Study On Mix Proportion Design And Performance Of Manufactured Sand Self-Compacting Concrete

Since self-compacting concrete has the characteristics of avoiding manual vibration during the pouring process,it can save resources and improve the construction environment during construction,and it has been widely used in high-rise and large-span engineering projects.However,high-quality natural sand resources for concrete preparation are becoming increasingly scarce,and other materials need to be found to replace them.Machine-made sand can be used instead of natural sand as the raw material for preparing self-compacting concrete,which can not only solve the shortage of natural sand and restricted mining,but also promote the use of machine-made sand in construction projects.In addition,in the process of preparing self-compacting concrete,there are many factors that affect the performance of self-compacting concrete,such as water-binder ratio,sand ratio,fly ash content and total amount of cementitious materials.How to obtain the best proportion of mix parameters and the best performance of self-compacting concrete through a small number of trials is the key issue of the research.This paper mainly studies the influence of water-binder ratio,sand ratio,fly ash content and total amount of cementitious material on the performance of machine-made sand self-compacting concrete,and obtains the best range of influence of various factors on concrete performance.The response surface method is used to design a four-factor five-level test,and the best mix ratio of self-compacting concrete is obtained through prediction and optimization of the established nonlinear regression model,and the best performance of the concrete is obtained.Frost resistance test and sulfate corrosion resistance test were carried out on the mechanized sand self-compacting concrete with the best mix ratio to verify whether the durability of self-compacting concrete meets the requirements.Analyze the hydration microstructure of self-compacting concrete with the best ratio through scanning electron microscopy experiments,and analyze the relationship with its macroscopic properties.The creative results and main conclusions obtained are as follows:1.When the water-binder ratio,sand ratio,fly ash content and total cementitious material content are in the range of 0.30～0.50,37%～57%,0%～60%and 422kg/m~3～550kg/m~3respectively,The self-compacting concrete prepared can meet the requirements of self-compacting performance and design strength.2.Through analysis of variance on the established regression models of slump expansion,J-ring expansion,segregation rate and 28d compressive strength,the results show that the fitting of each regression model is extremely significant.And get the linear effect,the quadratic effect of each factor and the interaction effect of any two factors on the degree of influence of the self-compacting concrete slump expansion,J-ring expansion,segregation rate and 28d compressive strength,so as to further obtain the importance of the regression coefficient of each regression model effect term.From the normal distribution,the comparison between the predicted value and the actual value of each performance response value,it can be seen that the regression model equation relationship between each factor and the performance response value is significant,and the established regression models have high prediction reliability.3.Taking slump expansion,J-ring expansion,segregation rate and 28d compressive strength as the target optimization values,the optimal test conditions for preparing self-compacting concrete are optimized by response surface method:water-binder ratio is 0.38,sand ratio is 47%,The fly ash content is 32%and the total cementitious material is 518kg/m~3.4.The frost resistance and sulfate erosion resistance of machine-made sand self-compacting concrete prepared under the best test conditions are stronger than the self-compacting concrete of the benchmark mix ratio,and it meets the durability design standard.5.The microscopic analysis of the mechanized sand self-compacting concrete with the best mix ratio was carried out through scanning electron microscopy experiments.From the test results,it can be seen that the concrete with the best mix ratio has a more uniform distribution of micro-cracks and fewer harmful pores,high compactness,and a better microstructure than the control group is more complete.