Response Surface Method Based On The Optimal Design And Application Of Manufactured Sand Concrete Mix Ratio

With the increasing depletion of river sand resources and the increasing awareness of environmental protection,the use of manufactured sand as a fine aggregate to replace river sand in the preparation of concrete is becoming more and more widespread in engineering applications.There are many factors affecting the performance of manufactured sand concrete,which leads to the problems and shortcomings in the application of manufactured sand concrete in engineering,and the application of manufactured sand in bridge engineering is still cautious.In this paper,we use the manufactured sand to prepare C50 strength grade concrete for bridges,and use river sand as the control group to explore the effects of water-cement ratio,mineral admixture and fine aggregate mixing ratio on the performance of manufactured sand concrete,and use them to optimize the manufactured sand concrete ratio.The main research contents and conclusions are as follows.(1)The slump and expansibility of manufactured sand concrete increase with the decrease of water-cement ratio,and under the same ratio,compared with river sand concrete,the fluidity of manufactured sand concrete is poor.the manufactured sand concrete with double admixture of fly ash and mineral powder has good working performance,and the slump and expansibility of manufactured sand concrete increase gradually with the increase of double admixture.the working performance of mixed sand concrete is better than that of full manufactured sand concrete,and the slump and expansibility of manufactured sand concrete increase gradually with the decrease of the proportion of manufactured sand in the mixture.The slump and expansion of concrete gradually increase as the proportion of manufactured sand in the mixed sand decreases,but it is still worse than that of river sand concrete.(2)The 28 d compressive strength,tensile strength and modulus of elasticity of manufactured sand concrete are more advantageous than that of river sand concrete under the same proportion.As the water-cement ratio decreases,the strength of mixed sand concrete tends to increase.the compressive strength and modulus of elasticity of mixed sand concrete with fly ash and mineral powder decreases in the early stage and increases in the later stage,while the tensile strength decreases in all ages.the strength of mixed sand concrete increases and then decreases as the proportion of mixed sand in the mix decreases,and when the proportion of mixed sand in the mix is 60%,the mechanical properties of mixed sand concrete are the best.The mechanical properties of mixed sand concrete are the best.(3)The early shrinkage of manufactured sand concrete is larger than that of river sand concrete,the smaller the water-cement ratio,the larger the early shrinkage of manufactured sand.double blending of fly ash and mineral powder can obviously inhibit the early shrinkage of manufactured sand concrete,and the early shrinkage of manufactured sand concrete gradually decreases with the increase of double blending.the larger the proportion of manufactured sand in mixed sand,the larger the early shrinkage of mixed sand concrete,and the concrete prepared by reasonable proportion of mixed sand is smaller than that of river sand concrete.Early shrinkage is less than that of river sand concrete.(4)The circular constraint method was used to investigate the cracking resistance of the manufactured sand concrete.The results show that the cracking strain of manufactured sand concrete increases with decreasing water-cement ratio,but the cracking age is earlier.the cracking age of mixed sand concrete with 60% of manufactured sand in the same proportion is smaller than that of concrete with single admixture of manufactured sand,but the cracking strain is higher.the cracking strain of manufactured sand concrete with double admixture of fly ash and mineral powder is higher and the age is longer,which can effectively reduce the risk of concrete cracking.(5)The multiple quadratic regression models between fly ash,mineral powder and slump,extension and 28 d compressive strength were established using the response surface method and analyzed by ANOVA.The results showed that the fitting effects of the models were significant.Finally,the best test conditions of 0.29 water-cement ratio,40% sand rate and 30%double admixture(20% of fly ash and 10% of mineral powder)were obtained through the optimization of response surface method and applied in the bridge project.