Everyone knows the formula for concrete is four-two-one: 1 part cement, 2 parts sand, 4 parts of aggregates, and water. But does the purity of the water matter?
On top of water purity, you need to think about the amount of water.
Humidity, temperature, direct sunlight, and the concrete mix ratio are all factors to consider. There is no room for error.
In general, drinking (potable) water is used to make concrete, but you might be wondering if that’s necessary. Does water quality for concrete matter? Water purity plays an important factor in the chemical reactions and the setting process…but how pure does the water need to be? Can we just use water from a lake or a sea to make concrete?
To answer the question of purity, researchers across the globe are looking at alternatives. After all, drinking water is a scarcity in many parts of the world.
Can seawater be used to mix concrete?
Our planet consists of 71% of water, and yet only 3% is suitable for drinking.
The remaining amounts have large quantities of salt and chemical compounds, like seawater. Such water isn’t suitable for human consumption or mixing concrete. So it might come as a surprise as the secret of Roman concrete was seawater! Many of the structures built by the Romans using the mixture are still standing strong to this day. So, what’s the problem?
Well, modern concrete mixture is different from the Roman formula. We do not use volcanic ash or lime and we still don’t know all the components that the Romans used!
A few years ago scientists found a mineral called leucite. It is rich in potassium and binds well with ash, but even with this discovery, seawater isn’t generally used to mix concrete.
Currently, salt found in seawater is the main enemy of concrete. It causes early corrosion of steel reinforcements. This is why water purity is important.
Yet, seawater is a convenient resource, especially if the works are happening near the coast. And there is so much of it! Japan is one of the countries that is looking for ways to use seawater to mix concrete, since being surrounded by water, Japan is perfectly placed to harness seawater for concrete.
Studies show that using Blast Furnace Slag Cement (BFS) instead of Ordinary Portland Cement (OPC) could be the solution.
BFS vs OPC concrete
What about different types of concrete? Does water purity matter then?
20 years of exposure tests have shown that BFS mixed with seawater withstood corrosion well. It was far better than any other cement type having high resistivity against chloride attacks. Not only that, but it also protected steel beams from oxidising! The addition of inhibitors like 2% Sodium nitrite or Nitryl/Chlorine countered the effect of corrosion. The best part – it is cheap! Penetrability and strength also showed to be like OPC. That means seawater can be used for mixing – at least, in theory.
What about in practice? Well, in practice, the biggest issue with BFS is the initial setting time. It is much higher than OPC. With setting times being so long the initial strength is also low. That is unsuitable for reinforced concrete (RCC) works.
Fast construction requirements with very tight schedules leave no space for BFS. As a result, usage of seawater only remains practical on paper.
Can you use water from a river or lake to mix concrete?
Is brackish water (water that is saltier than freshwater, but not as salty as seawater) another alternative?
In theory, it could be lucrative for developed industrial estates set on the river estuaries and lakes. Being able to use the surrounding water is a luxury that could save time, money, and drinking water.
Yet, the main challenge lies with various chemical compounds in rivers and lakes that could affect the quality of concrete. There’s just no knowing what the chemical compounds or possible pollutants are in river and lake waters. Sadly so many in the UK are polluted, making water from lakes and rivers less likely to be suitable for mixing concrete.
The Sultanate of Oman is one of the countries invested in finding ways to use brackish and oily waters. Their main priority is to build new roads or mix concrete for small non-RCC works. Staggering 630,000 m3/day of wastewater produced during the extraction of petroleum could meet their needs.
Can you use groundwater to create cement?
Researchers are looking at reactions of ground and production waters in OPC mixtures using tap water as control.
9 cement mortar cubes were created with OPC and the water samples. So far results show that non-freshwater samples were better at showing compressive strength. Yet, it also had increased slump and the weight of the produced units.
Heavy concrete can have a huge impact on calculations and increase strain on the foundation.
There were also concerns raised about the durability of such concrete. So groundwater is probably not the best option for mixing concrete.
What about treated sewer water?
Salty waters of seas and the brackish estuaries can be difficult to work with… but what about treated sewer water?
Treatment of sewer water has improved over the years, and so become the main process of achieving drinking water. Yet, there are questions raised if the water needs to go through all the filtration steps.
Domestic wastewater contains over 99.9% of pure water with the remaining part of dissolved solids and bacteria. Such water can is easy to treat and reuse. In agriculture, treated water is already in use. Some scientists are positive that construction sites could use treated sewer water but it could be more difficult to source than regular tap water.
Is it worth it?
Studies so far show that the quality of water obtained from the third stage of purification is great.
Treated sewer water has no adverse effects on the slump, initial and final setting times. It also meets the requirements of BS 8500 proving that it is possible. Results for water absorption and electrical resistivity are also great. They once again prove that such water does not impact durability short term. With that said, shrinkage and creep of concrete are yet to be tested. This means we do not know how durable concrete will be in the long run. It could flake or get smaller.
Another aspect to consider would be the logistics. How would someone deliver the said water safely? Where would you store it on site? With high contamination possibility and other human factors. Is it worth the hassle? Drinking water has all the required properties as it is.
What is the best type of water for mixing concrete?
Let’s consider the options.
Seawater can only be used for BFS mixes. Production water is too chemically varied. Biologically treated sewer water offers less flexibility and is not perfect.
Drinking water remains undefeated and the best for mixing concrete.
Alternatives are still in the research stage. As of now, they are far from reaching acceptable results for testing on construction sites. The chemical balance of water is key for creation of a strong concrete mixture.
As a result, drinking water is the only safe option. All chemical components are regulated and the supply is monitored and tested. There are no hidden surprises, and the mixture behaves according to the book. Simples!
Do you like what you are reading? Check out our other blog article about water for construction.