After concrete is poured at a construction site it’s important to wash out the machinery and equipment before the remaining concrete sets. Flushing water through pump truck hoppers and the chutes of ready-mix trucks creates washout out water, a slurry containing toxic metals that poses a potential risk of environmental damage if not managed and disposed of properly.
As unused wet concrete should never be dumped on bare ground to set, using concrete washout bags on their own or as part of a washout station, will protect ground water and surface water from washout contamination.
The toxic metals that concrete washout water contain are caustic and corrosive, being alkaline with a pH near 12. The high levels of chromium it contains pollutes the environment.
When washout waste makes contact with the ground, it changes the chemistry of the soil, hindering plant growth and leaching into groundwater. This can usually occurs if the waste has been incorrectly disposed of or rainfall has caused an uncovered washout container to overflow.
Washout waste can also run off the construction site to roads and storm water drains, either clogging drainpipes and causing flooding or contaminating surrounding surface waters. When these waters are contaminated, they cause harm to marine wildlife in rivers and lakes.
Construction workers are at risk of skin irritation and eye damage from washout waste. They should always wear the appropriate PPE to protect themselves with waterproof gloves and safety glasses or goggles.
As part of construction site best practice to minimise the risk of pollution, it’s necessary to designate a station on the site to wash down equipment and to collect and retain concrete washout waste in a bunded area. This will make it easier for the disposal or reuse of washout waste and should be set up on a sealed concrete area.
Concrete Washout Bags are an easy way to contain washout waste by placing the bag under the chute or hopper to catch the slurry. Bags should have handles that can be looped over a forklift to be transported when the concrete is dry. Once set, the concrete can be recycled or
For construction sites which cover a large distance, it may be necessary for the site to set up a Concrete Washout Station. This is a bunded area for washout waste to be stored and is used after the excess concrete has been contained in concrete washout bags. Its location should be determined by the following considerations:
Inspect the washout station daily, particularly after heavy rain to ensure there are no leaks or damage to your equipment. The washout area should not exceed 80% of its internal capacity to prevent the washout water from overflowing and contaminating the surrounding area.
Site best practice also includes induction to brief personnel on when and how to use the washout station. For example, this area isn’t usually designed to store excess concrete, instead, it should be contained in a concrete washout bag or returned to the closest batching plant to set for reuse. Also, set concrete should be cleared frequently to ensure the station can operate to full capacity, preventing overflows.
Each state and territory has its own guidelines regarding waste. Read up on your responsibilities here:
South Australia – https://www.epa.sa.gov.au/environmental_info/waste_management
Western Australia – http://www.wasteauthority.wa.gov.au/about/legislation/