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In this study, calcium sulfoaluminate (CSA) cement pastes were tested for heat of hydration and chemical shrinkage at temperatures of 20 °C, 30 °C and 40 °C. Apparent activation energy ( $$E_{a}$$ ) values were then calculated using both exponential and hyperbolic methods. The average $$E_{a}$$ of the CSA cements ranged from 42.24 to 80.22 kJ/mol, much higher than that of Type I Portland cement (38–45 kJ/mol). $${E}_{a}$$ increased slightly with the replacement of silica fume for cement. However, average $${E}_{a}$$ decreased by 18.4% when 20% Class C fly ash was used, but increased by 21.3% when 40% Class C fly ash was used. $$E_{a}$$ calculated from heat of hydration using the exponential method is 17% lower than that obtained using the hyperbolic method. When the exponential method was used, $${E}_{a}$$ values determined using heat of hydration were 30% higher than those obtained using chemical shrinkage.

In this study, effects of steel slag on the hydration and strength development of calcium sulfoaluminate (CSA) cement were investigated. Pastes with 0%, 10%, 20%, and 40% (by mass) of steel slag replacements for CSA cement were tested for setting time, chemical shrinkage, electrical resistivity, and compressive strength. The hydration products, bound water content, pore structure, and pH value of the pore solutions of these pastes were also analyzed. The results indicate that at early ages (from 2 h to 28 d), steel slag worked like a filler and had a dilution effect on CSA cement hydration. Therefore, setting time increased and chemical shrinkage, electrical resistivity, chemically bound water content, and compressive strength of the pastes reduced with increase of steel slag replacements. But, at late ages (≥90 days), these properties in pastes with steel slag replacements surpassed those of the plain CSA cement paste due to hydration of steel slag, which increased pH values of pore solutions and subsequently stabilized ettringite in the pastes. Steel slag replacement for CSA cement also accelerated stratlingite formation. Both ettringite stabilization and stratlingite formation appeared to be the primary mechanisms for strength compensation of CSA cement paste at late ages.

The objective of this paper is to investigate the relationship between the chemical shrinkage and electrical resistivity of portland cement pastes during the first 3 days. Plain cement pastes with water to cement (W/C) ratios 0.3, 0.4, and 0.5 were used in this paper. Chemical shrinkage was measured by dilatometry according to industry standards for test methods for chemical shrinkage of hydraulic cement paste. Electrical resistivity was measured by a noncontacting electrical resistivity apparatus. The relationship between electrical resistivity and degree of hydration was investigated. The results obtained show that the relationship between chemical shrinkage and electrical resistivity appears to be roughly linear after 12 h. Note that the electrical resistivity after 12 h can be used to determine the chemical shrinkage and degree of hydration.

The purpose of this paper is to investigate the setting process and evolution of electrical resistivity of Portland cement pastes with constant water to cement ratio (w/c) of 0.3 and with different dosages of naphthalene superplasticizer (SP) from 0 to 1.2 %. The setting process of cement paste was monitored by the Vicat needle test. The depth of penetration was recorded and used to calculate the shear resistance generated by the cement paste. Electrical resistivity was measured by a non-contacting electrical resistivity apparatus. The hyperbolic curve of electrical resistivity versus time was plotted to determine the ultimate electrical resistivity. The results show that the addition of SP to the pastes with a fixed w/c can cause longer setting time and delay the evolution of electrical resistivity. The final setting time (tf) and the occurring time of maximum rate of electrical resistivity (tr) were both delayed when the dosage of SP was increased. This may indicates that the electrical resistivity measurement can be used to monitor the setting process of cement. The compressive strength at 28 days and the ultimate electrical resistivity show a same tendency for the cement pastes with different dosages of SP. Thus, it would be possible to predict the compressive strength of hardened cement paste by its ultimate electrical resistivity.

The electrical resistivities of the calcium sulfoaluminate (CSA) cement pastes at different water to cement (W/C) ratios, over a period of 1440 min (or 24 h) were measured by a non-contacting electrical resistivity apparatus. The electrical resistivity–time curve decreased slightly after mixing, and then increased sharply around the setting time, followed by two peaks, and finally developed at a very low rate up to 1440 min. The porosity plays a dominant role in the electrical resistivity development of the CSA cement paste in the earlier period of hydration (before the initial setting time), while the ion concentration plays a major role at the later period (after the second peak). The electrical resistivity–time curve demonstrates the process of ettringite formation and transformation to monosulfate in the CSA hydration system, and this is confirmed by the SEM and XRD observations. The high temperature and the insufficiency of gypsum in the CSA cement system during hydration result in the decomposition of ettringite at the first peak, while at the second peak the decomposition of ettringite is due to the lack of gypsum. The relationship between W/C and electrical resistivity at 1 h follows a negative trend but a positive trend is observed at 24 h. The relationship between the compressive strength and the electrical resistivity at 24 h for the different W/C ratios follows a negative relationship.

Three cement pastes were prepared with the fixed water-binder ratio and different fly ash contents. The compression test and electrical resistivity measurement of the paste mixes were conducted during 48 h. The changes of the CH content and the non-evaporable water content in the cement-fly ash hydration systems with time were obtained by the thermal gravimetric analysis. The experimental results show that dilution effect of fly ash as micro-filler is dominant mechanism before 48 h, which appears to decrease in the CH content and the non-evaporable water content, also in compressive strength and electrical resistivity, with the increase of fly ash replacement. The relationships between CH content, non-evaporable water content and electrical resistivity show that electrical resistivity can be the indicators of hydration products CH and non-evaporable water. The correlation of the compressive strength fc and the electrical resistivity ρ can be obtained as fc=8.3429 ρ = 6.7088 for the period of 48 h. The early age compressive strength can then be predicted by electrical resistivity measurement.