Innovative strategy to reduce autogenous shrinkage in alkali-activated slag using hydrophilic carbon nanotube sponge

Abstract

Alkali-activated slag (AAS) cement is recognized as a sustainable alternative to Portland cement (PC) binders. However, its practical application in construction is hindered by significant autogenous shrinkage. This study presents an innovative internal curing strategy by incorporating a hydrophilic carbon nanotube sponge (H-CNTSP) into the AAS paste. Due to the high stiffness of the CNT framework, H-CNTSP exhibits remarkable absorption capacities for activator and pore solution, reaching 74 g/g and 67 g/g, respectively—236 % higher than that of conventional superabsorbent polymer (SAP). The addition of just 0.08 wt% H-CNTSP effectively reduces autogenous shrinkage by 71 %, attributed to the sustained liquid release, as confirmed by the monitoring of internal relative humidity. Moreover, the loss in mechanical properties typically associated with internal curing agents is significantly minimized, thanks to the formation of a CNT/reaction product nanocomposite layer with enhanced stiffness. This study offers a promising solution to address the limitations of the AAS system, paving the way for its broader implementation in engineering applications.