Enhanced cracking resistance of alkali-activated slag recycled aggregate concrete enabled by eco-friendly activators

Alkali-activated slag recycled aggregate concrete (AASRC) has garnered significant attention due to its excellent properties, low-carbon emissions, and efficient utilization of industrial and construction wastes. However, the high shrinkage susceptibility makes AASRCs prone to cracking, which limits their application in the construction industry. This study intends to enhance the cracking resistance of AASRCs through the use of eco-friendly activators. Two eco-friendly activator combinations were employed: water glass with sodium carbonate (WNC) and sodium carbonate with calcium oxide (CNC), with conventional water glass (WG) serving as the control. Also, three replacement levels of recycled coarse aggregate (RCA) with natural aggregate were investigated (0, 50, and 100 wt%). The mechanisms were comprehensively explored using X-Ray Diffraction, Mercury Intrusion Porosimetry and Scanning Electron Microscope with Energy Dispersive Spectroscopy tests. The results revealed that, compared to WG activator, the use of eco-friendly WNC and CNC activators effectively improved the cracking resistance of AASRCs, with the CNC activator providing the most favorable effect. This is primarily attributed to the decreased shrinkage of AASRCs by using WNC and CNC activators. Although the incorporation of RCA mostly increased the cracking potential of AASRCs, WNC- and CNC-activated concretes with 100 wt% RCA still outperformed WG-activated concretes without RCA. This study provides an effective and straightforward approach to enhance the cracking resistance of AASRCs by utilizing eco-friendly activators, beneficial for their large-scale application. • CNC activator exhibited best cracking resistance for AASRCs. • WGCs reached the ultimate cracking state, while WNCCs and CNCCs remained uncracked. • Replacing 50 wt% of NAs with RCAs delayed the cracking age from 6.04 d to 9.08 d. • Incorporating RCA diminished the cracking resistance of both WNCCs and CNCCs.