Testing Research On High Performance Recycled Concrete And Recycling

With the advance of "green concrete" concept, the recycled concrete has attracted more and more attention. However, due to the disadvantages of the properties of recycled aggregates, the performance of the recycled concrete was lower. Therefore, it has great importance to study on the preparation of good quality recycled aggregates and then improving various performances of recycled concrete. In this paper, the main way leading to the preparation of high performance recycled concrete made with100%recycled aggregates was studied, mainly focused on the effect of mineral admixtures on the basic performance of recycled concrete such as fly ash, slag and their mixtures as well as the possibility of multi-recycling of recycled concrete made with100%recycled aggregates.The results show that:(1) The simple crushing recycled aggregate after mechanical processing, can effectively improve the quality of recycled aggregate, water absorption, apparent density, bulk density, crush index and particle size distribution was improved to a certain extent.(2) In cases of the same proportion, compressive strength and the resistance to chloride ion permeability of recycled aggregate concrete is slightly lower than that of ordinary concrete, the recycled aggregate concrete mixed with mineral admixtures can improve all aspects of performance, morphological effect, mineral admixture of micro aggregate effect and volcano ash effect are the main factors to improve the performance of recycled aggregate concrete.(3) Fly ash, slag is not conducive to the7d compressive strength of recycled aggregate concrete, When the same content, the early strength of the recycled aggregate concrete which mixed with fly ash decreased more obvious,within the scope of the content less than40%,fly ash and slag can improve the90d compressive strength of the recycled aggregate concrete, and content is greater, the late strength increased more obvious, in addition, the effect of the double mixing fly ash and slag is better than the single doped with the same amount of fly ash or slag.(4) When the doping amount is same, different ratio of fly ash and slag (1:3,1:1,3:1) have a certain influence on the7d compressive strength of the recycled concrete, high early strength of recycled concrete with high content fly ash, but the90d compressive strength of recycled aggregate concrete has little effect.(5) The chloride ion permeability of recycled aggregate concrete is also affected by fly ash and slag content, content is greater, performance improvement is more obvious, but the anti carbonation properties of recycled concrete counterproductive, considering the compressive strength, anti chloride ion permeability and carbonation resistance, suggestions on the selection of the compound of fly ash and slag, and the dosage all was20%so as to achieve the purpose of high performance. (6) Numerical analysis of volcano ash effect will be able to quantify the contribution of mineral admixture on the strength of recycled aggregate concrete, accurately reflect the effect of different mineral admixtures in different ages of the recycled aggregate concrete on the performance, and consistent with the test conclusion.(7) Grey correlation analysis to quantitatively describe the dynamic process of fly ash, slag on the properties of recycled aggregate concrete, through correlation comparisons show that the total amount of mineral admixture is the biggest influence factors of performance, the secondary influence factors of compressive strength is the dosage of slag, the secondary influence factors of anti chloride ion permeability is the amount of fly ash.(8) Mineral admixture can reduce the volume percentage of the pore, whose diameter were between100-1000nm, of recycled aggregate concrete and refine the pore to improve its compactness.(9) The compressive strength and the resistance to chloride ion permeability of secondary recycled aggregate concrete are worse than recycled aggregate concrete, the compressive strength decreased about15%, the electric flux increases in the range of10%-30%,without changing concrete mix proportion, cycle number of recycled aggregate concrete is limited.