensifying the secondary heat release effect. Despite similar types of hydration products in all CAC pastes, the quantitative composition could vary [6]. Due to this conversion effect, the implementation of CAC in structural engineering practice is restricted.…”