Novel selection of environment-friendly cementitious materials for winter construction: Alkali-activated slag/Portland cement

Abstract

Cold weather concreting is known for its high energy consumption and staggeringly high levels of carbon dioxide (CO2) emissions, as concrete needs to prevent frost damage and the use of supplementary cementitious materials is not recommended. A novel environment-friendly binder, namely, alkali-activated ground granulated blast-furnace slag (GGBS)/Portland cement (PC) was presented to use for winter construction in this study. The performance of PC and alkali-activated GGBS/PC binder with the GGBS content of 70, 80, 90, and 100 wt%, respectively cured at the temperature of 20, −5, and −20 °C was comprehensively studied. Besides, the freezing point and the hydration process were researched to reveal the excellent performance of the new binders at sub-zero temperatures. Results of the compressive strength and setting time showed that the alkali-activated GGBS/PC binders exhibited the absolute advantage compared to PC, in particular, at sub-zero temperatures. Moreover, the performance of alkali-activated binder containing both GGBS and PC at sub-zero temperature was far better than that of a binder containing only GGBS, and almost the highest compressive strength was achieved when the GGBS content was 80 wt% (62.7 MPa in 28 days at −5 °C). The freezing point of PC paste was −4.8 °C, while that of an alkali-activated binder was significantly lower. The hydration of alkali-activated GGBS/PC binder was more intense, and binder exhibited a higher polymerization degree and involved the formation of highly cross-linked C–A–S–H gel. More importantly, CO2 emission during winter construction can be decreased by using this novel binder, leading to fewer insulation measures and a significant reduction of PC usage.