Terms of the trade: Aggregate

Aggregate is a granular material mix typically made of sand, stone, gravel, recycled concrete and crushed rock. It gives volume to the composite material, adding strength and reinforcement so that it is highly resistant to erosion and wear.

The material can be made to be fine with particles <6.5mm or of a coarser texture with particles ranging between 6.5 to 40mm.

Aggregate is an essential ingredient to make concrete used in construction. The quality of the material strongly influences the performance of concrete including how well it mixes and hardens as well as it’s durability long term.

What are common materials used in aggregates?

A quality aggregate will be clean and free of any soft particles or vegetable matter. If organic compounds such as soil are included in the mix, this can cause chemical reactions that can compromise the strength and properties of the concrete.

Some of the more common materials used to create aggregates include:

• Crushed Stone: Quarried stone is often used in mixes after it has been crushed and ground into a sand-like grain. The process can create a coarse or fine mix of varying colour tones.
• Gravel: Like stone, gravel or rock fragments can be crushed to create an aggregate of varying sizes in a range of natural colour tones.
• Sand: Composed of fine rock and mineral particles, sand is commonly used in aggregates. The composition of sand will vary depending on the source and is of a finer texture than gravel.
• Recycled Concrete: Existing concrete that has been broken into pieces and crushed is often used to form aggregates. They are typically of a coarse texture than some other materials.
• Pebbles: Tumbled pebbles are often used as they not only enhance the aesthetics of the concrete surface, they’re also versatile and highly slip resistant. The finish will vary depending on the size and type of pebbles used.

What is the difference between concrete and exposed aggregate?

Concrete is a building material that contains cement and a mix made of materials such as stone, gravel, sand or recycled concrete. Once it is poured, the concrete is smoothed out to create a clean finish.

Exposed aggregate is prepared and poured in a similar way to concrete, however, the top surface is removed after a few hours setting to exposed the material underneath. As it is a highly versatile material, it is often used in driveway and garden path applications.

If you are considering exposed aggregate for your landscape, you’ll need to pay greater attention to the materials used to create the aggregate mix.