Types of Aggregates Used in Construction
In this article, we will discuss the different types of aggregates, classifying them based on their source or origin, size, shape, and weight. Understanding these classifications is crucial for selecting the right aggregates for various construction applications.
What is aggregates?
Aggregates are granular materials consisting of a mixture of particles such as sand, gravel, crushed stone, or other mineral and rock fragments. These particles are combined to create a base or filler material used in the production of concrete, asphalt, mortar, and other construction materials. Aggregates provide strength, stability, and volume to the final construction product.
They play a vital role in building foundations, roads, bridges, dams, and other structures, acting as the main component that binds with cement, asphalt, or other binding materials to form a solid and cohesive mass. The size, shape, composition, and gradation of aggregates significantly influence the properties and quality of the resulting construction material. Aggregates are sourced from natural deposits, such as quarries, rivers, and mines, or they can be obtained through recycling processes using materials like crushed concrete or industrial byproducts.
TYPES OF AGGREGATES
Aggregates are a critical component in construction, providing structural support and enhancing the properties of various construction materials. They can be classified based on several factors, including their source or origin, size, shape, and weight. Understanding these classifications is essential for designing and producing construction materials that meet specific project requirements. Let’s delve into each classification:
Aggregate Classification Based on Source
Aggregates can be classified based on their source or origin. The source of aggregates plays a crucial role in determining their properties, composition, and suitability for various construction applications. Here are the main classifications of aggregates based on their source:
Natural Aggregates
Natural aggregates are granular materials composed of mineral fragments, rock particles, and other naturally occurring substances that are found in the Earth’s crust. These materials are typically sourced from deposits such as riverbeds, quarries, and mines, and they are used in construction to create concrete, asphalt, mortar, and other building materials. Natural aggregates provide structural support, stability, and volume to construction projects and are essential for the construction of roads, bridges, buildings, and infrastructure. Their properties, including size, shape, and composition, can vary based on their source and geological origin.
Artificial Aggregates
Artificial aggregates, also known as synthetic aggregates, refer to man-made granular materials that are produced through industrial processes. These aggregates are engineered to meet specific requirements and characteristics, making them suitable for various construction applications. They are created by processing and modifying raw materials or waste materials to achieve desired properties.
Crush Rock Aggregates
Crushed rock aggregates, also known as “crushed stone aggregates,” are granular materials created by mechanically crushing large rocks, stones, or boulders into smaller fragments or particles. These crushed fragments are then graded and categorized based on their size and used as a primary component in various construction applications. Crushed rock aggregates are commonly used in the production of concrete, asphalt, road bases, and other construction materials.
Recycled Aggregates
Recycled aggregate refers to granular materials created by processing and reusing construction and demolition waste or other discarded materials from various sources. These materials are typically obtained by crushing and screening waste concrete, asphalt, bricks, or other construction debris. The goal is to produce aggregates that can substitute for natural aggregates in construction applications.
Aggregate Classification Based on Size
Aggregates are classified based on their size, and this classification is important in determining the properties and uses of the aggregates in various construction applications.
Fine Aggregates
Fine aggregates are granular materials typically passing through a 4.75 mm (0.1875 inch) sieve during particle size analysis. They primarily consist of small-sized sand particles and are a crucial component in the production of concrete, mortar, and various construction materials. Fine aggregates significantly influence the workability, strength, and durability of these construction products.

Coarse Aggregates
Coarse aggregates are granular materials with particle sizes larger than 4.75 mm (0.1875 inches), typically retained on a 4.75 mm sieve during particle size analysis. These aggregates play a crucial role in providing structural strength and stability to construction materials such as concrete and asphalt. They are a fundamental component in a wide range of construction applications.

Aggregate Classification Based on Shape
Aggregates can be classified based on their shape, which is an essential characteristic influencing the properties and performance of construction materials. The shape of aggregates affects properties like workability, strength, durability, and surface texture in concrete and other applications.
- Rounded aggregates
- Irregular or partly rounded aggregates
- Angular aggregates
- Flaky aggregates
- Elongated aggregates
- Flaky and elongated aggregates
Rounded Aggregates
Rounded aggregates refer to granular materials with smooth and rounded particle shapes, typically obtained from natural sources where erosion and weathering processes have naturally rounded the edges and surfaces of the particles. These aggregates are characterized by their rounded appearance, lacking sharp or angular edges.

Applications
- Pumped Concrete: Rounded aggregates are suitable for pumped concrete due to their smooth surfaces, which facilitate the pumping process.
- Architectural Concrete: Used in architectural applications where a smooth, aesthetically pleasing finish is desired.
- Structural Concrete: Can be used in structural concrete for various applications where workability and ease of handling are essential.
Advantages
- Workability: Rounded aggregates improve the workability of concrete mixes, making them easier to handle and place.
- Pumping: Well-suited for concrete pumping due to their smoother surfaces and reduced friction during pumping.
Irregular or Partly Rounded Aggregates
Irregular or partly rounded aggregates refer to granular materials with shapes that are neither completely rounded nor angular. These aggregates have a mix of rounded, angular, and irregular particle shapes, which can be a result of natural geological processes or mechanical crushing. The irregular shape is a combination of different edges, curves, and surfaces, making them diverse in appearance and properties.

Applications
- General Concrete Applications: Suitable for a wide range of concrete applications, including structural concrete, where a balance between workability and strength is required.
- Road Construction: Used in road base and asphalt mixes, providing stability and good interlocking properties.
Advantages
- Balance of Properties: Irregular aggregates offer a balance between the workability of rounded aggregates and the interlocking strength of angular aggregates, providing versatility in applications.
- Strength and Stability: The mix of angular and rounded features contributes to good interlocking and provides stability and strength to the resulting concrete.
Angular Aggregates
Angular aggregates are granular materials with sharp, rough, and distinct edges and corners. Unlike rounded aggregates, which have smooth and rounded surfaces, angular aggregates have well-defined edges and irregular shapes. The sharp angles and rough surface textures of angular aggregates provide strong interlocking characteristics, contributing to the overall strength and stability of concrete.

Applications
- High-Strength Concrete: Preferred for applications where high-strength concrete is needed, such as in heavy-duty industrial floors, precast concrete, and structural elements.
- Road Construction: Used in road base, as they provide excellent stability and load-bearing capacity.
- Railway Ballast: Commonly used for railway ballast due to their ability to distribute and maintain the stability of the tracks.
- Foundation and Structural Concrete: Utilized in foundation work and structural components to ensure robustness and stability.
Advantages
- Strength and Stability: Angular aggregates provide strong interlocking, enhancing the strength and stability of concrete structures.
- Load-Bearing Capacity: Due to their strong interlocking properties, they offer excellent load-bearing capacity in construction applications.
Flaky Aggregates
Flaky aggregates, also known as flake aggregates or flat aggregates, refer to granular materials that have a flat and elongated particle shape, with a high length-to-width ratio. These particles have thin, flat, and plate-like shapes, often resembling flakes or flakes of irregular geometry. Flaky aggregates are generally not preferred in construction due to their adverse effects on the properties of concrete.

Applications
- Surface Dressing: Used in road construction for surface dressing to enhance skid resistance.
- Architectural Concrete: Utilized in architectural concrete for aesthetic purposes where specific surface textures are desired.
- Specific Applications: In some cases, flake aggregates can be used in specialized concrete applications.
Advantages
- Aesthetics: In architectural applications, flake aggregates can provide unique and visually appealing surface textures.
- Specialized Uses: Suitable for specific applications where a certain aspect ratio or surface texture is desired.
Elongated Aggregates
Elongated aggregates have a long, narrow shape with one dimension significantly larger than the others. Similar to flaky aggregates, elongated particles can negatively impact workability and compaction of concrete. Typically avoided in concrete mixes due to their adverse effects on the concrete’s properties.

Applications
- Specific Mix Designs: Used in specific mix designs where elongated particles may be intentionally incorporated for certain engineering purposes.
- Drainage Layers: Sometimes utilized in drainage layers where good interlocking is not a primary concern.
Advantages
- Specific Applications: Suitable for specific applications where an elongated shape is desired for engineering or functional reasons.
- Drainage: Can assist in creating effective drainage layers in construction projects.
Aggregate Classification Based on Shape Weight
Aggregate classification based on shape and weight refers to categorizing aggregates according to their geometric shape and density or weight. The shape and weight of aggregates significantly influence the properties and behavior of concrete and other construction materials.
Lightweight Aggregate
Lightweight aggregates are granular materials used in construction that are significantly lighter than traditional aggregates like sand, gravel, or crushed stone. These aggregates are typically produced from naturally occurring or synthetic materials, and their low density makes them suitable for applications where reduced structural weight and insulation properties are desired. Lightweight aggregates offer several advantages in construction, including energy efficiency and improved thermal insulation.
The unit weight of lightweight aggregates can reach 121 kN/m3. They are available in natural forms such as pumice, diatomite, sawdust, rice husk, volcanic cinders, and scoria, as well as manufactured ones such as foamed slag, sintered fly ash, bloated clay, coke breeze, expanded perlite, and so on.
Normal Weight Aggregate
Normal aggregates, also referred to as standard aggregates or conventional aggregates, are granular materials commonly used in construction applications. These aggregates have typical or standard properties in terms of size, shape, and density, making them a fundamental component in the production of concrete, asphalt, and other construction materials.
Normal weight aggregate yields concrete with unit weights ranging from 23 to 26 KN/m3 and a specific gravity ranging from 2.5 to 2.7. These aggregates have crushing strengths ranging from 15 to 40 MPa at 28 days.
Sand, gravel, and crushed rocks such as granite, basalt, quartz, sandstone, and limestone are typical aggregate examples.
Heavy Weight Aggregate
Heavyweight aggregates are materials with high density, typically exceeding the density of normal aggregates. These aggregates are used in specific applications where higher density and increased weight are desired to achieve specific engineering properties or functions. The high density of these aggregates is achieved by incorporating dense natural minerals or industrial byproducts into the concrete mix.
Heavyweight aggregates have specific gravities in the 2.8-2.9 range and unit weights in the 28-29 kN/m3 range.
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