This document discusses concrete overlays as a proven resurfacing strategy. It provides an overview of different types of concrete overlays, including bonded and unbonded overlays of concrete and asphalt pavements. Data is presented on the performance and longevity of concrete overlays constructed in Iowa over several decades, with many showing excellent performance up to 40 years. Thicker overlays and shorter joint spacings are associated with better performance. Overall, concrete overlays are shown to be a highly effective resurfacing solution with a expected service life of 30-40 years for Iowa's highway network.

1. CONCRETE
OVERLAYS
A PROVEN RESURFACING STRATEGY
Gordon Smith, P.E.,
Associate Director
National CP Tech Center

2. 40th
Annual Concrete Paving
Workshop
January 22, 2019
Lincoln, Nebraska

6. Highway agencies and industry are responding
with new ideas about building and modernizing
today’s pavement networks.
CHANGE IS ALL AROUND
US

7. NEW LIFE FOR AGING PAVEMENTS

8. Preservation Resurfacing Overlays Reconstruction
Preservation Mode!Preservation Mode!
$ $

9. SO, WHAT ARE WE DOING
ABOUT IT?
WE’RE WORKING IN PARTNERSHIP TO
DEVELOP STRATEGIES AND
GUIDELINES FOR PROJECT SPECIFIC,
COST EFFECTIVE CONCRETE
SOLUTIONS.

10. CONCRETE OVERLAYS FOR
EVERY NEED!
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15. WT BOL UBOL
Secondary 1177.6 88.4 490.5 1756.5
Primary 81.8 52.7 160.7 295.2
1259.4 141.1 651.2 2051.7
miles
Municipal 300,000 SY
(approximate)
Airport 739,840 SY
(24 Runways)

17. CONTENTS
1. Overview of Overlay
Families
2. Overlay Types and Uses
3. Evaluations & Selections
4. Six Overlay Summaries
(11”x17 “sheets)
5. Design Section
6. Miscellaneous Design
Details
7. Overlay Materials Section
8. Work Zones Under Traffic
9. Key Points for Overlay
Construction
10. Accelerated Construction
11. Specification Considerations
12. Repairs of Overlays

18. CONCRETE OVERLAYS
Bonded
Concrete
Overlay of
Concrete
Pavements
Bonded
Concrete
Overlay of
Asphalt
Pavements
Bonded
Concrete
Overlay of
Composite
Pavements
Bonded Overlay System
Unbonded
Concrete
Overlay of
Concrete
Pavements
Unbonded
Concrete
Overlay of
Asphalt
Pavements
Unbonded
Concrete
Overlay of
Composite
Pavements
Unbonded Overlay System
Thinner Thicker
BOND IS INTEGRAL TO DESIGN OLD PAVEMENT IS BASE

19.  Not a new design procedure!
 Background of recommended
overlay design techniques
 Detailed examples of how to
use the existing design
methodology
 Learn by example – then apply
for your situation!
 http://www.cptechcenter.org

21. Check Out
PavementDesigner
Pavement Design Simplified
for:• Streets and Roads
• JPCP
• RCC
• CRCP
• Overlays
• Parking Facilities
• Intermodal Yards
FREE Pavement
Design Program

22. NATIONWIDE CONCRETE
OVERLAYS GROWTH
As of: November 2017

23. CONCRETE OVERLAYS IN THE USA
 National perspective
 ACPA overlay project explorer:

25. IOWA’S HISTORY OF CONCRETE OVERLAY PERFORMANCE

26. ACKNOWLEDGEMENTS
 Full Report: Performance of Concrete Overlays in
Iowa
 Phase I of Iowa Highway Research Board TR-689
 Project Team:
 CP Tech Center: Jerod Gross, Dale Harrington, Dr.
Peter Taylor
 Iowa State University: Yu-An Chen, Dr. Halil
Ceylan, Inya Nnelanya, Dr. Omar Smadi

27. CONCRETE OVERLAYS IN IOWA
 Iowa: over 2,000 centerline miles of concrete
overlays have been constructed since the late ‘70s
 Over half constructed since 2005
 Mostly on county highway system

28. PROJECT BACKGROUND
 How well have Iowa’s overlays
performed? (How long do they last?)
 Approximately 470/506 overlay
projects are still in service today
 Includes 68/96 constructed before
1990
 Compare to older sources that
indicate expected service life for a
concrete overlay is only about 20
years Dallas County, IA, Constructed 1977

29. PROJECT BACKGROUND
 However, as of 2015, there had been no attempt to
characterize performance of overlays to determine
expected service life & what made projects successful
Dallas County, IA, Constructed 1992

30. PROJECT OBJECTIVES
 Define performance of Iowa’s concrete overlays
 Create performance curves
 Analyze specific design choices and characteristics and
link to performance
 Overlay type (thin bonded, unbonded)
 Thickness
 Joint spacing
 Traffic
 Incorporate lessons learned to improve overlay design and
performance

31. DATA COMPILATION & COLLECTION
 Automated pavement condition
data: Iowa Pavement Management
Program (IPMP)
 Opt-in program for local agencies
 Data collection began in early
2000s (opt-in)
 Since 2013, all streets & roads
are covered every other year
 This data then combined with
ICPA overlay project records to
produce the complete data set

32. OVERLAY TYPES
 Bonded Concrete Overlay of Concrete (BCOC)
 Bonded Concrete Overlay of Asphalt (BCOA)
 Defined as thickness ≤ 6 inches
 Unbonded Concrete Overlay of Concrete (UBCOC)
 Unbonded Concrete Overlay of Asphalt (UBCOA)
 Defined as thickness > 6 inches

33. DATA DISTRIBUTION
 Typical designs in Iowa
 Early on: 6 inches on asphalt
(“whitetopping”) or 6+ inches
unbonded on concrete
 Performance data for
projects up to 40 years old
Washington County, IA, Constructed 1977

34. DATA DISTRIBUTION
 Typical designs in Iowa
 ‘00s: more types of
projects, including
thinner overlays
 Advent of new design
procedures, shorter slabs,
fiber-reinforcement
 About 10 years worth of
data, with some
exceptions
Boone, IA, Constructed 2005

35. DATA DISTRIBUTION
 Full data set contains all overlay types/designs:

36. 36

37. DATA DISTRIBUTION
 Distribution based on slab thickness:

38. 38

39. 39

40. PERFORMANCE METRICS
 Performance characterized by PCI (Pavement Condition Index) & IRI
 IPMP PCI equation incorporates:
 IRI (accounts for 40% of PCI)
 Transverse Cracking
 Joint Spalling
 D-cracking
(no faulting)
Le Mars, IA, Constructed 2010

41. PERFORMANCE METRICS
 Performance charts:
 PCI scale:
 Excellent: 81-100
 Good: 61-80
 Fair: 41-60
 Poor: 21-40
 Very Poor: 0-20
Image: Pavement Interactive

42. RESULTS AND ANALYSIS
 PCI vs. Age (data set as a whole):
Figures: Chen and Ceylan

43. PCC OVERLAY PERFORMANCE
PCI (Ages 0-37 years)

44. PCI (Ages 21-30 years)
44

45. RESULTS AND ANALYSIS
 PCI vs. Age - BCOA only (organized by thickness):
Figures: Chen and Ceylan

46. RESULTS AND ANALYSIS
 PCI vs. Age - BCOA only (organized by joint spacing):
Figures: Chen and Ceylan
Short slab designs

47. RESULTS AND ANALYSIS
 PCI vs. Age - UBCOA only (organized by thickness):
Figures: Chen and Ceylan

48. RESULTS AND ANALYSIS
 PCI vs. Age - UBCOC only (organized by thickness):
Figures: Chen and Ceylan

49. RESULTS AND ANALYSIS
 IRI vs. Age (data set as a whole):
Figures: Chen and Ceylan
~40 years to IRI = 170

50. 50
PCC OVERLAY PERFORMANCE
IRI (Ages 0-37 years)

51. IRI (Ages > 30 years)
51

52. RESULTS AND ANALYSIS
 Key findings and trends:
 Overall performance of Iowa’s concrete overlays has been
excellent
 As a whole: about 35 years to PCI = 60
 About 40 years to IRI = 170 in/mi
 Good performance from each of BCOA, UBCOA & UBCOC
 Overlays of asphalt slightly better than UBCOC
 BCOC less successful overall, but performed well in context of
design life expectations

53. RESULTS AND ANALYSIS
 Key findings and trends:
 Thickness
 In general: thicker overlays have performed better for all overlay
types (e.g. for BCOA, 6” > 5” > 4”)
 Transverse joint spacing
 Good early performance from short slab designs (6”) on BCOA/thin
overlays
 Older designs with 15-20 foot slabs performed well long-term
 12 foot slabs—inconclusive
 Traffic—inconclusive
 Most of these projects are low-volume, <1,000 vpd
 Not enough truck traffic data available from local agencies

54. RESULTS AND ANALYSIS
 12 foot transverse joint spacing
 Across multiple splits, apparent decline in performance of
overlays with 12 foot joint spacing (even compared to
longer spacings)
 UBCOA (organized by joint spacing):
Figures: Chen and Ceylan

55. FIELD REVIEWS
 Field reviews were performed to:
 supplement data analysis
 verify findings
 investigate trends, outliers
Pottawattamie County, IA, Constructed 1993

56. FIELD REVIEWS
 Observed distresses:
 Materials-related
Pottawattamie County, IA, Constructed 1999

57. FIELD REVIEWS
 Observed distresses:
 Rough ride—construction or curling/warping
 Occasional faulting
Buchanan County, IA, Constructed 1996

58. FIELD REVIEWS
 Observed distresses:
 Load-related, possibly mis-designed
or under-designed
Dallas County, IA, Constructed 2006

59. FIELD REVIEWS
 Key takeaways:
 Observed performance generally matches data
 Poor performing outliers & early failure causes:
 Materials-related
 Load-related/under-design
 Rough ride
 In short... mostly the same issues that we run into with
conventional PCC pavements
 Be aware of increased potential for curling/warping
 Beyond above explanations, no direct observations to indicate that
there’s a specific problem with 12 ft joint spacing design

60. CONCLUSIONS
 Overall performance of Iowa’s concrete overlays has
been excellent
 Upwards of 30-40+ year performance life
 Overlays are very well-suited to county highways
 Good success to date on interstate, state highways, and
city streets as well

61. NEXT STEPS
 Move from performance history → survivability, performance
models
 Continue compiling data, keeping the database updated
Le Mars, IA, Constructed 2017

62. CONCRETE OVERLAY ON AN ASPHALT
MUNICIPAL STREET IN LOMBARD, IL
(2003)

63. I-70 @ GRAND JUNCTION,
CO.

64. RURAL ROAD IN MITCHELL
COUNTY, IOWA

65. NORTHBOUND US 81 NEAR STRANG AND BELVEDERE, NE
8” UNBONDED PCC OVERLAY (1982 AND 1984)
65

66. US 30 BETWEEN LEXINGTON AND COZAD, NE
5” UNBONDED OVERLAY OVER ASPHALT OVER OLD
PCC (2015)
66

67. A 6-INCH UNBONDED OVERLAY OVER FULL-DEPTH HMA
PLACED IN 2010 IN PIERCE COUNTY ON 556TH
STREET
JUST NORTH OF NORFOLK, NEBRASKA
67

68. CELEBRATING 50 YEARS OF LEADERSHIP AND SERVICECELEBRATING 50 YEARS OF LEADERSHIP AND SERVICE
I-70I-70
Western KansasWestern Kansas
6x6x6 Concrete Overlay6x6x6 Concrete Overlay
THIS ISTHIS IS
RESURFACING!RESURFACING!

70. Grundy County, IA, Constructed 1978
www.cptechcenter.org