Biyolojik kendiliğinden iyileşen çimento esaslı harçların performansa dayalı değerlendirilmesi

Concrete is the second most used material after water, and the demand for cement-based systems is rapidly increasing due to the urbanization. Because of the cement content, the concrete induces approximately 8% of total carbon emissions. It becomes a necessity to make the concrete industry more sustainable and decrease the carbon dioxide (CO2) emissions. Unfortunately, it is unfeasible to produce a concrete by not using cement. We have to reshape how we consume cement-based materials to achieve carbon neutrality in the sector. To date, it is evident that eliminating cement from structural concrete is not feasible, thus it will be more efficient to improve the service life of the structures. A major problem in concrete structures is early age microcracking. Early age microcracks occurring in concrete increase the permeability, consequently decreasing the durability. Recent studies showed that it might be possible to remediate microcracks in the cement-based materials by microbial-induced calcium carbonate precipitation (MICP). However, the main challenge of the application is to provide a suitable carrier to keep the bacterial cells viable in highly alkaline cement paste matrix. This study aims to develop a biological additive to trigger self-healing in cement-based systems by immobilizing Sporosarcina pasteurii (S. pasteurii) cells on natural minerals zeolite, metakaolin and perlite. Self-healing ability of bio-based additive was evaluated through healing of flexural cracks in early-age mortar (14 days and 28 days after mixing) samples. Screening of the healing process was done with stereomicroscopy analysis, ultrasonic pulse velocity test (UPV) and water absorption tests. An accelerated corrosion test was applied to self-healed reinforced mortars to evaluate impact of crack sealing on rebar corrosion. Moreover, the impact of biological additive on the drying shrinkage and the performance of cement-based mortar was also evaluated. According to conducted analyses, zeolite itself was found to be efficient in autogenous self-healing through its reactivity and internal curing mechanism. Metakaolin and perlite were not found to be suitable to immobilizing bacteria cells. It was concluded that the pore structure and the water absorption capacities of minerals are the main criteria to select a suitable carrier for bacteria cells. While the biological additive had not a significant impact on the initial setting time of cement-based mortar, the addition of bacteria cells decreased the early age compressive strength. Lastly, the mineral and bacteria addition increased the free drying shrinkage of the cement-based mortar.