Experimental Study On Performance Optimization Of Permeable Concrete

Permeable concrete have been widely applied in the sidewalks,parking lots,parks,airports,stadium and other fields as a kind of pavement materials with good social,environmental and economic efficiency.However,the application of permeable concrete was limited because of the very small amount of fine aggregate and high porosity,which significantly reduced the strength and durability.In view of this,it is of great engineering significance to carry out research on performance optimization of permeable concrete.The strength,interfacial transition zone and pore structure of permeable concrete were mainly studied in this paper,which were based on the coordination of the strength and permeability of permeable concrete.The paper focused on the influences of combination method of mixture,dosage of admixture,ratio of aggregate to binder,aggregate size and the molding method on the strength and permeability of permeable concrete.At the same time,the effects of different admixtures on the micro-hardness of the matrix as well as that of the interface were studied.Also,the relationship between the micro-hardness parameters and the macroscopic properties of the permeable concrete were compared.Moreover,a method of evaluating pore structure of permeable concrete was proposed.The pore structure characterization of permeable concrete under conditions of different ratio of aggregates to binders and aggregate size were compared and analyzed by using slice method and image software.The results showed that,(1)The maximum 56-day compressive strength was 39.7MPa,and the permeable coefficient was 1.25 mm/s.The optimal performance obtained when mix proportion parameter values are as follows: the water-binder ratio was 0.35,the ratio of aggregate to binder was 3.5,the aggregate type was 2.36~4.75 mm,the silica fume content was 5%,fly ash content was 10%,the molding pressure was 1.5MPa,and the feeding way of specimens mixture was the aggregate wrapped by net mortar.(2)Fly ash and micro-silica powder can effectively improve the weak area of interface.The enhancement effect was obviously when the concrete contained 10% fly ash,10% micro silicon powder and 1% latex powder.Under this combination,the hardness value of the cement matrix increased by 57.8%,the minimum hardness of the interface increased by 150%,the width of the interface area reduced by 57.1%.(3)The results of slice method and image analysis showed that,for permeable concrete with aggregate size range from 2.36 to 4.75 mm,the number of pores which pore diameters range from 0 to 2mm was the highest,but the total area was the lowest.While the number of pores which pore diameter greater than 3mm was the lowest,but the total area was the highest.Permeable concrete had excellent properties of permeability and strength when the equivalent pore diameters ranged from 1.34 to 1.47 mm.(4)The results of CT scan showed that the concrete pores were denser with smaller the particle size,and the connectivity path was more complex,so the water was easy to store but difficult to discharge.The porosity obtained by the CT scan was in good agreement with the results obtained by the slice image method.