Coarse aggregates are an essential component of a wide variety of construction applications. Sometimes, coarse aggregates are used on their own, such as a granular base placed under a slab or pavement. However, mainly construction aggregate is used as a component in a mixture, such as an asphalt or concrete mix. Both of these are examples of how coarse aggregates can be used. Rock larger than the standard but smaller than 2 inches is typically considered coarse aggregates.
| Table of Content
1. What are Coarse Aggregates? 2. How do we get the Coarse Aggregate? 3. How to find the density of coarse aggregate? 4. What properties of coarse aggregate make it the best construction aggregate? 5. Where do we use coarse aggregate? 6. What are the various types of coarse aggregate? 7. Types of coarse aggregate: Natural vs Manmade 8. Types of coarse aggregate: Fine vs Coarse Aggregate 9. What is water absorption of coarse aggregate? 10. What is aggregate in concrete? 11. Why do we use coarse aggregate in concrete? |
What are Coarse Aggregates?
Concrete has many different components; however, most concrete is composed of materials referred to as coarse aggregates. In contrast to fine aggregate, which is more analogous to sand in appearance, coarse aggregates more nearly resemble ordinary rock particles. It gives coarse aggregates a more comprehensive range of potential uses in the building industry. Coarse aggregates are an essential component of a wide variety of construction applications.
How do we get the Coarse Aggregate?
The majority of coarse aggregate comes from quarries produced by various operations, including blasting, crushing, and screening. The aggregate characteristics are determined by the type of rock used to create it, which could be sedimentary, igneous, or metamorphic.
How to find the density of coarse aggregate?
The density of coarse aggregate is an important property used in various contexts, such as when determining the required aggregate quantities for concrete or asphalt mix designs. The specific gravity of coarse aggregate, often referred to as its relative density, is the method used to describe the thickness of coarse aggregate most of the time.
The ratio used to characterise the thickness of the aggregate in comparison to the density of water is referred to as the relative density.
The range of 2.4 to 2.9 is normal for natural coarse aggregate. This range indicates that the coarse aggregate has a density between 2.4 and 2.9 times that of water. As a result, the thickness of the aggregate itself, expressed in units of mass per unit volume, can be calculated by multiplying the specific gravity by the density of water.
The moisture content of coarse aggregate, also known as the quantity of water in the coarse aggregate when the total is fully saturated with a dry surface, is referred to as the aggregate’s absorption. It indicates the potential amount of water aggregate particles can absorb when used in construction or incorporated into mixtures and density measurements.
Mix designs are adjusted based on this absorption capacity, which indicates the potential amount of water aggregate particles can absorb when used in construction or when incorporated into mixtures.
What properties of coarse aggregate make it the best construction aggregate?
The ideal aggregate concrete must have the following properties
- It needs to have a long life and be resilient.
- It must be tough and sturdy enough to withstand loads of weight.
- It cannot contain dust or organic materials; otherwise, it will decrease the bonding capacity.
- It can’t cause the cement to react in any way after mixing.
- It should not be a porous or soft material or have high porosity.
- It must not absorb more than 5% of the water it is exposed to.
- It must not react with other chemicals in any way.
- To the greatest extent possible, it ought to be of a cubical, spherical, or angular shape.
Where do we use coarse aggregate?
The following are some applications for coarse aggregate:
- Its primary function is to add volume to the concrete to bring down the project’s overall cost.
- It contributes to the increased crushing strength that concrete possesses.
- It is utilised in the railway ballast to assist in uniform load distribution.
- It is incorporated into the flexible pavement’s base course and supports the granular load transfer mechanism.
- It is a filter component to separate water from undesirable particles in water filter plants.
- Used in the rainwater system, specifically in the top layer.
What are the various types of coarse aggregate?
The shape is one of the most essential and effective characteristics that can be used to differentiate aggregates. The workability of the concrete and the desired result will guide our decision regarding the aggregate to use.
Although the shapes of aggregates purchased in bulk quantities from reputable suppliers are typically consistent, we can mix aggregates of varying conditions by the requirements and objectives of the project.
The following are the various forms that aggregates can take:
- The rounded
Natural aggregates are rounded aggregates as they have been smoothed out by weathering, erosion, and attrition processes, for example, the rocks, stones, and gravel found in riverbeds.
These aggregates produce the fewest possible voids, giving them a greater degree of workability as a result.
They are not utilised in high-strength concrete because their round shape causes poor interlocking behaviour and weak bond strength. The ratio of water to cement these aggregates require is relatively low.
- Irregular
Attrition shapes irregular aggregates, but this process does not entirely round them off. Compared to rounded aggregates, these particles have a lower high bond strength, but they cannot be used in high-strength concrete because of their shape. Instead, they are used for construction projects such as roads, etc.
- Angular
Because of the suitable interlocking property and high bond strength that angular aggregates possess, they are utilised to produce higher-strength concrete. However, the workability of coarse aggregate with angular shapes is low; filling voids with either rounded or smaller aggregates is used to make high-strength concrete.
- Flaky
It is said that an aggregate is flaky if its smallest dimension is less than three-fifths (0.6) of the aggregate’s mean dimension. The concrete should be able to flow and be pumped. Still, flaky aggregates will reduce the concrete’s capacity for flowing. They cause the concrete to become harsh and also lead to segregation in the concrete.
- Stretched out
When the greater length of the aggregate is more significant than 9/5th of its mean dimension, we refer to the aggregate as having an elongated shape. Since elongated aggregates also have a meagre crushing strength, they should not be utilised in constructing high-strength concrete or roads.
Types of coarse aggregate: Natural vs Manmade
Coarse aggregates are usually put into one of two categories: natural or artificial.
- Natural Aggregates
These are the kinds of aggregates that come from nature.
(a) Gravel:
Most gravel comes from river beds, stream deposits, and other places. These aggregates are made when bedrock breaks down and is then moved and dumped by water, ice, gravity, etc.
(b) Broken-up aggregates:
From the quarries, crushed aggregates are taken. They are inexpensive and easy to get. Crushed aggregates are small pieces of rock that have been broken up, washed, and sorted by machines.
- Artificial Aggregates
People use artificial aggregates because they are made of materials that are good for the environment. They are made from ash, solid waste from power plants, rice husk ash, furnace slag, granite powder, iron ore slag, over-burned brickbats, and so on.
Types of coarse aggregate: Fine vs Coarse Aggregate
What is the size of a fine aggregate?
Fine aggregates are small pieces of filler used in buildings. Fine aggregates are small details that pass through a 4.75 mm sieve but stay in place on a 0.075 mm sieve.
What is the size of coarse aggregate?
Coarse aggregates are filler materials that are bigger than fine aggregates. This coarse aggregate size stays in a 4.75 mm sieve.
What is water absorption of coarse aggregate?
The high water absorption of the lightweight aggregate reduces the workability and slump of concrete. Typically, a prewetting technique is recommended to compensate for the workability issue. Still, its use in the field requires more extraordinary delicacy. Therefore, measure the additional water absorption of coarse aggregate.
Its application in cement paste and concrete mixtures reveals that the absorption amount is unaffected by the mix proportion. Extra water absorption in cement-based materials is a material feature whose value is less than the water absorption determined by a conventional test method (water-soaking). Compensating for the extra water absorption permits dry lightweight aggregates in concrete, which are more durable and stable than surface-saturated dry lightweight aggregates.
What is aggregate in concrete?
Cement and aggregate are the essential elements of concrete. When the cement is still liquid, it is mixed into the aggregate. As a result, concrete is a substance that is exceptionally hardy and resistant to damage due to the binding between the cement as it dries and the particles. In addition, construction aggregate is made from various materials, which can uniquely impact the final product’s quality.
Why do we use coarse aggregate in concrete?
Concrete receives a significant portion of its strength, thermal characteristics, and elastic properties from aggregate and maintains its dimension and volume. Therefore, in addition to preventing cracking and controlling shrinkage, including coarse aggregate in concrete mix can be beneficial.
Because of its longevity, strength, workability, and capacity to take finishes, a particular construction aggregate is chosen during the aggregate selection process. And to go even further, variations in types of coarse aggregate, including size, weight, moisture content, and gradation, can also bring about shifts in the characteristics of the concrete.
This article provides a comprehensive overview of coarse aggregate’s role in concrete construction, especially emphasizing its impact on the strength and durability of concrete structures. I particularly appreciate the detailed explanation of various types of coarse aggregates and their properties. It’s fascinating to see how the choice of aggregate can significantly influence the performance of concrete in different applications, including retaining walls.
In terms of retaining walls, I wonder how the specific characteristics of coarse aggregate might affect the wall’s stability and drainage capabilities. Could you elaborate on the best practices for selecting coarse aggregates when designing retaining walls, especially in areas with high moisture content?
Types of Coarse Aggregate :
Flaky Aggregates:
When sixteen determines flaky aggregates, the thickness is less than 60% of the mean dimension, that is, the thickness of the flaky aggregate is less than their length and width. These irregular aggregates are generally not acceptable for the production of concrete, since they adversely affect the strength and workability of concrete.
Elongated Aggregates:
These aggregates are extended more as compared to their thickness and width. Like flaky aggregates, elongated aggregates also have detrimental effects on concrete performance and strength to make them unfit for any construction.
Flaky and Elongated Aggregates:
Shapes of these aggregates are intermediate between flat and elongated ones which makes them very challenging when producing concrete. They greatly impair its workability and are capable of compromising the structure as a whole.
Characteristics Requirements of Coarse Aggregate :
It is vital to have correct grading and selection of the various types of coarse aggregates to a concrete product. Some of the key requirements include:
Hardness and Strength:
Coarse aggregate has to be hard and strong so as to enhance workability of concrete mix and increase its durability.
Purity:
It should of course be kept clean from both mineral and organic materials which would eventually compromise the bond between the aggregate and the cement.
Moisture Resistance:
High water absorption affects concrete performance, so coarse aggregates should not allow water absorption.
Durability:
This means that the aggregate used must stand up to aggressive chemicals, weather and the other outside forces that would affect the ‘stability’ of the structure.
Specific Gravity:
The specific gravity of coarse aggregates should lie betweeen 2.6 and 2.9. Higher specific gravity increases the mass effects of concrete alongside enhancing its general strength.
Absence of Harmful Substances:
Chloride, sulfate or alkali should not be allowed in coarse aggregate because these materials affect the quality and durability of concrete.
Conclusion
Coarse aggregate is essential in construction, impacting concrete’s strength, durability, and workability. Types include flaky, elongated, and irregular aggregates, each suited to different projects. Selecting the right aggregate contributes to a structure’s stability and longevity. Walls and Dreams can guide you in choosing the optimal materials for durable, high-quality construction.