In construction, aggregate refers to the particulate materials used in making concrete and fine aggregate refers to aggregate with particles so small that they may pass through a sieve with a mesh size of 4.75 millimetres. To choose the ideal fine aggregate, you need to be well-versed in its size, density, and classification, since it is frequently employed in the construction process to enhance the concrete volume at a low cost. In this article, we will cover all there is to know about fine aggregate, including its many types and other specifics.
What is fine aggregate?
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Fine aggregate, which may be granular material or crushed stone, is a fundamental component of concrete. The quality of the fine aggregate and the density of the fine aggregate both have a significant impact on the hardened qualities of the concrete.
If the fine aggregate is chosen for its grading zone, particle geometry and surface characteristics, wear and skid resistance, soaking and surface moisture, then the concrete mixture will last longer, become sturdier, and cost less.
Fine aggregate: Size
The size of fine aggregate is defined as equal to or less than 4.75 mm. This means that the aggregates that can pass through a number 4 sieve with a mesh size of 4.75 mm are referred to as fine aggregates. These include clay, silt, and sand. Crushed gravel and crushed stone can also fall under this category.
Role of fine aggregate in a concrete mix
The majority of the volume in the formulations for making a concrete mix is taken up by fine particles, which serve as the structural filler. You are able to have a substantial influence on the output by modifying the makeup of the fine aggregate as well as its geometry, size, and other characteristics. The function of fine aggregate may be broken down into the following points:
- The use of fine aggregates helps the mixture to sustain its dimensions.
- The use of fine aggregate has the potential to affect both the elastic properties and the damage tolerance of the concrete.
- The quality of the fine aggregates also affects the proportions of the mixture as well as its hardening capabilities.
- In addition, the characteristics of the fine aggregates have a considerable bearing on the degree to which the concrete will shrink.
Fine aggregate: Properties
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When selecting the suitable aggregates to be included in a given concrete mix, there are a few factors that need to be taken into consideration, including the following:
Void content
The proportion of cementitious material needed for the mixture is determined by the size of the voids between the fine aggregates. Remember that angular aggregates raise void content while well-graded aggregate and better grading lower it.
Shape and texture
Size and pattern have a significant impact on how well concrete mixes. You should realise that coarse-textured, jagged, and longitudinal particles demand excess moisture for the formula while preparing an inexpensive concrete mix. But if the components are smooth, spherical, and compact, you’ll need little water to make usable concrete.
Absorption and surface moisture
To determine how much water will be needed in the concrete mixture, the absorption rate must be measured. The density of fine aggregate is determined by the interior bulk phase and void content.
Abrasion and skid resistance
When designing heavy-duty floors and pavements, it is important to account for the relative measure of wear caused by the rotation of the fine aggregate in a cylinder with an abrasive charge.
Grading zone of fine aggregate
To make high-quality concrete, you need to start with aggregates that meet certain criteria, such as being devoid of incorporated chemicals and coatings of clay or even other fine elements. For this reason, regulatory bodies have established grading zones of fine aggregate, with each zone denoting a different proportion of fine aggregate that has passed a sieve with a 600-micron opening:
| Zone | Percentage |
| Zone I | 15% to 34% |
| Zone II | 34% to 59% |
| Zone III | 60% to 79% |
| Zone IV | 80% to 100% |
Using the grading zones as a guide, you should be able to evaluate the integrity of the fine aggregate. On the other hand, if you want an accurate evaluation, you should seek the assistance of professionals who are familiar with the procedures for determining the best material based on its bulkage, bulk density, and specific gravity.
Types of fine aggregate
Based on different criteria, fine aggregate is classified into various types. Here is all you need to know about different types of fine aggregates.
Classification of fine aggregate based on the mode of origin
Based on its mode of origin, fine aggregate can be classified into the following.
Pit sand
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They have a distinct and angular contour to them. The wind performs the functions of translation and deposition. Clay may occasionally be seen covering over this kind of sand deposit. Before using this particular sort of sand, it will be best to first wash and clean it.
River sand
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Sand from rivers may be found in the in-plane region of river beds. Sand from rivers often has a spherical grain structure. This sand is pristine and devoid of any salt crystallizations or deposits. There are no traces of organic contaminants found. Sand like this is often used for building projects.
Sea sand
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This particular kind of sand may be seen on coastlines and beaches. These sand grains have a spherical appearance to them. It is fairly uncommon to see salts adhered to grains to the point that they cannot be readily removed. Salts like this may be problematic if they come into touch with the binding ingredient that is used in mortar or concrete.
Classification of fine aggregate based on constituents
Based on constituents of fine aggregate, it can be classified into the following types:
Clean sand
This is high-quality sand that has been processed to include quartz particles of a wide variety of grain sizes.
Silty sand
These are inadequately graded since they include a significant amount of silt in addition to various types of non-plastic particles.
Clayey sand
There are examples of badly graded sand, some of which include a significant proportion of clay and even plastic particles.
Classification of fine aggregate based on particle size
Fine aggregate is categorised into the following types according to its particle size.
| Type | Grain Size |
| Coarse | 2 – 1 mm |
| Medium | 1 – 0.25 mm |
| Fine | 0.25 – 0.15 mm |
Uses of fine aggregate
Fine aggregate has a number of general and specialised applications in a plethora of fields.
General applications of fine aggregate
The following is a list of some of the more general uses of fine aggregate:
- Making mortar to be used in masonry projects
- Preparing many kinds of mortar for plastering and painting
- Mixing concrete for a floor, rafters, and so forth
- Filling up craters
- Levelling the terrain
- Foundational cement
- Floorings
- Different kinds of precast modules, tiles, concrete pipelines, etc.
All about: sea sand
Specific applications of fine aggregate
The following are some examples of specialised applications for fine aggregate:
- To defend black cotton soil foundations
- To fill up canal bank breaches
- Temporary reservoir
- Absorbing excess bitumen from the roadway’s surface
- For play areas
- Moulding operations
- Sandblasting as a cleaning method
- Counter-weights
Tips for choosing the right fine aggregate for concrete mix
When choosing the right fine aggregate for optimal concrete results, here are a few things to remember.
- The chosen fine aggregate should be clean and completely free from organic material, lumps, and other impurities.
- The fine aggregate you choose should be strong and durable.
- It should have a tough floor.
- It should not react with cement after mixing.
- It should not absorb more than 5% of water.
- The chosen fine aggregate should not be soft and porous.
Fine aggregate: Impurities
There are two kinds of impurities present in most fine aggregates. These include:
Organic impurities in fine aggregate
Fine aggregate found in river beds contain many organic impurities such as humus, decayed vegetation, decayed animal materials, organic soil, etc.
Inorganic impurities in fine aggregate
Fine aggregate extracted from mines are usually loaded with inorganic impurities, which include clay and silt. The good news is that both these impurities can be easily removed by thoroughly washing the fine aggregate.
FAQs
Why is it known as an aggregate?
The word aggregation originates from the Latin ad, meaning to, and gregare, meaning herd.Thus, the original meaning of the phrase was to herd or flock. These days, the term simply describes any gathered grouping or accumulation.
What is the size of fine aggregates?
Fine aggregates have a particle size of 4.75 millimetres or less, as described by the size classification. Aggregates meet this definition when they are able to move freely through a sieve with a number 4 rating and a size distribution of 4.75 millimetres. Sand, sediment, and clay are all examples of fine aggregates that may be found in construction projects. The stone that has been crushed and gravel that has also been crushed might also be included in this category.
What use do fine aggregates serve?
When producing thin slabs of concrete or other structural components, as well as in situations when a smooth surface is needed, fine aggregate is employed, while coarse aggregate is employed when producing more substantial parts.
Which fine aggregate is the most usually used?
Sand and crushed stone with a particle size of fewer than 9.55 millimetres in diameter are examples of fine aggregates. The size of aggregate that is 20 millimetres in diameter is often the most frequent size utilised in construction. In most cases, a greater dimension of 40 millimetres is used for bulk concrete. The required amount of water and cement may be cut down using aggregates that have larger diameters.
Which aggregate is optimal for slabs?
For the greatest results when mixing with cement, use coarse, non-glassy materials like gravel or broken stone. In order to be used as aggregates, materials must be dense, robust, chemically inert, and impermeable. Concrete loses its strength and durability when it comes into contact with organic chemicals or is coated with dirt.
What kind of aggregate is employed in road construction?
The most frequent types of aggregates are sand, pebbles, and fragmented rocks, including quartz, sandstone, granite, basalt, and limestone. Other types of aggregates may also be employed.