Preparation And Application Of Recycled Aggregate Fair-faced Concrete With Self-cleaning Function

With the accelerating process of urbanization in our country,more and more old demolition and new construction projects not only consume a lot of natural resources,but also bring a lot of construction waste.It has caused serious pollution to the environment,so the recycling of construction waste is imminent.At the same time,due to the once pouring and forming of fair faced concrete,no secondary plastering is needed,which reduces the construction dust and the generation of construction waste.However fair faced concrte will expose its outer surface to the air for a long time,which is easy to be polluted.As a result,fair-faced concrete will lose its original finishing effect,and even affect the service life of concrete.Therefore,the recycled aggregate from waste concrete is used to prepare self-cleaning recycled aggregate fair faced concrete,which solves the problems of construction waste recycling,lack of natural aggregate resources,environmental pollution and concrete surface pollution.Green building materials with structure function integration have been formed,which have great economic,environmental and social benefits,and meet the requirements of sustainable development of construction industry.This paper focuses on the mix design and preparation technology of recycled aggregate self-cleaning fair faced concrete.Firstly,by exploring the influence law and significance of different factors on recycled aggregate fair faced concrete,the concrete mix proportion parameters are optimized to obtain the best mix proportion parameters;secondly,based on the optimal concrete mix proportion parameters,the effects of different photocatalyst concentration,photocatalyst introduction method and spraying age on the photocatalytic self-cleaning efficiency of concrete were studied;finally,the water content state of recycled coarse aggregate,mixing process,template treatment process and photocatalyst introduction method are optimized,and a relevant construction technology guide is formed.The main research contents and achievements of this paper are as follows:(1)Optimum mix proportion parameters of recycled aggregate fair faced concrete based on orthogonal test resultsTaking water binder ratio,sand ratio and cementitious material content as experimental factors,three levels were selected for each factor,working performance,mechanical properties and apparent properties as experimental indexes,and L9(3~4)orthogonal table was used for orthogonal test.The influence rules and significance of different factors on the test indexes were obtained.Combined with the comprehensive balance method,the optimal mix proportion parameters are determined to meet the requirements of workability,mechanical properties and apparent properties of recycled aggregate self-compacting fair faced concrete:water binder ratio 0.27,sand ratio 49%,and cementitious material content 500kg/m~3.(2)The influence of different factors on the photocatalytic self-cleaning efficiency of concrete is revealedOn the basis of optimizing the mix proportion of recycled aggregate self-compacting fair faced concrete,the effects of three different photocatalyst introduction methods,including recycled coarse aggregate loading method,surface spraying method and liner material loading method,different photocatalyst concentration and different spraying age on the photocatalytic self-cleaning efficiency of concrete were studied.It shows that with the increase of the concentration of photocatalyst,the photocatalytic self-cleaning efficiency of the three preparation methods is improved,but the improvement effect is different;the photocatalytic self-cleaning efficiency of concrete obtained by spraying at different ages is different,but it is not obvious;under the same photocatalyst concentration,the self-cleaning efficiency of the surface spray method is better than the other two methods.(3)The preparation process of recycled aggregate self-cleaning fair faced concrete was optimizedThe preparation process of recycled aggregate self-cleaning fair faced concrete was optimized from four aspects:water content state of recycled coarse aggregate,mixing process,template treatment process and photocatalyst introduction mode.It is found that the performance of concrete prepared by air dried recycled coarse aggregate is relatively good;in the secondary mixing process,the cement wrapped stone method can improve the performance of concrete most;the liner material treatment method is better than the treatment method of brushing release agent;the permeable template cloth loading method takes into account the apparent performance and self-cleaning effect of concrete,which is more in line with the performance requirements of recycled aggregate self-cleaning concrete.Based on the optimization of the preparation process,a technical guide for the construction of recycled aggregate fair faced concrete with self-cleaning function is compiled.