Autogenous healing of Engineered Cementitious Composites (ECC) based on MgO-fly ash binary system activated by carbonation curing. (30th March 2020)

• Record Type: Journal Article
• Authors: Zhang, Duo; Wu, Haoliang; Li, Victor C.; Ellis, Brian R.
• Is Part Of: Construction & building materials. Volume 238(2020)
• Publication Date: 2020-03-30
• Subjects: Engineered Cementitious Composites (ECC) -- Carbonation curing -- CO2 utilization -- Self-healing -- MgO cement; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2019.117672
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Rapid self-healing of carbonation-cured MgO-based PC-free ECC was demonstrated. Healing of microcracks occurred primarily at the crack surface. Tensile strength and ductility are not fully restored after self-healing. Nesquehonite was the primary mineral phase filling healed crack openings. Abstract: Developing self-healing of concrete cracks represents a critical approach for extending material longevity. If demonstrated on concretes with CO2 stored through carbonation curing, self-healing can further mitigate infrastructure lifecycle emissions. In this study, the self-healing process is investigated on novel Engineered Cementitious Composites (ECC) based on binary blends of reactive MgO cement and siliceous fly ash activated by carbonation. The self-healing was observed under cyclic wetting and drying exposures and was characterized by measurements of resonance frequency, optical microscopy and X-ray computed microtomography (XCT). Thermogravimetric analysis, X-ray powder diffraction and scanning electron microscopy were employed to assist in identifying healing products and mechanisms. It was found that micro-cracks could be autogenously filled in 7 wet-dry cycles, as evidenced by over 95% recovery of resonance frequency and healed crack appearance under optical microscopic observation. Nevertheless, the composite mechanical performance, particularly tensile strength and ductility, did not fully recover with respect to the uncracked specimens. The inadequate post-healing mechanical properties were consistent with XCT observations that indicated low material densities in the cracked area. Based on the chemical and microstructural characterizations, it was determined that nesquehonite crystallites were responsible for the crack filling. Although the nesquehonite filled cracks will be less permeable to invasion of reactive fluids, novel strategies are needed to establish more robust healing capability to completely restore the crack bridging and composite tensile performance.