Influence of Water-to-Binder Ratio on Autogenous Shrinkage and Electrical Resistivity of Cement Mortar
Yujiang Liu, Shiyi Zhang, Zhisheng Fang, Mingkai Sun, Yingfang Fan, Surendra P. Shah
Abstract
This study investigates the effects of nano-metakaolin and fly ash contents, the water-to-binder ratio, and other factors on autogenous shrinkage, internal relative humidity, and resistivity. Hydration heat, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and other micro-testing techniques were employed to characterize the hydration process, phase composition, and pore structure of cementitious materials. The experimental results show that lower water-to-binder ratios lead to faster and more significant decreases in internal relative humidity within cement pastes. When nano-metakaolin and fly ash are combined, fly ash effectively mitigates the excessive autogenous shrinkage caused by nano-metakaolin under low water-to-binder ratios. Lower water-to-binder ratios result in faster resistivity growth in cement pastes. Specifically, when the water-to-binder ratio decreased from 0.35 to 0.30 and 0.25, the 28-day resistivity of nano-metakaolin–fly ash cement pastes increased by 8.08% and 7.33%, respectively. Additionally, the water-to-binder ratio has a relatively minor impact on the autogenous shrinkage and resistivity of fly ash cement pastes. Higher water-to-binder ratios accelerate the hydration rate and increase porosity, leading to the gradual coarsening of pore distributions. When the water-to-binder ratio increased from 0.25 to 0.35, the 28-day porosity increased by 50.31%. In hydration systems with lower water-to-binder ratios, internal relative humidity decreases more rapidly, pores become refined, capillary stresses increase, and autogenous shrinkage behavior becomes more pronounced. This research provides a practical foundation for studying the early-age autogenous shrinkage behavior of cementitious materials.