Experimental Study On Compressive Strength And Microscopic Properties Of Recycled Concrete With Reinforced Coarse Aggregate

The waste concrete produces recycled coarse aggregate through the process of crushing,sieving and cleaning and so on,and then recycled concrete is produced,which can realize the recycling of waste concrete.On the one hand,the utilization of waste concrete resources can offset the shortage of natural aggregates such as sand and gravel;on the other hand,it can decrease the effect of construction waste occupying land and polluting the environment.The recycled coarse aggregate has rough surface,more angular angles,lower apparent density,higher water absorption and large crushing index,which defects make its performance inferior to the performance of natural coarse aggregate.In this paper,the regenerated coarse aggregate is strengthened by chemical immersion method,and then recycled concrete with reinforced coarse aggregate is tested for compressive strength and micro-performance,and compared with the test results of ordinary concrete.The major research work in this paper is as follows:(1)The recycled coarse aggregate was soaked for 3h,4h,4.5h and 5h respectively,and then its crushing value was tested according to the standard test method to determine the best soaking time for recycled coarse aggregate.The basic physical properties of natural coarse aggregate,recycled coarse aggregate and strengthened coarse aggregate were tested.The differences in the properties of three coarse aggregate gradations,mud content,apparent density,crushing index and water absorption were compared and analyzed.The results show that 5h was the best soaking time for the recycled coarse aggregate.The crushing index value of strengthened recycled coarse aggregate is 8.8%,which is 28.5% lower than that of the recycled coarse aggregate and has significant strengthening effect.(2)Based on the ordinary concrete mix ratio,the mix design of recycled concrete with reinforced coarse aggregate was studied.Designing 16 group a total of 48 C30 and C40 ordinary and coarse aggregate reinforced concrete block carried out compressive strength test,respectively to study the difference of slump between recycled concrete with reinforced coarse aggregate and ordinary concrete under the same mix ratio.The difference between the failure pattern and strength of the cube and prism blocks of the two concretes was investigated.Finally,the relationship between the compressive strength of recycled concrete with reinforced coarse aggregate cube and the axial compressive strength was established by regression analysis.The results show that recycled concrete with reinforced coarse aggregate has good workability.The strength of C30 recycled concrete with reinforced coarse aggregate is higher than that of ordinary concrete.The strength of C40 recycled concrete with reinforced coarse aggregate is slightly lower than that of ordinary concrete.(3)The formation mechanism and structure of the interfacial transition zone are analyzed.It is proposed that there are four interfacial transition zones for the recycled concrete with reinforced coarse aggregate.The old cement stone,interface transition zone morphology and interface transition zone thickness of recycled concrete with reinforced coarse aggregate were tested by scanning electron microscopy and energy dispersive spectroscopy,and compared with the test results of ordinary concrete.The results show that the thickness of the interfacial transition zone between the C30 and C40 recycled concrete with reinforced coarse aggregate cement stone and the original aggregate is different.The transition zone structure between recycled concrete with reinforced coarse aggregate silica fume cement hardened layer and the new mortar is relatively dense and has few pores.(4)Combined with the results of scanning electron microscopy and spectrometer test and the cross-section photograph of recycled concrete with reinforced coarse aggregate,the strengthening mechanism of recycled coarse aggregate and the effect of reinforced coarse aggregate on concrete strength were analyzed.The results show that the silica fume cement can wrap the recycled coarse aggregate into a whole and has a certain restraining effect on the interface transition zone between the old mortar and the original coarse aggregate.The silica fume cement hardened layer has a large water absorption,and the water-cement ratio near the strengthened coarse aggregate is lower than that of the ordinary coarse aggregate,which can reduce the thickness of the water film layer on the aggregate surface,thereby reducing the thickness of the interface transition zone and improving the concrete strength.