The Effect Of Enhancing Methods On The P Roperties Of Recycled Aggregate And Recycled Concrete

With the rapid development of Chinese construction industry,a large number of concrete structures are facing the problem of demolition or removal.So the abandoned concrete will be produced in large quantities.After cracking,cleaning,crushing,screening and grading of the abandoned concrete,the aggregates formed by a specific mixing ratio is called recycled aggregates,but recycled aggregates from the preparation of simple crushing and screening process exhibit some shortcomings such as grains with many edges and corners,rough surface and partly attached hardened cement mortar,in addition,a large number of micro-cracks are caused by the accumulation of damage in concrete blocks during crushing process,which all result in the large porosity,high water absorption,small packing density,large void fraction and high crushing index.The recycled concrete made of this kind of recycled aggregate has higher water requirement,lower strength after hardening,and lower durability of impermeability,frost resistance,carbonization resistance and chloride ion permeability than ordinary concrete.Therefore,the recycled aggregates prepared from the abandoned concrete is the research object in this paper,starting from the disadvantage of high water absorption and crushing index of recycled concrete,using physical-mechanical enhancing method,chemical enhancing method and physical-chemical synergistic enhancing method.The effects of enhancing method on water absorption,crushing value,and apparent density,mixing performance,mechanical properties and durability of recycled aggregate concrete were systematically studied.At the same time,the morphological characteristics of the surface microstructures of recycled aggregates were analyzed by scanning electron microscopy.The experimental results are as follows:(1)The water absorption,crushing value and apparent density of recycled aggregate are improved by physical-mechanical grinding.The water absorption,crushing value and apparent density of recycled aggregates were significantly improved after impregnation and enhancing with polyaluminium sulfate solution and water glass solution,besides,the enhancing efficiency of recycled aggregate by water glass solution is higher;(2)The basic properties of recycled aggregate have been improved more remarkably than that of single enhancing methods after physical-chemical synergistic enhancing of recycled aggregate.The synergistic enhancing of polyaluminium sulfate solution(solution concentration 20.0%)or water glass solution(modulus 2.8)has a significant effect on improving the basic properties of recycled aggregate;(3)The synergistic enhancing of recycled aggregate can obviously enhance the slump of recycled aggregate concrete,and improve the mixing fluidity of recycled concrete.At the same time,the synergistic enhancing of recycled aggregate can significantly enhance the compressive strength of recycled concrete for 3d,28 d and 90 d.When the replacement ratio of recycled aggregate is 100%,the compressive strength of recycled concrete strengthened with 20.0% polyaluminium sulfate solution increases 32.5%,26.6% and 25.2% respectively after 3,28 and 90 days compared with that of unenhanced recycled concrete,and the compressive strength of recycled concrete strengthened with water glass solution with modulus 2.8 increases 57.1%,51.5% and 50.1% respectively after 3,28 and 90 days compared with unenhanced recycled concrete;(4)The synergistic enhancing of recycled aggregate has different enhancing effects on the carbonation resistance,freeze-thaw cycling resistance and chloride ion permeability of the recycled concrete.Among them,the synergistic strengthening of water glass solution after 28 d makes the durability of recycled concrete close to that of natural concrete,which also shows the effectiveness of this strengthening method.