Anti-washout admixture is a type of admixture used in underwater concreting. Its main purpose is to enhance the rheological properties of cement paste. This is achieved by adding microbial polysaccharides or their derivatives such as hydroxyethyl cellulose and hydroxypropyl methyl cellulose to the concrete mix. The use of this admixture significantly improves the cohesiveness of concrete that is poured underwater, reducing the risk of washout or segregation caused by the surrounding water. It is widely used in large repairing and placement applications.
The Antiwashout admixture is also referred to as a viscosity improving admixture, as it modifies the viscosity of the concrete mix. In some cases, this admixture is used to create self-compacting concrete, which is highly desirable in the construction industry. However, like any other admixture, Antiwashout admixture has its advantages and disadvantages.
One of the main advantages of using Antiwashout admixture is its ability to improve the workability and cohesiveness of concrete that is poured underwater. This increases the durability of the concrete and ensures that it adheres to the structure it is poured into. Additionally, this admixture is easy to use and readily available in the market.
On the other hand, the use of Antiwashout admixture also has some disadvantages. It can increase the cost of the concrete mix, making it more expensive to produce. Additionally, the admixture can have a negative impact on the setting time of the concrete, which can affect the overall strength of the structure.
In terms of classification, Antiwashout admixture is considered a type of superplasticizer. This is because it modifies the viscosity of the concrete, making it easier to work with and improving its overall properties. When using this admixture, it is important to consider factors such as dosage, mixing time, and environmental conditions to ensure that it is used correctly.
In conclusion, Antiwashout admixture is a highly useful admixture in underwater concreting. It improves the cohesiveness and workability of the concrete, reducing the risk of washout and segregation. However, it is important to consider its advantages, disadvantages, and practical considerations when using it in concrete mixes.
Fig.1: Anti-washout Admixture
Advantages of Anti-Washout Admixture for Underwater Concreting
When placing concrete underwater, it is necessary to use an anti-washout admixture in the concrete mixture. This admixture helps to prevent segregation and bleeding of the mixture, which can be problematic when working underwater. By increasing the amount of anti-washout admixture used, the dispersion rate of the concrete is decreased. This decrease in dispersion rate is actually beneficial when concreting underwater, as it allows for a more controlled placement of the mixture. Overall, the use of an anti-washout admixture is a crucial factor to consider when working with concrete in an underwater environment.
Disadvantages of Anti-Washout Admixture
Anti-washout admixture is a type of admixture that is commonly used in concrete mixes. While it can be effective in preventing segregation and reducing bleeding, there are some significant disadvantages associated with its use.
One of the most notable drawbacks of anti-washout admixture is that it can decrease the strength and modulus of elasticity of concrete. This reduction is influenced by a variety of factors, such as the concrete batch design, the water-to-cement ratio, the amount of admixture added, and the type of admixture used. Research has shown that the compressive strength and modulus of elasticity of concrete containing anti-washout admixture are typically between 75-100% and 80-100% of that of concrete without the admixture.
As a result of this decrease in strength and modulus of elasticity, reinforced concrete members may require additional reinforcement bars to maintain their structural integrity. This can have cost implications and may also affect the overall design of the structure.
Despite these disadvantages, anti-washout admixtures remain a popular choice in the construction industry, particularly in projects that involve underwater or pumped concrete applications. It is important for engineers and builders to carefully consider the potential impacts of anti-washout admixture on their concrete mix designs and to evaluate whether the benefits of using the admixture outweigh the potential drawbacks.
Dosage of Anti-Washout Admixture for Underwater Concreting
To achieve the desired properties in a concrete mixture, such as flowability, depth of placement, and distance of horizontal flow, it is necessary to add an Antiwashout admixture. The amount of Antiwashout admixture required is determined based on several factors, including the water to cementitious materials ratio and the quantity of cementitious materials to be used. It is important to ensure that the right amount of Antiwashout admixture is added to achieve the desired properties and ensure the durability of the concrete.
Classification of Anti-Washout Concrete Admixtures
It can be divided into the following classes:
Class-AAnti-Washout Admixtures
Class A is a type of admixture that can improve the viscosity of mixing water. It is composed of both water-soluble synthetic and natural organic materials, and is typically used in ranges between 0.2 to 0.5% solid by mass of cement. The purpose of Class A is to prevent the water from separating from the cement mixture, which is also known as washout.
Anti-washout admixtures are a specific type of Class A admixture that contain various substances such as cellulose ether, pregelatinized starches, carageenans, polyacrylamides, polyethylene oxides, alignates, carboxyvinyl polymers, and polyvinyl alcohol. These materials are added to the cement mixture to ensure that it remains stable and does not experience any significant washout. This can help to improve the overall quality and durability of the cement mixture.
Class-B Anti-Washout Concrete Admixtures
Organic flocculants are substances that have the ability to dissolve in water and be absorbed by cement particles. This results in an increase in viscosity by enhancing the attractions between cement particles. These flocculants belong to Class B and are typically added to cement in small amounts, between 0.01% to 0.10% of the solid mass of the cement.
Examples of Class B organic flocculants include styrene copolymers that have carboxyl groups, synthetic polyelectrolytes, and natural gums. These substances are used in a variety of applications to improve the properties of cement. By increasing the viscosity of the cement, the organic flocculants can enhance its performance and make it more effective in a range of industrial and construction settings.
In summary, organic flocculants are a type of substance that can be dissolved in water and absorbed by cement particles. They belong to Class B and are typically used in small amounts, between 0.01% to 0.10% of the solid mass of cement. Examples of Class B organic flocculants include styrene copolymers with carboxyl groups, synthetic polyelectrolytes, and natural gums. These substances are known to enhance the viscosity of cement by increasing the attractions between cement particles, making it more effective in a range of applications.
Class-C Anti-Washout Concrete Admixtures
Class C anti-washout admixture is a type of material that is added to cement paste to enhance its properties. These admixtures are typically made up of emulsions of various organic materials, which not only improve the attraction between particles but also help to create very fine particles within the cement paste. The amount of Class C anti-washout admixture that is typically added to the mixture ranges from 0.10% to 1.50% by mass of the cement.
Some examples of Class C anti-washout admixtures include paraffin-wax emulsions, acrylic emulsions, and aqueous clay dispersions. These materials are chosen for their ability to provide stability within the aqueous cement phase, which is an important consideration when selecting an anti-washout admixture.
Paraffin-wax emulsions are one type of Class C anti-washout admixture that is used in cement paste. These emulsions are not stable in the aqueous cement phase, but they are able to provide extremely fine particles in the paste, which can help to improve its overall properties. Acrylic emulsions are another type of anti-washout admixture that are commonly used. These materials are stable in the aqueous cement phase, and they can provide a range of benefits to the mixture, including improved workability and increased strength. Aqueous clay dispersions are also frequently used as Class C anti-washout admixtures. These materials are able to improve the stability of the mixture, while also helping to provide very fine particles that can enhance the overall properties of the cement paste.
Class-D Anti-Washout Concrete Admixtures
The described materials are inorganic and possess a large surface area. They are utilized to increase the mixture capacity for water retention. The amount used typically ranges from 1 to 25% of the solid mass of cement. Examples of these materials include bentonites, pyrogenic silicas, silica fume, milled asbestos, and other types of fibrous substances.
Class-E Anti-Washout Concrete Admixtures
Class E Antiwashout admixture is a type of material that is added to mortar pastes to provide extra fine particles. These particles are inorganic in nature and are used in varying amounts, typically between 1 to 25% of the solid mass of cement. The purpose of adding Class E Antiwashout admixture is to prevent the mortar from washing out, which can occur when it is exposed to water.
There are various materials that fall under the Class E category of Antiwashout admixture. Some examples include fly ash, hydrated lime, kaolin, diatomaceous earth, other raw or calcined pozzolanic materials, and various rock dusts. These materials are typically finely ground and are added to the mortar paste during the mixing process.
The use of Class E Antiwashout admixture is an important consideration in construction projects where the mortar is likely to be exposed to water. Without this type of admixture, the mortar can easily wash out and lose its structural integrity. By adding extra fine particles to the mix, the mortar is able to resist the effects of water and maintain its strength over time.
Principal Considerations for Anti-Washout Concrete Admixtures
When adding an anti-washout admixture to a concrete mixture, practical considerations must be taken into account. One of the most important factors to consider is the amount of concrete being used and the capacity of the mixer being utilized. This is due to the fact that the anti-washout admixture significantly increases the viscosity of fresh concrete, resulting in an increase of 25 to 50 percent in the load of fresh concrete.
To maintain the flowability of the concrete mixture, a high range water reducing admixture is often added in combination with the anti-washout admixture. This decreases the water demand of the concrete mixture, which is increased due to the addition of the anti-washout admixture. However, it is important to note that the high range water reducing admixture increases the setting time, so the types and dosages of these admixtures need to be carefully considered.
Another important consideration is the capacity of the pump being used. During the pressure transmission period, it is possible for high dispersion resistance blockage to occur in pump lines if issues are encountered within the pressure transmission tube. Additionally, the large viscosity of the concrete mixture increases the pressure transmission resistance by 2 to 4 times that of conventional concrete. Therefore, it is important to ensure that the pump used has the capacity to handle the increased pressure transmission resistance.