Experimental Study On Mechanical Properties Of Aeolian Sand Concrete Under Freeze-thaw Cycles Conditions

With the gradual implementation of the 14th Five-Year Plan,the scale of infrastructure is expanding,construction sand resources are in short supply.Exploring new sources of construction sand has became an increasingly concerned issue in the engineering community.China is rich in desert and eolian sand resources are extensive.Using eolian sand to prepare concrete can effectively alleviate the contradiction between supply and demand of construction sand and reduce the construction cost.In this paper,the aeolian sand in northern Shaanxi is used as raw material to prepare concrete.The mechanical properties test,freeze-thaw cycle test and nuclear magnetic resonance technology are carried out to study the influence of different factors on the freeze-thaw degradation degree and mechanical properties of aeolian sand concrete from the macro and micro perspective.The freeze-thaw damage model and service life prediction model are established,which provided a theoretical basis for the construction and application of aeolian sand concrete in cold regions.The main research contents and conclusions are as follows:(1)Based on the slump test and mechanical properties test,the influences of water glue ratio(0.42,0.45,0.48),sand ratio(30%,32%,35%),aeolian sand replacement ratio(0%,20%,40%,60%,80%,100%)and other factors on the working performance of the mixture and the mechanical properties of concrete were studied.The results show that with the increase of water glue ratio,the slump of concrete increases and the compressive strength decreases.With the increase of sand ratio or aeolian sand replacement rate,the slump and compressive strength of concrete increase first and then decrease.(2)The pore structure characteristics of different proportions of aeolian sand concrete were analyzed by NMR technology,and the relationship between strength and porosity was established.The results show that the strength of aeolian sand concrete decreases linearly with the increase of total porosity,and decreases nonlinearly with the increase of harmful porosity.The expression of pore structure-strength relationship based on the two-factor index of harmful porosity and total porosity is in good agreement with the test results.(3)The influence of different factors on the frost resistance of aeolian sand concrete was studied from the macro and micro perspectives by conducting freeze-thaw cycles and mechanical properties tests,combined with nuclear magnetic resonance technology.The results show that the frost resistance of concrete is negatively correlated with the water glue ratio,and positively correlated with the sand rate and aeolian sand replacement rate.The increase in the proportion of small and medium pores in concrete can play a role in resisting freeze-thaw damage and improve the frost resistance.(4)The correlation between various pore sizes and freeze-thaw damage was analyzed by grey correlation degree,and the relationship between harmless porosity and mass loss rate and dynamic elastic modulus loss rate of concrete was established.The damage of pore structure of aeolian sand concrete is defined with harmless porosity as the index,and the service life prediction model of aeolian sand concrete is established based on this.