Coherent diffraction study of calcite crystallization during the hydration of tricalcium silicate

摘要

The aim of this work is using Bragg coherent X-ray diffraction imaging (BCDI) to study the calcite crystallization during carbonation of hydrated tricalcium silicate (C3S). Portland cement is a very complex synthesized product whose 50-70% mass is composed of C3S, which is the most important phase to produce calcium silicate hydrates and calcium hydroxide. Hence, its hydration contributes greatly to the hydration of cement and later to the carbonation of cement products when it reacts with CO2, often from the air, to form calcium carbonates. BCDI has emerged in the last decade as a promising high-resolution lens-less imaging approach for characterization of various samples. It has made significant progress with the development of X-ray sources and phase-retrieval algorithms. BCDI allows for imaging the whole three-dimensional structure of micro-and sub-micro-crystalline materials and can show the strain distribution at the nanometer spatial resolution. Results show that calcite crystallization follows a through-solution reaction and the growth model of the calcite crystal can be explained by using "phase domain" theory. During carbonation, calcite crystals grow by increasing the number of phase domains within them while the domain size remains at about 200-300 nm. (C) 2018 Elsevier Ltd. All rights reserved.