Refining the Simple Performance Tester for Use in Routine Practice (2008) / Chapter Skim
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From page 5... ...
The recommended test sequence in AASHTO TP62 for the development of a master curve for pavement structural design consists of testing a minimum of two replicate specimens at temperatures of 14, 40, 70, 100, and 130 °F at loading frequencies of 25, 10, 5, 1.0, 0.5, and 0.1 Hz. This testing provides a database of 60 dynamic modulus measurements from which the parameters of the master curve are determined by numerical optimization.
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From page 6... ...
Combining Equations 3 and 4 yields the shift factor as a function of temperature relationship used in the MEPDG for the construction of dynamic modulus master curves from laboratory test data.
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From page 7... ...
= shift factor as a function of temperature; TR = temperature, Rankine; = viscosity at the reference temperature of 70 °F, AASHTO T240 residue; A, VTS = viscosity-temperature parameters for AASHTO T240 residue; and c = fitting parameter. Substituting Equation 5 into Equation 2b and the result into Equation 1 yields the form of the dynamic modulus master curve relationship used in the MEPDG for the development of master curves from laboratory test data.
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From page 8... ...
2.4 Comparison of Master Curves Using Complete and Reduced Data Sets This section presents comparisons of master curves fitted to actual laboratory test data using the complete AASHTO TP62 data and a reduced data set where test data at the lowest temperature are eliminated and replaced with an estimate of the limiting maximum modulus from the Hirsch model.
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From page 9... ...
Comparison of fitted master curves for Lane 2 from the FHWA Pavement Testing Facility higher, 16,826 psi compared to 2,222 psi for the AASHTO TP62 data set. Both approaches fit the measured data well over the temperature range from 40 to 130°F and the shift factors for the two approaches are essentially the same.
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From page 10... ...
As shown, the two data sets produce reasonably similar average limiting maximum modulus values except for the ALF mixtures, which had four unrealistically high values in the AASHTO TP62 data set. The quality of the data for the low temperature test condition has a major impact on the limiting maximum modulus in the MEPDG master curve equation.
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From page 11... ...
The limiting maximum modulus also affects the limiting minimum modulus because of the symmetry inherent to the MEPDG dynamic modulus master curve. Figure 7 compares limiting minimum modulus values from the two data sets for individual mixtures.
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From page 12... ...
A low testing temperature of 40°F would allow reasonable priced environmental chambers to be used, and will eliminate the icing problems that occur when testing at temperatures below freezing. The recommended testing temperatures for the abbreviated dynamic modulus master curve testing are 40, 70, and 104°F.
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From page 13... ...
is shown in Figure 9, based on the average shift factors at 40 and 104°F shown in Figure 8. The recommended testing temperatures and frequencies for the abbreviated dynamic modulus master curve testing result in data over the range of reduced frequency at 70°F from approximately 10−4 to 105 with a small overlap of the high and low temperature data with the reference temperature data.
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From page 14... ...
where = dynamic modulus; ω = loading frequency, Hz; Tr = reference temperature, °K; T = test temperature, °K; Max = specified limiting maximum modulus; and δ, β, γ and ΔEa = fitting parameters. 2.7 Example Using the Abbreviated Dynamic Modulus Master Curve Testing This section illustrates the development of master curves using the proposed procedure.
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From page 15... ...
Moisture condensation and icing make testing at this temperature challenging even for highly experienced technicians. To aid in implementation of the abbreviated dynamic modulus testing protocol, a draft standard practice titled "Developing Dynamic Modulus Master Curves for Hot-Mix Asphalt Concrete Using the Simple Performance Test System" was prepared.
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