Evaluating constructability and properties of Advera and REVIX warm mix asphalt : final report

Final Report
Evaluating Constructability and Properties of Advera and REVIX Warm Mix Asphalt
Submitted to The Office of Materials and Research The Georgia Department of Transportation
Prepared By Dr. James Lai, PE 6100 Neely Farm Drive Norcross, Georgia 30092 Tel: (770) 416-9805
September 2008

1. Report No.:

2. Government Accession No.:

3. Recipient's Catalog No.:

FHWA-GA-08-0801

5. Report Date:

4. Title and Subtitle:

September 2008

Evaluating Constructability and Properties of Advera and REVIX Warm Mix Asphalt

6. Performing Organization Code:

7. Author(s): James S. Lai, Ph.D., P.E.
9. Performing Organization Name and Address: James S. Lai, Ph.D., P.E. (consultant) 6100 Neely Farm Drive Norcross, Georgia 30092

8. Performing Organ. Report No.: 08-01
10. Work Unit No.:
11. Contract or Grant No.: SPR00-0008-00-612 (RP 08-01)

12. Sponsoring Agency Name and Address: Georgia Department of Transportation Office of Materials & Research 15 Kennedy Drive Forest Park, GA 30297-2534

13. Type of Report and Period Covered: Final; April 2008 March 2009
14. Sponsoring Agency Code:

15. Supplementary Notes: Prepared in cooperation with the U.S. Department of Transportation, Federal Highway Administration.
16. Abstract:

This report presents the pilot study initiated by the Georgia Department of Transportation (GDOT) for assessing the potential use of warm mix asphalt mixes (WMA) in Georgia highway pavements. The pilot study included paving two different WMA mixes, the Advera WMA (developed by PQ Corporation) and the REVIX WMA (developed by Mathy Technology and Engineering Services Inc.), and a 9.5 mm Superpave control mix. The REVIX WMA mix and the Advera WMA mix for the test sections used the same 9.5 mm Superpave mix design. The main objective of this research study was to assess the constructability of these two WMA mixture types.
All the asphalt mixes were produced by an Astec continuous drum plant with a production rate of 220 tons per hour. For the REVIX WMA the mix discharge temperature was about 270 oF, about 45 oF lower than that for the 9.5 mm Superpave mix; the mix discharge temperature for the Advera WMA was about 285 oF, about 32 oF lower than that for the 9.5 mm Superpave mix.
During the paving of the REVIX and Advera WMA mixes, clumps of asphalt mixes were presented in the auger chamber and behind the end plates, and contributed to serious blemishes on the mat behind the paver. No similar problem was encountered during the construction of the 9.5 mm Superpave mix. The primarily cause contributed to the blemish problems for the REVIX WMA mix was due to lack of sufficient WMA additive in the mixture. It was determined by the REVIX WMA additive producer that the additive dosage used for the construction of the REVIX WMA test section was about 50% of the recommended dosage. For the Advera WMA test sections, the comment offered by the Advera WMA additive producer was that the method of incorporating the Advera additive into the drum mixer did not offered adequate mixing action and thus rendered the Advera additive less effective in improving the workability of the WMA produced.
Recommendations for improving the quality of the WMA paving operation and performance are offered.

17. Key Words: Warm Mix Asphalt, Advera, REVIX, Bituminous construction

18. Distribution Statement:

19. Security Classification (of this report): Unclassified

20. Security Classification (of this page): Unclassified

Form DOT 1700.7 (8-69)

21. Number of Pages: 39

22. Price:

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TABLE OF CONTENTS
Executive Summary ...........................................................................................................2
1.0 Introduction..................................................................................................................7 1.1 Background ................................................................................................................7 1.2 Objective and Proposed Research Study....................................................................8 1.3 Organization of This Report.......................................................................................8
2.0 Preparation and Pre-Construction Activities............................................................9 2.1 Developing Pilot Test Plan.........................................................................................9 2.2 Description of REVIX and Advera WMA Mixes ......................................................9 2.3 WMA and HMA Material Sources and Properties ..................................................10 2.4 Mix Design...............................................................................................................11
3.0 Assess Asphalt Plant and Paving Operations During Construction .....................13 3.1 Location of Test Sections .........................................................................................13 3.2 Asphalt Plant and Mix Production ...........................................................................14 3.3 Test Sections Paving Operations..............................................................................18 3.4 Discussions and Conclusions ...................................................................................25
4.0 Post-Construction Evaluation...................................................................................29
5.0 Conclusions and Recommendations.........................................................................30 5.1 Conclusions ..............................................................................................................30 5.2 Recommendations ....................................................................................................31
References .........................................................................................................................33 Appendix .........................................................................................................................34 Table A-1 9.5 mm Superpave Mix Job Mix Formula
Submitted by Reeves Construction Co. Table A-2 9.5 mm Superpave Mix Table A-3 9.5 mm Superpave Mix Asphalt Plant QC Test Results Table A-4 REVIX WMA Mix Asphalt Plant QC Test Results Table A-5 Advera WMA Mix Asphalt Plant QC Test Results
1

EXECUTIVE SUMMARY
Background Rising energy costs and increased awareness of emission problems in the production of hot mix asphalt (HMA) have brought attention to the potential benefits of warm mix asphalt (WMA) in the United States. A number of new WMA processes and products have become available that have the capability of reducing the temperatures at which asphalt mixes are produced and paved without compromising the performance of the pavement. These new products can reduce production temperatures by as much as 50F or more. Lower plant mixing temperatures would reduce fuel consumption by as much as 30 percent or more and thus reduce the operation costs. Lower plant mixing temperatures would also reduce gas emission by as much as 90 percent, which represents a significant cost savings to an asphalt plant for its emission control facility. Warm asphalt mixes will also allow longer haul distances and a longer construction season than if the mixes are produced at normal operating temperatures. Lowering the mixing temperature would reduce oxidative hardening of the asphalt and thus could result in improving the pavement's performance by reduced thermal cracking and block cracking.
However, lowering the mix productions, in drying the aggregates and in the mixing operation, could potentially cause WMA to be more susceptible to moisture damage and rutting. These potential distresses as well as the issues related to the constructability of WMA are important and need to be carefully evaluated to ensure the viability and long term performance of WMA.
Objective and Proposed Research Program The research study presented in this report was the first pilot study initiated by the Georgia Department of Transportation (GDOT) for assessing the potential use of WMA in Georgia highway pavements. The pilot study included placing two different WMA mixes, the Advera WMA (developed by PQ Corporation) and the REVIX WMA (also identified as Evotherm-3G WMA, developed by Mathy Technology and Engineering Services Inc.), and a 9.5 mm Superpave control mix. The two WMA test sections and the control section were a part of the 9.5 mm Superpave mix overlay construction project on State Route 57 in Washington County.
The objective of this research study was to assess the application of these two WMA mixture types through (1) assessing the constructability of the WMA mixes, (2) evaluating the properties of the WMA mixes through laboratory testing of the mixes produced during the construction of the test sections, and (3) conducting initial assessment of the performance of the WMA pavements. The proposed work for this research study consisted of following 5 tasks:
1. Develop the Pilot Test Plan: preparing a detailed plan covering all phases of the pilot study.
2. Coordinate Pre-Construction Activities: collecting pertinent properties of the aggregates and the binder and mix designs for the two WMA mixes and the control 9.5 Superpave mix used in this pilot study.
2

3. Coordinate Field Assessment During Construction: assessing the paving quality and collecting pertinent data during the construction of the WMA test sections and the control section.
4. Coordinate Post-construction Evaluation: coordinating laboratory testing and evaluating properties of the WMA mixes and the control mix collected in the asphalt plant during the construction and the cores taken from the test sections.
5. Prepare a Final Report: preparing a final report documenting all the work performed in this pilot study.

Major Findings 1. The REVIX WMA mix and the Advera WMA mix for the test sections used the same 9.5 Superpave mix design. The reason for using the same mix design was that the amount of additives used in these two WMA mixes was very small and should not affect the mix characteristics.

2. The asphalt mixes for the sections were produced by an Astec continuous drum plant
with a production rate of 220 tons per hour. The relevant mix production data for the
three mixes are summarized in Table A below. For the REVIX WMA, the mix discharge temperature was about 270oF, about 45oF lower than that for the 9.5 mm Superpave mix; and the mix discharge temperature for the Advera WMA was about 283oF, about 32oF
lower than that for the 9.5 mm Superpave mix. The quality control testing was performed
on the mixes produced in the asphalt plant, and the test results indicated that deviations
from the job mix formula (JMF) for the asphalt content and aggregate gradation were
within the acceptance limits for all three mixes tested.

Table A Summary of Asphalt Plant Production Data

Information Required
Mix Type
Date production and Q/C testing Tonnage produced Use of silo and typical storage time Mix discharge temperature Baghouse moisture problem, if any

Results / Remarks

9.5 mm Superpave

REVIX WMA

Advera WMA

May 2, 2008 May 5, 2008 May 6, 2008

1951 ton

900 ton

896 ton

15 minutes 315oF

15 minutes 270oF

15 minutes 283o F

none

none

none

3. The REVIX WMA test section was paved in the morning of May 5, followed by paving the 9.5 mm Superpave mix control section in the afternoon. The Advera WMA test section was paved in the morning of May 6 with a small portion of it (10 truck loads) paved the next morning. During these 3 days the weather was sunny and the temperature was about 60oF in the early morning and slowly increased to about 80oF in the afternoon. The relevant paving information is summarized in Table B. Paving operations for all of the test sections and the control section were about the same, except that the temperatures of the mixes at load out and behind the screed were different. During the paving of the REVIX and Advera WMA mixes, clumps of asphalt mixes were present in the auger

3

chamber and behind the end plates and contributed to serious blemishes on the mat behind the paver. Since no blemishes occurred in the 9.5 mm Superpave control section, the possibility that the problem could be caused by the paving equipment or improper paving operation was excluded.
Table B Summary of Paving Information

Information Required
Mix Type
Paving Date and time Temp. at load out, oF Temp. behind screed, oF Test section length paved Compacted mat thickness
In-place density (air voids)
Surface defects
Time open to traffic Pavement smoothness

9.5 mm Superpave 5/5/08, 2 pm
315 285 - 310 0.7 miles 1 inch Gage 6.2% Cores 5.8%
no
2 hrs. 664 mm/km

Results / Remarks

REVIX WMA

Advera WMA

5/5/08, 9 am 5/6/08, 9 am

255 285 265 - 285

235 265 230 - 260

1.8 miles 1.2 miles

1 inch 1 inch

Gage 8.5% Gage 6.9% Cores 9.7% Cores 8.2%

Serious

Serious

blemishes blemishes

2 hrs.

2 hrs.

862 mm/km 937 mm/km

Advera WMA 5/7/08, 9 am 270 - 300 250 - 280 0.8 miles 1 inch Gage 9.2% Cores 6.1% Serious blemishes 2 hrs.
775 mm/km

4. For the REVIX WMA test section, the primary cause contributing to the blemish problems was lack of sufficient WMA additive in the mixture. It was determined by the REVIX WMA additive producer that the additive dosage used for the construction of the REVIX WMA test section was about 50% of the recommended dosage. For the Advera WMA test sections, the only comment offered by the Advera WMA additive producer was that the method of incorporating the Advera additive into the drum mixer in the Reeves' asphalt plant did not offer adequate mixing action and thus rendered the Advera additive less effective in improving the workability of the WMA mix produced. The cause offered by the additive producer seemed plausible, although it deserves further investigation.
5. Compaction of the mat was followed immediately after paving. A 15-ton Ingersoll Rand DD-130 vibratory roller was used for the breakdown compaction. The breakdown compaction consisted of 4 passes of vibratory compaction. Then a pneumatic tire roller was used for the intermediate rolling, and the rolling was completed with a lighter steel wheel roller. The density of the compacted mat was first determined using a nuclear density gage immediately after the paving. Cores were taken a few hours later, and the densities were determined thereby as well. The air voids thus determined for the test sections and the control section are shown in Table B. The density determined by the nuclear gage and the cores, as well as the determination of the air voids were performed by the GDOT Technical Services Engineer.

4

6. Pavement smoothness was measured using the Laser Road Profiler at every 0.1 mile, and the results are presented in Table B.
7. In light of the problems encountered during the construction of the two WMA test sections as described above, testing of the mixes would not produce meaningful material properties information. Therefore, with consent from OMR the post-construction laboratory testing and evaluation mix properties proposed in Task 4 was suspended.
Recommendations 1. When using WMA in a paving project, the following information in addition to that
stipulated under GDOT Standard Specifications Section 400.1.03 should be included when the contractor submits the job mix formula after the contract has been awarded:
The amount of WMA additive as percent of net binder used in the mix or the percent of the total mix weights used, particularly when reclaimed asphalt pavement (RAP) is used
The procedure for incorporating the WMA additive into the mix, the mixing temperature, and mixing process in the laboratory mixing operation
Temperature and duration of aging, if different from the standard for aging at 135oC (275oF), in an oven for 2 hours after mixing and prior to compaction
Any deviation from the Superpave mix design procedures
2. Submit proposed job mix formula for approval at least 4 weeks (instead of 2 weeks) before the beginning the asphalt plant mixing operation. This would allow OMR sufficient time to conduct more thorough mix design verification testing.
3. It would be desirable to request the WMA additive supplier to conduct the mix design verification testing based on the job mix formula and the aggregates and the binder submitted by the contractor, and forward the verification mix design results to the OMR. It would be highly desirable that the WMA additive supplier also provide the following information for using the WMA additive for the process during the construction.
Minimum threshold mix temperature behind the screed Maximum allowable storage time (in silo and in trucks) Maximum allowable storage time in the truck
4. OMR should perform mix design verification testing based on the job mix formula and the aggregates and the binder submitted by the contractor and compare the results with that from the WMA additive supplier.
5. During the construction of the test section for the project, it may be desirable to intentionally vary the temperatures of the mix at load out, behind the screed, and during the holding time to assess the sensitivity of the temperatures and the storage time on the constructability of the WMA mix. This would provide valuable information for the contractor and for the Quality Control Technician during the
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mainline paving. If the results indicate that the WMA mix used is too sensitive to the temperature variation, the project engineer perhaps should consider requesting the contractor to use a Material Transfer Vehicle to mitigate the temperature sensitivity of the WMA mix used for the project. 6. OMR and the Office of Maintenance should cooperate to place additional WMA sections to gain experience of using different types of WMA mixes. The proposed research program for this pilot study presented in this report, including the Task 4 (Post-Construction Laboratory Testing and Evaluation of Mix Properties and Pavement Performance), can be used to evaluate the constructability and the properties of the mixes and document the experience with and performance of using different WMA mixes.
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CHAPTER 1: INTRODUCTION
1.1 Background Rising energy costs and increased awareness of emission problems in the production of hot mix asphalt (HMA) have brought attention to the potential benefits of warm mix asphalt (WMA) in the United States. A number of new WMA processes and products have become available that have the capability of reducing the temperature at which asphalt mixes are produced and paved without compromising the performance of the pavement. These new products can reduce production temperatures by as much as 50F or more (1-6). Lower plant mixing temperatures would reduce fuel consumption by as much as 30 percent or more and thus reduce the operation costs. Lower plant mixing temperatures would also reduce gas emission by as much as 90 percent (4). The typical expected reductions of various emissions as presented in (6) were: 30 to 40 percent for CO2 and sulfur dioxide (SO2), 50 percent for volatile organic compounds (VOC), 10 to 30 percent for carbon monoxide (CO), 60 to 70 percent for nitrous oxides (NOx), and 20 to 25 percent for dust. Lowering the emissions represents a significant cost savings to an asphalt plant for its emission control facility. Lower emissions may allow asphalt plants to be built in non-attainment areas, where there are strict air pollution regulations. Warm asphalt mixes will also allow longer haul distances and a longer construction season than if the mixes are produced at normal operating temperatures. Lowering the mixing temperature would reduce oxidative hardening of the asphalt and thus could result in improving the pavement's performance by reduced thermal cracking and block cracking. There are some other benefits, such as allowing more reclaimed asphalt pavement (RAP) to be incorporated in the mixes.
However, lowering the operation temperature, in drying the aggregates and in the plant mixing operation, could potentially cause WMA to be more susceptible to moisture damage and rutting (2-4). These potential distresses are important and need to be carefully evaluated to ensure the viability and long term performance of WMA.
WMA was developed in Europe in late 1990 and came to the U.S. as a result of a study tour to Europe organized by NAPA in 2002 (6). Since then more additives and processes for producing WMA have been produced and many demonstration projects have been constructed in the U.S. The following are the warm mix additives and processes available in the U.S. (5):
Sasobit, a wax based additive Aspha-min, a zeolite additive that releases small amount of water into the mix Advera, a zeolite additive Evotherm, a chemistry additive that includes ingredients to improve coating and
workability, adhesion promoters, and emulsification agents (the chemistry is delivered in an emulsion) Rediset, a warm mix additive that also functions as an anti-strip agent REVIX, the additives (broadly encompassing surfactants, polymers, acids, processing aids, waxes, etc.) incorporated into the asphalt binder that would improve coating and spreading over aggregate surfaces at reduced temperatures
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Astec foamed-asphalt, small quantities of water injected into the liquid asphalt stream of an Astec Double-Barrel plant
1.2 Objective and Pilot Test Program The research study presented in this report was the first pilot study initiated by the Georgia Department of Transportation (GDOT) for assessing the potential use of WMA in Georgia highway pavements. The pilot study included placing two different WMA mixes, the Advera WMA (developed by PQ Corporation) and the REVIX WMA (Also identified as Evotherm-3G WMA, developed by Mathy Technology and Engineering Services Inc.) and a 9.5 mm Superpave control mix. The two WMA test sections and the control section were a part of the 9.5 mm Superpave mix overlay construction project on State Route 57 in Washington County.
The objective of this research study was to assess the application of these two WMA mixture types through (1) assessing the constructability of the WMA mixes, (2) evaluating the properties of the WMA mixes through laboratory testing of the mixes produced during the construction of the test sections, and (3) conducting initial assessment of the performance of the WMA pavements. The proposed work for this study consists of following 5 tasks:
Task 1: Develop the Pilot Test Plan: This task consists of preparing a detailed plan covering all phases of the pilot study.
Task 2: Coordinate Pre-Construction Activities: This task consists of collecting pertinent properties of the aggregates, binder, and mix designs for the two WMA mixes and the control 9.5 Superpave mix used in this pilot study.
Task 3: Coordinate Field Assessment During Construction: This task consists of assessing the quality and collecting pertinent data during the construction of the WMA test sections and the control section.
Task 4: Coordinate Post-Construction Evaluation: This task consists of coordinating the laboratory testing and evaluation properties of the WMA mixes and the control mix collected in the asphalt plant during the construction and the cores taken from the test sections.
Task 5: Prepare a Final Report: This task consists of preparing a final report documenting all the work performed in this pilot study.
1.3 Organization of this Report This report is divided into 5 chapters. Chapter 2 presents the work performed under Task 1, preparing a detailed plan covering all phases of the pilot study, and Task 2, collecting pertinent properties of the aggregates and the mix designs. Chapter 3 presents the work proposed under Task 3 for assessing the asphalt plant production operations, the paving operations, and the quality of the two WMA test sections and the control section. The laboratory testing and evaluation program proposed under Task 4 are summarized in Chapter 4. Conclusions and recommendations are presented in Chapter 5.
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CHAPTER 2: PREPARATION AND PRECONSTRUCTION ACTIVITIES
This chapter presents the work performed under Task 1 Developing the Pilot Test Plan and Task 2- Coordinating the Pre-Construction Activities.
2.1 Developing Pilot Test Plan A detailed plan covering all phases of the pilot study was prepared and submitted to OMR on April 24, 2008. The plan included the activities for evaluating warm mix asphalt technology in the following three phases.
Pre-Construction laboratory evaluation of material properties. Evaluating mix production and paving and compaction operations, and
performing quality control during the construction of the test sections. Post-Construction evaluations of the performance of the WMA test sections and
the control section.
The plan was reviewed by OMR and comments and suggestions from OMR were incorporated in the revised plan. The activities conducted and the results obtained during the preconstruction phase are presented in this chapter, and those during the construction phase and post-construction phases are presented in later chapters.
2.2 Description of REVIX and Advera WMA Mixes
REVIX WMA The REVIX WMA additive was co-developed in the United States by Mathy Technology and Engineering Services Inc. and Paragon Technical Services Inc. The additive consists of surfactants which when mixed with asphalt binder will reduce resistance to coating and spreading over aggregate surface and thus can lower the temperatures required for achieving adequate mixing, spreading and compaction of the REVIX mix. The mechanisms of reducing the temperatures are based on reducing the internal friction between aggregate particles and the thin films of binders used to produce bituminous mixtures, which are different from other WMA mixes relying on the principles of foaming or viscosity reduction for lowering the production and compaction temperatures. It claims that the REVIX mixes are typically produced at 60 to 80oF lower than the same mixes without the REVIX additive and can also be compacted at 60 to 80 degrees below normal compaction temperatures.
The REVIX additive can be incorporated at the liquid asphalt terminal. Treated binder is delivered to the hot mix plant in ready-to-use form. Thus no modifications to the hot mix plant are needed. The quantity of REVIX used in producing the WMA mix is 0.3% by weight of asphalt binder used in the mix.
Advera WMA The Advera WMA additive was developed by PQ Corporation. It is a synthetic zeolite additive, a hydrated aluminosilicate containing 18-22% water. The product is in fine
9

powder form. The properly metered Advera powder is blown through the modified filler port of a drum mix asphalt plant. The port is located just after the entry of the asphalt binder in the drum plant. The quantity of Advera additive used in producing the WMA mix is about 0.025% - 0.03% by weight of the asphalt mix.
Since Advera additive contains 18-22% of water, water will be emitted from the zeolite structure upon heating above 100oC, causing micro-foaming in the asphalt mix. This would improve the workability of coating the asphalt films on aggregates, and thus can reduce the mixing and compaction temperatures about 50 70oF lower than that for the asphalt mixes without the additive. During the compaction, the steam that improved the workability of the mix is compressed out of the mix. If any residual moisture were remained in the mix, it will be re-absorbed by the Advera additive. Therefore, the microfoaming of water in the mix during the production of Advera WMA should have no adverse effect on the performance of the mix.
2.3 WMA and HMA Material Sources and Properties The REVIX WMA and Advera mix test sections used the same aggregates and asphalt binder that were used for producing the mixes for the construction of the 9.5 mm Superpave mix. The aggregate source and properties, the source and properties of the asphalt binder, and the mix properties are presented below.
Aggregate All the aggregates used for producing the mixes were from Aggregates USA at the Hitchcock Quarry (GDOT QPL Source Code 028C) at Postell, Georgia. The general character of the aggregates is Mylonite Gneiss/Amphibolite, and is classified as Group II aggregate. The properties of the aggregates are summarized in Table 1.
Table 1 Property of Aggregates

Specific Gravity Bulk S.S.D. App. 2.694 2.708 2.735

Percent Absorption
0.66

LA Abrasion Loss, %
37

Mg-Sulfate Soundness Loss
0.7

Asphalt Binder The asphalt binder used was a PG 67-22 from NuStar at Savannah Plant (GDOT QPL Source Code 0002).
Reclaimed Asphalt Pavement The reclaimed asphalt pavement (RAP) used in all three mixes was from the Reeves Construction Co. Postell Plant (GDOT QPL Source Code 004R)

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2.4 Mix Design

9.5 mm Superpave Mix The control section, which is a part of the normal overlay construction project on State Route 57 in Washington County, used a 9.5 mm Superpave mix. The amount of different sizes of aggregates and the RAP used for the mix is shown in Table 2. The aggregate gradation and optimum asphalt contents used for the mix design are shown in Table 3. The Job Mix Formula for this mix submitted by Reeves Construction Company to OMR is included in Table A-1 in the Appendix of this report. Table 4 summarizes some key mix design parameters shown in Table A-2.

Table 2 Aggregates Used for the Mixes

RAP
#7 #89 M10 W10 Hydrated Lime

15%
5% 35% 15% 29% 0.925%

Table 3 Gradation and Asphalt Contents

Sieve Size, mm
19.0 12.5 9.5 4.75 2.36 1.18 0.600 0.300 0.150 0.075 Optimum AC, %

JMF, % Passing
100 99 94 64 45 31 22 16 10 5.2
5.14

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Table 4 Volumetric Mix Design Data

% AC
5.00 5.50 5.14

Gmm
2.525 2.506

% Gmb @
Ninitial
88.7

% Gmb @
Ndesign
95.5

90.5 97.0

Gmb
2.413 2.423

% Air Voids
4.4 3.0 4.0

VMA
16.1 16.0

VFA
72.5 80.3

Dust Ratio
1.05 0.96

Optimum Asphalt Cement (AC) Content = 5.14% Air Voids at Optimum AC = 4.0% Aggregate Effective Specific Gravity = 2.732 Ninitial = 6 Ndesign = 65

Mix Design for REVIX and Advera Mixes The REVIX WMA mix and the Advera WMA mix for the test sections used the same 9.5 Superpave mix design. The reason for using the same mix design was that the amount of additives used in these two WMA mixes was very small and should not affect the mix characteristics, although other research studies (4) indicated that the air voids could be affected under the same compaction efforts, even with adjusting the mixing and compaction temperatures to account for the improved workability when using the WMA additives. Chapter 3 and Chapter 4 of this report will present the results and comparisons of the characteristics of the two WMA mixes and the control mix.

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CHAPTER 3: ASSESS ASPHALT PLANT AND PAVING OPERATIONS DURING CONSTRUCTION

3.1 Location of Test Section Site The two WMA test sections were constructed as a part of the 9.5 mm Superpave mix overlay construction project on SR 57 between the Washington County line on the west end of the project and SR 15 in Johnson County on the east end. The overlay project was about 14.6 miles long. The locations of the construction project and the test sections are shown in Figure 1. Reeves Construction Co. was the project contractor. The REVIX WMA test section was constructed in the morning of May 5, the 9.5 mm Superpave mix control section in the afternoon, and the major portion of the Advera WMA test section in the morning of May 6, with the remaining small portion (about 10 truckloads of the mix) in the morning of May 7. The weather on these 3 days was sunny, and the temperature was about 60oF in the early morning and increased to about 80oF in the afternoon.

Washington County

Johnson County

0

2 miles

0

1 mile

Figure 1 Location of the Test Sections 13

3.2 Asphalt Plant and Mix Production The asphalt plant was located at Postell, Georgia, about 50 miles from the test section sites, per Figure 2. It would take about 1.5 hours for the truck to deliver the mix from the asphalt plant to the test section sites.
Asphalt Plant

Test Sections

0

10 mile

Figure 2 Locations of Asphalt Plant and Test Section Sites

The asphalt mixes were produced by an Astec continuous drum plant with a production rate of 220 tons per hour. As mentioned in Section 2.3, all the aggregates used for producing the mixes were from Rinker Materials Co. at the Hitchcock Quarry at Postell, Georgia. The moisture contents of the aggregate stockpile were determined, and the results are presented in Table 5.

Table 5 Aggregate Stockpile Moisture Contents

Aggregate Type
#7 #89 W10 M10 RAP

Moisture Contents, %
0.1 1.1 5.7 2.3 0.8

9.5 mm Superpave Mix Table 6 summarizes the 9.5 mm Superpave mix plant production related information collected on May 2. The mix produced in the afternoon of May 5 for the construction of the control test section was identical to that was product on May 2. The mix discharge temperature was about 315oF. There was no visible moisture problem in the baghouse. Results of the quality tests for the asphalt content and aggregate gradation of the mix at the plant are summarized in Table 7. A copy of the data sheet recording the quality

14

control test results for the mix is included in Table A-3 in the Appendix of this report. The deviations from the job mix formula (JMF) of the asphalt content and aggregate gradation shown in Table 7 are within the acceptance limits. Five 5-gallon buckets of the mix were collected from the plant and sent to OMR for testing the properties of the mix as described in Chapter 4.
Table 6 9.5 mm Superpave Mix Plant Production Information

Information Required
9.5 mm Superpave Mix (Control) Tonnage produced Use of silo and typical storage time Mix discharge temperature Report regular QC testing results Baghouse moisture problem, if any

Results / Remarks
May 2, 2008 1951.17 ton 15 minutes
315 oF See Table 7
none

Table 7 9.5 mm Superpave Mix QC Test Results at Asphalt Plant

Sieve Size, mm
19.0 12.5 9.5 4.75 2.36 0.075 Optimum AC, %

JMF 100 97 92 66 45 7.0
5.60

Percent passing

Average (1) Deviation

100

0.0

97.4

0.6

93.4

1.4

64.9

1.2

44.7

1.0

7.2

0.2

5.41

0.14

Note (1): Average of 4 samples, see Table A-3

REVIX WMA Mix Production of the REVIX WMA mix at the plant was started at about 7 a.m. on May 5, 2008. The REVIX additive was pre-blended at the AC terminal and shipped to the asphalt plant. The plant operation for producing this mix was the same as that for producing the 9.5 mm Superpave mix, except the temperatures were lower. Table 8 summaries the plant production related information collected during the production of this mix. The mix discharge temperature was about 270oF, about 45oF lower than that for the 9.5 mm Superpave mix. There was no visible moisture problem in the baghouse. Results of the quality tests for the asphalt content and aggregate gradation of the mix at the plant are summarized in Table 9. A copy of the data sheet recording the quality control test results for the mix is included in Table A-4 in the Appendix of this report.

15

The deviations from the job mix formula (JMF) of the asphalt content and aggregate gradation shown in Table 9 are within the acceptance limits. Five 5-gal buckets of the mix were collected from the plant and sent to the GDOT OMR laboratory for testing the properties of the mix as described in Chapter 4.

Table 8 REVIX WMA Mix Plant Production Information

Information Required REVIX Warm Mix Asphalt Tonnage produced Method of introducing additive to the mix Use of silo and typical storage time Mix discharge temperature Report regular QC testing results Baghouse moisture problem, if any

Results / Remarks
May 5, 2008 900.22 ton AC terminal 15 minutes
270oF See Table 9
none

Table 9 REVIX WMA Mix QC Test Results at Asphalt Plant

Sieve Size,

Percent passing

mm

JMF Average (1) Deviation

19.0

100

100

0.0

12.5

99

97.1

1.9

9.5

92

91.8

0.2

4.75

66

65.8

0.2

2.36

45

45.2

0.2

0.075

7.0

5.9

1.1

Optimum AC, %

5.60

5.62

0.02

Note (1): Average of 3 samples, see Table A4

Advera WMA Mix Production of the Advera WMA mix at the plant started at about 7 a.m. on May 6, 2008. The properly metered Advera power was blown through the modified filler port of the drum asphalt plant. The port is located just after the entry of the asphalt binder in the drum plant. Other than that, the plant operation for producing this mix was the same as that for producing the 9.5 mm Superpave mix, except that the temperatures were lower. Table 10 summaries the plant production related information collected during the production of this mix. The mix discharge temperature was about 285oF, about 30oF lower than that for the 9.5 mm Superpave mix. There was no visible moisture problem in the baghouse. Results of the quality tests for the asphalt content and aggregate gradation of the mix at the plant are summarized in Table 11. A copy of the data sheet recording

16

the quality control test results for the mix is included in Table A-5 in the Appendix. The deviations from the job mix formula (JMF) of the asphalt content and aggregate gradation shown in Table 11 are within the acceptance limits. Five 5-gal buckets of the mix were collected from the plant and sent to OMR for testing the properties of the mix as described in Chapter 4.
Table 10 Advera WMA Mix Plant Production Information

Information Required Advera Warm Mix Asphalt Tonnage produced Method of introducing additive to the mix Use of silo and typical storage time Mix discharge temperature Report regular QC testing results Baghouse moisture problem, if any

Results / Remarks May 6, 2008 895.82 ton
See Note below 15 minutes 285o F See Table 11 none

Note: properly metered Advera powder was blown through the modified filler port of the drum asphalt plant.

Table 11 Advera WMA Mix QC Test Results at Asphalt Plant

Sieve Size, mm
19.0 12.5 9.5 4.75 2.36 0.075 Optimum AC, %

JMF 100 99 92 66 45 7.0
5.60

Percent passing

Average (1) Deviation

100

0.0

97.1

1.9

93.2

1.2

66.3

0.3

46.0

1.0

7.2

0.2

5.63

0.03

Note (1) Average of 3 samples, see Table A-5

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3.3 Test Sections Paving Operations The REVIX warm mix test section was paved in the morning of May 5, followed by paving of the 9.5 mm Superpave mix control section in the afternoon. The Advera WMA mix test section was paved in the morning of May 6 with a small portion of it (10 truck loads) paved in the morning of May 7. Locations of the test sections are shown in Figure 1. During these 3 days the weather was sunny and the temperature was about 60oF in the early morning and slowly increased to about 80oF in the afternoon.
Paving operations on all of the test sections and the control section were about the same, except that the temperatures of the mixes at load out and behind the screed were different. Table 12 summarizes the common paving operation information collected during construction of the sections. Tandem end-dump trucks were used for hauling the asphalt mixes. The hauling distance from the asphalt plant to the paving sites was about 45 miles and the hauling time was somewhere between 1 hour to 1 hour and 30 minutes. The mixes in the trucks were properly covered with tarpaulins during the hauling and waiting to be discharged into the paver. The PG 67-22 paving grade asphalt was used for the tack coat and the tack rate was between 0.04 and 0.06 gal/yd2. The compacted mat thickness for all sections was 1 inch.

Table 12 Summary of Laydown /Compaction Information for All Sections

Information Required Project location Contractor Truck type Haul distance/Haul time Release agent used (if any) Material sticking in truck beds? Use of transfer vehicles Paver type and model Use vibratory screed / heated screed? Compacted mat thickness Roller Train
-Vibratory roller / pattern
-Pneumatic roller Time and mat temp when open to traffic

Results / Remarks
SR 57 Johnson/ Washington Co.
Reeves Construction Company Tandem end-dump trucks
45 miles, 1 hr to 1 hr 30 min #1 Asphalt Release, Comp Technologies No No PF-3200 Blaw-Knox
w/Ultimat extendable screed Yes/ Yes 1 inch
1 vibrator roller, 1 pneumatic roller, 1 static finish roller
Ingersoll Rand DD-130 4 passes of vibration rolling
Ingersoll Rand PT-125 Continuous rolling
About 2 hours after compaction

Paving operations and information related to the quality of paving for each test sections are presented below.

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Paving REVIX Test Section Paving of REVIX test section started at about 9 a.m. on May 5. Temperatures of the mix at load out and behind the screed were frequently monitored during the paving. Temperatures of the mix at the load out were between 255oF and 285oF and that behind the screed between 235oF and 265oF. These were about 40oF to 50oF lower than that for the paving of the 9.5 mm Superpave mix. During the paving operation, severe blemishes were occurring on the mat behind the paver as shown in Figure 3, requiring a significant amount of hand work to correct by taking mix out of the spreader box and shoveling it onto the blemish areas to repair the mat. Various corrective actions, including raising the mix temperature, were attempted with little success. The possibility that paving equipment or improper paving operation was causing the problem was also considered. Since no blemishes occurred on the 9.5 mm Superpave control section, this possibility was excluded. It was noticed that clumps of asphalt mixes were present in the auger chamber and behind the end plates, the main cause for blemishes on the mat. The causes contributing to such problems were investigated and are presented in Section 3.4.
Compaction of the mat immediately followed behind the paver. A 15-ton Ingersoll Rand DD-130 vibratory roller was used for the breakdown compaction, which consisted of 4 passes of vibratory compaction. Then a pneumatic tire roller was used for the intermediate rolling, and the rolling was completed with a steel wheel roller. The density of the compacted mat was first determined using a nuclear density gage. A total of 11 gage readings were taken, and the air voids ranged from 7.2 % to 9.7% with the averaged air voids of 8.5 %. The cores were taken from the pavement a few hours after the paving and the density was determined therewith. The air voids among the 4 cores taken were 8.2%, 6.7%, 8.0% and 15.5%, with an average value of 9.7%.
Pavement smoothness was measured using the Laser Road Profiler at every 0.1 mile. A total of 18 readings were obtained and the results varied between 738 mm/km and 978 mm/km with an average value of 862 mm/km. Table 13 summarizes the pertinent date related to the construction of the REVIX test section.

Table 13 Summary of REVIX WMA Mix Test Section Paving Information

Information Required Paving Date and time Temperature range at load out Mix temperature behind screed Test section length paved Compacted mat thickness Quality of compacted pavement surface
- In-place density
- Record any surface defects
Time and mat temp when open to traffic Record pavement smoothness

Results / Remarks May 5, 2008, 9 am to 1:30 pm
255 to 285oF 235 to 265oF
1.8 miles 1 inch
Gage avg. 8.5% air voids Core avg. 9.7% air voids Many blemishes from throw back due to cold clumps dragging
2 hr. after paving 862 mm/km

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Figure 3A Blemishes from throw back
Figure 3-3B Blemishes from throw back Figure 3B Blemishes from throw back
20

Figure 3C Blemishes from throw back and casting the mix
Paving 9.5 mm Superpave Mix Control Section Paving of the 9.5 mm Superpave mix control section was started at about 2:30 pm on May 5. Temperatures of the mix at the load out were about 315oF and that behind the screed between 285oF and 310oF. The paving progressed quite smoothly, and no noticeable defects were observed. Other than slight gearbox streaks in the middle of the mat (see Figure 4), the mat was quite uniform and smooth and no blemish was observed during the entire paving of the control section. This would rule out that the blemish problems encountered during the paving of the REVIX test section were caused by the paving equipment or improper paving operations.
Compaction of this section was identical to that of the REVIX test section. Density of the compacted mat was first determined using a nuclear density gage and the air voids among the 4 gage readings were 5.3%, 6.0%, 6.2% and 6.8%, with average air voids of 6.2%. Five cores were taken from the section and the air voids among these 5 cores varied between 4.1% and 7.4%, with average air voids of 5.8%.
Pavement smoothness was measured using the Laser Road Profiler at every 0.1 mile. A total of 7 smoothness reading were obtained and the results indicated the smoothness readings ranged between 626 mm/km and 768 mm/km, with average smoothness of 664 mm/km.
Table 14 summarizes the pertinent date related to the paving of the control section.
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Table 14 Summary of 9.5 Superpave Mix Control Section Paving Information

Information Required Paving Date and time Temperature range at load out Mix temperature behind screed Test section length paved Compacted mat thickness Quality of compacted pavement surface
- In-place density
- Record any surface defects Time and mat temp when open to traffic Record pavement smoothness

Results / Remarks May 5, 2008, 2:30 PM
315oF 285 to 310oF
0.7 miles 1 inch
Gauge avg. 6.2% air voids Core avg. 5.8% air voids Few blemishes from throw back
664 mm/km

Figure 4 Paving of 9.5 mm Superpave mix
Paving Advera Test Section Paving of Advera test section started at about 9 a.m. on May 6. Temperatures of the mix at the load out were between 265oF and 285oF and that behind the screed between 230oF and 260oF, per Table 15. During the paving operation, severe blemishes occurred as shown in Figure 5. A significant amount of hand work was required to correct the blemishes. The severe mat tearing near the edge of the mat as shown in Figure 5A was caused by the buildup of cold asphalt mix behind the end plate (see Figure 5B). The problem that occurred in the Advera WMA test section was more severe than that in the REVIX WMA test section. At around 10 a.m., paving operation was stopped for about an hour for replacing the auger unit of the paver. By the time the paving operation was
22

resumed the mix had been kept in the trucks for up to 2.5 hours causing the temperature in the mix to decrease that further exacerbated the throw back problem. The mat blemish became so severe that the paving was stopped.
Given the issue with the auger replacement, the contractor elected to pave the remaining 10 truckloads of the mix in the morning of May 7. Temperatures of the mix at the load out were between 270oF and 300oF and that behind the screed between 250oF and 280oF, about 10oF to 20oF higher than that on the May 6 paving, per Table 16. The throw black problem was as bad as that which had occurred in the previous day. The causes contributing to such problems were investigated and are presented in Section 3.4 in this chapter.
Compaction of these two Advera sections was identical to that of the other 2 test sections paved on May 5. Density of the compacted mat was first determined using a nuclear density gage. During the May 6 paving, the air voids among the 11 nuclear density gage readings were taken, and the air voids varied between 4.6% and 9.9%, with average air voids of 6.9%. Four cores were taken and the air voids among them were 5.3%, 5.6%, 8.4% and 13.5% with average air voids of 8.2%. During the May 7 paving, the air voids among the 5 nuclear density gage readings varied between 8.3% and 9.9%, with average air voids of 9.2%. Five cores were taken and the air voids among them ranged between 5.6% and 6.6%, with average air voids of 6.1%.
Pavement smoothness was measured using the Laser Road Profiler at every 0.1 mile. A total of 12 smoothness readings were obtained on the section paved on May 6, and the readings varied between 713 mm/km and 1063 mm/km, with an average value of 937 mm/km. During the May 7 paving, a total of 8 smoothness readings were obtained. The smoothness reading varied between 647 mm/km and 1082 mm/km, with an average smoothness value of 775 mm/km.
Table 15 and Table 16 summarize the pertinent data related to the REVIX test sections paved on May 6 and May 7 respectively.

Table 15 Summary of Advera WMA Mix Test Section Paving Information (Paved on May 6)

Information Required Paving date and time Temperature range at load out Mix temperature behind screed Test section length paved Compacted mat thickness Quality of compacted pavement surface
- In-place density
- Record any surface defects
Time and mat temp when open to traffic Record pavement smoothness

Results / Remarks May 6, 2008, 9 am to 12:30 pm
265 to 285 oF 230 to 260 oF
1.2 miles 1 inch
Gauge avg. 6.9% air voids Core avg. 8.2% air voids Many blemishes from throw back due to cold clumps dragging
937 mm/km

23

Figure 5A Mat tearing on Advera test section Figure 5B Buildup of cold asphalt mix behind end plate
24

Table 16 Summary of Advera WMA Mix Test Section Paving Information (Paved on May 7)

Information Required Paving date and time Temperature range at load out Mix temperature behind screed Test section length paved Compacted mat thickness Quality of compacted pavement surface
- In-place density
- Record any surface defects
Record pavement smoothness

Results / Remarks May 7, 2008, 9 am
270 to 300oF 250 to 280oF
0.8 miles 1 inch
Gage avg. 9.2% air voids Core avg. 6.1% air voids Many blemishes from throw back due to cold clumps dragging
775 mm/km

3.4 Discussions and Conclusions Severe mat blemishes were encountered during the construction of the REVIX and Advera WMA test sections. It appeared that clumps of asphalt mix were present in the auger chamber and that buildup of cold asphalt mix behind the end plates was the cause of the problem. During the paving of the REVIX test section, temperatures of the mix at the load out were between 255oF and 285oF and that behind the screed between 235oF and 265oF. Those temperatures were comparable or slightly higher than that suggested in the REVIX's specifications. During the May 6 paving, temperatures of the mix at the load out were between 265oF and 285oF and that behind the screed between 230oF and 260oF. During the May 7 paving temperatures were bumped up by another 10-15oF, with temperatures of the mix at the load out between 275oF and 300oF and that behind the screed between 260oF and 280oF. Even so, the mat blemish problem persisted. Those temperatures were higher than what were suggested in the Advera specifications.
The possibility that the problem was caused by the paving equipment or improper paving operation was also looked into. The same paving equipment and the same paving operations were used for paving the 9.5 mm Superpave mix in the afternoon of May 5 and the paving was successful without encountering the same problem; hence, it was concluded that the paving equipment or improper paving operations were not the contributing causes.
The following are the comments on the causes of the problems offered by the suppliers of the WMA additives.
REVIX WMA The following comments were offered by Mr. Gaylon Baumgardner of Paragon Technical Services, Inc./Ergon Asphalt and Emulsions, Inc.
Mr. Baumgardner pointed out that the problem was due to (1) lack of sufficient WMA additive in the mixture to compensate for the total active binder in the mix; and (2)

25

extended laydown/compaction delays. He pointed out that the REVIX additive dosage used for the construction of the REVIX WMA test section was about 50% of the typical dosage used for non-RAP mixtures normally used elsewhere. With the 15% RAP in the mix used for this test section, the effective additive dosage was less than 50%. He also commented that this was the lowest level of additive attempted in field projects since the inception of this technology. He further commented that if sufficient REVIX (3G) additive were added in the mix, it would alleviate any problems caused by reaction of the available RAP due to extended storage, haul and laydown times. He also mentioned that since the problems occurred in this test section, Paragon Technical Services has prepared asphalt mixes using the same waterless WMA process in conjunction with RAP contents as high as 40% (assuming using higher additive dosage). These mixtures exhibited excellent coating ability and had no difficulties of compaction at lower temperatures (212oF) after extended storage. However, it remains to be seen whether the 212oF temperature mentioned above for the WMA mixes prepared in the laboratory would be adequate during the field paving operation.
The explanations offered by Mr. Baumgardner for the causes of the blemish problem during the paving of the REVIX test section were reasonable. With insufficient amount of REVIX additive used in the binder, the viscosity of the binder could not be lowered sufficiently at the lower temperature to allow for adequate paving. It is important that the proper dosage required for the mixes and the corresponding mixing temperatures and compaction temperatures to meet the paving and compaction requirements will have to be tested under the actual paving environments. It is conceivable that such threshold values could depend on different job mix formulas, different types of aggregates, different gradations, and different amount of RAP, etc. It would be extremely valuable for the REVIX additive producer to provide threshold values data for the laydown temperatures and compaction temperatures and the maximum storage time allowed (in the silo and in the trucks) beyond which the WMA mix could not be laid down and compacted successfully. It is suggested that such information should be provided by Paragon Technical Services when performing the mix design verification for a WMA mix. Such information would be very useful for the contractors and for quality control purposes.
Advera WMA The following comments were offered by Mr. Ed Myszak, Program Director of Warm Mix Asphalt Technology Group of PQ Corporation.
Mr. Myszak pointed out that the Reeves' asphalt plant was a drum for drying the aggregate which then feeds into a pug mill where the asphalt is added. He pointed out that Advera WMA needs to get intimately mixed with the asphalt prior to coating the aggregate. During the mixing operation for producing the Advera WMA in this project, the Advera additive was blown into the spray points in the pug mill. In his opinion, it was not totally successful. He did not believe that the Advera additive was properly incorporated and blended into the asphalt. He commented that instead of using the drum plant feed equipment, such as the one used in this project, the Advera additive should be pre-blended with the asphalt prior to input into the pug mill. He pointed out that Advera WMA has been used successfully for 9.5 mm Superpave mixes elsewhere. He believed that had the mix was produced using a "true drum plant," or had the batch plant feed equipment been available, the construction of the test section could have been successful.
26

The causes offered by Mr. Myszak for the blemish and severe mat tearing that occurred during the construction of this test section seemed plausible. Whether the method of incorporating Advera additive into the asphalt in the Reeves's asphalt plant was the primary contributing factor deserves further investigation. Additional factors may have contributed to the paving problem as well.
The mechanism for the Advera additive to offer improved workability of coating the asphalt films on aggregates and lower the mixing and compaction temperatures was the generation of micro-forming from the water in the zeolite structure of the Advera additive. Hence, the stability of the micro-forming and how long it would remain effective would be important factors affecting the workability of the WMA mix. It seems conceivable that the moisture in the additive for generating the micro-forming would gradually evaporate and thus diminish its effectiveness for improving the workability of the mixes. Also, as temperature in the mix dropped below a certain threshold value, the microforming could collapse back to water and thus lose its effectiveness for improving the workability for the mixes.
Figure 6 clearly shows the existence of such a threshold temperature for foamed asphalt. It shows that when the temperature drops to slightly above the temperature of boiling water (212oF), the viscosity of the micro-formed asphalt would increase rapidly beyond the compactability range.
Figure 6 Effect of temperature on viscosity of foamed asphalt (8)
The WMA mixes in the hauling truck, particularly those mixes near the top surface in the truck, would be susceptible to this increase in viscosity, even when the mix was properly covered with tarpaulins. The hard crust thus developed would cause cold clumps to form in the mixes during the load out. Unlike in the HMA, the cold clumps from the WMA would be more difficult to be broken loose in the auger chamber due to the relatively lower temperature than that of the HMA. Therefore information on the threshold values for the temperatures at load out, at laydown and compaction, and for maximum storage time (in the silo and in the trucks) beyond which the mix could not be laydown and compacted successfully for the Advera WMA are very important and should be provided by the Advera additive producer. Again, such threshold values could depend
27

on variables such as different job mix formulas, different types of aggregates, different gradations, and different amounts of RAP, etc.
28

CHAPTER 4: POST-CONSTRUCTION EVALUATION
This phase of the study was to evaluate the pertinent properties of the WMA mixes and the control mix by performing a series of laboratory tests with the samples prepared in the laboratory using the WMA mixes and the control mix collected from the asphalt plant during the construction and from the cores taken from the test sections.
However, in light of the problems encountered during the construction of the two WMA test sections as presented in Section 3-3, and since the problems were primarily in the WMA mixes (due to insufficient dosage of the REVIX additive and possible inadequate mixing for the Advera additive), testing of the mixes would not produce meaningful material properties information. Therefore, with consent from OMR this phase of the study was suspended.
The original laboratory testing program is presented below.
1. Determine moisture content of the mixes at load out: AASHTO T329.
2. Gyratory compaction of six 6-in. diameter samples for each of the mixes to specified Ndesign compaction effort without reheating mix other than to desired compaction temperature. Record time needed to reheat samples (if any).
3. Perform the volumetric properties measurements on the samples prepared in (2).
4. Perform the Asphalt Pavement Analyzer (APA) rutting tests on the samples prepared in (2) according to GDOT-115 for determining rutting potential of the mixes at the recommended climatic high temperature for the site.
5. Determine maximum specific gravity of the mixes.
6. Prepare 6-8 samples to 6 0.5 percent air voids and a height of 95 mm for Tensile Strength Ratio Testing according to GDT-66.
7. Perform Hamburg Tests for moisture susceptibility and rutting susceptibility
8. Perform beam fatigue tests. Samples for beam samples for fatigue testing should be prepared to the anticipated in-place air void content. Improved densification tends to improve fatigue life. Therefore, every effort should be made to capture the effect of improved compaction obtained with WMA (AASHTO T321).
9. Perform bond strength tests on the 6-in. diameter cores taken from the test sections and the control section and tested to evaluate the bond strength developed between the different mixes with the existing pavement surface. Ten (10) cores were taken from each of the test sections on May 21.
29

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions The following conclusions are offered based on the work that has been performed for this study.
1. The REVIX WMA mix and the Advera WMA mix for the test sections used the same 9.5 Superpave mix design. The reason for using the same mix design was that the amount of additives used in these two WMA mixes was very small and should not affect the mix characteristics.
2. The WMA mixes and the control mix were produced by an Astec continuous drum plant with a production rate of 220 tons per hour. For the REVIX WMA the mix discharge temperatures were between 255oF and 285oF and that behind the screed between 235oF and 265oF, about 40 oF to 50oF lower than that for the 9.5 mm Superpave mix; the mix discharge temperature for the Advera WMA was about 285oF, about 32oF lower than that for the 9.5 mm Superpave mix.
3. Paving operations on all of the test sections and the control section were about the same, except that the temperatures of the mixes at load out and behind the screed were different. During the paving of the REVIX and Advera WMA mixes, clumps of asphalt mixes were present in the auger chamber and behind the end plates, resulting in severe blemishes and tearing in the mat behind the paver. Since no blemishes occurred on the 9.5 mm Superpave control section, the possibility that the problem was caused by the paving equipment or improper paving operation was excluded.
4. For the REVIX WMA test section, the primary cause contributing to the problems was lack of sufficient WMA additive in the mixture. It was determined by the REVIX WMA additive producer that the additive dosage used for the construction of the REVIX WMA test section was about 50% of the recommended dosage.
5. For the Advera WMA test sections, the opinions offered by the Advera WMA additive producer were that the method for incorporating the Advera additive into the drum mixer in the Reeves' asphalt plant did not offer adequate mixing action and thus rendered the Advera additive less effective in improving the workability of the WMA produced. The cause offered by the additive producer seemed plausible, although it deserves further investigation.
6. In light of the problems encountered during the construction of the two WMA test sections, and since the problems were primarily in the WMA mixes (due to insufficient dosage of the REVIX additive and possible inadequate mixing for the Advera additive), testing of the mixes would not product meaningful material properties information. Therefore, after discussion with OMR, it was decided to suspend the proposed work for Task 4 Post-construction Laboratory Testing and Evaluation of Mix Properties.
30

5.2 Recommendations Since the use of WMA mixes is still relatively new in the U.S. and in Georgia, asphalt paving contractors are less familiar in dealing with such products than with HMA mixes. Also, different WMA products could possess different characteristics in terms of mixing, paving, temperature sensitivity, etc. Therefore it would be prudent to exercise more caution during the construction of WMA mixtures, at least at the beginning. The following recommendations are offered with an aim toward better understanding and improving the quality of the WMA paving operation and performance.
1. When using WMA in a paving project, the following information in addition to that stipulated under GDOT Standard Specifications Section 400.1.03 should be included when the contractor submits the job mix formula after the contract has been awarded:
The amount of WMA additive as percent of net binder used in the mix or the percent of the total mix weights used, particularly when reclaimed asphalt pavement (RAP) is used.
A viscosity vs. temperature chart similar to that shown in Figure 6 on page 27 shall be submitted by the suppliers
The procedure for incorporating the WMA additive into the mix, the mixing temperature and mixing process in the laboratory mixing operation.
Temperature and duration of aging, if different from the standard for aged at 135oC (275oF), in an oven for 2 hours after mixing and prior to compaction.
Any deviation from the Superpave mix design procedures.
2. Submit proposed job mix formula for approval at least 4 weeks (instead of 2 weeks) before the beginning the asphalt plant mixing operation. This would allow the OMR sufficient time to conduct more thorough mix design verification testing.
3. It would be desirable to request that the WMA additive supplier to conduct the mix design verification testing based on the job mix formula and the aggregates and the binder submitted by the contractor and forward the verification mix design results to the OMR. It would be highly desirable that the WMA additive supplier also provide the following information for using the WMA additive for the process during the construction.
Minimum threshold mix temperature behind the screed Maximum allowable storage time (in silo and in trucks) Maximum allowable storage time in the truck
4. OMR should perform mix design verification testing based on the job mix formula, aggregates, and binder submitted by the contractor and compare the results with those from the WMA additive supplier.
5. During the construction of the test section for the project, it may be desirable to intentionally vary the temperatures of the mix at load out, behind the screed, and
31

during the holding time to assess the sensitivity of the temperatures and the storage time on the constructability of the WMA mix. This would provide valuable information for the contractor and for the Quality Control Technician during the mainline paving. If the results indicate that the WMA mix used is too sensitive to the temperature variation, the project engineer perhaps should consider requesting the contractor to use a Material Transfer Vehicle to mitigate the temperature sensitivity of the WMA mix used for the project. 6. OMR and the Office of Maintenance should cooperate to place additional WMA sections to gain experience of using different types of WMA mixes. The proposed research program for this pilot study presented in this report, including Task 4, (PostConstruction Laboratory Testing and Evaluation of Mix Properties and Pavement Performance), can be used to evaluate the constructability and the properties of the mixes and document the experience with and performance of using different WMA mixes.
32

REFERENCES
1. Hurley, G.C. and B. D. Prowell. "Evaluation of Potential Processes for Warm Mix Asphalt," Presented at the 2006 Annual Meeting of the Association of Asphalt Paving Technologists.
2. Prowell, B.D., Hurley, G.C., and Crews, E. "Field Performance of Warm Mix Asphalt at the NCAT Test Track" Presented at the 86th Annual Meeting of the Transportation Research Board, January 21-25, 2007, Washington, DC.
3. Hurley, G.C. and B. D. Prowell. "Field Performance of Warm Mix Asphalt," Presented at the TRB 2008 Annual Meeting.
4. Muench, Stephen T., et al. "Assessing the Potential for Warm Mix Asphalt Technology Adoption," TRB 2007 Annual Meeting. January 2007.
5. Brown, D. C. "Warm Mix: the Lights are Green, Hot Mix Asphalt Technology," Jan/Feb 2008.
6. Corrigan, M., et al. "Warm-Mix Asphalt: European Practice," Federal Highway Administration Technical Report, FHWA-PL-08-007, February 2008.
7. Diefenderfer, S.D., K.K. McGhee, and B.M. Donaldson. "Installation of Warm Mix Asphalt Projects in Virginia," Virginia Transportation Research Council, Report No FHWA/VTRC 07-R25, April 2007.
8. Swanson, Malcolm. "Double Barrel Green System An Equipment Means to Produce Warm Mix," a PowerPoint Presentation, ASTEC Industrial, Inc.
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APPENDIX
Table A-1 9.5 mm Superpave Mix Job Mix Formula Submitted by Reeves Construction Co.
Table A-2 9.5 mm Superpave Mix Table A-3 9.5 mm Superpave Mix Asphalt Plant QC Test Results Table A-4 REVIX WMA Mix Asphalt Plant QC Test Results Table A-5 Advera WMA Mix Asphalt Plant QC Test Results
34

Table A-1 9.5 mm Superpave Mix Job Mix Formula Submitted by Reeves Construction Co.
35

Table A-2 9.5 mm Superpave Mix 36

Table A-3 9.5 mm Superpave Mix Asphalt Plant QC Test Results 37

Table A-4 9.5 mm REVIX WMA Mix Asphalt Plant QC Test Results 38

Table A-5 9.5 mm Advera WMA Mix Asphalt Plant QC Test Results 39

40