Pavement Maintenance II Part 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 Samples available to pass around for your information.

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. When it comes to maintaining pavement, it’s generally considered a good idea to keep the water away. Remember that from the Drainage: Key to Roads that Last class? Since the late 60’s paving fabrics have been used in hot mix overlay systems to reduce or delay the rate of reflective cracking through a new overlay. Used to be thought that the fabric was only good for a stress-relieving interlayer--that is, it would retard reflective and fatique crakcing Now paving fabrics are viewed as an effective means to waterproof the system.

How does it work? AC Overlay Existing AC Pavement Base or Subgrade Fabric Existing AC Pavement Typically, a levelling course is placed followed by at tack coat of about 0.25 gal/sy of hot asphalt cement tack coat onto the surface. The non-woven fabric is then placed on the tack coat and a HMA overlay is placed on top of the fabric. The heat and pressure activate the asphalt tack coat, drawing it up into the fabric and bonding it to the overlay. The resultant interlayer is fairly thick asphalt-saturated fabic reinforced layer. The layer forms a waterproofing membrane and a stress absorption layer. Base or Subgrade

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. With severly distressed pavements--difficult to get good bond. When using where water is a problem, water may come up through the base and be absorbed into the fabric. Remember capillary action in soils? The wet layer then saturated the AC and stripping (separation of the asphalt from the rock) can occur. Problem with silt and clay subgrades.

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 Petromat: nonwoven paving fabric, installed in combination with an asphalt cement tack coat Petrotac: A nonwoven paving fabric that is pre-saturated with asphalt cment at the factory. The product is self adhesive. Frequently used to waterproof bridge decks prior to paving with asphalt. Pro-Guard: a high strength strip membrane that has tow layers on fabrics which sandwich a layer of asphalt cement product. The product is installed over large, filled cracks where additional strength is desired. The product requires an asphalt cement tack coat base be installed prior to placement. Petro-Grid: Geocomposite paving fabric manufactured with a standard Petromat layer and a layer of Fiberglass grid bondd together. The Petromat forms the waterproofing layer while the Fiberglass provides extremely high tensile strength reinforcement to the paving section.

What is a “Thin” HMA Overlay? 3/8 inch 1/4 inch 1/2 inch What is a “Thin” HMA Overlay? Overlay  1.5” A thin overlay is typically considered an overlay less than or equal 1.5”.. Some consider this type of overlay more of a surface treatment in that it restores friction and seals up a pavement but it does also provide some structure which should also contribute to the life of the pavement.

Why Thin Hot Mix Overlays? Restores Serviceability Low Initial Cost & Life Cycle Cost Minimal Road User Delays/Impacts Adds Structure Reduces Noise Thin overlays significantly improved pavement smoothness after treatment. Can also level ruts, fill cracks and patches and provide structure. Compared to chip seals and slurry seals that generally only fill cracks and cover patches.

Cost Comparison of Pavement Treatments 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 Here is a summary of costs for some of the surface treatments that have been discussed. Each agency must determine which treatments are the most cost effective for their particular applications.

Construction Issues Structurally Sound Pavement Section Surface Preparation Correct Localized Weak Areas Clean Surface/Adequate Tack Laydown Time Available for Compaction is Reduced Breakdown Must Stay Close to Paver

Need a structurally sound pavement for compaction... Confinement isn’t so easy in the field. When compacting a mat, confinement from the bottom comes from whatever base is under the mat; that base must be stable. If the section is not structurally sound, there is nothing to compact against and even a thin overlay will not reach optimum compaction.

Correct localized areas... Good preparation is one key to success.

Surface Preparation Tack 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 Diluted 1:1?

Tack Coat Application Look for good uniform coverage...

Uniform application?

Refer back to Joel’s talk about inspecting the spray bar… All nozzles set at the same angle. Proper overlap to prevent ridges from forming.

What role does compaction play in producing good quality asphalt pavement? Compaction accomplishes three things: First, it packs the aggregate into a strong, highly stable arrangement which increases the number of particle contact points. Second, compaction reduces the air voids to about 5% to keep the mix stable and impermeable to air and water. Third, it provides a smooth surface that gives a superior ride and increases pavement life.

The correct temperature range for compaction is typically between about 185 degrees F and about 300 degrees F. The most efficient temperature will probably be at the upper, hotter and of this range; here the asphalt cement acts more like a lubricant and the aggregate becomes easier to pack into a dense fit. New asphalts allow for compaction at lower temperatures so will need to fit the situation, however, 185F is a good bottom temp.

Mix Temp. = 275F 90F 60F 30F 30 20 10 30 20 10 Time avail. for Compaction, min Assume minimum AC temp is 180 degrees. Note that for an 1 1/2 inch layer, for air temperature of 60F, there is only 10 minutes to get compaction. Also, depends some on mat temperature, humidity and wind. Point--thin lifts less time. 1 2 3 4 Compacted Thickness, in

Temperature is Critical One of the most important factors is the mat temperature. Too cold and the mix cannot be compacted - too hot and the mix will not support the rollers. What temperature should the mix be at behind the paver? 240F > 185ºF

Compaction-Lift/Layer Thickness 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 2X nom maximum size is the minimum. Thinner lift loses heat fast!

BE SURE TO USE A MIX THAT IS FINE ENOUGH TO PREVENT EXCESSIVE DRAGGING OF THE SCREED ON THE COARSE AGGREGATE. NORMALLY THAT REQUIRES D OR C MIX.

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

Joints are critical areas which often suffer from poor compaction Joints are critical areas which often suffer from poor compaction. It takes a lot of cooperation between the paver operator, the rakers, and the roller operator to get a good joint. Studies show that longitudinal joints, unless paved in echelon, normally show a lower density on the cold side of the joint because the cold side lacked edge confinement during compaction. However, the cold side confines the hot side of the joint, creating a higher density on the hot side.

Pinch from the hot side of the mat.

“Easy Does It” is a good technique to keep in mind when starting, stopping, and turning on the mat. Start and stop slowly and smoothly. Change directions and steer gradually and only while the roller is still moving. “Easy Does It”. Don’t over compact!

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

Introduction to Cold In-Place Recycling Milling Machine Crusher Mixer-Paver This slide shows a photo a cold in-place recycling operation. Page 1-6 Many options for pavement recycling including RAP--ODOT allows no more than 30% RAP in most of their HMAC. Hot in place Recycling: soften the asphalt with heat, scarify it and then mix it with a recycling agent and lay it down like a conventional mix. Good for surface type distresses not caused by structure like raveling, oxidation, etc. Cold Recycling--can be done at a plant or what we are talking about here where it is done in place.

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 Recycling of asphalt pavements has many advantages, such as: (1) Reduced cost of construction, (2) conservation of aggregate and binders, (3) preservation of existing pavement geometrics, (4) preservation of environment, (5) conservation of energy, and (6) less user delay, particularly for in-place recycling. Page 1-1

Advantages for the Road Significant Structural Improvements Most Pavement Distress Treated Ride Quality Improved The primary benefits of cold in-place recycling include significant structural improvement by improving the existing pavement materials, treatment of most types of pavement distress, and improvement of ride quality. Also, in this procedure, hauling cost is minimized, air quality problem (smoke or fumes) is minimized since no heat is applied, and widening of the existing pavement is possible. Page 3-9

Primary Distresses The main types of pavement distress consist of surface distress (raveling, bleeding), deformation (corrugation, rutting), and cracking (alligator, transverse cracks). Page 1-7

Prepare Construction Area Compact Equipment Train Pulverize, Crush, Add and Mix Recycling Agent, and Place on Roadway Prepare Construction Area Compact Single Machine Pulverize, Add and Mix Recycling Agent, and Place on Roadway In the cold in-place recycling method, all existing pavement materials are used along with a recycling agent. Recycling agent is typically an emulsion or emulsified recyling agent. The depth of treatment is typically from 3 to 4 in. Can go deeper if other chemicals are added like PCC, lime or fly ash are used to improve the early strength gain and resistance to moisture damage. The RAP is sized if needed. RAP is run through a screen and resized if needed. The mix is placed and compacted with conventional HMA equipment. Page 3-9 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 Train Emulsion Milling Machine Paver This slide shows a cold in-place recycling train. Generally, the train consists of milling machine, crusher, and mixer-paver. Definitely a large system for an urban type system…but there are other options.

Roller Recycler Tanker This slide shows a schematic of a recycling machine used with emulsion tanker. In the case of a single machine with emulsion tanker, the single machine mills the existing pavement, injects emulsion and mixes the emulsion with RAP. The milled and mixed material is then laid down with a screed. Page 1-5

Single Machine Emulsion Tanker Recycler Single units do not contain screening and crushing units, making control of the maximum particle size more difficult. Most single unit trains are capable of producing uniform RAP with a maximum size of 2 inches. The size can be controlled by the forward speed of the machine--reducing the speed results in a finer RAP. Pavements that are badly alligator cracked, make controlling the maximum particle size difficult. A spray bar in the cutting chamber adds the liquid recylcing additive. Single units provide the lowest degree of process control because the recycling additive application rate is not directly linked to the treatment volume. Roadways that are badly distorted due to rutting, edge drop-off, etc. are not good candidates for CIR with the single unit because proper recycling additive application rate would be difficult to ensure. Dry additives can be added by just placing it on the pavement prior to milling. One pass of the single unit is sufficient to adequately pulverize and mix all ingredients. Advantages: Simple operation, high production capacities.

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 Curing and compaction are needed in CIR operation. Curing is needed to reduce water and volatiles in the mix. The rolling can be delayed or the mix can be bladed to aerate the mix. For compaction, heavy pneumatic tired rollers are used for breakdown. After that, steel wheel or pneumatic tire roller can be used. The rolling should be such as to achieve optimum compaction in the mix. Page 12-4

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 Before the application of wearing surface, additional curing is needed to avoid trapping of moisture. A fog seal may be applied, if necessary before allowing traffic. As wearing course, a HMA overlay or double surface treatment may be used. Page 12-4

CIR Examples Let’s look at some examples...

This slide shows a view of the pavement before recycling. Milled to 3 inches. A MS-2 emulsion was used as the recycling agent. View before Recycling

The recycled mix was laid through a screed to give a compacted base course of 5 in thick. After allowing traffic on it for a couple of weeks, a 1.5” AC lift was placed as a wearing surface. View after Recycling

Milled and recyled to 3 in deep. CSS-1h was used as the recycling agent. View before Recycling

View after Recycling (Good Condition) Wearing surface was a single chip seal. After three winters, however,... View after Recycling (Good Condition)

View after Recycling (Poor Condition) This slide shows a pavement section in poor condition after CIR. A single seal coat was used in this section. Since a CIR mix is not adequately water resistant, a single coat may not be adequate to protect it, and potholes can develop after the loss of the seal coat. At least a double seal coat must be used in CIR jobs. Page 2-20, 2-23 View after Recycling (Poor Condition) Single Seal Coat

Final Considerations Availability of Equipment CIR? Availability of Equipment Availability of Experienced Contractor First cost Life cycle cost The final selection of a rehabilitation alternative should depend upon availability of equipment, availability of experienced contractor, first cost, life cycle cost. Page 3-7, 3-8

Full Depth Reclamation Construction Methods and Case Study The objective of this session is to discuss the construction methods and equipment for Full Depth Reclamation (FDR).

Definition Recycling method where all of asphalt pavement section and a predetermined amount of underlying materials are treated to produce a stabilized base course. FDR is defined as recycling method where all of asphalt pavement section and a predetermined amount of underlying materials are treated to produce a stabilized base course. Page 16-1

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. The major advantages of FDR are that 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. The other advantages are that frost susceptibility may be improved, low production cost, conservation of materials and energy, no air quality problems. Page 16-1

Common Recycling Additives Emulsified Asphalts (MS and SS) Portland Cement Lime Fly Ash Calcium Chloride Foamed Asphalt The commonly used recycling additives are emulsified asphalts, Portland cement, lime, fly ash, calcium chloride, and foamed asphalt. Pages 16-8, 16-11.

Main Steps Pulverize existing pavement, Introduce additive and mix, Shape the mixed material, Compact, Apply a wearing course. The main steps in FDR consist of: pulverization of existing pavement, introduction of additive and mix, shaping the mixed material, compaction and application of a wearing course. Page 16-2

Milled the existing surface with a CMI RS-650 pulverizer Milled the existing surface with a CMI RS-650 pulverizer. The equipment is capable of pulverizing to a depth of 10 inchesand can cover 4000 feet of a 24-foot road in a day.

The pulverizer breaks the AC into pieces smaller than two inches and mixes them with the existing base.

Following the pulverizing, the material was compacted and traffic was allowed back on.

In some cases, they were pulverizing one lane while traffic was running in the adjacent lane.

On one of the sections that was reclaimed, material was removed to make room for a 4-inch AC overlay. Curb and gutter section.

The second day, the contractor added cement to the base material which was mixed in to a depth of 6 to 8 inches) depending on the pavement design. The base material was then watered and greded. And last, a 4-inch AC wearing course was placed . On other projects, the County has placed a chip seal for a wearing surface.

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. FDR can improve pavement structure, restore profile and eliminate cracks Steps consist of pulverization, introduction of additive, shaping of mixed material and compaction. Usually proper aeration of mix required before the application of overlay. Page 16-14

Objectives Review uses of paving fabrics, Explore thin hot mix overlays, Investigate cold in-place recycling, and Full depth reclamation. We will be discussing preventive maintenance techniques for both AC-surfaced pavements (including asphalt overlays of concrete pavements) and PCC-surfaced pavements. Listed here are the preventive maintenance techniques for AC pavements that we will be discussing. Note that many of these treatments are also rehabilitation treatments, but we will be discussing them as potential preventive maintenance treatments.

Questions? Rehabilitation