Potential use of fly ash based nano silica as mineral additive to improve the mechanical properties of self-healing mortar

Hydrogel-based self-healing mortar often experiences strength decrease that may impact concrete performance under mechanical load. While the addition of commercial colloidal nano silica can improve the strength of hydrogel-based self-healing mortar, they can be relatively expensive. This work examines the synthesis of an alternative and affordable nano-silica, aiming to improve the mechanical strength of hydrogel-based self-healing mortar. Nano silica is extracted from abundantly available mineral admixture, i.e., fly ash through chemical purification methods. Two concentrations of 2 % and 5 % nano silica by mass replacement of cement are used in the mortar mixture. X-ray diffraction was conducted to ensure that nano silica produced is in amorphous form. The hydration kinetics of resulting paste, workability, compressive strength, healing capacity and capillary water absorption of resulting mortar were investigated. The results prove the production of high-quality nano silica from fly ash with sufficient amorphous phase. The hydration kinetics indicate that the incorporation of nano-silica derived from fly ash at a dosage of 2 % accelerates the hydration reaction. This acceleration corresponds with the observed enhancement in the compressive strength of hydrogel-loaded mortar, where the addition of 2 % nano-silica fly ash produced strength values comparable to those of the reference sample while maintaining the self-healing capability. Therefore, a dosage of 2 % nano-silica fly ash by cement weight is recommended as an effective mineral additive for improving the mechanical performance of hydrogel-based self-healing mortars. • The nano silica purified from fly ash has sufficient amorphous phase of SiO 3 . • The presence of nano silica fly ash could alter the delay in the formation of hydration peak due to excess water released from the hydrogel. • The addition of 2 % of nano silica fly ash into hydrogel-based mortar has successfully maintained the compressive strength. • Nano silica fly ash can be used as an alternative mineral admixture that can improve the strength of hydrogel based self-healing mortar.