Controlling the hydration rate of alkali-activated slag by the slow release of NaOH

The reaction of alkali-activated slag is very fast and challenging to adjust with the common retarder used in Portland cement. Thus, achieving control of the hydration rate of alkali-activated slag by the slow release of NaOH may be an effective method. In this study, the slow release of NaOH was achieved by controlling the reaction rate of Na₂CO₃ and Ca(OH)₂, which has never been reported elsewhere. The thickening property, compressive strength, isothermal calorimetry, UCA, XRD, and TGA were tested in this paper. The results show that, compared with NaOH-activated slag, Na₂CO₃–Ca(OH)₂-activated slag demonstrated improved strength, better adjustability for thickening time, and a better right-angle-set property. For the same thickening time, the amount of EDTMPS retarder added in the Na₂CO₃–Ca(OH)₂-activated slag was only 1/10 of that used in the NaOH-activated slag. And the thickening time adjustable temperature of the Na₂CO₃–Ca(OH)₂-activated slag can reach 120 °C.