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Hussain U. Bahia - One of the best experts on this subject based on the ideXlab platform.

  • mechanisms controlling shearing resistance of mixtures in the superpave Gyratory Compactor
    Transportation Research Board 94th Annual MeetingTransportation Research Board, 2015
    Co-Authors: Nima Roohi Sefidmazgi, Hussain U. Bahia
    Abstract:

    Rutting performance characterization of asphalt mixtures has attracted a lot of attention after the implementation of the Superpave Volumetric Mixture design method due to the lack of a stability or strength test in the volumetric design criteria. Different test and analysis methods have been proposed with a goal of accurately, as well as simply, predicting the rutting performance of designed mixtures. The simplicity and cost effectiveness of using the Superpave Gyratory Compactor (SGC) made many researchers interested to find a fundamental and practical way for rutting characterization during compaction. One of the promising tools used for characterization of asphalt mixture internal friction and stability during compaction in SGC is the Gyratory Pressure Distribution Analyzer (GPDA). This study is focused on understanding the mechanisms and fundamental material characteristics that control the shearing resistance of asphalt mixtures throughout the compaction in SGC. The main cause of reduction in internal friction of some mixtures during compaction is shown to be the buildup of pore binder pressure and static liquefaction at lower air voids although some other factors may affect this phenomenon as well. It is shown that the mixtures with lower aggregate packing, measured using an image analysis method in this study, are more prone to reduction in internal friction. It is thus necessary to ensure that higher packing and more contact points be formed by selection of gradation to reduce the risk of instability resulting from liquefaction (loss of internal friction). Measuring internal friction is a necessary compliment to volumetric mixture design.

  • Implementation of WisDOT Project 0092-01-02: Using the SuperPave Gyratory Compactor to Measure Mechanical Stability of WisDOT Asphalt Mixes
    2008
    Co-Authors: Ahmed Faheem, Andrew Hanz, Hussain U. Bahia
    Abstract:

    Due to the Wisconsin Department of Transportation's (WisDOT’s) commitment for the transitioning from the current empirical pavement design procedures to the new Mechanistic Pavement Design, WisDOT Project 0092-01-02: “Using the Gyratory Compactor to Measure Mechanical Stability of Asphaltic Mixtures” was selected as one of the first the research projects to implement. The project investigated the potential for the SuperPave Gyratory Compactor to provide estimates of the mechanical behavior of mixtures that can be used in the new design procedure. Mechanistic Pavement Design procedures require measurements collected with complex equipment and test methods in order to quantify the mechanical behavior of hot mix asphalt (HMA) mixes. These test methods are not practical enough to be used for quality control or quality assurance in practice. Also, logistical issues and high costs associated with equipment procurement and training has prevented WisDOT from cataloging common HMA mixes to date. These limitations identified the need for a surrogate test to allow industry and the agency to obtain information related to the mechanical properties of HMA mixtures commonly used in Wisonsin and to develop simple quality management test protocols. Research results from Project # 0092-01-02 showed potential to use the Superpave Gyratory Compactor, which is used currently for volumetric mixture design and for quality management as the surrogate test. The results of this test are expected to bridge the gap between specifying HMA mixtures based on only volumetrics, which is the current practice, and evaluating their mechanical properties, which will be needed for the new pavement design procedure. This implementation project served the purpose of synthesizing the fundamental concepts and recommendations published in the original research study report into a package that can easily be understood and applied to everyday practice.

  • using the superpave Gyratory Compactor to estimate rutting resistance of hot mix asphalt
    Transportation research circular, 2007
    Co-Authors: Hussain U. Bahia, Ahmed Faheem
    Abstract:

    Several approaches have been introduced lately to characterize the performance-related properties of asphalt mixtures. The majority of these efforts are focused on developing special equipment to test mixtures at conditions similar to those acting on pavements due to moving traffic. Because the Superpave Gyratory Compactor (SGC) is used routinely for compaction, and because it has components to measure load and densification, this study investigated its use for estimating the stability of asphalt mixtures as a surrogate or an estimate for results of the proposed method for the simple performance test. Several asphalt mixtures were produced using four different aggregate sources, different asphalt contents, and different gradations. Each mixture was compacted using the SGC. To evaluate if the results from the SGC can be related to rutting, mixtures were also tested using the new repeated compression test procedure recommended by the NCHRP Project 9-19 and used in the "Mechanistic–Empirical Pavement Design Guide." Densification curves produced by the SGC were used to determine volumetric properties of the mix and to calculate the traffic densification index (TDI), which is the value of the area under the densification curve from 92% density to 98% density and which represents the densification experienced due to traffic loading during the pavement service life. One more index, the traffic force index (TFI), is calculated. The TFI is the amount of work done to change the density of the mix from 92% to 98% measured using a special accessory added to the SGC called the pressure distribution analyzer (PDA). The results from the mixture rutting tests were used to estimate the rutting rate and the flow number (FN), which is the point at which the mixture starts to exhibit tertiary flow. The FN, which is considered an important mixture property, is shown to have a strong correlation to the TFI derived from the mixtures’ resistance behavior measured in the SGC and the PDA. The TFI was found to be strongly correlated to the TDI, giving the opportunity to estimate the mixture resistance to compaction forces using its volumetric behavior. The main finding of the study is that the SGC gives information that can be used to characterize the stability of asphalt mixtures. Such information could be used as an initial screening criterion to select mixtures for various traffic levels.

  • estimating results of a proposed simple performance test for hot mix asphalt from superpave Gyratory Compactor results
    Transportation Research Record, 2005
    Co-Authors: Ahmed Faheem, Hussain U. Bahia, Hossein Ajideh
    Abstract:

    This study intended to use the Superpave® Gyratory Compactor (SGC) as a basis for estimating the stability of asphalt mixtures as a surrogate for proposed method for the simple performance test. Several asphalt mixtures were produced with varying aggregate sources, asphalt contents, and gradations. Every mixture was compacted with the SGC and evaluated with the repeated compression test procedure for rutting measurements recommended by NCHRP Project 9-19 and the AASHTO 2002 pavement design manual to evaluate whether the results from the SGC can be related to the rutting of mixtures. Densification curves produced by the SGC were used to determine the volumetric properties besides the calculation of the traffic densification index (TDI), which represents the densification experienced by traffic loading during pavement service life. The traffic force index (TFI) was also calculated with a special accessory added to the SGC during compaction (the pressure distributor analyzer). The TFI represents the work done by the traffic to densify the mixture. Results from the mixture rutting tests were used to estimate the flow number (FN). The FN, an important mixture property, is shown to have a strong correlation to the TFI. The TFI was also found to be strongly correlated with the TDI and gives an opportunity to estimate the mixture resistance to compaction forces with the use of its volumetric behavior. The main finding of the study is that the SGC appears to give information that can be used to characterize the stability of the mixtures. Such information could be used as an initial screening criterion to select mixtures for various traffic levels.

  • using Gyratory Compactor to measure mechanical stability of asphalt mixtures
    2004
    Co-Authors: Hussain U. Bahia, Ahmed Faheem
    Abstract:

    In this study several asphalt mixtures were produced using four different aggregate sources, different asphalt contents, and different aggregate gradations. Every mixture was compacted using the Superpave Gyratory Compactor (SGC). To evaluate if the densification results from the SGC can be related to rutting of mixtures, the new axial compression test procedure for rutting measurements recommended by the National Cooperative Highway Research Program project 9-19 and used in the AASHTO 2002 pavement design manual, was also used for evaluating the rutting behavior for laboratory produced samples. Densification curves produced by the SGC were used to determine volumetric properties of the mix as well as for the calculation of the construction and the traffic densification indices. The construction densification index (CDI), which is the value of the area under the densification curve from density at 8 gyrations to density of 92% Gmm, represents the work done during the construction period to achieve 8% air voids. The traffic densification index (TDI), which is the value of the area under the densification curve from 92% density to 98% density, represents the work needed to resist traffic loading during pavement service life. Two more indices are calculated, construction force index (CFI) and traffic force index (TFI). CFI is related to the amount of work done to raise the density of the mix to 92%. The TFI is the amount of work done to increase the density of the mix from 92% to 98%. The results from the mixture rutting tests were used to estimate the rutting rate and the flow number (FN), which is the point at which the mixture starts to exhibit tertiary flow. The FN, which is considered an important mixture property, is shown to have a strong correlation to the TDI derived from the mixture volumetric behavior measured in the SGC. The main finding of the study is that SGC appears to give information that can be used to characterize the stability of the mixtures. Such information could be used as an initial screening criterion to select mixture for various traffic ESAL (equivalent single axle load) levels, in addition to indicating an expected performance level.

Ahmed Faheem - One of the best experts on this subject based on the ideXlab platform.

  • Implementation of WisDOT Project 0092-01-02: Using the SuperPave Gyratory Compactor to Measure Mechanical Stability of WisDOT Asphalt Mixes
    2008
    Co-Authors: Ahmed Faheem, Andrew Hanz, Hussain U. Bahia
    Abstract:

    Due to the Wisconsin Department of Transportation's (WisDOT’s) commitment for the transitioning from the current empirical pavement design procedures to the new Mechanistic Pavement Design, WisDOT Project 0092-01-02: “Using the Gyratory Compactor to Measure Mechanical Stability of Asphaltic Mixtures” was selected as one of the first the research projects to implement. The project investigated the potential for the SuperPave Gyratory Compactor to provide estimates of the mechanical behavior of mixtures that can be used in the new design procedure. Mechanistic Pavement Design procedures require measurements collected with complex equipment and test methods in order to quantify the mechanical behavior of hot mix asphalt (HMA) mixes. These test methods are not practical enough to be used for quality control or quality assurance in practice. Also, logistical issues and high costs associated with equipment procurement and training has prevented WisDOT from cataloging common HMA mixes to date. These limitations identified the need for a surrogate test to allow industry and the agency to obtain information related to the mechanical properties of HMA mixtures commonly used in Wisonsin and to develop simple quality management test protocols. Research results from Project # 0092-01-02 showed potential to use the Superpave Gyratory Compactor, which is used currently for volumetric mixture design and for quality management as the surrogate test. The results of this test are expected to bridge the gap between specifying HMA mixtures based on only volumetrics, which is the current practice, and evaluating their mechanical properties, which will be needed for the new pavement design procedure. This implementation project served the purpose of synthesizing the fundamental concepts and recommendations published in the original research study report into a package that can easily be understood and applied to everyday practice.

  • using the superpave Gyratory Compactor to estimate rutting resistance of hot mix asphalt
    Transportation research circular, 2007
    Co-Authors: Hussain U. Bahia, Ahmed Faheem
    Abstract:

    Several approaches have been introduced lately to characterize the performance-related properties of asphalt mixtures. The majority of these efforts are focused on developing special equipment to test mixtures at conditions similar to those acting on pavements due to moving traffic. Because the Superpave Gyratory Compactor (SGC) is used routinely for compaction, and because it has components to measure load and densification, this study investigated its use for estimating the stability of asphalt mixtures as a surrogate or an estimate for results of the proposed method for the simple performance test. Several asphalt mixtures were produced using four different aggregate sources, different asphalt contents, and different gradations. Each mixture was compacted using the SGC. To evaluate if the results from the SGC can be related to rutting, mixtures were also tested using the new repeated compression test procedure recommended by the NCHRP Project 9-19 and used in the "Mechanistic–Empirical Pavement Design Guide." Densification curves produced by the SGC were used to determine volumetric properties of the mix and to calculate the traffic densification index (TDI), which is the value of the area under the densification curve from 92% density to 98% density and which represents the densification experienced due to traffic loading during the pavement service life. One more index, the traffic force index (TFI), is calculated. The TFI is the amount of work done to change the density of the mix from 92% to 98% measured using a special accessory added to the SGC called the pressure distribution analyzer (PDA). The results from the mixture rutting tests were used to estimate the rutting rate and the flow number (FN), which is the point at which the mixture starts to exhibit tertiary flow. The FN, which is considered an important mixture property, is shown to have a strong correlation to the TFI derived from the mixtures’ resistance behavior measured in the SGC and the PDA. The TFI was found to be strongly correlated to the TDI, giving the opportunity to estimate the mixture resistance to compaction forces using its volumetric behavior. The main finding of the study is that the SGC gives information that can be used to characterize the stability of asphalt mixtures. Such information could be used as an initial screening criterion to select mixtures for various traffic levels.

  • estimating results of a proposed simple performance test for hot mix asphalt from superpave Gyratory Compactor results
    Transportation Research Record, 2005
    Co-Authors: Ahmed Faheem, Hussain U. Bahia, Hossein Ajideh
    Abstract:

    This study intended to use the Superpave® Gyratory Compactor (SGC) as a basis for estimating the stability of asphalt mixtures as a surrogate for proposed method for the simple performance test. Several asphalt mixtures were produced with varying aggregate sources, asphalt contents, and gradations. Every mixture was compacted with the SGC and evaluated with the repeated compression test procedure for rutting measurements recommended by NCHRP Project 9-19 and the AASHTO 2002 pavement design manual to evaluate whether the results from the SGC can be related to the rutting of mixtures. Densification curves produced by the SGC were used to determine the volumetric properties besides the calculation of the traffic densification index (TDI), which represents the densification experienced by traffic loading during pavement service life. The traffic force index (TFI) was also calculated with a special accessory added to the SGC during compaction (the pressure distributor analyzer). The TFI represents the work done by the traffic to densify the mixture. Results from the mixture rutting tests were used to estimate the flow number (FN). The FN, an important mixture property, is shown to have a strong correlation to the TFI. The TFI was also found to be strongly correlated with the TDI and gives an opportunity to estimate the mixture resistance to compaction forces with the use of its volumetric behavior. The main finding of the study is that the SGC appears to give information that can be used to characterize the stability of the mixtures. Such information could be used as an initial screening criterion to select mixtures for various traffic levels.

  • using Gyratory Compactor to measure mechanical stability of asphalt mixtures
    2004
    Co-Authors: Hussain U. Bahia, Ahmed Faheem
    Abstract:

    In this study several asphalt mixtures were produced using four different aggregate sources, different asphalt contents, and different aggregate gradations. Every mixture was compacted using the Superpave Gyratory Compactor (SGC). To evaluate if the densification results from the SGC can be related to rutting of mixtures, the new axial compression test procedure for rutting measurements recommended by the National Cooperative Highway Research Program project 9-19 and used in the AASHTO 2002 pavement design manual, was also used for evaluating the rutting behavior for laboratory produced samples. Densification curves produced by the SGC were used to determine volumetric properties of the mix as well as for the calculation of the construction and the traffic densification indices. The construction densification index (CDI), which is the value of the area under the densification curve from density at 8 gyrations to density of 92% Gmm, represents the work done during the construction period to achieve 8% air voids. The traffic densification index (TDI), which is the value of the area under the densification curve from 92% density to 98% density, represents the work needed to resist traffic loading during pavement service life. Two more indices are calculated, construction force index (CFI) and traffic force index (TFI). CFI is related to the amount of work done to raise the density of the mix to 92%. The TFI is the amount of work done to increase the density of the mix from 92% to 98%. The results from the mixture rutting tests were used to estimate the rutting rate and the flow number (FN), which is the point at which the mixture starts to exhibit tertiary flow. The FN, which is considered an important mixture property, is shown to have a strong correlation to the TDI derived from the mixture volumetric behavior measured in the SGC. The main finding of the study is that SGC appears to give information that can be used to characterize the stability of the mixtures. Such information could be used as an initial screening criterion to select mixture for various traffic ESAL (equivalent single axle load) levels, in addition to indicating an expected performance level.

Emily Oquinn - One of the best experts on this subject based on the ideXlab platform.

  • specimen geometry study for direct tension test based on mechanical tests and air void variation in asphalt concrete specimens compacted by superpave Gyratory Compactor
    Transportation Research Record, 2000
    Co-Authors: Ghassan R Chehab, Emily Oquinn
    Abstract:

    Reliable materials characterization and performance prediction testing of asphalt concrete requires specimens that can be treated as statistically homogeneous and representative of the material being tested. The objective of this study was to select a proper specimen geometry that could be used for uniaxial tensile testing. Selection was based on the variation of air void content along the height of specimens cut and cored from specimens compacted by the Superpave Gyratory Compactor (SGC) and on the representative behavior under mechanical testing. From measurement and comparison of air void contents in cut and cored specimens, it was observed for several geometries that sections at the top and bottom and those adjacent to the mold walls have a higher air void content than do those in the middle. It is thus imperative that test specimens be cut and cored from larger-size SGC specimens. Complex modulus and constant crosshead-rate monotonic tests were conducted for four geometries—75 × 115, 75 × 150, 100 × ...

  • specimen geometry study for direct tension test based on mechanical tests and air void variation in asphalt concrete specimens compacted by superpave Gyratory Compactor asphalt mixtures 2000
    Transportation Research Record, 2000
    Co-Authors: Ghassan R Chehab, Emily Oquinn, Richard Y Kim
    Abstract:

    Reliable materials characterization and performance prediction testing of asphalt concrete requires specimens that can be treated as statistically homogeneous and representative of the material being tested. The objective of this study was to select a proper specimen geometry that could be used for uniaxial tensile testing. Selection was based on the variation of air void content along the height of specimens cut and cored from specimens compacted by the Superpave Gyratory Compactor (SGC) and on the representative behavior under mechanical testing. From measurement and comparison of air void contents in cut and cored specimens, it was observed for several geometries that sections at the top and bottom and those adjacent to the mold walls have a higher air void content than do those in the middle. It is thus imperative that test specimens be cut and cored from larger-size SGC specimens. Complex modulus and constant crosshead-rate monotonic tests were conducted for four geometries-75 x 115, 75 x 150, 100 x 150, and 100 x 200 mm-to study the effect of geometry boundary conditions on responses. On the basis of graphical and statistical analysis, it was determined that there was an effect on the dynamic modulus at certain frequencies but no effect on the phase angle. Except for 75 x 115 mm, all geometries behaved similarly under the monotonic test. From these findings and other considerations, it is recommended that the 75- x 150-mm geometry, which is more conservative, and the 100- x 150-mm geometry be used for tensile testing.

Ghassan R Chehab - One of the best experts on this subject based on the ideXlab platform.

  • specimen geometry study for direct tension test based on mechanical tests and air void variation in asphalt concrete specimens compacted by superpave Gyratory Compactor
    Transportation Research Record, 2000
    Co-Authors: Ghassan R Chehab, Emily Oquinn
    Abstract:

    Reliable materials characterization and performance prediction testing of asphalt concrete requires specimens that can be treated as statistically homogeneous and representative of the material being tested. The objective of this study was to select a proper specimen geometry that could be used for uniaxial tensile testing. Selection was based on the variation of air void content along the height of specimens cut and cored from specimens compacted by the Superpave Gyratory Compactor (SGC) and on the representative behavior under mechanical testing. From measurement and comparison of air void contents in cut and cored specimens, it was observed for several geometries that sections at the top and bottom and those adjacent to the mold walls have a higher air void content than do those in the middle. It is thus imperative that test specimens be cut and cored from larger-size SGC specimens. Complex modulus and constant crosshead-rate monotonic tests were conducted for four geometries—75 × 115, 75 × 150, 100 × ...

  • specimen geometry study for direct tension test based on mechanical tests and air void variation in asphalt concrete specimens compacted by superpave Gyratory Compactor asphalt mixtures 2000
    Transportation Research Record, 2000
    Co-Authors: Ghassan R Chehab, Emily Oquinn, Richard Y Kim
    Abstract:

    Reliable materials characterization and performance prediction testing of asphalt concrete requires specimens that can be treated as statistically homogeneous and representative of the material being tested. The objective of this study was to select a proper specimen geometry that could be used for uniaxial tensile testing. Selection was based on the variation of air void content along the height of specimens cut and cored from specimens compacted by the Superpave Gyratory Compactor (SGC) and on the representative behavior under mechanical testing. From measurement and comparison of air void contents in cut and cored specimens, it was observed for several geometries that sections at the top and bottom and those adjacent to the mold walls have a higher air void content than do those in the middle. It is thus imperative that test specimens be cut and cored from larger-size SGC specimens. Complex modulus and constant crosshead-rate monotonic tests were conducted for four geometries-75 x 115, 75 x 150, 100 x 150, and 100 x 200 mm-to study the effect of geometry boundary conditions on responses. On the basis of graphical and statistical analysis, it was determined that there was an effect on the dynamic modulus at certain frequencies but no effect on the phase angle. Except for 75 x 115 mm, all geometries behaved similarly under the monotonic test. From these findings and other considerations, it is recommended that the 75- x 150-mm geometry, which is more conservative, and the 100- x 150-mm geometry be used for tensile testing.

Richard Y Kim - One of the best experts on this subject based on the ideXlab platform.

  • specimen geometry study for direct tension test based on mechanical tests and air void variation in asphalt concrete specimens compacted by superpave Gyratory Compactor asphalt mixtures 2000
    Transportation Research Record, 2000
    Co-Authors: Ghassan R Chehab, Emily Oquinn, Richard Y Kim
    Abstract:

    Reliable materials characterization and performance prediction testing of asphalt concrete requires specimens that can be treated as statistically homogeneous and representative of the material being tested. The objective of this study was to select a proper specimen geometry that could be used for uniaxial tensile testing. Selection was based on the variation of air void content along the height of specimens cut and cored from specimens compacted by the Superpave Gyratory Compactor (SGC) and on the representative behavior under mechanical testing. From measurement and comparison of air void contents in cut and cored specimens, it was observed for several geometries that sections at the top and bottom and those adjacent to the mold walls have a higher air void content than do those in the middle. It is thus imperative that test specimens be cut and cored from larger-size SGC specimens. Complex modulus and constant crosshead-rate monotonic tests were conducted for four geometries-75 x 115, 75 x 150, 100 x 150, and 100 x 200 mm-to study the effect of geometry boundary conditions on responses. On the basis of graphical and statistical analysis, it was determined that there was an effect on the dynamic modulus at certain frequencies but no effect on the phase angle. Except for 75 x 115 mm, all geometries behaved similarly under the monotonic test. From these findings and other considerations, it is recommended that the 75- x 150-mm geometry, which is more conservative, and the 100- x 150-mm geometry be used for tensile testing.