Reasarch On The Influence Of Acid Rain On Mechanical And Frost-resistance Properties Of Recycled Concrete

With the development of urban construction,the construction waste has increased rapidly.In order to improve the utilization rate of the construction industry and relieve the pressure on the environment,based on the preparation of construction waste in China,the recycled aggregate is made for replacing the natural aggregate into the concrete and the mixing ratio of the recycled coarse aggregate is considered for improving the ability of the recycled aggregate in this paper.Considering the effect of acid rain problem and freezing-thawing,based on experimental research,this paper analyzes the basic mechanical properties of recycled concrete after acid rain erosion and its anti-freezing performance,and uses Scanning Electron Microscopy and Energy Dispersive Spectroscopy to analyze the mechanism.In addition,this paper uses the parameter identification method in the least squares method to reprocess the data.The following are the main research contents:(1)Through analysis and research on the existing classification process,standards and measurement indicators of construction waste,the suitable production process and operation standard of recycled coarse aggregate is adopted for the region.And then water absorption,crushing indicators are determined for carrying out relevant concrete test,the results found that "effective water-cement ratio" can significantly improve the mechanical properties of recycled concrete.(2)Through the development trend of acid rain in China and the simulated acid rain erosion test method,this paper determined the concentration ratio of sulfate ion and nitrate ion 6:1,and prepare acid rain solution with pH value of 2.5 and 3.5 by using nitric acid and ammonium sulfate.The spray scheme was then designed and the acid rain spray equipment was installed for the simulation of acid rain erosion.(3)In the test,the coarse aggregate content,acid rain pH value and erosion days were selected as the main test factors,and the admixture content as a secondary test factor.Accoding to the above factors,apparent,neutral depth,compressive strength,axial compressive strength,elastic modulus,and frost resistance were performed.It is found that the replacement ratio of recycled coarse aggregate is 35%,which is more suitable for resisting lower pH(2.5)acid rain erosion.The replacement ratio of recycled coarse aggregate is 0% and 50%,which is more suitable for higher pH(3.5)acid rain erosion.According to the influence of admixture on the compressive strength of recycled concrete,10% silica fume is better when single doping,10% silica fume and 30% fly ash are better when double doping.(4)In this paper,the concrete dynamics modulus of each group after freeze-thaw cycle is to firstly achieve the standard value of damage,and the mass loss rate is less than 5%;Natural concrete has the best frost resistance compared with recycled concrete under different pH acid rain erosion conditions.(5)The interface analysis of concrete was carried out by Scanning Electron Microscopy and Energy Dispersive Spectroscopy to analyze the variation of apparent,mechanical and frost resistance of recycled concrete after erosion.This paper also refers to the existing recycled concrete and its erosion coefficient model after acid rain erosion,and the corresponding model parameters are identified to obtain suitable parameter values.