Experimental Study On Structure And Performance Of Sidewalk Permeable Pavement

Due to the significance of rainwater retention,runoff purification and comfortable walking,the research on permeable sidewalks have received global attention.In this work,we have investigated the structure and performance of permeable sidewalk in the preparation,utilization,and maintenance stages.The mixture ratio of the permeable concrete base was optimized by orthogonal test.The results of the variance analysis showed that the order of factors affecting the 28 d compressive strength was: target voidage > water-cement ratio > aggregate particle size,and the order of factors affecting permeability coefficient was: target voidage > aggregate particle size > watercement ratio.After a comprehensive consideration of the two indicators,the optimal mixture ratio was 18% to 22% of the target voidage,0.22 to 0.28 of the water-cement ratio,and 9.5 to 19 mm of the aggregate size.At this stage,the 28 d compressive strength and the permeability coefficient were higher than 25 MPa and 6 mm/s,respectively.The single factor test was used to optimize the mixture ratio of the permeable cement stabilized macadam base.Considering the 7d compressive strength and permeability coefficient,the optimal mixture ratio could be obtained,where the 4.75 mm throughput rate was 8%~15%,the maximum particle size was 26.5mm,the cement dosage was 7%~9%,and the water-cement ratio was 0.40~0.44.At this stage,the 7d compressive strength and the permeability coefficient were higher than 5.5 MPa and 14 mm/s,respectively.The permeability coefficient of structures composed of three kinds of surface(smoothsurface ceramic permeable brick,rough-surface ceramic permeable brick,permeable concrete)and two kinds of base(permeable concrete,permeable cement stabilized macadam)was compared.The results showed that the surface layer significantly affect the water permeability of the entire structure.The difference in permeability coefficient of structures with the same base but different surface was 2.9 mm/s,while the permeability coefficients of the structures with the same surface but different base differed only by 0.07 mm/s.The two structures with permeable concrete as the top layer had the best permeability,which the permeability coefficient was greater than 4 mm/s.A rainfall simulation device was used to investigate the runoff control effect of the permeable concrete sidewalk.When the return period was 1yr,10 yr,50yr,100 yr and the duration was 30 min,60min,120 min,the runoff control effect of device 1 was compared.The permeable pavement had good runoff control effect on small return period and short duration rainfall.The device did not produce runoff,when the return period was 1yr and the rainfall duration was less than 120 min.For heavy rainfall,the runoff control effect of the permeable pavement was weakened,but it was still much better than the impervious pavement.When the return period was 100 yr and the rainfall duration was 120 min,the runoff retention time of device 1 was 46.5min,and the runoff reduction rate was 43.8%.Based on the effect of runoff control,the suitable thickness of the subbase was 25~40cm,and the effect of continuing thickening was not significant.Moreover,the drainage effect of flexible pipes and graded gravel drains were compared.When the rainfall return period was 1yr,10 yr and 50 yr and the rainfall duration was 60 min,the peak drainage flow of the soft pipe was 4.4%,8.9% and 11.1% higher than that of the graded gravel drain,respectively.The clogging recovery of the permeable concrete surface layer was studied by simulation tests.The results showed that the particle size of the surface blockage was 0.08-0.60 mm.The three cleaning methods which are high pressure cleaning,vacuum suction and high pressure cleaning + vacuum suction can restore the permeability coefficient of surface layers to 83.0%,78.0% and 65.1%,respectively.The significance of running the three stage tests(mixture ratio design of base,analysis of runoff control effect,recovery of the surface layer)is that the results can be used as technical guidance for the design and application of permeable pavements of sidewalks.