Towards a Bacteria-Based Agent to Make Concrete Self-Healing
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Towards a Bacteria-Based Agent to Make Concrete Self-Healing Renee M. Mors1 and Henk M. Jonkers1 1 Materials & Environment, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600 GA Delft, The Netherlands ABSTRACT A bacteria-based healing agent for concrete is currently under development in the Microlab of TU Delft. The agent consists of organic mineral precursor compound and bacteria in a protective reservoir. Cracks in the concrete matrix may be sealed and blocked by calcium carbonate based crystals, formed by bacterial conversion of mineral precursor compound. Given the solubility of the agent components, healing agent material may be prematurely released during the wet mixing stage, potentially influencing cement hydration and functionality of other concrete additions. Several materials have been selected as potential mineral precursor compound, being organic salts and a carbohydrate. Tests on standard mortar specimens show that strength development is not compromised when calcium lactate is added to the standard mixture. Calcium lactate was added to the mortar mixture either pure or in combination with a superplasticizer, either based on sulfonated naphthalene or modified polycarboxylate ether, to determine possible interferential effects.
INTRODUCTION Since 2006 a bacteria-based self-healing concrete is being developed in our laboratory. A two-component healing agent is added to the concrete in dry form during the mixing stage [1]. The healing agent consists of spore-forming alkali-resistant bacteria and organic feed, serving as mineral precursor compound for crack healing. Upon cracking of the concrete matrix incoming water contacts the released healing agent contents. The water activated bacteria subsequently convert the present feed into calcium carbonate based minerals. Precipitation of mineral crystals on the crack surface seals and plugs the cracks, making the concrete matrix less permeable to water and other deleterious substances. The organic feed, i.e. the mineral precursor compound, is incorporated together with bacterial spores in dry form in a reservoir. The reservoir-contained agent is to be added to the mortar at the mixing stage, being a wet process. Contact with mixture make up water may cause some premature healing agent dissolution, resulting in a release of healing agent content into the mixing water. Here the organic material has the potential to interact with the cement hydration process and/or affect mixture workability properties. This paper presents bending and compressive strength development of several mortar mixtures containing healing agent compounds. A number of organic salts and a carbohydrate were tested for suitability as bacterial feed as well as for negligible retardation of concrete setting. Of all compounds tested, only calcium lactate appeared suitable and was therefore chosen for further testing. Additional tests for determining effect of calcium lactate addition in combination with two types of superplasticizer on mixture workab
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