Study on the adhesion of bacterially precipitated biocement to different stone substrates

Biocementation, or MICP (Microbiologically Induced Calcite Precipitation), has been used with success to repair cracks and consolidate porous stones and other construction materials. An experimental study was performed to investigate biocement adhesion to three different stone materials (limestone, shist and basalt) and to a poly methyl methacrylate (PMMA) control plate. Adhesion strength was quantified by pull-out tests performed under controlled conditions, this being the novel contribution of this paper. The mineralogical composition of the materials, roughness and contact angles with the treatment solutions were determined to better understand adhesion mechanisms. The thickness of the biocement coating on the different materials was measured and visualized under microscope, aiming to conclude that the biocement adheres to the porous and rough stone substrates, which serve as nucleation sites for the precipitation. Adhesion measurements were done after 2 and 4 treatments to understand biocement coating process and the influence of the thickness of the precipitated layer. The adhesion forces recorded, although affected by experimental error, allow understanding that detachment occurs between the precipitate and the substrate. The results suggest that time may affect this adhesion due to the creation of more bacterial attachment and because the thickness of the biocement layer has increased. • The best results were found for stones having calcium minerals (limestone and the basalt investigated). • Polymeric materials such as PMMA are not adequate for this treatment. • The biocement layers precipitated are thin (around 0.2 mm) and may have flakes that do not contribute to adhesion. • The detachment of the biocement occurred in the contact between the biocement and the stone.