Mix Optimization Design And Application Research On Pumping Machine-made Sand Concrete For Li-rong Expressway In Guizhou Province

With the continuous deepening of ecological environment protection in various areas,the restricted mining measures of natural sand resources also have been increasingly strengthened,so the technology of mixing concrete with machine-made sand instead of natural sand has been more and more widely used in road engineering construction.It has achieved significant economic,social and environmental benefits.Accordingly,in view of the fact that natural sand resources are scarce in Guizhou Province,the thesis relies on the construction project of Li-rong(from Li-bo to Rong-jiang)Expressway to carry out the mix optimization design and application research on pumping machine-made sand concrete,and it has an important practical significance and engineering application value.1)According to the actual situation of the supported project,the performance tests of raw materials such as machine-made sand,cement,coarse aggregate,water and water reducer were carried out,and all the results meet the technical requirements.However,the stone powder content in the machine-made sand is slightly higher,so it is necessary to carry out the mix optimization design for the machine-made sand concrete.2)Considering the four factors of cement content,water binder ratio,sand ratio and water reducer content and their three levels,the orthogonal experimental design was used to analyze the influences of various factors on the compressive strength at different ages and the slump for machine-made sand concrete.The results show that the order from large to small in the influencing factors of 28d compressive strength is:water binder ratio>water reducer content>sand ratio>cement content,and the order from large to small in the influencing factors of slump is:water binder ratio>cement content>sand ratio>water reducer content.Hereby,the optimization mix ratio of pumping machine-made sand concrete meeting the requirements of compressive strength and workability was determined.3)Taking the optimization mix ratio as the reference mix ratio,the tests were carried out to analyze the influences of various sand ratios of machine-made sand on the concrete performances under the conditions of keeping water binder ratio,cement content and water reducer content unchanged,and the control ranges of sand ratio for the pumping concrete of different strength grades were obtained.The results show that with the increase of sand ratio,the 28d compressive strengths of C30 and C40 machine-made sand concrete increase first and then decrease,while that of C50 concrete decreases gradually.Meanwhile,the slump of C30 concrete increases first and then decreases,that of C40 concrete increases gradually,while that of C50 concrete decreases gradually.Hereby,the empirical correlation between the 28d compressive strength and the various factors such as cement content,water binder ratio,sand ratio and water reducer content was built through the multiple linear regression analysis to provide a basis for determining the reasonable mix ratio in construction site.4)Relying on the construction of second contract section in Li-rong Expressway,the engineering application and the performance verification were conducted for the optimization mix ratio of the pumping machine-made sand concrete,and the corresponding key technologies of construction quality control were put forward.The results show that all the performances of the pumping machine-made sand concrete meet the technical requirements,and the economic and environmental benefits are remarkable.In summary,the research in the thesis can provide a reasonable reference for the mix optimization design and the engineering applications of machine-made sand concrete.