Traces of CH in a C4A3$-C2S hydration system

A C(4)A(3)$-C2S (ye'elimite-belite) clinker system with different C2S and C(4)A(3)$ contents is synthesized from analytical reagents and a C(4)A(3)$-C2S hydration system is established with a water-cement ratio of 0.4. The traces of calcium hydroxide or portlandite (CH) in the C(4)A(3)$-C2S hydration system were characterized using X-ray diffraction (XRD), thermo-gravimetric (TG) analysis, Fourier transform infrared (FTIR) spectroscopy and pH tests. The Rietveld quantitative phase analysis (RQPA) method was used to determine the compositions of the C(4)A(3)$-C2S hydration products. The hydration process and microstructure evolution of the system were also investigated. The hydration of the C(4)A(3)$-C2S involves two key process: one the consumption of AH(3) phase and another the generation and stabilization of CH phase. The occurrence of the CH traces in C(4)A(3)$-C2S hydration system can be described in terms of the changes in the C2S content and the curing age. When the C2S content is less than 55 wt%, the newly generated AH(3) preferentially reacts with the C2S to generate C(2)ASH(8). When the content of C2S is between 55 wt% and 85 wt%, the C2S begins direct hydration but the generated CH is immediately consumed by the C(2)ASH(8). When the C2S content is higher than 85 wt%, the CH generated by the hydration of C2S becomes stable in the C(4)A(3)$-C2S hydration system. (C) 2018 Elsevier Ltd. All rights reserved.