Balanced Mix Design (BMD) for Asphalt Mixtures...Balanced mix design (BMD) is an innovative...
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Balanced Mix Design (BMD) for Asphalt Mixtures Based on data collected from 2015 through 2018, it has been determined that recycled asphalt materials (RAM), PG binder grade, asphalt content, and use of certain additives (WMA, anti-stripping agents, etc.) are critical in developing a “balanced” asphalt mixture overall. Aaron Schwartz, Ian Anderson, Nick Van Den Berg VTrans – Highway Division Construction & Materials Bureau – Materials & Certification Section Background Balanced mix design (BMD) is an innovative methodology in evaluating asphalt mix designs by utilizing performance – related tests correlated to various engineering properties to analyze the rutting, cracking, and moisture susceptibilities of the mixtures. VTrans is currently using two (2) test methods for this endeavor. The Hamburg Wheel Tracker Test (HWTT) equipment at left; Illinois Flexibility Index Test (I-FIT) equipment at right Methodology The HWTT has been used for investigative purposes beginning in 2015 to analyze the rutting and moisture susceptibilities of asphalt mixtures. It is a “torture” test in which a compacted asphalt mixture is subjected to a moving, concentrated load as part of analyzing the rate of permanent deformation. The I-FIT has also been used for investigative purposes after equipment was purchased in 2017 using FHWA SHRP2 R07 funds. It is a cracking resistance test utilizing semi- circular bend (SCB) geometry, in which a compacted mixture cut into a half-disc has a notch parallel to the direction of load application. At left: Specimens before and after HWTT testing. At right: Specimens after I-FIT testing. Moving Forward VTrans will begin requiring that HWTT and I-FIT results be submitted with all mix designs beginning in the 2020 construction season. This will enable further analysis of test data to determine further refinements to existing specifications, such as pass/fail criteria, sample preparation procedures, and the possibility of introducing these test methods into existing VTrans Quality Assurance (QA) specifications for asphalt materials with associated incentive/disincentive pay factors. Analysis Outputs from the HWTT are the measured rut depth and the stripping inflection point (SIP), which is when the aggregate – binder bond in the mixture breaks, leading to stripping and/or raveling. The primary output from the I-FIT is the Flexibility Index (FI), a parameter derived from the measured fracture energy and the post-peak slope of the load-displacement curve that is meant to characterize the brittleness and cracking resistance of the asphalt mixture.
Transcript of Balanced Mix Design (BMD) for Asphalt Mixtures...Balanced mix design (BMD) is an innovative...
Balanced Mix Design (BMD) for Asphalt Mixtures
Based on data collected from 2015 through2018, it has been determined that recycledasphalt materials (RAM), PG binder grade,asphalt content, and use of certain additives(WMA, anti-stripping agents, etc.) are criticalin developing a “balanced” asphalt mixtureoverall.
Aaron Schwartz, Ian Anderson, Nick Van Den BergVTrans – Highway Division
Construction & Materials Bureau – Materials & Certification Section
BackgroundBalanced mix design (BMD) is an innovative methodology in evaluating asphalt mixdesigns by utilizing performance – related tests correlated to various engineeringproperties to analyze the rutting, cracking, and moisture susceptibilities of the mixtures.VTrans is currently using two (2) test methods for this endeavor.
The Hamburg Wheel Tracker Test (HWTT) equipment at left; Illinois Flexibility Index Test (I-FIT) equipment at right
MethodologyThe HWTT has been used for investigative purposes beginning in 2015 to analyze therutting and moisture susceptibilities of asphalt mixtures. It is a “torture” test in which acompacted asphalt mixture is subjected to a moving, concentrated load as part ofanalyzing the rate of permanent deformation.The I-FIT has also been used for investigative purposes after equipment was purchasedin 2017 using FHWA SHRP2 R07 funds. It is a cracking resistance test utilizing semi-circular bend (SCB) geometry, in which a compacted mixture cut into a half-disc has anotch parallel to the direction of load application.
At left: Specimens before and after HWTT testing. At right: Specimens after I-FIT testing.
Moving ForwardVTrans will begin requiring that HWTT and I-FIT results be submitted with allmix designs beginning in the 2020 construction season. This will enable furtheranalysis of test data to determine further refinements to existingspecifications, such as pass/fail criteria, sample preparation procedures, andthe possibility of introducing these test methods into existing VTrans QualityAssurance (QA) specifications for asphalt materials with associatedincentive/disincentive pay factors.
AnalysisOutputs from the HWTT are the measured rut depth and the strippinginflection point (SIP), which is when the aggregate – binder bond in the mixturebreaks, leading to stripping and/or raveling.The primary output from the I-FIT is the Flexibility Index (FI), a parameterderived from the measured fracture energy and the post-peak slope of theload-displacement curve that is meant to characterize the brittleness andcracking resistance of the asphalt mixture.
