Aggregates Types and Classifications

Aggregates types and classifications are to be discussed here. People have used sand and stone for foundations for thousands of years. Significant refinement of the production and use of aggregate occurred during the Roman Empire, which used aggregate to build its vast network of roads and aqueducts. The invention of concrete, which was essential to architecture utilizing arches, created an immediate, permanent demand for construction aggregates. There are many types of aggregates, with the four most common ones being described here.

 

Gravel Aggregates

Gravel aggregates are made by crushing natural stone and sifting quarried rock. They don’t have much strength compared to granite aggregates but are cheaper to purchase. Their most attractive feature, which ultimately isn’t that useful in the context of construction, is the low radioactive content. Gravel aggregates are used for concretes and foundations. There are two further sub-categories of gravel aggregates, round gravel and scrabbled stone. The former is sourced from the sea or river gravels. 

 

Sand Aggregates

Sand is considered to be the finest aggregate. It does have different gradations that include kiln-dried silver sand, builder’s sand, and sharp sand. The finest of these is kiln-dried silver sand. Finer sands are considered to be a good aggregate for grouts and mortars. Coarser sands are a popular choice as an aggregate for concrete mixes.

 

Granite Aggregates

Experts believe these granites to be among the best aggregates to produce high-quality concrete. This is because granite aggregates come in a variety of shapes, sizes, and even colors, include red, grey, and pink. This allows them to be used as a decorative feature. Granite is composed of mica crystals, quartz, and feldspar. The color of the stone will ultimately depend on granite’s composition.

 

Limestone Aggregates

These aggregates are created by crushing sedimentary rocks, they are most commonly used in reinforced concrete and road construction, aside from gravel and granite. Limestone aggregates are more jagged and bulkier compared to the relatively smoother gravel. These materials are highly versatile and can be used for hardscaping in the construction industry to create practical or decorative elements in a project. 

 

Aggregates Classified According to Shape

It is not easy to attain the required shape of the aggregate due to the way it is produced in the first place, since the source rocks are blasted and crushed. Only the most ideal parent rock should be used along with the ideal crushing machine to extract aggregates. Aggregates can be classified according to the following types:

 

Angular aggregates

As the name suggests, these aggregates consist of finely shaped edges that form at the intersection of planar surfaces. These aggregates are obtained by crushing the rocks. The percentage of voids is between 38 to 45%, which results in reduced workability. They have more compressive strength due to stronger bonds, making them useful in manufacturing high strength concrete. 

 

Rounded Aggregates

Rounded aggregates are found in the form of seashore gravel. They are shaped entirely by attrition. They cause the least amount of voids, hence a higher workability. This also means a lower water to cement ratio is needed. Rounded aggregates are not considered for intensive projects that require exceptional strength due to their weak bond strength and poor interlocking behavior.

 

Elongated Aggregates

When one length of the aggregate is larger than the other two dimensions, the material is called elongated aggregate.

 

Flaky Aggregates

When the aggregate thickness is smaller compared to the other two dimensions, the material is said to be flaky aggregate.

 

 

Flaky and Elongated Aggregates

When the width is larger than its thickness and the aggregate length is larger than its width, the material is then called Flaky and Elongated Aggregates.

 

Irregular aggregates

Irregular aggregates are available in the form of gravel and pit sands. They are partly shaped by attrition. They result in about 35 percent of voids. This results in lesser workability than rounded aggregates. Their strength is slightly higher, but not high enough for high strength concrete. 

 

Ballast and Aggregates

There is no difference between ballasts and aggregates, and they are virtually synonyms of each other.  All in ballast is a mixture of gravel and sand to create a coarse aggregate with a diameter of around 20mm. The result is a very strong coarse grade concrete that is suitable for hard standings, building bases, and foundations. It is not ideal for use in the drainage of water due to the fine content. All-in-ballast can be used for a wide range of domestic and construction applications. 

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Sources

www.mpmoran.co.uk/blog/2019/08/28/detailing-the-use-of-aggregates-in-construction/

en.wikipedia.org/wiki/Construction_aggregate