Pavement Maintenance IIPart 2: Rehabilitation Alternatives

Idaho Roads Scholar Program

Objectives

Review use of paving fabrics with thick AC overlays,

Explore thin hot mix overlays, Investigate cold in-place recycling, and Discuss full depth reclamation.

When to Rehabilitate?

Rough road, Excessive pavement distress, Loss of skid resistance, Excessive maintenance needs, Inadequate structure for planned

use.

Rehabilitation Alternatives

Thick overlay with paving fabric, Thin overlay, Cold in place recycle (CIR), Full depth reclamation.

Paving Fabrics

Paving Fabric Basics

Keeps water out of the base and subgrade

Provides support to retard reflection of existing cracks and distresses

Controls evaporation over the long-term, keeping uniform moisture content in the subgrade.

How does it work?

AC Overlay

Existing AC Pavement

Base or Subgrade

Fabric

Selection Considerations

Can provide strength up to equivalent of 1.0 inch of AC (if pavement is stable and fabric is properly installed)

Cost of fabric (based on DOT studies) is about the same as 0.5 inches of AC

Application Considerations

Not suitable for severely distressed pavements.

Generally not suitable where there is inadequate base/subgrade support.

Do not use where free water problems exist.

Construction Considerations Minimum overlay

thickness when using a fabric is 1.5 inches.

Major contributor to failure is lack of tack and/or uniformity of tack coat application.

Read manufacturer’s literature for detailed instructions.

Sample Products

3/8 inch3/8 inch

1/4 inch1/4 inch

1/2 inch1/2 inch

Overlay 1.5”

What is a “Thin” HMA Overlay?

Why Thin Hot MixOverlays?

Restores Serviceability Low Initial Cost & Life Cycle Cost Minimal Road User Delays/Impacts Adds Structure Reduces Noise

Treatment

Fog seal

Slurry seal

Chip seal

Thin HMA O’lay

Life, years

1 - 2

3 - 5

4 - 7

10 - 15

Cost ($/yd2)

0.25 - 0.35

0.85 - 1.00

0.90 - 1.20

2.50 - 3.50

Cost Comparison of Pavement Treatments

Construction Issues Structurally Sound Pavement Section Surface Preparation

Correct Localized Weak AreasClean Surface/Adequate Tack

LaydownTime Available for Compaction is

ReducedBreakdown Must Stay Close to Paver

Need a structurally sound pavement for compaction...

Correct localized areas...

Surface PreparationTack Coats Applied to bound surface Light application of asphalt emulsion

(0.03-0.07 gal/sy residual asphalt) Example materials

SS-1,1h CSS-1,1h

Tack Coat Application

Uniform application?

30

20

10

0

1 2 3 4

Tim

e av

ail.

for

Com

pac

tion

, min

Compacted Thickness, in

30F60F90F

30

20

10

0

Mix Temp. = 275F

Temperature is Critical

> 185ºF

Compaction-Lift/Layer Thickness

Thinner lift loses heat fast!

1/2 inch Dense Mixes 1 to 1 1/2 inch Thick Lift

3/8 inch Mixes 3/4 to 1 inch Thick Lift

½ inch Open Mixes 1 inch Thick Lift

Compaction Equipment

For all types of rollers, the primary compaction variables that can be controlled during the rolling process are:

Roller speed Number of roller passes Rolling zone Rolling pattern

Easy does it!

Thin Overlays: Rules of Thumb

Pre-level rutted areas Minimum lift thickness is 1 1/2” Roll while mix is hot (>185ºF) Minimum of 3 passes

Milling Machine Crusher

Mixer-Paver

Introduction to Cold In-Place Recycling

Advantages Reduced cost of construction Conservation of aggregate and binders Preservation of existing pavement geometrics Hauling Costs Minimized Minimal Air Quality Problems Conservation of energy Less user delay

Significant Structural Improvements Most Pavement Distress Treated Ride Quality Improved

Advantages for the Road

Primary Distresses

Equipment Train

Pulverize, Crush, Add and Mix Recycling Agent, and Place on Roadway

Single Machine

Pulverize, Add and Mix Recycling Agent, and Place on Roadway

Prepare Construction Area

Compact

Tack and Place Surface Course

Depth of treatment typically 3 to 4”.

Cold Milling Mill below depth of distress

(rutting, surface-initiated cracking)

Don’t leave “scabs” of HMA Avoid milling to within ½ inch

of layer interface

Cold In-Place Recycling TrainMilling Machine

Paver

Emulsion

Roller Recycler Tanker

Emulsion Tanker

Recycler

Single Machine

Curing and Compaction

Curing or Aeration Needed to Reduce Water and Volatiles

Delay Rolling or Blade the Mix Use Steel-Wheel, Pneumatic-Tired or

Vibratory Rollers; Use Heavy Pneumatic-Tired Roller for Breakdown

Achieve Optimum Compaction

Application of Wearing Surface

Additional Curing Needed to Avoid Moisture Retention

Apply Fog Seal, if Necessary, Before Allowing Traffic

Wearing Course: HMA Overlay or Double Surface Treatment

View before Recycling

View after Recycling

View before Recycling

View after Recycling (Good Condition)

View after Recycling (Poor Condition)Single Seal Coat

Final Considerations

Availability of Equipment Availability of Experienced Contractor First cost Life cycle cost

CIR?

Full Depth ReclamationConstruction Methods

and Case Study

Definition

Recycling method where all of

asphalt pavement section and a

predetermined amount of underlying

materials are treated to produce a

stabilized base course.

Advantages Pavement structure (especially poor base)

improved without significantly affecting pavement geometry,

Eliminates ruts, rough areas, and potholes and restores desired profile,

Eliminates alligator, transverse, longitudinal and reflection cracking,

Provides a uniform pavement structure.

Advantages (continued)

Frost susceptibility may be improved, Low production cost,

Conservation of materials and energy, No air quality problems.

Common Recycling Additives

Emulsified Asphalts (MS and SS) Portland Cement Lime Fly Ash Calcium Chloride Foamed Asphalt

Main Steps

Pulverize existing pavement, Introduce additive and mix, Shape the mixed material, Compact, Apply a wearing course.

Summary

FDR can improve pavement structure, restore profile and eliminate cracks.

Steps consist of pulverization, introduction of additive, shaping of mixed material and compaction.

Proper aeration of mix required.

Objectives

Review uses of paving fabrics, Explore thin hot mix overlays, Investigate cold in-place recycling, and Full depth reclamation.

Questions?

Rehabilitation