Research On The Influence Of Pore Characteristics On The Performance Of Permeable Concrete

In recent years,with the advancement of national industrialization and urbanization,hardened pavement engineering has been applied to urban construction,resulting in the inability of surface water to be effectively discharged underground,and in severe cases,urban waterlogging.At the same time,a large amount of surface runoff has caused the urban "heat island effect" to become more and more serious.Based on this,more and more cities have proposed the construction goal of "Sponge city".Among them,permeable pavement materials are the core of the current construction of "Sponge city",whose special pore structure can effectively drain surface water,thus alleviating urban waterlogging and heat island effects.And permeable concrete is the mainstream product of permeable paving materials,gradually receiving widespread attention in the industry.This article takes permeable concrete as the research object and studies the changes in its performance under different mix ratio conditions.Research has found that the workability of cementitious material slurry has a significant impact on the strength and permeability of permeable concrete.Excessive flow can cause the slurry to deposit at the bottom of the concrete and block the pores,resulting in the permeability of the slurry;If the flow is too small,it will cause the mixed concrete to become loose and dry,reduce the aggregate linking ability,and thus affect the compressive strength.The size of aggregate particle size is negatively correlated with strength.When the connected porosity is similar,the strength of small particle size permeable concrete is higher than that of large particle size.This article uses recycled aggregates obtained from broken waste concrete to prepare recycled permeable concrete.By changing the amount of recycled aggregates,adding silica fume and fine aggregates,a recycled permeable concrete with a compressive strength of nearly 30 MPa after 28 days,a permeability coefficient of 1.5mm/s or greater,and a volume content of no less than 50% of recycled aggregates was prepared.And it was found that when the recycled aggregate content is less than 30%,it can effectively improve the compressive strength of the concrete.Through slicing analysis of concrete specimens with different porosity and aggregate particle sizes,combined with image analysis software such as Image Proplus and Photoshop,the characteristic parameters of concrete planar pore structure were analyzed.It was found that the pore area,equivalent perimeter,and equivalent diameter of the pore size were positively correlated with the aggregate particle size and permeable concrete porosity.At the same time,it was found that the plane pore area of permeable concrete is less than 2mm ~2Hole diameter ≥ 30 mm ~2 The total number of holes accounts for no less than 10% of all holes.When the aggregate particle size is 10-16 mm and 5-10 mm,it is less than 2mm ~2 Hole diameter ≥ 30 mm ~2 The common proportion of pores is not less than 50%.When the aggregate particle size is 2.36-5mm,the distribution of pores is relatively concentrated.At the same time,the distribution of pore area with different porosity shows the characteristics of "large at both ends and small in the middle" mentioned earlier.As the porosity increases,0-2mm ~2 The variation pattern of small pores is that they first increase and then decrease,and≥ 30 mm ~2 The overall trend of the large pores is gradually increasing.The influence of pore structure parameters on the macroscopic properties of permeable concrete was studied.The study showed that the connectivity porosity,plane porosity,average pore area,average equivalent perimeter were negatively correlated with compressive strength,and positively correlated with permeability coefficient.The correlation between the influence of each pore structure parameter on the compressive strength is that Ferrette’s average diameter>average equivalent perimeter>plane void area>effective void ratio>plane void ratio>average void number;The correlation between the influence of permeability coefficient and its magnitude is as follows: effective porosity>average diameter of Ferret>plane porosity>average equivalent circumference>average pore area>average number of pores;A one-dimensional and multivariate linear empirical formula for compressive strength and permeability coefficient based on pore structure characteristic parameters was established.