Study of autonomous filling by bio calcite produced by Bacillus Pseudofirmus on Portland cement pastes

Micro-cracks in concrete cause aesthetic inconvenience and can induce possible forms of deterioration. In this context, the present work discusses an autonomous process to fill surface micro-cracks using a bacterial bio-mineralisation process. Indeed, Bacillus Pseudofirmus can develop carbonate bio-deposition while developing in an alkali and high pH that is not dissimilar to the cementitious environment. The objective of this work is to study the possibility for this bacterial strain to develop bio-deposition on different cementitious cements (CEM I, CEM II/A, CEM III/A). The question is whether the deposits develop and are capable of filling a hole in the various cements, how long it takes them to do so, and what quality of carbonates they form in terms of mineralogy and deposit structure. After preparing an endospore storage solution and defining its bio-mineralization media, initial tests conducted on gelatinous agar optimal environment were carried out to validate the process. The endospores and the mineralization media were then applied on many cement pastes samples (plates with a groove and holes placed in cement). The results show the development of bio-deposition in all three cementitious environments. The bacterial strain was found to be capable of filling a hole of 1 mm diameter in less than 3 weeks. Compared to a laboratory environment (Petri dish with agar) it was noted that carbonated phases (calcite, Mg-Calcite, etc.) can include impurities which come from soluble elements of the cement while the structure of the deposition is also different. • Bacillus Pseudofirmus enabled calcite mineralization on 3 pure cement pastes • Bacillus Pseudofirmus enabled the complete filling of 9 mm3 holes in cement pastes • The bio-induced precipitation of calcite leads to the coating of bacterial cells