Study On Mechanical And Thermal Properties Of Greenhouse Walls Solidified With Fibers And Microorganisms

The rise of"Gobi agriculture"effectively alleviates the conflict between grain and vegetable land competition.Greenhouse planting makes use of the abundant light resources in Hexi Corridor,which improves the utilization rate of non-arable land and benefits thousands of families with out-of-season fruits and vegetables.In the Gobi area greenhouse wall practices such as rammed earth wall,sand bag wall,cement wall and other generally large thickness,long distance transportation of materials also increases the time limit and cost,if the future greenhouse abandoned and easy to cause resource waste and environmental pollution,so still need to actively explore the new wall practices suitable for the Gobi greenhouse.In recent years,the emerging microbial curing technology（MICP）can consolidate loose sand and stone into a whole,and has the advantages of simple operation,small construction disturbance,environmental friendly,and is widely used in the repair of concrete cracks,soil reinforcement,ancient building restoration and other fields.MICP technology can make use of the abundant sand and stone resources in the Gobi area.After solidification,it can be used as the material for the construction of greenhouse wall,which is both economical,environmental protection and efficient.At the same time,combined with fiber reinforcement technology,it not only improves the brittle failure and poor uniformity in MICP reinforcement,but also promotes the overall strength and stability of the solidified sample.This paper uses fiber combined MICP technology to consolidate sand and stone,and explores the feasibility of application in the construction of greenhouse enclosure structure from two perspectives of mechanical and thermal properties.The main conclusions are drawn as follows:（1）The MICP technology combined with fiber can improve the CaCO₃precipitation amount,dry density,impermeability and strength of the sample.The highest CaCO₃ precipitation amount is 18.43%when cotton fiber is mixed with 0.4%,the lowest permeability coefficient is when polypropylene fiber is mixed with 0.4%,and the dry density of the sample is about 12%higher than that of the plain sand sample.The compressive strength of the sample is positively correlated with the amount of CaCO₃ precipitation in the sample.The UCS of the sample increases by 17.5%compared with that of plain sand when the content of polypropylene fiber is 0.4%-0.6%.According to various indexes,the fiber content should be 0.4%-0.6%,and the curing effect of combined polypropylene fiber is the best.（2）The co-curing mechanism is analyzed from macro and micro perspectives.Firstly,the encapsulation of CaCO₃ increases the biting force between sand grains and between fibers and sand grains,and the cementation of CaCO₃ strengthens the"anchoring and reinforcing"effect of fibers.Second,the fibers form a spatial network structure in the interior,which inhibits the relative displacement of sand grains under load,and produces a certain tensile stress to restrain the strength loss and crack development.Through the calculation of the bearing capacity of MICP cured wall,it is concluded that the vertical pressure on the upper surface of the wall is 15.215k N,and the pressure on the lower surface is 184.82k N.The cured wall meets the bearing capacity requirements.（3）The CaCO₃ filling void increases the heat conduction of the material,which adheres to the sand and fiber to form a CaCO₃"thermal bridge",and assumes the heat transfer between sand particles.When the two kinds of wall thickness is the same,the thermal conductivity and heat storage coefficient of MICP solidified wall are lower than that of rammed thick earth wall,and the thermal resistance is higher,indicating that MICP solidified wall has better thermal insulation performance,heat storage performance is slightly lower than that of rammed thick earth wall,but the high thermal inertia index is more conducive to creating a stable greenhouse thermal environment.By simulating the temperature field in the wall,it is found that the thickness of the heat stabilization layer can be appropriately reduced to increase the cultivated land area,indicating that the application of MICP technology in the construction of greenhouse wall has a certain feasibility.