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Safety Edge

Safety EdgeSM Demonstration Project

Seaford, Delaware

Field Report
January 30, 2011

Downloadable Version
PDF [2.47 MB]

cover page

1. Report No. 2. Government Accession No 3. Recipient’s Catalog No
4. Title and Subtitle

Safety EdgeSM Project, Seaford, Delaware

5. Report Date
January 30. 2011
6. Performing Organization Code
7. Authors
Harold Von Quintus and Jagannath Mallela
8. Performing Organization Report No.
9. Performing Organization Name and Address
Applied Research Associates, Inc.
100 Trade Centre Drive, Suite 200
Champaign, IL 61820
10. Work Unit No.

11. Contract or Grant No.

12. Sponsoring Agency Name and Address
Office of Infrastructure
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
13. Type of Report and Period Covered Report
August 2010–January 2011
14. Sponsoring Agency Code
Supplementary Notes
Contracting Officer’s Technical Representative: Byron Lord and Mary Huie
Contracting Officer’s Technical Manager: Andy Mergenmeier
16. Abstract

In a coordinated effort with highway authorities and industry leaders, the Every Day Counts initiative serves as a catalyst to identify and promote cost effective innovations to bring about rapid change to increase safety of our nations highway system, decrease project delivery time, and protect our environment. The Safety EdgeSM concept is an example of one such initiative in which the edge of the road is beveled during construction for the purpose of helping drivers who migrate off the roadways to more easily return to the road without over correcting and running into the path of oncoming traffic or running off the other side of the roadway.

This field report documents the observations made on the construction of Safety EdgeSM on a two lane highway warm mix asphalt (WMA) overlay project near Seaford, Delaware. Safety EdgeSM paving devices from two manufacturers were demonstrated during this project. Details regarding the performance of each device along with the shape and physical properties of the finished Safety EdgeSM are presented for the purpose of understanding what processes and techniques were most successful in forming the Safety EdgeSM.

The findings from this overlay project and other similar ongoing projects form the basis for understanding the construction process and material performance necessary to bring this innovation into common highway practice and make our Nation’s highways safer.

17. Key Words
Safety EdgeSM, Slope, WMA, Advant-Edger, TransTech Shoulder Wedge Maker
18. Distribution Statement
No restriction. This document is available to the public through the Highways for LIFE website: http://www.fhwa.dot.gov/hfl/
Security Classif.(of this report)
Unclassified
19. Security Classif. (of this page)
Unclassified
20. No. of Pages
30
21. Price

SI* (Modern Metric) Conversion Factors


Foreword

The purpose of this field report is to provide a summary of observations made during the warm mix asphalt (WMA) Safety EdgeSM project located along Old Furnace Road just northeast of Seaford, Delaware. These observations and data are to be used with similar information from other Safety EdgeSM projects to facilitate the development of standards and guidance for Safety EdgeSM construction and long term performance.

All field and laboratory test results, WMA mixture design data, observations made during paving, and comments provided by construction personnel are included in the Field Evaluation Form that is provided as a separate document to this field report.  This field report is a summary of the observations and field data measured during construction on August 25 to 27, 2010. In addition, it includes the results from field tests performed on a section that was paved on August 19 and 20, 2010.

Table of Contents

Topic Page

Foreword
Summary of Observations
Overall Opinion of the Safety EdgeSM
Slope of the Safety EdgeSM
Placement
Compaction
Shoulder Construction
WMA Mixture and Safety EdgeSM
FIELD EVALUATION OF WMA OVERLAY WITH SAFETY EDGESM
Introduction
Pavement Structure and Project Conditions
Field Evaluation
Slope Measurements
Cores
Longitudinal Profile Measurements
Observations Made During Paving with Safety EdgeSM
Surface Preparation
Placement/Paving Operations
Compaction Operations. 21
HMA Mixture Characteristics and the Safety EdgeSM. 24
Other Observations. 27
Findings and Conclusions. 28
Appendix
Data Tables from Field Measurements. A-2
Photographs of Selected Cores Recovered from the Project.. A-6

Summary of Observations

This section of the report provides a summary and listing of important observations made during the paving operations, interview with paving personnel, and findings from the field measurements taken during paving that are expected to have a significant impact on the performance of this project.

Overall Opinion of the Safety EdgeSM

  • The Safety EdgeSM did not have a detrimental impact on the contractor’s paving operation during mainline paving.  A couple of issues, however, were encountered that need to be resolved and are noted in the following bullet items.

Slope of the Safety EdgeSM

  • The average slope of the Safety EdgeSM was found to vary from 37 to 50° for the different sections.  It was the opinion of construction personnel that the slope of the Safety EdgeSM device would need to be flattened to about 20 to 25° to meet the planned 30° requirement.

Placement

  • The Safety EdgeSM was formed using two devices at different times during paving; the TransTech Shoulder Wedge Maker device and the Advant-Edger device.  The TransTech device was used to place warm mix asphalt (WMA) during the week of August 19.  The Advant-Edger device was used during observations made for this field report.  Both were properly bolted to the screed.  The project superintendent commented that there was no difference between the two devices, but the screed operator commented that the Advant-Edger seemed to work better, resulting in a smoother edge condition.

  • Both contractor and agency personnel voiced a concern that paving across intersections or in areas with higher longitudinal profile; the Safety EdgeSM devices raise the screed relative to the profile set by the longitudinal ski.  Both also commented that it was difficult to get a good tie-in to existing driveways and other hard surfaces.

Compaction

  • The WMA density or percent compaction of the Safety EdgeSM sections was found to be higher than for the non-Safety EdgeSM sections.  Thus, the Safety EdgeSM is believed to have a confining effect on rolling an unconfined edge.  This observation is considered a benefit to the use of the Safety EdgeSM.

  • The air voids of the interior WMA mat were considered good to fair with a mean value from 7.3 to 8.9 percent for the different sections.  The air voids determined along the edge of the mat were high; varying from 8.6 to 13.5 percent.  High air voids have a detrimental impact on pavement performance.

Shoulder Construction

  • Existing fine to coarse-grained soil was planned to be used for the shoulder backing material.  Placement of the backing material was not observed because the contractor planned to place it after all paving had been completed.

WMA Mixture and Safety EdgeSM

  • Longitudinal segregation or different surface texture was observed along the edge of each slat conveyor of the paver.

  • The planned WMA overlay thickness was 2.0 inches.  The average overlay thickness for the Safety EdgeSM sections was found to vary from 2.0 to 2.7 inches.

This Safety EdgeSM project should be monitored over time to determine its long-term performance and the frequency of any required maintenance operations, as well as the life cycle cost of the Safety EdgeSM and its effectiveness over time.

FIELD EVALUATION OF WMA OVERLAY WITH SAFETY EdgeSM

Introduction

A series of field tests were carried out to assess the placement and condition of the warm mix asphalt (WMA) overlay placed along Old Furnace Road just northeast of Seaford, Delaware, with and without the use of the Safety EdgeSM devices.  The paving contractor for this project was American Infrastructure. The Contractor used the TransTech Shoulder Wedge Maker device during the first part of the project and the Advant-Edger device for the latter part.  The purpose of this field study was to evaluate the quality of the in-place WMA mixture and Safety EdgeSM by investigating three issues or features.

  1. Correct use of Safety EdgeSM device during paving.
  2. Safety EdgeSM versus non-Safety EdgeSM portions of project.
  3. Slope of the Safety EdgeSM.

The location of the project was in Sussex County, as shown in Figure 1.  The project started just east of the intersection between U.S. Highway 13 (Sussex Highway) and Old Furnace Road, and ended at the intersection between Old Furnace and Cokesbury Road; just west of Old Furnace. The Safety EdgeSM sections were located along the eastern portion of the project.

Pavement Structure and Project Conditions

The project consisted of repairing some localized areas with extensive cracking and distortions, widening the roadway by 2 ft, and placing a 2-inch lift of a 9.5-mm WMA mix over the existing HMA pavement.  Figure 2 shows the typical cracking and surface condition of the existing pavement along this project.  Figure 3 provides a general view of the Figure 2 in WMA overlay and typical cross section of the pavement.  In preparation for the WMA overlay, the following activities and repairs were made.

  • The existing shoulder was graded along some areas of the project to remove grass and other debris (refer to Figure 4).
  • About 1 ft of HMA was placed to widen the roadway on each side (refer to Figure 5).
  • Localized repairs or patches were placed in selected areas of the roadway where extensive cracking and distortions have occurred.
  • An emulsion tack coat was placed on the existing surface and patches (refer to Figure 5).

The ditches along the edge of the pavement were generally shallow (1 to 3 ft) with shallow slopes (10 to 30°).  No lane-shoulder drop-offs were observed; however, the shoulder had been graded and the roadway widened on each side of the roadway prior to visiting the project.  Figure 3 through Figure 6 include general views of the roadway during construction.  The Safety EdgeSM backing material was planned to be an on-site fine to coarse-grained soil.  The backing material was scheduled to be graded back to the Safety EdgeSM near the end of this rehabilitation project, after paving.


Figure 1. Site location.

 
Figure 2. Typical condition of the existing surface (with tack coat applied).




Figure 3. WMA overlay placed in the westbound lane.

 
Figure 4. Edge of pavement graded in some areas to remove grass and debris.

 DE_Safety Edge_July2010 015
Figure 5. 1.0-ft widening strip placed on both sides of the roadway.


Figure 6. General view of the roadway and right-of-way.

Field Evaluation

Four sections were identified and marked during the paving operation; three Safety EdgeSM sections and one section without the Safety EdgeSM device.  Station numbers were unavailable for referencing the sections, so all sections were located related to telephone poles along the project. The following summarizes the four sections included within this project.

  1. Area #1, Advant-Edger Safety EdgeSM section, westbound lane; telephone pole #44155, localized station numbers increase to the west from the designated telephone pole.
  2. Area #2, Advant-Edger Safety EdgeSM section, westbound lane; telephone pole #44128, localized station numbers increase to the west from the designated telephone pole.
  3. Area #3, TransTech Shoulder Wedge Maker Safety EdgeSM section, westbound lane; telephone pole #44010, localized station numbers increase to the west from the designated telephone pole.
  4. Area #4, non-Safety EdgeSM section, westbound lane; telephone pole #44128. This non- Safety EdgeSM section was to be located on August 21, 2010, but the plant was not operating because of electrical problems.  Thus, the section was located within Area #2 of the Advant-Edger.  The non-Safety EdgeSM was designated along the centerline joint—the opposite side of the paver without the Safety EdgeSM device.

Field tests were conducted within each test section for measuring slope and WMA density.  Slope measurements were taken using a straight-edge (4-ft aluminum level) and 6-inch ruler (refer to Figure 7), while density readings were taken adjacent to and 3 ft from the mat’s edge using a Troxler 3430 nuclear density gauge (refer to Figure 8).


Figure 7. Safety EdgeSM angle measurement.


Figure 8. Troxler 3430 nuclear density gauge used to measure WMA density.

Eight cores were taken in the test sections established during the paving operation.  The eight cores were obtained at four different locations within the Safety EdgeSM sections.  The cores were taken for calibration of the nuclear density gauge readings, and to observe the mix near the center of the mat and adjacent to the mat’s edge.  Cores were planned for two other locations in the non-Safety EdgeSM section.  However, paving on the last day of the field visit was cancelled because of electrical problems at the plant.  The two cores used for acceptance (away from the edge) from the area designated as Area #2 were requested to increase the number of data points for determining the correction or adjustment factors between the nuclear density gauge and laboratory measured densities.  Bulk specific gravities of these additional cores were not obtained.

Slope Measurements

Slope measurements were taken using a straight-edge to measure the width and thickness of the taper of the Safety EdgeSM; prior to any rolling and after final rolling.  The average slope of the Safety EdgeSM sections is summarized in Table 1.

Table 1. Summary of the Safety EdgeSM slope measurements.
Section/Area Designation Slope of Safety EdgeSM
Mean, degrees Coefficient of
Variation, %
Prior to Rolling; mean of two areas 34.1 5.2
After Final Rolling
1 Advant-Edger 45.4 10.8
2 Advant-Edger 50.0 11.4
3 TransTech Shoulder Wedge Maker 36.6 24.3

The slope of the Safety EdgeSM prior to rolling the unconfined edge was 34.1°.  The average slope for the Safety EdgeSM created with the TransTech device after final rolling was about the same as prior to rolling, while the slope for Advant-Edger section was much steeper after final rolling. The Safety EdgeSM created with the TransTech device was placed on August 19 or 20, and the Safety EdgeSM created with the Advant-Edger device was placed on August 25 and 26.  The WMA mixture was observed to shove and “push out” under the steel wheel vibratory roller for the paving on August 26.  The reason for the difference in Safety EdgeSM slopes between the two devices is unknown, but it was reported that the mixture did change and corrections to production had to be made between the two paving dates.  In fact, the production plant was shut down on August 26 to make adjustments to the WMA mixture.

The other important observation relates to the variability of the Safety EdgeSM slope measurements, as listed above.  The coefficient of variation of the Safety EdgeSM slope created by the Advant-Edger device prior to any rolling was about half the value determined after final rolling.  The coefficient of variation of the Safety EdgeSM slope for the TransTech device after final rolling was significantly greater than for the other sections.  The reason for the higher variability but lower slope was unknown.

All slope measurements are listed in Tables A-1 through A-3 of Appendix A.  Figure 9 includes a comparison between the slope of the Safety EdgeSM after final rolling and thickness of the Safety EdgeSM for the three sections.  As shown, no correspondence between thickness and the slope of the Safety EdgeSM exists.

Figure 9. Comparison of the Safety EdgeSM slope and thickness of the WMA adjacent to the edge of the HMA overlay.

Other slope measurements were made at random along the Safety EdgeSM in other areas of the project and the results were the same as for the specific Safety EdgeSM sections established for future performance reviews.  Thus, the slope of the Safety EdgeSM was found to be steeper than what was planned.

Cores

A total of eight cores were drilled along the project.  Two cores were taken at each station or location; in the same areas where the densities were measured with the Troxler nuclear density gauge.  These cores were taken to measure the bulk specific gravity of the WMA for developing a correction factor for the nuclear density gauge readings taken adjacent to the edge and within the center of the mat.  Figure 10 shows the location of the cores and nuclear density gauge readings relative to the edge of the WMA mat.  Photographs of all eight cores recovered from the roadway are included in the appendix.  A summary of these test results; core thickness and bulk specific gravities (saturated surface dry) converted to bulk densities is included in Table A-4 in Appendix A.  Figure 11 is a comparison of the core densities taken along the edge and 3 ft from the edge (center of the steel drum breakdown roller) for the Safety EdgeSM sections.  As expected, densities 3 ft from the edge are higher than along the edge of the mat (unconfined edge).



Figure 10. Photos showing location of cores and nuclear density tests made with the Troxler 3430 gauge (nuclear density readings were taken and then the WMA mix was cored).


Figure 11. Comparison of core densities adjacent to the edge of pavement and 3 ft from the edge.

Nuclear Density Results

Density measurements were made with a Troxler 3430 gauge.  Two readings were taken at each point; one with the gauge parallel and the other perpendicular to the centerline.  Two points were marked at each station or location; one point adjacent to the Safety EdgeSM and the other 3-ft from the edge.

Nuclear density gauge readings were taken before drilling each core.  Figure 12 is a comparison of the nuclear gauge readings and densities measured on the cores.  As shown, there is a positive bias for the readings taken adjacent to the edge of the mat.  Adjustment factors were determined for the nuclear gauge readings taken at the edge of the mat and 3 ft from the edge. The adjustment factors are included in Table A-4 and the nuclear density gauge readings at each point are listed in Table A-5 and Table A-6 in Appendix A.  The following summarizes the adjustment factors determined for this project.

Location Adjustment Factor
Near Center of Steel Drum 0.957
Adjacent to Safety EdgeSM 1.000

These factors were used to adjust the nuclear density gauge readings to be consistent with the densities that would be measured in the laboratory.  The adjusted densities using the correction factors are included in Table A-5 and A-6 in Appendix A.

Figure 13 shows a comparison of the adjusted nuclear density gauge readings taken adjacent to the Safety EdgeSM and 3 ft from the edge.  Figure 13 also includes a comparison of the WMA air voids between both of these areas.  As shown, the air voids are higher adjacent to the Safety EdgeSM, in comparison to 3 ft from the Safety EdgeSM.


Figure 12. Comparison of the nuclear gauge readings and densities measured on cores recovered from the WMA mat.


Figure 9 included a comparison between the WMA thickness (near the Safety EdgeSM) and slope of the Safety EdgeSM.  The thickness of the WMA has little to no effect on the slope of the Safety EdgeSM.  Figure 14 shows a comparison of the density and WMA overlay thickness.  As shown, there is also little correspondence between the overlay thickness and air voids or densities.


Figure 14. Comparison of WMA thickness at the edge of the mat and WMA air voids.

Longitudinal

Longitudinal profile measurements were not planned nor measured for this project.

Observations Made During Paving with Safety EdgeSM

This section discusses the observations made during the paving and rolling operations that could have a significant impact on the performance of the Safety EdgeSM over time.  As stated in the Introduction to the Field Report section, the objective of this field study was to evaluate the quality of the in-place WMA material and Safety EdgeSM by investigating three features.

  1. Correct use of Safety EdgeSM device during paving.
  2. Safety EdgeSM versus non-Safety EdgeSM portions of project.
  3. Slope of the Safety EdgeSM.

Surface Preparation

The following lists the different activities performed by the contractor prior to placing the WMA overlay.

  • The edge of the pavement was graded to remove grass and other debris along the edge of the roadway prior to placing the overlay (refer to Figure 4).
  • The roadway was widened by 1 ft on each side (refer to Figure 5).
  • Localized WMA patches were placed in selected areas along the project where extensive cracking and surface distortions have occurred.
  • An emulsion tack coat was applied prior to the WMA overlay.  The application of the tack coat was uniform and covered the entire surface (refer to Figure 5 and Figure 6).

Placement/Paving

Figure 15 shows the equipment used to place the WMA overlay.  The paving contractor operated the paver in the automatic longitudinal grade control mode and used non-contact sonic sensors for controlling the grade.  The production plant was down for about 1.5 hours to make some WMA mixture revisions on August 26 to bring the mixture into specification.  Free water was observed flowing from the back of a few truck beds.  Excess water could explain some of the mixture tenderness characteristics observed during compaction (explained in the next section on Compaction Operations).

Figure 16 shows the Advant-Edger device attached to the screed.  The project superintendent commented that there was no difference between the two devices, but the screed operator commented that the Advant-Edger seemed to work better than the TransTech device, resulting in a smoother edge condition.  Figure 17 shows the slope and surface texture of the Safety EdgeSM; prior to and after rolling.

Both contractor and agency personnel stated the Safety EdgeSM device would raise the screed relative to the profile set by the longitudinal ski when paving across intersections or in areas with higher longitudinal profile with hard surfaces.  In addition, both commented that it was difficult to get a good tie-in to existing driveways and other hard surfaces.  Figure 18 shows the line caused by the tip of the Safety EdgeSM device along the edge of pavement over an intersection driveway.

DE_Safety Edge_July2010 008

  DE_Safety Edge_July2010 009
Figure 15. Equipment used to place the WMA overlay.

 DE_Safety Edge_July2010 017
Figure 16. Advant-Edger device attached to the screed.

 
Figure 17. Typical surface texture and slope of the Safety EdgeSM sections.

DE_Safety Edge_July2010 064
Figure 18. Point of Safety EdgeSM scratching the surface of an intersecting driveway.

Compaction

Figure 19 shows the two rollers that were used to compact the 9.5 mm WMA mixture.  The primary or breakdown roller was a Volvo DD118 double drum steel wheel vibratory roller, while the finish roller was a Volvo DD112 double drum steel wheel vibratory roller.  The field evaluation forms identify the number of passes and coverage used by all rollers (a pass is defined as one movement of the roller in one direction, while coverage is defined as each point on the mat receiving a pass of the roller).

In summary, each roller performed seven passes with two coverages.  The following summarizes the rolling pattern (number of passes and location for each roller) used by the contractor.

  • Breakdown or primary roller pattern; the roller’s vibratory setting was on high frequency and on setting 5 (on a scale of 1 to 10) for the amplitude:
    • First pass was along the Safety EdgeSM in the vibratory mode with the roller’s edge extended over the Safety EdgeSM by 4 to 6 inches.
    • Second pass; same location as for the first pass, but in the reverse direction and in vibratory mode.
    • Third pass was along the centerline construction joint in the vibratory mode with the roller’s edge extended over the longitudinal joint by 4 to 6 inches.
    • Fourth pass; same location as for the third pass, but in the reverse direction and in vibratory mode.
    • Fifth pass was down the center of the mat in vibratory mode.
    • Sixth pass; same location as for the fifth pass, but in the reverse direction and in vibratory mode.
    • Seventh pass was along the Safety EdgeSM in the vibratory mode with the roller’s edge extended over the Safety EdgeSM by 4 to 6 inches.

  • Finish roller pattern; the roller’s vibratory setting was on high frequency and low amplitude:
    • First pass was along the Safety EdgeSM in the vibratory mode with the roller’s edge extended over the Safety EdgeSM by 4 to 6 inches.
    • Second pass; same location as for the first pass, but in the reverse direction and in vibratory mode.
    • Third pass was along the centerline construction joint in the vibratory mode with the roller’s edge extended over the longitudinal joint by 4 to 6 inches.
    • Fourth pass; same location as for the third pass, but in the reverse direction and in vibratory mode.
    • Fifth pass was down the center of the mat in vibratory mode.
    • Sixth pass; same location as for the fifth pass, but in the reverse direction and in vibratory mode.
    • Seventh pass along the Safety EdgeSM side of the mat in static mode.  Additional passes that were needed based on periodic density measurements made with the nuclear density gauge were in the static position.

A control strip was not used to confirm that the roller pattern being used was achieving an adequate density of the mix.  The Contractor used a Pavement Quality Indicator (PQI) non-nuclear density gauge to ensure that density was being met during paving.  The non-nuclear and nuclear density gauge readings and the densities of the cores suggest that adequate density was obtained for this mixture 3 ft from the edge, but the density was low near the edge.

Volvo double drum vibratory steel wheel roller used in breakdown or primary position for compacting the WMA overlay.
Volvo double drum vibratory steel wheel roller used in the vibratory and static mode that was used in the finish position for compacting the WMA overlay.
Figure 19. Rollers used for compacting the 9.5 mm WMA overlay mixture.

Figure 20 shows a comparison of the adjusted nuclear density gauge readings and air voids adjacent to the Safety EdgeSM in comparison to 3 ft from the edge.  Table 2 summarizes the average air voids and slopes of the Safety EdgeSM for the different sections along this project, and is followed by the following important points from these density and slope measurements:

Figure 20. Comparison of volumetric properties between the areas adjacent to the edge and 3 ft from the edge (center of the steel drum roller) for the different sections.

Table 2. Summary of the average slope and air voids.
Section Identification Average Slope Air Voids at Edge Air Voids near Mat Center
Mean COV Mean COV
Non-Safety EdgeSM Section --- 13.5 28.9 8.92 24.2
Area #1; Advant Section 45.4 8.6 30.7 7.3 19.3
Area #2; Advant Section 50.0 9.4 33.4 7.6 28.3
Area #3; TransTech Section 36.6 11.2 13.1 8.4 12.3
  • The air voids measured along the mat’s edge of the Safety EdgeSM sections are significantly lower than measured along the non-Safety EdgeSM section.  The Safety EdgeSM provided additional confinement along the edge.
  • The air voids measured along the mat’s edge of the Advant-Edger Safety EdgeSM sections are slightly higher than measured within the center of the Volvo double drum steel wheel roller.  It was expected that the extra pass of the roller along the Safety EdgeSM provides additional densification of the mix.
  • The other important observation was the difference between the Advant-Edger and TransTech sections. The TransTech section had higher air voids but lower slopes in comparison to the Advant-Edger sections.  The reason for this difference was unknown, because the roller pattern used to compact the TransTech section was not recorded during placement.  Two additional roller passes (one for each of the rollers) along the Safety EdgeSM was used to compact the Advant-Edger sections.  It was expected that this additional pass increased the density (lower air voids) but steepened the slope.

HMA MixtureSM

The WMA mixture design data was obtained from the Delaware DOT.  The WMA mixture design parameters are documented in the Field Evaluation Form, which is a separate document to this field report.  This WMA includes 21 percent Recycled Asphalt Pavement (RAP) and 6 percent shingles.

The WMA mixture volumetric properties and gradation were considered reasonable.  Figure 21 shows the surface texture of the finished HMA mat along different areas of the project; with and without surface defects or surface texture differences.  The surface texture and condition were relatively uniform within specific areas of the project.  Some agency personnel voiced a concern about the use of some Superpave mixtures; they can be very tender and move under steel wheel rollers.

The WMA mixture did shove and "push out" during the compaction operation, steepening the slope of the Safety EdgeSM.  The WMA mixture exhibited tenderness under the steel wheel rollers. As an example, roller marks were present after the breakdown roller completed its rolling pattern, checking was observed during the rolling operation, and shear cracks were observed along the roller’s edge (Figure 22 shows these examples).  Chatter from the Volvo breakdown roller was observed in those areas exhibiting the more severe checking and shear cracks (refer to Figure 22).

The temperature of the WMA delivered to the project site was reported to be approximately 260 °F and 160 to 170 °F during finish rolling.  In some cases, the WMA temperature was below 150 °F during the last pass of the finish roller.  The WMA temperature could be related to the roller marks being left in the mat, checking and chatter observed in specific areas, and the steeper slopes than planned.

Longitudinal segregation or surface texture difference was observed along the edges of the slat conveyor (refer to Figure 23).  Bulk mixture samples (for gradation testing), nuclear gauge density tests, and cores were not taken within these locations.

Example showing an area with a tight surface, fine texture of the mat; small surface voids.

Example showing an area with a coarse surface texture of the mat; large surface voids.

Example showing an area with localized crushed aggregate at the surface of the mat.
Figure 21.  Surface texture of the overlay after final rolling.

Checking and shear crack along the edge of the roller.  Chatter left on the surface from the vibratory roller.

Figure 22. Surface defects observed after rolling.


Figure 23. Longitudinal segregation or surface texture differences along the edge of both slat conveyors.

Thus, it was not confirmed whether these areas shown in Figure 23 were caused by segregation or surface texture difference near the surface.  It was expected that these areas were a result of longitudinal segregation along the edges of the slat conveyor of the paver.  Densities were taken with the nuclear density gauge for the non-Safety EdgeSM section near the area in question and some of these densities were found to be low (and high air voids).

The distance between the end of the auger and screed end plate was approximately 24 inches (refer to Figure 15 and Figure 16). This distance should be less than 18 inches.  The distance between the end of the auger and screed end plate was not believed to be a contributing factor to the steeper slope.

Other Observations

The following lists the observations and comments made by construction personnel and on-site personnel.

  • A shallower angle of the Safety EdgeSM device will be needed to meet the planned 30° angle.

  • There were different opinions on the use of the two Safety EdgeSM devices (Advant-Edger and TransTech). One opinion was that there was no difference between two devices, while another opinion was that the Advant-Edger device resulted in a smoother edge.

  • The densities measured along the Safety EdgeSM created by the TransTech device were consistently lower than those measured along the edge created by the Advant-Edger device.  However, the densities measured within the center of the mat (away from the Safety EdgeSM) are also higher for the Advant-Edger section (about 147 pounds per cubic foot (pcf)) in comparison to the TransTech section (145 pcf). This observation indicates that this difference is more related to the rolling pattern and/or WMA mixture between the different days of paving rather than related to the Safety EdgeSM devices.

  • Some construction personnel voiced an opinion that the planned 30° slope of the Safety EdgeSM will not be met using Superpave designed mixtures that are tender.

  • After the evaluation, the Delaware DOT management stated that overlays greater than 1.25 inch will have the Safety EdgeSM.

  • Paving across driveways and other features with hard surfaces causes the screed to rise resulting in a reduction of smoothness in localized areas.

Findings and Conclusions

As previously stated, the objective of this field study was to evaluate the quality of the in-place WMA material and Safety EdgeSM by investigating three features.

  1. Correct use of Safety EdgeSM device during paving.
  2. Safety EdgeSM versus non-Safety EdgeSM portions of project.
  3. Slope of the Safety EdgeSM.

This section of the field report summarizes the findings and conclusions made during the paving/compaction operations related to the long term performance of the WMA mixture and Safety EdgeSM.

  • The average slope of the Safety EdgeSM from the TransTech Shoulder Wedge Maker device was 36°, while it was 45 and 50° for the Advant-Edger device; both exceeding the planned value of 30°.  It was expected that the slope of the Safety EdgeSM device may need to be reduced to a value of about 25° to end up with a 30° slope after rolling.

  • The average air voids along the edge of the mat were lower for the Safety EdgeSM than for the non-Safety EdgeSM section. The reason for this decrease in air voids and increase in density was believed to be related to the added confinement from the Safety EdgeSM material. This observation is considered a benefit from the use of the Safety EdgeSM.

  • Breakdown and finish rolling did steepen the slope of the Safety EdgeSM, especially during the paving operations on August 25 and 26. It was expected that the magnitude of this increase will be mixture dependent. There was much less of an increase in slope during the previous week’s paving. The reason for the increase in the slope of the Safety EdgeSM during paving on August 25 and 26 was probably related to the tenderness of the WMA, as discussed above.  Mix behavior under the steel wheel rollers was not observed during the week of August 19.

  • WMA thickness variations measured along the sections had no impact on the slope of the Safety EdgeSM or the density adjacent to the Safety EdgeSM.

The pavement should be inspected after the final shoulders have been constructed.  Local soil is planned to be used as the backing material for the Safety EdgeSM.  Care should be taken to observe the material placement and ensure that meets proper relative elevation to the WMA mat.  Long term monitoring of the shoulder should be performed to see how well the fine- to coarse-grained shoulder material remains in place and observe any deformation or erosion.

APPENDIX A

Data tables and core photographs

Data Tables from Field Measurements

This section of the field report provides a summary and listing of all field measurements recorded during the paving operations.  These data are also included in the detailed evaluation forms for the Safety EdgeSM projects.

Table A-1. Safety EdgeSM slope measurements for sections placed with the Advant-Edger device after final rolling.

Table A-2. Safety EdgeSM slope measurements for sections placed with the TransTech shoulder wedge maker device after final rolling.

Table A-3. Safety EdgeSM slope measurements for sections placed with the Advant-Edger device; prior to rolling.

Table A-4. Nuclear density adjustment ratios; core density/nuclear density.

Table A-5. Density readings made with a nuclear density gauge (Troxler Gauge 3430) for the sections placed

Table A-6. Density readings made with a nuclear density gauge (Troxler Gauge 3430) for the section placed with the TransTech Shoulder Wedge Maker device and the section without the Safety EdgeSM.

Photographs of Selected Cores Recovered from the Project

This section of the field report provides a photograph of the cores that were recovered for laboratory density testing, and visual observations of the mixture along the edge and 3 feet from the edge.  No systematic visual differences were noted between the different core sets.

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Page last modified on May 18, 2012.
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