An alkali-responsive mineral self-healing agent with mechanical property enhancement for cementitious composites

Self-healing cementitious materials are regarded as an effective choice to increase the sustainability of the resource and environment. In this study, an alkali-responsive mineral self-healing agent (AMS) was prepared inspired by bone repair. The healing component, phosphate, was loaded into the halloysite nanotubes (HNTs) and encapsulated by the layer-by-layer (LbL) self-assembly method. The structure and alkali-responsive behavior of AMS, the effect of AMS on the mechanical properties of cement pastes, the stability of AMS before cement cracking, and its effect on the self-healing efficiency of the cement pastes were investigated with a range of analytical techniques. Results showed that AMS was successfully encapsulated and endowed with excellent alkali responsiveness. The incorporation of AMS was effective in reinforcing the mechanical performances of cement pastes. XRD analysis showed that the phosphate encapsulated in AMS can be mostly retained until cracks appear. When cracks occurred, the B-type carbonated calcium-deficient hydroxyapatite was found as the main product in the crack environment. The surface crack around 130 mu m in the damaged specimens containing 5% AMS was fully sealed and healed, and its damaged compressive strength was almost completely recovered after curing for 28 days. The synergistic effect of autonomous healing triggered by AMS and autogenous healing behavior promotes the self-healing process and improves the self-healing efficiency of the hardened cement pastes.

Automated summary

In this study, an alkali-responsive mineral self-healing agent (AMS) was developed by loading phosphate into halloysite nanotubes (HNTs). The incorporation of AMS effectively reinforced the mechanical properties of cement pastes and promoted self-healing efficiency. XRD analysis showed the stability of phosphate encapsulated in AMS before crack occurrence. The presence of AMS in damaged cement pastes triggered autonomous healing and significantly improved self-healing efficiency.