Phase profiling of carbonated cement paste: Quantitative X-ray diffraction analysis and numerical modeling

Abstract

The objective of this paper is to understand the phase changes of the carbonated cement paste by comparing experimental and numerical modeling results. Phase assemblages of hydrates and anhydrous clinkers at various depths of cement paste after carbonation were investigated using Quantitative X-ray diffraction (QXRD) analysis and numerical modeling. Carbonation with CO2 at 10 vol% and ~ 55% relative humidity was applied at ambient temperature. The paste specimens aged 14 days and 28 days were exposed to this CO2 condition for 14 days and 28 days. QXRD analysis was conducted for the various depths of specimens with 5-mm intervals from the carbonation front, and thermogravimetry analysis was also carried out to compare the results from QXRD. To explain the phase profiles from the experiments, a multi-reaction model considering hydration, carbonation, and transportation in the cement matrix was developed. The experimental results of the phase profile demonstrated good agreement with the numerical results. It was confirmed that carbonation with high concentration led to the consumption of anhydrous clinker as well as the occupation of CaCO3 in most of the volume in the skeleton of the cement paste.