Pitfalls in the use and interpretation of TGA and MIP techniques for Ca-leached cementitious materials

Abstract

The study of Ca-leaching of cement-based materials has necessitated the use of accelerated leaching experiments because of extremely slow leaching kinetics. The microstructural and mineralogical changes resulting from such leaching experiments are typically studied using Mercury intrusion porosimetry (MIP) and Thermal gravimetric analysis (TGA), respectively. This paper closely examines the pitfalls associated with applying these techniques to study the behaviour of leached materials. In this context, accelerated leaching experiments of cement paste samples with two water/cement ratios (0.325 and 0.425) are used as the basis. MIP and TGA results for both leached and intact paste samples are presented in terms of pore size distribution and phase fractions (portlandite, calcium carbonate and C-S-H), respectively. Results suggest that specifically for leached materials, a theoretical correction over and above that suggested by MIP manufacturer is needed to correctly interpret MIP data for original samples. However, TGA should not be used to study the leached materials subjected to accelerated leaching using ammonium nitrate solution. Keywords: Microstructure, Mineralogy, Mercury intrusion porosimetry, Thermal gravimetric analysis, Micromechanics, Cement paste