The impact of metakaolin on the hydration of tricalcium silicate: effect of C-A-S-H precipitation

Introduction: Metakaolin (MK) is used as supplementary cementitious material to reduce the CO 2 footprint of Portland cements. However, early hydration cement (OPC) often retarded due its use. The present work investigates mechanisms this retardation. Focus laid on interaction MK with main clinker phase C 3 S (Ca SiO 5 , pure form alite) that known govern kinetics OPC. Methods: Hydration reactions and were analysed by optical emission spectroscopy, electron microscopy, thermal analysis, X-ray diffraction reaction calorimetry. Results: Results showed compared sodium ions presence calcium reduced maximum amounts silicate aluminate released into solution MK. For + mixtures, C-A-S-H was formed at surfaces both within minutes a composition (CaO) 1.3 (SiO ) 0.8 (Al O 0.2 (H O) 2.7 . solubility constant determined. Discussion: appeared be an unsuitable substrate for C-S-H nucleation. Therefore, formation during expected play important role in retardation hydration. Indeed, when seeds are formed, less leading lengthen duration induction period. sulfate reduces amount most consumed ettringite. Consequently, induce increase such observed mixtures.