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From crushed rock to driveways: the story of concrete

A quarry is where just about all concrete has its genesis.

Every day, we interact in some way with concrete. Whether we're driving to work, sitting in the post office, shoveling snow from our driveways or even directly cleaning concrete pavers, we're dealing in big and small ways with one of history's most significant inventions.

But how much do we really know about this vital creation that we depend on every day? Before it ever even gets to a concrete mixer, ready to be poured onto a slab, concrete goes through an entire journey. A better understanding of the kinds of trials, tribulations and tests that it experiences might help you appreciate this everyday natural wonder a little more – not to mention lead you to prioritize surface protection for concrete areas. 

Quarrying the aggregate

In a sense, all types of concrete start life as granular materials known as aggregate. According to the Portland Cement Association (PCA), these tiny rock particles – which are typically granite, but also include crushed stone and sand – make up around 60-75 per cent of the finished product. But this material doesn't simply turn up in a concrete mixer – first it has to be dredged and quarried up. 

Aggregate is sourced in a number of ways. Gravel and sand can be dug up from the a lake, river, seabed or pit, for example. Meanwhile, on a quarry site, workers will detonate an explosive next to a rock wall, resulting in piles of boulders, rocks and cobbles. It's also possible to recycle existing concrete. 

This material is then taken away for processing. It's first crushed down, at which point it officially transforms from raw rock material into aggregate. The next step is screening, the process whereby aggregate is sorted according to size, by being passed over multiple meshed wire screens, through which it drops through – similar in principle to the way a sieve works. 

This material is washed to ensure the appropriate gradation, and is then transported away for further processing. When choosing aggregate for concrete, typically a range of sizes, shapes and types are chosen in order to influence its physical properties. 

Forming the cement

Of course, the other major ingredient that goes into concrete is cement. While many people think these terms are synonymous, cement is actually a distinct substance. 

As the PCA outlines, cement is a chemical combination of a number of ingredients itself, including iron, aluminum, calcium and silicon. It therefore also relies on the same quarrying, screening and crushing process that goes into making aggregate, with crushed rock being added to these other elements.

You can think of it as the creation of one very unappetizing meal – materials such as limestone, chalk and shells are thrown together with slate, clay, iron ore and blast furnace slag. Pop the mixture in the cement kiln, turn the temperature up to around 2,700 degrees, leave to simmer and voila – you have a rock-like material that, once ground down into powder, is what we know as cement. 

Cement can be made using a dry or wet process, the latter simply involving having the raw materials ground with water before being placed into the kiln for firing. 

Creating the concrete

This where it all comes together. The cement and aggregates are combined, along with the other crucial ingredient – plain old H2O. The water chemically reacts with the cement in a process known as hydration, coating the aggregate and sand and creating a paste that hardens, binding the aggregate together. 

The key to making a successful lot of concrete is getting the proportions right. If you want the concrete to last, you need enough paste to fill all the gaps between aggregates, but not so much that you cause cracking. It's a fine balance, proving that concrete is both a science and something of an art. 

Concrete can also be transformed into a concrete paver by pouring a mixture of it into a mold with coloring agent. If you want this to last, too, you not only need to get the proportions right, you need to carry out some form of concrete paver protection

Dry-Treat's INTENSIFIA™ is a breathable, semi-impregnating sealer that protects against concrete's natural porosity. Not only that, but it will provide color enhancement to the surface, making it look better than ever. 

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