Multi-scale characterization of SAP impact on self-healing behavior in UHPC under varied crack widths and environments

This paper studies the effects of the content and particle size of superabsorbent polymer (SAP) on the self-healing behavior of precracked Ultra-high-performance concrete (UHPC) under different crack widths. In this experiment, bending and compression-resistant internal damage to UHPC was first created with different amounts and particle sizes of SAP added, and then the damaged specimens were placed in a water environment, a dry environment, and a water-dry cycle environment for self-healing. Finally, the self-healing effect of pre-cracked UHPC was evaluated from the changes in crack width, recovery of mechanical properties, and changes in ultrasonic speed. In addition, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to conduct microscopic analysis of the products of the self-healing reaction. The experimental results show that SAP itself does not participate in self-healing chemical reactions. It mainly seals cracks by absorbing water and expands and promotes the continued hydration of the internal gelling materials of UHPC through water storage to improve the self-healing performance. Therefore, in a dry environment, SAP has almost no effect on the self-healing performance of UHPC. In moisture-rich environments, SAP can significantly improve the healing of macroscopic cracks with a width greater than 50 μm. In addition, the experimental results also show that under the same environment, changes in SAP content and particle size have a consistent effect on the recovery of UHPC's mechanical properties and the recovery of ultrasonic speed. The results of this study can promote the application of internal curing in the self-healing of UHPC cracks and further reduce the maintenance cost of UHPC throughout its life cycle. • SAP can improve self-healing properties without significantly reducing strength. • Adding SAP to UHPC can completely self-heal cracks within 150 μm. • UHPC crack closure is often accompanied by recovery of mechanical properties. • SAP can best improve the self-healing effect of UHPC in a water environment.