Improved self-healing of mortars with partial cement replacement

Making the European Union’s economy sustainable is the “European Green Deal” strategy announced by The European Commission. One of the major aims is becoming climate-neutral by 2050. Since global cement production accounts for approximately 8% of anthropogenic carbon dioxide emissions, the development of concrete with waste by-products as alternative binders and efficient self-healing properties would be a significant milestone towards the circular economy. The self-healing efficiency of cementitious composites with alternative binders requires further improvement as there is still insufficient information on this topic. The latest results for cement mortars showed the promotion of crack closure, both internally and externally, when the healing medium is a mixture of phosphate-based retarding admixture and water. The current study verifies whether satisfactory healing may also be achieved for cementitious composites with 20%cw slag and fly ash replacement subjected to phosphate-based exposure. The efficiency of the proposed solution is compared with other types of environmental conditions such as deionized or lime water immersion. The self-healing process is quantitatively assessed after 4 weeks of healing based on the crack closure and flexural strength regain. All exposure conditions applied resulted in efficient external crack closure; however, the phosphate-based retarding admixture showed the most impressive internal filling of the crack (Figure 1). Based on the Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS) analysis, the majority of the self-healing products were identified as calcium carbonate crystals. Calcium phosphate compound and calcium silicate hydrate (C-S-H) were visible inside the crack in case of retarding admixture exposure contributing also to a limited flexural strength recovery.