Set Controlling Additive for Thermal-Shock Resistant Cement

Abstract

The present work discusses retardation of hydration of sodium metasilicate (SMS)-activated calcium aluminate cement (CAC)/ Class F fly ash blend at 85oC. Screening of common retarders, including citric-, tartaric-, and boric-acids, via isothermal calorimetric measurements identified tartaric acid as the most efficient in delaying the set of the blend. None of these retarders compromised the development of long-term compressive strength or toughness at concentrations of up to 1% by weight of blend (bwob) at 200- and 300o C. The reaction products of tartaric acid and the components of the blend were characterized by XRD and Fourier-transform infrared. The main conclusions drawn from this study were that SMS not only activates the hydration of waterinert fly ash F, but also delays the set of the CAC/Class F fly ash blend. Adding tartaric acid further retards the set of the blend and formation of crystalline hydrates at 85oC, so promoting sodalite crystallization at 300oC. Hypothesis to explain the set-retarding mechanism are proposed.