Types of Aggregate In Construction
The following aggregate types are most used on construction sites,
- Rounded Aggregate
- Irregular Aggregates
- Angular Aggregates
- Flaky Aggregates
- Elongated Aggregates
- Flaky and Elongated Aggregates
Aggregate In Construction
Aggregates are one of the important and essential constituents of concrete. Aggregate provides the body to the concrete, reduces shrinkage, and affects the economy. Aggregate makes concrete strong and durable.
Generally, aggregate in concrete occupies around 70-80 percent of the volume of concrete, their impact on various characteristics and properties of concrete is, undoubtedly considerable.
Before studying the properties of concrete one should know about the aggregates which constitute major volumes in concrete. It is a fact that without studying the properties of aggregate the study of concrete is incomplete.
In concrete, the only standard factory-made material is cement. Other materials like aggregate, and cement is natural organic materials and their properties can vary to some extent. An in-depth study of aggregate is essentially required to study the properties of concrete.
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What Is Aggregate?
Aggregates can be defined as crushed stones used in concrete. Aggregate in concrete occupied about 70 – 80 % of the total volume which provides the main body of concrete. Aggregate makes concrete strong and durable when mixed with cement, sand, and water.
Types of Aggregates
Different types of aggregates are classified into the following groups:
- Types of aggregates according to a source.
- Types of aggregates according to the unit weight.
- Types of aggregates according to size.
A. Types of Aggregates According to Source
1. Natural Aggregates
Natural aggregates are generally used in a natural state having rock fragments or are used after mechanical processing such as crushing, washing, and sizing.
Some natural aggregate deposits known as pit-run gravel consist of gravel and sand that can be easily used in concrete after minimal processing.
Natural sand and gravel are generally dug or dredged from a pit, river, lake, or seabed
2. Crushed Rock Aggregates
Crushed rock aggregate is generally excavated or quarried stone that has been crushed and screened to the desired standard particle size and distribution.
Crushed aggregate particles are completely crushed. This gives the aggregate good compaction and load-bearing properties.
These aggregates are generally suitable to use in the courses of streets, roads, and other areas exposed to traffic.
3. Artificial Aggregates
These aggregates are made from different waste materials.
Artificial aggregate is sometimes manufactured for severing special work: –
- To make lightweight concrete: burned clays, artificial cinders, foamed slag, expanded shales, and slate, sintered fly ash exfoliated vermiculite is used.
- To make high-density concrete: steel rivet punching and iron ore (Magnetite) have been used.
4. Recycled Aggregates
Recycled aggregates are manufactured from crushing inert construction and demolition waste. It is generally known as recycled concrete aggregate when it is mainly made from crushed concrete and recycled aggregate when it contains substantial quantities of materials other than crushed concrete.
Currently, only recycled aggregate made from construction or demolition waste is recommended for use in new concrete construction.
Aggregate recycling is a simple process there is no complex method involved. The recycling method includes breaking, removing, and crushing existing concrete into a material with a specified size and quality. Reinforcement and other mixed items in concrete must be removed from the aggregate.
Serve precautions must be taken to restrict other material contamination with aggregate that can be troublesome, such as asphalt, soil and clay balls, chlorides, glass, gypsum board, sealants, paper, plaster, wood, and roofing materials.
In general, the following are some applications of recycled aggregate without processing:
- Many types of general bulk fill
- Bank protection
- Base or fill for drainage structures
- Road construction
- Noise barriers and embankments
Recycled aggregates with new concrete include:
- Pavements, shoulders, median barriers, sidewalks, curbs, and gutters
- Bridge foundations
- Concrete bases
- Bituminous concrete.
B. Types of Aggregates According to Unit Weight
The aggregates are also classified per different unit weights, shown in Table 1. In this, aggregates are classified on the basis of bulk specific gravity as lightweight, normal-weight, and heavy-weight aggregates.
|Category||Bulk Specific Gravity||Examples||Typical Applications|
|Ultra-lightweight||Vermiculite, Ceramic||Can be sawed or nailed, Also used|
for its insulating properties
|Lightweight||Gs < 2.4||Expanded perlite, shale, or slate Burned clay Crushed brick||Structural lightweight concrete |
1350 to 1850 kg/m3 Masonry units
Also used for its insulating properties
|Normal weight||2.4 < Gs < 2.8||Crushed limestone, Sand, River gravel, Crushed recycled concrete||Used for normal concrete projects|
Produce normal-weight concrete
2200 to 2400 kg/m3
|Heavyweight||Gs > 2.8||Steel or iron shot Steel or iron pellets||Produce high-density concrete|
up to 6400 kg/m3
• Radiation shielding
• additional applications where high
the mass-to-volume ratio is desired
C. Types of Aggregates According to Size
The biggest particle size may have a diameter of around 150 mm, and the smaller aggregate has a diameter of up to 5 to 10 microns. Aggregates are classified accordingly to particle size as follows:
5. Coarse Aggregates
The aggregate particle which retains on a 4.75 mm sieve is known as Coarse aggregate.
6. Fine aggregates
Aggregate which passed through a 4.75 mm sieve knows as Fine Aggregate. Fine aggregates are generally occupied 35% to 45 % of the volume of total aggregates.
4. Classification of Aggregates Based on Shape
As we know that aggregate used construction is made from naturally occurring rock by blasting or crushing and which makes it difficult to gain the required shape.
But, the shape of aggregate play important role in the workability of concrete. Therefore the shape of aggregates is important factor to be considered.
Types of aggregates according to shape are classified as under,
- Rounded aggregates
- Irregular or partly rounded aggregates
- Angular aggregates
- Flaky aggregates
- Elongated aggregates
- Flaky and elongated aggregates
7. Rounded Aggregate
The rounded aggregates are totally nature-made shapes and available in the form of seashore gravel. This aggregate allows minimum percentages of voids (32–33%), hence offering more workability.
They also perform well with a low water-cement ratio. These aggregates are not considered suitable for high-strength concrete due to their poor interlocking behavior and weak bond strength.
8. Irregular Aggregates
The rounded aggregates have partly nature-made shapes and these are available in the form of pit sands and gravel. These aggregates may have around 35- 37% of voids.
Irregularly shaped aggregate offers lesser workability when compared to rounded aggregates. It has bond strength slightly good compared to rounded aggregate but not as required for high-strength concrete.
9. Angular Aggregates
The angular aggregate has well-defined edges and these are obtained by crushing the rocks. These aggregates offer a maximum percentage of voids (38-45%) and hence give less workability.
Angular aggregates give a high specific area compared to rounded aggregates. With a greater specific surface, they show higher bond strength than rounded aggregates. Also, angular aggregate shows a better interlocking property in concrete that contributes to the strength of concrete.
10. Flaky Aggregates
A flaky aggregate is those whose thickness is less compared to length and width or other, when the least dimension of aggregate is less than 60% of its mean dimension than that aggregate is called flaky aggregate.
11. Elongated Aggregates:
Elongated aggregates are those whose length is larger compared to width and thickness or the length of aggregate is greater than 180% of its mean dimension.
12. Flaky and Elongated Aggregates
If the length of the aggregate is larger than its width and the width is larger than its thickness then it is said to be a flaky and elongated aggregate.
In conclusion, aggregates are an essential component of concrete and other construction materials, and the type and classification of aggregates used can have a significant impact on the quality and durability of the final product.
There are several different types of aggregates available, including natural and artificial materials such as gravel, sand, crushed stone, and recycled materials like crushed concrete and asphalt.
The selection of aggregates depends on several factors, including the desired properties of the final product, the availability and cost of materials, and environmental considerations.
Classifying aggregates is also an important consideration, as different classifications can impact the performance and durability of the concrete or construction material.
The most common classifications of aggregates include coarse and fine aggregates, with further sub-classifications based on particle size and shape.
Ultimately, the proper selection and classification of aggregates are critical to the success of any construction project.
By understanding the different types and classifications of aggregates, designers, and builders can make informed decisions that result in high-quality, durable, and safe structures that meet the needs of the project and the people who will use them.
What is aggregate?
Aggregate refers to a granular material used in construction, such as sand, gravel, crushed stone, or recycled concrete. It is mixed with cement to form concrete, providing strength, stability, and durability to various construction projects.
How are aggregates classified?
Aggregates can be classified based on various factors, including size, shape, origin, and density. The common classifications of aggregates include coarse aggregates, fine aggregates, all-in aggregates, single-size aggregates, gap-graded aggregates, well-graded aggregates, rounded aggregates, irregular aggregates, crushed aggregates, natural aggregates, artificial aggregates, lightweight aggregates, heavyweight aggregates, absorption-graded aggregates, porous aggregates, non-porous aggregates, and organic aggregates.
What are the types of aggregates?
Crushed Stone: Crushed and angular rock fragments.
Gravel: Rounded or angular rock fragments larger than 2 mm.
Sand: Fine granular material composed of small rock particles.
Manufactured Sand: Artificially produced sand from crushed rocks.
Recycled Concrete Aggregate: Crushed concrete obtained from demolished structures.
Slag Aggregates: By-products of industrial processes, such as iron or steel production.
Geosynthetic Aggregates: Synthetic materials used in construction applications.
Expanded Clay Aggregates: Lightweight clay aggregates created by heating clay.
Expanded Shale Aggregates: Lightweight aggregates made from shale through heating.
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