Study On Frost Resistance Durability Of Cemented Sand And Gravel By Compound Admixtures

As a new building material,CSG Material has a wide application prospect because of its low cost and easy construction.From the existing research and engineering examples,it is found that the CSG Material has the disadvantages of poor impermeability and frost resistance,which affects the popularization and application of CSG Material.Scholars at home and abroad have done little research on this problem.From the perspective of concrete research which is similar to cemented gravel,this study summarizes the methods that can improve the frost resistance and durability of cemented gravel,and selects the way that admixture can improve cemented gravel from these methods for research.The research process is carried out by indoor test and theoretical analysis.Firstly,the selected polycarboxylate superplasticizer,air entraining agent(sodium dodecyl sulfate,triterpenoid saponin),graphene oxide and nano-silica powder additives are compounded in different proportions,and the samples after rapid freeze-thaw test are tested by orthogonal test.Then,the composite additives are optimized by range analysis and dominance theory.Finally,the test conclusion is verified by improving Multimoora’s comprehensive evaluation of CSG Material.The purpose is to prepare a kind of composite admixture which can improve the frost resistance durability of cemented gravel.The specific research results are as follows:(1)In the experiment of determining composite admixtures by orthogonal test,different admixtures have different influences on the compressive strength of CSG Material.Through range analysis,it is water reducer that has the greatest influence on the compressive strength of CSG Material before and after freezing and thawing,and graphene oxide that has the greatest influence on the relative compressive strength of CSG Material.In the rapid freeze-thaw test,the water reducing agent has the greatest influence on the quality loss of CSG Material after 20 freeze-thaw cycles,and the sodium dodecyl sulfate has the greatest influence on the relative dynamic elastic modulus.(2)The optimum mixture ratio determined by the range analysis method of the results obtained by orthogonal test is proved to be universal under different waterbinder ratio and sand ratio.The proportion of the composite admixture in the application of cementitious materials(by mass)is respectively 0.04% of triterpenoid saponin,0.06% of graphene oxide,0.5% of nano-silica powder and 0.4% of water reducer.(3)Through SEM test,it can be seen that different admixtures have different effects on cementitious gravel,but their main effects can be reflected in SEM pictures.Meanwhile,the study points out that graphene oxide and nano-silicon powder have composite reinforcing effect.The products obtained by microscopic morphology can confirm that there is no obvious mutual inhibition of rechecked admixtures.According to gray level co-occurrence matrix analysis,entropy information has a positive correlation with compressive strength and a negative correlation with porosity in different orthogonal test groups.(4)Through nuclear magnetic porosity test,the porosity of specimens with different composite admixtures increases with the increase of frost resistance times.Through the range analysis of orthogonal group data,it can be concluded that water reducing agent and nano silicon powder have great influence on porosity.At the same time,it is found that the absolute value of pore size distribution of harmful pores before and after freezing and thawing is basically consistent with the compressive strength and the relative compressive results before and after freezing and thawing.(5)The improved Multimoora method is used to evaluate the comprehensive performance of the cementitious gravel with different admixtures,and finally the most favorable admixture proportion form in the test group is determined.The comprehensive evaluation results of CSG Material by this method are consistent with the optimal admixture ratio obtained by the difference analysis results of actual index data obtained by orthogonal test.This shows that the improved Multimoora method can accurately and quickly optimize the dosage of cementitious gravel admixture.