Study On Thermal Conductivity Of Modified Raw Soil

With the acceleration of urbanization,the increasing building waste and the increasingly severe building pollution,earth building has become the focus of scholars all over the world because of its green and environmental protection ecological function.Loess has a long history of application as an earth building material in China.Inspired by the rejuvenation of buildings with earth,people usually add a certain amount of modifier,like cement and fibers,to the soil in order to obtain higher engineering mechanical properties of soil and to make the earth building stronger.The thermal conductivity,heat transfer and heat storage characteristics of loess and its modified soil can significantly affect the thermal insulation and heat dissipation effect of buildings.In this study,loess,cement-stabilized soil and polypropylene fiber-reinforced cement-stabilized soil are taken as research objects.The effects of water content,dry density,cement dosage and curing age on thermal conductivity of loess and modified raw soil are studied by thermal conductivity test.The causes of thermal conductivity test results are discussed by XRD and mercury injection test.Then,the finite element software ANSYS is used to analyze the thermal conductivity of loess and modified soil.A model of temperature field distribution in solar greenhouse with different modified soils as thermal insulation wall under extreme temperature load is established.The results are as below.(1)Water content and dry density have significant effects on thermal conductivity of soils.The thermal conductivity of loess,cement-stabilized soil and polypropylene fiber reinforced cement-stabilized soil increases with the increase of soil water content and dry density.(2)The influence of cement content on the thermal conductivity of solidified soil is not obvious.The thermal conductivity of solidified soil will be reduced by adding polypropylene fiber.Under the same conditions of water content and K,the thermal conductivity of cement-stabilized soil is always greater than that of polypropylene fiber reinforced cement-stabilized soil.(3)Curing age has no significant effect on thermal conductivity of solidified soil.When the curing age is 7 days,14 days and 28 days,the thermal conductivity of the solidified soil is lower than that of the solidified soil before initial setting.The relationship between thermal conductivity and water content of solidified soil with different cement content in different curing age tends to be a fitting line.Under different compaction conditions,the fitting lines of thermal conductivity-water content relationship of solidified soil are approximately parallel.(4)The mathematical model of thermal conductivity of loess is established.The model takes into account the contribution of thermal conductivity of different mineral components to the thermal conductivity of loess,and also the influence of pore water distribution on the thermal conductivity of loess.Comparing the predicted value with the experimental data,the predicted value matches the measured value favorably.(5)The heat transfer models of loess,cement-stabilized soil and polypropylene fiber reinforced cement-stabilized soil were solved by finite element analysis software ANSYS.Taking the solar greenhouse as the engineering background and the actual temperature change in winter in Northwest China as the load,the temperature changes in the wall and the greenhouse when the building materials of the wall are loess,cement-stabilized soil and polypropylene fiber reinforced cement-stabilized soil respectively are analyzed.The temperature field distribution of the greenhouse is further simulated,and the thermal insulation performance of the three building materials is evaluated comprehensively.