PAVEMENT MAINTENANCE IIPart 1b: Chip Seal Construction

IdahoRoads Scholar Program

Objectives Review how to set up a good chip

seal, Investigate equipment operation, and

field checks, Identify common problems and

possible solutions.

Field Checks

Weather/Surface Condition Traffic Control Aggregate Asphalt Asphalt and Chip Distributor Rollers Sweeping

Weather/Surface Condition

Dry or Damp Surface

Temperature Rain/Humidity

Wind

Surface Temperature

Proper Traffic Control is Essential!

Aggregate Requirements for Successful Seal Coat

Must be clean. Less then 1% passing #200 sieve.

Cubical chips are better then flat chips.

Must be crushed. At least 2 crushed faces.

More single sized the better.

Dirty Chips

> 1% passing the #200 sieve Impedes the ability of binder to

bond chip to roadway. Limits amount of binder that can

be applied. Creates dust after sweeping.

Aggregate Condition

Emulsions => Damp Surface

Asphalt Cement => Dry Surface

Can only glue down a single layer of chips.

Must have chips at least 60 to 70% embedded to withstand traffic and snow plow damage.

Should see emulsion at top of chips before emulsion breaks.

Chip Considerations

Which are the better chips?

Distributors

Asphalt Distributor Components

Nozzles

Spray Bar Height

Application Rate

Product Temperature

Nozzle Angle

Spray Bar Height

Triple Coverage

Test Shot

Apply Asphalt Product for Known Distance & Width

Calculate Amount of Applied Asphalt Product

Calculate Spread Rate

Product Temperature

Typically 140 to 185oF

Check At Distributor

Common Emulsion: CRS-2P

Develops strength in hours that normally take days.

Sweep same day. Requires clean chips. Must place chips within one minute

of placement of binder. Eliminates bleeding

Higher softening point

Sample Asphalt Product

Sample Location Truck or Trailer Nozzle

Sample Container 1 Gallon Plastic w/Lined

Screw Cap, Wide Mouth

Chip Spreaders

Chip Spreader Issues

Correct Application Rate

Uniform Application Rate

Test Shot to Insure Correct Application Rate

Apply aggregate for known distance and width

Calculate Amount of Aggregate

Calculate Spread Rate

Check Rollers

Type

Weight

Speed

Rolling

Best Pneumatic-Tire Roller

Buns Up: Check Embedment

Factors Affecting Breaking and Curing Weather Conditions:

temperature, humidity, wind Water Absorption Aggregate moisture content:

although wet aggregate may facilitate coating, it tends to slow the curing process

Mechanical forces: roller pressure forces water from mix

Surface area: excessive fines or dirty aggregate accelerate breaking

Surface chemistry

Broom

Safety

Approved Vests

Communication

Eye Contact

Typical Problems

Streaked Appearance Bleeding/Flushing Loss of Cover Aggregate Bad Centerline Joint Utilities/New Patches Tight Alignment or Steep Grades Heavy Tree Canopy Fall Weather

Common Chip Seal Problems

Rules of Thumb for Seal Coats• Make sure pavement is clean• Use high quality materials• Proper application rate for binder• Proper application rate for aggregates.

Extra aggregates only cause failure.• Keep distance between the distributor

and the chipper to minimum. Aggregate must be placed before emulsion starts to break.

Rules of Thumb for Seal Coats, cont.

Minimum of three rollers. Keep speed under 5 mph. Compaction must be completed before emulsion is broken.

Final sweeping of roadway as soon as possible. No later then the next morning.

Remember that Details count.

Questions?

Chip Seals