Crack and Seat Concrete Pavement Before an Overlay
Crack and seat is a way to prepare an old concrete pavement for an asphalt overlay. Equipment cracks each slab into smaller pieces, then a heavy roller pushes the pieces down so they sit firmly on the base. The cracked pavement still acts as a stiff layer, but the shorter pieces move less with temperature, so fewer cracks reflect up through the new asphalt.
Asphalt tonnage calculator →The problem: joint movement
Concrete slabs expand and contract with temperature and curl with moisture. On a long slab, that movement is concentrated at the joints. When asphalt is placed over the top, the joints keep moving and the overlay cracks right above them. See reflective cracking through an overlay.
How crack and seat works
- Repair badly failed areas and fix drainage.
- Crack the slabs with a guillotine-type drop hammer or similar breaker, producing pieces commonly about 1 to 3 feet across. The cracks should go through the slab without pulverizing it.
- Seat the pieces with a heavy pneumatic roller, often 35 to 50 tons, so none rock under load.
- Tack and overlay with asphalt, typically in more than one lift.
Crack and seat vs break and seat vs rubblization
| Method | Concrete type | Result |
|---|---|---|
| --- | --- | --- |
| Crack and seat | Plain jointed concrete | Medium pieces, slab still stiff |
| Break and seat | Jointed reinforced concrete | Steel ruptured or debonded, medium pieces |
| Rubblization | Any, often badly deteriorated | Small pieces, acts like a granular base |
Crack and seat keeps more of the concrete's stiffness than rubblization, so the overlay can be thinner. Rubblization removes slab action entirely and suits pavements in worse condition. A different approach is whitetopping, which puts concrete on top of asphalt.
Things that affect success
- Piece size: too large and joints still move; too small and the base loses stiffness.
- Seating: rocking pieces cause cracks and bumps.
- Overlay thickness: thicker overlays delay reflective cracks longer.
- Drainage: water in the cracks and base weakens the structure.
- Reinforcement: steel that is not broken keeps the pieces acting together.
Seating roller
A rubber tire roller is the usual seating tool because its heavy, pneumatic load presses each piece down without breaking it further.
Overlay example (made-up numbers)
A 12-foot lane, 3,000 feet long, gets a 4-inch overlay after crack and seat. Area is 36,000 square feet, or 4,000 square yards. At about 110 lb per square yard per inch, 4 inches is about 880 tons. See asphalt overlay cost and run your own numbers in the asphalt tonnage calculator.
Questions people ask
What is crack and seat?
A rehabilitation method for plain jointed concrete pavement: the slabs are cracked into smaller pieces, then a heavy roller seats the pieces firmly on the base before an asphalt overlay.
Why crack concrete before overlaying it?
Shorter pieces move less with temperature changes, so less movement is concentrated at old joints and fewer reflective cracks show through the overlay.
What size pieces does crack and seat produce?
Commonly pieces about 1 to 3 feet across, larger than the small rubble produced by rubblization.
What is break and seat?
The version used on reinforced concrete. The slab must be broken hard enough to rupture the steel or its bond, otherwise the pieces still act as one.
What roller seats the pieces?
A heavy pneumatic tire roller, often in the 35 to 50 ton range, pushes the cracked pieces down onto the base to eliminate rocking.
Does crack and seat stop reflective cracking completely?
No. It reduces and delays reflective cracking compared with a plain overlay, but some cracks can still appear, especially over thin overlays.
Related guides
- Rubblization
- Reflective cracking through an overlay
- Rubber tire roller
- Whitetopping
- Asphalt overlay cost
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