Use of bacteria to repair cracks in concrete
ABSTRACT As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique is investigated in this study. Ureolytic bacteria such as Bacillus sphaericus are able to precipitate CaCO3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated crystals can thus fill the cracks. The crack healing potential of bacteria and traditional repair techniques are compared in this research by means of water permeability tests, ultrasound transmission measurements and visual examination. Thermogravimetric analysis showed that bacteria were able to precipitate CaCO3 crystals inside the cracks. It was seen that pure bacteria cultures were not able to bridge the cracks. However, when bacteria were protected in silica gel, cracks were filled completely.
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ABSTRACT: Bacterial carbonate precipitation, which is based on urea hydrolysis, has been used as a surface treatment technique to decrease the permeation properties of concrete. Since permeability acts as the main reason of concrete degradation in harsh environments, this study evaluates microbial surface treatment in order to prevent sulphate ions penetration. Five groups of concrete specimens were cast and cured and were then surface treated applying three different microbial suspensions employing Sporosarcina pasteurii, Bacillus subtilis and Bacillus sphaericus bacteria. Durability was assessed through the mass losses, volume changes (expansion), water absorption and compressive strength. In order to consider further permeation properties, chloride penetration of biologically treated concrete was examined by a rapid chloride permeability test (RCPT). Experimental results and a durability loss index (DLI) indicated that biological surface treatment reduces concrete degradation in sulphate environments and improves durability characteristics. Also, the RCPT results confirmed that this technique limits chloride penetration into the concrete.Biosystems Engineering 05/2015; 133. DOI:10.1016/j.biosystemseng.2015.03.008 · 1.37 Impact Factor
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ABSTRACT: A novel chemical self-healing system based on microcapsule technology for cementitious composites is established. The key issue for such a system is how to release the healing agent and how to activate the healing mechanism. The present study focuses on the release behavior. The smart release behavior of the healing agent in the microcapsule is characterized by the EDTA (Ethylene Diamine Tetra-acetic Acid) titration method. The experimental results show that the release of the corrosion inhibitor covered with polystyrene resin (PS) is a function of time, and is controlled by the wall thickness of the microcapsule. Moreover, the pH value affects the release rate of the corrosion inhibitor; the release rate remarkably increases with the decreasing pH value.Cement and Concrete Composites 11/2014; 56. DOI:10.1016/j.cemconcomp.2014.10.006 · 2.76 Impact Factor
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ABSTRACT: The concept of self-healing, whereby materials such as polymers, composites and cementitious construction materials are able to sense damage or deterioration and regulate, adapt and repair themselves automatically, is applied here to natural and anthropogenic soil structures. Damage in such structures can be difficult to detect and monitor, and will have significant consequences, but maintenance and repair are costly and disruptive. This paper presents an overview of the self-healing concept, its potential within geotechnical engineering and results from preliminary experiments exploring the potential for self-healing through the actions of living organisms such as bacteria. We report a simple experimental example, which demonstrates the potential for bacterial activity in microbially induced calcium carbonate precipitation of coarse-grained soils to persist and heal damage. Sands stabilized through calcium carbonate precipitation effected by Sporosarcina pasteurii were sheared and rehealed with only additional supply of nutrients, recovering a proportion of the original strength. This example is a simple demonstration of the ability of living organisms to adapt and respond to damage, and suggests the potential for this ability to be harnessed by engineers to design structures that can heal themselves.7th International Congress on Environmental Geotechnics, Melbourne, Australia; 11/2014