Experimental Study On The Influence Of Moisture Content On Thermal Conductivity Of Lightweight Insulating Concrete

Since lightweight insulating concrete has better thermal insulation properties,and the block made of it can significantly save construction supplies,lightweight thermal insulation concrete was widely used in engineering.In the process of building energy consumption calculation,the thermal conductivity of materials is usually taken as the fixed value under the normal temperature and dry state.However,the lightweight insulating concrete material has a high porosity and a wide distribution of pores,which makes the thermal conductivity change obviously with the environmental humidity.Therefore,in the high-humidity areas,when the thermal conductivity of lightweight insulating concrete is taken as the fixed value in the dry state,the calculation of building load and energy consumption will be inaccurate,which will lead to the deviation of equipment selection.Because of the above problems,this paper studied the commonly used thermal conductivity test method and the preparation schemes of wet materials,analyzed the applicability and uncertainty of the experimental program for porous building materials theoretically.Besides,this paper uses different test methods of thermal conductivity and the preparation schemes of wet materials to carry out pre experiments,tests the thermal conductivity of dry materials at different temperatures,obtains the balanced wetted materials with different moisture content,and proves the test method of thermal conductivity of wetted materials through comparative experiments.Finally,the experimental results were compared and analyzed,the applicable range of different thermal conductivity tests and wet material preparation schemes were obtained.A reliable experimental scheme for studying the influence of moisture content on the thermal conductivity of porous building materials was established.According to the experimental scheme determined in this paper,the aerated concrete(AC)and foaming cement(FC)commonly used in engineering,new coral sand concrete(CSC)and aerogel-incorporated concrete(AIC)being developed are chosen as typical experimental materials to carry out experiments and analyze concretely.The SEM and porosity of the material were obtained by using scanning electron microscopy and mercury porosimeter to characterize the microstructure and pore size distribution of the material.To obtain the influence of temperature on the thermal conductivity of the dry material and compare the changes in thermal conductivity of wetted materials under different humidity,the thermal conductivity of dry materials was measured by using the steady-state method.To study the influence of moisture content on the thermal conductivity of materials,the balanced wetted materials at different humidity were obtained by constant temperature and humidity culture method.Meanwhile,the moisture absorption equilibrium process and the sorption isotherms of materials were obtained,the thermal conductivity of materials under different humidity was tested by the transient method.To characterize the hygroscopic property of the materials,the water absorption coefficient of the materials was tested by the self-built experimental device.Combined with the pore structure and hygroscopic property of the material,the influence of moisture content on the thermal conductivity of lightweight insulating concrete materials was analyzed.Experimental research shows that the thermal conductivity of lightweight insulating concrete is little affected by temperature and does not increase monotonically with increasing temperature.At 20~50℃,the thermal conductivity of FC increases by 6.82%,whereas that of AC increases by 5.16%,CSC increases by 0.47%,AIC increases by an average of 11.55%;The effect of moisture content on the thermal conductivity is obvious,which is positively related to the hygroscopic property and porosity of the material;The change in thermal conductivity with relative humidity can be divided into three stages and can be fitted to a polynomial function.When the relative humidity changes from 0% to 100%,the thermal conductivity of AC increases by an average of 89.35%,whereas that of CSC increases by an average of 39.25%,FC increases by an average of 73.85%,AIC increases up to 76.33%.