Open-graded friction course(OGFC) is applied to pavement surfaces to increase driving safety under wet conditions, and recently, to reduce tire/pavement noise. The durability of OGFC, however, has been a concern since...Open-graded friction course(OGFC) is applied to pavement surfaces to increase driving safety under wet conditions, and recently, to reduce tire/pavement noise. The durability of OGFC, however, has been a concern since conventional OGFC mixes last typically less than ten years before major maintenance or rehabilitation is needed. This work investigates a new open-graded asphalt mixture that uses epoxy asphalt as binder to improve mix durability. One type of epoxy asphalt that has been successfully applied to dense-graded asphalt concrete for bridge deck paving was selected. A procedure of compacting the mix into slab specimens was developed and a series of laboratory tests were conducted to evaluate the performance of the new mix, including Cantabro loss, permeability, friction, shear strength, and wheel rutting tests. Results show superior overall performance of the open-graded epoxy asphalt mix compared to conventional open-graded asphalt mix. There are also preliminary indications that the OGFC mix with 4.75-mm NMAS gradation can improve the resistance performance to raveling, while the OGFC mix with 9.5-mm NMAS gradation can improve the performance of surface friction at a high slip speed.展开更多
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 propa...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.展开更多
The primary goal of this study is the design and construction of semi-flexible pavement(SFP)mixture in accordance with the engineering and mechanical criteria.This study involves the use of a range of gradation curves...The primary goal of this study is the design and construction of semi-flexible pavement(SFP)mixture in accordance with the engineering and mechanical criteria.This study involves the use of a range of gradation curves,air void contents,cellulose and synthesized fibers,and neat and modified asphalt binders to prepare the open-graded asphalt(OGA)mixtures.To analyze the characteristics of these mixtures,a variety of test,namely binder drainage,semi-circular bending(SCB),Cantabro,wheel tracking,indirect tensile strength(ITS),and permeability tests were conducted.Additionally,to analyze the prepared grouting material,flexural strength,compressive strength,and fluidity tests were conducted.In the final stage,SFP was compared to HMA in terms of engineering characteristics and performance.According to the results,SFP was more resistant to skid,rutting,fire,and moisture damage,while HMA had a better performance in fracture tests,including SCB test.According to the results of the mechanical performance tests conducted on OGA mixtures,the highest and lowest values for air void content to achieve the highest mechanical performance level were 30%-35%and 25%,respectively.Also,based on the laboratory results,it was determined that the required void ratio for constructing OGA mixtures was 24%-26%based on the bitumen type and fibers amount in the mixture.Finally,SFP mixture can be regarded as a viable alternative to common pavements thanks to its high resistance to rutting and moisture damage,long freezing-thawing fatigue life,and adequate fire and skid resistance.展开更多
The expansion and contraction of an open-graded friction course(OGFC)with a nominal maximum aggregate size of 13.2 mm(OGFC-13)with three air void contents(AVCs)and six saturation degrees(SDs)exposed to freeze-thaw(FT)...The expansion and contraction of an open-graded friction course(OGFC)with a nominal maximum aggregate size of 13.2 mm(OGFC-13)with three air void contents(AVCs)and six saturation degrees(SDs)exposed to freeze-thaw(FT)cycles were measured using strain gauges.Cantabro tests were conducted on OGFC-13 specimens before and after FT cycles to evaluate the degradation of raveling resistance.The effects of SD,AVC,and the number of FT cycles on the expansion and contraction of OGFC-13 and degradation of raveling resistance were analyzed.Results show that OGFC with low water saturation will contract to stability during the freezing process,whereas fully saturated OGFC will contract first and then expand to be stable.OGFC with a medium saturation experienced three stages,namely,contraction,expansion,and contraction,during the freezing process.For the OGFC with a low SD,the decrease in the void content can effectively reduce the low temperature shrinkage.By contrast,for the OGFC with a high SD,lower void content produces more temperature shrinkage at the beginning of freezing and less expansion at the end of freezing.The decreases in SD and AVC can effectively improve the raveling resistance of OGFCs exposed to FT cycles.展开更多
In the last decades,a new type of distress has been observed more and more frequently on asphalt pavements.This distress,ascribable to fatigue failure,has been named top-down cracking(TDC) because it consists in longi...In the last decades,a new type of distress has been observed more and more frequently on asphalt pavements.This distress,ascribable to fatigue failure,has been named top-down cracking(TDC) because it consists in longitudinal cracks that initiate on the pavement surface and then propagate downwards.A series of surveys recently carried out on Italian motorways highlighted that TDC can affect up to 20%-30% of the slow traffic lane.Therefore,in order to achieve a better understanding of such distress,this paper reviews causes,models and experimental tools and highlights future challenges for TDC.The literature review indicates that TDC can evolve on the pavement surface in three stages(i.e.,single crack,sister cracks,alligator cracking) and,below a certain depth,the cracks can form angles of 20°-40° with respect to the vertical plane.Even though multiple factors contribute to TDC development,thick pavements are more likely to fail due to TDC induced by tire-pavement contact stresses,especially in the presence of open-graded friction courses(OGFCs).Moreover,in literature there are several TDC models based on mechanics(e.g.,fracture mechanics or continuum damage mechanics) which allow a rigorous study of crack initiation and propagation.Future challenges include the identification of a reliable and feasible test method,among those proposed in literature,to study the TDC performance of asphalt mixtures and the implementation of TDC in pavement management systems(PMSs) through the definition of criteria for TDC recognition in the field as well as for the rehabilitation depth evaluation.Finally,more research is needed for open-graded asphalt mixtures,which present critical drawbacks in terms of TDC.展开更多
基金Project(51408125)supported by the National Natural Science Foundation of ChinaProject(2242015R30029)supported by the Fundamental Research Funds for the Central UniversitiesChina
文摘Open-graded friction course(OGFC) is applied to pavement surfaces to increase driving safety under wet conditions, and recently, to reduce tire/pavement noise. The durability of OGFC, however, has been a concern since conventional OGFC mixes last typically less than ten years before major maintenance or rehabilitation is needed. This work investigates a new open-graded asphalt mixture that uses epoxy asphalt as binder to improve mix durability. One type of epoxy asphalt that has been successfully applied to dense-graded asphalt concrete for bridge deck paving was selected. A procedure of compacting the mix into slab specimens was developed and a series of laboratory tests were conducted to evaluate the performance of the new mix, including Cantabro loss, permeability, friction, shear strength, and wheel rutting tests. Results show superior overall performance of the open-graded epoxy asphalt mix compared to conventional open-graded asphalt mix. There are also preliminary indications that the OGFC mix with 4.75-mm NMAS gradation can improve the resistance performance to raveling, while the OGFC mix with 9.5-mm NMAS gradation can improve the performance of surface friction at a high slip speed.
基金sponsored by Autostrade per l’Italia S.p.A.(Italy),which gave both financial and technical support within the framework of the Highway Pavement Evolutive Research(HiPER)project。
文摘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.
文摘The primary goal of this study is the design and construction of semi-flexible pavement(SFP)mixture in accordance with the engineering and mechanical criteria.This study involves the use of a range of gradation curves,air void contents,cellulose and synthesized fibers,and neat and modified asphalt binders to prepare the open-graded asphalt(OGA)mixtures.To analyze the characteristics of these mixtures,a variety of test,namely binder drainage,semi-circular bending(SCB),Cantabro,wheel tracking,indirect tensile strength(ITS),and permeability tests were conducted.Additionally,to analyze the prepared grouting material,flexural strength,compressive strength,and fluidity tests were conducted.In the final stage,SFP was compared to HMA in terms of engineering characteristics and performance.According to the results,SFP was more resistant to skid,rutting,fire,and moisture damage,while HMA had a better performance in fracture tests,including SCB test.According to the results of the mechanical performance tests conducted on OGA mixtures,the highest and lowest values for air void content to achieve the highest mechanical performance level were 30%-35%and 25%,respectively.Also,based on the laboratory results,it was determined that the required void ratio for constructing OGA mixtures was 24%-26%based on the bitumen type and fibers amount in the mixture.Finally,SFP mixture can be regarded as a viable alternative to common pavements thanks to its high resistance to rutting and moisture damage,long freezing-thawing fatigue life,and adequate fire and skid resistance.
基金The National Natural Science Foundation of China (No. 52178421)the Natural Science Foundation of Jiangsu Province(No. BK20191300)the Fundamental Research Funds for the Central Universities (No. B210202036)。
文摘The expansion and contraction of an open-graded friction course(OGFC)with a nominal maximum aggregate size of 13.2 mm(OGFC-13)with three air void contents(AVCs)and six saturation degrees(SDs)exposed to freeze-thaw(FT)cycles were measured using strain gauges.Cantabro tests were conducted on OGFC-13 specimens before and after FT cycles to evaluate the degradation of raveling resistance.The effects of SD,AVC,and the number of FT cycles on the expansion and contraction of OGFC-13 and degradation of raveling resistance were analyzed.Results show that OGFC with low water saturation will contract to stability during the freezing process,whereas fully saturated OGFC will contract first and then expand to be stable.OGFC with a medium saturation experienced three stages,namely,contraction,expansion,and contraction,during the freezing process.For the OGFC with a low SD,the decrease in the void content can effectively reduce the low temperature shrinkage.By contrast,for the OGFC with a high SD,lower void content produces more temperature shrinkage at the beginning of freezing and less expansion at the end of freezing.The decreases in SD and AVC can effectively improve the raveling resistance of OGFCs exposed to FT cycles.
基金sponsored by Autostrade per l’Italia S.p.A. (Italy)which gave both financial and technical support within the framework of the Highway Pavement Evolutive Research (HiPER) project。
文摘In the last decades,a new type of distress has been observed more and more frequently on asphalt pavements.This distress,ascribable to fatigue failure,has been named top-down cracking(TDC) because it consists in longitudinal cracks that initiate on the pavement surface and then propagate downwards.A series of surveys recently carried out on Italian motorways highlighted that TDC can affect up to 20%-30% of the slow traffic lane.Therefore,in order to achieve a better understanding of such distress,this paper reviews causes,models and experimental tools and highlights future challenges for TDC.The literature review indicates that TDC can evolve on the pavement surface in three stages(i.e.,single crack,sister cracks,alligator cracking) and,below a certain depth,the cracks can form angles of 20°-40° with respect to the vertical plane.Even though multiple factors contribute to TDC development,thick pavements are more likely to fail due to TDC induced by tire-pavement contact stresses,especially in the presence of open-graded friction courses(OGFCs).Moreover,in literature there are several TDC models based on mechanics(e.g.,fracture mechanics or continuum damage mechanics) which allow a rigorous study of crack initiation and propagation.Future challenges include the identification of a reliable and feasible test method,among those proposed in literature,to study the TDC performance of asphalt mixtures and the implementation of TDC in pavement management systems(PMSs) through the definition of criteria for TDC recognition in the field as well as for the rehabilitation depth evaluation.Finally,more research is needed for open-graded asphalt mixtures,which present critical drawbacks in terms of TDC.
