Experience with PG of RAP Binders

Western Regional Superpave Center (WRSC)

University of Nevada, Reno

June 27, 2011

This document summarizes recent experiences of the WRSC researchers with the PG of RAP binders from two studies: a) laboratory simulated RAP and b) actual RAP materials.

Laboratory Simulated RAP

This experiment was conducted as part of the Asphalt Research Consortium work on RAP mixtures (1). The laboratory simulated RAPs were produced in efforts to evaluate the impact of extraction methods on the properties of RAP aggregates and binders. This document only presents the data on the properties of RAP binders.

Aggregates: One source from Nevada and one source from California

Binder: Neat PG64-22

Simulated RAPs:

Plant Waste*: Loose mix aged for 48 hours at 275oF

Old RAP: Loose mix aged for 48 hours at 275oF followed by 5 days at 185oF

Extraction Methods: Centrifuge AASHTO T164-A and Reflux AASHTO T164-B

Recovery Method: Rotovapor ASTM D5404

*In practice the plant waste RAP represents the stockpile where the plant dumps the access materials produced at the beginning and end of each production shift.

The recovered binders from the two simulated RAPs were graded using the processes recommended by AASHTO M320 and M323. The main difference between the two grading processes is that the M323 does not require the RAP binder to be aged in the PAV prior to the identification of the intermediate and low temperature grades. It is expected that this difference only impacts the intermediate and low temperature of the RAP binders. Table 1 compares the measured intermediate and low temperatures of the binders recovered from the two simulated RAPs.

Table 1. Intermediate and Low Temperatures of RAP Binders Graded with M320 and M323

Aggregate / Simulated RAP / Extraction Method / M320 / M323
Int. Temp (C) / Low Temp (C) / Int. Temp (C) / Low Temp (C)
Nevada / Plant Waste / Centrifuge / 20.6 / -25.6 / 18.2 / -29.0
Reflux / 20.9 / -25.9 / 18.4 / -29.3
Old RAP / Centrifuge / 21.5 / -18.3 / 22.5 / -24.6
Reflux / 22.6 / -18.9 / 22.0 / -24.8
California / Plant Waste / Centrifuge / 20.3 / -25.0 / 17.2 / -28.9
Reflux / 19.5 / -25.1 / 17.6 / -29.1
Old RAP / Centrifuge / 20.6 / -18.0 / 21.6 / -24.2
Reflux / 21.1 / -18.9 / 20.0 / -24.3

A review of the data presented in Table 1, reveals the following observations:

  • The differences among the intermediate and low temperatures of the binders extracted by the centrifuge and reflux are minimal. Therefore, both methods can be used to extract RAP binders.
  • As expected, both the intermediate and low temperatures of the simulated Plant Waste RAP are consistently lower than the intermediate and low temperatures of the simulated Old RAP.
  • The intermediate temperatures identified by the process recommended in M323 are approximately 2oC lower than the intermediate temperatures identified by M320 for the simulated Plant Waste RAP and almost identical for the simulated Old RAP.
  • The low temperatures identified by the process recommended in M323 are approximately 5oC lower than the low temperatures identified by M320 for both types of simulated RAPs.

Actual RAP

This experiment was conducted as part of a research project for the Northern Nevada Regional Transportation Commission (2). The research evaluated the impact of adding RAP on the design and performance properties of HMA mixtures. This document only presents the data on the properties of RAP binders.

Aggregates: One source from Nevada

Target Binder: Neat PG64-22, and Polymer-modified PG64-28

RAP Sources:

Plant Waste*: from Granite Hot Plant

15 Years RAP: from local street

20 Years RAP: from Local street

Extraction Methods: Centrifuge AASHTO T164-A

Recovery Method: Rotovapor ASTM D5404

*In practice the plant waste RAP represents the stockpile where the plant dumps the access materials produced at the beginning and end of each production shift.

The recovered binders from the three RAPs were graded using the processes recommended by AASHTO M320 and M323. The main difference between the two grading processes is that the M323 does not require the RAP binder to be aged in the PAV prior to the identification of the intermediate and low temperature grades. It is expected that this difference only impacts the intermediate and low temperature of the RAP binders. Table 2 compares the measured intermediate and low temperatures of the binders recovered from the three RAPs. It should be noted that the original binder grades for the 15 and 20 years old pavements are not the same and therefore, the temperatures of the RAP binders should not be directly compared.

Table 2. Intermediate and Low Temperatures of RAP Binders Graded with M320 and M323

RAP
Source / Extraction Method / M320 / M323
Int. Temp (C) / Low Temp (C) / Int. Temp (C) / Low Temp (C)
Plant Waste / Centrifuge / 26.1 / -9.7 / 22.9 / -14.0
15 Years Old / Centrifuge / 32.2 / -6.5 / 28.7 / -8.9
20 Years Old / Centrifuge / 30.1 / -8.7 / 26.8 / -10.0

A review of the data presented in Table 2, reveals the following observations:

  • As expected, both the intermediate and low temperatures of the Plant Waste RAP are consistently lower than the intermediate and low temperatures of the Old RAPs.
  • The intermediate temperatures identified by the process recommended in M323 are approximately 3.3oC lower than the intermediate temperatures identified by M320 for all three RAP sources.
  • The low temperatures identified by the process recommended in M323 are approximately 4oC lower than the low temperatures identified by M320 for the Plant Waste RAP and 2oCfor the Old RAPs.
  • In general, for the determination of both intermediate and low temperatures of RAP binder, the process recommended in M323 for grading of RAP binders is less conservative than the actual PG process recommended in M320.

Since the RAP materials evaluated in this research were from actual materials and pavements, the study was extended to cover the impact of the PG process used to grade the RAP binder on the identified intermediate and low temperatures of the virgin binder. This exercise was conducted for the following combinations:

  • Target Binder Grade: PG64-22 and PG64-28
  • RAP Content: 15, 30 and 45 percent

The blending chart method was used to estimate the required virgin binder critical temperatures as stated in the following equation:

where: TBlend= the critical temperature of the blended asphalt binder

Tvirgin= the critical temperature of the virgin asphalt binder

TRAP= the criticaltemperature of the recovered RAP binderfollowing M320 or M323

%RAPbinder = percent RAP binder in the RAP expressed as a decimal

Table 3 summarizes the estimated critical temperatures of virgin binders as a function of target binder grade and RAP content. It should be noted that the data in Table 3 represent the critical intermediate and low temperatures of the virgin binder, therefore, a lower intermediate temperature of the RAP binder will require a higher intermediate temperature for the virgin and vice versa. For example, the data in Table 2 show that the M320 process identified an intermediate temperature of the Plant Waste binder of 26.1oC while the M323 identified an intermediate temperature of 22.9oC. When these intermediate temperatures are used in the blending chart equation to determine the critical temperature of the virgin binder at 45% RAP for a Target grade of PG64-22, the results are; 24.1oC by M320 and 26.7oC by M323.

Table 3. Critical Temperatures of Virgin Binders

Target PG / RAP
Content (%) / RAP Source / M320 / M323
Int. Temp (C) / Low Temp (C) / Int. Temp (C) / Low Temp (C)
PG64-22 / 15 / Plant waste / 24.8 / -12.4 / 25.4 / -11.6
15 Years / 23.7 / -13.0 / 24.3 / -12.5
20 Years / 24.1 / -12.6 / 24.7 / -12.4
30 / Plant waste / 24.5 / -13.0 / 25.9 / -11.1
15 Years / 21.9 / -14.4 / 23.4 / -13.3
20 Years / 22.8 / -13.4 / 24.2 / -12.9
45 / Plant waste / 24.1 / -13.9 / 26.7 / -10.4
15 Years / 19.1 / -16.5 / 22.0 / -14.5
20 Years / 20.8 / -14.7 / 23.5 / -13.6
PG64-28 / 15 / Plant waste / 21.5 / -19.5 / 21.8 / -18.7
15 Years / 20.2 / -20.0 / 20.8 / -19.6
20 Years / 20.6 / -19.6 / 21.2 / -19.4
30 / Plant waste / 20.2 / -21.6 / 21.6 / -19.7
15 Years / 17.6 / -22.9 / 19.1 / -21.9
20 Years / 18.5 / -22.0 / 19.9 / -21.4
45 / Plant waste / 18.6 / -24.8 / 21.3 / -21.3
15 Years / 13.7 / -27.4 / 16.5 / -25.4
20 Years / 15.4 / -25.6 / 18.1 / -24.5

A review of the data in Table 3 leads to the following conclusions:

  • Regardless of the source of RAP and target PG, the M320 process results in virgin binder intermediate temperature that is 1oC lower at the 15% RAP and 3oC lower at the 45% RAP as compared to the M323 process.
  • The difference in the recommended low temperatures between the M320 and M323 processes depends on the source of RAP:
  • For Plant Waste, the M320 process results in virgin binder low temperature that is 1oC lower at 15% RAP and 3.5oC lower at 45% RAP as compared to the M323 process.
  • For Old RAPs, the M320 process results in virgin binder low temperature that is similar at 15% RAP and 2oC lower at 45% RAP as compared to the M323 process.

RECOMMENDATIONS

Based on the findings of both experiments presented in this document, the following recommendations can be made:

  • Both the Centrifuge and Reflux methods as prescribed in AASHTO T164 are appropriate to extract RAP binder.
  • The use of the M320 process is more appropriate for determining the intermediate temperature of all types of RAP binders and the low temperature of the Plant Waste RAP binders. Since in some cases, the intermediate temperature may control the low temperature grade, it is therefore recommended to follow the M320 process to identify both the intermediate and low temperatures of RAP binders.

REFERENCES

  1. Loria, L., “Evaluation of New and Existing Methods to Assess Recycled Asphalt Pavements Properties for Mix Designs,” PhD Dissertation, Department of Civil & Environmental Engineering, University of Nevada, Reno, NV, May 2011.
  1. Hajj, E.Y. Sebaaly, P.E., and Shrestha, R., “A Laboratory Evaluation on the Use of Recycled Asphalt Pavements in HMA Mixtures,” Research Report Washoe Regional Transportation Commission, Reno, NV, December 2007.

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