Investigation on the calcium leaching behaviors of cellulose ethers containing cement pastes

Abstract

Cellulose ethers (CE) are generally used as viscosity modifying admixtures in cement-based materials. However, previous investigations scarcely focus on the effect of CE on the calcium leaching behaviors of host materials. This work studied the calcium leaching behaviors in CE-containing cement pastes. The resistance to the calcium leaching was evaluated by the leaching depth, pH values and compressive strength. Electrochemical impedance spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and mercury intrusion porosimetry were implemented to reveal changes in the cement hydrates and microstructural properties to disclose the underlying mechanisms. Results indicate that CE decrease the amounts of CH and C-S-H because of the retardation effect on cement hydration. CE-containing samples exhibit CH crystals with eroded edges and a smaller size, and C-S-H phases with a disordered morphology and smaller dimension, thus increasing the rate of decomposition of CH and C-S-H. CE increases the total porosity by inducing capillary pores and large pores, which results in the decreasing pore connectivity and increasing tortuosity in cement pastes. The degradation of cement pastes during calcium leaching is prominently decided by the content of CH and C-S-H, instead of the initial pore structure. Consequently, CE increase the leaching degree of cement pastes with increasing the CE contents. Additionally, a non-destructive method is proposed to determine the leaching depth for CE-added cement pastes through establishing relationships between the leaching depth and damage factor.