Bio-healing for micro-crack treatment in cementitious materials: Toward a quantitative assessment of bacterial efficiency

Bio-healing for micro-crack treatment in cementitious materials: Toward a quantitative assessment of bacterial efficiency

Ducasse-Lapeyrusse, J.
Gagné, R.
Lors, C.
Damidot, D.

2013-06-16

Bio-healing is a promising approach to enhancing natural self-healing and thus completely heal large micro-cracks (> 200 ?m) in cementitious materials. The aim of this research is to better understand bio-healing of cementitious materials in order to accelerate the healing kinetics and maximize sealing efficiency of large micro-cracks. The bio-healing approach generally consists in soaking micro-cracks in a culture medium containing a bacterial strain. However, it is difficult to precisely assess the efficiency of the bacterial-mediated precipitation in the bio-healing process with respect to the impacts of natural self-healing and precipitation induced by the culture medium. The aim of this work is to study the healing of well-defined micro-cracks on mortars subjected to more and more complex healing mechanisms. First, cracked mortars were subjected to natural self-healing, then to a precursor solution (calcium lactate), and finally, to a culture medium containing a bacterial strain. However, before this last step, an important part of this study focused on assessing the growth kinetics of a bacterial strain: Bacillus cohnii. Mortars specimens (W/C = 0.485) were submitted to controlled cracking at 28 days (under sustained load) using a mechanical expansive core. Two micro-crack categories were created (100 ± 5 ?m and 195 ± 30 ?m). The healing kinetics was evaluated from air-flow measurements that were used to compute the evolution, over time, of the apparent crack opening (1, 3 and 6 months of conservation at 23°C and 100% R.H.) Overall, self-healing was faster and more complete when cracks were soaked in calcium lactate solutions compared to natural healing. Thus, precursor solutions significantly improved the healing kinetics of the larger micro-cracks (> 150 ?m). On the other hand, the optimum growth conditions for Bacillus cohnii were evaluated at different nutrient concentrations and pH values. Finally, a method was developed in order to evaluate the bacterial activity semi-quantitatively.

mortar
bio-healing
self-healing
Bacillus cohnii
calcium lactate

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Conference proceedings

conference paper

(c) 2013 Ducasse-Lapeyrusse, J.; Gagné, R.; Lors, C.; Damidot, D.