Experimental Research On Mechanical Properties Of Recycled Aggregate Concrete And Optimization Of Mix Proportion

As a green concrete, the recycled aggregate concrete has been applied in actual engineering because of its low consumption, low energy consumption, no pollution, circulation and regeneration. The research in properties and application of recycled aggregate and recycle aggregate concrete is increasingly concerned. Based on the 16 groups of orthogonal experiments, the effect on the properties of recycled aggregate concrete which is caused by the following three factors in the mix proportion, the water-binder ratio, the recycled aggregate replacement ratio and the fly ash replacement ratio is researched in this article. The effect on the properties of steel fiber reinforced recycled concrete which is caused by these three factors is also researched based on the experiments on steel fiber reinforced recycled concrete. At last, taking economy into account, mix proportion of recycled pumped concrete is optimized. The main contents are included as follow:1. Experiments on the slump and mechanical properties of recycled aggregate concrete are conducted, the experimental results are done by analytical hierarchy process (AHP). The effect weight of levels of three factors on slump and 28-day, 90-day mechanical properties is obtained to compare. The orders of the main influence factors are obtained, and the effects on the slump and mechanical properties are analyzed when the levels change. At the same time, a special influence of characteristics of fly ash is found on properties of recycled aggregate concrete, which is different on properties of ordinary concrete. The late splitting tensile strength and late flexural strength is influenced by the characteristics of recycled aggregate. The analysis of variance is also done. The degree of significance of the factors on the slump and mechanical properties is obtained.2. Experiments on the 28-day compressive strength and 28-day splitting tensile strength of steel fiber reinforced recycled concrete are conducted. The experimental results and the percentage of strength improving because of the steel fiber are done by AHP. The effect weight of levels of three factors on the mechanical properties and the percentage of strength improving is obtained to compare. The orders of the main influence factors are obtained. And the effects on the mechanical properties and the percentage of strength improving are analyzed when the levels change.3. The Bowromi Formula of ordinary concrete is modified. Different forms of Bowromi Formula of recycled aggregate concrete are obtained by the regressive analysis. They can be used as reference in the mix proportion design of recycled aggregate concrete.4. The working performance, the strength and the economic factors of concrete are taken into account. The constraint condition and the optimization model of mix proportion of recycled pumped concretes of which strength grades are C30, C25, C20, C15 are established. And the optimization of mix proportion is done by Matlab Genetic Algorithm Tool. The optimized mix proportion and the corresponding cost are obtained, and are compared to the former mix proportion before optimization. Some conclusions are obtained: the recycled aggregate in the experiments is not suitable for making concrete of which strength grades are higher than C30. The recycled aggregate can be used as coarse aggregate when making concrete of which strength grades are lower than C20, then the costs are economic.