ECC is characterized by high ductility and high toughness, and the generation of a large number of fine cracks gives the material a significant self-healing ability, thereby improving its safety and durability. In some northern regions of China, the soil pH value exceeds 9 in alkaline environments, sulfate content in marine environments can generally reach 1400-2700 mg/l, structures are typically subjected to dry-wet cycles in areas of water level fluctuations, and water is a necessary condition for the occurrence of self-healing. In order to comprehensively and systematically analyze the self-healing performance of ECC under different environments and preloading conditions, the tensile and flexural properties of ECC after self-healing under three environments (5% Na₂SO₄, saturated Ca(OH)₂, and water) were investigated in this paper, providing a basis for the further application of ECC materials in engineering practice.

Three environments were designed: 1) 5% Na₂SO₄ solution (by mass) under dry-wet cycles; 2) Saturated Ca(OH)₂ solution under dry-wet cycles; 3) Water environment which served as a control group. The preloaded specimens were placed in them individually.

A total of 9 batches of dog-bone specimens under three different environments were prepared. The group preloading to 1% and 2% strain and the intact specimens without preloading were placed in the self-healing environment. After reaching the corresponding age, tensile tests were conducted to obtain stress-strain curves under different conditions, and the recovery of tensile strength and ultimate deflection was analyzed.

Besides, 9 batches of four point bending thin plates under three different environments were prepared, the ultimate strength was obtained from the intact specimens, and 20% and 40% of the value were selected as the preloading levels for bending tests. The preloaded group and intact specimens without preloading were placed in the self-healing environments for the flexural tests to obtain the load-deflection curves, the recovery of properties such as flexural strength, ultimate deflection, and flexural toughness were investigated.

Preloading to 1% strain gained a significant advantage in restoring the tensile strength of specimens at different ages in three different environments. The tensile strength of ECC was improved when subjected to dry-wet cycle in both Na₂SO₄ and Ca(OH)₂ solutions, with a supreior recovery ability observed in the Ca(OH)₂ environment. It is also noted that under a 1% preload, the tensile strength increased by about 36.33% throughout the 90 d aging process.

Reloading after pre-tensioning led to a significant improvement on the tensile ductility of specimens at 0 d, with an increase in ultimate tensile strain of up to 138.4% with the preloading level increasing from 0% to 2%. The water environment had a significant effect on the ductile healing of intact specimens without preloading at long ages, with an increase in ultimate tensile strain of 137.52% with age from 0 d to 90 d, while the Na₂SO₄ and Ca(OH)₂ environments weakened the ductility of cracked ECC specimens, with the largest decreases of 52.78%-65.39% at 2% preloading, and the Na₂SO₄ environment had a better effect on the maintenance of ductility in the specimens. At 90d of self-healing, increasing preloading levels weakened the tensile ductility of the specimens, with the greatest decrease in water.

Under the unsoaked condition, 20% preloading increased the flexural strength of the bent plate, but weakened the flexural ductility. As the age of self-healing increased, the initial flexural strength and ultimate flexural strength of the specimens under 40% preloading were improved, and Na₂SO₄ environment was more effective, with an increase of 28.91% and 40.35%, respectively, compared with that at 0 d. Preloading by 20% significantly increased the ultimate deflection, and the best effect was achieved in water, with an increase of up to 202.83% compared with 0 d. Flexural ductility was positively correlated with multi-seam cracking pattern. Na₂SO₄ and Ca(OH)₂ environments were effective in restoring the flexural strength of the specimens at a short age, and had a positive effect on the healing of microcracks. After 90 d of self-healing, the initial flexural toughness ratio and residual flexural toughness ratio of the preloaded 20% thin plate recovered best. Ca(OH)₂ environment was favorable to enhance the pre-peak flexural toughness, and the water environment was favorable to enhance the post-peak flexural toughness.

The tensile and flexural properties of ECC after self-healing in three environments were investigated. The results showed good tensile and flexural self-healing properties. A 1% preloading level was clearly beneficial for tensile strength recovery at all ages in the three environments. Although Dry-wet cycling in Na₂SO₄ and Ca(OH)₂ enhanced the tensile strength of ECC, it reduced the tensile ductility of preloaded ECC specimens. The greatest decrease in ductility occured at 2% preloading, and the Na₂SO₄ environment was more effective in maintaining it. After 90 d of self-healing, tensile ductility of the specimens decreased with increasing preloading levels. A 40% preloading level had the most significant effect on flexural strength recovery after long-term aging, particularly in the Na₂SO₄ environment. The ultimate deflection recovery of the specimen was most significant at a 20% preloading level, with better performance in water. Furthermore, 20% preloading significantly improved the flexural toughness after 90 d of self-healing.