A synergistic approach to microbial presence on concrete: cleaning and consolidating effects

Biological techniques for cleaning and repair of concrete and stone can be an ecological alternative to traditional conservation techniques. Weathered concrete samples fouled by lichens were treated with Thiobacillus bacteria and an appropriate nutrient, by submersion or sprinkling. The general effect of cleaning was documented by the use of colorimetry and microscopy. For remediation of decayed concrete, biomineralisation of mortar samples of different porosity by ureolytic sludge was tested. For the most porous mortar samples and when urea, nutrient broth and an external calcium source were provided, the amount of water absorbed after 200 hours was decreased by a factor of five compared to untreated samples. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses revealed a dense layer of calcite and vaterite crystals.