Timber Engineering Europe
Wash Out and Wash Water in Construction
Concrete is a product that has no place in modern construction, not least for its damaging effect on the planet at the
birth of the odious stuff, but for the after effects it leaves behind. In the past, I have discussed the massive embodied
energy emissions this outdated and unwelcome material creates as well as many other reasons for not using it in
construction. There are two very undesirable and hugely unwanted effects of concrete production and use, that the vast
majority of us do not know about, simply because they are never brought to our attention!
The first effect I refer to is:
Washout is exactly what it says it is - Washing out concrete carrying or delivering apparatus, such as mixers, pumps,
trucks and hoppers. In each case after every operation, the equipment must be thoroughly cleaned - its obvious why,
because if the machinery was not cleaned with copious quantities of water, the concrete would set and very expensive
plant would have to be sent to the scrap yards. It has been a known "punishment" in the industry for a disaffected
concrete worker to leave a couple of cubic metres in a drum or in a chute over the weekend, resulting in a massive
solid problem for the boss on Monday!
So where does the washout and wash water go? This is an operation that is rarely mentioned, because although rules
may exist, nobody supervises the washout operations. If the residue of the washout operation permeates the earth or worse a
drain, it leaves deposits of Chromium V1, Copper, Iron, Selenium, Vanadium and Zinc.
The lime found in cement and concrete products easily dissolves in water, just like sugar. Lime is alkaline, so as a result
concrete slurry and any water that comes into contact with cement or concrete, becomes strongly alkaline (pH11-13). This
is deadly to aquatic life.
Plants, insects and animals can be burnt or killed by high pH water. High pH substances such as slurry or concrete wash
water will attack the sensitive membranes of fish and eels, including the gills and the skin; effectively burning them much
the same way acid burns us.
Often fish and eels try to jump out of the stream to escape the burning water resulting in death by suffocation. All
life in a stream can be wiped out by a concrete or cement slurry or washout discharge, and will take years to rectify. A
recent report from New Zealand indicated that 30% of fish that died as a result of poison discharge were killed by washout
In the USA alone the amount of concrete washout material and wash water generated each year accumulates to approximately:
- 34 times more concrete than was used to build the Sears Tower in Chicago (2 million cubic fee/72,000 cubic yards),
the World's tallest building until 1996
- Enough concrete to build an 8-lane freeway system 175 miles long
- Nearly 3/4 the amount of concrete used to construct the entire Hoover Dam and
Enough water to provide a city of 50,000 people for nearly three months.
Imagine how much wasted water is used not just making concrete, but with the wash water needed several times a day.
The second little known, but large problem is Cement Carbon Emissions
We all hear about the effect of concrete in construction and the main carbon emission offender is only one component
of concrete - Cement. While most of the population has been busy worrying about travelling by air and car in a responsible
manner, the cement industry has been quietly pumping more CO2
emissions into the air, more than the entire
aviation industry. Cement manufacture is responsible for 5% of all global industrial carbon emissions and is increasing
rapidly. China alone was responsible for 540,000 tonnes of carbon dioxide emission last year, as a result
of cement manufacture.