Study On The Strength And Microstructure Of New Type Of Grouting Material

With the deepening of urbanization,the development and utilization of urban underground space has become the focus of national construction.For some underground projects in complex strata,especially in soft clay layer with high water content and sand layer with high liquefaction degree,ordinary cement-based grouting materials cannot meet people's requirements for large tunnel projects,since they have some defects such as poor water-solubility and low early strength and they are vulnerable to groundwater dilution and easy to be sedimented to layers.New type of grouting material has the characteristics of rapid setting,early strength,high stone rate,high water content and economic environment,which can be used as an excellent grouting material.In order to improve the strength characteristics of new type of grouting material so that it can be more widely used,studying on the influence of raw materials on strength and microstructure of new type of grouting material is necessary,because it will be helpful to understand the mechanism of new type of grouting material.Effect of lime,SiO₂,water to binder ratio and curing age on strength of new type of grouting material is analyzed by test.Different limes have different impacts on new type of grouting material with different water to binder ratios.When the water to binder ratio is 1.0,the strength of new type of grouting material increases with the increasing content of CaO in lime.When the water to binder ratio is 2.0,the situation is opposite.Different kinds of Si O₂ have different effect on new type of grouting material.The addition of micro-SiO₂ improves the strength of new type of grouting material by about 5%when the mix formulations are reasonable,while the addition of nano-SiO₂ causes about 20%strength loss of new type of grouting material.The strength of new type of grouting material decreases when the water to binder ratio increases,when the water to binder ratio increases by 0.5,the strength decreases by about 40%.With the increasing of curing age,the compressive strength of new type of grouting material increases,while the Bending strength increases before decreasing.Effect of lime,SiO₂,water to binder ratio and curing age on pore structure of new type of grouting material is also analyzed by BET and MIP test.For new type of grouting material with water to binder ratio of 1.0 and 1.5,the pore volume of pores with pore diameter of 0-200 nm accounts for 14.61%-19.98%,and that of 200-1000 nm makes up 61.55%⁷7.06%,and the volume percentages of pore with pore size of 1000-10000 nm and with pore size more than 10000nm are 3.56%²0.09%and 2.57%³.40%,repectively.The test shows that new type of grouting material is a kind of large porous material.The pore test results of new type of grouting material are consistent with the results of strength test.New type of grouting material with lower strength has bigger pore volume and has more apertures which are in large pore size.The influence of lime,SiO₂,water to binder ratio and curing age on hydration products,mainly include the phase composition and microstructure,of new type of grouting material is studied by TGA-DSC and SEM analysis.The curves obtained by TGA-DSC test show 3 distinct endothermic peaks near 90°C,230°C and 660°C,indicating that the main hydration products of new grouting material are ettringite,gibbsite and C-S-H/C-A-S-H gel;SEM-EDS analysis obtained the same conclusion.When the amount of the above hydrtion products is larger,the microstructure of new grouting material is more compact and thus the macroscopic strength is better.Using 3D-XRM system and 3D visualization software to realize 3D reconstruction of new type of grouting material.The quantitative analysis on each composition is made from the 3D reconstruction model of new type of grouting material.This test provides a reference method to study the microstructure of new type of grouting material.Compared the results obtained by the three different methods of measuring pore used in this study,and it is concluded that each method has its own advantage:BET is more suitable for testing pores with pore diameter of less than 50nm;3D-XRM shows superiority in testing micron-level pores;MIP is able to demonstrate the pore size distribution of the new grouting material more completely.