Comparative study on different methods of activation of recycled powder grouts

The high-value utilization of recycled powder (RP), primarily derived from construction and demolition waste, has been limited due to its low reactivity. In this study, the effect of RP subjected to three types of inorganic alkalis (sodium hydroxide, sodium carbonate, and calcium hydroxide [CH]), two alkanolamines (diethanolisopropanolamine [DEIPA] and triisopropanolamine [TIPA]), elevated temperatures, and their combined activation on the technical properties of RP grouts was analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to investigate the development of the mineral composition and micromorphology of the grout pastes. The results indicated that alkali and thermal activation of RP had negative effects, while combined activation improved the fluidity of the grout pastes. The compressive strength of alkali-activated groups was slightly enhanced at 1 day but significantly decreased at 28 days. In contrast, the compressive strength of grouts activated with CH, alkanolamines, and thermal treatment was found to be improved at all ages. The compressive strength of the grout paste containing 40% combined-activated RP was measured at 43.1, 73.3, and 95.7 MPa at 1, 3, and 28 days, respectively, which represented increases of 20.4, 19.6, and 17.7%, respectively, compared to the non-activated grout. Combined activation demonstrated the most improvement in the microstructural density of the grouts when compared to the single-activation mode.