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Candidate for fully permeable shoulder retrofit validation site
Mix Design Guidance Helps Contractors Meet Asphalt Performance Related Specifications.
Caltrans has adopted mechanistic-empirical (ME) methods for flexible pavement
design, and is using performance-related construction specifications on
long-life rehabilitation projects for hot mix asphalt. Performance-related
specifications (PRS) are used to help ensure that as-built materials
meet the performance requirements assumed in ME pavement structural
designs. For hot mix asphalt, producers need to meet specified
values for stiffness, fatigue resistance, and rutting resistance. PRS
pose new challenges for materials producers and contractors who have
never had to relate volumetric mix design parameters to achievement of
mechanistic parameters for fatigue life and rutting resistance
based on results from performance-related laboratory tests.
The objective of this project was to provide guidance to mix designers and contractors
to support their decision making regarding changes to mix designs to achieve PRS
requirements. The initial guidance was prepared based on UCPRC experience
supporting Caltrans and mix producers on previous AC Long-Life projects, and several
decades of research experience. A Caltrans approved Superpave mix design was the
starting point. A total of three sets of adjustments to this mix design were
evaluated following the initial guidance and the effects on PRS laboratory
test results were checked to see whether the guidance caused the expected
improvements. The initial mix design guidance was found to be generally
consistent with the laboratory test results for the example mix albeit with
some minor exceptions. The mix design guidance was then revised based on
findings from this study. It is recommended that the revised guidance be
used on AC Long-Life projects or any projects where PRS are used, and that
more data collected to make further improvements.
The mix design guidance report, which includes the flow chart for adjusting mixes to meet
PRS on Page 9, is here.