Experimental Study On Meso-structures Of MICP-treated Calcareous Sand Based On CT Image Processing

Microbial-induced calcite precipitation(MICP)is a promising method to improve soil properties by using microbial activities to decompose urea and induce cement.The voids of Soil are filled with cement and the soil particles are bonded by cement so that the loose soil is cemented into consolidated soil with integrity.Therefore,the mechanical properties of soil are improved.At present,the research on MICP-treated calcareous sand is mainly focused on its macroscopic mechanical properties and microstructure,but little attention is paid to the mesostructure.The study of meso-structure is helpful to understand the macroscopic physical and mechanical properties of MICP treated calcareous sand.In order to study the meso-structure of MICP-treated calcareous sand by the CT scan.In this paper,microbial-induced strontium carbonate precipitation(MISP)treated calcareous sand is adopted.Biomineralization tests were carried out in different strontium chloride concentration solutions.Unconfined compressive strength test,X-ray diffraction analysis(XRD),scanning electron microscopy(SEM),and mercury injection porosimetry(MIP)analysis were carried out to research the physical and mechanical properties and microstructure of MISP-treated calcareous sand,and to analyze the difference between the MISP-treated calcareous sand and the MICP-treated calcareous sand.The CT scan was used to obtain the fault image of the MISP-treated calcareous sand to realize 3d visualization of meso-structure of the MICP-treated calcareous sand.Qualitative and quantitative analysis of meso-structure of MICP-treated calcareous sand was conducted based on a 3D meso-structure reconstruction model of the MISP-treated calcareous sand.The main conclusions are as follows:(1)There are differences in the crystal structures of cement between the MISP-treated calcareous sand and the MICP-treated calcareous sand,but they are consistent in the macroscopic mechanical behaviors.The mechanism of the MISP-treated is consistent with the MICP-treated.Meso-structure of the MICP-treated calcareous sand and the MISP-treated calcareous sand is generally consistent and can be characterized and studied mutually.(2)Scanning the untreated calcareous sand and the MISP-treated calcareous sand by micro-CT scan to obtain the CT images of the meso-structure.The best way of the CT scan image processing was obtained.3d visualization of the MISP-treated calcareous sand mesostructure model and qualitative analysis of meso-structure characteristics of the MISP-treated calcareous sand was achieved.(3)MICP-treated can fill the pores of calcareous sand and change the shape of pores.MICP-treated reduces the proportion of long columnar pores in calcareous sand so that the permeability of calcareous sand reduces.Most of the cement is connected and forms the cement skeleton rather than just sticking to the surface of the calcareous sand particles.And with the number of grouting increases,the proportion of cement in the skeleton is higher,which is beneficial to improve the strength of microbial solidified calcareous sand.(4)The CT scan test is more favorable for characterization of the large pore diameter,and the MIP test is better to study the small pores.In the MIP test,the large pores easily infiltrated are easily neglected.However,the CT scan test is not good to study the pore diameter which is close to voxel size.The CT scan image analysis and MIP analysis should be coordinated to characterize the MICP-treated calcareous sand microstructures.