Critical features of microstructure development of early-age cement paste revealed by non-contact electrical resistivity measurement

The microstructure evolution of cement paste governs the material properties on the macrostructural level. Recently, a non-contact electrical resistivity measurement has been applied to study the pore structure evolution of early-age cement-based materials. In this study, the capillary pore tortuosity development of early-age cement paste is predicted by the non-contact electrical resistivity measurement. The results demonstrate that the capillary pore tortuosity of cement paste evolves slightly at the first few hours but begins to increase substantially at the percolation threshold of the hard core/soft shell (HCSS) particles. By coupling the predicted evolution with the HCSS model, it is found that the capillary porosity and the thickening rate of the hydration product shell increase with the increase of the water to cement (w/c) ratio. Early-age C-S-H gel is revealed to grow in a lengthened manner, and the greater is the w/c ratio, the more elongated is the C-S-H gel. The juxtaposition of the nanometre-sized elementary bricks is the hidden force for the elongated growth of C-S-H gel. It is disclosed that the initial distance between cement particles is a fundamental factor that governs the microstructure development of cement paste. The hydration of cement preferentially achieves the particle percolation, and the hydration products grow more loosely when the initial distance between cement particles is greater.