Performance Design And Promotion Of Recycled Aggregate Pervious Concrete Based On Mesostructure Prediction

The application of construction waste as recycled aggregate in pervious concrete is beneficial to saving natural resources,reducing environmental pollution,improving ecological environment,and has good economic and ecological benefits.Previous studies on pervious concrete usually used the total porosity as the parameter to design the performance,which ignored the influence of the micro structure(pore structure,cement paste distribution,aggregate characteristics,etc.)that determines the macro performance of pervious concrete deeply.Therefore,the existing models and methods are difficult to achieve the accurate performance design of pervious concrete.The essential reason is the lack of understanding of the mesostructure of pervious concrete and the lack of corresponding mesostructure prediction methods.In addition,due to the introduction of recycled aggregates which have a weak physical and mechanical properties,the strength and permeability of pervious concrete were difficult to meet the application requirement.The long-term properties,such as frost resistance,fatigue characteristic and deterioration of permeability were still unclear,which restricted the application of recycled aggregate pervious concrete.In view of the above problems,a method for predicting the mesostructure of pervious concrete was proposed,a performance design model and numerical simulation model of pervious concrete considering the influence of multiple factors were established,a comprehensive performance enhancement method of recycled aggregate pervious concrete was proposed and the deterioration law of the long-term performance of recycled aggregate pervious concrete was revealed.This study provides theoretical basis and technical support for performance design and service life evaluation of recycled aggregate pervious concrete.This paper mainly conducts research in the following aspects:A method for predicting the mesostructure of pervious concrete including recycled aggregate was proposed.Combined with computed tomography(CT)scanning and image processing technology,the distribution characteristics and formation mechanism of cement paste in pervious concrete were clarified.The method for controling the cement paste dosage by using the max paste coating thickness(MPCT)was proposed to avoid the blocking in the pouring process,and the influence of paste rheology on MPCT was discussed.Combined with the formation mechanism of cement paste in pervious concrete and the image digital morphological operation method,the cement paste distribution was embedded in the CT image of aggregate distribution,and the mesostructure of pervious concrete was predicted.The comparison between the predicted structure and the measured structure shows that the proposed mesostructure prediction method has high reliability.This part of research provides data support for the follow-up performance design.A macro performance design model and numerical simulation model of pervious concrete were established.The influence of various mix design factors on the performance of pervious concrete was studied,such as the aggregate type(natural and recycled),the aggregate size,admixture,porosity,water to binder ratio,etc.By linking the predicted micro structure of pervious concrete to the measured macro performance,the design models of compressive strength and permeability coefficient of pervious concrete considering the characteristics of aggregate and cement paste were established,which solves the problem of low reliability of performance design caused by relying solely on porosity.With the help of image three-dimensional reconstruction and numerical simulation technology,the numerical models of water seepage and uniaxial compression of pervious concrete were established,which provide a convenient and reliable method to supplement the data of the macro performance design model,expand the application range of the model,and explain the failure mechanism of pervious concrete.Finally,the designed recycled aggregate pervious concrete was applied to practical projects,which has achieved a satisfactory result.A method for improving the performance of recycled aggregate pervious concrete was proposed.Two strategies were adopted to modify the recycled aggregate pervious concrete: soaking the recycled aggregate with silane emulsion and mixing silane emulsion with cement paste.The macro test results show that the aggregate surface modification can effectively improve the strength and frost resistance of pervious concrete on the premise of ensuring the water permeability,while the cement paste modification can only enhance its frost resistance.The mechanism of silane modification was analyzed by various micro test methods,and results show that the surface modification of aggregate can effectively improve the compactness of the interface transition zone between aggregate and paste.This study provides an effective method for expanding the application range of recycled aggregate pervious concrete.The deterioration law of long-term performance of recycled aggregate pervious concrete was revealed.Firstly,the research on the frost resistance of recycled aggregate pervious concrete was carried out,the effects of porosity and the doasge of air entraining agent on the strength,permeability coefficient and frost resistance of concrete were quantified,the distribution law of bubbles in pervious concrete was revealed,and the failure mechanism of recycled aggregate pervious concrete under freeze-thaw conditions was expounded,which is helpful to guide the frost resistance design of recycled aggregate pervious concrete in cold areas.Secondly,the fatigue performance of recycled aggregate pervious concrete was studied,and the influences of stress level and cement to binder ratio on fatigue life were quantified,the fatigue life prediction model of recycled aggregate pervious concrete with different reliability was established by using the parameters of stress level and porosity,the changing of total strain,residual strain and bending modulus with fatigue cycle were revealed.Finally,the deterioration mechanism of permeability considering the consolidation of contaminants was studied,the deterioration and maintenance mechanism of permeability were revealed from the meso level,such as contaminants distribution,clogging depth and pore diameter change,the deterioration model of water permeability was established by using the parameters of the contaminant dosage,aggregate size and concrete porosity.This part of research reveals the long-term performance deterioration law of recycled aggregate pervious concrete,and provides a theoretical and data reference for the service life evaluation of recycled aggregate pervious concrete.