Experimental Study On Sand Soil Reinforcement By Microorganism Combined With Carbon-based Materials Induced Calcium Carbonate Precipitation

The emergence of microbial induced calcium carbonate precipitation(MICP),a biomineralization technology,has attracted the attention and research of researchers in many fields.MICP technology has good cementation and curing properties and is a potential environmentally friendly foundation and edge slope improvement technology.Based on this technology,the cementation and solidification of sandy soil were studied by utilizing the urease-producing bacteria streptomyces palustris,and activated carbon and activated carbon fiber as a carbon-based material combined with urease-producing bacteria to induce calcium carbonate precipitation.The specific contents of this paper are as follows:(1)For the cementing and solidifying test of the different content with activated carbon materials,the cementing solution with different pore volume and the bacterial solution with different pore volume are considered firstly to received the suitable injection dosage.The test results were evaluated by analyzing the solid bacteria rate in the process of MICP treatment,calcium carbonate content,the relationship between calcium carbonate content and solid bacteria rate,unconfined compressive strength,the relationship between unconfined compressive strength and calcium carbonate content,X-ray diffraction analysis(XRD)and scanning electron microscopy(SEM).The test concluded that: The dosage of the cementing solution plays an important role in the production of calcium carbonate and the improvement of the mechanical properties of the test piece.As the dose of cementation solution increases,the calcium carbonate content and mechanical properties are gradually improved.But the injection of more doses of bacteria solution(more than 1.4 times the pore volume)will almost no effect on the increase of calcium carbonate content and mechanical properties.Compared with the control test piece without adding activated carbon material,the solid bacteria rate is gradually increased with the increase of the amount of activated carbon material.The calcium carbonate content produced by the MICP cementation test and the mechanical properties of the cured molded specimens gradually increase with the increase of the amount of activated carbon.(2)Based on the optimized dosage of the solution of the bacteria and the cement solution,grouting reinforcement test was carried out for mixing activated carbon fiber materials with different contents.The test results were evaluated by analyzing solid bacteria rate,calcium carbonate content,the relationship between calcium carbonate content and solid bacteria rate,unconfined compressive strength and tensile strength under saturation and drying conditions,the relationship between unconfined compressive strength and tensile strength and calcium carbonate content,water absorption rate,softening coefficient,compression-tension ratio,X-ray diffraction analysis(XRD),electron microscopy scanning(SEM).The test concluded that: The solid bacteria rate,calcium carbonate content and mechanical properties of the specimens in the MICP cementation test of activated carbon fiber materials are also gradually increased with the increase of the amount of activated carbon fiber materials.With the increase of the content of activated carbon fibers,the water absorption of the specimens decreases gradually,the softening coefficient increases,and the compression-pull ratio increases compared with the control specimens.(3)Microscopic test results show that the addition of carbon-based materials(activated carbon and activated carbon fibers)does not change the type of calcium carbonate crystals produced in MICP cemented specimens.and most of them are vaterite and aragonite crystals.In addition,a large number of needle-cluster aragonite crystals appeared in the cementing and curing specimens of activated carbon fibers,and needle-cluster aragonite crystals are unique to aragonite,which can improve the mechanical properties of calcium carbonate products.