Effect of fly ash and superabsorbent polymer on concrete self-healing ability

Abstract

Concrete that contains self-healing supplementary materials is a feature of many sustainable structures because it decreases maintenance costs and extends service life. Many self-healing studies have suggested that concrete needs to have extensive exposure to water in order to promote crack-sealing. This paper investigates the benefits of using fly ash and superabsorbent polymer (SAP) to promote self-healing. Eight mix proportions with varying fly ash and SAP replacement ratios were examined. Self-healing efficiency was evaluated by temporal decreases in water discharge through a crack, crack closure observation, stereomicroscopy, scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG/DTA), and energy-dispersive X-ray spectroscopy (EDS). The specimens were preloaded to generate a crack, and these pre-cracked specimens were healed either by continuous water immersion or exposure to wet-dry conditions. Crack width was found to decrease with increase in the fly ash replacement ratio, whereas higher volume of SAP was found to mitigate water discharge through the crack by the swelling of the SAP gel. These effects in combination achieved a maximum of 100% crack closure and permeability restoration by 28 days of healing. As the results, midterm self-healing ability of concrete can be enhanced by the coupling effect of fly ash and SAP. The crack closure was found to be associated with the development of self-healing products such as calcium carbonate and C-S-H.