Effects of flat and elongated aggregates on the performance of porous asphalt mixture

Four fat and elongated(F&E)contents(0%,original,30%,and 40%)were investigated to evaluate the effects of F&Eparticles on the performance of porous asphalt mixture(P A).Laboratory tests including volumetric determination,two-dimensional image analysis,Cantabro loss tests,breakdown tests,and permeability tests were conducted to evaluate the volumetric properties,the state of stone-onstone contact,durability,skeleton stability and permeability of PA,respectively.The test results indicate that the F&E content was a significant factor for total air voids,aggregate skeleton break down,and permeability.The functionality,rutting resistance,long-term durability,and skeleton stability decrease with the increase of F&E content since F&E aggregates in porous asphalt mixtures have a tendency to breakdown.Compared with traditional dense graded mixtures,PA is more sensitive to the F&E content due to an open graded aggregate structure.Therefore,the stricter requiement for F&E content should be met for porous asphalt mixtures than the one for traditional deese graded mixture.

Design Method and Performance for Large Stone Porous Asphalt Mixtures

Design method for large stone porous asphalt mixtures （LSPM） was analyzed to avoid the early distresses of semi-rigid asphalt pavements. Based on stone-to-stone skeleton structure concept, processes of LSPM gradation design was given. The gradation composite design for LSPM shows that the LSPM nominal maximum size （ N MS） should be larger than 26.5 mm, and the NMS sieve passing percentage should be greater than 50%. Through experiments and calculations on the volume properties of the aggregate, the range of aggregate gradation curve of LSPM was given. In terms of asphalt binder＇s normalized test results, MAC-70 and SBS modified asphalt were selected as the asphalt binders. The applicability of large scale Marshall Method and gyratory compaction method to shape specimens was investigated. Based on the asphalt mixture performance evaluation, the optimum asphalt content range （3.1%-3.6%）, the bitumen film＇s thickness range （13-16 μm） and the air void range （13%-18 %） were recommended. Finally, LSPM was tested by the laboratory performance tests including rutting resistance test, fatigue test and water stability test. The theoretic and practical analysis shows that LSPM has a good performance on water permeability, rutting resistance and reflection crack resistance.

Application of Biochar on the runoff purification performance of porous asphalt pavement

Biochar is currently applied in many low-impact development measures,such as biofilters and filter strips.However,its application in permeable pavement is limited.Due to the wide range of raw material sources,biochar may also contain nutrients and heavy metals.Whether its leachate will cause contamination during application remains unknown.Based on the static leachate contamination test,this study first evaluated the leachate contamination risks of three types of biochar and porous asphalt mixture(PA)with three biochar fillers.Through the pavement infiltration test,the purification performance of PA with biochar fillers and filter layers was further analysed.The results show that biochar contains nitrogen and phosphorus,and the leaching contamination of coconut shell is the most obvious;when the biochar is applied as a filler in PA,the leaching contamination decreases,while the pollutant purification performance is not obvious;when 3−5 mm rice straw biochar is used as a filter layer,the removal rate of total suspended solids can be 100%,but it is accompanied by more serious nitrogen and phosphorus leaching,and the greater the thickness,the more serious the degree of leaching.Deionized water cleaning can remove the phosphates contained in biochar,but have little effect on nitrogen.Therefore,before the application of biochar,cleaning measures should be taken to minimize its leaching contamination.