Experimental Study On Mixture Proportion Design And Drying Shrinkage Characteristics Of Foamed Concrete

Foamed concrete has the advantages of light weight,thermal insulation,fire resistance,sound insulation and seismic resistance,and is widely used in various engineering fields.The porosity of foamed concrete is the key to determine the performance.At present,the mix proportion design method of foamed concrete is based on dry density,and the porosity needs to be estimated by experimental measurement or theoretical formula.Therefore,it is necessary to study the mix design method based on porosity.The drying shrinkage rate of foamed concrete is 6～10 times of ordinary concrete,which is more harmful to the function and use of foamed concrete.It is necessary to study the relationship between porosity and drying shrinkage.In this paper,the basic properties of foaming agent were determined,and the foaming agent with good stability was selected to prepare foamed concrete.The mix design method of foamed concrete with porosity as the design goal was established,and the accuracy of the mix design method was verified by experiments.The effects of porosity on physical properties,mechanical properties,thermal properties and durability were studied.The change of drying shrinkage rate of foamed concrete with drying time was studied and analyzed.Based on Kelvin’s law,the physical relationship between porosity and drying shrinkage was analyzed,and the prediction model of drying shrinkage was improved.ABAQUS finite element simulation software was used to analyze the influence of bubble hole size change on the drying shrinkage of foamed concrete.The main conclusions are as follows:（1）A new mix design method of foamed concrete with porosity as the design goal is proposed,and the accuracy of the design method is verified by experiments.Vacuum saturation method can measure the porosity of foamed concrete whose porosity range is less than 80%.In this study,foamed concrete with 90%porosity is designed.Due to the weak internal pore wall,it is unable to accurately measure the water absorption,so it is not able to accurately measure the real porosity results.The results of dry density method for determining the porosity of foamed concrete are closer to the design porosity.Through comparative analysis,it is found that the dry density method is more accurate than the vacuum saturation method.（2）Foamed concrete was prepared by the improved mix design method.The effects of porosity on the basic properties of foamed concrete were studied,including physical properties,mechanical properties,thermal properties and durability.Foamed concrete was prepared by the proportion design method based on porosity,which laid the foundation for the in-depth study of the porosity of foamed concrete.（3）The drying shrinkage of foamed concrete is divided into three processes,which are the early slow shrinkage process,the middle rapid shrinkage process and the later stable shrinkage process.The early slow shrinkage process of foamed concrete with high porosity is very short.The higher the porosity of foamed concrete is,the greater the drying shrinkage rate is,and the faster the early water loss rate is.The lower the porosity of foamed concrete is,the smaller the drying shrinkage rate is,and the slower the early water loss rate is.The dynamic elastic modulus and static elastic modulus of foamed concrete decrease with the increase of porosity,and the elastic modulus has a good correlation with porosity.（4）Based on Kelvin’s law,the physical relationship between porosity and drying shrinkage was analyzed,the relationship between porosity and drying shrinkage was studied,the constant parameterα_H was determined,and the drying shrinkage prediction model was improved.（5）ABAQUS finite element analysis simulation software was used to calculate the deformation shrinkage rates of bubble holes with different sizes.The results show that bubble holes with pore sizes of 0.4 mm～0.8 mm will not affect the drying shrinkage of foamed concrete.