Experimental And Improvement Optimization Of Fly Ash-silica Fume-Nano-SiO₂ Permeable Concrete

With the rapid development of urbanization in my country,the urban ground is gradually covered by various impervious concrete.A large number of urban waterlogging,groundwater level drop,noise pollution,heat island effect and other phenomena are increasingly affecting people’s normal life.Under the background of the construction of"sponge city",permeable concrete with certain mechanical strength and high water permeability was born.Permeable concrete has continuous pores,good air and water permeability,which can not only promote the circulation of groundwater,but also improve the urban ecological environment.The use of permeable concrete as a ground paving material is of great significance to urban construction.In this paper,several different blending materials are used,through design orthogonal experiment and optimization experiment,the basic performance and optimization improvement of pervious concrete are studied,and the following main conclusions are obtained:（1）When calculating the mix ratio of permeable concrete,this article improves the traditional volume method to make the mix ratio calculation more convenient and quick.Based on the four-factor three-level orthogonal test,the target porosity,fly ash,silica fume,and nano-SiO₂ are used as the orthogonal test factors,and the compressive strength,effective porosity,and water permeability of the permeable concrete are used as evaluation indicators.The pass is extremely poor.Analysis and variance analysis revealed the influence of four factors on the performance indexes of permeable concrete.Considering the strength and water permeability of permeable concrete under different levels of various factors,the optimal mix ratio of the three indexes is determined.（2）The relationship between the compressive strength and porosity of the permeable concrete,the compressive strength and the coefficient of water permeability,the porosity and the coefficient of water permeability are established,and their fitting relations are given;a simple glass device designed by ourselves is used to prevent water permeability.The permeability coefficient of concrete was measured.（3）On the basis of the orthogonal test of permeable concrete,the performance test of permeable concrete was optimized.From the macroscopic and microscopic perspectives,fly ash,silica fume and nano-SiO₂were used as admixtures for single admixing and compound admixing.Influence of permeable concrete mechanical properties.The results show that（1）under the premise of not affecting the permeability coefficient of permeable concrete,the contribution of the three mineral admixtures to the compressive strength and flexural strength of permeable concrete is nano-SiO₂>fly ash>silica fume.（2）The mechanical strengths of compound fly ash（10%）,silica fume（8%）and nano-SiO₂（2%）are all higher than the mechanical strength of the three mineral admixtures.（3）Analyzing the SEM images of permeable concrete samples,it can be seen that the small number of large Ca（OH）₂crystals,the compact structure of hydration products,and the microstructure of small pores are beneficial to enhance the mechanical strength of permeable concrete.The three admixtures will have Obviously superimposed effect.（4）Through construction cost analysis,cost calculation,maintenance costs and water-saving benefits,it is found that permeable concrete is more cost-effective than ordinary concrete during the entire construction and life cycle,providing a reference for engineering construction in the field of permeable concrete.