An experimental method to design porous asphalts to account for surface requirements

Porous asphalts have supplementary surface and volumetric properties(e.g., acoustic absorption, drain ability, texture, and friction). These properties are linked to intrinsic factors(e.g., gradation and bitumen content) and extrinsic factors(e.g., traffic load), while their evolution over time depends on complex phenomena and processes that cause their deterioration and therefore affect safety, noise, and budget. Despite the decay of so many and complex properties over time, there is a lack of criteria to synergistically optimize the pavement system. Consequently, the objective of this study is to set up and validate a design method that synergistically addresses the most relevant properties of friction courses as a part of a pavement structure. The abovementioned method is based on indepth analyses of the literature and on laboratory and on-site tests carried for several years in order to evaluate the decay over time of the main surface and volumetric properties.Results show that (1) the level of fulfilment of single requirements varies over time and among the characteristics;(2) a sound optimization of the design of the mix in order to balance the different characteristics is needed;(3) further studies are needed because of uncertainty in predicting the main surface properties.

Bond condition between surface layer and immediate layer in porous asphalt pavement

Through the shear tests on composite specimens using four different kinds of tack coat material （epoxy resin, SBS modified emulsified asphalt, SBS modified asphalt and H# bridge waterproof material）, the bond condition between layers of porous asphalt pavement under traffic load, temperature variation and moisture situation is evaluated. The test results show that the bond strength decreases with the rise in temperature, and the relationship between shear strength and temperature can be expressed by a logarithm curve at a high reliability. Under the action of traffic load, the value of shear strength of the mixture right under the centre of the wheel track is smaller than that of other parts of the pavement. It is also found that some effects concerning moisture have comparative effects on the bonding of the two layers. Given all the results achieved during the study, it will be quite rewarding to make rational comparisons during selecting the sound type of tack coat.

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.

Porous Flame-retarded Asphalt Pavement for Highway Tunnel

A new way to improve the tunnel fire protection by using flame-retarded porous asphalt pavement containing ATH powders was introduced. Based on the miniature burning test designed and conducted, the burning time and temperature of porous asphalt （PA） and flame-retarded porous asphalt （FRPA） were studied comparing with cement concrete pavement, dense-graded lIMA and SMA. Results of burning test and pavement performance test indicate that FRPA is appropriate and suitable as the pavement material of highway tunnel.

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.

Mechanical Properties of Sustainable,Self-healing Porous Asphalt Concrete

Long lifetime sustainable porous asphalt concrete containing steel fibers was designed. The material is self healing in such a sense that some external stimulus is needed in the form of heating by induction energy. Steel wool was added to porous asphalt concrete to enhance its electrical conductivity and induction heating was applied to increase the temperature to heal the micro-cracks and repair the bonding between aggregate and binder. The main purpose of this paper is to examine the mechanical properties of this sustainable porous asphalt concrete including indirect tensile strength,work of fracture,particle loss resistance and water sensitivity. It is found that adding steel fibers to porous asphalt concrete to increase the healing performance also can improve its overall mechanical properties.

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.

A semi-empirical model for top-down cracking depth evolution in thick asphalt pavements with open-graded friction courses

Thick asphalt pavements with open-graded friction course(OGFC) are exposed to topdown cracking(TDC), a distress consisting of longitudinal cracks that initiate on the pavement surface close to the wheel path and propagate downwards. The main objective of this study is to develop a semi-empirical model for the prediction of TDC depth evolution for such pavements. For this purpose, a series of cores were taken from different Italian motorway pavements affected by TDC and analyzed in the laboratory. Cracked cores taken from the wheel path area were analyzed to determine TDC depth, whereas intact cores taken from the middle of the lane(not affected by traffic loadings) were tested to obtain the volumetric and mechanical properties of the OGFC mixture. The proposed model, developed on the basis of the results already available in literature and on the findings of the laboratory investigation, predicts the evolution of TDC depth as a function of the applied traffic loadings(in terms of 12-ton fatigue equivalent single axle loads, i.e., ESALs). The model is sigmoidal with a maximum TDC depth assumed equal to 150 mm. The shape parameter of the sigmoidal function depends on the indirect tensile strength(ITS) of the OGFC mixtures(which takes into account indirectly also the volumetrics and stiffness of the OGFC), whereas the evolutive translation factor depends on the age of the OGFC mixture. After excluding some outliers, the model was able to predict the measured TDC depth very well. Moreover, in-situ observations allowed a preliminary validation of the proposed model. This model can be used in pavement management systems(PMSs) to plan surface repairs due to TDC in a timely manner, thus minimizing pavement damage and maintenance costs.