Evaluation of maintenance strategies: Final Report 628

              e
e
Evaluation of
Maintenance Strategies
NOVEMBER 2013
Arizona Department of Transportation Research Center
SPR 628
EVALUATION OF
MAINTENANCE STRATEGIES
Final Report 628
November 2013
Prepared by:
Stephen B. Seeds, P.E.
David G. Peshkin, P.E.
Applied Pavement Technology, Inc.
115 W. Main Street, Suite 400
Urbana, IL 61801
Prepared for:
Arizona Department of Transportation
206 South 17th Avenue
Phoenix, AZ 85007
i n cooperation with
U.S. Department of Transportation
Federal Highway Administration
This report was funded in part through grants from the Federal Highway Administration, U.S.
Department of Transportation. The contents of this report reflect the views of the authors,
who are responsible for the facts and the accuracy of the data, and for the use or adaptation
of previously published material, presented herein. The contents do not necessarily reflect the
official views or policies of the Arizona Department of Transportation or the Federal Highway
Administration, U.S. Department of Transportation. This report does not constitute a standard,
specification, or regulation. Trade or manufacturers’ names that may appear herein are cited
only because they are considered essential to the objectives of the report. The U.S.
government and the State of Arizona do not endorse products or manufacturers.
Technical Report Documentation Page
1. Report No.
FHWA‐AZ‐13‐628
2. Government Accession No.
3. Recipient's Catalog No.
4. Title and Subtitle
Evaluation of Maintenance Strategies
5. Report Date
November 2013
6. Performing Organization Code
7. Author
Stephen B. Seeds and David G. Peshkin
8. Performing Organization Report No.
9. Performing Organization Name and Address
Applied Pavement Technology, Inc.
115 W. Main Street,
Suite 400
Urbana, IL 61801
10. Work Unit No.
11. Contract or Grant No.
SPR‐PL1 (171) 628
12. Sponsoring Agency Name and Address
Arizona Department of Transportation
206 S. 17th Avenue
Phoenix, AZ 85007
13.Type of Report & Period Covered
Final Report
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared in cooperation with the U.S. Department of Transportation, Federal Highway Administration
16. Abstract
In the mid‐1990s, the Arizona Department of Transportation (ADOT) initiated the Maintenance Cost
Effectiveness study (SPR 371) with the development of plans and an experiment design to evaluate the
effectiveness of a variety of asphalt pavement maintenance treatments. During 1999 and 2001, ADOT oversaw
the construction of hundreds of experimental sections throughout the state under the Phase I, Wearing Course
Experiment (nine treatments and 82 sections at three sites), and the Phase II, Preventive Maintenance
Experiment (24 treatments and 137 sections at four sites). Work continued in 2006 and 2007 under the
Evaluation of Maintenance Strategies study (SPR 628) for ADOT with a yearlong program of pavement
performance monitoring involving manual pavement distress surveys and automated skid, friction, and surface
texture measurements at all the experimental sites. The project culminated with a detailed analysis of key
pavement performance data to compare the performance of the individual treatments and determine their
overall effectiveness. This report documents the independent findings of both the Phase I and II experiments.
17. Key Words
bituminous pavements, pavement maintenance,
cost‐effectiveness, wearing course, surface
treating, sealer/rejuvenator, test sections, sealing
compounds, pavement maintenance, highway
maintenance
18. Distribution Statement
Document is available to the U.S.
public through the National
Technical Information Service,
Springfield, VA, 22161
23. Registrant's Seal
19. Security Classification
Unclassified
20. Security Classification
Unclassified
21. No. of Pages
177
22. Price
SI* (MODERN METRIC) CONVERSION FACTORS
APPROXIMATE CONVERSIONS TO SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
in inches 25.4 millimeters mm
ft feet 0.305 meters m
yd yards 0.914 meters m
mi miles 1.61 kilometers km
AREA
in2 square inches 645.2 square millimeters mm2
ft2 square feet 0.093 square meters m2
yd2 square yard 0.836 square meters m2
ac acres 0.405 hectares ha
mi2 square miles 2.59 square kilometers km2
VOLUME
fl oz fluid ounces 29.57 milliliters mL
gal gallons 3.785 liters L
ft3 cubic feet 0.028 cubic meters m3
yd3 cubic yards 0.765 cubic meters m3
NOTE: volumes greater than 1000 L shall be shown in m3
MASS
oz ounces 28.35 grams g
lb pounds 0.454 kilograms kg
T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")
TEMPERATURE (exact degrees)
oF Fahrenheit 5 (F-32)/9 Celsius oC
or (F-32)/1.8
ILLUMINATION
fc foot-candles 10.76 lux lx
fl foot-Lamberts 3.426 candela/m2 cd/m2
FORCE and PRESSURE or STRESS
lbf poundforce 4.45 newtons N
lbf/in2 poundforce per square inch 6.89 kilopascals kPa
APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
mm millimeters 0.039 inches in
m meters 3.28 feet ft
m meters 1.09 yards yd
km kilometers 0.621 miles mi
AREA
mm2 square millimeters 0.0016 square inches in2
m2 square meters 10.764 square feet ft2
m2 square meters 1.195 square yards yd2
ha hectares 2.47 acres ac
km2 square kilometers 0.386 square miles mi2
VOLUME
mL milliliters 0.034 fluid ounces fl oz
L liters 0.264 gallons gal
m3 cubic meters 35.314 cubic feet ft3
m3 cubic meters 1.307 cubic yards yd3
MASS
g grams 0.035 ounces oz
kg kilograms 2.202 pounds lb
Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T
TEMPERATURE (exact degrees)
oC Celsius 1.8C+32 Fahrenheit oF
ILLUMINATION
lx lux 0.0929 foot-candles fc
cd/m2 candela/m2 0.2919 foot-Lamberts fl
FORCE and PRESSURE or STRESS
N newtons 0.225 poundforce lbf
kPa kilopascals 0.145 poundforce per square inch lbf/in2
*SI is the symbol for th International System of Units. Appropriate rounding should be made to e comply with Section 4 of ASTM E380.
(Revised March 2003)
v
Contents
Executive Summary ......................................................................................................................................... 1
Chapter 1. Introduction ................................................................................................................................ 7
Background ............................................................................................................................................... 7
Project Objectives ..................................................................................................................................... 7
Project Approach ...................................................................................................................................... 8
Report Overview ....................................................................................................................................... 8
Chapter 2. Review of Experiment Design ..................................................................................................... 9
Phase I: Wearing Course Experiment ........................................................................................................ 9
Phase II: Preventive Maintenance Experiment ....................................................................................... 12
Chapter 3. Project Data Collection ............................................................................................................. 17
Performance Data ................................................................................................................................... 17
ADOT Staff Surveys ................................................................................................................................. 24
Treatment Costs ..................................................................................................................................... 34
Chapter 4. Treatment Performance and Effectiveness .............................................................................. 37
Determination of Deduct Values for Various Distress Types .................................................................. 37
Review of Wearing Course Treatments at Phase I Test Sites .................................................................. 38
Review of Preventive Maintenance Treatments at Phase II Test Sites ................................................... 60
Chapter 5. Summary Findings and Recommendations .............................................................................. 87
References .................................................................................................................................................. 97
Appendix A: Test Section Descriptions ....................................................................................................... 99
Appendix B: Available Binder and Aggregate Details .............................................................................. 111
Appendix C: Performance/Condition Data for Wearing Courses and Preventive
Maintenance Experiments ................................................................................................. 129
Appendix D: Deduct Value Calculation ..................................................................................................... 139
Appendix E: Performance Comparison Tables: Wearing Course Experiment ........................................ 145
Appendix F: Performance Comparison Tables: Preventive Maintenance Experiment .......................... 161
vi
List of Figures
Figure 1. Pavement Condition Survey Recording Form ....................................................................... 19
Figure 2. ADOT Profilometer ................................................................................................................ 21
Figure 3. ADOT Skid Testing Van .......................................................................................................... 21
Figure 4. HydroTimer Outflow Meter................................................................................................... 22
Figure 5. CT Meter ............................................................................................................................... 22
Figure 6. DF Tester ............................................................................................................................... 23
Figure 7. DV Curves for Longitudinal and Transverse Cracking .......................................................... 140
vii
List of Tables
Table 1. Cost‐Effectiveness Rankings for the Phase I Wearing Course Treatments ......................... 3
Table 2. Cost‐Effectiveness Rankings for the Phase II Preventive Maintenance Treatments .......... 5
Table 3. Description of Phase I Treatments ...................................................................................... 9
Table 4. Overall Layout of Phase I, Wearing Course Experiment .................................................... 11
Table 5. Overall Layout of Phase II, Preventive Maintenance Experiment ..................................... 14
Table 6. Types of Pavement Performance Data Collected .............................................................. 17
Table 7. Trigger and Failure Levels for ADOT Distresses ................................................................. 18
Table 8. Survey Results on Flush Coats (Fog Seals) ......................................................................... 30
Table 9. Survey Results on Aggregate Seals .................................................................................... 31
Table 10. Survey Results on Slurry Seals and Microseals (Microsurfacings)..................................... 32
Table 11. Summary of Available Unit Cost on Experimental Treatments ......................................... 35
Table 12. PCI Ranges for Each Pavement Condition ......................................................................... 37
Table 13. DV Ranges for Each Pavement Condition .......................................................................... 38
Table 14. Equation Coefficients for Relationships between Pavement Performance
Measures and Pretreatment Milling Depth ...................................................................... 40
Table 15. Skid Performance of the I‐10 Wearing Course Sections ................................................... 46
Table 16. Skid Performance of the I‐8 Wearing Course Sections ..................................................... 46
Table 17. Skid Performance of the SR 74 Wearing Course Sections ................................................. 47
Table 18. Weathering Performance of the I‐10 Wearing Course Sections ....................................... 49
Table 19. Weathering Performance of the I‐8 Wearing Course Sections ......................................... 50
Table 20. Weathering Performance of the SR 74 Wearing Course Sections .................................... 50
Table 21. Fatigue Cracking Performance of the I‐10 Wearing Course Sections ............................... 51
Table 22. Fatigue Cracking Performance of the I‐8 Wearing Course Sections ................................. 51
Table 23. Fatigue Cracking Performance of the SR 74 Wearing Course Sections ............................. 52
Table 24. LTD Cracking Performance of the I‐10 Wearing Course Sections ..................................... 53
Table 25. LTD Cracking Performance of the I‐8 Wearing Course Sections ....................................... 53
Table 26. LTD Cracking Performance of the SR 74 Wearing Course Sections ................................... 54
Table 27. Overall Performance Comparison of Phase I Wearing Course Treatments
Based on 60th Percentile SNs and DVs ............................................................................... 55
Table 28. Comparison of Cost‐Effectiveness of Phase I Wearing Course Treatments ...................... 59
Table 29. Weathering Performance of the SR 66 Preventive Maintenance Sections....................... 64
Table 30. Weathering Performance of the SR 83 Preventive Maintenance Sections....................... 65
Table 31. Weathering Performance of the SR 87 Preventive Maintenance Sections....................... 66
Table 32. Weathering Performance of the U.S. 191 Preventive Maintenance Sections .................. 67
Table 33. Flushing Performance of the SR 66 Preventive Maintenance Sections ............................ 70
Table 34. Flushing Performance of the SR 83 Preventive Maintenance Sections ............................ 71
Table 35. Flushing Performance of the SR 87 Preventive Maintenance Sections ............................ 72
Table 36. Flushing Performance of the U.S. 191 Preventive Maintenance Sections ........................ 73
viii
Table 37. LTD Cracking Performance of the SR 66 Preventive Maintenance Sections ..................... 75
Table 38. LTD Cracking Performance of the SR 83 Preventive Maintenance Sections ..................... 76
Table 39. LTD Cracking Performance of the SR 87 Preventive Maintenance Sections ..................... 77
Table 40. LTD Cracking Performance of the U.S. 191 Preventive Maintenance Sections ................ 78
Table 41. Overall Performance Comparison of Phase I Wearing Course Treatments Based
on 60th Percentile DVs and FIs ........................................................................................... 80
Table 42. Comparison of Cost‐Effectiveness of Phase II Preventive Maintenance Treatments ....... 84
Table 43. Ranking of Phase II Preventive Maintenance Treatments Based on
Cost‐Effectiveness and Performance ................................................................................ 85
Table 44. Effect of Milling Depth on Treatment Performance ......................................................... 88
Table 45. Performance Summary and Overall Ranking of Wearing Course
Treatments at the I‐10 and I‐8 Experimental Sites ........................................................... 90
Table 46. Cost‐Effectiveness Summary and Overall Ranking of Wearing Course
Treatments at the I‐10 and I‐8 Experimental Sites ........................................................... 91
Table 47. Performance Summary and Overall Ranking of Wearing Course
Treatments at the SR 74 Experimental Site ...................................................................... 92
Table 48. Cost‐Effectiveness Summary and Overall Ranking of Wearing Course
Treatments at the SR 74 Experimental Site ...................................................................... 92
Table 49. Performance Summary and Overall Ranking of the Preventive Maintenance
Treatments at the SR 66, SR 83, SR 87, and U.S. 191 Experimental Sites ......................... 93
Table 50. Cost‐Effectiveness Summary and Overall Ranking of the Preventive Maintenance
Treatments at the SR 66, SR 83, SR 87, and U.S. 191 Experimental Sites ......................... 95
Table 51. Test Section Descriptions for I‐10 Wearing Course Treatments ....................................... 101
Table 52. Test Section Descriptions for I‐8 Wearing Course Treatments ......................................... 102
Table 53. Test Section Descriptions for SR 74 Wearing Course Treatments .................................... 103
Table 54. Test Section Descriptions for SR 66 Preventive Maintenance Treatments ....................... 104
Table 55. Test Section Descriptions for SR 87 Preventive Maintenance Treatments ....................... 105
Table 56. Test Section Descriptions for SR 83 Preventive Maintenance Treatments ....................... 106
Table 57. Test Section Descriptions for U.S. 191 Preventive Maintenance Treatments .................. 107
Table 58. Binder and Aggregate Details Available for AR‐ACFC I‐10 Wearing Course Sections ....... 113
Table 59. Binder and Aggregate Details Available for SMA I‐10 Wearing Course Sections .............. 113
Table 60. Binder and Aggregate Details Available for PEM I‐10 Wearing Course Sections .............. 114
Table 61. Binder and Aggregate Details Available for ACFC I‐10 Wearing Course Sections ............. 114
Table 62. Binder and Aggregate Details Available for P‐ACFC I‐10 Wearing Course Sections .......... 115
Table 63. Binder and Aggregate Details Available for AR‐ACFC SR 74 Wearing Course Sections ..... 116
Table 64. Binder and Aggregate Details Available for P‐ACFC SR 74 Wearing Course Sections ....... 116
Table 65. Binder and Aggregate Details Available for TB‐ACFC SR 74 Wearing Course Sections ..... 117
Table 66. Binder and Aggregate Details Available for CRS‐2P/Crown SR 66
Preventive Maintenance Sections ..................................................................................... 117
Table 67. Binder and Aggregate Details Available for Novachip/Koch Materials SR 66 Preventive
Maintenance Sections ....................................................................................................... 117
ix
Table 68. Binder and Aggregate Details Available for PASS CR/Western Emulsion
SR 66 Preventive Maintenance Sections ........................................................................... 118
Table 69. Binder and Aggregate Details Available for HF CRS‐2P/Copperstate
SR 66 Preventive Maintenance Sections ........................................................................... 118
Table 70. Binder and Aggregate Details Available for Microsurfacing/Southwest Slurry
SR 66 Preventive Maintenance Sections ........................................................................... 119
Table 71. Binder and Aggregate Details Available for AR‐ACFC/ADOT SR 66
Preventive Maintenance Sections ..................................................................................... 119
Table 72. Binder and Aggregate Details Available for AC15‐5TR/Paramount
SR 66 Preventive Maintenance Sections ........................................................................... 120
Table 73. Binder and Aggregate Details Available for CRS‐2P/Crown SR 83
Preventive Maintenance Sections ..................................................................................... 120
Table 74. Binder and Aggregate Details Available for AR‐ACFC/ADOT
SR 83 Preventive Maintenance Sections ........................................................................... 121
Table 75. Binder and Aggregate Details Available for CM‐90/Koch Materials SR 83
Preventive Maintenance Sections ..................................................................................... 121
Table 76. Binder and Aggregate Details Available for HF CRS‐2P/Copperstate
SR 83 Preventive Maintenance Sections ........................................................................... 122
Table 77. Binder and Aggregate Details Available for AC15‐5TR/Paramount
SR 83 Preventive Maintenance Sections ........................................................................... 122
Table 78. Binder and Aggregate Details Available for Slurry Seal/Southwest Slurry
SR 83 Preventive Maintenance Sections ........................................................................... 123
Table 79. Binder and Aggregate Details Available for AC15‐5TR/Paramount
SR 87 Preventive Maintenance Sections ........................................................................... 123
Table 80. Binder and Aggregate Details Available for CM‐90/Navajo Western
SR 87 Preventive Maintenance Sections ........................................................................... 124
Table 81. Binder and Aggregate Details Available for PASS Oil/Western
Emulsion SR 87 Preventive Maintenance Sections ........................................................... 124
Table 82. Binder and Aggregate Details Available for Novachip/Koch Materials SR 87
Preventive Maintenance Sections ..................................................................................... 124
Table 83. Binder and Aggregate Details Available for CRS‐2P/Crown SR 87
Preventive Maintenance Sections ..................................................................................... 125
Table 84. Binder and Aggregate Details Available for CRS‐2LM/Copperstate
SR 87 Preventive Maintenance Sections ........................................................................... 125
Table 85. Binder and Aggregate Details Available for CM‐90/Koch Materials U.S. 191
Preventive Maintenance Sections ..................................................................................... 125
Table 86. Binder and Aggregate Details Available for AC15‐5TR/Paramount
U.S. 191 Preventive Maintenance Sections ....................................................................... 126
Table 87. Binder and Aggregate Details Available for CRS‐2P/Crown U.S. 191
Preventive Maintenance Sections ..................................................................................... 126
x
Table 88. Binder and Aggregate Details Available for AR‐ACFC/ADOT U.S. 191
Preventive Maintenance Sections ..................................................................................... 127
Table 89. Binder and Aggregate Details Available for P‐ACFC/Paramount
U.S. 191 Preventive Maintenance Sections ....................................................................... 127
Table 90. Binder and Aggregate Details Available for HF CRS‐2P/Copperstate
U.S. 191 Preventive Maintenance Sections ....................................................................... 128
Table 91. Binder and Aggregate Details Available for Slurry Seal/Southwest Slurry
U.S. 191 Preventive Maintenance Sections ....................................................................... 128
Table 92. Performance/Condition Data for I‐10 Wearing Course Sections ...................................... 131
Table 93. Performance/Condition Data for I‐8 Wearing Course Sections ........................................ 132
Table 94. Performance/Condition Data for SR 74 Wearing Course Sections ................................... 133
Table 95. Performance/Condition Data for SR 66 Wearing Course Sections ................................... 134
Table 96. Performance/Condition Data for SR 87 Wearing Course Sections ................................... 135
Table 97. Performance/Condition Data for SR 83 Wearing Course Sections ................................... 136
Table 98. Performance/Condition Data for U.S. 191 Wearing Course Sections ............................... 137
Table 99. DV Coefficients for Low Severity Distresses ...................................................................... 141
Table 100. DV Coefficients for Medium Severity Distresses ............................................................... 142
Table 101. DV Coefficients for High Severity Distresses ..................................................................... 143
Table 102. ADOT Wearing Course Performance Comparison: Skid Number ...................................... 147
Table 103. ADOT Wearing Course Performance Comparison: Weathering ....................................... 149
Table 104. ADOT Wearing Course Performance Comparison: Bleeding ............................................ 151
Table 105. ADOT Wearing Course Performance Comparison: Fatigue Cracking ................................ 153
Table 106. ADOT Wearing Course Performance Comparison: Longitudinal,
Transverse, and Diagonal Cracking ................................................................................... 155
Table 107. ADOT Wearing Course Performance Comparison: Rutting ............................................... 157
Table 108. ADOT Wearing Course Performance Comparison: Patching ............................................. 159
Table 109. ADOT Preventive Maintenance Treatment Performance Comparison:
Weathering ........................................................................................................................ 163
Table 110. ADOT Preventive Maintenance Treatment Performance Comparison: Flushing ............. 165
Table 111. ADOT Preventive Maintenance Treatment Performance Comparison:
LTD Cracking ...................................................................................................................... 167
xi
List of Acronyms
AADT average annual daily traffic
ACFC asphalt concrete friction course
ADOT Arizona Department of Transportation
ADT average daily traffic
ANOVA analysis of variance
AR‐ACFC asphalt rubber‐asphalt concrete friction course
ASTM American Standards Test Methods
B/C benefit/cost
CalTrans California Department of Transportation
CRA crumb rubber asphalt
CRS cationic rapid setting
CS chip seal
CT circular texture
DCOF dynamic coefficient of friction
DF dynamic friction
DOT Department of Transportation
DV deduct value
EB eastbound
ESAL equivalent single‐axle load
FHWA Federal Highway Administration
FI flushing index
HMA hot‐mix asphalt
LTD longitudinal, transverse, and diagonal
LTPP Long Term Pavement Preservation (program)
MCES mean cost‐effectiveness score
MP Milepost
MPD mean profile depth
MTD mean texture depth
NCHRP National Cooperative Highway Research Program
P‐ACFC polymer modified‐asphalt concrete friction course
PASS polymerized asphalt surface sealer
PCI Pavement Conditions Index
PEM permeable European mixture
PG performance grade
PPTG Pavement Preservation Task Group (CalTrans)
SB styrene butadiene
SBS styrene butadiene styrene
SMA stone matrix asphalt
SN skid number
xii
SPR State Planning and Research
SR State Route
TB‐ACFC terminal blend asphalt concrete friction course
TSA top size aggregate
USAEC United States Army Corps of Engineers
WB westbound
1
EXECUTIVE SUMMARY
The Arizona Department of Transportation (ADOT) initiated the Maintenance Cost‐Effectiveness
study (SPR 371) in the mid‐1990s, developing plans and an experiment design to evaluate the
effectiveness of various asphalt pavement maintenance treatments. During 1999 and 2001, ADOT
oversaw the construction of hundreds of experimental sections throughout the state under the
Phase I, Wearing Course Experiment, and the Phase II, Preventive Maintenance Experiment. Work
continued in 2006 and 2007 under Evaluation of Maintenance Strategies (SPR 628) for ADOT with a
yearlong program of pavement performance monitoring involving manual pavement distress
surveys and automated skid, friction, and surface texture measurements at all experimental sites.
The project culminated with a detailed analysis of many key pavement performance data to
compare the performance of the individual treatments and determine their overall effectiveness.
This report documents the independent findings for both the Phase I and II experiments.
PHASE I: WEARING COURSE EXPERIMENT
The wearing course experiment was conducted on three Arizona highways with moderate to heavy
traffic: Interstate 10 (I‐10), Interstate 8 (I‐8), and State Route 74 (SR 74). Nine treatments and 82
experimental sections were built at these sites. Sixty‐four sections were constructed on I‐10 and I‐8
in 1999 and another 18 were constructed on SR 74 in 2001. Six treatments were placed on I‐10 and
I‐8. Four were friction courses with different binders and top size aggregates (TSAs): asphalt
concrete friction course (ACFC) (PG 64‐16, 3/4‐inch TSA); asphalt rubber‐asphalt concrete friction
course (AR‐ACFC) (PG 64‐16, CRA‐1, 1/2‐inch and 3/4‐inch TSA); and polymer modified‐asphalt
concrete friction course (P‐ACFC) (PG 76‐22, 3/4‐inch TSA). The remaining two were a stone matrix
asphalt (SMA) mix (PG 70‐28, 3/4‐inch TSA) and a permeable European mix (PEM) (PG 76‐22, 1‐1/4‐
inch TSA). Three wearing course treatments were placed on SR 74. All three were friction courses
with different binders and a single 3/8‐inch TSA: AR‐ACFC (PG 64‐16, CRA‐1), P‐ACFC (PG 76‐22+),
and terminal blend asphalt concrete friction course (TB‐ACFC) (PG 76‐22 TR+). At all three sites,
researchers performed milling and overlaying at preplanned depths and thicknesses (before
applying the wearing course) to evaluate their impact on treatment performance.
When evaluating the wearing course treatments, researchers considered seven pavement
performance measures: skid resistance; weathering; bleeding; fatigue cracking; longitudinal,
transverse, and diagonal (LTD) cracking; rutting; and patching. The evaluation focused on the first
five performance measures since a review of the data showed almost no rutting and no patching.
The wearing course experiment design made it possible to investigate the impact of milling depth
and overlay thickness on the performance of the five key distress types. Overall, the results varied
considerably and did not support a finding that milling depth (and its corresponding overlay
thickness) had a consistent and meaningful effect on any performance measures. (The analysis did
2
indicate that milling and overlay affected LTD cracking the most.) The variability associated with the
milling and overlay effects is part of the overall performance variability of each treatment.
Several pavement performance measures originated from visual survey data where the distresses
were rated in terms of severity and extent. The two components to the rating made it difficult to
compare the performance between treatments. Consequently, researchers used the method that
makes up part of the standard Pavement Condition Index (PCI) rating procedure to combine the two
rating components for a given distress into a single deduct value (DV).
Researchers used two primary approaches to evaluate performance data and assess treatment
performance and cost‐effectiveness. One approach used statistical tools such as analysis of variance
(ANOVA) and Student’s t testing. Because of treatment variability, however, there were difficulties
using this approach to make statistically valid performance comparisons between the treatments at
each experimental site. Nevertheless, the approach did identify those treatments that performed as
well as the best‐performing treatment.
The second approach ranked the treatments within the different performance categories based
upon their 60th percentile distress level. This approach provided a good, practical alternative for
comparing treatment performance and, by extension, cost‐effectiveness. The performance ranges
were based upon the definitions used in the standard PCI rating procedure, and the treatments
were grouped within the ranges based upon their 60th percentile performance measures (e.g.,
60th percentile DV for weathering and 60th percentile skid number). After researchers ranked each
treatment’s five performance measures, the results were averaged to determine an average
condition and overall treatment ranking. The best‐performing treatment at the I‐10 and I‐8 sites was
the AR‐ACFC (PG 64‐16, CRA‐1, 1/2‐inch TSA), while the AR‐ACFC (PG 64‐16, CRA‐1, 3/4‐inch TSA),
PEM (PG 76‐22, 1¼‐inch TSA) and ACFC (PG 64‐16, 3/4‐inch TSA) were close seconds, and the P‐ACFC
(PG 76‐22, 3/4‐inch TSA) and SMA (PG 70‐28, 3/4‐inch TSA) a not‐too‐distant third. At the SR 74 site,
the AR‐ACFC (PG 64‐28+, CRA‐1, 3/8‐inch TSA) performed the best, while the P‐ACFC (PG 76‐22+,
3/8‐inch TSA) was a close second and the TB‐ACFC (PG 76‐22 TR+, 3/8‐inch TSA) a distant third.
After the performance assessment, researchers evaluated the cost‐effectiveness of the wearing
course sections using a benefit/cost (B/C) approach. They calculated the benefit for each
performance measure as the difference between the measured performance at the 2007 testing
date and a nominal minimum performance level. The cost component of the B/C approach was the
unit cost of the treatment (in $/sy). Researchers then assigned a cost‐effectiveness level to the B/C
value for each performance measure and treatment type, ranging from very low to very high. Then
they calculated a mean cost‐effectiveness score (MCES) for each treatment based upon the average
of each treatment’s cost‐effectiveness values. (Since there are five cost‐effectiveness levels, the
MCES values can range from 0 to 5.) The MCES values then were used to rank each treatment’s
overall cost‐effectiveness. Table 1 summarizes the results for the I‐10, I‐8, and SR 74 sites. At the I‐
10 and I‐8 sites, the ACFC (PG 64‐16, 3/4‐inch TSA) was the most cost‐effective and ranked in the
3
Table 1. Cost‐Effectiveness Rankings for the Phase I Wearing Course Treatments.
Site
Cost‐
Effectiveness
Ranking
Wearing Course
Treatment
MCES
Performance
Ranking
I‐10
and
I‐8
A
ACFC
(PG 64‐16, 3/4‐inch TSA)
4.3 2
B
AR‐ACFC (PG 64‐16,
CRA‐1, 1/2‐inch TSA)
4.0 1
C
P‐ACFC
(PG 76‐22, 3/4‐inch TSA)
3.8 3
D
AR‐ACFC (PG 64‐16,
CRA‐1, 3/4‐inch TSA)
3.6 2
D
SMA
(PG 70‐28, 3/4‐inch TSA)
3.6 3
E
PEM
(PG 76‐22, 1¼‐inch TSA)
3.5 2
SR 74
C
AR‐ACFC (PG 64‐16,
CRA‐1, 3/8‐inch TSA)
3.8 1
D
P‐ACFC (PG 76‐22+,
3/8‐inch TSA)
3.6 2
F
TB‐ACFC (PG 76‐22 TR+,
3/8‐inch TSA)
3.0 3
second performance level, while the AR‐ACFC (PG 64‐16, CRA‐1, 1/2‐inch TSA) was the second‐most
cost‐effective and the only treatment ranked at the highest performance level. At the SR 74 site, the
AR‐ACFC (PG 64‐16, CRA‐1, 3/8‐inch TSA) was the most effective and performed the best.
PHASE II: PREVENTIVE MAINTENANCE EXPERIMENT
Researchers conducted the Preventive Maintenance experiment on four Arizona state highway
segments: SR 66, SR 83, SR 87, and U.S. 191. In this experiment, researchers used 24 treatments and
137 sections. SR 66 and SR 83 had 28 sections each, while SR 87 and U.S. 191 had 21 and 60
sections, respectively. The treatment applied to most of the sections was some form of chip seal;
however, there were also some friction courses, a slurry seal, a microsurfacing, and a thin‐bonded
wearing course. The treatments were all constructed in 2000 and 2001.
For the Preventive Maintenance assessment, researchers only included weathering, flushing, and
LTD cracking in the evaluation. Skid resistance was not included because skid testing was performed
4
at only one of the four sites. Researchers made various attempts to consider other measures of
surface friction and texture, but none was successful. (The localized field test data did indicate,
however, that all preventive maintenance treatments maintained a very high level of surface texture
and/or friction through 2007.) Since pretreatment rutting and fatigue cracking data were not
available, these measures were not included in the evaluation. Instead of bleeding, flushing data
were used to evaluate each treatment’s propensity to bleed or flush under high temperatures and
traffic loading. The same DV approach used for the wearing course treatments was used to compile
the weathering and LTD cracking data for the preventive maintenance treatments.
The same rigorous statistical approach (involving ANOVAs and Student’s t tests) used to compare
wearing course treatment performance was applied to compare preventive maintenance treatment
performance. In addition, researchers used the simple yet practical approach (involving the
calculation of a 60th percentile DV and the ranking of each treatment at each site into one of eight
different conditions) to compare treatments’ overall performance. Following is a ranking of the
treatments in the four identified performance levels. The number of sections representing each
treatment ranges from two to 10 (so it is not exactly an “apples‐to‐apples” comparison).
 Level 1: Chip seal (PASS CR)/Western Emulsion, AR‐ACFC/not identified, Novachip/Koch
Materials, ACFC/ADOT, and microsurfacing/Southwest Slurry.
 Level 2: Chip seal (CRS‐2P)/ADOT (future construction), AR‐ACFC/ADOT, P‐ACFC/Paramount,
chip seal (CRS‐2)/ADOT, AR‐chip/International Slurry Surfacing, chip seal (CRS‐2P)/ADOT,
chip seal (HF CRS‐2P)/Copperstate, chip seal (HF CRS‐2P)/ADOT, and chip seal (CM‐90)/Koch
Materials.
 Level 3: Double chip seal/ADOT, DACS&B/ADOT, chip seal (PASS oil)/Western Emulsion, chip
seal (CRS‐2)/Copperstate, and double application/not identified.
 Level 4: Chip seal (AC15‐5TR)/Paramount, slurry seal/Southwest Slurry, chip seal (CRS‐
2P)/Crown, and chip seal (CM‐90)/Navajo Western. These treatments were ranked in this
category because they had two or more sections that did not perform well. (Researchers
recommend that they be investigated further.)
Researchers evaluated for cost‐effectiveness of the preventive maintenance sections using the same
B/C approach that was used for the wearing course treatments. They calculated the benefit for
each of the three performance measures (weathering, flushing index, and transverse cracking) as
the difference between the measured performance at the 2007 testing date and a nominal
minimum performance level. The cost component of the B/C approach was the unit cost of the
treatment (in $/sy).
Table 2 summarizes the results of the cost‐effectiveness analyses for the preventive maintenance
sections. Two treatments had the highest cost‐effectiveness ranking and the highest performance
ranking: chip seal (PASS) by Western Emulsion and microsurfacing by Southwest Slurry. Six of the
remaining eight treatments—all chip seals—were also in the highest cost‐effectiveness ranking;
however, they were in the second performance ranking level. The last two treatments with the
5
Table 2. Cost‐Effectiveness Rankings for Phase II Preventive Maintenance Treatments.
Cost‐
Effectiveness
Ranking
Preventive Maintenance Treatment MCES
Performance
Ranking
A
Chip seal (PASS CR)/Western Emulsion 5.00 1
Microsurfacing/Southwest Slurry 5.00 1
Chip seal (CRS‐2)/ADOT 5.00 2
Chip seal (CRS‐2P)/
ADOT (future construction)
5.00 2
Chip seal (CM‐90)/Koch Materials 4.83 2
Chip seal (CRS‐2P)/ADOT 4.78 2
Chip seal (HF CRS‐2P)/ADOT 4.67 2
Chip seal (HF CRS‐2P)/Copperstate 4.67 2
Chip seal (CRS‐2)/Copperstate 4.83 3
Chip seal (AC15‐5TR)/Paramount 4.67 4
B
ACFC/ADOT 4.33 1
Chip seal (PASS Oil)/Western Emulsion 4.50 3
Slurry seal/Southwest Slurry 4.50 4
Chip seal (CRS‐2P)/Crown 4.42 4
Chip seal (CM‐90)/Navajo Western 4.33 4
C
DACS&B/ADOT 4.17 3
Double chip seal/ADOT 4.11 3
D
AR‐ACFC/not identified 3.67 1
AR‐ACFC/ADOT 3.78 2
P‐ACFC/Paramount 3.67 2
AR‐chip/International Slurry 3.67 2
Double application/not identified 3.67 3
F Novachip/Koch Materials 2.42 1
highest cost‐effectiveness ranking level were on the low end of the performance rankings. It is
interesting to note that the chip seal (AC15‐5TR) made the highest cost‐effectiveness ranking since it
had some sections that did not perform well. However, the rankings of the remaining preventive
maintenance treatments clearly indicate that treatment cost has more of an impact on the
assessment of cost‐effectiveness than performance.
6
7
CHAPTER 1. INTRODUCTION
BACKGROUND
In 1995, the Arizona Department of Transportation (ADOT) initiated research project SPR 371,
Maintenance Cost‐Effectiveness study. Beginning in 1999, 193 test sections were constructed
throughout Arizona following guidelines developed under that research project. Those test sections
were divided into three experiments or phases: wearing courses (Phase I), surface treatments
(Phase II), and sealer‐rejuvenators (Phase III). Although the agency brought significant resources to
bear in the experimental layout, design, and construction of these test sections, ADOT did not
regularly or systematically monitor test section performance after construction.
A formal study of test section performance could provide invaluable information about pavement
maintenance in Arizona at the state, district, and local levels. For example, by analyzing performance
results from the various test sections, ADOT could better understand what pavement treatments
work best under different pavement conditions, environments, and traffic; how various materials
perform; and how the performance of proprietary and warranted treatments compares to more
conventional applications. Because the test sections were repeated in multiple environmental
conditions, a study of those sections would be expected to generate findings applicable in most
areas of the state.
In 2007, recognizing that many of the test sections were reaching the point where meaningful
performance trends could be identified, ADOT initiated SPR 628, Evaluation of Maintenance
Strategies. This report presents that project’s findings.
PROJECT OBJECTIVES
Specific objectives of SPR 628 included the following:
 Review ADOT’s current maintenance strategies.
 Document the materials used in each of the test treatments of SPR 371.
 Fully evaluate the test sections constructed under SPR 371.
 Evaluate the performance of the maintenance strategies used on the SPR 371 sections.
 Identify maintenance treatment effectiveness based on factors such as cost, type of distress,
location, constructability, and service life.
 Develop a specific provisional guideline of effective maintenance strategies for ADOT.
This report addresses all of the Phase I and II objectives from the original SPR 371 project. The last
objective was accomplished primarily by identifying the maintenance strategies that were the most
and least cost‐effective based on the study findings. Because the Foundation for Pavement
8
Preservation (King and King 2007) studied the Phase III test sections in greater detail, those sections
were not examined in this project.
PROJECT APPROACH
Below is a summary of the project approach:
1. Review available documentation about the test sections. This review included studying
information about the experiment design, section construction (including some field notes),
materials specifications, laboratory test results, and initial performance findings taken
immediately after construction.
2. Interview ADOT staff. Researchers contacted ADOT staff at headquarters and the districts
to identify current strategies and learn where they are used, how well they perform, and
their typical problems.
3. Collect performance information. Researchers collected pavement performance data under
a cooperative effort with ADOT. Applied Pavement Technology staff conducted the
pavement distress/condition surveys, including evaluating the pavement sections for
weathering; bleeding; flushing; fatigue cracking; longitudinal, transverse, and diagonal (LTD)
cracking; rutting; and patching. ADOT crews conducted field measurements to determine
skid number (SN), texture, dynamic friction, and outflow. The primary emphasis was to
collect information similar to how ADOT evaluates pavements as part of its pavement
management data collection effort; the secondary focus was to collect data to evaluate the
typical performance of selected treatments.
4. Analyze performance information. Using both statistical and practical engineering
approaches, researchers evaluated select performance data for both the Wearing Course
and Preventive Maintenance experiments. The results are presented in a series of tables
that group or rank the treatments within different pavement conditions (performance
levels) for several key performance criteria. The tables also reflect the Student’s t test
results that identify which treatments exhibited similar performance.
5. Calculate treatment cost‐effectiveness. To determine the cost‐effectiveness of the
treatments, researchers compared the estimated cost and performance of treatments using
different criteria and then ranked them into overall effectiveness levels.
REPORT OVERVIEW
The remainder of this report is organized into four chapters. Chapter 2 summarizes the design
details for both the Wearing Course and Preventive Maintenance experiments. Chapter 3 describes
the data collection activities, including pavement performance data and information obtained from
ADOT staff about current maintenance strategies. Chapter 4 describes the statistical and
engineering analyses conducted to assess treatment performance and estimated cost, and to
identify those that may be best suited for future ADOT practice. Chapter 5 provides this study’s key
findings and recommendations.
9
CHAPTER 2. REVIEW OF EXPERIMENT DESIGN
Evaluating ADOT’s maintenance strategies under this project focused on experimental sections
constructed at the test sites for the Phase I, Wearing Course Experiment, and Phase II, Preventive
Maintenance Experiment. This chapter presents the design, layout, and general description of the
two experiments. Much of the documentation in this chapter was extracted from the original SPR
371 report (Peshkin 2006) and then revised and updated as appropriate.
PHASE I: WEARING COURSE EXPERIMENT
ADOT’s traditional bituminous pavement wearing courses have been asphalt concrete friction
courses (ACFCs) or asphalt rubber‐asphalt concrete friction courses (AR‐ACFCs). However, following
construction, these traditional treatments often required applying flush coats to prevent future
raveling. The Phase I test sections received premium treatments for wearing courses on Interstates
and high‐volume non‐Interstate routes. One of the goals of the Phase I experiment was to evaluate
treatments that could extend the life of a new bituminous pavement surface, with a target service
life of 12 to 15 years that required little or no maintenance.
The primary objectives of Phase I were to generate performance data on the long‐term benefits of
different surfaces and determine how to improve ADOT practice. As part of the original experiment,
64 test sections were constructed on Interstate 8 (I‐8) and Interstate 10 (I‐10) during the summer
and fall of 1999, covering the first five wearing course treatments shown in Table 3. Eighteen
additional sections with three treatment types were then constructed on State Route 74 (SR 74).
Table 3. Description of Phase I Treatments.
Treatment Description
ACFC Asphalt concrete friction course was typically used as the main wearing course by
ADOT until it was replaced by AR‐ACFC.
AR‐ACFC Asphalt rubber‐asphalt concrete friction course is a typical wearing course used by
ADOT on Interstates and some non‐Interstate roadways. Performance should be
linked to ADOT’s historical data.
P‐ACFC Polymer modified‐asphalt concrete friction course is rarely used on ADOT
roadways.
PEM Permeable European mixture was developed by Georgia DOT for urban freeways
that are three or more lanes wide. PEM typically has 18 to 20 percent porosity.
SMA Stone matrix asphalt was developed by Maryland DOT as a wearing course.
TB‐ACFC Terminal blend asphalt concrete friction course employs an asphalt rubber binder
prepared through a thorough mixing and blending of asphalt and ground
tire rubber at the producer’s terminal.
10
All of the treatments were designed to have a 3/4‐inch top size aggregate (TSA) with the exception
of the permeable European mixture (PEM), which was designed to have a 1‐1/4‐inch TSA. Similarly,
except for the AR‐ACFC, all polymer‐modified treatments used the same PG 76‐22 binder and were
modified with either SB or SBS polymers. The PEM and stone matrix asphalt (SMA) used both
polymer modification and fibers to control asphalt draindown, while the polymer modified‐asphalt
concrete friction course (P‐ACFC) only used polymer modification. The binder for the terminal blend
asphalt concrete friction course (TB‐ACFC) is defined as a PG 76‐22TR+ to indicate the use of ground
tire rubber blended and mixed at the terminal (production facility).
While the wearing course treatments were placed on both the travel lane and the passing lane, only
the travel lane is considered part of the experiment. As such, the passing lane had to be constructed
first to refine the placement process for the travel lane construction.
Table 4 shows the overall layout of the sections in the Phase I, Wearing Course Experiment. Table 51
through Table 53 in Appendix A provide general information about the Phase I sections. Table 58
through Table 65 in Appendix B provide additional material details obtained from the available
construction records.
I‐10 and I‐8 Test Sections
The 32 test sections on I‐10 were located between milepost (MP) 186.48 and MP 195.0 in the
eastbound direction; the 32 test sections on I‐8 were located between MP 88 and MP 92.5 in both
the eastbound and westbound directions. The average elevation of both of these sites is
approximately 1400 ft. In 2001, ADOT reported the average annual daily traffic (AADT) at 35,200 to
38,700 vehicles on I‐10 and 8800 vehicles on I‐8 (Peshkin 2006).
To accelerate ADOT’s ability to draw conclusions about these surfaces’ performance, researchers
milled off different thicknesses of the existing pavement’s surface and constructed a hot‐mix asphalt
(HMA) overlay before applying the wearing course treatment. The milling depths and corresponding
overlay thicknesses were 2.5 inches/2.0 inches, 3.5 inches/3.0 inches, and 4.5 inches/4.0 inches for
the I‐10 sections, and 1.0 inch/2.0 inches, 2.0 inches/2.0 inches, and 3.0 inches/2.0 inches for the I‐8
sections. For the control sections, the milling depth/overlay thickness combinations were
2.5 inches/3.0 inches and 2.5 inches/2.0 inches for the I‐10 and I‐8 sites, respectively.
Researchers had expected to use the occurrence of similar distresses in the sections of different
structural capacity to differentiate between the pavements’ structural performance and their
performance due to environmental factors. Also, with sections of different structural capacity,
researchers could explore the effects of applying treatments at different times in the pavement’s
structural life. Each treatment was placed on two sections, including the control treatment (which
consisted of a 1/2‐inch TSA AR‐ACFC).
11
Table 4. Overall Layout of Phase I, Wearing Course Experiment.
(Each cell shows the number of wearing course sections
followed by the milling depth and overlay thickness in parentheses.)
Wearing Course
Treatment
Phase I Sites
I‐10 I‐8 SR 74
AR‐ACFC (PG 64‐16, CRA‐1,
1/2‐inch TSA)
Control Section
2 (2.5/3.0
and 3.5/3.0)
2 (2.5/2.0)
AR‐ACFC (PG 64‐16, CRA‐1,
3/4‐inch TSA)
2 (2.5/2.0) 2 (1.0/2.0)
2 (3.5/3.0) 2 (2.0/2.0)
2 (4.5/4.0) 2 (3.0/2.0)
ACFC (PG 64‐16,
3/4‐inch TSA)
2 (2.5/2.0) 2 (1.0/2.0)
2 (3.5/3.0) 2 (2.0/2.0)
2 (4.5/4.0) 2 (3.0/2.0)
P‐ACFC (PG 76‐22,
3/4‐inch TSA)
2 (2.5/2.0) 2 (1.0/2.0)
2 (3.5/3.0) 2 (2.0/2.0)
2 (4.5/4.0) 2 (3.0/2.0)
PEM (PG 76‐22,
1‐1/4‐inch TSA)
2 (2.5/2.0) 2 (1.0/2.0)
2 (3.5/3.0) 2 (2.0/2.0)
2 (4.5/4.0) 2 (3.0/2.0)
SMA (PG 70‐28,
3/4‐inch TSA)
2 (2.5/2.0) 2 (1.0/2.0)
2 (3.5/3.0) 2 (2.0/2.0)
2 (4.5/4.0) 2 (3.0/2.0)
Control Section 1 (2.0/2.0)
AR‐ACFC
(PG 64‐16, CRA‐1,
3/8‐inch TSA)
4 (0.0/0.0)
1 (2.0/2.0)
2 (3.5/3.5)
P‐ACFC (PG 76‐22+,
3/8‐inch TSA)
0 (0.0/0.0)
3 (2.0/2.0)
2 (3.5/3.5)
TB‐ACFC (PG 76‐22TR+,
3/8‐inch TSA)
2 (0.0/0.0)
2 (2.0/2.0)
2 (3.5/3.5)
12
SR 74 Test Sections
This site had 18 sections between MP 16.8 and MP 18.7 in both the eastbound and westbound
directions (between Interstate 17 and U.S. Route 60 in the Phoenix area), plus one control section.
These test sections were constructed on SR 74 in April 2001 by change order and include AR‐ACFC,
P‐ACFC, and TB‐ACFC. The average elevation of this site is 1500 ft, and the 2001 AADT was reported
as 4500 vehicles. Some test sections were placed directly on the existing pavement, while others
were placed over either a 2‐inch or a 3‐1/2‐inch mill and overlay, as shown in Table 4.
PHASE II: PREVENTIVE MAINTENANCE EXPERIMENT
The Phase II test sections were part of the Preventive Maintenance experiment, which for ADOT
typically involves surface treatment maintenance activities such as chip seals and slurry seals applied
to lower volume bituminous‐surfaced roadways. This experiment compares state‐of‐the‐practice
(and usually proprietary) treatments to ADOT’s traditional chip seals to determine effectiveness.
Test sections for the Phase II experiment were located on State Route 66 (SR 66), State Route 83
(SR 83), State Route 87 (SR 87), and U.S. Route 191 (U.S. 191).
All treatments were replicated and their locations were randomly assigned within a project location.
The core experiment consisted of developing 3/4‐mile‐long test sections, one lane wide, on lower
volume two‐lane highways. The intent was to use one roadway direction for one replicate and the
opposite roadway direction for the other, duplicating the same basic layout at all project sites.
This project’s core experiment design was developed as part of the SR 66 test section preparation.
At the SR 66 test site, the vendor/contractor selected the system to be tested and developed the
specifications. As such, it was expected that the test sections represented the industry’s best
treatments for the pavement conditions. These systems and specifications were then meant to be
used at the remaining project site locations. The original design consisted of 28 test sections: 16
designed and warranted by the contractor and 12 designed by ADOT. The proprietary products
included as part of the SR 66 core experiment were:
 Paramount AC15‐5TR, 5/8‐inch chip size cover material only.
 Crown Asphalt CRS‐2P (performance graded), 5/8‐inch chip size cover material only.
 Koch Materials CM‐90, 5/8‐inch chip size cover material only.
 Copperstate HFE CRS‐2P, 5/8‐inch chip size cover material only.
 Southwest Slurry Type III slurry seal.
 International Slurry Surfacing asphalt rubber chip.
 Koch Materials Novachip.
 Copperstate CRS‐2LM.
 Western Emulsion PASS CR, 5/8‐inch chip size cover material only.
13
The following treatments were part of the core experiment:
 5/8‐inch cover material.
 3/8‐inch cover material.
 Double application chip seal.
 Double chip seal.
 ACFC.
 AR‐ACFC.
 CRS‐2.
 CRS‐2P.
Investigators used the 5/8‐inch cover material as the reference material for binder comparison test
sections, such as with the CRS‐2 and CRS‐2P, because it was supposed to be the least sensitive to
construction quality.
Table 5 provides the overall layout of the Preventive Maintenance experiment test sections.
Because some of the treatments are the same but constructed by different contractors, the
contractor (or producer) of the treatment is listed in the table. Additional information about the
Phase II sections is provided in Appendix A (Table 54 through Table 57) and Appendix B (Table 66
through Table 91).
SR 66 Test Sections
The SR 66 test site was located between MP 110.25 and MP 123.17 in the westbound direction and
between MP 110.75 and MP 123.17 in the eastbound direction. In 2000 this two‐lane highway had
an AADT of approximately 2200 vehicles and approximately 41,000 equivalent single‐axle loads
(ESALs) per year. The average elevation at this site is 4500 ft, and the surface (before applying a
treatment) was an old chip seal. The 28 test sections were constructed from August 10 to 16, 2000.
Some highlights of the SR 66 test site follow:
 The contractor selected the surface treatment system and developed materials and
construction specifications for the test sections.
 Construction specifications required a two‐year warranty.
 Macrotexture was used as the performance criterion and measured using an outflow meter.
The warranty was based on meeting a minimum mean texture depth (MTD) following
construction and staying above that minimum for two years.
The test site was part of an overall 60‐mi long construction project in which pavement conditions
were similar. Prior to construction, participating material suppliers were required to visit the site
and agree that pavement conditions throughout the test section were similar, so that differing
pavement conditions for a specific test section were not later offered as an explanation for
differential performance.
14
Table 5. Overall Layout of Phase II, Preventive Maintenance Experiment.
Preventive
Maintenance
Treatment Producer
TSA (inches)
Phase II Sitesa
SR 66 SR 83 SR 87 U.S. 191
Control N/A N/A 3b 4c
ACFC ADOT No information 2
AR‐ACFC ADOT 3/8 2d 2 4
No information No information 3e
P‐ACFC Paramount 3/8 2d 4
AR‐chip International
Slurry Surfacing
No information 2 2 4
Chip seal
(AC15‐5TR)
Paramount 5/8 2 2 2 4
Chip seal
(CM‐90)
Navajo Western 5/8 2 2
Koch Materials 5/8 2 4
Chip seal (CRS‐2) ADOT 5/8, 3/8 2 4
Copperstate 5/8 2 2
Chip seal (CRS‐2P) ADOT 5/8 2 2 4
3/8 2
ADOT (future
construction)
No information 4
Crown 5/8 2 1 2 4
Chip seal
(HF CRS‐2P)
ADOT 3/8 4
Copperstate 5/8 2 4
Chip seal
(PASS CR/Oil)
Western Emulsion 5/8 2 2 2
DACS&B ADOT Blotter (B) on 1/2 2
B = 3/8
2
B = #4
Double chip seal ADOT 3/8 on 5/8 2 4 4
Double application ADOT No information 2
Microsurfacing Southwest Slurry Type III 2
Slurry seal Southwest Slurry Type III 2 4
Novachip Koch Materials 1/2 2 2 2 4
Total sections (including control) 28 28 21 60
aThe numbers in each cell represent the number of preventive maintenance sections.
b2‐inch mill and overlay.
cNo treatment (or overlay) applied.
dNo information available on TSA.
eFirst chip seal (CRS‐2P) section failed (due to rain) and was replaced by an AR‐ACFC section.
SR 83 Test Sections
SR 83, a two‐lane pavement, was constructed in 1960. The average elevation is 4895 ft. The 2001
AADT was 3200 vehicles. From June to August 2001, 28 test sections were constructed between
MP 33.20 and MP 43.50. This site was laid out similarly to SR 66, used a Paramount PG 76‐22TR+ P‐ACFC,
and incorporated AR‐ACFC and ACFC sections with surface treatments.
15
SR 87 Test Sections
While the SR 66 project was advertised for bidding, an opportunity arose to place additional test
sections on SR 87 north of Winslow, Arizona. Since the original intent was to duplicate the 16 vendor
test sections to be placed on SR 66, a change order was executed and six of the eight vendors
participated. Due to cost considerations and the available budget for the project, three options used
on SR 66 were not used on SR 87: AR‐chip, slurry seal, and AR‐ACFC.
Another significant difference between the SR 66 test sections and the SR 87 test sections was that
the SR 87 test sections were placed on a one‐year‐old, 2‐inch overlay while the SR 66 test sections
were placed over an old chip seal, which provided an additional opportunity to address treatment
timing. Consequently, four test sections were left blank (i.e., control sections where no surface
treatment was placed). Researchers planned to apply surface treatments to two of these test
sections in five to seven years, and the remaining two sections would serve as control sections for
the treated sections.
The 21 test sections on SR 87 were located north of Winslow between MP 393.463 and MP 385 in
both the northbound and southbound directions, and were constructed in June and July of 2000. In
2000 this two‐lane pavement had an AADT of approximately 500 vehicles and about 20,000 ESALs
per year.
The final treatments placed on SR 87 were:
 Crown CRS‐2P (5/8‐inch aggregate and performance‐graded binder).
 Copperstate CRS‐2LM (5/8‐inch aggregate and latex modified binder).
 Novachip.
 ADOT double chip seal (5/8‐inch and 3/8‐inch aggregate).
 ADOT double application (1/2‐inch aggregate and blotter sand).
 Western Emulsion PASS oil (5/8‐inch aggregate).
 Paramount AC15‐5TR (tire rubber modified binder).
 Navajo Western CM‐90 (5/8‐inch aggregate).
Two sections of each of these treatments were constructed and five sections were left untreated.
Three of the untreated sections are identified simply as “do nothing,” but the others were included
to have untreated pavement to return to in five to seven years, place a treatment, and evaluate the
effect of treatment timing on pavement performance.
In 2001 the SR 87 test site was also used as a sealer/rejuvenator test site (part of Phase III of ADOT’s
Maintenance Cost‐Effectiveness study). The Paramount AC15‐5TR, a control section, and a portion
of pavement outside the test section all received the sealer/rejuvenator treatments, creating a new
set of side‐by‐side comparisons. While the sealer/rejuvenator test sections are addressed
16
elsewhere, it is important to recognize that this test site was modified after construction to include
these additional sections. The sealer/rejuvenator test sections are also significant because of the
extensive testing and evaluation that have been planned at this location. Some key aspects of the
sealer/rejuvenator study are briefly discussed in Appendix G of the SPR 371 report (Peshkin 2006).
U.S. 191 Test Sections
The U.S. 191 test site is located south of Alpine, Arizona, at an approximate elevation of 7000 ft. One
portion of the site is located between MP 200.5 and MP 219.25, and a second portion of the site is
located between MP 181 and MP 185. The site was constructed in June and July 2001. Between
these two test sections, the pavement received a standard treatment of AC15‐5TR (rubberized chip
seal) with precoated chips, which was placed in May 2001. Available information for this pavement
from MP 225 and higher (just north of the test sections) indicates that it was originally built in 1962
with 16 inches of base material and a 2.5‐inch bituminous surface, and that the most recent
treatment was a 2‐inch asphalt rubber wearing course constructed in 1999. In August 2000 the
pavement north of the test sections was reported to exhibit 20 to 30 percent small block cracking,
and alligator cracking and transverse cracking at 20‐ft to 25‐ft intervals. The 2001 AADT reported
was 100 vehicles.
Key characteristics of this test site include the following:
 It was the only high elevation location (i.e., cold climate).
 The incorporation of nontreated sections allowed for the eventual study of the effect of
treatment timing on pavement performance (by applying treatments in the future).
 The overlap of treatments provided for a comparison between wearing course (Phase I) and
surface treatment performance.
The portion of the test site between MP 181 and MP 185, where sections were left untreated, was
overlaid in 1999. The treatments placed at U.S. 191 were:
 HF CRS‐2P.
 Type III slurry seal.
 Novachip.
 ADOT double chip seal (5/8‐inch and 3/8‐inch aggregate).
 CRS‐2 (3/8‐inch aggregate).
 AR‐ACFC.
 ACFC.
 CM‐90 (5/8‐inch aggregate).
 AC15‐5TR.
 CRS‐2P (5/8‐inch aggregate).
 AR‐chip seal.
17
CHAPTER 3. PROJECT DATA COLLECTION
Late in 2007, ADOT and Applied Pavement Technology collected pavement performance data from
all the experimental sections at the Wearing Course and Preventive Maintenance treatment sites.
The data, which included several different types of pavement distress as well as measures of
roughness, friction, and surface texture, provide a sound basis for evaluating and comparing the
performance of different treatments. This chapter briefly summarizes the data collection efforts;
Appendix C provides supplemental details.
To gather information about ADOT’s current maintenance strategies, researchers interviewed ADOT
headquarters staff by phone in 2007 and submitted questionnaires to district staff in 2011. The
survey results are documented in this chapter.
Finally, researchers obtained cost information for the various treatments from four primary sources
that was used to estimate unit costs for many of the pavement maintenance treatments included in
the project. Summary results are also provided in this chapter.
PERFORMANCE DATA
The primary basis for evaluating the performance of the Phase I and II experimental treatments is
the field performance and condition data collected between October and December 2007. The data
included the type of flexible pavement condition information that ADOT gathers for its pavement
management process as well as data on pavement surface characteristics that impact pavement
safety and ride quality (i.e., friction resistance, surface texture, and roughness). ADOT and Applied
Pavement Technology staff gathered the data using both manual and automated data collection
techniques. Table 6 identifies the specific performance data collected as part of the manual
condition surveys, automated field testing, and other field testing.
Table 6. Types of Pavement Performance Data Collected.
Manual
Condition Survey
Automated Field
Testing
Other Field
Testing
 Weathering (raveling)
 Bleeding
 Flushing
 Longitudinal and transverse
cracking
 Fatigue cracking
 Rutting
 Patching
 Roughness
 Friction
 Outflow meter
 Dynamic Friction
Tester
 Circular Texture
Meter
18
Appendix C provides summary tables on a site‐by‐site basis of all the performance data collected for
this project. Following are descriptions of the different data collection operations as well as some
important notes and observations about data collection at each test site.
Manual Condition Surveys
Applied Pavement Technology performed manual pavement condition surveys while ADOT provided
traffic control. At the beginning of the survey, the field crew confirmed the site location information
and pavement markings against original documentation. Then they identified representative 500‐ft‐long
segments within each section. Typically these were located near the middle of the test section
so any difficulties associated with “sympathetic” failure and construction variability at the start and
end of each test section construction were not reflected in the section’s performance evaluation.
In general, all surveys and measurements were made in the outer travel (truck) lane of the section.
Of the seven distress types surveyed, four—weathering, bleeding, longitudinal and transverse
cracking, and fatigue cracking—were surveyed and recorded according to distress definitions
identified in the Federal Highway Administration’s (FHWA) Distress Identification Manual for the
Long‐Term Pavement Performance (LTPP) Program (FHWA 2003). As the long‐term pavement
performance (LTPP) protocol requires, each of these four distresses were characterized by severity,
extent, and type. The three remaining distress types (rutting, flushing, and patching) were surveyed
according to ADOT definitions with threshold values as shown in Table 7. Maximum rut depths were
measured at 50‐ft intervals (50, 100, 150, 200, and so on) in the outer and inner wheel path using a
ruler and 6‐ft straightedge. All other distresses were measured over the entire section. Figure 1
shows the standard form used to record manual pavement condition survey data.
Table 7. Trigger and Failure Levels for ADOT Distresses.
Distress Type Measurement Units Range Trigger Failure
Rutting Inches 0‐2 0.5 1.0
Flushing Rating 5a‐0 3.5 2.5
Patching Percent of area 0%‐100% 25% 50%
aA rating of 5 indicates no flushing.
19
Figure 1. Pavement Condition Survey Recording Form.
20
Digital photographs were also taken at each section to document typical pavement conditions. The
photographs are stored in the electronic project archives and include the following for each section:
 Section overview (looking forward).
 View of shoulder.
 View of typical drainage conditions.
 Typical distresses and their severity levels.
 Close‐up of typical surface conditions.
 Section overview (from the end of the section looking backward).
Automated Field Testing
ADOT performed surface profile and skid testing surveys using its van‐mounted equipment at
roughly the same time as the manual pavement condition surveys (between October and December
2007). Figure 2 is a photo of the ADOT profilometer used for surface profile measurement. It uses a
series of lasers (mounted at the front of the van), vertical accelerometers (to correct for the effects
of the vertical up and down movements of the van), and other internal instrumentation to record
the longitudinal and transverse pavement surface profiles.
The surface profile data were used primarily to determine the average rut depths on the high‐volume
Interstate sections where lane closure (for manual measurement) was not possible. The
data were also used to help develop correlations with other roughness measures and not intended
for use in evaluating treatment performance. Appendix C includes rut depth data, but not the actual
surface profile data. For automated friction testing, ADOT used its skid testing van (Figure 3), but
only on higher volume Interstate highway sections where the manually operated field test devices
could not be used. This served as the basis for the SNs presented in Appendix C.
Other Field Testing
ADOT used its outflow meter (Figure 4), Circular Texture (CT) meter (Figure 5), and Dynamic Friction
(DF) Tester (Figure 6) to measure pavement surface and friction characteristics in the test sections.
Since all three are manually operated devices, ADOT performed these tests on the test sections at
the same time as the manual condition surveys. The outflow meter provides an estimate of the MTD
using a correlation that is based upon the amount of time required for water to flow out of the
cylinder. The CT meter (ASTM 2012) uses a laser to determine a pavement surface texture
characteristic known as the mean profile depth (MPD) within an 11‐inch diameter circle. The DF
device measures the dynamic coefficient of friction (DCOF) that characterizes the pavement
surface’s frictional resistance.
21
Figure 2. ADOT Profilometer.
Figure 3. ADOT Skid Testing Van.
22
Figure 4. HydroTimer Outflow Meter.
Figure 5. CT Meter.
23
Figure 6. DF Tester.
Data Collection Notes (by Site)
Following are key observations recorded at each test site:
 I‐10 (Casa Grande, Arizona). Researchers surveyed 32 test sections (all in the eastbound
direction) at this location on December 5, 2007. Due to heavy highway traffic volumes, they
conducted the manual survey from the shoulder with an ADOT attenuator following the
survey crew. Distresses were estimated since the crew could not enter the lane of traffic.
ADOT collected all of the data (including rutting depths) using its profilometer. No outflow
or DF tests were conducted at this site.
 I‐8 (Gila Bend, Arizona). Researchers surveyed the 16 test sections in the westbound
direction on December 7, 2007, and the 16 test sections in the eastbound direction on
December 8, 2007. The right (truck) lane was surveyed using a moving lane closure. ADOT
performed in‐place CT and outflow measurements while the manual distress surveys were
conducted. ADOT also collected skid measurements using its automated van. DF tests could
not be collected during the closure period.
 SR 74 (Peoria, Arizona). Researchers surveyed 18 sections in both directions on
December 10, 2007. Full lane closures were employed at this site for the manual surveys.
ADOT performed outflow and CT measurements during the manual condition surveys. ADOT
was also able to collect friction data using its automated equipment as the DF equipment
was malfunctioning during the closure period.
 SR 66 (Kingman, Arizona). Researchers surveyed 14 test sections in both directions, for a
total of 28 sections, on December 11, 2007. Again, ADOT provided full lane closures, and the
24
manual condition surveys were conducted in the outside (truck) lane. ADOT collected
outflow, CT, and DF measurements while the manual distress surveys were conducted.
 SR 83 (Sonoita, Arizona). All 28 test sections were surveyed on December 6, 2007, with 14
sections in each direction of traffic. The manual distress surveys as well as ADOT’s outflow,
CT, and DF testing were conducted in the outside (truck) lane using a moving closure
provided by ADOT. None of the test sections was marked along the highway right of way,
and the mileposts had to be used to help locate each section.
 SR 87 (Winslow, Arizona). These 21 test sections were surveyed on December 12, 2007,
nine in the northbound direction and 12 in the southbound direction. Once again, the
manual condition surveys and ADOT’s outflow, CT, and DF tests were conducted in the
outside (truck) lane under lane closure provided by ADOT.
 U.S. 191 (Alpine, Arizona). These 60 test sections were located on a very remote mountain
highway and were surveyed during the week of October 22, 2007. MP 181 to MP 185
included 12 test sections (six in each direction of traffic) while MP 200.5 to MP 219.25
included 48 test sections (24 in each direction of traffic). The manual condition surveys were
performed in the outside (truck) lane using moving lane closure provided by ADOT. Outflow,
CT, and DF tests were also completed during this closure.
ADOT STAFF SURVEYS
ADOT staff at headquarters (Phoenix) and in district offices were interviewed in July 2007 and July
2011, respectively, to identify ADOT’s current maintenance strategies (with emphasis on ADOT
policy related to the treatments used in the maintenance effectiveness test sections), problems with
maintenance strategies, and potential solutions. The 2007 surveys were conducted by phone and
included 11 questions. The 2011 surveys were questionnaires that sought more detailed treatment
information about materials, selection criteria, construction problems, performance, and solutions.
2007 Phone Interviews
In July 2007, researchers interviewed Doug Forstie, Joel Miller, Bill Hurguy, and Yongqi Li by phone.
Forstie described ADOT’s pavement preservation program as a subset of the overall pavement
program. According to Forstie, of the $120 million spent annually, about $100 million was spent on
major projects and $7 million on the preventive maintenance surface treatment program. The latter
was accomplished mostly through a procurement process and included flush coats, chip seals, slurry
seals, and thin overlays. Contractors completed the construction work while ADOT provided traffic
control and completed the striping. Li and Hurguy said that the pavement preservation program did
not include treatments that add structure (including HMA overlay with a thickness greater than
25
1 inch). Since AADT was not always available for rural roads, average daily traffic (ADT) was used.
The ADT is composed of traffic counts taken for more than one day but less than one year.
A compilation of the survey responses follows:
1. What treatments are currently specified by ADOT?
The interviewees reported that ADOT did not have a specification and that the treatments
were selected based upon past practice, where the district maintenance supervisors decide
what, when, and where. (Note: ADOT’s current 2008 Standard Specifications for Road and
Bridge Construction includes Section 404 on bituminous treatments.) The typical treatments
specified by the districts included:
a) Flush coats and fog seals. These contain various types of emulsions and were used
extensively by some districts and on a limited basis by others. (Note: One reviewer
considered a flush coat to be a fog seal with a rejuvenating agent.)
b) Chip seals. The typical emulsions for these included RS, polymer‐modified CRS, and RS
with PASS oil. Hot‐applied AR binder has also been used, but not normally. The
aggregate (chip) TSA was typically 3/8‐ or 1/2‐inch and may be coated or uncoated. In
some cases, double applications were used.
c) Cinder seals. These were basically a chip seal with cinder aggregates (1/2‐inch cinders
and cinder fines) that allow for some aggregate buildup.
d) Sand seals. Like chip seals, sand seals were shot a little lighter (0.2 gal/sy or less) and
used washed fines or cinder fines. These were used by some districts that had poor
experience with chip seals.
e) Scrub seals. These typically involved applying an emulsified polymer‐ or latex‐modified
binder (usually PASS oil) followed by a system of shop brushes that worked the binder
into the pavement surface. The surface was then covered with either sand (southern
areas of the state) or cinders (northern areas).
f) Slurry seals and microseals (microsurfacings). These were either Type I, II (most
common), or III, and were completed under a statewide contract.
g) Thin HMA overlays. These were less than 2 inches thick and saw limited use.
h) Novachip. ADOT has used a thin‐bonded wearing course, but only occasionally because
of its proprietary nature.
i) Blade‐laid overlays. These were constructed with either cold‐mix asphalt or HMA
placed over short stretches, and were rarely used.
j) Crack sealing. ADOT used both asphalt and AR sealant using a “blow‐and‐go” approach.
Designations included ERA to CRF, PASS oil, and MC‐250.
26
2. What are the applicable specifications for those treatments?
The specifications came either from ADOT Contracts and Specifications or from the district.
Typically, the aggregate specifications came from Contracts and Specifications while the
asphalt binder specifications were provided by on‐call vendors. Any new or unconventional
treatment went through Contracts and Specifications or through ADOT Procurement. With a
new treatment, an ADOT Regional Materials Lab engineer would have to review and
approve the vendor’s specification. If Procurement reviewed the treatment, it was typically
written into the special provisions.
3. What guidelines are available to assist in the selection and scheduling of these treatments?
There were no formal guidelines for project selection or scheduling. Treatment selection
and timing were based on the local supervisor’s background and experience.
4. How long do the treatments last and provide measureable benefit?
a) Flush coats and fog seals. These provide a one‐ to two‐year service life, depending on
the pavement being treated. With rubberized asphalt and rubberized friction courses,
the application can be lighter since they do not oxidize or begin raveling as soon. The
first application on a rubber treatment will occur about three years after construction,
where it may be one to two years for conventional HMA. Longevity depends on the
condition of the surface. If the treatment was applied when it was first needed, it might
last two to five years.
b) Chip seals. Conventional chip seals may provide seven to 10 years of service on a good
surface (level, no cracking, and limited rutting). If the pavement has a rough surface
profile and experiences significant snowplow damage, the service life may be much
shorter. Older pavements that have been crack sealed and exhibit some rutting, surface
roughness, or patching may start peeling at the centerline (and not last very long). Chip
seals placed early in the season (May or June) provide longer service lives since they
have more time to cure.
c) Hot‐applied chip seals with coated 1/2‐inch chip. These resist snowplow damage much
better than conventional chip seals.
d) Cinder seals. These provide a rough, noisy ride after construction; however, they do not
peel like conventional chip seals. The service life is in the range of seven to 10 years on a
smooth road, and five to seven years on a rough road.
e) Polymer‐modified chip seals. These perform better and can be placed later in the
season, but cost more. They are more forgiving when the quality of the chip is less than
desirable. The polymer‐modified binder holds the aggregate better and may provide an
additional one to two years of service as compared to a conventional chip seal.
27
f) Sand seals. These have a service life of five to seven years if the pavement surface
condition is good, and three to five years if the pavement surface condition is poor.
g) Scrub seals. The service life may be five to seven years, depending on the surface
condition. There may be flushing problems in southern areas of the state, especially if
the sand is overapplied.
h) Slurry seals. These are rarely used as a preventive maintenance treatment. In most
cases, they are used as a stop‐gap measure to provide some life extension to a
distressed pavement. Depending on the extent and severity of the distress, the amount
of repair, and the environmental setting, the service life may be one to seven years.
i) Microseals. These are used primarily for rut filling, with a service life of seven to
10 years if the pavement condition is good, or three to seven years if the pavement
condition is poor.
j) Thin HMA overlays. Not every district has the lay‐down capability. A quality blade‐laid
overlay depends on the experience of the blade operator.
k) Cold‐mix overlays. If sealed 60 days after placement, they can perform well. If they are
sealed before the moisture is allowed to evaporate, ruts may return within six months.
5. What types of pavements are the treatments applied to?
a) Flush coats and fog seals. These are applied to all HMA‐surfaced pavements, preferably
soon after construction.
b) Chip seals. These are recommended for low‐volume, HMA‐surfaced roads (less than
3000 ADT), but can also be used on older HMA pavements that exhibit some cracking
and distortion. They are not recommended for use on Interstate highways or in urban
areas with a lot of turning movements.
c) Sand, scrub, and cinder seals. These are applicable for low‐volume, HMA‐surfaced
roads, including those that exhibit some cracking and distortion. Cinder seals are used
mostly in northern areas of the state. Sand and scrub seals are used mostly in southern
areas (primarily because there are no cinders).
d) Slurry seals and microseals. These are used primarily on Interstate highways under
most conditions, including high altitude, but operators must be aware of curing
conditions.
6. Is there a retreatment schedule?
There is no formal schedule. However, there are some emerging guidelines. For example,
highway sections should be examined or inspected every three years. (The range was two to
five years.)
a) Flush coats and fog seals: two‐ to four‐year rotation.
b) Other treatments: Three‐ to seven‐year rotation.
28
7. What are the pavement distresses present when the treatments are applied?
The maximum benefit from the various surface treatments was obtained when they were
applied before any significant structural distress developed. However, there were no formal
guidelines for targeting treatments to certain types, severities, and extents of distress. So,
the practice was to place the treatments on pavements that exhibit a range of distress
conditions, “from hairline cracks to block cracking” (and beyond). The secret to achieving
the expected minimum service life was to crack seal and patch the existing pavement prior
to treatment application.
8. What pavement distresses, when present, indicate that the treatments should not be
applied?
As indicated in question 7, there were no formal guidelines for targeting treatments to
various types and ranges of pavement distress (minimum or maximum). However, the
interviewees identified several general rules of thumb:
a) Do not chip seal pavements with moderate to severe flushing. (Cinder seals, slurry seals,
and microseals may be considered if the flushing is not severe.)
b) In general, avoid pavements that exhibit severe cracking, rutting, and/or raveling.
c) Do not chip seal during the monsoon season.
d) Do not slurry seal or microseal if there is a chance of freezing.
e) Do not place seals if it is too hot or too humid.
9. What specification modifications are needed to ensure improved treatment performance?
a) Better guidance on what emulsions to use for flush coats and fog seals, and when to use
them on rubberized asphalt mixes.
b) More guidance on the asphalt (binder) to use for rubberized asphalt mixes.
c) Guidance on when to use rejuvenators.
d) No tolerances on the joints of friction courses.
e) Tighter surface profile specifications, to avoid any irregularities that will increase
snowplow damage.
f) Specifications that are defined and made available to all.
10. What problems are experienced in the design, construction, or placement of the
treatments?
a) Because of low confidence in the flush coat application rate, ADOT often used the more
expensive PASS treatment.
29
b) The lack of familiarity with some treatments led to design, construction, and
performance problems and more hesitancy to use the treatments.
11. Are treatments in use that are not currently documented by DOT specifications?
Only two proprietary treatments were identified: Novachip and Armor Coat.
Questionnaires
In June 2011, researchers distributed a questionnaire to representatives of all 10 ADOT districts.
Custom data entry forms were provided to gather detailed information about spray‐applied, slurry‐applied,
and paver‐applied treatments. Four districts—Kingman, Safford, Tucson, and Yuma—
replied with completed forms that characterized their use of flush coats, scrub seals, chip seals
(conventional and polymer‐modified), slurry seals, and microseals (microsurfacings). The results are
compiled in Table 8 through Table 10.
Following are some general observations about the survey results for all treatments. All are
consistent with phone survey results:
 There are essentially no standard specifications, although the Tucson District did reference
relevant sections of ADOT’s Construction Manual (ADOT 2008) for flush coats and polymer‐modified
chip seals.
 There is almost no information from which to estimate the range in pavement distress
within which each treatment can be used.
 There is very little information about materials and construction problems. The Safford
District indicated that dirty aggregate and excess rock/chip loss can be problems on its chip
seal projects, and delayed curing, rapid wear or disintegration, and excessive aggregate loss
can be problems with its slurry seal projects.
 The information provided on the altitude range for the different treatments may be
influenced by the actual range in altitude within each district.
30
Table 8. Survey Results on Flush Coats (Fog Seals).
Treatment Type Flush coat Flush coat Flush coat Flush coat
District Kingman Safford Tucson Yuma
Treatment Designation – PASS SR 86 (MP 115
to MP 122) PASS oil
Unit Cost ($/sy) 0.19‐0.21 0.50‐1.00 0.20 0.25‐0.30
Relevant Specifications Not identified Procurement
state funded
404‐3.13
Fog coat/flush Not identified
Materials Information
Binder/emulsion type PASS PASS PASS CSS‐1
Dilution (%) 50:50 50:50 50:50 50:50
Binder application rate (gal/sy) 0.08‐0.10 0.08‐0.14 0.08 0.10
Additives – Rejuvenator,
stabilizer – Rejuvenator
Allowable Road Conditions
Roadway types
Interstate
highway
(IH)/rural,
state highway
(SH)/rural
IH/urban,
IH/rural
SH/urban,
SH/rural
SH/rural
IH/urban,
IH/rural
SH/urban,
SH/rural
ADT range (vehicles/day) 1,000‐10,000 Unlimited 1,000‐3,000 >3,000
Altitude range
(ft above sea level)
2,000‐>5,000 >2,000 – <2,000
Min./Max. Pavement Distress
Raveling/weathering (% area) – – – N/A
SN/friction number – – – N/A
Flushing/bleeding (% area) – – – N/A
Transverse crack spacing (ft) – 5 min./20 max. – N/A
Block cracking (% area) – – – N/A
Fatigue cracking (% area) – 20 min./
50 max. – N/A
Rut depth (inch) – 1 min./2 max. – N/A
Treatment Performance
Expected life (yr) 2 3 1‐2 3
Distress type/level at failure Cracking Visual Raveling –
Material/Construction Problems
Poor binder viscosity – – – N/A
Poor aggregate embedment – – – N/A
Dirty aggregate – – – N/A
Excess rock/chip loss – – – N/A
Premature flushing/fat spots – – – N/A
Other – None – N/A
Additional Comments – – – –
31
Table 9. Survey Results on Aggregate Seals.
Treatment Type Scrub seal Chip seal Chip seal
Polymer‐modified
chip seal
Polymer‐modified
chip seal
District Safford Kingman Safford Tucson Yuma
Treatment Designation – –
Double
application
emulsion
SR 85
(MP 57.9 to
MP 61.2)
–
Unit Cost ($/sy) 1.00‐1.50 0.45 2.00‐3.00 0.97 3.10
Relevant Specifications Not identified Not identified Special
procurement
404‐3.14 Chip
seal coat
CRS‐2P with
SS‐1
Materials Information
Binder/emulsion type CRS PASS CRS‐2P CRS‐2P CRS‐2P
Dilution (%) 50:50 Con. – – 50:50
Binder application rate (gal/sy) 0.10‐0.20 0.35‐0.42 0.40‐0.50 0.47 0.45
Aggregate type No
information
No
information Crushed stone ADOT chip Crushed rock
TSA (inch) – 3/8 5/16‐3/8 3/8 3/8
Aggregate application rate (lb/sy) – 22 25‐35 26 25
Additives – – Polymer – –
Allowable Road Conditions
Roadway types SH/rural SH/rural SH/rural SH/rural SH/rural
ADT range (vpd) <1,000 – <1,000‐10,000 1,000‐3,000 3,000‐10,000
Altitude range
(ft above sea level) <2,000‐5,000 2,000‐3,500 2,000‐>5,000 – <2,000
Min./Max. Pavement Distress
Raveling/weathering (% area) 20/50 norm. – Varies – N/A
SN/friction number – – 50 – N/A
Flushing/bleeding (% area) – – N/A – N/A
Transverse crack spacing (ft) – – Varies – N/A
Block cracking (% area) – – Varies – N/A
Fatigue cracking (% area) – – Varies – N/A
Rut depth (inch) – – 1‐2 – N/A
Treatment Performance
Expected life (yr) – – 5+ 10 7‐10
Distress type/level at failure – – – Stripping and
raveling –
Materials/Construction Problems
Poor binder viscosity – – – – N/A
Poor aggregate embedment – – – – N/A
Dirty aggregate – – Yes – N/A
Excess rock/chip loss – – Yes – N/A
Premature flushing/fat spots – – – – N/A
Other
Pavement
failure/lost
cause
– – – N/A
Additional Comments – – – – –
32
Table 10. Survey Results on Slurry Seals and Microseals (Microsurfacings).
Treatment Type Slurry seal Microseal/
microsurfacing
Microseal/
microsurfacing
District Safford Safford Yuma
Treatment Designation – – –
Unit Cost ($/sy) Not identified 2.00‐3.00 4.00
Relevant Specifications – Manufacturer or
vendor –
Materials Information
Binder/emulsion type CSS‐1H, CQS‐1H CSS‐1H Polymer‐modified
emulsified asphalt
Binder content
(% by weight of mix) 8‐12 6‐11 6‐11.5
Aggregate type Crushed stone Crushed stone Crushed stone
Application rate
(lb/sy of dry aggregate) 25‐30 25‐35 32
Additives – Polymer 4% solid polymer
Allowable Road Conditions
Roadway types SH/urban, SH/rural IH/urban, IH/rural,
SH/urban, SH/rural
IH/urban, IH/rural,
SH/urban
ADT range (vpd) 3,000‐20,000 >3,000 >3,000
Altitude range (ft above sea level) – >2,000 <2,000
Min./Max. Pavement Distress
Raveling/weathering (% area) Varies Varies N/A
SN/friction number – Varies N/A
Flushing/bleeding (% area) – Varies N/A
Transverse crack spacing (ft) – Varies N/A
Block cracking (% area) – Varies N/A
Fatigue cracking (% area) – Varies N/A
Rut depth (inch) – Varies N/A
Treatment Performance
Expected life (yr) 3‐5 3‐7 5
Distress type/level at failure Block cracking Raveling –
Materials/Construction Problems
Delayed curing
(Late opening to traffic) Yes – N/A
Excessive scuffing – – N/A
Rapid wear or disintegration Yes – N/A
Excessive aggregate loss Yes – N/A
Premature flushing/fat spots – – N/A
Other – – N/A
Additional Comments – – –
33
Following are more specific observations by treatment type.
Flush Coats/Fog Seals
All four districts responding provided feedback about flush coat or fog seal treatments:
 The range in unit cost for three of the districts was $0.19/sy to $0.30/sy. At $0.50/sy to
$1.00/sy, the unit cost range in the Safford District seems very high.
 Three of the districts identified PASS as the choice of binder/emulsion. Yuma District, on the
other hand, identified CSS‐1 as its typical binder/emulsion.
 The dilution of the emulsion was the same for all four districts (50:50), and the binder
application rates seemed very consistent (0.08 gal/sy to 0.14 gal/sy).
 Three of the four districts permit the application of flush coats on both Interstate and state
highways. Only the Tucson District limits its application to state highways. The Safford and
Yuma districts permit flush coats in both rural and urban settings, while the Kingman and
Yuma districts limit their application to rural settings.
 Three of the districts permit using flush coats on pavements with relatively high‐traffic
levels. The Tucson District limits application to pavements with relatively low‐traffic levels.
 The expected life of a flush coat in the Kingman and Tucson districts is about one to two
years. In the Safford and Yuma districts, it is about three years.
 The Kingman District reported cracking as the distress type at failure (of the flush coat); the
Tucson District reported raveling. The Safford and Yuma districts did not respond.
Scrub Seals
Only the Safford District provided feedback on scrub seals. This treatment is used only on rural state
highways with ADT levels less than 1000 vehicles per day. The unit cost of $1.00/sy to $1.50/sy is
relatively high compared to the conventional chip seals.
Chip Seals
All four districts provided information about their use of chip seals. The only consistent features are
that they all use 3/8‐inch TSA (which it is safe to assume is all crushed material) and they are only
permitted on rural state highways.
 The treatment type and designation information are a little confusing, but it appears that
three of the four districts employ a cationic, rapid‐setting, polymer‐modified emulsion (CRS‐
2P) while the Kingman District uses the PASS emulsion (which is also considered polymer‐modified).
The Safford District uses a double application of emulsion (and supposedly chip),
while the other districts use a single application.
 The range in unit cost is $0.97/sy to $3.10/sy. (The $0.45/sy reported by the Kingman
District is unusually low and may be due to a transcription error.)
 The binder application rate across all four districts ranges from 0.35 gal/sy to 0.47 gal/sy.
34
 The aggregate application rate across all four districts ranges from 22 lb/sy to 35 lb/sy.
 The allowable range in ADT is from about 1000 to 10,000 vehicles per day for both the
Safford and Yuma districts. The high end of the ADT range for the Tucson District is only
3000 vehicles per day.
 The expected life of the chip seals that employ a CRS‐2P binder is from five to 10 years. The
Kingman District does not indicate an expected life for its PASS‐based chip seal.
 Only one district (Tucson) identified the typical types of distress at failure of the chip seal.
They were stripping and raveling.
Slurry Seals
Only one district provided information about slurry seals. The Safford District uses slurry seals on its
state highways in both rural and urban settings. The allowable range in ADT is between 3000 and
20,000 vehicles per day while the expected life is between three and five years. No unit cost
information was provided.
Microseals/Microsurfacings
Only the Safford and Yuma districts provided information about their use of microseals
(microsurfacings). The Safford District uses microseals on both state and Interstate highways in both
rural and urban settings. The Yuma District uses microseals on all but rural state highways. Both
districts will use microseals on high‐volume highways (ADT greater than 3000) and target an
application rate of about 25 lb/sy to 35 lb/sy (of dry aggregate). The Yuma District expects a service
life of five years, while the Safford District has a similar expectation (three to seven years).
TREATMENT COSTS
Because of the contracting method used to construct the experimental wearing course and
preventive maintenance treatments, no information is available about unit construction costs of
those treatments. Considering the size and nature of the experiment, there would probably be some
questions about how representative those costs would be if they did exist. Accordingly, cost
information was gathered from four sources to estimate each treatment’s representative unit cost:
 ADOT bid tabs. In May 2011, ADOT analyzed its bid tabulations to determine the typical unit
costs for various wearing course and preventive maintenance treatments.
 ADOT questionnaire. In the questionnaire circulated to all districts in July 2011, four ADOT
districts provided unit cost information for the treatments they typically use.
 California Department of Transportation (Caltrans) Pavement Preservation Task Group
(PPTG). In 2007, the PPTG Strategy Selection Committee surveyed DOT personnel and
industry representatives to gather cost information about various preventive maintenance
treatments used in the state.
35
 HollyFrontier Companies. 2011 estimates for most of the treatments used in the
experiment were provided as a courtesy by an asphalt producer in Phoenix.
Table 11 presents the relevant cost data from these sources along with the recommended unit cost.
Table 11. Summary of Available Unit Cost on Experimental Treatments.
Type of Treatment
Unit Cost ($/sy)
ADOT Bid
Tab
Review
2011
ADOT
District
Survey 2011
Caltrans
PPTG/SSC
Survey
2011
HollyFrontier
Estimate
2011
Recom‐mended
Flush coat (fog seal) 0.25 – 0.15‐0.30 – 0.25
Flush coat (PASS) 0.27 0.19‐0.30 0.20‐0.50 0.25‐0.50 0.27
Scrub seal – 1.00‐1.50 – 0.75‐1.50 1.25
Chip seal (CRS‐2) 1.66‐1.88 0.97‐3.10 1.80‐2.00 1.50‐1.75 1.70
Chip seal (CRS‐2P) – – – 1.50‐2.00 1.80
Chip seal (HF CRS‐2P) – – – 1.50‐2.00 1.80
Chip seal (PASS oil/CR) – – – – 1.80
Chip seal (CM‐90) – – – 1.50 1.50
Chip seal (AC15‐5TR,
Paramount)
– – – 1.50‐2.00 1.80
Double application
chip seal
– 2.00‐3.00 – 2.50‐3.00 2.75
Double application
chip seal and blotter
– – – 2.00‐2.50 2.25
AR‐chip seal – – 3.75‐4.55 3.00‐4.00 3.50
Slurry seal (Type III) 1.56 – 1.60‐2.20 1.50‐2.00 1.60
Microseal (Type III
microsurfacing)
1.97 2.00‐4.00 2.00‐2.80 3.00+ 2.00
ACFC 3.30 – – 3.00‐4.00 3.30
AR‐ACFC 3.65 – – 3.50‐4.50 3.65
P‐ACFC – – – 3.00‐3.50 3.20
P‐ACFC (Paramount) – – – 3:00‐3.50 3.20
P‐ACFC (PG 76‐22+) – – – 3.00‐3.50 3.30
SMA – – – 3.00‐4.00 3.50
PEM – – – 4.00 4.00
Bonded wearing course
(Novachip)
– – 10.00‐14.00 6.00‐7.00 6.50
36
37
CHAPTER 4. TREATMENT PERFORMANCE AND EFFECTIVENESS
This chapter summarizes the review of the performance and effectiveness of the treatments at both the
wearing course experiment (Phase I) and the preventive maintenance experiment (Phase II) sites.
Included are descriptions of the process used to format the pavement distress/condition data for
analysis and comparison, the statistical and graphical approaches used to analyze the performance data,
the steps followed to determine treatment effectiveness, and the findings of the treatment
performance and effectiveness comparisons.
DETERMINATION OF DEDUCT VALUES FOR VARIOUS DISTRESS TYPES
For purposes of pavement condition assessment, most pavement distresses are characterized by their
type, severity, and extent. Transverse cracking, for example, is measured in terms of crack width
(severity) and length (extent). The problem with this method of characterizing pavement distress is that
it makes it difficult to compare (on a uniform basis) the performance of different pavements or, in this
case, different pavement treatments. For example, consider two pavements, the first exhibiting 200 ft of
narrow (0.1‐inch wide) transverse cracking and the second, 30 ft of wide (0.7‐inch wide) transverse
cracking. It’s hard to answer which pavement is in better condition.
The U.S. Army Corps of Engineers (USACE) helped solve this problem by applying the Pavement
Condition Index (PCI) rating procedure (ASTM 2011). In the PCI method, the overall pavement condition
is given as a value between 0 (failed condition) and 100 (excellent condition). The PCI at any time is
computed by subtracting the deduct values (DVs) associated with each observed distress type from 100.
The DV for any given distress is calculated using a system of polynomial equations that were developed
to translate the effect of extent and severity. A description of the DV equations developed by USACE is
presented in Appendix D.
In the PCI procedure, a given pavement is characterized in one of seven conditions depending on its PCI
value. These conditions are represented in Table 12.
Table 12. PCI Ranges for Each Pavement Condition.
PCI Range Condition Color Code
85‐100 Good Green
70‐84.99 Satisfactory Light green
55‐69.99 Fair Yellow
40‐54.99 Poor Light red
25‐39.99 Very poor Red
10‐24.99 Serious Dark red
0‐9.99 Failed Gray
38
For this study, these PCI ranges were converted to equivalent ranges in DV. Also the high end of the
good range was divided into good and very good to better distinguish performance of the experimental
treatments. Table 13 shows the pavement conditions associated with the new DV ranges.
Table 13. DV Ranges for Each Pavement Condition.
DV Range Condition Color Code
0.00‐5 Very good Dark green
5.01‐15 Good Green
15.01‐30 Satisfactory Light green
30.01‐45 Fair Yellow
45.01‐60 Poor Light red
60.01‐75 Very poor Red
75.01‐90 Serious Dark red
90.01‐100 Failed Gray
REVIEW OF WEARING COURSE TREATMENTS AT PHASE I TEST SITES
The matrix in Table 4 illustrates the overall layout of the Phase I experiment, including the number of
wearing course sections within each cell of the matrix. This table provides the basis for analyzing and
comparing the performance of the different wearing course treatments seven years after construction.
From an analytical standpoint, two important points must be made about the experiment’s structure:
 It is valid to compare the performance of the wearing course treatments within an individual
experimental site.
 Although near identical mixes were placed on the I‐8 and I‐10 sites at basically the same time
(summer/fall 1999), it is not statistically valid to compare the wearing course treatments’
performance between these sites because of the differences in traffic, environment, and
underlying pavement structure. For these same reasons and because they were constructed
significantly later (April 2001), it is also not statistically valid to compare the section
performance at the SR 74 site with those in the I‐8 and I‐10 sites.
Researchers used a statistical approach to make valid performance comparisons between the wearing
course treatments for the following pavement distress/performance criteria:
 Skid resistance.
 Weathering.
 Bleeding.
 Fatigue cracking.
 LTD cracking.
39
Rutting and patching were also initially considered; however, none of the sections exhibited any
significant levels of these distresses. Surface texture, flushing, swelling, and edge cracking were not
evaluated because these distresses were either considered surrogates for distresses that were being
considered (e.g., surface texture for skid resistance) or were not worth the effort required to evaluate
their impact on treatment comparisons (e.g., edge cracking).
Skid resistance was characterized by SN while all other distress/performance criteria were characterized
by a DV that corresponds to the observed extent and severity. The DVs were calculated using the USACE
DV equations (described earlier) and the pavement distress data obtained as part of the field
performance data collection operations.
Analysis of Pretreatment Milling and Overlay
The wearing course experiment design made it possible to investigate the impact of milling depth and
overlay thickness on wearing course performance. As shown in Table 4, the overlay thickness is constant
(2 inches) while the milling depth varies from 1 to 3 inches in the I‐8 sections. In the I‐10 sections, the
milling depth varies from 2.5 to 4.5 inches while the overlay thickness varies correspondingly from 2 to
4 inches. The fact that they vary in a colinear fashion means that it is not possible to determine their
independent effects. Finally, for the SR 74 sections, the overlay thickness is identical to the milling
depth, which varies from 0 to 3.5 inches.
The bar charts in Appendix E illustrate how the milling depth and overlay thickness affect different
performance measures. In some cases—SN, for example (Table 102)—there is a clear correlation. In
other cases, such as weathering (Table 103), there is no apparent correlation.
To investigate the relationships further, simple linear regression analyses were performed in which
milling depth served as the independent (x) variable and the key performance measures served as the
dependent (y) variable. If the correlation between x and y was significant (i.e., F greater than Fcrit), then
the coefficients (a0 and a1) generated for the linear relationship (below) are considered valid:
y = a0 + a1∙x (Eq. 1)
The results of the regression analyses for four dependent variables—SN, weathering, fatigue cracking,
and LTD cracking—are presented in Table 14 for the I‐10, I‐8, and SR 74 sites. Bleeding was not included
because it was not observed on any of the sections.
40
Table 14. Equation Coefficients for Relationships between Pavement Performance
Measures and Pretreatment Milling Depth.
Distress/
Performance
Criteria
Treatment
Type
I‐10 Site I‐8 Site SR 74 Site
a0 a1 r2 a0 a1 r2 a0 a1 r2
SN
ACFC 71.0 ‐1.75 0.73 No correlation
AR‐ACFC 76.0 ‐4.00 0.84 61.5 0.75 0.28 No correlation
P‐ACFC 75.9 ‐2.25 0.84 62.2 0.50 0.15 No correlation
PEM 64.4 ‐2.25 0.79 No correlation
SMA 67.2 ‐2.25 0.65 64.0 ‐1.25 0.40
TB‐ACFC 71.4 1.14 0.21
Weathering
DV
ACFC No correlation No correlation
AR‐ACFC No correlation No correlation 4.0 1.06 0.61
P‐ACFC ‐1.1 4.03 0.25 No correlation ‐25.9 18.3 0.59
PEM ‐3.4 1.60 0.26 No correlation
SMA ‐3.8 1.33 0.30 No correlation
TB‐ACFC No correlation
Fatigue
Cracking DV
ACFC 64.1 ‐14.9 0.35 10.3 ‐3.88 0.30
AR‐ACFC No correlation 5.9 ‐2.20 0.65 2.7 5.07 0.49
P‐ACFC 51.8 ‐11.7 0.30 No correlation 66.3 ‐22.1 0.33
PEM 30.3 ‐6.70 0.33 2.9 ‐1.10 0.30
SMA ‐46.8 17.2 0.29 2.0 ‐0.75 0.30
TB‐ACFC 87.6 ‐28.3 0.80
LTD Cracking
DV
ACFC 81.4 ‐16.3 0.94 25.0 ‐5.18 0.43
AR‐ACFC 7.3 5.55 0.30 43.0 ‐12.0 0.64 34.7 ‐3.98 0.21
P‐ACFC 73.0 ‐11.8 0.65 37.1 ‐7.13 0.34 No correlation
PEM 72.3 ‐13.9 0.93 53.2 ‐14.7 0.88
SMA ‐8.1 10.1 0.38 44.8 ‐9.63 0.77
TB‐ACFC 55.0 ‐13.1 0.80
Key observations from the I‐8 site analysis follow:
 Researchers used milling depth as the independent variable (x) because it was the only factor
that varied in the experiment. Overlay thickness was constant at 2.0 and, therefore, could not
be used to explain variations in wearing course performance.
 The I‐8 sections were constructed in 1999, so the performance of the wearing course treatments
reflects eight years of service.
41
 For SN, a statistically significant correlation was found with milling depth for three of the five
wearing course types: AR‐ACFC, P‐ACFC, and SMA. For the remaining two wearing course types
(ACFC and PEM), no significant correlation in the data was detected. Although they were found
to be significant, even the correlations for the AR‐ACFC, P‐ACFC, and SMA treatments are
questionable. The coefficient of determination (r2), which basically indicates how much of the
variability in the data is explained by the relationship, for all three relationships is low (0.15 to
0.40). In addition, the sensitivity of the SN to milling depth for all three relationships is relatively
low. For example, the SMA equation (which has the highest sensitivity) has an a1 coefficient of
‐1.25, which means that an increase in milling depth of 2 inches translates to a reduction in SN
of only 2.5. Overall, the experiment results indicate that the impact of pretreatment milling
depth (along with a fixed 2‐inch HMA overlay) on SN is small enough for all five wearing course
treatments to be considered negligible.
 For weathering, no significant correlations were found for any of the wearing course
treatments. Accordingly, the effect of pretreatment milling depth (along with a fixed 2‐inch
HMA overlay) on weathering is 0 for all five wearing course treatments.
 For fatigue cracking, statistically significant correlations were found for four of the five
treatments. However, the r2 values were low (0.30) for three of them. Of the four relationships,
the one with the most sensitivity of DV to milling depth has an a1 coefficient of ‐3.88, which
means that for every inch of increased milling depth, there is a 3.88 reduction in DV after eight
years of service. Interestingly, all of the equations have negative a1 coefficients, giving some
indication of a reasonable result. The relationship with the best fit (highest r2) has a negative a1
coefficient of ‐2.20, which translates to a 2.2‐point DV reduction after eight years of service for
every inch of milling depth. Overall, the low r2 values and small a1 coefficients make it difficult to
conclude that pretreatment milling depth (along with a fixed 2‐inch HMA overlay) has a
meaningful impact on fatigue cracking performance of all five wearing course treatments.
 For LTD cracking, significant correlations were generated for all five wearing course treatments.
Two of the relationships had relatively low r2 values (0.34 and 0.43) while the remaining three
had moderate to high r2 values (0.64 to 0.88). Overall, the data strongly suggest that increased
milling depth reduces the extent and/or severity of LTD cracking after eight years of service. The
PEM wearing course treatment, where there is a 15‐point DV reduction for every inch increase
in milling depth, seems to be affected the most. The ACFC treatment has the least impact with
only a 5‐point DV reduction after eight years of service for every inch increase in milling depth.
Overall, the magnitude of the r2 values and a1 coefficients indicates that milling depth (along
with a fixed 2‐inch HMA overlay) does have a meaningful impact on LTD cracking performance.
Based upon the results, the impact is greatest for the PEM, AR‐ACFC, and SMA treatments.
Key observations from the I‐10 site analysis follow:
 Milling depth (instead of overlay thickness) was the independent variable for conducting the
statistical analyses and developing the relationships for the I‐10 experimental sections, primarily
to maintain consistency with the relationships developed for the I‐8 site. However, each milling
depth has a corresponding HMA overlay with a thickness that is 0.5 inch thinner.
42
 The I‐10 sections were constructed in 1999, so the wearing course treatment performance
reflects eight years of service.
 For SN, good to very good correlations were found for all five wearing course treatments
(r2 values in the range of 0.65 to 0.85). Interestingly, the findings indicate that increasing the
milling depth (and overlay thickness) results in lower SNs after eight years of service. The
treatment with the greatest sensitivity is the AR‐ACFC, which after eight years has an 8‐point
lower SN for a 4.5‐inch mill and 4‐inch overlay compared to a 2.5‐inch mill and 2‐inch overlay.
Overall, the impact of milling depth (and corresponding HMA overlay thickness) on SN was
significant, but relatively small, especially when considering how high the SNs were for all five
treatments. All of the treatments had about the same level of sensitivity.
 For weathering, only three relationships for the wearing course treatments had a statistically
significant correlation. However, the r2 values were low (0.25 to 0.30). In addition, there is some
additional uncertainty with the three relationships because the positive a1 values mean higher
DVs after eight years of service for the higher levels of milling and overlay performed prior to
wearing course application. Overall, the impact of milling depth (and corresponding HMA
overlay thickness) on weathering is not considered meaningful for any of the five wearing
course treatments.
 For fatigue cracking, four of the five wearing course relationships had a statistically significant
correlation. However, all five had low r2 values (0.29 to 0.35). The a1 values for three
relationships are negative, indicating that after eight years of service, the DVs will be 13 to 30
points lower for a 4.5‐inch mill and 4‐inch overlay as compared to a 2.5‐inch mill and 2‐inch
overlay. Only the relationship for the SMA wearing course, with a positive a1 of 17.2, is
questionable. Overall, it is difficult to conclude that the milling depth and the corresponding
HMA overlay thickness have a meaningful impact on fatigue cracking performance. Despite the
magnitude and reasonableness of the a1 values for the ACFC, P‐ACFC, and PEM treatments, the
high positive a1 value for the SMA treatment and the low r2 values create too much uncertainty.
 For LTD cracking, relationships were developed for all five wearing course treatments. However,
the r2 values for two of the relationships were below 0.40. For both of those relationships, the a1
values were positive, indicating that an increased milling depth (and overlay thickness) results in
a higher (unreasonable) DV after eight years than a thinner milling depth and overlay thickness.
The other three relationships (ACFC, P‐ACFC, and PEM) have r2 values in the range of 0.65 to
0.94 and negative a1 values, which result in much lower (and more reasonable) DVs after eight
years for the higher milling depths and thicker overlays. ACFC had the greatest sensitivity, which
after eight years has a 32‐point lower DV for a 4.5‐inch mill and 4‐inch overlay as compared to a
2.5‐inch mill and 2‐inch overlay. P‐ACFC had the lowest sensitivity and a 24‐point lower DV.
Overall, there is a good indication that milling depth and the corresponding HMA overlay
thickness have a meaningful impact on LTD cracking performance. The three relationships with
good to high r2 values all have a1 values that reflect reasonable results. The two relationships
that reflect questionable a1 values also have poor r2 values. The treatments that clearly show
better LTD cracking performance with increased milling depth and overlay thickness (prior to
wearing course placement) are the ACFC, PEM, and P‐ACFC wearing courses.
43
Key observations from the SR 74 experimental section analysis follow:
 For consistency, milling depth was the independent variable. However, since milling depth and
overlay thickness are the same for this part of the experiment, it did not matter whether milling
depth or overlay thickness was used as the independent variable.
 The AR‐ACFC and P‐ACFC wearing course treatments used at this site were slightly different
from the AR‐ACFC and P‐ACFC treatments used at the I‐10 and I‐8 sites.
 The SR 74 experimental sections were constructed in 2001, so the performance reflects six years
of service.
 For SN, no correlation with milling depth was found for the AR‐ACFC and P‐ACFC wearing course
treatments. In addition, the TB‐ACFC treatment is suspect because its low r2 value is so low.
Accordingly, it is reasonable to conclude that milling depth and the corresponding overlay
thickness have no impact on SN after six years.
 For weathering, no correlation with milling depth existed for the TB‐ACFC wearing course
treatment. With r2 values of 0.61 and 0.59, the relationships for AR‐ACFC and P‐ACFC,
respectively, have some validity; however, the positive a1 values of 1.06 and 18.3, respectively
produce results that are counterintuitive. Since the a1 values for three of the I‐10 treatments
were positive, too, there is reason to question intuition and i this phenomenon further.
 For fatigue cracking, correlations were found for all three wearing course treatments. The
relationship derived for the TB‐ACFC treatment had the highest r2 value (0.80) and, with an a1
value of ‐28.3, exhibited the highest DV sensitivity for fatigue cracking to the milling depth. This
means that the DV calculated for a 4.5‐inch mill and 4‐inch overlay after eight years of service is
about 57 points lower than the DV calculated for a 2.5‐inch mill and 2‐inch overlay. The
relationship derived for the P‐ACFC treatment has a low r2 value (0.33); however, with an a1
value of ‐22.1, it has a sensitivity that is comparable to that of the TB‐ACFC treatment. The
relationship for the AR‐ACFC treatment has an r2 value of 0.49, but the a1 value is +5.07 and
inconsistent with the expected effect of increased mill depth and overlay thickness on DV.
Overall, the results make estimating the impact of milling and overlay on fatigue cracking
performance difficult. However, the results suggest that the TB‐ACFC and P‐ACFC treatments
perform better with increased pretreatment milling and overlay.
 For LTD cracking, no correlation existed for the P‐ACFC treatment. However, correlations were
found for the AR‐ACFC and TB‐ACFC treatments. With r2 values of 0.21 and 0.80, respectively,
the AR‐ACFC relationship is considered questionable and the TB‐ACFC relationship is considered
valid. The a1 values are both negative and consistent with the negative a1 values determined for
the I‐10 and I‐8 LTD cracking relationships. Overall, the results indicate that LTD cracking is
affected by milling depth and thickness of HMA overlay placed prior to the wearing course. The
TB‐ACFC treatment reflects the highest performance benefit.
44
Analysis of Treatment Performance
Researchers compared the individual treatment performance within each experimental site using a
statistically rigorous approach and a basic ranking process. Since the pretreatment milling and overlay
analysis did not show a consistent effect for any distress type (with the possible exception of LTD
cracking), the mill and overlay variability was not considered in the comparison.
To determine if the overall variability of treatment performance was low enough to compare the
differences in performance between treatments, researchers performed an analysis of variance
(ANOVA). If the overall variability established by the ANOVA was too high, there was no statistical
justification for comparing treatment performance within a given site. If the overall variability was low
enough, then the mean performance of each treatment was compared against the treatment exhibiting
the best performance using a Student’s t test (Ross 2004). The t tests were performed assuming a null
hypothesis that there is no difference between the mean performance of the two sections, a one‐tail
comparison, an alpha level of 0.10 (i.e., 90 percent confidence level), and equal section variances (most
of the time). In some instances, the performance variability of one section was so different that it was
necessary to assume unequal variances.
The output of the t test includes:
 A calculated t‐value (t) for a given performance comparison between any one treatment and the
treatment that exhibited the best performance.
 A critical t‐value (tcrit) that is determined from the Student’s t distribution (based upon the
number of performance measurements within each section, the alpha level, and the one‐tail
comparison).
 A probability value (P) that represents the probability that t is less than or equal to tcrit.
In evaluating the test results, the null hypothesis is accepted if t is less than or equal to tcrit. If t is greater
than tcrit, then the null hypothesis is rejected and the alternate hypothesis (i.e., the performance of the
two sections is different) is accepted. In simpler terms, if t is greater than tcrit, then there is a statistically
significant difference in the performance of the two sections. The P‐value indicates the probability that
the section with the poorer performance may actually perform better than the section with the best
performance. Thus, a low P‐value translates to a higher likelihood that performance of the two sections
is different, and when P is less than the selected alpha level of 0.10, researchers reject the null
hypothesis that the performance of the two sections is equal.
In addition to this more rigorous statistical approach, researchers devised a simpler yet practical
approach for grouping the different treatments based upon their overall performance. For a given
treatment and a given distress/performance measure, they calculated a 60th percentile value for the
distress measure (usually DV) using the mean and standard deviation of the distress as well as the
standard normal deviate that corresponds to 60 percent of the area in a normal distribution. Then they
used the 60th percentile value to rank each treatment at each site within one of the eight conditions
45
(defined in Table 13). Originally, the mean (or 50th percentile) value was used to rank the treatments,
but it did not effectively discriminate against treatments with higher levels of performance variability.
Researchers did not use the results of the Student’s t analysis as a basis for grouping (or regrouping) the
treatments into different conditions primarily because it is possible to have treatments that exhibit
significantly different performance and still be in the same condition. It is also possible that a treatment
in a poorer condition could have equal statistical performance (compared to the best‐performing
treatment) only because the treatment variability was high.
A discussion of the seven pavement performance categories follows.
SN
Table 102 in Appendix E provides the section data, measured SNs, mean and standard deviation of SNs,
and graphical results used to visually compare the skid performance of the Phase I sections. ANOVAs
conducted on the skid data from all three sites confirm what is apparent by visual examination—that
the overall variability is low enough to compare the skid performance of the treatments within each site.
Tables 15, 16, and 17 summarize the findings relative to the skid performance and treatment
comparisons on the I‐10, I ‐8, and SR 74 sections, respectively. The sections are sorted from apparent
best to worst based on their 60th percentile SNs. In practice, an SN of 35 suggests the pavement should
receive some type of treatment to restore skid resistance since values below 35 significantly increase
the likelihood of wet weather accidents. Unlike most of the other pavement distress measures, the
USACE did not develop any equations to relate SN to DV. Thus, for this study researchers employed
engineering judgment to relate ranges in SN to different conditions:
 Failed: SN less than 30.
 Poor: SN between 30 and 34.99.
 Fair: SN between 35 and 39.99.
 Satisfactory: SN between 40 and 49.99.
 Good: SN between 50 and 59.99.
 Very good: SN greater than 60.
46
Table 15. Skid Performance of the I‐10 Wearing Course Sections.
Wearing
Course
Treatment
Sections
SN Student’s t Test Results
Mean Range Std.
Dev.
60th
%ile Cond. Variance t tcrit P
(t<tcrit)
Null
Hyp.
P‐ACFC
(¾‐inch TSA)
6 68.0 65‐71 2.2 67.4
Very
good
– – – – –
ACFC
(¾‐inch TSA)
6 64.8 63‐68 1.8 64.4
Very
good
Equal 2.71 1.37 0.011 Reject
AR‐ACFC
Control
(½‐inch TSA)
2 63.5 58‐69 7.8 61.5
Very
good
Equal 1.47 1.44 0.096 Reject
AR‐ACFC
(¾‐inch TSA)
6 62.0 57‐68 3.9 61.0
Very
good
Equal 3.29 1.37 0.004 Reject
SMA
(¾‐inch TSA)
6 59.3 57‐64 2.5 58.7 Good Equal 6.38 1.37 0.000 Reject
PEM
(1¼‐inch
TSA)
6 56.5 53‐59 2.3 55.9 Good Equal 8.95 1.37 0.000 Reject
Table 16. Skid Performance of the I‐8 Wearing Course Sections.
Wearing
Course
Treatment
Sections
SN Student’s t Test Results
Mean Range Std.
Dev.
60th
%ile Cond. Variance t tcrit P
(t<tcrit)
Null
Hyp
P‐ACFC
(¾‐inch TSA)
6 63.2 62‐65 1.2 62.9
Very
good
– – – – –
AR‐ACFC
(¾‐inch TSA)
6 63.0 62‐65 1.3 62.7
Very
good
Equal 0.24 1.37 0.409 Accept
ACFC
(¾‐inch TSA)
6 62.7 62‐63 0.5 62.5
Very
good
Equal 0.96 1.37 0.181 Accept
SMA
(¾‐inch TSA)
6 61.5 59‐64 1.8 61.1
Very
good
Equal 1.93 1.37 0.041 Reject
PEM
(1¼‐inch
TSA)
6 60.7 58‐64 2.2 60.1
Very
good
Equal 2.49 1.37 0.016 Reject
AR‐ACFC
(½‐inch TSA)
Control
2
No
data
– – – – – – – – –
47
Table 17. Skid Performance of the SR 74 Wearing Course Sections.
Wearing
Course
Treatment
Sections
SN Student’s t Test Results
Mean Range Std.
Dev.
60th
%ile
Cond. Variance t tcrit P
(t<tcrit)
Null
Hyp.
P‐ACFC
(3/8‐inch TSA,
PG 76‐22+)
5 73.8 69‐81 4.4 72.7
Very
good
– – – – –
TB‐ACFC
(3/8‐inch TSA,
PG 76‐22 TR+)
6 73.3 67‐76 3.4 72.5
Very
good
Equal 0.20 1.38 0.424 Accept
AR‐ACFC
(3/8‐inch TSA,
PG 64‐16,
CRA‐1)
7 68.9 66‐71 1.7 68.4
Very
good
Equal 2.73 1.37 0.011 Reject
Since all wearing course sections exhibited SN values greater than 50 after eight years of service, they all
performed very well and any treatment can be used successfully to provide good skid resistance. A
closer examination of the results from both statistical and practical perspectives indicates the following:
 I‐10 site. Table 15 indicates that the skid performance of the P‐ACFC treatment was significantly
better than all the other treatments from a statistical standpoint. However, from a practical
standpoint, the ACFC and both AR‐ACFC treatments provided comparable skid performance. All
three treatments were grouped in the very good range. With SN values roughly 10 points below
the P‐ACFC treatment, the SMA