Coupling effect of cementitious capillary crystalline waterproof material and exposure environments on self-healing properties of engineered cementitious composites (ECC)

Due to the healing mechanism of self-healing technologies, there are some limitations and challenges for application in concrete structures. Based on the characteristics of cementitious capillary crystalline waterproof material (CCCW) in powder and active materials moving along cracks, this work presents CCCW as a direct internally mixed self-healing material, and quanti-tatively explored the coupling effect of CCCW and exposure environments on the self-healing properties of engineered cementitious composites (ECC). Four types of ECC mixtures with CCCW doping of 0%, 1.5%, 3% and 4.5% were prepared. Exposure environments contained water, air and saturated calcium hydroxide solution. The self-healing behavior of ECC was evaluated by the recovery of mechanical properties, water impermeability and closure behavior of crack. Microscopic analysis of healing products was performed by scanning electron micro-scope (SEM), thermogravimetric analysis (TG) and X-ray diffraction (XRD). The test results showed that the recovery of mechanical properties and water impermeability of ECC was improved by directly adding CCCW. The percentage of re-opened healed cracks number in specimen EC45 with 4.5% CCCW content was 83.33% lower than that in specimen EC0 without CCCW. The normalized closure rate of crack area was raised by 167.98% by mixing 4.5% of CCCW in saturated calcium hydroxide solution, compared with that without CCCW. While it was enhanced by 132.44% in water. There was a superimposed enhancement of CCCW and calcium hydroxide solution. Microscopic analysis of healing products showed that CCCW facilitated the production of healing products, especially in saturated calcium hydroxide solution. Finally, the additive effect coefficient Ki was introduced to quantitatively characterize the coupling effect of environments and CCCW on the self-healing properties of ECC.