Heat Generation and Thermal Properties of Limestone Calcined Clay Cement Paste

Abstract

In mass concrete construction, huge amount of cement is usually used and normally creates high temperature gradient across the thick section. Replacing suitable supplementary cementitious materials (SCMs) to ordinary Portland cement (OPC) is one of the potential strategies to reduce temperature rise of concrete. Although many benefits on the durability of concrete using limestone calcined clay cement (LC2 cement) have reported, very few studies have been published regarding the risk of thermal cracking when LC2 cement is used. Heat of hydration and thermal properties of LC2 cement are necessary parameters of the thermal cracking analysis and must be clarified before its application to the mass concrete construction. In this study, the calorimetric heat flow and cumulative heat of hydration are tested with isothermal calorimetry. The intensity of aluminum peak from calorimetric heat flow is the main hydration peak of LC2 cement pastes. The intensity of aluminum peak increases with higher LC2 cement replacement due to high Al2O3 content of LC2 cement. After the age of 12 h, the cumulative heat generation of LC2 cement pastes becomes lower than that of OPC pastes. Moreover, thermal properties which are specific heat (c), thermal conductivity (k) and coefficient of thermal expansion (CTE) of LC2 cement pastes are also investigated. The results showed that the specific heat of LC2 cement pastes decreases for 8% and 14% with 30% and 45% replacements, respectively, compared with OPC pastes. With higher LC2 cement replacement, the thermal conductivity decreases while the coefficient of thermal expansion increases. These changes are believed to be related to the pore structure development of LC2 cement pastes. Moreover, semi-adiabatic temperature rise is tested to observe the temperature rise. The peaks of temperature are 66.9 °C and 60.6 °C in the case of 30% and 45% LC2 concrete, respectively, which are lower than that of OPC concrete.