Study On Mix Proportion Design And Mechanical Properties Of Middle-High Strength Recycled Concrete

With the development of urbanization, result in a large amount of construction waste, most of which are waste concrete, lots of waste concrete has caused great pollution on social environment. The situation of waste concrete recycling is imminent; the development of concrete trade must take the road of sustainable development. Using recycled concrete preparation technology can not only solve the pollution problems caused by waste concrete, can also bring certain economic benefits to the society. At present, the research and application of recycled aggregate concrete confined to low-intensity fields, middle-high strength recycled aggregate concrete researches have not been systematically studied. This thesis aims to study on mix proportion design of middle-high strength recycled aggregate concrete and its mechanical properties, discuss the secondary mixing processes which apply to recycled aggregates、 feasibility of using low strength recycled aggregates to prepare high strength recycled concrete and strength prediction on high strength recycled aggregate concrete by using neural network technology.The research route of thesis is cement (42.5 General Portland cement)+active mineral admixtures (double mixing technology of silica fume and fly ash)+high efficiency water reducing agent (naphdalin series water reducer), based on research results of thesis (improved secondary mixing process), has successfully achieved high strengthened target of recycled concrete, provides certain theoretical principle and reference value for the generalization and application of recycled concrete. Use water cement ratio (A)、recycled coarse aggregates replacement rate (B)、Silica fume content (C) and fly ash content (D) as influencing factors, each one has four levels, Use orthogonal table L16 (45) to arrange 16 sets of orthogonal experiments. By range analysis and variance analysis of orthogonal experimental results of 7days、28days and 60days, analyze influences of all factors at all levels on mechanical properties of middle-high strength recycled concrete. And obtain the best mixture ratio of the 28days’cube compressive strength is:A2B3C4D2, namely water-binder ratio=0.32, recycled coarse aggregate replacement ratio= 75%,silica fume content=10%, fly ash content=15%. And the results show that when recycled coarse aggregate replacement ratio is 75% or 100%, the compressive strength difference is small, less than 5%, so in order to maximize the use of recycled coarse aggregates, comprehensive analysis of the optimum combination is:A2B4C4D2.Multiple linear regression analysis on compressive strengths after 28days of middle-high strength recycled aggregate concrete shows that compressive strength and cement-water ratio don’t have a simple linear relationship, this is the root cause of why Bolomey Formula does not apply to middle-high strength recycled aggregate concrete. Do the compressive strengths prediction on 7days,28days and 60days of middle-high strength recycled concrete by using SPSS Neural network, results show that all observations have been well-predicted. Using modern computer technology to forecast the strengths of engineering material is very favorable, and also has certain reliability and forward-looking. The thesis models on the Slater formula to make nonlinear regression of 7days and 28days compressive strengths of middle-high strength recycled concrete, the result is f28=f7+2.185(f7)0.5.This formula can calculate the strengths of 28days by using middle-high strength recycled concrete’s early strengths (of 7days). After this, practical application of middle-high strength recycled concrete, which can control the progress of construction, such as concrete removal、lifting components、relaxing prestressed steel bars、 stacking products、manufactured dates, it provides a certain theoretical basis and has certain reference value.