Investigation of the early-age microstructural development of hydrating cement pastes through electrical resistivity measurements

The non-contact electrical resistivity method was employed to investigate the microstructural development of three grades of cement under a fixed water-to-cement ratio (w/c) and the same curing conditions. The method was verified by measuring the heat of hydration and estimating the degree of hydration of the three pastes. The results showed that the existence of a linear relationship between the compressive strength at 28 d (f 28) and bulk electrical resistivity at 72 h (ρ72); thus, the proposed method can be used to assess the strength of cement. Moreover, the results indicated that the quality of cement can be further distinguished by interpreting the trend in the resistivity curve. The high-strength cement will have lower electrical resistivity values during cement dissolution due to the higher content of ions in the pore solution, while it will have higher resistivity values during cement hardening due to the greater amount of hydrates. The electrical resistivity of the cement solution (ρ0) filtered from the cement paste at an early age was measured to demonstrate the effect of the ionic concentration on the bulk electrical resistivity in the initial hydration period. The measured liquid resistivity of cement can be used as an indication of clinker reactivity; higher-strength cement will always have lower measured values. The rate of electrical resistivity development curve was plotted to elucidate the setting range of cement pastes based on three critical points. The time at the second critical point (C2) coincided with the final setting time determined using a Vicat needle. New general relationships between the gel-space ratio and electrical resistivity were developed. Furthermore, autogenous shrinkage was measured for the three cement pastes, and the behaviour could be anticipated from the electrical resistivity measurements.