Study On Sulfate Resistance Of Recycled Aggregate Permeable Concrete

In this paper,the recycled aggregate of 5-10 mm was obtained from the abandoned C40 concrete campus pavement by mechanical crushing,vibrating screen screening and manual re screening.Two schemes were designed to prepare the recycled aggregate permeable concrete:① constant water cement ratio of 0.3,different design porosity(18%,20%,22%,24%,26%)to prepare the recycled aggregate permeable concrete ② constant porosity of 18%,Different water cement ratios(0.31,0.32,0.33,0.34,0.35)were used to prepare recycled aggregate permeable concrete.The basic mechanical properties of recycled aggregate pervious concrete with different design porosity and water cement ratio and the changes of basic properties after 15,30,60 and 90 days of erosion by 5%sodium sulfate solution were studied.At last,the neural network is used to predict the compressive strength of recycled aggregate permeable concrete under different design porosity after 90 days erosion.The main achievements are as follows:(1)The recycled aggregate pervious concrete with different design porosity not only affects its basic mechanical properties,but also affects its physical properties.As a whole,it shows that the design porosity increases,the chamber degree of the test block decreases,the permeability coefficient increases,and the compressive strength decreases.When the design porosity is 26%,the density of recycled aggregate permeable concrete is the smallest,the permeability coefficient is the largest,and the compressive strength is the smallest.The measured values are 1665kg/m3,4.9mm/s,and 5.13mpa,respectively.The measured porosity range is 18.7%-28.4%,and the compressive strength range is 5.13-8.42MPa,meeting the design requirements of the initial scheme and the use requirements of the current permeable concrete.(3)When the water cement ratio is 0.35,the density,porosity and compressive strength of recycled aggregate permeable concrete are the smallest,the porosity and compressive strength are the largest,and the measured values are 1652kg/m3,27.90%and 5.73mpa,respectively The relationship between porosity and permeability coefficient data of this test can be obtained,and the fitting degree of the two is 0.984.(4)In the sulfate corrosion test,the compressive strength and corrosion resistance coefficient of recycled aggregate permeable concrete under different design porosity are inversely proportional to the design porosity after being eroded by sodium sulfate solution for 15d,30d,60d and 90d,and the test results show that the sulfate resistance grade is ks60;in the case of a certain design porosity,when the erosion time increases,the compressive strength and corrosion resistance coefficient first increases and then increases After 30 days of erosion,the compressive strength and corrosion resistance coefficient are the largest.Under different water cement ratio,the compressive strength and corrosion resistance coefficient of recycled aggregate permeable concrete decreased with the increase of water cement ratio after 15,30,60 and 90 days of sodium sulfate solution erosion.According to the test,the sulphate resistant grade is ks90;when the water cement ratio is fixed,the corrosion resistance coefficient of compressive strength increases first and then decreases with the erosion time,and reaches the maximum after 90 days of erosion.(5)The test blocks of recycled aggregate permeable concrete with different design porosity eroded by sodium sulfate solution at 0d,15d,30d,60d and 90d were cut and photographed.The cross-section pores were extracted by image image method.It was found that with the increase of erosion time,the plane pores of the cross-section firstly decreased and then increased.The connectivity of the internal pores of recycled aggregate permeable concrete was not caused by It is determined by one or two indexes,but by the indexes which can represent the change of internal pore characteristics.After 90 days of erosion,the area and porosity of plane pores are the largest.This shows that the number of pores in recycled aggregate permeable concrete increases,and the damage of sodium sulfate solution increases.(6)By using design porosity,compressive strength,permeability coefficient,density,mass loss rate,plane pore area,number of pores,equivalent pore diameter and other indicators to build neural network,the compressive strength of recycled aggregate permeable concrete after 90 days of erosion is predicted.It is found that the average absolute error between the measured value and the predicted value is within 1.177mpa,the maximum relative error is 12.67%,and the average relative error is within 1.177mpa The difference is 9.32%.The accuracy of the prediction results is high,and the prediction effect of the whole model is good.Therefore,by setting different input parameters,the comprehensive influence of wet and dry cyclic sulfate erosion on recycled aggregate permeable concrete can be described and its strength can be predicted.