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.