| Recycled aggregates（RAs）,as one of the ways of construction and demolition waste recycling,have the characteristics of high porosity,high water absorption,low bulk density,etc.and the surface is rough and porous.Based on the above characteristics,Recycled Aggregate Pervious Concrete（RAPC）is prepared by partially replacing natural aggregates with recycled aggregates,which is used in road,parking and other application scenarios,and can solve problems such as reuse of construction and demolition waste.At the same time,the RAs with porous structure is an ideal medium for the application of photocatalytic materials,and the wide surface area formed by its pores can provide a large number of attachment points for photocatalytic materials.By introducing photocatalytic technology,it is endowed with multi-functional properties and realizes the purification treatment of gas and liquid pollutants.Therefore,in this study,recycled aggregates,composite photocatalytic material and pervious concrete were combined,and the composite photocatalytic material was loaded on recycled coarse aggregate to prepare permeable concrete with photocatalytic-adsorption synergistic degradation performance.The physical and mechanical properties of concrete are studied and its basic properties are tested.According to the constructed pollutant testing system,the synergistic degradation performance of concrete to pollutants under different environmental conditions was explored,and its photocatalytic-adsorption behavior mechanism was revealed.The main research contents and achievements of this thesis are as follows:（1）Study on the composite of TiO2/LDHs and the properties of TiO2/LDHs-loaded recycled aggregatesPhotocatalytic material TiO2/LDHs was prepared by the composite process.The microstructure was observed by SEM,TEM and XRD.By soaking method,TiO2/LDHs were made into suspensions with different concentrations,and recycled aggregate was soaked in the suspensions.The porous media characteristics of recycled aggregates were fully utilized to realize the loading of TiO2/LDHs in the aggregates,and the effects of different concentrations of TiO2/LDHs suspensions on the loading capacity,water absorption and apparent density of recycled aggregate were comparatively studied.The study found that:The average size of nano-TiO2 is about 20-30 nm,and its morphological characteristics are micron particles formed by spherical agglomeration.TiO2 particles on TiO2/LDHs are dispersed on the surface TiO2/LDHs laminates,and the agglomeration phenomenon is improved.When the concentration of TiO2/LDHs suspension is higher,the loading of TiO2/LDHs on recycled aggregate is higher.When the concentration of TiO2/LDHs suspension is 1.0%,the maximum loading is 5.85%,the water absorption decreases to 3.73%,and the apparent density increases to 2151.35kg/m3.The structure of TiO2/LDHs-loaded recycled aggregates is more compact,and the micro cracks on the surface are filled.（2）Preparation and properties of TiO2/LDHs-loaded recycled aggregates pervious concreteThrough soaking method,TiO2/LDHs recycled aggregate permeable concrete was prepared by loading different concentrations of TiO2/LDHs suspension on recycled aggregate,and its basic properties and influencing mechanism were studied,such as porosity,permeability coefficient,compressive strength,freeze-thaw resistance and so on.The results show that:When the concentration of TiO2/LDHs suspension is higher,the porosity and permeability coefficient of recycled aggregates pervious concrete decrease,while the compressive strength and frost resistance increase.When the concentration of TiO2/LDHs suspension is 0.8%,the porosity of the specimen is 14.67%,the water permeability coefficient is 1.65mm/s,and the compressive strength reaches 27.4MPa.After 25 freeze-thaw cycles,the strength loss rate and mass loss rate are less than 5%,which meets the requirements of specifications.（3）The degradation efficiency and mechanism analysis of gaseous pollutantsAccording to the standard Test method for air-purification performance of photocatalytic materials and products-Removal of nitrogen oxides（GB/T 39716-2020）,a gas-solid catalytic degradation test system was constructed,and the test parameters of the test system were calibrated,and the reaction equilibrium curve of NO gas was obtained according to the blank group test.The degradation efficiency of recycled aggregates pervious concrete for gaseous pollutant NO under different TiO2/LDHs loading and different environmental conditions was analyzed,and its degradation mechanism was revealed.Finally,through repeated photocatalytic experiments,the durability of photocatalytic efficiency was explored,and the nitrogen elution amount and recovery rate of photocatalytic products were tested.The test results show that:When the concentration of TiO2/LDHs suspension is 0.6%,the photocatalytic degradation rate of NO gas reaches72.54%.When the ambient temperature is 25℃,the maximum photocatalytic degradation rate of NO gas is 72.9%.When the irradiance of light intensity is 40W/m2,the maximum photocatalytic degradation rate of NO gas is 87.08%.After three times of washing photocatalytic test,the sample showed good stability,and the photocatalytic degradation rate was still 58%.The nitrogen content in the eluent was determined by soaking the sample.（4）The degradation efficiency and mechanism analysis of liquid pollutantsAccording to the standard Test Method for Water Purification Performance of Photocatalytic Materials（GB/T 23762-2020）,a liquid-solid catalytic degradation test system was constructed,and the test parameters of the test system were calibrated.The recycled aggregates pervious concrete prepared with different TiO2/LDHs-loading was compared,and its photocatalytic degradation performance for organic contaminated Methylene Blue solution and adsorption removal performance for inorganic pollutant sodium nitrate were tested respectively.The reaction process was described and analyzed by using photocatalytic kinetic equation and adsorption kinetic equation,and the synergistic purification mechanism of photocatalysis and adsorption in aqueous solution was revealed.Compared with different TiO2/LDHs loading,the photocatalytic degradation performance of recycled aggregates pervious concrete for organic pollution Methylene Blue solution and the adsorption and removal performance of inorganic pollutant sodium nitrate solution.The photocatalytic kinetic equation and adsorption kinetic equation were used to describe and analyze the reaction process,revealing the mechanism of photocatalytic-adsorption synergistic purification in aqueous solution,and doing valuable exploration for promoting the application of photocatalytic-adsorption synergistic recycled aggregates pervious concrete.The test results show that:When the concentration of TiO2/LDHs suspension is 0.6%,the degradation effect is the best,and the removal rate of 3h reaches 65%.The photocatalytic degradation process follows Langmuir quasi-first-order reaction kinetics model.When the concentration of TiO2/LDHs suspension is 0.8%,the adsorption effect is the best,and the removal rate reaches 56.8%in 72 hours.The adsorption equilibrium process of nitrate ion follows Lagergren quasi-first-order adsorption kinetic model.The durability tests of photocatalytic and adsorption repeatability were carried out for three times,and all the samples showed certain stability.The photocatalytic degradation rate of methylene blue remained at 60%,and the adsorption removal rate of sodium nitrate remained at 50%.According to the above research,it is concluded that the photocatalytic-adsorption synergistic degradation mechanism of TiO2/LDHs recycled aggregates pervious concrete is the directional migration of pollutants,thus realizing the purification of liquid pollutants. |
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