Road pavements, when exposed to traffic and temperature variations are subjected to a set of degr... more Road pavements, when exposed to traffic and temperature variations are subjected to a set of degradations on its surface, mainly to pavement cracking. Pavement cracking constitutes one of the main degradation of flexible pavements and it provokes distress states in the pavement which are responsible for the users' discomfort and safety reduction. Moreover, it allows the intrusion of water and the subsequent reduction of the pavement bearing capacity.
Neste artigo apresenta-se o resultado dum estudo de reabilitação estrutural dum pavimento flexíve... more Neste artigo apresenta-se o resultado dum estudo de reabilitação estrutural dum pavimento flexível dum arruamento urbano degradado, usando para tal um conjunto de ensaios de deflectometria com Viga Benkelman, para o registo das deflexões do pavimento e posterior avaliação das propriedades de deformabilidade de cada camada constituinte do pavimento. Com base nesta avaliação estrutural realizou-se um estudo de dimensionamento duma camada de reforço recorrendo a três de metodologias de dimensionamento diferentes considerando dois tipos de materiais alternativos, concretamente uma mistura betuminosa convencional e uma mistura com betume modificado com borracha (BMB). As metodologias
Reflective cracking is a major concern for engineers facing the problem of road maintenance and r... more Reflective cracking is a major concern for engineers facing the problem of road maintenance and rehabilitation. The problem appears due to the presence of cracks in the old pavement layers that propagate into the pavement overlay layer when traffic load passes over the cracks and due to the temperature variation. The stress concentration in the overlay just above the existing cracks is responsible for the appearance and crack propagation throughout the overlay. The analysis of the reflective cracking phenomenon is usually made by numerical modeling simulating the presence of cracks in the existing pavement and the stress concentration in the crack tip is assessed to predict either the cracking propagation rate or the expected fatigue life of the overlay. Numerical modeling to study reflective cracking is made by simulating one crack in the existing pavement and the loading is usually applied considering the shear mode of crack opening. Sometimes the simulation considers the mode I of crack opening, mainly when temperature effects are predominant. Thus, this paper presents a study where multiple cracks are modeled to assess the reflective cracking phenomenon and to compare to the case of only one crack. The modeling with only one crack was made simulating both mode I and mode II of crack opening taking into account the traffic effects. The influence of multiple cracks was expressed in terms of stress and strain in the zone above existing cracks. One of the conclusions from the current study is that the presence of multiple cracks can lead to a state of stress/strain higher than those obtained with only one crack. Also the position of the crack modeled in the finite elements analysis have a significant influence in the state of stress/strain obtained. However, the consideration of only one crack is sufficient to obtain significant results in the reflective cracking modeling.
This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack ret... more This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack retardation in overlays over rigid pavements. These interlayers are known in California as asphalt rubber absorbing membrane interlayers (SAMI-R) or as asphalt rubber aggregate membrane interlayers (ARAM-I) chip seals. The paper focuses on the performance in terms of field project reviews, laboratory performance tests and finite element analysis. SAMI-R has been given a reflective cracking equivalent thickness of 15 mm of asphalt rubber hot mix overlays or 30 mm of dense graded hot mix overlays. The finite element analysis confirms the quantified reflective cracking benefits of SAMI-R and provides optimum design alternatives to conventional dense grades asphalt concrete overlays. The paper concludes that SAMI-R is effective in minimizing reflective cracking distress and in extending pavement life.
Fatigue resistance is used in the analysis and design of pavements to predict their life cycle. I... more Fatigue resistance is used in the analysis and design of pavements to predict their life cycle. It is evaluated through time consuming laboratory tests, mainly when performed at very low strain levels. At low strain levels the testing time can last more than one day. Due to the heterogeneity of the material, a large number of samples are tested during days or weeks. The results of fatigue tests are expressed in terms of the number of cycles for the tensile strain level applied. Two constants (k 1 and k 2) obtained from a statistical analysis take part in this relationship. To know these two constants, at least two fatigue tests are needed, performed at different strain levels. k 1 and k 2 can be correlated and, in this case, the relationship between the fatigue life and the strain level has only one constant, which can be evaluated using the results obtained by a fatigue test. This paper presents the evaluation of the k 1 and k 2 relationship for Portuguese mixtures based on the results of 32 different asphalt mixtures composed by four different types of aggregate gradations.
Journal of transportation engineering, Sep 1, 2013
Traffic on a road pavement is characterized by a large number of different vehicle types, and the... more Traffic on a road pavement is characterized by a large number of different vehicle types, and these can be considered in pavement design by using truck factors to transform the damage they apply to the pavement to the damage that would be applied by a standard axle. The truck factors to convert trucks into standard axles or the load equivalent factors to convert axles into standard axles are defined by considering the average loads for each axle. This process includes the vehicles that travel with axle loads above the maximum legal limit. There are also a substantial number of overloaded vehicles in terms of total vehicle weight. These axles/vehicles cause significant damage to the pavements, increasing the pavement construction and rehabilitation cost. Thus, this paper investigates the impact of overloaded vehicles on road pavements by studying the truck factors for different vehicle cases applied to a set of pavements composed of five different asphalt layer thicknesses and five different subgrade stiffness moduli. The study revealed that the presence of overloaded vehicles can increase pavement costs by more than 100% compared to the cost of the same vehicles with legal loads.
This paper presents a study on the influence of the effects of temperature variations, in compari... more This paper presents a study on the influence of the effects of temperature variations, in comparison to the traffic effects, on the reflective cracking behavior. It intends to contribute to the improvement of the pavement overlay design methods which consider reflective cracking as one among distress criteria. The development of this study was based on the numerical simulation of the overlay behavior, through the implementation of numerical thermal and mechanical models based on the finite element, considering the simultaneous action of traffic and temperature variations and their influence on reflective cracking. For overlay design purposes, it is important to consider temperature variations in the evaluation of the overlay behavior produced by the reflective cracking. The expected performance of an asphalt rubber hot mix, produced by the wet process with 20% crumb rubber was compared to a conventional asphalt taking into account the performance of these mixes.
A finite element model has been developed to calculate the temperature of a pavement located in t... more A finite element model has been developed to calculate the temperature of a pavement located in the Northeast of Portugal. The goal of the case study presented in this paper is the validation of this model. Input data to the model are the hourly values for solar radiation and temperature, and mean daily values of wind speed obtained from a meteorological station. The thermal response of a multilayered pavement structure is modeled using a transient thermal analysis for four months time-period (December 2003-April 2004) and the analysis was initiated with the full depth constant initial temperature obtained from field measurements. During these four mo nths, pavement temperature was measured at a new pavement section, located at IP4 main road, near Bragança, in the north of Portugal. At that location, seven thermocouples were installed in the AC layers, at seven different depths. These pavement data was used to validate this simulation model, by comparing model calculated data with measured pavement temperatures. As conclusion, the 3-D finite-element analysis proved to be an interesting tool to simulate the transient behavior of asphalt concrete pavements. The suggested simulation model can predict the pavement temperature at different levels of bituminous layers with a good accuracy.
This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack ret... more This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack retardation in flexible pavement preservation and rehabilitation strategies. These interlayers are known in California as asphalt rubber absorbing membrane interlayers (SAMI-R) or as asphalt rubber aggregate membrane interlayers (ARAM-I) chip seals. These interlayers have been used successfully as part of cape seals and as part of an overlay system. The paper focuses on the performance in terms of field project reviews, laboratory performance tests and finite element analysis. The paper concluded that SAMI-R are effective in minimizing reflective cracking distress and in extending pavement life.
Fatigue resistance of asphalt mixtures represents an important parameter for pavement design. Thi... more Fatigue resistance of asphalt mixtures represents an important parameter for pavement design. This fatigue resistance is calculated through laboratory tests which require some time depending on the strain level applied to the specimen. For very low strain levels, identical to the one installed in the pavement, one test may last more than one week depending on the testing frequency. The time needed for the development of the fatigue law may last longer. Recent developments introduced an energy approach, based on the ratio of dissipated energy change, which leads to a plateau value that requires short testing to predict the specimen failure. This paper presents the implementation of this approach to evaluate the fatigue resistance of Portuguese asphalt mixtures. Three asphalt mixtures were studied. The first mixture was tested using two strain levels and three specimens for strain level. The second mixture was tested using three strain levels and three specimens per strain level, whereas the last mixture was tested with 18 specimens, 6 per strain level. The approach seems to have potential to be used for fast evaluation of the fatigue response of asphalt mixtures.
The fatigue resistance of asphalt mixtures is calculated through laboratory tests which require s... more The fatigue resistance of asphalt mixtures is calculated through laboratory tests which require some time depending on the strain level applied to the specimen. For very low strain levels, identical to the one installed in the pavement of this study, one test may last more than one week depending on the testing frequency. The time needed for the development of the fatigue law may last longer. The number of specimens used to calculate the fatigue resistance of an asphalt mixture plays an important role in the precision of pavement design. Thus, this paper presents a study to evaluate the number of tests to assess the fatigue resistance of asphalt mixtures through the four-point bending technique. The results obtained from the analysis of three different asphalt mixtures tested by applying 3 strain levels and 6 specimens for each strain level were used to evaluate the fatigue resistance dispersion to identify the number of tests to define a fatigue law.
Road pavements, when exposed to traffic and temperature variations are subjected to a set of degr... more Road pavements, when exposed to traffic and temperature variations are subjected to a set of degradations on its surface, mainly to pavement cracking. Pavement cracking constitutes one of the main degradation of flexible pavements and it provokes distress states in the pavement which are responsible for the users' discomfort and safety reduction. Moreover, it allows the intrusion of water and the subsequent reduction of the pavement bearing capacity.
Neste artigo apresenta-se o resultado dum estudo de reabilitação estrutural dum pavimento flexíve... more Neste artigo apresenta-se o resultado dum estudo de reabilitação estrutural dum pavimento flexível dum arruamento urbano degradado, usando para tal um conjunto de ensaios de deflectometria com Viga Benkelman, para o registo das deflexões do pavimento e posterior avaliação das propriedades de deformabilidade de cada camada constituinte do pavimento. Com base nesta avaliação estrutural realizou-se um estudo de dimensionamento duma camada de reforço recorrendo a três de metodologias de dimensionamento diferentes considerando dois tipos de materiais alternativos, concretamente uma mistura betuminosa convencional e uma mistura com betume modificado com borracha (BMB). As metodologias
Reflective cracking is a major concern for engineers facing the problem of road maintenance and r... more Reflective cracking is a major concern for engineers facing the problem of road maintenance and rehabilitation. The problem appears due to the presence of cracks in the old pavement layers that propagate into the pavement overlay layer when traffic load passes over the cracks and due to the temperature variation. The stress concentration in the overlay just above the existing cracks is responsible for the appearance and crack propagation throughout the overlay. The analysis of the reflective cracking phenomenon is usually made by numerical modeling simulating the presence of cracks in the existing pavement and the stress concentration in the crack tip is assessed to predict either the cracking propagation rate or the expected fatigue life of the overlay. Numerical modeling to study reflective cracking is made by simulating one crack in the existing pavement and the loading is usually applied considering the shear mode of crack opening. Sometimes the simulation considers the mode I of crack opening, mainly when temperature effects are predominant. Thus, this paper presents a study where multiple cracks are modeled to assess the reflective cracking phenomenon and to compare to the case of only one crack. The modeling with only one crack was made simulating both mode I and mode II of crack opening taking into account the traffic effects. The influence of multiple cracks was expressed in terms of stress and strain in the zone above existing cracks. One of the conclusions from the current study is that the presence of multiple cracks can lead to a state of stress/strain higher than those obtained with only one crack. Also the position of the crack modeled in the finite elements analysis have a significant influence in the state of stress/strain obtained. However, the consideration of only one crack is sufficient to obtain significant results in the reflective cracking modeling.
This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack ret... more This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack retardation in overlays over rigid pavements. These interlayers are known in California as asphalt rubber absorbing membrane interlayers (SAMI-R) or as asphalt rubber aggregate membrane interlayers (ARAM-I) chip seals. The paper focuses on the performance in terms of field project reviews, laboratory performance tests and finite element analysis. SAMI-R has been given a reflective cracking equivalent thickness of 15 mm of asphalt rubber hot mix overlays or 30 mm of dense graded hot mix overlays. The finite element analysis confirms the quantified reflective cracking benefits of SAMI-R and provides optimum design alternatives to conventional dense grades asphalt concrete overlays. The paper concludes that SAMI-R is effective in minimizing reflective cracking distress and in extending pavement life.
Fatigue resistance is used in the analysis and design of pavements to predict their life cycle. I... more Fatigue resistance is used in the analysis and design of pavements to predict their life cycle. It is evaluated through time consuming laboratory tests, mainly when performed at very low strain levels. At low strain levels the testing time can last more than one day. Due to the heterogeneity of the material, a large number of samples are tested during days or weeks. The results of fatigue tests are expressed in terms of the number of cycles for the tensile strain level applied. Two constants (k 1 and k 2) obtained from a statistical analysis take part in this relationship. To know these two constants, at least two fatigue tests are needed, performed at different strain levels. k 1 and k 2 can be correlated and, in this case, the relationship between the fatigue life and the strain level has only one constant, which can be evaluated using the results obtained by a fatigue test. This paper presents the evaluation of the k 1 and k 2 relationship for Portuguese mixtures based on the results of 32 different asphalt mixtures composed by four different types of aggregate gradations.
Journal of transportation engineering, Sep 1, 2013
Traffic on a road pavement is characterized by a large number of different vehicle types, and the... more Traffic on a road pavement is characterized by a large number of different vehicle types, and these can be considered in pavement design by using truck factors to transform the damage they apply to the pavement to the damage that would be applied by a standard axle. The truck factors to convert trucks into standard axles or the load equivalent factors to convert axles into standard axles are defined by considering the average loads for each axle. This process includes the vehicles that travel with axle loads above the maximum legal limit. There are also a substantial number of overloaded vehicles in terms of total vehicle weight. These axles/vehicles cause significant damage to the pavements, increasing the pavement construction and rehabilitation cost. Thus, this paper investigates the impact of overloaded vehicles on road pavements by studying the truck factors for different vehicle cases applied to a set of pavements composed of five different asphalt layer thicknesses and five different subgrade stiffness moduli. The study revealed that the presence of overloaded vehicles can increase pavement costs by more than 100% compared to the cost of the same vehicles with legal loads.
This paper presents a study on the influence of the effects of temperature variations, in compari... more This paper presents a study on the influence of the effects of temperature variations, in comparison to the traffic effects, on the reflective cracking behavior. It intends to contribute to the improvement of the pavement overlay design methods which consider reflective cracking as one among distress criteria. The development of this study was based on the numerical simulation of the overlay behavior, through the implementation of numerical thermal and mechanical models based on the finite element, considering the simultaneous action of traffic and temperature variations and their influence on reflective cracking. For overlay design purposes, it is important to consider temperature variations in the evaluation of the overlay behavior produced by the reflective cracking. The expected performance of an asphalt rubber hot mix, produced by the wet process with 20% crumb rubber was compared to a conventional asphalt taking into account the performance of these mixes.
A finite element model has been developed to calculate the temperature of a pavement located in t... more A finite element model has been developed to calculate the temperature of a pavement located in the Northeast of Portugal. The goal of the case study presented in this paper is the validation of this model. Input data to the model are the hourly values for solar radiation and temperature, and mean daily values of wind speed obtained from a meteorological station. The thermal response of a multilayered pavement structure is modeled using a transient thermal analysis for four months time-period (December 2003-April 2004) and the analysis was initiated with the full depth constant initial temperature obtained from field measurements. During these four mo nths, pavement temperature was measured at a new pavement section, located at IP4 main road, near Bragança, in the north of Portugal. At that location, seven thermocouples were installed in the AC layers, at seven different depths. These pavement data was used to validate this simulation model, by comparing model calculated data with measured pavement temperatures. As conclusion, the 3-D finite-element analysis proved to be an interesting tool to simulate the transient behavior of asphalt concrete pavements. The suggested simulation model can predict the pavement temperature at different levels of bituminous layers with a good accuracy.
This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack ret... more This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack retardation in flexible pavement preservation and rehabilitation strategies. These interlayers are known in California as asphalt rubber absorbing membrane interlayers (SAMI-R) or as asphalt rubber aggregate membrane interlayers (ARAM-I) chip seals. These interlayers have been used successfully as part of cape seals and as part of an overlay system. The paper focuses on the performance in terms of field project reviews, laboratory performance tests and finite element analysis. The paper concluded that SAMI-R are effective in minimizing reflective cracking distress and in extending pavement life.
Fatigue resistance of asphalt mixtures represents an important parameter for pavement design. Thi... more Fatigue resistance of asphalt mixtures represents an important parameter for pavement design. This fatigue resistance is calculated through laboratory tests which require some time depending on the strain level applied to the specimen. For very low strain levels, identical to the one installed in the pavement, one test may last more than one week depending on the testing frequency. The time needed for the development of the fatigue law may last longer. Recent developments introduced an energy approach, based on the ratio of dissipated energy change, which leads to a plateau value that requires short testing to predict the specimen failure. This paper presents the implementation of this approach to evaluate the fatigue resistance of Portuguese asphalt mixtures. Three asphalt mixtures were studied. The first mixture was tested using two strain levels and three specimens for strain level. The second mixture was tested using three strain levels and three specimens per strain level, whereas the last mixture was tested with 18 specimens, 6 per strain level. The approach seems to have potential to be used for fast evaluation of the fatigue response of asphalt mixtures.
The fatigue resistance of asphalt mixtures is calculated through laboratory tests which require s... more The fatigue resistance of asphalt mixtures is calculated through laboratory tests which require some time depending on the strain level applied to the specimen. For very low strain levels, identical to the one installed in the pavement of this study, one test may last more than one week depending on the testing frequency. The time needed for the development of the fatigue law may last longer. The number of specimens used to calculate the fatigue resistance of an asphalt mixture plays an important role in the precision of pavement design. Thus, this paper presents a study to evaluate the number of tests to assess the fatigue resistance of asphalt mixtures through the four-point bending technique. The results obtained from the analysis of three different asphalt mixtures tested by applying 3 strain levels and 6 specimens for each strain level were used to evaluate the fatigue resistance dispersion to identify the number of tests to define a fatigue law.
A 3-D finite element model has been developed to calculate the temperature of a pavement located ... more A 3-D finite element model has been developed to calculate the temperature of a pavement located in the Northeast of Portugal. The goal of the case study presented in this paper is the validation of this model. Input data to the model are the hourly values for solar radiation and temperature, and mean daily values of wind speed obtained from a meteorological station. The thermal response of a multilayered pavement structure is modeled using a transient thermal analysis for four months time-period (December 2003 - April 2004) and the analysis was initiated with the full depth constant initial temperature obtained from field measurements. During these four months, the pavement temperature was measured at a new pavement section, located in IP4 main road, near Bragança, in the north of Portugal. At this location, seven thermocouples were installed in the AC layers, at seven different depths. These pavement data was used to validate this simulation model, by comparing model calculated data with measured pavement temperatures. As conclusion, the 3-D finite-element analysis proved to be an interesting tool to simulate the transient behavior of asphalt concrete pavements. The suggested simulation model can predict the pavement temperature at different levels of bituminous layers with good accuracy.
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