Study On Performance Prediction And Freeze-thaw Durability Enhancement Of Recycled Aggregate Pervious Concrete

At present,the resource utilization of construction waste has an important strategic significance in China.As a kind of main recycled product,recycled aggregate(RA)pervious concrete has significant scientific research and engineering application value.Because of its porous characteristics,it is always a difficult problem to design the strength and permeability of pervious concrete.The existing performance correlation models based on pore characteristics is not practical.Therefore,it is urgent to develop the more practical and reliable method for performance prediction and design of pervious concrete.In addition,poor freeze-thaw durability is one of the main factors restricting the practical application of RA pervious concrete.So it is necessary to study the freeze-thaw durability enhancement of RA pervious concrete.Based on this,this paper has carried out a series of research work,the main contents are as follows:With the usage of X-ray tomography and image processing technology,the cement paste distribution in the actual pervious concrete was extracted.The distribution characteristics of cement paste in pervious concrete mixture was revealed by using the maximum paste coating thickness on aggregate surface and the actual paste coating thickness.The effects of aggregate size and rheology of cement paste on the maximum paste coating thickness on aggregate surface were studied by experiment.The experimental results show that the yield stress,apparent viscosity and fluidity of paste have a highly exponential relationship with the maximum paste coating thickness on aggregate surface.The mesostructure prediction method of pervious concrete was proposed.The mesostructure characteristics such as thickness distribution of cement paste,pore structure were predicted and extracted.The predicted distribution is in good agreement with the actual distribution,which verifies the reliability of this method.Based on the above-mentioned mesostructure prediction method,and using the mean thickness of cement paste and mean aggregate size,the performance prediction model of pervious concrete was established.The performance design method of pervious concrete was developed.Based on the predicted pore structure,the three-dimensional numerical simulation study on permeability of pervious concrete was carried out.Silane emulsion was used to modify the RA surface and cement matrix in RA pervious concrete respectively.The effect of two modification methods on the freeze-thaw durability and compressive strength of pervious concrete were studied,and the mechanism of freeze-thaw deterioration of RA pervious concrete was revealed.The mechanism of silane modification and its influences on the pore structure of cement paste,cement hydration and interfacial transition zone(ITZ)were analyzed by means of Fourier transform infrared(FTIR)spectrometer,mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM).The experimental results show that RA surface silane modification is a good method to improve the freeze-thaw durability of RA pervious concrete.