Short answer
The difficulty in pile head breaking is not removing the concrete but removing it without damaging the rebar. As surplus concrete comes off the pile head, the reinforcement inside has to be left exactly as it is and exposed cleanly, because that rebar will tie the pile to the cap. Rebar that has been bent, nicked or touched by a weld weakens that tie. So the work has two stages: bulk concrete removal and cleaning around the rebar. The attachment choice follows those two stages, and no attempt is made to finish the job with one attachment.
Two stages, two different jobs
The first stage is bulk removal: most of the concrete mass at the pile head is broken away. What matters here is speed rather than precision, because the rebar is still inside the mass and the risk of direct contact is low.
The second stage is cleaning: the concrete left around the rebar is taken off without damaging it. What matters here is the opposite; control rather than speed. The attachment for the first stage is not suitable for the second.
The commonest mistake on site is trying to do both stages with one attachment at one pace. Take the bulk removal attachment in among the rebar and the rebar bends; take the cleaning attachment into the mass and the job drags.
The order
- 1
Mark the cut-off level
The level at which the pile is cut comes from the design and is marked on the pile before breaking starts. Breaking begun without a mark carries the risk of going below the level, and that cannot be undone.
- 2
Clear the surrounding concrete and ground
Open up around the pile head. A breaker working buried in the ground can neither see the material nor keep the broken pieces from falling back in.
- 3
Do the bulk removal
Most of the mass is taken with a breaker. Set the tool above the cut-off level and away from the rebar rather than along the pile axis.
- 4
Change attachment before going near the rebar
Once the rebar is exposed, work does not continue with a breaker. At this stage a pulveriser or a small breaker is used, under control.
- 5
Clean around the rebar
The remaining concrete is taken parallel to the rebar and without straining it. The aim is to crush the concrete, not to use the rebar as a lever.
- 6
Dress and check the cut face
The remaining face is checked against the level and the condition of the rebar assessed. Where rebar has been bent, how it is to be corrected is decided against the design and the specification.
Choosing the attachment
- Bulk removal: hydraulic breaker. It opens the mass quickly. Sized to the pile diameter and the machine.
- Cleaning around the rebar: pulveriser. It crushes concrete off the rebar without bending it, and is the best suited attachment for this job.
- Tight spaces and small diameter piles: a small breaker or a concrete cutter, particularly where a clean cut face is required.
- Collecting the broken concrete: grapple. Clearing by hand is both slow and risky.
- Many piles and repeated work: dedicated pile breaking arrangements speed this up; on a one-off job the set-up time eats that advantage.
Do not use the rebar as a lever
Resting a broken piece of concrete against the rebar and pushing it with the attachment is a common move on site and the one that damages rebar most. Once bent, correcting it is a problem of its own: hot straightening changes the material properties, cold straightening can leave cracks. Not bending it is the best answer.
Do and don’t
Do
- Mark the cut-off level before breaking starts.
- Separate the two stages and change attachment between them.
- Put the breaker down once the rebar is exposed.
- Clear broken pieces regularly; accumulated rubble blocks both sight and access.
- If you have gone below the level, stop and refer to the design; the remedy is not decided on site.
Don't
- Do not use the rebar as a lever or a support.
- Do not take the breaker in among the rebar; contact between tool and rebar damages both.
- Do not go below the cut-off level; it cannot be undone.
- Do not try to do both stages with one attachment.
- Do not break a pile head while it is still buried; clear around it first.
Why this is a discipline of its own
Pile head breaking looks like demolition but its aim is the opposite. In demolition the aim is to remove the structure; here the aim is to expose part of the structure without damaging it.
That opposite aim changes the measure of success too. In demolition success is measured in speed; in pile head breaking it is measured by the condition of the exposed rebar. Fast work that bent the rebar is worse than slow, clean work.
What follows confirms it: when pile head breaking is finished, whoever takes the work over looks at the rebar, not at the concrete. How this stage connects to the others is covered on the foundation work page.