Abstract
Initial hydration and setting were continuously monitored in calcium sulfoaluminate clinker (KCSA) mixed with water or 2 M NaOH with isothermal conduction calorimetry, ultrasonic pulse velocity (UPV) measurement, the Vicat apparatus, and (in- and ex-situ) X-ray diffraction. P-wave acceleration (ap) proved highly useful to detect very rapid initial reactions, not generally perceptible with other techniques. Setting in the water-hydrated KCSA pastes was mediated by ettringite formation. Flash setting due to calcium aluminate hydrate precipitation was observed in the 2 M NaOH-hydrated clinker. Ye’elemite reacted most intensely at later times in both pastes, inducing AFt and AH3 precipitation and the formation of smaller proportions of other calcium aluminate hydrates that densified the matrix.
Highlights
The primary component in calcium sulfoaluminate cements (CSA), ye’elemite or Klein’s compound, synthesises at around 1250 °C, a clinkerisation temperature lower than needed to manufacture portland cement [1,2]
Ultrasound, in turn, is a non-destructive technique highly sensitive to microstructural changes in materials able to deliver more information on cement setting than traditional Vicat apparatus testing. It has been used with promising results to monitor hydration in situ in portland cement in the presence of additions or admixtures [31,32,33,34,35] and in calcium aluminate cement [36,37], but has been scantly if ever applied to CSA or KCSA
The i.tech ALI PRE GREEN industrial calcium sulfoaluminate clinker (KCSA) used in this study was supplied by Heidelberg Cement Hispania
Summary
The primary component in calcium sulfoaluminate cements (CSA), ye’elemite or Klein’s compound, synthesises at around 1250 °C, a clinkerisation temperature lower than needed to manufacture portland cement [1,2]. The type of SCM and the content affect the behavior of the material both in the fresh and hardened state (rheology, viscosity, setting time, resistance to compression, shrinkage) All these studies attest to the complexity of CSA cement hydration and the effect of the chemical environment (pH) on reactivity. Ultrasound, in turn, is a non-destructive technique highly sensitive to microstructural changes in materials able to deliver more information on cement setting than traditional Vicat apparatus testing It has been used with promising results to monitor hydration in situ (first 25 h) in portland cement in the presence of additions or admixtures [31,32,33,34,35] and in calcium aluminate cement [36,37], but has been scantly if ever applied to CSA or KCSA
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