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Classification of Aggregates

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    Posted on 29th March 2018 by Hintons

    Classification of Aggregates

    Aggregates form an essential part of many construction projects, from large-scale commercial to smaller domestic works. Whether you need aggregates to form a sub-base for foundations or paving, decorative aggregates for driveways and footpaths – or simply need something to fill in unsightly holes – you should know which kind of aggregates will work best.

    In this article, we’ll run through the different classifications of aggregates, based on their varying properties.


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    Classification of aggregates based on: Grain Size

    If you separate aggregates by size, there are two overriding categories:

    • Fine
    • Coarse

    The size of fine aggregates is defined as 4.75mm or smaller. That is, aggregates which can be passed through a number 4 sieve, with a mesh size of 4.75mm. Fine aggregates include things such as sand, silt and clay. Crushed stone and crushed gravel might also fall under this category.

    Typically, fine aggregates are used to improve workability of a concrete mix.

    Coarse aggregates measure above the 4.75mm limit. These are more likely to be natural stone or gravel that has not been crushed or processed. These aggregates will reduce the amount of water needed for a concrete mix, which may also reduce workability but improve its innate strength.

    Classification of aggregates based on: Density

    There are three weight-based variations of aggregates:

    • Lightweight
    • Standard
    • High density

    Different density aggregates will have much different applications. Lightweight and ultra lightweight aggregates are more porous than their heavier counterparts, so they can be put to great use in green roof construction, for example. They are also used in mixes for concrete blocks and pavements, as well as insulation and fireproofing.

    High density aggregates are used to form heavyweight concrete. They are used for when high strength, durable concrete structures are required – building foundations or pipework ballasting, for example.

    Classification of aggregates based on: Geographical Origin

    Another way to classify aggregates is by their origin. You can do this with two groups:

    • Natural – Aggregates taken from natural sources, such as riverbeds, quarries and mines. Sand, gravel, stone and rock are the most common, and these can be fine or coarse.
    • Processed – Also called ‘artificial aggregates’, or ‘by-product’ aggregates, they are commonly taken from industrial or engineering waste, then treated to form construction aggregates for high quality concrete. Common processed aggregates include industrial slag, as well as burnt clay. Processed aggregates are used for both lightweight and high-density concrete mixes.

    Classification of aggregates based on: Shape

    Shape is one of the most effective ways of differentiating aggregates. The shape of your chosen aggregates will have a significant effect on the workability of your concrete. Aggregates purchased in batches from a reputable supplier can be consistent in shape, if required, but you can also mix aggregate shapes if you need to.

    The different shapes of aggregates are:

    • Rounded – Natural aggregates smoothed by weathering, erosion and attrition. Rocks, stone, sand and gravel found in riverbeds are your most common rounded aggregates. Rounded aggregates are the main factor behind workability.
    • Irregular – These are also shaped by attrition, but are not fully rounded. These consist of small stones and gravel, and offer reduced workability to rounded aggregates.
    • Angular – Used for higher strength concrete, angular aggregates come in the form of crushed rock and stone. Workability is low, but this can be offset by filling voids with rounded or smaller aggregates.
    • Flaky – Defined as aggregates that are thin in comparison to length and width. Increases surface area in a concrete mix.
    • Elongated – Also adds more surface area to a mix – meaning more cement paste is needed. Elongated aggregates are longer than they are thick or wide.
    • Flaky and elongated – A mix of the previous two – and the least efficient form of aggregate with regards to workability.

    Knowing the various aggregate classifications is a good starting point when planning a concrete construction project. If you’re in need of specific advice for the kind of aggregates required for your needs, it helps to talk to the pros. A reliable aggregates supplier will be able to provide the perfect selection of aggregates for your project, ensuring they meet the quality requirements to form an integral part of your concrete mix.

    Hintons Waste provide prompt and efficient supply of quality recycled aggregates ad hardcore throughout South and West London. To arrange delivery or collection – or to enquire about the range of aggregates we supply  simply get in touch with us today.


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