Coarse Aggregate - Types and Quality in Detail
Coarse aggregate is used in concrete to construct the various types on structures because they provide strength and durability to the structures. Coarse aggregate is used in cement-concrete mix where cement particles react with water to form a gel-like substance during hydration process which is called calcium-silicate-hydrate (C-S-H) gel. The C-S-H gel acts as a glue and binds the aggregates together to form a solid and durable concrete structure.
What is Coarse Aggregate?
Coarse aggregate is a natural construction material that is commonly used in the production of concrete. The concrete may be cement based concrete, bitumen based concrete or any other types of concrete. The coarse aggregate is also known as stone, aggregate stone or gravel and it consists of particles that is greater than 4.75 mm. Generally, the particle size of coarse aggregate used in construction range from 3/8 inch to 1.5 inches (9.5 mm to 37.5 mm) in diameter.
The purpose of using coarse aggregate in concrete is to provide strength and durability to the final structure. The use of coarse aggregate also helps to reduce shrinkage and cracking by providing a solid framework for the cement paste to adhere. The coarse aggregate can be sourced naturally from riverbeds or quarries or it can be manufactured by crushing rock or gravel.
The type of coarse aggregate used in concrete depends on various factors such as the specific application, strength requirements and availability of materials.
The purpose of using coarse aggregate in concrete is to provide strength and durability to the final structure. The use of coarse aggregate also helps to reduce shrinkage and cracking by providing a solid framework for the cement paste to adhere. The coarse aggregate can be sourced naturally from riverbeds or quarries or it can be manufactured by crushing rock or gravel.
The type of coarse aggregate used in concrete depends on various factors such as the specific application, strength requirements and availability of materials.
Types of Coarse Aggregates Based on Nature:
Coarse aggregates are a key component in the production of concrete and are generally defined as particles larger than 4.75 mm in diameter. There are several types of coarse aggregates commonly used in construction:
Gravel
Gravel is the most common type of coarse aggregate and is composed of rock fragments that have been naturally rounded and smoothed by water. Gravel can be further categorized based on its size with larger gravel typically being used in construction applications.
Crushed Stone
Crushed stone is made from crushed rock and is available in various sizes. It is a popular choice for use in construction because of its durability and resistance to erosion.
Recycled Concrete Aggregate
Recycled concrete aggregate is made from old concrete that has been crushed and reused. It is an environmentally friendly option and is often used in road construction.
Blast Furnace Slag Aggregate
Blast furnace slag aggregate is a byproduct of iron and steel production. It is formed when molten slag is cooled rapidly and then crushed into aggregate. It is a durable and high-quality option for use in concrete.
Lightweight Aggregate
Lightweight aggregate is made from materials such as expanded shale, clay or slag. It is a popular choice for use in precast concrete products because it reduces the weight of the final product.
Types of Coarse Aggregates Based on Shape
Coarse aggregates are typically defined as particles larger than 4.75 mm in size and are commonly used in the construction industry. There are three types of coarse aggregates based on their shape:
Rounded Gravel
This type of coarse aggregate is naturally rounded and comes from river beds or glacial deposits. They have smooth edges and are used in concrete mixes where a smooth surface finish is desired.
Angular Gravel
Angular gravel is crushed stone or rock that has sharp edges and corners. They are commonly used in concrete mixes where a strong bond between the aggregate and the cement paste is required.
Flaky Gravel
Flaky gravel which is also known as elongated gravel, is a type of coarse aggregate that has a flat and elongated shape. They are not recommended for use in concrete mixes because they can create voids and reduce the strength of the concrete. They are often used as a decorative stone in landscaping projects.
Types of Aggregates Based on Gradation
Aggregates are an essential component of concrete and other construction materials. They are typically classified based on their gradation or particle size distribution. Proper gradation of aggregates is critical in ensuring the desired properties and performance of the final product. The following are the three types of aggregates based on gradation:
Well-Graded Aggregate
Well-graded aggregates have a wide range of particle sizes that are evenly distributed, from large to small. They contain all the particle sizes required for maximum density and minimum void space. This type of aggregate provides good workability, strength and durability to the concrete mix. It also allows for better compaction and reduces the risk of segregation.
Poorly-Graded Aggregate
Poorly-graded aggregates contain a limited range of particle sizes, with some sizes being overrepresented and others underrepresented. This results in a high percentage of voids in the aggregate which can lead to weaker and less durable concrete. Poorly-graded aggregates are not recommended for use in high-strength concrete or where durability is a concern.
Gap-Graded Aggregate
Gap-graded aggregates contain a limited range of particle sizes with some sizes intentionally left out or “gapped”. This type of aggregate is used to achieve specific properties such as high strength or improved workability. Gap-graded aggregates are commonly used in the production of asphalt concrete where a specific range of particle sizes is required for optimum performance.
List of Quality Tests For Coarse Aggregate?
These are several tests performed on the coarse aggregates to check the quality. But some specific tests are performed as per requirements of the project.
Grain Size Analysis (GSA) or Sieve Analysis of Coarse Aggregate
In this test the sample is weighted and passed through a series of sieves with decreasing diameter of sieve size from top to bottom and after shaking the sieves, the retained samples at each sieves are weighted and its percentage passes through sieves are determined. The material passed through the sieves should be in a range specified by the project or as per local standard.
Elongation and Flakiness Test
Elongation refers to the ratio of the length of an aggregate particle to its maximum thickness. A high elongation value indicates that the aggregate particle is elongated and not well-rounded. Elongated particles have a negative impact on the workability of concrete because they tend to reduce its strength and increase its porosity.
Flakiness refers to the ratio of the thickness of an aggregate particle to its width. A high flakiness value indicates that the aggregate particle is flat and not well-rounded. Flaky particles also have a negative impact on the workability of concrete because they tend to reduce its strength and increase its porosity. Therefore, more erelong and more flaky particles should be avoided in construction.
Flakiness refers to the ratio of the thickness of an aggregate particle to its width. A high flakiness value indicates that the aggregate particle is flat and not well-rounded. Flaky particles also have a negative impact on the workability of concrete because they tend to reduce its strength and increase its porosity. Therefore, more erelong and more flaky particles should be avoided in construction.
Total Deleterious Material Test
Deleterious materials are those that can have a negative impact on the quality of the coarse aggregates. These materials can include things like clay, shale, soft fragments and other impurities that can weaken the aggregate and reduce its ability to bond with other materials.
The sample of aggregate is taken and lab tests are performed to analyse deleterious materials in coarse aggregate. This test may involve visual inspection, chemical testing or other methods depending on the specific characteristics of the aggregate and the types of deleterious materials that may be present.
The sample of aggregate is taken and lab tests are performed to analyse deleterious materials in coarse aggregate. This test may involve visual inspection, chemical testing or other methods depending on the specific characteristics of the aggregate and the types of deleterious materials that may be present.
Specific Gravity (SPG), Water Absorption and Surface Moisture Test
The Specific Gravity Test (SPG) is a measure of the density of a material relative to the density of water. It is an important test for coarse aggregates used in construction field because it provides information on the quality and suitability of the aggregate to use in concrete.
The SPG test is conducted by determining the weight of a sample of dry coarse aggregate and then immersing it in water for a specified period of time. After then weight in water is taken and the sample is removed from the water to weight again to determine the weight of the water absorbed by the aggregate. The specific gravity, water absorption and surface moisture can be calculated by using formulae.
The specific gravity of coarse aggregate is typically between 2.5 and 3.0 depending on the type of rock or mineral from which it is taken. A lower specific gravity indicates that the aggregate is more porous and may be less durable while a higher specific gravity indicates that it is more dense and may be more resistant to wear and weathering. But the aggregate with low water absorption indicates that it is less porous and high water absorption value indicates aggregate is more porous.
The SPG test is conducted by determining the weight of a sample of dry coarse aggregate and then immersing it in water for a specified period of time. After then weight in water is taken and the sample is removed from the water to weight again to determine the weight of the water absorbed by the aggregate. The specific gravity, water absorption and surface moisture can be calculated by using formulae.
The specific gravity of coarse aggregate is typically between 2.5 and 3.0 depending on the type of rock or mineral from which it is taken. A lower specific gravity indicates that the aggregate is more porous and may be less durable while a higher specific gravity indicates that it is more dense and may be more resistant to wear and weathering. But the aggregate with low water absorption indicates that it is less porous and high water absorption value indicates aggregate is more porous.
Bulk Density Test
The bulk density test is a common method used to determine the density of coarse aggregates. This test is essential in the construction industry as it helps to determine the quality of the aggregate material used in concrete production.
The test involves measuring the mass of a known volume of the aggregate material. A container of known volume is filled with the aggregate material and compacted to eliminate any air voids. The mass of the container and the aggregate is then measured and the bulk density is calculated by dividing the mass of the aggregate by the volume of the container.
A higher bulk density can result in a stronger and more durable concrete mix. Conversely, a lower bulk density can lead to a weaker and more porous concrete.
The bulk density of coarse aggregates typically ranges from 1.2 to 1.8 kg/liter. But, the exact range can vary depending on the specific type and source of the aggregate material.
The test involves measuring the mass of a known volume of the aggregate material. A container of known volume is filled with the aggregate material and compacted to eliminate any air voids. The mass of the container and the aggregate is then measured and the bulk density is calculated by dividing the mass of the aggregate by the volume of the container.
A higher bulk density can result in a stronger and more durable concrete mix. Conversely, a lower bulk density can lead to a weaker and more porous concrete.
The bulk density of coarse aggregates typically ranges from 1.2 to 1.8 kg/liter. But, the exact range can vary depending on the specific type and source of the aggregate material.
Aggregate Impact Value Test (AIV)
The Aggregate Impact Value (AIV) test is a method to determine the strength of coarse aggregates used in construction. The test measures the impact resistance of the aggregates by subjecting them to a standard amount of impact from a falling weight.
During the AIV test, the aggregates are placed in a cylindrical mould and the weight is dropped from a specified height onto the sample. The percentage of fines produced from the impact is then measured and compared to the original weight of the sample. The resulting AIV value is expressed as a percentage.
The aggregate impact value helps to determine the suitability of aggregates for use in pavement construction, road building and other applications where durability is important. By using the AIV test, engineers and builders can select the right type of aggregates for their project and ensure that the resulting structure will be strong and long-lasting.
During the AIV test, the aggregates are placed in a cylindrical mould and the weight is dropped from a specified height onto the sample. The percentage of fines produced from the impact is then measured and compared to the original weight of the sample. The resulting AIV value is expressed as a percentage.
The aggregate impact value helps to determine the suitability of aggregates for use in pavement construction, road building and other applications where durability is important. By using the AIV test, engineers and builders can select the right type of aggregates for their project and ensure that the resulting structure will be strong and long-lasting.
- The aggregate impact values below 10% are considered to indicate exceptionally strong aggregates.
- AIV values between 10% and 20% are considered to indicate strong aggregates.
- AIV values between 20% and 30% are considered to indicate medium strength aggregates.
- AIV values between 30% and 40% are considered to indicate weak aggregates.
- AIV values above 40% are considered to indicate exceptionally weak aggregates.
Loss Angles Abrasion Value Test (LAA)
The Los Angeles Abrasion (LAA) test is a common method used to determine the hardness and durability of coarse aggregates used in construction. The test involves subjecting a sample of the aggregate to a certain number of revolutions inside a drum containing steel balls.
The aggregate is weighed before and after the test and the difference in weight is used to calculate the LAA value which is expressed as a percentage of the original weight. The lower LAA value indicates greater the abrasion resistance of the aggregate.
This test is important because it helps determine the suitability of coarse aggregates for use in road construction, particularly in areas with high traffic volumes. Aggregates with a low LAA value are more resistant to wear and tear which means they can withstand heavy traffic and last longer without requiring repair or replacement.
The aggregate is weighed before and after the test and the difference in weight is used to calculate the LAA value which is expressed as a percentage of the original weight. The lower LAA value indicates greater the abrasion resistance of the aggregate.
This test is important because it helps determine the suitability of coarse aggregates for use in road construction, particularly in areas with high traffic volumes. Aggregates with a low LAA value are more resistant to wear and tear which means they can withstand heavy traffic and last longer without requiring repair or replacement.
- LAA Value 10% or less : Excellent
- LAA Value 10 to 30% : Good
- LAA Value 30 to 50% : Average
- LAA Value 50 to 70% : Poor
- LAA Value Above 70% : Very Poor
Aggregate Crushing Value Test
The ACV test is useful in determining the quality of the aggregate and its suitability for different applications, such as road construction, building construction and concrete production. The test is conducted on a sample of aggregate with a specified size and weight which is placed in a cylindrical mould and subjected to a compressive load.
The results of the ACV test are expressed as a percentage which is the ratio of the weight of fines produced to the total weight of the sample. A lower percentage indicates a stronger aggregate but a higher percentage indicates a weaker aggregate.
Aggregate Crushing Strength Test
The Aggregate Crushing Strength Test is a crucial test for evaluating the mechanical properties of coarse aggregates. It ensures that the aggregates used in concrete production are strong enough to withstand the stresses and pressures of daily use.
During this test a sample of coarse aggregate is subjected to a specified load by CTM and the crushing strength of the aggregate is determined.
This involves applying a compressive force to the sample until it breaks or fails and the maximum load that can be sustained by the aggregate is recorded.
The test results are important for determining the suitability of the aggregate for use in concrete as well as for assessing the quality and durability of the concrete itself. High-quality aggregates with strong crushing strength are essential for producing durable concrete that can withstand the demands of heavy usage and adverse weather conditions.
During this test a sample of coarse aggregate is subjected to a specified load by CTM and the crushing strength of the aggregate is determined.
This involves applying a compressive force to the sample until it breaks or fails and the maximum load that can be sustained by the aggregate is recorded.
The test results are important for determining the suitability of the aggregate for use in concrete as well as for assessing the quality and durability of the concrete itself. High-quality aggregates with strong crushing strength are essential for producing durable concrete that can withstand the demands of heavy usage and adverse weather conditions.
10% Fine Value Test
The 10% Fine Value test of aggregate is a commonly used test for determining the strength of coarse aggregates. It measures the ability of the aggregates to withstand a uniform applied compressive load.
In this test a sample of coarse aggregate is placed in a cylindrical mould and compacted with a standard proctor. The aggregate is then subjected to a uniform rate of load so as cause a total penetration in 10 minutes of abut 10 mm for un-crushed aggregates, 20 mm for crushed aggregates and 24 mm for honeycombed aggregates. The force required to achieve this is recorded and the fines below 2.36 mm are weighted and 10% fine value is calculated by using formula.
In this test a sample of coarse aggregate is placed in a cylindrical mould and compacted with a standard proctor. The aggregate is then subjected to a uniform rate of load so as cause a total penetration in 10 minutes of abut 10 mm for un-crushed aggregates, 20 mm for crushed aggregates and 24 mm for honeycombed aggregates. The force required to achieve this is recorded and the fines below 2.36 mm are weighted and 10% fine value is calculated by using formula.
Alkali Aggregate Reactivity Test
Alkali Aggregate Reactivity is a chemical reaction that occurs between the alkalis in cement and certain types of reactive minerals found in some coarse aggregates. This reaction can cause the concrete to crack and deteriorate over time compromising the structural integrity of the concrete.
To prevent this problem, it is important to test the coarse aggregates for their reactivity before using them in concrete construction.
Alkali reactivity of cement-aggregate is determined by measuring the expansion developed by the combinations in mortar bars during storage under prescribed conditions of test.
To prevent this problem, it is important to test the coarse aggregates for their reactivity before using them in concrete construction.
Alkali reactivity of cement-aggregate is determined by measuring the expansion developed by the combinations in mortar bars during storage under prescribed conditions of test.
Soundness Test of Aggregate
Soundness test of aggregate is a measure of its ability to resist changes in volume caused by chemical reactions, particularly when the aggregate is exposed to water or moisture. This test is important to ensure that the aggregate used in construction is durable and stable.
The soundness test involves exposing the aggregate to a solution of sodium or magnesium sulfate which simulates the effects of exposure to moisture. The aggregate is repeatedly immersed, dried and any changes in volume are measured as percentage loss.
Polished Stone Value Test
- Polished Stone Value is a measure of the resistance of a road aggregate to the polishing action of vehicle tires. It is an important factor in the construction of high-quality road surfaces particularly those designed to provide good skid resistance. This test of aggregate is determined by subjecting a sample of the material to a standard polishing process then measuring the frictional resistance of the polished surface using a specialized testing apparatus.
- The polished stone value of an aggregate is determined by the intrinsic properties of aggregate including its mineral composition, texture and strength.
- Aggregates with a higher polished stone value rating are generally more resistant to polishing and offer better skid resistance. This is important for road surfaces where vehicles need to maintain good traction to ensure safe driving conditions particularly in wet or slippery conditions.
- Its value is measured on a scale of 0 to 100 with 100 being the highest value. A polish stone value of 60 or greater is typically required for high-quality road surfaces such as those used for high-speed highways or runways and lower values are suitable for lower-speed roads and surfaces with less demanding skid resistance requirements.
Petrographic Examination of Aggregate
- Petrographic examination of aggregate is a detailed analysis of the physical and chemical properties of rocks and minerals that make up the aggregate used in construction. This examination is typically carried out to determine the suitability of the aggregate for use in various applications such as concrete, asphalt and road base.
- The process involves analyzing the mineral composition, texture and structure of the aggregate sample under a microscope. This is done to identify any potential problems that may arise during the construction process such as poor bond strength, alkali-silica reactivity and other chemical reactions that can lead to degradation and structural damage.
- Petrographic analysis can also involve testing for other properties such as density, porosity and strength. These tests help to determine the overall quality and durability of the aggregate.
- Petrographic examination of aggregate is an important step in ensuring the safety and longevity of construction projects. By identifying potential issues with the aggregate before construction begins, engineers and construction professionals can make informed decisions about the materials to use and how to properly design and construct the project.
Uses of Coarse Aggregate
Coarse aggregates are a type of construction material that is typically made up of materials such as gravel, crushed stone, or recycled concrete. They are an essential component in the production of concrete and other construction materials. The following are some common uses of coarse aggregates:
Concrete Work
The most common use of coarse aggregate is in the production of concrete. Coarse aggregates are mixed with cement, sand and water to create concrete that is used in the construction of buildings, bridges, roads and other structures. The coarse aggregate provides strength and stability to the concrete mix and is essential for its overall performance.
Road construction
Coarse aggregates are also used in the construction of roads and highways. They are used as a base layer for the road pavement and provide support and stability to the pavement structure. They also help to improve drainage and reduce the risk of potholes and other road damage.
Railroad Ballast
Coarse aggregates are used as railroad ballast which is the foundation for railroad tracks. The coarse aggregate provides stability and support to the tracks and helps to distribute the weight of the trains evenly. It also helps to prevent the tracks from shifting or settling over time.
Drainage Systems
Coarse aggregates are used in drainage systems to improve drainage and reduce the risk of flooding. They are used as a base layer in drainage trenches and in the construction of drainage pipes and culverts. The coarse aggregate helps to improve the flow of water and prevent clogging.
Landscaping
Coarse aggregates are also used in landscaping applications such as in the construction of retaining walls and decorative features. They provide a natural and attractive appearance and help to prevent erosion and soil displacement.
What are the Qualities of a Good Coarse Aggregate?
A coarse aggregate is a type of building material that is used in the construction industry. It is typically made up of materials such as gravel, crushed stone or recycled concrete. The following are some qualities of a good coarse aggregate:
Strength: A good coarse aggregate should be strong and able to withstand the forces that will be applied to it during construction.
Durability: The aggregate should be durable and able to withstand the effects of weathering and other environmental factors.
Shape: The shape of the aggregate particles should be uniform and not contain any flat or elongated particles that can lead to weak points in the structure.
Size: The size of the particles should be consistent and within a specific range to ensure proper compaction and stability.
Cleanliness: The aggregate should be clean and free from impurities such as clay, silt, and organic matter that can affect its performance.
Hardness: The aggregate should be hard enough to resist abrasion and wear over time.
Gradation: The gradation or distribution of particle sizes should be uniform and within specified limits to ensure good workability and strength.
Adhesion: The aggregate should have good adhesion properties to ensure that it bonds well with the cement paste.
By having these qualities, a good coarse aggregate can provide the necessary strength and stability to construction projects.
Read About Vastu For New Homes.
