Effects of self-healing on the microstructure, transport, and electrical properties of 100% construction- and demolition-waste-based geopolymer composites

This study aims to investigate the self-healing capability of engineered geopolymer composites (EGCs) produced with 100% construction and demolition waste (CDW)-based materials. In order to determine the effect of ground granulated blast furnace slag (S) addition on CDW-based mixtures, additional geopolymer mixtures were produced with slag substitution without changing the Si/Al ratio. NaOH is the primary activator; however, Na2SiO3 and Ca(OH)2 are also investigated as additional activators. Half of the specimens were preloaded to crack them, and all specimens were exposed to wetting and drying cycles. At different wetting and drying cycles, electrical impedance and water absorption rates were determined to assess self-healing; additionally, optical images were captured. X-ray diffraction and scanning electron microscopy investigations were carried out to characterize the self-healing products. The test results show that the chemical structure of the CDW-based geopolymeric composite provides self-healing capability, which essentially originates from its calcium and sodium content sourced from raw material and activator. Based on microstructural test results, CDW-based geopolymer composites are healed with CaCO3 formations, and slag incorporation makes self-healing reactions steadier. However, when NaOH exists with Ca(OH)2 and Na2SiO3, a higher early geopolymerization process consumes the ions that participate in the autogenous self-healing process. Na2CO3 is recognized as an early healing product; however, some Na2CO3 is dissolved during the progressive wetting period. At the end of the healing period, CaCO3 is detected as a major healing agent. Additionally, continuing geopolymerization has been identified in the healed cracks. Within this context, the results confirm that the self-healing behavior of EGC is similar to Portland cement-based cementitious composites