Rubblization: Breaking Concrete Pavement for an Overlay

Rubblization turns an old concrete road into the base for a new asphalt road without hauling the concrete away. Special breakers pulverize the slab in place into small, tightly fitting pieces. The broken layer is rolled and then covered with asphalt. Because the concrete no longer acts as slabs with joints, cracks have nothing to reflect from.

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Why it is used

Old jointed concrete pavements often fail at the joints. Overlaying them with asphalt only hides the problem for a while: the slabs keep moving with temperature, and the joints reflect up through the overlay as cracks (see reflective cracking through an overlay). Removing the concrete is expensive and slow. Rubblization keeps the material in place as a strong base, cuts trucking and allows faster construction.

Equipment

Resonant pavement breaker: a heavy vibrating shoe tuned to resonate with the slab, cracking it into small pieces with little disturbance to the subgrade.
Multiple-head breaker (MHB): a row of hammers dropping across the lane, followed by a grid-pattern roller to break pieces further.

After breaking, steel-drum vibratory rollers seat the rubble, and any exposed steel reinforcement is cut and removed.

Typical steps

Survey the subgrade and test pits to make sure it can support the work.
Install edge drains or improve drainage where needed.
Remove asphalt patches and overlays as required.
Rubblize the slab to the specified piece size.
Cut and remove exposed steel, fill soft spots.
Compact with vibratory and static rollers.
Place the asphalt overlay, often in several lifts.

Rubblization vs crack and seat

	Rubblization	Crack and seat
---	---	---
Piece size	Small, granular-like	Larger pieces, roughly 1 to 3 feet
Slab action	Eliminated	Reduced
Overlay	Usually thicker	Usually thinner
Best for	Badly deteriorated slabs, reinforced concrete	Plain jointed concrete in fair shape

For the alternative, see crack and seat. Another option is whitetopping, which overlays asphalt with concrete.

Risks to manage

Weak subgrade: the rubble needs firm support; soft spots must be fixed.
Vibration: work near buildings, bridges and utilities needs care.
Water: poor drainage softens the base and shortens life.

Overlay quantity example (made-up numbers)

A two-lane, 24-foot-wide road, 2 miles long, gets a 6-inch asphalt overlay after rubblizing. Area is 24 × 10,560 = 253,440 square feet, or 28,160 square yards. At about 110 lb per square yard per inch, 6 inches is roughly 9,300 tons. See asphalt overlay cost for pricing language and run your own numbers in the asphalt tonnage calculator.

Questions people ask

What is rubblization?

A rehabilitation method that breaks a worn concrete pavement into small, interlocking pieces in place so it acts like a strong granular base under a new asphalt overlay.

What equipment is used for rubblization?

Mainly resonant pavement breakers, which vibrate a shoe at high frequency, and multiple-head breakers, which drop a row of hammers across the slab.

What size pieces does rubblization produce?

Small pieces near the top, often a few inches, grading to larger pieces at the bottom of the slab, depending on the equipment and the slab.

Why rubblize instead of overlaying concrete directly?

Overlaying intact concrete lets joints and cracks reflect up through the asphalt. Rubblizing destroys the slab action so there are no joints left to reflect.

Does rubblization need edge drains?

Drainage is a key part of most rubblization projects, and many agencies install edge drains before breaking so water does not soften the rubblized layer and subgrade.

When is rubblization not a good choice?

Over very weak or wet subgrade, where the broken concrete cannot be supported, and where nearby structures or utilities are sensitive to vibration.

Related guides

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