Hygrothermal stability of ettringite in blended systems with CAC-OPC-CŠ

Abstract

The hygrothermal stability of ettringite in cementitious systems composed of calcium aluminate cement (CAC) blended with ordinary portland cement (OPC) and calcium sulfate (CŠ) has been investigated for five simulated environmental conditions- i) 23 °C-100% RH (Relative Humidity), ii) 23 °C-50% RH, iii) 38 °C-50% RH, iv) 50 °C-50% RH, and v) 60 °C-50% RH. Two types of ternary systems were used, one rich in CAC (with a higher mass ratio of CAC compared to OPC) and the other rich in OPC (with a higher mass ratio of OPC compared to CAC), both with a water-to-cement (w/c) ratio of 0.35. The volume change and mechanical properties were evaluated by dimensional change, mass change, compressive strength, and flexural strength measurements. Hydration and microstructural properties were evaluated by isothermal calorimetry, thermogravimetric analysis (TGA), and Quantitative X-Ray Diffraction (QXRD) via the G-factor method. QXRD results showed that the studied CAC-rich binder formed 26.0 ± 1 wt% and the OPC-rich binder 28.9 ± 1 wt% ettringite after 24 h of hydration. However, with the increase in temperature, decrease in relative humidity, and time of exposure, the OPC-rich binder showed higher shrinkage, higher mass loss, and a significant decrease in ettringite content compared to the CAC-rich binder.