Aggregates must be pure, hard, solid particles free from ingested chemicals or adhesives of clay as well as other fine materials for a good concrete mix that could trigger the concrete to deteriorate.
Aggregates, which make up 60 to 75 percent of the overall concrete volume, are classified into two different categories: fine and coarse.
All particles larger than 0.19 inches are coarse aggregates but usually vary between 3/8 and 1.5 inches in diameter. Gravels make up much of the remaining coarse aggregate used in concrete with crushed stone.
Natural gravel and sand from a pit, river, lake, or seabed are normally mined or dredged. By crushing quarry rock, boulders, cobbles, or large-sized gravel, crushed aggregate is made.
To obtain proper cleanliness and gradation, aggregate is treated after harvesting: crushed, screened, and washed. If required, the output can be upgraded by a benefaction method such as jigging or heavy media separation.
Until processed, to minimize segregation and deterioration and avoid contamination, the aggregates are treated and stored.
Aggregates greatly impact the freshly mixed and hardened properties of concrete, the proportions of the mixture, and the economy.
Selection of aggregates is therefore an essential process. Although some variance is anticipated in aggregate properties, the characteristics considered include:
- Form of particles and texture of surfaces
- Abrasion and resistance to skids
- Weights of a unit and voids
- Absorption and moisture on the surface
Grading refers to the determination of the aggregate particle-size distribution. Grading limits and maximum aggregate size are defined since the amount of aggregate used as well as the specifications for cement and water, workability, pumpability, and toughness of concrete are influenced by these properties.
When the gap-graded aggregate is defined, those aggregate particle sizes are excluded from the spectrum of scale.
Gap-graded aggregate is used in exposed aggregate concrete to achieve uniform textures. In order to prevent segregation, close control of mixed proportions is required.
How to do Shape and Size Matter in Aggregate?
The characteristics of freshly mixed concrete are determined more by particle form as well as surface texture than with the characteristics of concrete.
Rough-textured, angular, and elongated particles consume more water than smooth, rounded, compact aggregates to create workable concrete.
Consequently, to preserve the water-cement ratio, the concrete mixture should also be raised. Flat and elongated particles are usually excluded or are restricted by mass to approximately 15 percent of the overall aggregate.
Unit-weight tests in concrete the quantity the graded aggregate and the voids between them will fill.
The quantity of cement paste needed for the mixture is influenced by the air voids among particles. The void material is augmented by angular aggregates.
The void content is minimized by greater sizes of well-graded aggregate and better grading.
While choosing the aggregate, absorption including surface moisture of the aggregate is determined since the internal structure of the aggregate consists of a solid material including voids which may or may not contain water.
The quantity of water in the concrete mixture should be modified to also include the aggregate’s moisture requirements.
If the aggregate is to be used in concrete constantly subject to abrasion, such as in heavy-duty floors or pavements, abrasion and skid resistance of an aggregate is important.
Various minerals at various concentrations in the aggregate wear and polish. In highly abrasive conditions, to reduce wear, harder aggregates can be chosen.
Fine Aggregate Vs Coarse Aggregate:
In accordance with materials which are used to combine with concrete in building activities, the terms fine and coarse aggregate are used.
Aggregate is a composite substance that helps to tie the concrete together as it provides concrete strength and strengthening.
Many ingredients, such as sand, gravel, stone, crushed rock and sometimes even waste slug from the iron and steel industry, are used to form aggregates.
In general, aggregate is graded as fine and coarse. In this article, the distinctions between these two aggregate forms will be discussed.
Ingredients play a very significant role in the quality of concrete. Crushed stone that is coarse occurs to be low cost in low to moderate strength concrete as it helps to make up the volume required to fill the base.
However, if high-performance concrete is needed where the concrete strength is similar to the aggregate strength, fine aggregate is required so that the framework does not have a weakness.
Mixing both fine and coarse aggregate in concrete is necessary because coarse aggregate is unable to cover the surface area in the way that fine aggregate does.
It is important to note that the contribution of the coarse aggregate is much smaller than the fine aggregate to cover the surface area.
As far as form is considered, to achieve maximum packing density followed by cubical and flaky forms, spherical aggregate is considered the highest.
Oversized aggregate creates trouble on the field in a simple way when setting the concrete. If it is for coarse or fine aggregate, it must be noted that the particle size does not change greatly as it hampers a good performing concrete.
If a coarse or fine aggregate is used, particle size should be as uniform as possible in order to provide a concrete that works satisfactory manner.
It is clear that the concrete placer requires aggregate to be such that concrete with little to no effort can be put and compacted. The best way to attain this goal is to go for particles with spherical aggregates.
These are filler materials used in concrete mixtures, but the substance produced by a combination of smaller grain and mineral particles is referred to as a fine aggregate, and the coarse aggregate is regarded as the material containing gravel, cobble, and boulders.
Coarse aggregates are particles less than 4.75 mm in size; for larger aggregates, however, the range can be found from 9.5 mm and 37.5 mm in diameter.
Fine aggregates, on the other hand, are so small in scale that they can pass through a 9-mm sieve.
Difference Between Fine and Coarse Aggregate: According to Size-
The fine aggregates could be categorized into coarse sand, medium sand, and fine sand under the IS requirements. But from the other hand, we will have various coarse aggregate groups, including principal, secondary and recycled.
Fine aggregates consisting of natural sand and stone are classified into Zone 1 to Zone 4 on their ability to move through 600 microns.
From Zone-1 to Zone-4, the zones gradually become finer. 90 to 100 percent of the fine aggregate passes 4.75 mm of IS sieve according to areas, and 0 to 15 percent passes 150 microns of IS sieve.
The coarse aggregate has a nominal scale of 40 mm, 20 mm, 16 mm as well as 12.5 mm.
Also, Read: Lab Test on Aggregates at Site
Difference Between Fine and Coarse Aggregate: According to Source-
Not only are the size parameters included in the basic distinction between fine and coarse aggregates, but you can distinguish these two based on their origins.
The coarse aggregate can be defined into three categories according to the source:
- Uncrushed Gravel or Stone produced by natural rock disintegration.
- Crushed gravel or stone obtained by grinding hard stone or gravel.
- Partially Crushed Gravel or Stone, which is created by combining the two aggregates above
We can have three distinct types of fine aggregates according to the source, such as:
- Natural Sand is the product of rock disintegration. The process by streams or glacial agencies of disintegration and deposition is entirely natural.
- It is formed when hard stones are crushed. It is formed when hard stones are crushed.
- Crushed Gravel Sand, as the name suggests when crushing of natural gravel occurs, shapes it.
For making thin-walled and traditional reinforced concrete structural elements, fine aggregates are used. It is commonly used in highway and airfield construction due to its fine-grained structure.
The use of fine aggregate increases the amount of binder needed, which can be decreased by coarse aggregate use.
Therefore, to obtain strength and durability from any concrete construction, an accurate proportion of both fine and coarse aggregate is required.