Influence of ultra-fine pozzolanic materials on the self-healing capabilities of ultra-high performance concrete under carbonation conditioning

This work studies the autogenous self-healing of ultra-high performance concrete (UHPC) incorporating two ultra-fine pozzolanic materials, silica fume (USF) and ultra-fine fly ash (UFFA), under carbonation conditioning. Both ultra-fine pozzolanic materials stimulate the healing of cracks by promoting the secondary hydration of the cement matrix. USF and UFFA form healing products primarily consisting of C-S-H and ettringite, respectively, and the latter product closes the cracks more effectively. Under carbonation conditioning, UFFA accelerates CaCO₃ formation with residual uncarbonated ettringites as the structural skeleton, improving the impermeability recovery. USF generates silica gel as a bonding layer between the CaCO₃ crystals and the cement matrix after decalcification, which induces more multi-dimensional cracking upon regenerated structures under flexural reloading, thereby enhancing the mechanical property restoration of UHPC. UFFA-modified UHPC is ideal for applications requiring high impermeability, whereas USF-incorporated UHPC is better suited for scenarios with high load-bearing demands.