Short answer
A pulveriser is built to crush concrete away from the rebar: wide jaws, force aimed at crushing. A shear is built to cut metal: narrow blades, force concentrated on a single cutting line. Confusing them is one of the most expensive mistakes on site. Crushing concrete with a shear blunts and cracks the blade edge; cutting heavy sections with a pulveriser spreads the jaw and strains the mechanism. In reinforced concrete demolition the right structure is using both in sequence.
Two attachments, two force distributions
Pulveriser jaws squeeze material over a wide face. Because concrete is brittle, that squeeze crumbles it and frees the rebar inside. The aim is separation, not cutting.
Shear blades concentrate force along a narrow line; a shear cuts metal like a guillotine. The blade edge is hardened for that job and its sharpness has to be preserved.
Concrete is abrasive and brittle as far as a shear blade is concerned: it blunts the edge, leaves micro-cracks and permanently lowers cutting performance. The reverse also holds: a pulveriser jaw is not designed to cut heavy metal, so forcing it spreads the jaw and eats the pivot bearings.
What the mix-up actually costs
- Concrete with a shear: the blade edge blunts, cracks and sometimes breaks off. A blade set is the most expensive maintenance item on a shear.
- Heavy sections with a pulveriser: the jaw spreads and the pivot and cylinder are strained. That damage is structural, not consumable.
- Working with the wrong tool also loses time: because nothing gets done, the same spot is squeezed repeatedly.
- Separation quality drops: concrete crushed with a shear does not release clean rebar, and the scrap is worth less.
The pressure to manage with one attachment
The cause of the mix-up is usually not ignorance but the second attachment not being on site. The operator carries on with what is fitted. So this is as much a planning matter as a training one: in reinforced concrete demolition, decide from the start which attachment is needed at which stage, and have it on site.
The right sequence in reinforced concrete demolition
- Break the structure into pieces with a breaker or pulveriser; large masses come down to a manageable size.
- Crush the concrete off the rebar with the pulveriser. This stage decides how clean your scrap will be.
- Cut the exposed rebar with the shear. Here the shear does its real job and its blade is protected.
- Feed the remaining concrete to a crusher bucket to bring it down to a reusable size.
- Skip the sequence and each stage makes the next harder; the step most often skipped is the second.
Fixed and rotating jaws
On pulverisers and shears the jaw is either fixed or rotates through 360 degrees. A rotating type lets you position the attachment to the material and saves constantly repositioning the machine.
In high demolition and confined spaces the gain from a rotating type is clear. For separation work at ground level a fixed type is adequate and lighter.
A rotating type has a separate rotation circuit, and its flow differs from the main working circuit. The spec table shows two separate rows, and both have to be compared when assessing machine compatibility.