NCAT Report 09-XX

EVALUATION OF MIXTURE

PERFORMANCE AND

STRUCTURAL CAPACITY OF

PAVEMENTS UTILIZING

SHELL THIOPAVE®

Phase I: Mix Design, Laboratory Performance Evaluation and Structural Pavement

Analysis and Design

By

David Timm Adam Taylor

Nam Tran Mary Robbins Buzz Powell

August 2009

By Andrea Kvasnak and Adam Taylor

LABORATORY EVALUATION OF ZYDEX WARM MIX (ZYCOSOIL & DENSICRYL) FOR USE IN WARM MIX ASPHALT PREPARATION Final Report By Adam Joel Taylor April 2011

LABORATORY EVALUATION OF ZYDEX WARM MIX (ZYCOSOIL & DENSICRYL) FOR USE IN WARM MIX ASPHALT PREPARATION

Final Report

By

Adam Joel Taylor

Assistant Research Engineer National Center for Asphalt Technology

Phone: (334)-844-7337 E-mail: tayloa3@auburn.edu

National Center for Asphalt Technology

Auburn University, Auburn, Alabama

Sponsored by

Zydex Industries India

April 2011

Taylor

iii

ACKNOWLEDGEMENTS This project was sponsored by Zydex Industries India. The project team appreciates and thanks Zydex Industries for their sponsorship of this project as well as Dr. Ajay Ranka and Dr. Prakash Mehta for their support.

DISCLAIMER The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the sponsor(s) or the National Center for Asphalt Technology, or Auburn University. This report does not constitute a standard, specification, or regulation. Comments contained in this paper related to specific testing equipment and materials should not be considered an endorsement of any commercial product or service; no such endorsement is intended or implied.

Taylor

iv

TABLE OF CONTENTS Introduction .................................................................................................................................... 1

1. Background .......................................................................................................................... 1

2. Objectives............................................................................................................................. 2

3. Scope .................................................................................................................................... 2

Mix Design and Mixing Procedure .................................................................................................. 3

1. Aggregate Blend ................................................................................................................... 3

2. Procedure for Adding Zycosoil and Densicryl ...................................................................... 4

3. Mix Design Verification Results ........................................................................................... 7

Performance Testing Results .......................................................................................................... 8

1. Tensile Strength Ratio Testing and Results .......................................................................... 8

2. Hamburg Wheel-Tracking Testing and Results .................................................................. 10

3. APA Testing and Results ..................................................................................................... 14

Conclusions and Recommendations ............................................................................................. 17

REFERENCES .................................................................................................................................. 18

APPENDIX A ................................................................................................................................... 19

APPENDIX B ................................................................................................................................... 20

APPENDIX C ................................................................................................................................... 21

Taylor

v

LIST OF FIGURES Figure 1: Power 45 Chart of Blend Gradation ................................................................................. 3

Figure 2: Photograph of Modifying Binder with Zycosoil ............................................................... 5

Figure 3: Photograph of Densicryl Addition of Asphalt Binder (above) and Foaming Binder (below) ............................................................................................................................................ 6

Figure 4: Height versus Gyrations of 5.5% AC Samples .................................................................. 8

Figure 5: Graphical Summary of TSR Results .................................................................................. 9

Figure 6: Photos of Broken TSR Samples for HMA (left) and WMA (right) .................................. 10

Figure 7: Hamburg Wheel-Tracking Device .................................................................................. 11

Figure 8: Example of Hamburg Data Analysis ............................................................................... 12

Figure 9: Graphical Summary of Hamburg Results ....................................................................... 13

Figure 10: Average Stripping Inflection Point versus Compaction Temperature ......................... 14

Figure 11 : Asphalt Pavement Analyzer (APA) .............................................................................. 15

Figure 12: Graphical APA Results .................................................................................................. 16

LIST OF TABLES Table 1: Mix Design Consensus Properties ..................................................................................... 4

Table 2: Summary of Mix Design for WMA and HMA .................................................................... 7

Table 3: Locking Point and Average Air Voids at 5.5% AC .............................................................. 7

Table 4: Summary of TSR Results .................................................................................................... 9

Table 5: Summary of Hamburg Testing Results ............................................................................ 13

Table 6: Summary of APA Results ................................................................................................. 15

Taylor

1

INTRODUCTION

1. Background

In 2009, NCAT undertook a study for Zydex Industries, India to study the efficacy their Zycosoil technology as an anti-stripping agent for hot mix asphalt pavement materials. The compound is an organosilane compound which reacts with aggregate, soil, clay, and stone powder surfaces and converts silanol (water loving) groups to Alkyl Siloxane (liquid asphalt loving). This makes the aggregate particles water resistant and offers long-term moisture protection (Kim and Moore, Laboratory Evaluation of ZycoSoil as an Anti-Stripping Agent on Superpave Mixtures 2009). The initial NCAT study looked at the effects of Zycosoil on Superpave binder properties as well as its effects on selected mixture properties. The results of the testing showed that the addition of Zycosoil did not affect the base binder (PG 64-22) enough to alter its PG grade. For mixture properties, a Superpave mix design using moisture susceptible aggregate was prepared with and without 0.05% Zycosoil (by weight of binder) in the asphalt binder. The results of this study were promising, with the Zycosoil modified mixture outperforming the control mixture in terms of moisture susceptibility (Kim and Moore, Laboratory Evaluation of ZycoSoil as an Anti-Stripping Agent on Superpave Mixtures 2009). Based on the results of the initial study, another study was conducted at NCAT to determine the optimum percentage of Zycosoil to be utilized for optimal mix moisture resistance. Zycosoil dosages of 0, 0.05%, and 0.1% by weight of binder were utilized. Binder grading of each Zycosoil dosage again showed no effect on the PG grade of the binder. Two dense-graded mixtures were prepared with moisture susceptible granite to determine the effect of the Zycosoil dosage on mixture properties. The results showed the 0.1% dosage of Zycosoil gave the best moisture protection for the asphalt mixes without reducing the tensile strength of these mixes (Kim and Moore, Laboratory Evaluation of Zycosoil as an Anti-Stripping Agent for Superpave Mixtures - Phase II 2009). Zydex Industries, India has recently developed a new polymer-based warm mix additive (WMA) technology that is designed to be used in conjunction with Zycosoil. This additive is called Densicryl (high molecular weight acrylic polymer dispersion). This additive was designed to allow mixing and compaction of WMA at temperatures of around 250°F and 235°F, respectively. Polymers, as a class of material, are known to be beneficial to improve reinforcement of material properties. Densicryl was designed to minimize the tensile strength reduction common in WMA in spite of the reduced oxidation of the asphalt binder at lower mixing and compaction temperatures. Densicryl is a liquid product which can be added into the binder tank by a metering pump while the asphalt binder is being re-circulated or loaded. It can also be co-injected into the binder with a metering pump 2-3 meters prior to the binder entering the mixing drum. The addition of Densicryl to Zycosoil modified asphalt binder creates a ‘foaming’ effect which is helpful to

Taylor

2

achieve thorough mixing at lower temperatures. Zydex Industries, India has asked NCAT to perform an initial laboratory evaluation of this WMA technology. This study will conduct a mix design using the Zycosoil and Densicryl modified asphalt binder to determine if the design produces significantly different results than that of a control mixture (produced at a higher temperature). Additionally, the laboratory resistance of this mixture to rutting and moisture susceptibility was evaluated. These two performance issues are commonly seen with laboratory evaluations of WMA (Hurley, Evaluation of New Technologies for Use in Warm Mix Asphalt 2006). Most WMAs tend to show increased rutting in the laboratory compared to a control HMA due to reduced oxidation of the binder at the lower mixing and compaction temperatures. Lower mixing and compaction temperatures also tend to increase the susceptibility of many WMAs to moisture damage due to the softer binder film and/or incomplete drying of the aggregate which may cause weaker bonds between the aggregate and the asphalt binder (Kvasnak, et al. 2010). However, while these issues tend to show up with regularity in the laboratory, they have not been as prevalent in the paved field pavements (as indicated by the results of NCAT WMA Field Trials) (Hurley, Prowell and Kvasnak, Missouri Field Trial of Warm Mix Asphalt Technologies: Construction Summary 2010) (Kvasnak, et al. 2010). While a full-scale field evaluation would be needed for complete data on technology performance, a laboratory evaluation centered on rutting and moisture susceptibility tests is useful for assessing new WMA technologies. NCAT has conducted numerous evaluations of this type over the last few years (Hurley and Prowell, Evaluation of Aspha-Min Zeolite for use in Warm Mix Asphalt 2005) (Hurley and Prowell, Evaluation of Evotherm for use in Wam Mix Asphalt 2006) (Hurley and Prowell, Evaluation of Sasobit for use in Warm Mix Asphalt 2005).

2. Objectives

The purpose of this study was to compare the laboratory performance of a WMA using Zycosoil and Densicryl to that of an HMA designed with moisture susceptible aggregate.

3. Scope

The effects of the Zycosoil and Densicryl package were evaluated using multiple laboratory tests to determine the effect of this additive on mixture rutting resistance and moisture damage resistance. First, a mix design verification was conducted to verify the mixes use met Superpave design tolerances. This verification was also used to determine if the addition of the Zycosoil and Densicryl had any tangible effect on the compaction of the mixture. Both the WMA and HMA control were then tested using Tensile Strength Ratio (TSR), Asphalt Pavement Analyzer (APA), and Hamburg Wheel-Tracking Tests. Both the TSR and Hamburg can be used to determine a mixture’s laboratory moisture susceptibility while the APA and Hamburg can be used to determine a mixture’s resistance to rutting.

Taylor

3

MIX DESIGN AND MIXING PROCEDURE

1. Aggregate Blend

For this study, it was desirable to determine the effect of adding the Zycosoil and Densicryl package to an HMA mixture with moisture susceptible aggregate and no anti-stripping agent. In this way, the effect of adding the Zycosoil and Densicryl could be compared against a baseline reading with no additional variables. For this study, an HMA mix design was selected that has been used by NCAT in the past. The mixture is currently in-service at the NCAT Test Track in section E8. This mixture was selected because the aggregate used is known to be very susceptible to moisture damage. The HMA design is a 9.5mm NMAS Superpave mixture designed to 65 gyrations. The mix was designed using a PG 67-22 binder, in accordance with AASHTO T323-07 and AASHTO R35-09. A crushed granite aggregate quarried in Lithia Springs, GA was used as the aggregate for this mix design. No hydrated lime or other mineral fillers or fibers were used. The gradation of the blend used for this design is plotted on a 0.45 Power chart in Figure 1. The aggregate consensus properties were measured and recorded in Table 1. The weighted average of these properties indicates this gradation is acceptable for a surface course designed for 10-30 Million ESAL according to AASHTO T323-07.

Figure 1: Power 45 Chart of Blend Gradation

Taylor

4

Table 1: Mix Design Consensus Properties

Stockpile Fractured Face Count (% 1 Crushed Face/%

2+ Crushed Faces)

Flat and Elongated Particles (% 5:1)

FAA (%)

Sand Equivalency

Lithia Springs 89s 100/100 0 n/a n/a

Lithia Springs 810s

n/a n/a 47.6 82.3

Lithia Springs W10s

n/a n/a 45.9 92

Weighted Average

100/100 0 46.9 85.8

AASHTO M323* 95/90 <10 >45 >45

* = 10-30 Million ESAL Design, Less than 100 mm from the surface

2. Procedure for Adding Zycosoil and Densicryl

The Zycosoil liquid anti-strip was pre-blended with the asphalt binder at a dose of 0.1% by weight of binder. The Zycosoil was added drop-wise to the hot asphalt binder from a 1 mL syringe while it was continuously stirred with a glass stirring rod. A typical dosage for a gallon of binder (approximately 3000 grams) was approximately 3 mL. The Zycosoil modified binder was continuously stirred for an additional 10 minutes after the Zycosoil was added. It was then allowed to heat for 30 minutes at the mixing temperature prior to mixing to allow the binder to re-heat and for the Zycosoil to distribute uniformly throughout the asphalt binder. A photograph of the Zycosoil blending process is shown in Figure 2. The Densicryl WMA additive was added during the mixing process. First the aggregate was pre-heated to the desired temperature (typically 20°F above the mixing temperature). Next, the required amount of Densicryl was extracted into a 5 mL syringe. The Densicryl was added at a rate of 0.5% by total weight of asphalt binder. At the beginning of the mixing process, the hot aggregate was added to the mixing bowl and stirred to form a small crater in the aggregate. The desired amount of asphalt binder is added to this crater, followed by the correct dosage of Densicryl (A typical dosage of Densicryl for 300 grams of asphalt binder would be about 1.5 mL). The Densicryl and asphalt are then immediately stirred together using a stirring rod to incorporate them. For a correctly prepared sample, a significant amount of ‘bubbles’ should be evident in the asphalt binder. This indicates the functioning of the nano-foaming technology. A photo of this mechanism is shown in Figure 3. Preparation of the rest of the mixture sample is the same as for any other Superpave gyratory sample, except at the lower target WMA temperature. For this project, the control HMA was mixed between 320-330°F and compacted between 290-300°F. The Densicryl and Zycosoil modified asphalt (hereafter referred to as ‘WMA’) was mixed

Taylor

5

at 250°F and compacted at 235°F, per the sponsor’s request. This represents a 60-70°F drop in mixing and compaction temperature, which would create a substantial savings in fuel consumption for plant production.

Figure 2: Photograph of Modifying Binder with Zycosoil

Taylor

6

Figure 3: Photograph of Densicryl Addition of Asphalt Binder (above) and

Foaming Binder (below)

Taylor

7

3. Mix Design Verification Results

To determine the optimum binder content for each mix, two design pills were compacted at the binder contents surrounding the anticipated optimum. For the HMA, duplicate samples were compacted at 5.5 and 6.0 percent by weight of mix. For the WMA, duplicate samples were compacted at 5.0, 5.5, and 6.0 percent by weight of mix. Table 2 shows a summary of the mix design results for both the WMA and HMA at the optimum AC content, and how the critical volumetric properties compare to the AASHTO M323-07 requirements. It can be seen the WMA and HMA had approximately the same optimum binder content (5.7 versus 5.8 percent) at significantly different mixing and compaction temperatures. The WMA and HMA also had similar volumetric properties as well (VMA, VFA, and Dust Proportion) that fell within the requirements of AASHTO M323-07. Table 2: Summary of Mix Design for WMA and HMA

Mix ID Optimum AC (%)

Gsb Gmm Design Air Voids

%

VMA (%) VFA (%) Dust Proportion

WMA 5.7 2.614 2.419 4.0 16.2 75.3 1.1

HMA 5.8 2.614 2.419 4.0 16.3 75.4 1.1

AASHTO M323*

4.0

> 15 73 - 76 0.6 - 1.2

* = 9.5 mm NMAS 3-30 M ESAL Design To determine whether the two mixes showed similar behavior during the compaction process, the gyratory heights were collected for the two design pills with a binder content closest to the optimum (in this case, 5.5% AC). Based on this data, a locking point could be determined. Locking point represents the first gyration where a reduction in sample height did not occur (i.e. the same height was recorded for consecutive gyrations). This data is recorded in Table 3. Based on this data, the average locking points for the two mixes are almost the same, albeit with more variation for the WMA. The height versus gyration data for each sample compacted at 5.5% AC is shown as Figure 4. Based on this figure, the compaction behavior of the WMA and HMA was almost identical. Therefore, the WMA and HMA showed almost identical compaction behavior despite a 65°F difference in compaction temperature. Table 3: Locking Point and Average Air Voids at 5.5% AC

Sample ID Locking Point Average LP Sample Air Voids (%)

Average Air Voids (%)

WMA #15-5.5 37 41.5 4.8 4.7

WMA #16-5.5 46 4.6

HMA #9-5.5 44 42.5 4.7 4.8

HMA #10-5.5 41 4.8

Taylor

8

Figure 4: Height versus Gyrations of 5.5% AC Samples

PERFORMANCE TESTING RESULTS

1. Tensile Strength Ratio Testing and Results

Tensile Strength Ratio (TSR) moisture susceptibility testing was performed for this project in accordance with AASHTO T283-07. The AASHTO T283-07 methodology uses 95 mm samples compacted in a Superpave Gyratory Compactor. These samples were mixed in the laboratory, and the loose mixtures were allowed to rest at room temperature for 2 ± 0.5 hours prior to being aged 16 ± 1 hours at 60oC, per the test procedure. The samples were then compacted at the desired compaction temperature and allowed to rest overnight prior to their bulk specific gravity being determined. The target air void level for these samples was 7.0 ± 0.5%. A set of three specimens were vacuum saturated so that 70-80% of the internal voids were saturated with water. The samples were then placed in a freezer for a minimum of 16 hours prior to being placed in a warm water bath (60oC) for 24 hours. This process constitutes one ‘freeze-thaw’ cycle. These ‘conditioned’ specimens, along with a group of three unconditioned specimens that had not been saturated, were then tested for indirect tensile strength using a Marshall press apparatus. All samples are placed in a 25oC water bath for two hours to equilibrate their temperature prior to testing. The ratio of the indirect tensile strengths of the conditioned and unconditioned samples is recorded as the tensile-strength ratio (TSR). In accordance with AASHTO R35-09, the minimum TSR criteria is 0.8 for moisture-resistant mixes, indicating less than a 20% reduction in splitting tensile strength given conditions conducive to moisture-induced damage. Table 4 shows a tabular summary of the TSR results while Figure 5

Taylor

9

presents them graphically. The data shows that the Zycosoil-Densicryl modified WMA had a significantly higher TSR than the HMA with no anti-stripping agent (0.82 for the WMA versus 0.49 for the HMA). This is because the WMA conditioned tensile strength of 84 psi is significantly higher than that of the HMA (63.4 psi). Conditioned tensile strength is very important to the structural performance of in-service pavements which are exposed to water and moisture. This result was expected given previous experience with this aggregate blend and with the Zycosoil material. The reduction in the degree of stripping can also be seen in Figure 6, which shows photos of broken conditioned TSR samples for both the WMA and HMA. It is also notable that the WMA had a lower unconditioned splitting tensile strength than the HMA by about 30 psi. This is likely a consequence of reduced binder aging at the significantly lower compaction temperature for the WMA. The TSR test results for the individual specimens are tabulated in APPENDIX A. Table 4: Summary of TSR Results

Mix ID Compaction Temperature

Range (F)

Conditioned Splitting Tensile

Strength (psi)

Unconditioned Splitting Tensile

Strength (psi)

TSR

Control HMA 300-310 63.4 129.7 0.488

Zycosoil-Densicryl Modified

235-245 84.0 102.0 0.824

Figure 5: Graphical Summary of TSR Results

Taylor

10

Figure 6: Photos of Broken TSR Samples for HMA (left) and WMA (right)

2. Hamburg Wheel-Tracking Testing and Results

Hamburg wheel-track (Hamburg) testing, shown in Figure 7, was performed to determine both the rutting and stripping susceptibility of the mixtures tested for this project. Testing was performed in accordance with AASHTO T 324-04. Three replicates were tested per mix. The specimens were originally compacted using an SGC to a diameter of 150 mm and a height of 115 mm. These specimens were then trimmed so that two specimens, with a height between 38 mm and 50 mm, were cut from the top and bottom of each gyratory-compacted specimen. The air voids on these cut specimens were 7 ± 0.5 percent. AASHTO T324-04 recommends that all laboratory mixed samples undergo the short-term conditioning procedure in AASHTO R30-08 prior to being heated to the appropriate compaction temperature and compacted. AASHTO R30-08 defines short-term conditioning for mechanical mixture-property testing as aging the loose mix in a pan (with the mix ranging between 1 and 2 inches thick) for four hours at 275°F (135°C), and stirring the mixture every hour. However, this method does not take into account the compaction temperature of many WMA technologies being below 275°F. Therefore, for this project the WMA aging was treated two ways. First, the WMA was aged using the AASHTO R30-08 procedure, except the aging temperature was lowered to 235°F (112.8°C). The other data set involved aging the WMA using the AASHTO R30-08 procedure (including the recommended temperature), and then compacting the mixture at that temperature. The HMA was conditioned and compacted according to the standard AASHTO R30-08 protocol. In this way, the effect of temperature conditioning could be evaluated in the data set.

Taylor

11

The specimens were tested under a 158 ± 1 lbs wheel load for 10,000 cycles (20,000 passes) while submerged in a water bath which was maintained at a temperature of 50oC. While being tested, rut depths were measured by an LVDT which recorded the relative vertical position of the load wheel after each load cycle. After testing, these data were used to determine the point at which stripping occurred in the mixture under loading and the relative rutting susceptibility of those mixtures. Testing would be terminated early in the event of severe rutting or stripping. Severe rutting would be defined as greater than ½” and severe stripping as dramatic increase in the rutting rate of the mixture. Figure 8 illustrates typical data output from the Hamburg device. These data show the progression of rut depth with number of cycles. From this curve two tangents are evident, the steady-state rutting portion of the curve and the portion of the curve after stripping. The intersection of these two curve tangents defines the stripping inflection point of the mixture. The slope of the steady-state portion of the curve is also quantified and multiplied by the number of cycles per test to determine the steady-state rut depth at 10,000 cycles. Comparing the stripping inflection points and steady-state rutting of the ten different mixtures gives a measure of the relative moisture and deformation susceptibility of these mixtures.

Figure 7: Hamburg Wheel-Tracking Device

Taylor

12

Figure 8: Example of Hamburg Data Analysis

Table 5 gives a summary of the following data for the three data points tested: average and standard deviation of the steady-state rutting at 10,000 cycles, and the average and standard deviation of the stripping inflection point. Figure 9 shows a graphical summary of this data as well. Complete data for the individual samples can be found in APPENDIX B. Based on Figure 9, the steady-state rutting value appears lower for the HMA than for each WMA tested. However, an ANOVA of the steady-state rutting data shows no statistical difference between the rutting of the WMA and the rutting of the HMA (p-value = 0.545, α = 0.05). Typically, a steady-state rutting value at 10,000 cycles of less than 10 mm is considered good for a mix with a PG 67-22 binder (Kvasnak, et al. 2010). The results show that the stripping inflection point (SIP) of the WMA which was R30 aged and compacted at 235°F was less than half of that exhibited by the HMA. However, the WMA which was R30 aged and compacted at 275°F had a stripping point which was only slightly less than that of the HMA. In fact, the relationship between compaction temperature and stripping inflection point was perfectly linear for this mix, as shown in Figure 10. In this study, all of the mixes had SIP values below 5,000, whereas a desired target for a moisture resistant PG 67-22 mixture is greater than 5,000 (Kvasnak, et al. 2010). In terms of measuring mixture quality, the HMA results tend to agree with the results from the TSR test, while the WMA results do not (the HMA outperformed the WMA in the Hamburg test). Therefore, a closer look may need to be taken at the aging procedure and testing temperature for WMA mixes that are to be tested in the Hamburg device.

Rut Depth (mm)

30% Rich HB 13A and 13B

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500

Cycles

Rut D

epth

(m

m)

Stripping Inflection Point ~ 5550 cycles

Steady-State Rutting Tangent

Tangent Post-Stripping

Taylor

13

Table 5: Summary of Hamburg Testing Results

Mix ID Compaction Temperature

(F)

Average Steady-State Rutting at

10,000 cycles (mm)

Average Stripping Inflection Point (SIP)

Standard Deviation Rut Depth

(mm)

Standard Deviation

SIP (cycles)

HMA 300 7.07 4133.3 3.75 450.9

WMA 235 9.10 1900.0 2.00 150.0

WMA 275 9.17 3400.0 1.01 200.0

Figure 9: Graphical Summary of Hamburg Results

Taylor

14

Figure 10: Average Stripping Inflection Point versus Compaction Temperature

3. APA Testing and Results

The rutting susceptibility each mix design was evaluated using the Asphalt Pavement Analyzer (APA) as shown in Figure 11. Testing was performed in accordance with AASHTO T340-10. The specimens used for this testing were prepared to a height of 75 mm and an air void level of 7 ± 0.5 percent, per the specification. Six replicates were tested for each mix. The samples were tested at a temperature of 64oC (the high PG grade of the binder). The samples were loaded by a steel wheel (loaded to 100 lbs) resting on a pneumatic hose pressurized to 100 psi for 8,000 cycles. Manual depth readings were taken at two locations on each specimen. This reading was taken after 25 conditioning cycles and after the loading was applied to determine the specimen rut depth. Automated rut depth measurements were also recorded by the testing software.

Taylor

15

Figure 11 : Asphalt Pavement Analyzer (APA)

Table 6 shows a summary of the average and standard deviation of the APA rut depth measurements for both the WMA and HMA. Figure 12 presents these results graphically. Based on this data, similar results were achieved for both mixes through both manual and automated measurements. An ANOVA of the manual rut depth measurements indicated there was no statistical difference between the rutting resistance of the WMA and the HMA (p-value = 0.177, α = 0.05). However, an ANOVA of the automated rut depth measurements indicated the WMA and HMA had a difference in APA performance that was statistically significant (p-value = 0.0176, α = 0.05). Therefore, it can be concluded based on the average results and the statistical analysis that the WMA has slightly higher rutting susceptibility than the HMA. However, the results are not significantly different from a practical standpoint and indicate the WMA and HMA both have good rutting resistance. These findings are in agreement with those suggested by the Hamburg Wheel-Tracking results. The test results for the individual APA specimens are attached in APPENDIX C. Table 6: Summary of APA Results

Mix ID Average Manual Rut Depth (mm)

Average Automated Rut

Depth (mm)

Standard Deviation Manual Rut Depth (mm)

Standard Deviation Automated Rut

Depth (mm)

WMA 4.14 3.94 0.81 0.50

HMA 3.52 3.26 0.67 0.32

Taylor

16

Figure 12: Graphical APA Results

Taylor

17

CONCLUSIONS AND RECOMMENDATIONS

This study was designed to examine the effectiveness of the Densicryl warm mix asphalt (WMA) technology at producing an asphalt mixture that is resistant to rutting and moisture damage in the laboratory. This technology was used in conjunction with the Zycosoil liquid anti-stripping agent. The results of this study are as follows:

1. For this study, the control HMA was mixed at a target of 330oF and compacted at a target of 300oF in the laboratory. The Zycosoil and Densicryl modified WMA was mixed at a target of 250oF and compacted at a target of 235oF in the laboratory. A mix design verification was performed with both the WMA and HMA on a blend that is currently being used at the NCAT Test Track. The results of this verification showed that the WMA and HMA had almost identical mix design volumetric parameters and no reduction in compaction quality was seen with the WMA versus that of the HMA, which was compacted at a temperature which was 65oF higher.

2. Tensile-Strength Ratio testing showed an increase in the TSR value from 0.49 for the HMA to 0.82 for the WMA. The low TSR value for the HMA illustrates the degree of moisture susceptibility of the aggregate blend, since no anti-stripping agent was utilized. The WMA had a lower unconditioned splitting tensile strength than the HMA by approximately 30 psi. This is likely a consequence of reduced binder aging at the significantly lower compaction temperature for the WMA. However, the WMA’s conditioned tensile strength of 84 psi is significantly higher than that of the HMA (63.4 psi), as evidenced by the TSR values. This is very important to the structural performance of an in-service pavement which is exposed to water and moisture.

3. In the Hamburg Wheel-Tracking test, there was no statistical difference in the steady-state rutting performance of the WMA and HMA. The WMA did have a lower stripping inflection point than the HMA, indicating greater susceptibility to moisture damage. However, Hamburg tests on the WMA with different compaction temperatures showed the stripping inflection point in this test was directly related to the mixture compaction temperature.

4. The results of the APA rutting susceptibility test showed the WMA to be slightly more susceptible to rutting than the HMA but that the difference was not significant from a practical point of view.

Based on the results of this laboratory study, Densicryl along with Zycosoil appears to be a promising WMA technology. A field evaluation of a pavement test section is recommended in order to evaluate the field performance characteristics of a pavement produced with this technology.

Taylor

18

REFERENCES

1. Hurley, Graham C. Evaluation of New Technologies for Use in Warm Mix Asphalt. MS Thesis, Auburn, AL: Auburn University, 2006.

2. Hurley, Graham C, and Brian D Prowell. Evaluation of Aspha-Min Zeolite for use in Warm Mix Asphalt. NCAT Report 05-04, Auburn, AL: NCAT, 2005.

3. Hurley, Graham C, and Brian D Prowell. Evaluation of Evotherm for use in Wam Mix Asphalt. NCAT Report 06-02, Auburn, AL: NCAT, 2006.

4. Hurley, Graham C, and Brian D Prowell. Evaluation of Sasobit for use in Warm Mix Asphalt. NCAT Report 05-06, Auburn, AL: NCAT, 2005.

5. Hurley, Graham C, Brian D Prowell, and Andrea N Kvasnak. Missouri Field Trial of Warm Mix Asphalt Technologies: Construction Summary. NCAT Report 10-02, Auburn, AL: NCAT, 2010.

6. Kim, Jaeseung, and Jason R Moore. Laboratory Evaluation of Zycosoil as an Anti-Stripping Agent for Superpave Mixtures - Phase II. Unpublished, Auburn, AL: NCAT, 2009.

7. Kim, Jaeseung, and Jason R Moore. Laboratory Evaluation of ZycoSoil as an Anti-Stripping Agent on Superpave Mixtures. Unpublished, Auburn, AL: NCAT, 2009.

8. Kvasnak, Andrea N, Jason R Moore, Adam J Taylor, and Brian D Prowell. Preliminary Evaluation of Warm Mix Asphalt Field Demonstration: Franklin, Tennessee. NCAT Report 10-01, Auburn, AL: NCAT, 2010.

Taylor

19

APPENDIX A

Raw TSR Test Data

Table A1: All Raw TSR Test Data

Mix ID

Compaction Temp (F)

Freeze-Thaw Cycles

Sample ID

Va Saturation (%)

Failure Load (lb)

Splitting Tensile Strength (psi)

TSR

HMA 300 1 30 7.1 70.2 2350 68.23 0.488

HMA 300 1 27 7.0 73.0 2050 59.42

HMA 300 1 29 6.9 71.3 2150 62.41

HMA 300 0 26 7.1 N/A 3850 111.58

HMA 300 0 28 7.0 N/A 4320 125.37

HMA 300 0 8 7.0 N/A 5250 152.27

WMA 235 1 5 6.6 74.7 3020 87.45 0.824

WMA 235 1 14 7.2 70.6 2780 80.58

WMA 235 1 15 7.2 72.2 2900 84.04

WMA 235 0 6 7.2 N/A 3550 102.87

WMA 235 0 13 7.0 N/A 3450 100.04

WMA 235 0 31 7.0 N/A 3550 102.99

Taylor

20

APPENDIX B

Raw Hamburg Test Data Table B1: All Raw Hamburg Test Data

Mix Aging Temp

Sample ID

Air Voids of Cut Sample (%)

Average Voids

Slope of Steady-State Rutting Curve

Rutting Rate (mm/hr)

Total Rut Depth (mm) (Based on Rate)

Stripping Inflection Point (cycles)

HMA #4

275 4A 7.6 7.4 0.001075 2.709 10.749 4600

4B 7.2

HMA #11

275 11A 7.1 7.2 0.000720 1.814 7.200 3700

11B 7.3

HMA #12

275 12A 7.4 7.3 0.000325 0.819 3.250 4100

12B 7.2

WMA #1

235 1A 6.7 6.5 0.001040 2.621 10.399 1750

1B 6.2

WMA #9

235 9a 7.1 6.9 0.001010 2.545 10.099 1900

9B 6.7

WMA #10

235 10A 7.3 7.1 0.000680 1.714 6.800 2050

10B 6.9

WMA #32A &35A

275 32A 7.2 7.2 0.001010 2.545 10.099 3400

35A 7.1

WMA #33

275 33A 7.4 7.2 0.000930 2.344 9.299 3200

33B 6.9

WMA #34

275 34A 7.2 7.0 0.000810 2.041 8.099 3600

34B 6.8

Taylor

21

APPENDIX C

Raw APA Test Data Table C1: Raw APA Test Data

Mix ID Test Temperature (°C)

Sample Height (mm)

Pressure (psi)

Loading Force (lbs)

Sample ID

Sample Air Voids (%)

Manual Rut Depth (mm)

Automated Rut Depth (mm)

WMA 64 75 100 100 10 6.6 3.19 3.08

WMA 64 75 100 100 1 6.8 4.68 4.45

WMA 64 75 100 100 6 6.9 3.65 3.77

WMA 64 75 100 100 9 6.7 3.67 3.85

WMA 64 75 100 100 8 6.7 4.24 4.25

WMA 64 75 100 100 5 6.7 5.41 4.25

HMA 64 75 100 100 11 7.5 3.2 3.19

HMA 64 75 100 100 14 7.3 3.32 3.04

HMA 64 75 100 100 13 7.4 2.8 3.1

HMA 64 75 100 100 4 6.8 3.12 2.92

HMA 64 75 100 100 15 7.3 4.6 3.73

HMA 64 75 100 100 12 7.5 4.05 3.57