Abstract
Specimens of fresh paste, mortar and concrete with W/C ratios of 0.30, 0.35, 0.40, 0.45, 0.50 and 0.55 were prepared to monitor electrical resistivity for a period of 24 h from casting using non-contact electrical resistivity measurement. A general equation $$\rho (t) = K_{\text{P}} \left( {1 - V_{\text{a}} } \right)^{ - m} \ln (Dt)$$ was obtained from the electrical resistivity development of the mixtures during the decelerating period of the hydration process, and the physical meanings of the parameters in the general equation were identified. The densification rate of the hydration system was obtained from the slope of electrical resistivity development with time, and the hydration rate of each cement particle in unit volume of the cement paste matrix was identified. The influence of aggregate and W/C on the parameters was analyzed. The same aggregate volume fraction was used in all of the mortar and concrete samples. A mortar sample has a faster densification rate than that of a concrete sample at each W/C due to the higher specific surface area of the total aggregate particles in the mortar, resulting in a higher tortuosity for the ions migration. The very close D values of the pastes, the mortars and the concretes with the same W/C, and the slightly increasing trend with W/C, present the characteristics of the hydration rate of each cement particle in unit volume of the cement paste matrix. Mixtures with lower W/C have higher densification rates, and the quantitative relationships were obtained for the paste, mortar and concrete samples, respectively. The densification rate of a mixture can be used as an index for deriving its W/C based on the quantitative relationship obtained from electrical resistivity measurement. The densification rate of a hydration system and the hydration rate of each cement particle in the hydration system, as important hydration parameters, can help to reveal the hydration kinetics that are correlated with hardening properties of concrete.
Published Version
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