An important issue for every construction site where concrete is poured is how to handle the waste water created when cleaning concrete skips, trucks and pump lines. Due to the highly alkaline nature of concrete washout water, it must be managed carefully to ensure compliance with the regulations and to avoid damage to the environment.
What’s the Challenge?
Concrete washout water is highly alkaline due to the presence of calcium hydroxide. It typically has a pH value of between 11 and 13.6. At this level of alkalinity, even small quantities represent a serious risk to the environment. It’s illegal to discharge untreated water into the sewers or allow it to drain away on site.
The maximum pH for water diverted into sewers is pH10 while it must be lowered to pH9 before it can be released into watercourses. In addition, a contractor must request permission from the local authorities to release the wash water into the drains.
Strategies for Treatment
It is a common misconception that diluting the concrete washout with fresh water will eliminate any harmful effects. However, the pH scale is logarithmic meaning an impractical volume of water is required – it’s ineffective and highly wasteful. For example, 100,000 litres of fresh water would be needed to neutralise 1 litre of water at ph12.
The conventional method for treating concrete waste water is to chemically lower the pH using acid or carbon dioxide. This can prove expensive, especially where large volumes of water need to be treated. Also, in addition to the issues of safely storing the acid on site, water can be over-dosed and become acidic. This can be equally damaging to the environment.
The Alternative – Recycling Washout Water
An effective solution is to reclaim water for use in the concrete production process. As a result, it helps reduce the amount of fresh mains water consumed. With as much as 170 litres of water required to produce 1m3 of concrete – the benefit of reusing water is clear.
The recycling process is simple and removes many of the issues traditionally associated with managing concrete washout on site.
How We Can Help
Our Concrete Washout system is a compact, self-contained unit and can be easily relocated as work on site progresses. The process is as follows:
- Concrete skips, trucks and pumps are washed out into a tray that captures and contains the water.
- Filtration bags in the tray filter out the large particles. The filtration bags can be lifted from the tray and disposed of.
- Smaller sediment particles settle and the water flows over a weir into the next section.
- The visibly clean, but alkaline water filters into the final section of the tray where it is pumped into a storage tank.
- The pump in the water tank pumps the water into an empty delivery truck after a completed pour, which returns to the production facility.
The water can also be reused for wet-curing of concrete structures or washing out concrete skips, trucks and pump lines.
Recycling the water in this way provides contractors with a strategy for dealing with a waste product that would otherwise require a specialist approach while also reducing the impact of concrete on the environment. A robust waste management plan should always address this issue for sites where concrete is being poured.
To find out more about our Concrete Washout System click here
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