Abstract
The studies focused on the kinetics of early hydration in the high-calcium aluminate cement (CAC 70)—by-pass cement kiln dusts (BPCKD)—mixtures. For this purpose, the mixtures of cement with this additive or with some potential constituents of dusts were produced. The microcalorimeter was applied to follow the kinetics of hydration. The investigations with the aim of finding the relationship between the components of initial mixtures and the modification of hydration process were carried out. The rheological properties were characterized, and the chemical shrinkage characteristics were produced. The phase assemblage characterization and microscopic observations were done as well. In case of the high-calcium aluminate-based binders, the modification of setting process was observed; the rheological properties and chemical shrinkage were affected too. The acceleration of heat evolution—the shortening of so-called induction period in the presence of BPCKD additive—was observed. The results were compared to those obtained for the CAC with ordinary Portland cement additive. The results of calorimetric measurements are discussed in terms of the chemical and phase assemblage of this additive as compared to the Portland cement clinker precursors and potassium chloride—the solid and liquid components of the dust.
Highlights
Monocalcium aluminate phase CaO·Al2O3—CA is the principal phase in aluminate cements [1]
The by-pass cement kiln dust (BPCKD), ordinary Portland cement (OPC) and calcium aluminate cement (CAC70) samples used in this study were supplied by cement plants
The reaction of calcium aluminate cements with water followed by calorimetry gives two strong peaks with socalled induction period between them; there is a few hours lasting latent period in which a dissolution of initial substance to attain the supersaturation of liquid phase and slow nucleation of less soluble hydration products takes place
Summary
Monocalcium aluminate phase CaO·Al2O3—CA (notation commonly used in cement chemistry: C = CaO, A = Al2O3, H = H2O) is the principal phase in aluminate cements [1]. The compound corresponding to the formula 12CaO·7 A l2O3 is the second aluminate phase. On reaction with water at ambient temperature, a setting and hardening of calcium aluminate paste take place and the hydrated calcium aluminate phases, such as CaO·Al2O3·10H2O—CAH10, 2CaO·Al2O3·8 H2O—C2AH8 (hexagonal hydrates) and aluminum hydroxide (AH3), are formed [1,2,3]. Further transformation of hexagonal hydrates into the thermodynamically stable cubic one (C3AH6), known as “conversion,” leads to the destruction of hardened material because of the release of water and formation of AH3 gel. University of Science and Technology AGH, al.
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