Experimental Study on Urease Activity and Cementation Characteristics of Soybean

A new and more ecologically sound cementing material known as "bio-cement" has been found to have the capacity to consolidate loose gravel into sand columns offering a certain degree of strength, and to fill and repair cracks in concrete to restore resilience. The typical representative is the microbial induced calcium carbonate deposition technology(MICP) and enzyme induced calcite precipitation (EICP). As part of this research, EICP with soybean urease as the core was studied. The test results show that soybean urease activity is significantly affected by pH and urea concentration values, while the external nickel source is not found to impair a stimulating effect on activity. When the concrete specimens were immersed in the composite solution of soybean urease, urea, and calcium chloride after having been subjected to a high temperature, a continuous layer of white precipitations quickly appeared on the surface of the specimens. Measured using a metalloscope, the thickness of the precipitations was found to reach up to 2.0 mm, while the surface water absorption rate was reduced by 70%. The effects of this combined outcome are believed to significantly protect and improve the durability of the concrete specimens previously subjected to a high temperature. At the same time, the composite solution is shown to be capable of cementing fly ash, with the cubic strength of the finished samples reaching 4.0 MPa after 3 days. Results from the use of a scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction(XRD), reveal that both the white precipitations on the surface of the concrete specimens and the cement binding the fly ash particles are calcite crystals. It is concluded from these preliminary study results that the use of soybean urease as a bio-cement had proved successful.