Concrete is the most widely used construction material in the world, and for good reason. Its strength, durability, and versatility make it an essential component in countless structures, from buildings to bridges to dams. However, to achieve the desired characteristics and performance, concrete is often enhanced by the addition of admixtures. These substances not only improve the properties of concrete but also make it more cost-efficient and eco-friendly. In this article, we will delve into the world of admixture of concrete, exploring its various types, functions, and benefits. Whether you are a construction professional or simply curious about the science behind concrete, this article will provide a comprehensive understanding of admixtures and their role in enhancing the world’s most widely used building material.
What is admixture of concrete and its types and uses.
Admixtures are products that are added to concrete during the mixing phase in order to improve the properties of the final concrete mixture. They are used to alter the color, durability, strength, workability, or segregation of concrete. Admixtures are commonly used in construction to improve the quality of concrete and make it easier to work with. There are various types of admixtures available in the market which are used for different purposes. In this article, we will discuss what admixtures are, their types, and their uses in concrete.
What is Admixture of Concrete?
Admixtures are supplementary products that are added in small quantities to the concrete to achieve the desired properties. They are added during the mixing process or during the transportation of concrete. Admixtures can be classified into two main categories: chemical admixtures and mineral admixtures.
Chemical admixtures are water-soluble chemicals that are added to concrete in the form of solution, liquid, or powder. They are used to modify the properties of fresh or hardened concrete. They improve the workability, delay the setting time, reduce the water content, and enhance the strength and durability of concrete. Chemical admixtures can be further classified into seven types as follows:
1. Water-Reducing Admixtures: These admixtures reduce the amount of water required to mix concrete without affecting the workability. They help to increase the strength and durability of concrete by reducing the water-cement ratio.
2. Retarding Admixtures: As the name suggests, these admixtures slow down the setting time of concrete. They are commonly used in hot weather conditions to prevent the concrete from setting too quickly.
3. Accelerating Admixtures: These admixtures accelerate the setting time of concrete and are used in cold weather conditions to speed up the construction process.
4. Air-Entraining Admixtures: These admixtures are used to create air bubbles in concrete. They increase the workability of concrete and improve its freeze-thaw resistance.
5. Superplasticizers: Superplasticizers are used to increase the flow of concrete without increasing the water content. They are also known as high-range water-reducing admixtures and can improve the workability of concrete by up to 30%.
6. Corrosion-Inhibiting Admixtures: These admixtures are used to prevent the corrosion of reinforcement bars in concrete. They work by forming a protective layer around the steel bars, which prevents water and oxygen from reaching them.
7. Shrinkage-Reducing Admixtures: These admixtures reduce the shrinkage of concrete during the drying process. They also help to reduce the formation of cracks in the concrete.
Mineral admixtures are inert materials that are added to concrete to improve its properties. They are obtained from natural sources and have cementitious properties. They can also be manufactured by industrial processes. Mineral admixtures can be further classified into three types as follows:
1. Pozzolanic Admixtures: These admixtures are made from volcanic ashes, shale, or fly ash. They react with calcium hydroxide in the presence of water to form a cementitious compound, which improves the strength and durability of concrete.
2. Siliceous Admixtures: These admixtures contain amorphous silica and are used to increase the strength and durability
Use of admixture in concrete
Admixtures are ingredients that are added to concrete during its mixing to enhance its properties and improve its performance. These chemicals are added in small quantities and can significantly change the properties of freshly mixed or hardened concrete. The use of admixtures provides numerous benefits such as increased strength, improved workability, reduced water/cement ratio, and decreased setting time, among others. In this article, we will discuss the types, benefits, and applications of admixtures in concrete.
Types of Admixtures:
1. Accelerators: Accelerating admixtures are used to speed up the setting and hardening process of concrete. These admixtures are commonly used in cold weather conditions to achieve rapid strength gain and reduce the curing time.
2. Retarders: Retarding admixtures are used to slow down the setting time of concrete. They are used in hot weather conditions to prolong the workability of concrete. Retarders are also used in large concrete pours to prevent cracking and improve the finish of concrete surfaces.
3. Water Reducers: These admixtures are also known as plasticizers and are used to reduce the amount of water needed for concrete mixtures. By reducing the water content, water reducers improve the workability and pumpability of concrete.
4. Air-Entraining Admixtures: Air-entraining admixtures produce tiny air bubbles in concrete that improves its durability against freeze-thaw cycles by allowing the water to expand during freezing without damaging the concrete structure.
5. Superplasticizers: These admixtures are used to increase the workability of concrete without increasing the water content. Superplasticizers are commonly used in self-compacting concrete and high-strength concrete constructions.
Benefits of Admixtures:
1. Improved Workability: Admixtures can significantly improve the workability of concrete by reducing the water content or adding air bubbles. This makes the concrete easier to place and finish, leading to cost savings on labor and equipment.
2. Increased Strength: Admixtures can enhance the strength of concrete and reduce the amount of cement needed to achieve desired strength. This not only results in cost savings but also reduces carbon emissions from cement production.
3. Durability: Air-entraining admixtures improve the durability of concrete by reducing the number of voids and preventing cracking due to freeze-thaw cycles. Retarding admixtures can also improve the durability of concrete by preventing cracking due to a rapid temperature change.
4. Cost Savings: The use of admixtures in concrete can result in cost savings by reducing the amount of cement, improving workability, and reducing labor and equipment costs.
Applications of Admixtures:
1. Bridge Construction: Admixtures are widely used in bridge construction to achieve high strength and durability required for this type of structure. Accelerators are also used to speed up the construction process and reduce curing time.
2. High-Rise Buildings: Superplasticizers are commonly used in high-rise buildings to improve the workability and strength of concrete used in vertical structures.
3. Mass Concrete Structures: Admixtures are used in mass concrete structures such as dams and retaining walls to prevent cracking due to a high temperature rise during hydration.
4. Ready-Mix Concrete: Admixtures are commonly used in ready-mix concrete as they can enhance its properties and make it easier to transport and place at the construction site.
In conclusion, the use of admixtures in concrete has revolutionized the construction
Concrete admixture types according to origin
Concrete admixtures are chemical compounds used in concrete mixes to improve its durability, workability, and strength. They are added to the concrete during the mixing process and play a significant role in enhancing the properties of concrete. Admixtures can be classified into various types based on their origin, including organic, inorganic, and mineral admixtures.
1. Organic Admixtures:
These are admixtures that are derived from natural products such as carbohydrates, lignin, tannin, and cellulose. They are organic substances and are extracted from organic matter such as plants, animals, and microorganisms. Examples of organic admixtures include:
i) Lignosulfonates: These are extracted from wood pulp and are widely used as water-reducing agents in concrete. They are particularly useful in hot weather concreting as they reduce the water content in concrete without affecting its workability.
ii) Hydrocarbons: These are derived from petroleum and are used as air-entraining agents in concrete. They create small air bubbles in the concrete, which improve its workability and resistance to freezing and thawing.
iii) Starch and sugar: These organic admixtures improve the slump and strength of concrete. They also act as retarders, which delay the setting time of concrete, allowing more time for placement and finishing.
2. Inorganic Admixtures:
These are derived from non-organic materials such as salts, oxides, and hydroxides. They are primarily used to modify the setting time and strength of concrete. Examples of inorganic admixtures include:
i) Calcium chloride: This is a commonly used admixture in concrete, which accelerates the rate of hydration and setting of concrete, especially in cold weather conditions.
ii) Calcium nitrate: This is another admixture that accelerates the setting time of concrete. It is particularly useful in hot weather conditions where the concrete sets too quickly.
iii) Fly ash: This is a by-product of coal combustion and is used as a partial replacement for cement in concrete. It increases the long-term strength of concrete and reduces the heat of hydration.
3. Mineral Admixtures:
These are derived from natural or synthetic sources and are used to improve the properties of concrete. Examples of mineral admixtures include:
i) Silica fume: This is a by-product of silicon and ferrosilicon alloy production. It is a highly reactive pozzolanic material that improves the strength and durability of concrete.
ii) Ground granulated blast furnace slag (GGBFS): This is a by-product of iron production and is used as a partial replacement for cement in concrete. It improves the workability, durability, and resistance to sulfates and alkalis.
iii) Metakaolin: This is a pozzolanic material derived from the calcination of kaolin clay. It improves the compressive strength, durability, and workability of concrete.
In conclusion, concrete admixtures play a crucial role in modern construction, and their use has greatly enhanced the properties of concrete. Different types of admixtures from various origins have unique characteristics and are used depending on the specific requirements of a construction project. As a civil engineer, it is essential to have a good understanding of the different types of admixtures and their applications to ensure the successful completion of a construction project.
Concrete admixture types according to function
Concrete admixtures are chemical additives that are used to improve the properties of concrete, such as strength, workability, and durability. They are added to the concrete mix during mixing or directly into the concrete truck during transportation to the construction site. Admixtures are classified according to their function, and different types of admixtures are used based on the specific needs of the project.
1. Plasticizers and Superplasticizers:
These admixtures are used to improve the workability and flow of concrete. Plasticizers, also known as water reducers, reduce the water content in the concrete mix, making it easier to work with and reducing the chances of segregation. On the other hand, superplasticizers are highly effective water reducers, allowing for much higher water reduction in the concrete mix without affecting the workability. This results in a high-strength and highly workable concrete mix.
2. Air-Entraining Admixtures:
Air-entraining admixtures are used to improve the freeze-thaw resistance of concrete. They create tiny air bubbles in the concrete mix, which improves its ability to withstand freeze-thaw cycles without cracking. This is particularly important in areas with cold weather conditions.
Accelerators are used to speed up the setting time of concrete. They are often used in cold weather conditions or when a project has tight deadlines. Adding accelerators to concrete allows for faster strength gain, reducing the time needed for curing and formwork removal.
Retarders are the opposite of accelerators, and they are used to slow down the setting time of concrete. They are particularly useful in hot weather conditions or when the concrete needs to be transported over long distances. Retarders allow for more time to place and finish the concrete before it sets, reducing the risk of cracking or low strength.
5. Corrosion Inhibitors:
Corrosion inhibitors are used to protect the reinforcing steel in concrete from rusting. They form a protective layer around the steel, preventing it from coming into contact with oxygen and moisture, which are the main causes of corrosion. This type of admixture is essential for structures exposed to harsh environmental conditions, such as marine or industrial environments.
6. Shrinkage Reducing Admixtures:
Shrinkage reducing admixtures are used to reduce the drying shrinkage of concrete. They work by reducing the surface tension of water in the concrete mix, allowing it to evenly distribute throughout the concrete. This results in less shrinkage and cracking, making it a crucial admixture for large concrete structures.
7. Waterproofing Admixtures:
As the name suggests, waterproofing admixtures are used to make concrete impermeable to water. They work by reducing the size of the capillary pores in concrete, making it difficult for water to pass through. This type of admixture is commonly used in basements, underground structures, and water tanks.
In conclusion, the choice of concrete admixture depends on the specific requirements of each project. By using the right admixtures, engineers can enhance the properties of concrete and ensure the success and durability of the structure. It is important to consult with a professional and experienced supplier to determine the best admixtures for a specific project.
In conclusion, admixtures play a crucial role in enhancing the properties and performance of concrete. From improving workability to increasing strength and durability, the use of admixtures offers numerous benefits to concrete construction. With the various types of admixtures available, it is important to understand their purpose and dosage to achieve the desired results. By carefully selecting and incorporating admixtures, concrete can be customized to meet specific project requirements and overcome construction challenges. The proper use of admixtures not only improves the quality of concrete but also saves time and reduces costs. Therefore, it is essential for construction professionals to have a thorough understanding of admixtures and their types to utilize them effectively in their projects.