| In recent years,the phenomenon of "city looking at the sea" is prominent.Urban rainwater cannot quickly infiltrate into the ground,thus forming surface runoff.Meanwhile,the shortage of urban water resources has been severe.At present,most of the research and the existing concrete mix design at home and abroad are mainly based on the empirical formula,resulting in the actual engineering concrete mix design economy is poor.This study relates the thickness of cement slurry to the performance of permeable concrete,and proposes the mix design of permeable concrete based on the optimal encapsulation thickness:First,the fitting formula of the maximum package thickness(MPT)is calculated.W,WR,Si and NS series of tests were set up to measure the rheological properties of cement slurry,including fluidity and viscosity.After mixing W,WR,Si and NS series with medium size aggregate,the maximum package thickness(MPT)was calculated.Finally,the relationship between the maximum package thickness and the rheological properties is fitted with a formula.Second,calculate the cement slurry package thickness(PCT).The volume of cement slurry is equal to the porosity of reclaimed aggregate under tight packing minus the target porosity.After setting the range of target porosity,the volume of cement slurry can be obtained from the target porosity and the porosity under tight packing.Then the specific surface area of the aggregate is calculated by the formula of the specific surface area of the aggregate,and the surface area of the aggregate is further obtained.The PCT can be obtained by dividing the volume of cement slurry by the surface area of the aggregate.Third,test the compressive strength and permeability coefficient of permeable concrete.Will W,WR,Si and NS four series water mud all meet the thickness of the package(PCT)in the biggest package or less thickness(MPT)in the condition of cement slurry and particle size of aggregate mixing,molding and maintaining of permeable concrete block permeable coefficient and compressive strength value of the test,the results show that the porous concrete compressive strength increases with the increase of the thickness of cement paste package,adding 5%cement dosage of the cement dosage of nanometer silica fume and 0.5%silicon is helpful to improve the compressive strength of porous concrete;The permeability coefficient decreases with the increase of the thickness of cement slurry,and the addition of silica fume with cement content less than 5%is beneficial to improve the permeability coefficient of pervious concrete.Fourth,Entropy method is used to determine the mix ratio of pervious concrete based on the optimal package thickness.he entropy method is used to calculate the composite level index of permeability coefficient and compressive strength of pervious concrete test block.In conclusion,in this paper,the permeability coefficient and compressive strength were taken as the main target parameters,and the maximum film thickness(MPT)of cement slurry determined by the flow characteristics of cement slurry and the package thickness(PCT)determined by the target porosity were taken as the main design parameters.A design method for the proportion of permeable concrete based on the optimum film thickness is presented. |
