Calcite Precipitation at Cement–Bentonite Interface. Part 1: Effect of Carbonate Admixture in Bentonite

Abstract

Calcium leaching from cementitious materials into bentonite is a key process for the long-term alteration of cement-clay interfaces of engineered barrier systems. Strong chemical gradients between cement and clay drive the precipitation of minerals such as calcium silicate hydrate (C-S-H) and calcite. To analyze the mineralogical and porosity evolution at the cement-clay interface, composite specimens consisting of cement paste and bentonite mixed with various amounts of sodium carbonate were subjected to immersion and chloride migrations tests and were investigated by electron probe micro-analysis (EPMA), thermogravimetry/differential thermal analysis (TG-DTA), and X-ray diffraction (XRD) after 4-20 months of immersion. The results show that adding sodium carbonate to the bentonite enhanced the formation of calcite in the form of a surface layer on the cement paste. This suggests pore clogging at the interface and implies the existence of a threshold amount of carbonate addition above which pore clogging occurs. This is the first of two papers; the accelerated evolution of the samples in the presence of an electrical field is discussed in the second paper.

Review of secondary phases formed under natural alkaline conditions at low temperatures and implications for cement–bentonite interactions in radioactive waste repositories

“…This indicates that 14 Å tobermorite can potentially form during the alteration of bentonite close to cementitious materials with Stage I and II alkaline leachates (Table 5). Contrary to this, the formation of 14 Å tobermorite has not been reported in previous laboratory and in situ experiments showing alkaline alteration of bentonite or clay, but rather the formation of C-S-H, C-A-S-H, 11 Å tobermorite, or Al-tobermorite (Fernández et al, 2016;Lalan et al, 2016;Fernández et al, 2017;Lerouge et al, 2017;Nakarai et al, 2021;Ramírez et al, 2005;Sánchez et al, 2006;Yokoyama et al, 2011;Techer et al, 2012). The tendency for C-S-H to form at low temperatures was recognized from these experiments, which lasted up to 15 y (Appendix A in the Supplementary material).…”

Modified ground calcium carbonate mineral powder using in asphalt concrete: modification mechanism characterization at macro and micro levels

“…As per Figure 4, it can be observed that the reaction temperature for several modified GCC falls within the range of 200 °C-300 °C, as Frontiers in Materials frontiersin.org reported in studies by Yuan et al (2019) and Nakarai et al (2021). Upon comparing the curve of unmodified GCC with the curves of modified GCC, it is evident that unmodified GCC shows minimal mass loss and remains relatively stable as the temperature increases in the temperature range of 200 °C-600 °C, while modified GCC exhibits varying degrees of mass loss with the increase of temperature, and the extent of mass loss roughly corresponds to the amount of modifying agent added.…”

A Review of Lightweight Self-Healing Concrete

“…The addition of carbonates to clay-like LWAs increased the content of calcium ions, and the strong chemical gradient between cement and clay promoted the formation of C-S-H gels and other white precipitation products [ 29 , 60 ]. In this way, self-healing is initiated.…”