What are Construction Aggregates? The complete guide.
Aggregates are one of the most un-sexy aspects of the construction industry- they are literally just rocks after all; however, this often-overlooked area is the foundation of any building or civil project.
The term aggregates is used to describe a range of different construction materials that are used to build everything from ponds to cities, they can include sand, gravel, crushed stone, and even soil. These materials can sound quite boring, but they are literally the building blocks of our modern society and have played a key role in our growth and urbanisation.
You can trace aggregate production back to the Roman Empire (what did they ever do for us?), when aggregates are produced using raw materials, they are called primary or quarried aggregates.
Over the last few decades, it has become popular to produce aggregates from demolition waste such as concrete, bricks, and tiles. Aggregates made from these materials are known as recycled or secondary aggregates.
A typical aggregates yard.
What are they used for?
Aggregates are mainly used in the construction industry, you will find them used as the foundations for roads, buildings, bridges, and walkways. They make up roughly 90% of an asphalt pavement and approximately 80% of a concrete mixture. Some other common applications you will find aggregates are:
Road construction
Bedding
Drainage
Capping
Sub-bases
Brick making
Backfill
On average 38,000 tonnes of aggregates are needed to construct one mile of road!
How are construction aggregates made?
The process for making construction aggregates depends on whether you are using quarried or recycled aggregates, the processes are similar, but you’ll notice some key differences. Let’s look at each one:
Quarried aggregate production:
Planning- If you are producing quarried aggregates then you’re going to need a quarry. The first step is to plan the site and decide how the aggregates will be extracted.
Stripping- To get at the raw materials the site needs to be stripped. This involves removing trees, brush, and a top layer of material known as overburden.
Extraction- This is where the material is removed from the ground, either by digging if it is loose or by blasting using explosives.
Transportation- Once you’ve extracted the material, you need to move it to a processing area. This is typically done by large dump truck style machines.
Processing- Here the extracted materials are crushed and screened using machinery to produce the finished aggregate. Depending on the aggregate it may need further processing or to be mixed with other materials to create a finished product.
An aggregates processing area.
Recycled aggregate production:
Waste collection- Material from demolition sites is collected and sorted to remove any unwanted materials such as metal or wood.
Transportation- Again, the materials are transported to a processing area. Usually done in a tipper lorry.
Processing- As with quarried aggregates, the material is crushed and screened to produce the desired aggregate. The main difference here is that the raw material comes from waste and not the ground. This makes recycled aggregates much more environmentally friendly and cost-effective.
What are aggregates made of?
Limestone- commonly used to create sub-bases due to its high strength and levelling properties, limestone can also be used in concrete production and can be used as a neutralising agent for soil.
Sandstone- is used to make sand which is a very commonly used building material used to make bricks and concrete. Sandstone makes up 20-25% of all sedimentary rock and is made up of very small grains.
Granite- granites high strength and durability make it a popular choice as a base material for aggregate production. Granite is used in the production of high-grade concrete, road manufacturing, and decorative applications due to its different shades and colours.
Demolition waste- unfortunately the other materials in this list are non-renewable (unless you fancy waiting a few million years), meaning that there is a limited supply. Recycled aggregates are made from demolition waste and use materials such as bricks, concrete, and soil. This creates a more sustainable product that in many cases is just as good as quarried materials and far cheaper.
Naturally formed limestone.
What makes aggregates good?
High-quality aggregates will have predictable, uniform, and consistent material properties. This is achieved during the processing stages discussed above, it’s very important when you are manufacturing aggregates that no contaminating materials get into your aggregates.
Hopefully, this short guide has convinced you that aggregates are a vital part of any construction project and not just a pile of boring rocks! If you have any questions about aggregates or waste management, drop them in the comments below or contact the team here, we love talking rubbish!
Further reading
https://www.sixtownswaste.co.uk/blog/turning-rocks-into-treasure-how-aggregates-are-made
https://www.sixtownswaste.co.uk/blog/which-is-the-best-aggregate-for-drainage
https://www.sixtownswaste.co.uk/blog/which-skip-size-do-i-need-choosing-the-right-skip-for-you
Sources
https://aem.org/news/construction-aggregates-101-what-they-are-and-why-they-matter
https://www.gmat.co.uk/a-quick-guide-to-construction-aggregates/
https://www.aggregate.com/blog/essential-guide-construction-aggregates
