Determination of Creep Compliance and Tensile Strength of Hot-Mix ...

RECOMMENDATIONSMore work is needed to better understand the effects that recycled materials haveon the binder/mix properties as they relate to creep compliance and tensile strength.MoDOT has recently increased the allowable percentage of RAP and also allows theusage of recycled asphalt shingles (RAS) in HMA. The binder in RAP and RAS isusually much stiffer than the virgin binder and this poses challenges not only to themix designer but the pavement designer as well. A fuller understanding of the effectsof RAP and RAS in HMA would require an experimental program to be performed inthe laboratory so that the various factors could be controlled and/or monitored betterthan if the mixes were plant-produced.In the draft final version of the Recommended Practice for Local Calibration of theM-E Pavement Design Guide (13), it is recommended that a minimum of 25pavement test sections be analyzed for non-load related cracking; e.g. thermalcracking. It is also suggested that measured distress data for each pavement sectioncover at least 10 years of service. Thus, the combination of 25 pavement sectionsand 10 years of data per section may not correspond well with the plant-producedmixtures that were investigated in this study; i.e. RAP and SMA mixtures arerelatively new and there may not be sufficient pavement sections available inMissouri to produce a reliable calibration – validation of the M-E PDG thermalcracking distress models. An alternative to using plant-produced mixes would be toobtain cores from the selected pavement sections and perform IDT creep/strengthtests (along with other material characterization tests) on the cores, similar to thework that was done in the state of Montana (14).IDT creep/strength test data is not only used for calibration – validation purposes,but becomes part of an “input library” for the M-E PDG. As new mix types areadopted by MoDOT, the thermal cracking parameters of creep compliance, tensilestrength, and tensile failure strain should, at some point, be determined. MoDOTcould perform a further refinement of the thermal cracking distress modelparameters once a sufficient number of new mixes have accumulated.41