Abstract
The application of bacterial urease driven carbonate precipitation has led to the development of a new biomaterial thatcanfillthecracks and pores of concrete automatically. In the structures, concrete cracks are formed due to different factors such as sustained service loads. Accordingly, increasing crack width facilitates permeation of aggressive liquids and/or gases in the concrete elements which results in considerable damages in reinforced concrete members. In this study, the effect of sustained service loads on the steel corrosion and self-healing process of reinforced concrete beams containing Sporosarcina pasteurii bacteria have been investigated. Therefore, bio-treated concretes containing culture medium and calcium nitrate-urea or calcium chloride-urea as bacteria nutrients were used in the mix designs. The physical, mechanical and hydraulic properties of bio-treated concretes (e.g., compressive strength, flexural bearing capacity, water flow through the cracks, and microstructural tests) were characterized to evaluate the performance of biological self-healing. Results showed that the compressive and tensile strength of bio-treated samples were increased relative to the control treatment by 44% and 36%, respectively. In addition, water flow tests showed that the bio-treated concretes are able to completely fill the cracks. However ultrasonic measurements as well as recovered tensile strength tests revealed that the healing is not complete, where up to 84% of healing degree was seen in the bio-treated concretes. Although applying the service loads significantly delays the self-healing process, the bio-treated concrete beams were completely healed up to 28 days of re-curing in the water flow test, where a slight healing was observed for the control beams. Moreover, results revealed that the corrosion probability of the reinforcements decreased when calcium nitrate used as bacteria nutrient, but it is significantly increased in case of calcium chloride usage. Finally, the morphology of precipitated CaCO3 crystals showed that CaCO3 was mainly precipitated in the form of calcite and vaterite crystals.
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