Continuous tracking of the relationship between resistivity and pore structure of cement pastes

• The quantitative relationship between electrical resistivity and pore structure is established.
• The effect of type of pores on electrical resistivity is explored.
• The evolution of resistivity is not only controlled by capillary pores but also C–S–H phases.

The electrical resistivity changes with time of cement pastes with water to cement ratio of 0.23, 0.35 and 0.53 were in situ continuously monitored by using a non-contact resistivity apparatus. To aid in understanding the evolution of effective resistivity, a hydration model CEMHYD3D was then utilized to simulate the early age formation of microstructure. Based on the effective media theory, the relationship between the change of relative resistivity and the evolution of total porosity, tortuosity factor and constrictivity is established. The results show that a lower water to cement ratio shows a smaller porosity and constrictivity as well as a higher tortuosity factor. Moreover, according to the experimental and simulated results, it is found that the evolution of resistivity is not only controlled by capillary pores but also C–S–H phases. Before arriving fully de-percolation time of capillary pores, the reduction of pores connectivity shows a higher influence on the paste resistivity than the decrease of capillary porosity. After that, the resistivity change of cement paste is mainly determined by the volume fraction of C–S–H.