Study On Mix Ratio Optimization Design And Durability Of Manufactured Sand Concrete For Road

Sand is an important resource in the field of civil engineering.However,with the large-scale construction and rapid development of infrastructure in China,natural sand as a non-renewable resource is on the verge of shortage,and it is urgent to find other resources that can replace natural sand to supplement.Manufactured Sand is a fine artificial aggregate made from rocks,mine tailings or industrial slags.Manufactured Sand is a good alternative to natural Sand in terms of source and material.In recent years,government have also introduced the corresponding policies to develop manufactured sand concrete.Traffic facilities construction is an important part of infrastructure construction in our country.Manufactured sand concrete is also more and more used in road and bridge engineering.However,the appearance and physical properties of manufactured sand are different from those of natural sand,which leads to the difference in the properties of concrete mixed with manufactured sand and traditional concrete,thus restricting its application in practical engineering.In order to further understand the influence of relevant parameters of manufactured sand on concrete performance,this paper based on the Puyan Expressway from Sanming Youxi Zhongxian to Jianning Lixin Project(YA11-HP-052,2017-2021),carried out the optimization design of the mix of manufactured sand concrete and the study of road mechanical properties and durability,to provide guidance for the project.The main research contents and results are as follows:1.Optimal design and test of mix ratio of manufactured sand and concrete.Based on the comprehensive consideration of the physical characteristics of manufactured sand,the optimization design theory of mix ratio of manufactured sand concrete with medium and high strength grade was put forward based on the modification of aggregate dosage.Based on the optimization theory,five groups of mix ratio of manufactured sand concrete with good comprehensive performance and meeting the pumping requirements were obtained.The mixture ratio calculated by this theory is basically the same as that calculated by Huang’s compactness grading design theory.The results also show that increasing the sand percentage is helpful to improve the workability of manufactured sand concrete,and adding appropriate amount of cellulose ether can also effectively improve the water retention and cohesion of manufactured sand concrete.2.Study on basic mechanical properties of manufactured sand concrete.Nine groups of mixtures of manufactured sand and concrete were designed.The compressive strength,bending strength and splitting tensile strength of manufactured sand concrete with different mixing ratios of manufactured sand(0%,30%,50%,70%),fly ash content(0%,20%,30%,40%)and stone powder content(0%,5.8%,11.6%)were tested respectively.The results show as follows: 1)with the increase of manufactured sand content,the basic mechanical properties of manufactured sand concrete first increase and then decrease,and there is an optimal manufactured sand content(about 30%~50%).2)Fly ash will reduce the early compressive strength of manufactured sand concrete,but appropriate amount of fly ash is conducive to the improvement of mechanical properties in the later stage.The optimal content of fly ash in manufactured sand concrete is 30%,and more than 30% fly ash will result in significant decrease of mechanical properties.3)Appropriate amount of stone powder can exert the filling effect and activity effect in manufactured sand concrete,which is beneficial to improve the late compressive strength of manufactured sand concrete.The insufficient or excessive content of manufactured sand and gravel powder will result in the decrease of the flexural strength,splitting tensile strength and early compressive strength of manufactured sand concrete.3.Study on chloride ion permeability resistance of manufactured sand concrete.To keep the above variables consistent,RCM method and dry-wetting cycle method of chlorine salt solution were used to carry out the experimental study of chloride ion permeability resistance of manufactured sand concrete,and the numerical simulation of chloride ion permeability was carried out with COMSOL.The results show that: 1)with the increase of the mixing ratio of manufactured sand,the chloride diffusion coefficient of manufactured sand concrete decreases first and then increases,and the chloride penetration resistance of concrete is the best when the mixing ratio of manufactured sand is 50%.2)With the increase of fly ash content,the chloride ion permeability resistance of manufactured sand concrete is firstly enhanced and then weakened.If the fly ash content is too high,the chloride ion permeability resistance of manufactured sand concrete is significantly reduced.In this paper,30% fly ash content in the test can minimize the chloride ion penetration rate in concrete;3)Appropriate amount of stone powder is beneficial to improve the chloride ion permeability resistance of manufactured sand concrete.Lack of stone powder or too much stone powder will lead to the decrease of chloride penetration resistance of manufactured sand concrete.4)The chloride ion penetration results simulated by COMSOL are in good agreement with the test results,which proves the accuracy of the test results and the reliability of the software simulation.And according to the life prediction results,the appropriate dosage of manufactured sand can effectively improve the service life of concrete in chlorine salt environment.4.Study on carbonation resistance of manufactured sand concrete.Also keeping the same variables,the changes of quality,compressive strength and carbonation depth of manufactured sand concrete before and after carbonation were studied experimentally,and MATLAB was used to construct BP neural network to predict the carbonation depth of manufactured sand concrete.The results show that: 1)In the standard carbonization environment,the carbonization reaction can increase the quality and compressive strength of manufactured sand concrete;2)The carbonation resistance of machine-made sand concrete is better than that of natural sand concrete.However,with the increase of the proportion of manufactured sand,the carbonation resistance of concrete first increases and then decreases.The carbonation resistance of concrete is the best when the proportion of manufactured sand is 50%.3)The incorporation of fly ash will reduce the carbonation resistance of manufactured sand concrete.With the increase of fly ash content,the carbonation resistance of manufactured sand concrete first increases and then decreases,but the carbonation depth is higher than that of manufactured sand concrete without fly ash.4)Insufficient or excessive stone powder can reduce the carbonation resistance of manufactured sand concrete,but excessive stone powder in manufactured sand concrete is more adverse to the carbonation resistance of manufactured sand concrete;5)The prediction result of 28 d carbonation depth of manufactured sand concrete by BP neural network has a high goodness of fit,and the predicted value is in good agreement with the measured value,which proves that this method can be directly applied to practical engineering to save the test workload.The mix ratio of manufactured sand and concrete designed in this paper has been applied to part of bridge engineering from Youxi Zhongxian to Jianning Lixin section in Sanming Jingjing of Puyan Expressway.Other research results also provide guidance for this project.