Research On Sand Cementation And Concrete Cracks Repairment By Microbially Induced Carbonate Precipitation Technology

Microbially induced carbonate precipitation technology is a latest progress inbio-mineralization. The technology uses the Sporosarcina pasteurii and nutrientsolution (mixture liquid of urea and calcium salts) to induce calcium carbonatecrystallization with higher adhesive properties. It can not only bond sand particle toprepare high-strength microbial mortar used for repairing concrete cracks, but alsodirectly fill the crack to get strength and improve durability as well. This technologyprovides a new method for repairing concrete cracks.Firstly, this paper uses biochemical method for analysis of some factorsinfluencing urease activity. It has been found that Sporosarcina pasteurii has betterurease activity in conditions of temperature between40~50℃, pH value of alkalineenvironment in9and low calcium concentration, which lays the foundation for thefollow-up test.Secondly, an alternative source of calcium other than CaCl2should be selectedaccording to the requirement of the technology applying to concrete. Before applicationof concrete, microbial mortar with different strength grades was prepared with CaCl2,Ca(NO3)2and Ca(CH3COO)2, then the differences in mechanical properties andphysical properties were compared. The results showed that, in the same batches ofgrouting(1~3) and the same bacteria activities (1.1~2.35), the uniaxial compressivestrength and splitting tensile strength of Ca(CH3COO)2, samples reached1.3~2.4timesof those of CaCl2samples. The former has a more uniform pore distribution, and itsmineral composition is acicular aragonite. It approved that Ca(CH3COO)2can be thealternative source of CaCl2.Next, the influencing factors of mineral composition and crystal morphology ofcalcium carbonate precipitation were explored. It has been found that the type andconcentration of calcium source, the concentration of bacterial suspension, the testenvironment can all affect the crystal structure and morphology of calcium carbonate.Moreover, the acicular aragonite only can be product in the sand column cementitiousenvironment with the introduction of Ca(CH3COO)2 Then, research of different calcium sources used for microbial crack repairtechniques and microbial surface coating technology was conducted. The crackedcement mortar specimens has been successfully bond by grouting and the flexuralstrength was restored to350kPa. The water absorption rate decreased by10%usingbruising method on the surface of cement mortar. Little effect difference has beenshown with several calcium sources.Finally, a field test has been conducted by the MICP technology to treatabasement leakage. After grouting, the results of permeability field test,ultrasonic measurement, ground penetrating radar detection, concrete coringobservation, XRD analysis and SEM analysis show that the treated soil becomesdenser and more uniform; there is lots of CaCO3precipitation in the crack，thereis little water leakage in the basement when subjected to raining after fourmonths.