CONCRETE OVERLAYS NORTH CAROLINA

OCTOBER 2014

Gary Fick

Overlay Guide

• 1st Edition – 2007 • 2nd Edition – 2008 Added “Managing

Concrete Work Zones Under Traffic”

• 3rd Edition – published May

2014 • http://www.cptechcenter.org

/technical-library/documents/Overlays_3rd_edition.pdf

Overlay Guide

• What’s New? 1. Coring the existing pavement is mandatory

Overlay type

Construction traffic and maintenance of traffic

2. Identify and quantify all vertical constraints – design to mitigate the impact

3. Geotextiles are well suited as separation layers – added materials and construction recommendations

4. Reduce plan sets to simplify the project

Overlay Guide

• What’s New (cont’d.)? 5. Maintenance of traffic (staging)

State the criteria

Allow the contractor to stage and innovate

6. Structural fiber reinforcement

CONCRETE OVERLAYS - INTRODUCTION

• Vast experience and performance history in the U.S.

• Different overlay types for existing pavement types

• Robust solutions to fit project needs (short-medium-long term)

• Versatile solutions to fit varying facility types

Concrete Overlays - Introduction

• 1,152 concrete overlays in the U.S., dating from to 1901 through 2012

• Concrete overlays have been successfully constructed in 45 different states

OVERLAYS COMPRISE 14% OF MARKET!

117,380,000

17,070,000

Square Yards in '09 and '10

Full Depth Concrete

[Source: Oman and ACPA]

ADOPTION OF BONDED VS. UNBONDED

Based on over 1,000 concrete overlays from NCHRP Synthesis 99, NCHRP

Synthesis 204, and ACPA’s National Overlay Explorer

(by number of projects)

HISTORICALLY, MOSTLY ON CONCRETE

… BUT MORE AND MORE ON ASPHALT

7,000450,000

1,200,000

5,456,100

3,226,700

Total by 1993

Total by 1999

Total by 2004

2009 2010

Square Yards, Thin Overlays

THIN (< 6 in.) CONCRETE OVERLAYS IN THE U.S.

SYSTEM OF CONCRETE OVERLAYS

Concrete Overlays

Concrete

Pavements Asphalt

Pavements Composite

Pavements

Bonded Overlay System

Concrete

Pavements Asphalt

Pavements Composite

Pavements

Unbonded Overlay System

Bond is integral to design Old pavement is subbase

CONCRETE OVERLAYS - INTRODUCTION

• Intersections • “Gateway Drug” for many DOTs

• Rural secondary roads • Midwest “farmer special”

CONCRETE OVERLAYS - INTRODUCTION

• Urban arterial • “Get in and Stay Out”

CONCRETE OVERLAYS - INTRODUCTION

• Rural primary/interstate • “Paver’s Dream”

CONCRETE OVERLAYS - INTRODUCTION

Concrete Overlays - Introduction

• Urban freeway/interstate • “Transformer”

85,000 AADT

THE WHEN IS IMPORTANT… Restoration

Resurfacing Reconstruction

EVALUATION OF EXISTING PAVEMENTS AND SELECTION OF OVERLAY TYPE

•Determine existing pavement type and condition – coring is mandatory

•Identify and quantify all constraints •Analyze pre-overlay repairs and bonded vs.

bonded •Determine appropriate overlay type – bonded

or unbonded •Proceed to design phase

• Vertical and horizontal constraints need to be identified in the pavement evaluation

Existing structures

Overhead clearances – overpasses, signs and utilities

Barrier rails

Existing cross-slope variability and new cross-slope requirements

Drainage structures

Existing foreslopes

Intersections, driveways and field entrances

IDENTIFY AND QUANTIFY CONSTRAINTS

EXPECTATIONS… • How much will it cost? Why? Because our budget is

fixed How long do you need it to

last?

• Thickness, cost and

service life are interrelated

Thickness

Cost

Service Life

Traffic Loading

2010 OVERLAY COST SURVEY • Based on 33 project in 6 states in 2009 • Includes concrete, placing overlay, and jointing • Excludes pre-overlay repair and sep. layer (if used)

http://www.cptechcenter.org/t2/documents/OverlayCosts-Fick.pdf

TYPES OF CONCRETE OVERLAYS Bonded Unbonded

2” – 5” 4” – 11”

BONDED OVERLAY OF ASPHALT OR COMPOSITE PAVEMENTS

2”–5” thickness

Existing pavement condition Fair or better structural condition with surface distress Applications •To eliminate surface defects such as rutting and shoving

•Improve surface characteristics like friction, noise, and rideability

•To increase structural capacity where traffic loads dictate

FEASIBILITY FOR A CONCRETE OVERLAY ON ASPHALT

• HMA pavements with some structural integrity

­ Limited structural (fatigue) cracking

­No stripping/raveling in HMA layers

­HMA thickness after milling - 3 in minimum

• Rutting in HMA layers ok

PURPOSE OF ASPHALT MILLING FOR BONDED CONCRETE OVERLAY

Remove distortions of 2” or more

Reduce high spots to insure minimum overlay depth

Match adjacent lanes

Enhance bond

Meet vertical elevation requirements

Restore profile

KS I-70 – 6x6’x6”x30 Miles!!

PCC JOINT SAWING CRITICAL • Effective curing • Timely joint sawing

• Can be the controlling factor for overlay placement rate

BONDED OVER ASPHALT/COMPOSITE KEYS TO SUCCESS

Bonding is critical

Small square panels reduce curling, warping, & shear stresses in bond.

Mill to remove surface distresses, or improve bonding.

Be sure to leave 3” of HMA after milling.

Joints in the overlay should not be placed in wheel paths, when possible.

Application of curing compound is critical.

TYPES OF CONCRETE OVERLAYS Bonded Unbonded

2” – 5” 4” – 11”

USES AND ADVANTAGES - UNBONDED OVERLAY OF CONCRETE PAVEMENTS

•Use when existing pavement is in poor or worse condition, including with material-related distress such as D-cracking, when underlying pavement and subbase are stable and uniform except for isolated areas that can be repaired.

•Use to restore structural capacity of the existing pavement and increase pavement life equivalent to full-depth pavement.

4” - 11” thickness

UNBONDED OVERLAYS CAN BE PLACED OVER DETERIORATED

CONCRETE PAVEMENTS

EXISTING CONCRETE AND ITS SUBBBASE MUST PROVIDE:

Uniform support

Construction platform

UNBONDED CONCRETE OVERLAY ON CONCRETE

SEPARATION LAYER

• Required for good performance ­ Isolate overlay from existing distress

Prevent reflective cracking

Provide cushioning

Allow for drainage ­ Provide construction platform for

overlay construction

• Recommended separation layer material: ­ HMA ­ Geotextile fabric

GEOTEXTILE SEPARATION LAYER (INTERLAYER)

Minimize turning movements avoid wrinkles

UNBONDED OVERLAY OF CONCRETE PAVEMENTS: KEYS TO SUCCESS

•Full-depth repairs - only where structural integrity is lost at isolated spots.

•Separation layer (normally 1” asphalt or geotextile fabric)

•Use to restore structural capacity of the existing pavement and increase pavement life equivalent to full-depth pavement

•Shorter joint spacing helps minimize curling and warping stresses

•No need to match joints with those of the underlying concrete pavement

Maintenance of Traffic (MOT)

• Depends on concrete overlay thickness If edge drop-off criteria is exceeded, then MOT

is just like full depth PCC reconstruction Otherwise, similar to MOT for asphalt projects

• Options include: Construction adjacent to traffic (lane at a time)

Positive separation or cones

Pilot car operation for two lane roadways

Crossovers and construct full width Staged intersections or full closure with

accelerated opening (48 to 72 hr) • All concrete overlays are accelerated construction!

US-69 Adjacent to Traffic

• Four lane divided • One lane at a time • Adjacent to traffic

US 18 Single Lane Paving With

Through Traffic

Traffic Shift

Centerline Safety Wedge

WHAT HAVE WE LEARNED?

• Concrete overlays can be a solution for all types of existing pavements

• Long history of proven performance

• Nothing magic about it: same materials, similar construction, jointing and curing are important.

QUESTIONS?

THANK YOU!