Experimental Study On Reinforcement Of Aeolian Sand By Calcium Bicarbonate From Pseudo-karstification Solution

Desertification has directly threatened nearly a quarter of the world’s land area,and desert is widely distributed in our country.Severe weather such as sandstorm,floating dust and dust not only bring great threat to people’s life and health safety,but also seriously hinder the development of economy and society.Therefore,sand reinforcement and desertification control have always been important problems to be solved urgently in environmental engineering and geological engineering.This study based on the Calcium Bicarbonate from Pseudo-karstification improved soil reinforcement technology,which is environmental friendly,developed a device for preparing CFPK solution under constant temperature and high pressure conditions.The prepared CFPK solution was used to reinforce the aeolian sand.The effects of calcium carbonate source,carbon dioxide pressure,temperature on CFPK solution concentration and CFPK solution solidified sand were studied by conductivity test,surface strength test,wind erosion test,X-ray diffraction test and scanning electron microscope test and so on.The mechanism of strengthening aeolian sand by CFPK solution was revealed.The conclusions are as follows:(1)Invent a device for preparing CFPK solution under constant temperature and high pressure.The operation process is simple,and the raw material sources are extensive,which can achieve high purity and high concentration saturated calcium bicarbonate solution.(2)Calcium carbonate source has almost no effect on the concentration of CFPK solution,but the reaction rates of different calcium carbonate sources are different,and the reaction rate of heavy calcium carbonate is the fastest.Due to the high aggregation and high compactness of calcium carbonate crystals generated when heavy calcium carbonate is used as calcium carbonate source,the surface strength and wind erosion resistance of solidified sand using heavy calcium carbonate as calcium carbonate source are better than that of pure calcium carbonate,biological calcium carbonate and light calcium carbonate.(3)With the increase of carbon dioxide pressure and the increase of CFPK solution concentration,the calcium carbonate content,surface strength and wind erosion resistance of solidified sand are continuously enhanced.An irregular hexahedral calcium carbonate crystal formed by the decomposition of calcium bicarbonate from pseudo-karstification between sand particles and on sand surfaces.The different properties of solidified sand at different carbon dioxide pressures are mainly due to the different amount of calcium carbonate crystals formed.The higher the carbon dioxide pressure is,the more calcium carbonate crystals formed.(4)When the carbon dioxide pressure did not exceed 3 MPa,the concentration of CFPK solution first increased and then decreased with the increase of temperature,and the surface strength and wind erosion resistance of solidified sand also increased first and then decreased.When the pressure was 4 MPa,with the increase of temperature,the concentration of CFPK solution gradually decreased,and the surface strength and resistance to wind erosion of solidified sand also gradually decreased.The main reason for the above properties of solidified sand at different temperatures is that the volume of newly formed calcium carbonate is different.When the temperature is lower,the volume of the newly formed calcium carbonate crystals is larger.When the temperature is higher,the volume of the new calcium carbonate crystals is smaller,and the small crystals are connected with each other,and there are gaps of different sizes and shapes between the crystals.(5)When CFPK solution is sprayed on the surface of aeolian sand,calcium bicarbonate will decompose and form calcite calcium carbonate with cementation and filling effect,which improves the integrity of solidified sand surface and enhances its surface strength and wind erosion resistance.In order to improve the curing effect of CFPK solution,it is recommended to choose heavy calcium carbonate as the calcium carbonate source for the preparation of calcium bicarbonate from pseudo-karstification solution,and to increase the carbon dioxide pressure as much as possible.When the carbon dioxide pressure is 1MPa,the temperature is selected at about 35℃.When the carbon dioxide pressure is 2-3MPa,the temperature is about 25℃.When the carbon dioxide pressure is 4MPa,the temperature should be below 15℃.