Research On Mechanism And Performance Of High-strength Microbial Mortar

Microbial grouting reinforcement to repair the deterioration of masonrystructures involves injecting microorganisms and nutrient solution (a cementationsolution) into existing granular system pores to induce the generated calciumcarbonate cementation to form a microbial mortar of certain strength. Microbialgrouting reinforcement is used when traditional grouting materials, such as lime,cement and epoxy, cannot be employed. The effects of the main factors for thestrength formation of microbial mortar were systematically studied through the sandcolumn grouting model experiments, combined with microbial reinforcementsimplified model, the site filling experimental and theoretical simulation analysis, andthe preparation method of high-strength microbial mortar was found. The material andmechanical properties of microbial mortar with different intensity levels weresystematically and comprehensively tested and analyzed for the first time. A solidexperimental and theoretical basis was laid for the using of microbial groutingtechnology in high-quality reinforcement for historical masonry buildings. The mainresearch work and contribution are as follows:To improve the capacity of proliferative and urease-producing, the wild strain ofSporosarcina pasteurii was isolated and screened after NTG (Nitrosoguanidine)mutated. The urease activity of bacterium from different batches varies less, and thesecharacteristics can be genetically stably inherited. Meanwhile, ureolytic bacteriaisolated from soil which can withstand high concentration of urea and calcium ion, thestrain of UR49D is comparable with wild stain of S. pasteurii in urease activity andspecific urease activity, while the capability to keep a high in situ urease activity isbetter.Secondly, the controllable microbial grouting parameters, such as the fillingparticle size distribution, strains of the bacterium, gelling concentration, groutingtimes is optimized, uniaxial compressive strength of the microbial mortar iseffectively controlled, and microbial mortar samples with UCS2MPa to the55MPais successfully made.The mechanical properties of the microbial mortar, such as uniaxial compressivestrength, splitting tensile strength, compressive strength under cyclic loading anduniaxial compressive fatigue, were tested, and the crystal structure of the carbonatecementation and pore-size distribution of the microbial mortar were analyzed. The results indicate that in strength, deformation and durability, this new material issuperior to conventional cement–lime mortar. This new type of microbial mortar isideal for the in situ reinforcement of deteriorated masonry structures.By simplifying the reinforcement model and field test studies, we can find thatsome difficulties are still exist with the microbial grouting of small cracks, but thereinforcement structure with missing or hollowing part is relatively easy to implement,outdoor construction under low winter temperature should be avoid, reducing itsimpact to the microbial activity.Finally, through appropriate simplification, the relatively complex microbialmortar formation process of particles system is mathematical modeled. Theparameters changes such as calcium carbonate precipitation, urea concentration,porosity are simulated using a one-dimensional finite element program, providing atheoretical basis for high strength microbial grouting.