Prediction of the Self-Healing Width of Cement-Based Materials with Calcium Alginate Hydrogel Considering the Distribution of Unhydrated Cement in Cracks

Abstract

Currently, the study results of the self-healing width of concrete based on the rehydration of unhydrated cement (UHC) are between 10 and 760 μm, which are quite different due to the differences in material composition, experimental conditions, and measurement methods. This paper proposes a method for predicting the self-healing widths of cracks based on backscattering image analysis. Considering the particle-size distribution and the occurrence probability of different sections of UHC, the healing widths of local cracks and through-crack in cement-based materials with and without calcium alginate (CA) hydrogel were predicted, and were compared with those observed using scanning electron microscope. The predicted results show that the healing width of local cracks is 33 μm. The self-healing widths of penetrating cracks in cement-based materials with and without CA is 7 and 10 μm, respectively. The experimental results indicate that the self-healing widths of cement-based materials with and without CA are 36 and 17 μm, respectively. The prediction results were close to the experimental results. However, the predicted self-healing width of cement-based materials mixed with CA is less than that without CA due to the smaller density of healing products. Cement is one of the most important building materials. However, the manufacturing process of cement releases a large amount of carbon dioxide, accounting for 5%–7% of carbon dioxide emissions. The carbon dioxide emissions and the consumption of cement can be reduced by extending the service life of structures. However, cement-based materials are brittle materials, which are prone to cracking because of the shrinkage, restraint, and force of the concrete. The generation of cracks is accelerated by the intrusion of harmful ions such as Cl− and SO42−, which results in the corrosion of the steel bars inside the cement-based materials. This reduces the service life of the cement-based materials. The cracks inside the self-healing cement-based materials can be healed, which can reduce the invasion of harmful ions and prolong the service life of cement-based materials. The prediction of self-healing ability will provide some principles and guidance for designing self-healing concrete and promoting the self-healing ability.