Concrete installation doesn’t get the applause it deserves. So many of us simply picture slabs of grey that run parallel to roads, taking it for granted that concrete will be there when they want to walk on flat, firm surfaces. But concrete is an almost miraculous material: first used by the Romans to connect their vast empire, concrete contractors use the material has barely changed over the last 2,000 years. Barely anything else we use today can be traced the same way!
Over the centuries, concrete has made the Coliseum and the gigantic dome of the Pantheon in Rome, the Panama Canal, and the Hoover Dam. It took a lot of innovation to shape this concrete, but it clearly has stood the test of time. It took more innovation to change how we install concrete to make it work for your home!
The Chemistry of Concrete
Concrete at a very, very basic level is a fairly simple mixture: aggregate (coarse or fine sand or gravel) mixed with a cement paste (lime or calcium silicate mixed with water). This mixture is then poured out and shaped in its form. Ta-da! But it’s actually more complicated than that, and what kind of mixture, in certain proportions, can determine how strong the hardened product is, how it cures, and what it will be used for.
For the best example of using certain materials for extra strength, let’s go back to the Romans: their concrete was, in one way at least, stronger than what we use today in Canada. It stood up despite frequent earthquakes and seawater because the aggregate was made up of volcanic ash and rocks, giving it a higher resistance to fracturing. It’s why the Pantheon, the largest unreinforced concrete dome in the world, still stands almost 2,000 years later!
It was this technological achievement that made concrete suitable for roads, aqueducts, and important buildings, many of which still stand all over the Mediterranean region. The technology we have today has changed the way concrete contractors pour it, shape it, and let it harden.
Changing Concrete Installation With Admixtures
We mentioned above a fairly simple recipe: aggregate, cement, and water. This is usually mixed at a 1 (cement): 2 (sand): 3 (gravel) ratio, with water, slowly added in a drum to keep it consistent. Nowadays, pouring concrete involves something called an “admixture”, an extra ingredient added before or during mixing. The admixture used is based on what the installer wants from the concrete:
- Air entrainers make tiny air pockets in the concrete to improve durability during freezing and thawing cycles. It is carefully added at the worksite.
- Accelerating admixtures are used to speed up early strength development and curing.
- Retarding admixtures do the opposite – they slow down the speed at which the concrete cures, usually due to hot weather that can make pouring concrete and finishing it hard.
- Water-reducing admixtures do pretty much what they say they’ll do: reduce the water needed in the mixture. This allows concrete pourers to make high strength concrete without raising the amount of cement.
- Superplasticizers go even further than water-reducers, reducing the amount of water while raising the flowability of the concrete so that none of the strength is lost. It can also reduce permeability and increase the durability of the concrete.
Admixtures will change almost with the weather. Depending on your needs and the working conditions, the appropriate admixture will be used to make the concrete as strong as possible. Pouring concrete is very hard work and very careful chemistry!
Other Technological Achievements in Concrete Installation
Concrete installation is a backbreaking job, and while the mixture has changed with the times, laying it hasn’t really needed an upgrade. Wood is still used to shape, level (the back-and-forth movement of a board over poured concrete to make it level is called screeding) and separate curing concrete. Water is still used to slow the curing process and strengthen the concrete. Many homeowners still like the look of a broom brushed along the surface! But how we lay it down has indeed changed since the days of Julius Caesar, and this is because of reinforcement.
As mentioned above, the Pantheon still marvels us today because it’s unreinforced. Today, we wouldn’t make any buildings without reinforcement designed to absorb tension. Concrete has low tensile strength and requires the extra material to prevent it from being pulled apart and causing structural failure. This is usually in the form of rebar, steel bars embedded in the poured concrete, or wire mesh. It can’t prevent all the cracking that comes with age, but it will hold it all together.
Concrete has surpassed steel as the most widely-used building material, and it’s not hard to see why: it’s durable, easy to mix, and made with fairly simple ingredients. But it requires a lot of patience and know-how to mix it all together under the right conditions. Technology has changed how we use concrete and how we can pour it so it lasts. Hopefully, in two thousand years, your pool or patio is still standing as a testament to our hard work.