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Microbially induced calcium carbonate precipitation (MICP) presents a sustainable, environmentally friendly solution for repairing cracks in cement-based materials, such as mortar and concrete. This self-healing approach mechanism enables the matrix to autonomously close its own cracks over time. In this study, specimens (50 mm in diameter and 25 mm in height) were exposed to submersion and a wet–dry cycle environment. The solution considered a nutrient-rich suspension with calcium lactate, urea, calcium nitrate, and Bacillus subtilis or Sporosarcina pasteurii in a biomineralization approach. The self-healing efficiency was assessed through optical microscopy combined with image processing, focusing on the analysis of the superficial crack closure area. S. and B. subtilis exhibited notable capabilities in effectively healing cracks, respectively, 8 mm2 and 5 mm2 at 35 days. Healing was particularly effective in samples placed in a submerged environment, especially with a 69 mM concentration of calcium lactate in bacterial suspensions containing B. subtilis, where 87.5% of a 4 mm2 crack was closed within 21 days. In contrast, free calcium ions in the solution, resulting from anhydrous cement hydration, proved ineffective for S. pasteurii biomineralization in urea-rich environments. However, the addition of an external calcium source (calcium nitrate) significantly enhanced crack closure, emphasizing the critical role of calcium availability in optimizing MICP for bio-agents in cement-based materials. These findings highlight the potential of MICP to advance sustainable self-healing concrete technologies.

The use of different technologies have contributed to the increase in durability facing the aggressive agents that damage the concrete structures. Therefore, it is possible to reduce the capillary porosity in concrete lowering the ratio water/binder; using pozzolan, hydrophobic or waterproofing products in the mixture; applying hydrophobic products or waterproofing in the concrete surface; replacing pure cements for compounds cements, pozzolanic cements or cements with blast furnace slag; among other actions. The waterproofing has the function to prevent the water or fluid passage in liquid or steam state, thereby protecting structures. The waterproofing creates a barrier when coating is applied to close surface pores with the aim of preventing the water pervasion by any transport mechanism. This paper has evaluated the use of crystalline waterproofing as admixtures, as well as a coating, sanding and no-sanding, in order to know the benefits it can bring to the concrete water absorption, comparing their performance with other concretes with or without silica fume admixture. Developed tests were: total absorption, under pressure water penetration (30 kPa) and compressive strength test. The results have showed that the silica fume admixture is more efficient than the analyzed crystalline waterproofing, as it has contributed to the compressive strength increase and decrease of water absorption and penetration. The crystalline waterproofing admixture has contributed to compressive strength increase; however, there was also an increase in the absorption and penetration. On the other hand, the coating waterproofing has not influenced the compressive strength, but reduced absorption and penetration when sanded.

The durability assurance in reinforced concrete is necessary during the design conception and mix design as a preventive measure. Permeability in cementitious materials is a crucial durability indicator that can be influenced by many factors, from capillary porosity to cracks. Under those circumstances, it might be helpful to have concrete with the ability to reduce permeability. In this paper, the effectiveness of incorporating a crystalline admixture, both as an admixture and surface treatment, through characterisation tests, durability tests, and self-healing analyses. A concrete with silica fume as an admixture was also produced for comparison to the use of crystalline admixture (CA). The silica fume showed more efficiency in all assessed properties relative to both the reference and CA for condition with limited water availability. Crystalline admixture is also beneficial over reference concrete when used as an admixture, increasing the compressive strength and decreasing the ingress of chloride and carbon dioxide. The concrete with surface treatment had similar behaviour of reference concrete. Additionally, healing products from the use of crystalline admixture take the form of a needle shape in concrete.