A performance study of high-strength microbial mortar produced by low pressure grouting for the reinforcement of deteriorated masonry structures

Microbial grouting reinforcement to repair the deterioration of masonry structures involves injecting microorganisms and nutrient solution (a cementation solution) into existing granular system pores to induce the generated calcium carbonate cementation to form a microbial mortar of certain strength. Microbial grouting reinforcement is used when traditional grouting materials, such as lime, cement and epoxy, cannot be employed. In this paper, based on experimental study, the main biochemical factors that affect microbial mortar strength were investigated. In addition, the mixture ratio and laboratory preparation method for high-strength microbial mortars were determined. Microbial mortars of different strengths were successfully produced, through which the maximum uniaxial compressive strength reached 55 MPa. The mechanical properties of the microbial mortar, such as uniaxial compressive strength, splitting tensile strength, compressive strength under cyclic loading and uniaxial compressive fatigue, were tested, and the crystal structure of the carbonate cementation and pore-size distribution of the microbial mortar were analyzed. The results indicate that in strength, deformation and durability, this new material is superior to conventional cement–lime mortar. This new type of grouting is ideal for the in situ reinforcement of deteriorated masonry structures. The preparation method for high-strength microbial mortar, the material’s tested mechanical properties and the quantitative relationships of the material’s grouting parameters are reported. The material provides a novel method to reinforce deteriorated masonry structures, particularly historical masonry structures.

► High-strength microbial mortar with a UCS up to 55 MPa was obtained without cement.
► Splitting tensile strength was measured for both microbial mortar and cement–lime mixed mortar samples.
► Cyclic compressive loading tests were performed on both microbial mortar and cement–lime mixed mortar samples.
► The pore-size distribution of microbial mortar and cement–lime mixed mortar samples was measured.
► The crystal formation for in situ microbial induced carbonate precipitation was quantitatively analyzed.