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REPORT
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Publication Number: FHWA-HRT-11-058
Date: December 2011

 

Investigation of Low and High Temperature Properties of Plant Produced Rap Mixtures

RESEARCH APPROACH

This section describes the approach used in both phase I and phase II of the current study to evaluate the effects of RAP on the properties of plant-produced asphalt mixtures. The results from phase I are summarized in the next section and full details are provided in the final unpublished report. Where appropriate, the results from testing mixes produced by the phase I contractor are combined with those of the phase II contractors for completeness.

Mix Design, Production, and Sampling

In phase II of this study, four contractors replicated the experiment conducted by one contractor in phase I of this experiment. Each contractor designed six mixtures, as shown in table 1, to be as similar as possible. The mixes are SUperior PERforming Asphalt PAVEments (Superpave®) mixes with a nominal maximum aggregate size (NMAS) of 0.37 inches 3/8 inches (9.5 mm). Each contractor’s set of mixes used one source of RAP, one set of virgin aggregates, and one source of each of two binder grades. That is, each binder grade was from one source per plant, although the different binder grades may have come from different sources. The RAP contents ranged from zero (the control mix) to 40 percent, as shown in table 1.
AMENDED 1/10/2012

The contractors generally did a complete mix design on one mixture and then altered the binder grade or aggregate/RAP stockpile percentages to fill the other cells. These alternate mixes were typically verified to conform substantially to the mix design requirements with a one-point mix design. The mix designs and/or quality control (QC) testing results provided by the contractors are in appendix A of this report.

In almost all cases, the mix design gradations for a given contractor agreed within a range of 3 percent or less on each sieve. Consequently, variations in the voids in the mineral aggregate (VMA) and sometimes total binder content occurred as the aggregate properties changed when RAP was added to the mixtures. One contractor used exactly the same mix design gradation for all six mixes and varied the binder content to achieve 4 percent air voids (AV) at design. The greatest differences in the gradations were for contractor 1. Those mix designs agreed within less than 3 percent except on the 0.37- 3/8-inch (9.5-mm) 0.09-, 0.05-, and 0.02-inch (9.5-, 2.36-, 1.18-, and 0.6-mm) No. 8, No. 16, and No. 30 sieve. None of the mixes from contractor 1 were consistently higher or lower than the others, even where the greatest ranges occurred. That is, the higher RAP contents did not necessarily yield finer mixes or vice versa. Contractors 1 and 4 provided coarse mix designs, whereas contractors 2, 3, and 5 offered fine mixes (compared to the primary control sieve control point of 46 percent passing the 0.09-inch (2.36-mm) No. 8 sieve).(4)
AMENDED 1/10/2012

Two different binder grades, PG58-28 and PG64-22, were used. PG64-22 is the standard binder for the area, and PG58-28 is the grade that would be selected for the 25 percent RAP content mixtures. For the 40 percent RAP content mixtures, a blending chart would be required to determine the appropriate virgin binder grade according to the current AASHTO standards.(4)

Table 1 . Experimental design for each plant showing mix designations.

Asphalt
Binder Grade

RAP

0 Percent

15 Percent

25 Percent

40 Percent

PG 64-22

Mix A

Mix B

Mix C

Mix D

PG 58-28

 

 

Mix E

Mix F


Note: Blank cells indicate that the binder grade and RAP percentage mix was not evaluated.

The mixes were produced through the contractors’ hot mix plants (over as short a time frame as practical) using any processing they typically use with RAP mixes. It was requested that approximately 100 T (90.7 90 Mg) of each mixture be produced before sampling. The contractors placed the mixes wherever they could, typically on commercial or local road projects.
AMENDED 1/10/2012

The contractors sampled the mixes from a truck at the plant and stored the samples in sealed 5-gal (18.93 20-L) buckets. The contractors also sampled the RAP stockpile and virgin binder. The following minimum samples were requested:

The contractors were asked to provide information on the maximum theoretical specific gravity of each mix, binder content, gradation, plant type, tonnage, and any RAP processing techniques used. In some cases, this level of detail was not provided.

The details of the contractors who agreed to participate in this study and information about their plants are provided in table 2. RAP from Michigan would have been produced originally using a softer binder grade than the Indiana sources because of the climate and prevailing specifications.

Table 2 . Participating contractors and plant details.

Contractor

Plant Location

Plant Type

Processing

1

Indianapolis, IN

Gencor counterflow drum with embedded burner

Minus one-half in screened

2

Ada, MI, and Evansville, IN
AMENDED 1/10/2012

CMI parallel flow drum

Minus five-eighths in crushed/screened

3

Huntington, IN

ASTEC, Inc. double drum

Minus one-half in screened

4

Evansville, IN

CMI parallel flow drum

Minus one-half in screened

5

Leesburg, IN

Two drums (aggregate dryer with separate mixing drum)

Minus one-half in crushed/screened

Laboratory Testing Plan, Test Procedures, and Data Analysis

The laboratory testing plan was designed to examine the following:

The following tests were conducted on various samples:

Collaborations

The research team provided samples of one contractor’s mixtures (set of six) to the FHWA Turner-Fairbank Highway Research Center (TFHRC) for study. Researchers at TFHRC performed fatigue testing on these materials, utilizing a pull-pull fatigue test as a part of their research. Those results are summarized later in this report.

Samples were also provided to Dr. Hussain Bahia from the University of Wisconsin—Madison University of Wisconsin–Madison, for his use in a RAP mortar testing procedure. Those results will be reported by Dr. Bahia separately as part of his overall project. |E*| and binder testing data were shared with Dr. Jo Daniel at the University of New Hampshire as she developed plans for a pooled fund study of plant-produced RAP mixtures in the Northeast. Lastly, samples of binders recovered from one set of mixes were provided to Dr. Eric Kalberer at the Western Research Institute for Atomic Force Microscopy compatibility testing.
AMENDED 1/11/2012

 


The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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