How to demolish a concrete batching plant safely in Australia: licences, silica dust and decontamination

Concrete batching plants come and go with the projects around them. A plant gets set up for a motorway or a precinct, runs for a few years, and then somebody has to get rid of it. Fixed plants at the end of their life are the same job with more concrete in the ground.

These are the five questions asset owners, project managers and site engineers ask us, answered for Australia and in the order the work actually runs.

How do you remove a concrete batching plant?

In this order, and not in any other.

1. Decide the end state. Most batching plants are modular and a lot of them are relocated or sold rather than scrapped. Dismantling for relocation, decommissioning for a mothball, and demolition for the land are three different jobs after the isolation stage. Decide first.
2. Investigate. Hazardous material survey, a look inside every silo, a contamination assessment of the ground, and a services and underground tank search.
3. Isolate. Power, water, compressed air and admixture supply positively isolated and locked. Not switched off. Locked.
4. Empty and decontaminate. Cement and fly ash silos, aggregate bins, the mixer, admixture tanks, the slurry pit and the wash out area. This step is most of the job and it is the one people skip.
5. Dismantle or demolish. Height first. Silos, the batching tower and the aggregate bin structure come down in a controlled sequence with the steel separated for recovery.
6. Slabs, footings and ground. Concrete out and crushed, contaminated soil classified and removed, site validated.

Everything below expands on the parts of that list where people get hurt or get a bill they were not expecting.

Do I need a licence to pull down a concrete batching plant?

Almost certainly yes, and the answer depends on which state you are in and what the plant looks like.

In New South Wales, demolition work is licensed through SafeWork NSW. The higher licence class covers structures above fifteen metres, pre and post tensioned structures, work involving floor propping, chemical installations, and work using large mobile cranes. A batching plant with a cement silo and a batching tower is very often over fifteen metres, so it lands in that class. Even where the structure is lower, the contractor needs a demolition licence for the work, and licensed asbestos removal is a separate licence again.

In Queensland, the contractor needs a demolition work licence issued by Workplace Health and Safety Queensland, and demolition involving a load bearing structure of six metres or more in height has to be notified to WHSQ at least five days before it starts. Load shifting machinery on a suspended floor is notifiable as well.

Separately from the contractor's licence, the project itself needs approval. In most councils that means development consent or a complying development certificate for the demolition, and if the plant held an environment protection licence for its operation, that licence has to be dealt with as part of closing the site.

Perfect Contracting holds the SafeWork NSW demolition licence covering the higher class of work, a Workplace Health and Safety Queensland demolition licence, a SafeWork NSW Class A friable asbestos removal licence, and a NSW EPA waste transport licence. If somebody quoting you cannot show you their equivalents, that is the end of the conversation.

How do you safely demolish a concrete batching plant in Australia?

The structure is not the dangerous part. These are.

Silos. Cement and fly ash set hard when they get damp, and every silo on a shut plant has material hung up on the walls, bridged over the cone, or both. That material looks solid from the hatch and it is not. Nobody goes into a silo to clear it, not on a harness, not for five minutes. It is cleared from outside through existing access points, in stages, with the outlet monitored. We have written about why nobody should be inside the vessel in detail, and a silo with material still hung up in it is a silo that can fail during demolition.

Height. The batching tower, the silos and the aggregate bin structure are taken down top first, cut and lowered under control. Never pulled over. High reach machines where the height calls for it, and an engineer's sequence where the structure was designed for loads you are about to remove.

Aggregate bins. Same problem as silos on a smaller scale. Wet sand and fines bridge and hang up. Emptied and confirmed empty from outside.

The mixer and the batching floor. Set concrete in the mixer, around the discharge and under the batching floor. It comes out with breakers before the structure moves, under the dust controls described below.

Admixture tanks. Retarders, accelerators, plasticisers and air entrainers are chemicals with data sheets. Drained, rinsed and the rinse water captured, not hosed to the drain.

Slab and footings. Silo and tower footings on a batching plant are substantial. Breakers, saw cuts where an edge matters, and the material crushed for reuse where it is clean.

How do you safely decontaminate a concrete batching plant?

Decontamination on a batching plant is about three things. Cementitious dust, alkaline water and the ground.

Cementitious dust. Silos, dust collectors, ductwork, the batching floor and every ledge on the structure are coated in cement and fly ash. Cement dust is alkaline, it burns skin and eyes, and it contains crystalline silica. It is vacuumed out under controls before demolition, not knocked down with the dust still on it. The recovered material is a waste stream in its own right.

The slurry pit and wash out area. Every batching plant has somewhere the trucks and the mixer were washed out. That area holds set concrete, cement slurry and highly alkaline water, and the ground under and around it has usually been taking overflow for years. The pit is pumped out with the water treated or disposed of as liquid waste, the set material is broken out and classified, and the surrounding soil is sampled before anyone assumes it is clean fill.

Returned concrete and stockpiles. Most plants have a pile of returned or rejected concrete somewhere. It is crushed and recycled if it is clean. It is classified separately if it is mixed with soil or slurry.

Hazardous material. Older plants carry asbestos in gaskets, switchboards, control room sheeting and lagging, and lead in old paint. Surveyed, removed under licence, cleared. Perfect Contracting does this in house rather than subcontracting it.

The ground. Hydrocarbons around the fuel store, the generator and the truck wash, alkaline contamination around the slurry pit, and fill of unknown origin under the hardstand. A contamination assessment before the slabs come up tells you what you are going to have to classify and where it can go. Finding it afterwards costs multiples more.

How do you deal with silica dust during removal of a concrete batching plant?

This is the question that matters most, because silica is the hazard on this job that hurts people twenty years later rather than on the day.

Respirable crystalline silica comes from breaking, cutting, grinding and crushing concrete and from disturbing aggregate fines and cement dust. Australia adopted a workplace exposure standard for respirable crystalline silica of 0.05 milligrams per cubic metre as an eight hour average, and the regulators in every state treat it as a high priority. Perfect Contracting does not manufacture, supply, cut or process engineered stone under any circumstance, and the same discipline applies to every other silica source we touch.

Water is the first control. Water suppression on every breaker, saw and crusher, and water carts on the hardstand and the haul route. Dust you can see is dust somebody is breathing.

Extraction is the second. On tool extraction for hand cutting and grinding, and dust removed by vacuum rather than by broom or compressed air. Sweeping dry cement dust is exactly how the fine fraction gets airborne.

Enclosed cabs. Excavator and crusher operators work in sealed cabs with filtered air. A cab with the door open is not a control.

Respiratory protection is the last line, not the first. Fitted and fit tested respirators, at a minimum a P2, and powered air purifying respirators for the highest exposure tasks. Respiratory protection covers the residual risk after the water and the extraction have done their job. It does not replace them.

Health monitoring. Where workers are at risk of silica exposure, health monitoring is required, not optional, and the records follow the worker. Any contractor who does not have a health monitoring programme for their demolition crew is not controlling silica, whatever their safe work method statement says.

Air monitoring. On a job with this much cementitious material, air monitoring during the dusty phases is how you know the controls are working rather than assuming it. Results go to the client as part of the job records.

Our own note on the silica regulations covers the rules in more depth.

What not to do

• Do not send anyone into a silo or an aggregate bin. The material will move.
• Do not demolish with the dust still on the structure. Vacuum first.
• Do not break concrete dry. Every breaker, saw and crusher runs wet.
• Do not hose the slurry pit or the admixture rinse to the stormwater drain. That is a pollution incident.
• Do not assume the ground is clean fill. Sample under the wash out area before the slab comes up.
• Do not let anyone without a demolition licence quote the job. The liability for what happens sits with whoever engaged them.
• Do not sell or relocate the plant without a hazardous material survey. You will be shipping somebody else's asbestos.

Who should be doing this

A contractor with the demolition licence for your state, the asbestos licence and the waste transport licence in their own name, their own plant and their own crushers, and a silica control programme they can show you rather than describe. Batching plants are a routine job for a contractor set up for industrial demolition and a dangerous one for anybody else.

Perfect Contracting works on plant decommissioning and industrial demolition across New South Wales and Queensland and travels for the right project. If you have a batching plant to remove, relocate or demolish, call 02 8015 6345 or read more about our plant decommissioning work.