What are the Different Types of Aggregate?

Aggregates are essential constituents of concrete because they give it body and prevent erosion. Aggregates account for 70-80 percent of the overall volume of concrete. As a result, learning more about aggregates is essential before learning about concrete. Aggregates are classified based on a variety of factors. However, this article will discuss aggregates based on their shape, size, source, and unit weights.

Types of Aggregate Based on Shape

We know that aggregate is formed by slamming or crushing naturally present rocks. As a result, achieving the required aggregate shape takes time and effort. However, the shape of the aggregate will influence the workability of the concrete. As a result, we must be conscious of aggregate form. This applies not only to the parent rock but also to the crushing machine.

Aggregates are classified into the following types based on their shape:

Flaky and Elongated Aggregates

Flaky and elongated aggregates have a length greater than their width and a width greater than their thickness. These are typically obtained from uncrushed rocks.

Rounded Aggregate

The rounded aggregates are entirely formed by attrition erosion and are available as seashore gravel. Rounded aggregates have the lowest percentage of voids and thus have greater workability, and they necessitate a lower water-cement ratio. Because of their poor interlocking behaviour and low bond strength, they are not suitable for high-strength concrete.

Flaky Aggregates

Flaky aggregate is defined as having a thin aggregate thickness compared to its width and length. In other words, flaky aggregate is defined as having a least dimension less than 60% of its mean dimension.

Elongated Aggregates

When the aggregate’s length exceeds 180% of its mean dimension, it is named “elongated aggregate”.

Irregular Aggregates

Shrinkage shapes the irregular or partially rounded aggregates, which are available as pit sands and gravel. Irregular aggregates may contain 35- 37% voids. When compared to rounded aggregates, these will have less workability. The bond strength is slightly higher than that of rounded aggregates, but it is lower than that required for high-strength concrete.

Types of Aggregate Based on Size

Aggregates are in a variety of sizes in nature. The size of the aggregate used may be related to the proportions of the mix and the type of work. The size distribution of aggregates is referred to as aggregate grading. The size classification of aggregates is as follows: Fine Aggregates and Coarse Aggregates.

Fine Aggregate

When aggregate is sorted through a 4.75mm sieve, the aggregate that passes through it is referred to as fine aggregate. Natural sand is commonly used as fine aggregate, but silt and clay are also included. Loam is a smooth deposit comprised of sand, silt, and clay. The fine aggregate’s purpose is to fill voids in the coarse aggregate and increase the workability.

Coarse Aggregate

The aggregate retained after passing through a 4.75mm sieve is known as coarse aggregate. This category includes gravel, cobble, and boulders. Some conditions may influence the maximum size aggregate used. In general, 40mm aggregate is used for normal-strength concrete, and 20mm aggregate is used for high-strength concrete.

Types of Aggregates According to Source

We have categorized aggregates based on their shapes and sizes. Let us now examine the aggregates in terms of their source. Aggregates are typically classified into four categories based on their source.

Natural Aggregates

Natural aggregates are typically used in their natural state with rock fragments or after industrial processing, such as crushing, washing, and sizing. Pit-run gravel is a type of natural aggregate deposit that consists of gravel and sand and can be easily used in concrete after minimal processing.

Artificial Aggregates

These aggregates are composed of various waste materials. Artificial aggregate is sometimes manufactured for specialized purposes, such as lightweight and high-density concrete.

Crushed Rock Aggregates

Crushed rock aggregate is typically unearthed or excavated stone that has been crushed and filtered to achieve the desired particle size and distribution. Crushed aggregate particles have been comprehensively crushed, resulting in good compression and load-bearing properties for the aggregate. These aggregates are generally appropriate for use in streets, roads, and other transit areas.

Recycled Aggregates 

Crushing inert construction and demolition waste yields recycled aggregate. It is commonly referred to as recycled concrete aggregate when it is primarily composed of crushed concrete and recycled aggregate when it contains significant amounts of materials other than crushed concrete. Only recycled aggregate derived from construction or demolition waste is recommended for new concrete construction.

Types of Aggregates According to Unit Weight

The aggregates are also classified according to their unit weights. This list will categorize aggregates based on bulk-specific gravity into a lightweight, normal-weight, and heavyweight aggregates.

• Ultra-lightweight: Such as ceramic and vermiculite. It is commonly used for its insulating properties.
• Lightweight: For example, burned clay, crushed brick, shale, or perlite. It is commonly used in masonry units and has good insulating properties.
• Normal-weight: Such as crushed sand or river gravel. Used for standard concrete projects and produces standard-weight concrete.
• Heavyweight: Such as steel or iron shot and pellets. These can be used to make high-density concrete and are helpful in situations where a high mass-to-volume ratio is expected.

You can read our previous article at https://emininsaat.com.tr/en/the-differences-between-cement-and-concrete/