Hydration mechanisms of composite binders containing copper slag at different temperatures

Abstract

The hydration mechanisms of composite binders containing copper slag at different temperatures (20 °C and 50 °C) were investigated by hydration heat determination, TG/DTG, non-evaporable water content measurement and X-ray diffraction (XRD). The compressive strengths of mortars containing copper slag cured at different temperatures were also determined. In addition to plain cement, quartz powder with a similar particle size and the same replacement ratio as copper slag was selected as the control sample. The results show that the addition of quartz powder has a slight acceleration effect on the hydration of cement, while the addition of copper slag has a strong retarding effect on the hydration of cement. The second exothermic peak of the composite binder containing copper slag is delayed as the copper slag content increases, but this trend weakens at high temperatures. The hydration heat of the composite binder containing copper slag decreases with increasing copper slag addition. Moreover, the hydration heat of the composite binder containing copper slag is higher than that of the composite binder containing an equal mass of quartz powder within 72 h. Copper slag has pozzolanic activity and consumes Ca(OH)2 in hardened paste, although the pozzolanic activity of copper slag is low. However, the pozzolanic activity of copper slag is enhanced at high temperature. Furthermore, the reaction of copper slag does not produce new crystalline products compared to those produced by cement. Moreover, compared to hardened plain cement, the hardened composite binder containing copper slag has a higher non-evaporable water content gain rate. The mortar containing copper slag also has a higher compressive strength gain rate than the mortar containing equal mass quartz powder. Although the compressive strength of mortar containing copper slag is lower than that of plain cement mortar, it is higher than that of mortar containing quartz powder.