Civil site engineers need to have a thorough understanding of concrete admixtures (additives) and their properties to effectively enhance the properties of concrete for use in construction projects with specific requirements. These additives are crucial in achieving the desired workability of concrete in instances where the water cement ratio is low. Additionally, they play a critical role in improving the setting time of concrete for long distance transportation.
It is important for civil site engineers to be aware of the different types of concrete admixtures and their respective properties. This knowledge enables them to make informed decisions when selecting and applying these additives to concrete works. By understanding the unique properties of each additive, engineers can ensure that the concrete used in construction projects meets the desired specifications and standards.
In summary, concrete admixtures are essential components in the construction industry, and their proper selection and application can greatly enhance the quality and durability of concrete. Civil site engineers should be knowledgeable about the types and properties of these additives to ensure that the concrete used in their projects meets the required standards and specifications.
Definition of Concrete Admixtures
According to the definition provided by BIS (IS – 9103: 1999) on page one, a concrete admixture is a substance that is distinct from water, aggregates, hydraulic cement, and additives such as Pozzolana or slag, as well as fiber reinforcement. This substance is included as an ingredient in concrete or mortar and is added to the batch just before or during the mixing process to alter one or more properties of the concrete in either its plastic or hardened state. In simpler terms, a concrete admixture is a material used in the production of concrete to modify its properties during or after its mixing, and it is not part of the main ingredients of concrete, such as water, cement, and aggregates.
Reasons for Using Admixtures (ACI Committee Report Page – 298)
Admixtures play a crucial role in altering the characteristics of concrete or mortar to better fit the requirements of a particular project, improve cost efficiency, or achieve other desired outcomes such as reducing energy consumption. These substances are added to the mixture in order to modify its properties and make it more suitable for the intended purpose.
The use of admixtures can serve a variety of important purposes, including improving workability, increasing strength and durability, enhancing setting time, and reducing water demand. Admixtures can also be employed to create special finishes or textures, improve resistance to extreme weather conditions, or increase the rate of strength development.
Overall, the use of admixtures provides greater flexibility in designing and constructing concrete and mortar structures, as well as reducing costs and improving performance.
To modify properties of fresh concrete, mortar and grout to:
To improve the workability of concrete without increasing its water content or to decrease the water content while maintaining the same workability, various techniques can be employed. These techniques include the use of superplasticizers, which are chemical admixtures that allow for the reduction of water content while improving the workability of concrete. Another approach is to use pozzolanic materials, such as fly ash or silica fume, which can also enhance the workability of concrete without increasing its water content.
The setting time of concrete can also be adjusted by the use of chemical admixtures. Retarding agents, such as lignosulfonates, can be added to prolong the setting time of concrete, while accelerating agents, such as calcium chloride, can be used to speed up the setting time. These adjustments can be useful in situations where concrete needs to be transported over long distances or in high temperatures.
To reduce or prevent settlement in concrete, proper mixture design is crucial. Using a proper proportion of coarse and fine aggregates, as well as controlling the amount of water added during mixing, can help prevent segregation and improve the homogeneity of the mix. The use of vibration during pouring and compaction can also help to reduce settlement.
Bleeding, which is the separation of water from the mix, can be controlled by using admixtures that modify the rate or capacity for bleeding. For example, using air-entraining agents can create small bubbles in the mix, which can help to stabilize the mixture and reduce bleeding. Additionally, using finely ground pozzolanic materials can also help to reduce bleeding.
To improve pumpability, it is essential to ensure the right consistency of the mix. Using a lower water-cement ratio can help to create a stiffer mix that is easier to pump. Additionally, the use of pump-friendly admixtures, such as viscosity modifiers, can improve pumpability.
Finally, to reduce the rate of slump loss, which is the reduction in workability over time, the use of retarding agents can be beneficial. Retarding agents slow down the hydration process, allowing for more time to work with the mix before it sets. Using proper curing techniques, such as covering the concrete with wet burlap or using a curing compound, can also help to reduce slump loss.
To modify the properties of hardened concrete, mortar and grout to:
There are several ways to enhance the performance of concrete and mortar. One approach is to retard or reduce heat evaluation during early hardening, which can help prevent cracking and improve the overall durability of the material. Additionally, accelerating the rate of strength development at early ages can be beneficial for structures that need to bear loads quickly.
Another important consideration is increasing the strength of the material. This can involve enhancing compressive, tensile, or flexural strength, depending on the specific needs of the project. Improving durability and resistance to severe conditions of exposure can also be achieved through a variety of methods, such as decreasing permeability or controlling expansion caused by the reaction of alkalies with certain aggregate constituents.
To improve the bond between concrete and steel reinforcement, it may be necessary to increase the bond of concrete itself to the reinforcement. Additionally, increasing the bond between existing and new concrete can be important for repair and restoration projects. Furthermore, improving impact and abrasion resistance can be achieved through the use of specialized additives or coatings.
Inhibiting corrosion of embedded metal is another important consideration, as it can help prevent structural damage and prolong the lifespan of the concrete. Finally, for aesthetic purposes, it may be desirable to produce colored concrete or mortar. Overall, there are numerous strategies that can be employed to enhance the performance of concrete and mortar, depending on the specific needs of the project.
When Concrete Admixtures Used?
When attempting to achieve certain outcomes in a cost-effective manner, it may not always be possible to create properties by adjusting the composition of fundamental materials. It is also important to note that while the use of additives can enhance certain properties of concrete, it is not a solution for poor quality concrete. Adequate concrete practice must still be followed, and the appropriate dosage of additives must be accurately determined and administered.
How to Use Concrete Admixtures?
To ensure proper job execution, it is important to adhere to the job specification guidelines. One must always use the correct admixture and avoid using any from unmarked containers as it can lead to errors or accidents. Additionally, it is essential to keep containers closed when not in use to prevent accidental contamination.
When adding admixtures, it is important to use the correct dosage and avoid adding even a small amount extra, as it can negatively impact the outcome of the job. A dispenser can be used to ensure precise measurements.
At the end of each workday, it is crucial to wash thoroughly to prevent any potential health hazards or contamination. It is also best to add admixtures to the mixing water, following the manufacturer’s recommended dosage, as this is usually sufficient.
Trial mixes are necessary to determine the most effective dosage for each job. By conducting trials, one can adjust the dosage as needed to achieve optimal results. Following these guidelines will ensure proper job execution and satisfactory results.
Types of Concrete Admixtures (Additives)
According to the American Concrete Institute Committee report and IS 9103: 1999, there are various types of admixtures that can be used in concrete. These include accelerating admixtures, which speed up the setting time of concrete, retarding admixtures, which slow down the setting time of concrete, and water-reducing and set controlling admixtures, which reduce the amount of water needed in the mix and control the setting time.
Air-entraining admixtures are also commonly used, as they introduce tiny air bubbles into the concrete to increase its durability and resistance to freeze-thaw cycles. Super plasticizing admixtures are another type, which allow for a higher degree of workability in the concrete mix without compromising its strength or durability.
Admixtures for flowing concrete can also be used to make the concrete easier to pour and work with, while miscellaneous admixtures can serve various other purposes such as improving the concrete’s color or preventing corrosion.
Another classification of admixtures can be found in the book “Concrete Admixtures: Use and Applications” edited by M. R. Rixom, which provides further insights into the types and uses of these materials.
1. Air Entraining Admixture
Air-entraining agents are chemical additives that are commonly used in construction materials to enhance their properties. These agents are added to improve the workability of the material, making it easier to handle and shape during the construction process. Additionally, air-entraining agents can increase the durability of the material, making it more resistant to damage and wear over time.
One important benefit of air-entraining agents is their ability to improve resistance to frost action. In cold climates, water can penetrate building materials and freeze, causing damage as it expands. Air-entraining agents can help prevent this damage by creating tiny air bubbles within the material, which provide space for the water to expand into when it freezes.
Reducing bleeding is another benefit of air-entraining agents. Bleeding occurs when water in the construction material rises to the surface and evaporates, leaving behind a layer of fine particles that can weaken the material. By creating air bubbles within the material, air-entraining agents help to prevent water from rising to the surface and reduce bleeding.
There are several types of air-entraining agents, including natural wood resins, neutralized vinsol resins, polyethylene oxide polymers, and sulfonated compounds. These agents are selected based on the specific properties required for the construction material. Overall, air-entraining agents are an important tool for improving the performance of construction materials and ensuring their long-term durability.
Mechanism of Air Entraining Concrete Admixtures
Anionic surface active agents have hydrocarbon structures that contain negatively charged hydrophilic groups such as COO, SO3, and OSO. When these agents are released in water, large anions are produced. On the other hand, if the hydrocarbon ion is positively charged, the compound is considered cationic. Therefore, cationic surface active agents produce positively charged bubbles.
It is important to note that surface active agents of all classes have the ability to cause air entrainment in concrete. However, their efficiency and characteristics of the air-void system can vary widely. Anionic surface active agents, specifically, produce bubbles that are negatively charged, while cationic agents cause bubbles to be positively charged.
Properties of Air entraining Admixtures
Foaming agents are a type of chemical that produce gas, and are commonly used in concrete mixes. Their primary function is to introduce millions of small, stable bubbles into the mix, which are uniformly distributed and account for approximately 5% of the mix’s volume. This results in a number of benefits for the properties of fresh concrete, including increased workability and cohesion, and reduced segregation and bleeding.
In addition to their positive effects on fresh concrete, foaming agents also have significant benefits for hardened concrete. It is well known that the presence of air in concrete can lead to a loss of strength, with a 4% reduction in strength for every 1% of air present. However, this loss can be minimized by reducing the water content in the mix. Furthermore, the use of foaming agents has been shown to improve the durability of hardened concrete, making it more resistant to wear and tear over time. Overall, foaming agents are an important tool in the construction industry, helping to improve the quality and longevity of concrete structures.
2. Accelerating Admixtures
Accelerating admixtures are a type of substance that is commonly used in concrete construction to speed up the setting process. These admixtures can help concrete to achieve a higher level of early strength development, which is particularly useful in situations where the freshly cast concrete needs to be used or loaded quickly.
The use of accelerating admixtures can be beneficial in a variety of construction projects where there is a need for concrete to set and cure quickly. By using these admixtures, construction workers can achieve a higher level of productivity and efficiency on the job site, as they can move on to the next phase of the project more quickly.
In addition to their ability to speed up the setting process, accelerating admixtures can also improve the overall quality of the concrete. They can help to reduce the risk of cracking and other forms of damage that can occur when concrete sets too slowly or unevenly. This can ultimately lead to a longer lifespan for the finished construction project.
Overall, the use of accelerating admixtures is a common practice in concrete construction that can provide many benefits for both the construction workers and the finished project itself. By accelerating the setting process and improving the quality of the concrete, these admixtures can help to ensure that construction projects are completed efficiently and to a high standard.
Main uses of Accelerating Concrete Admixtures
The following paragraph discusses admixtures suitable for use in winter conditions and emergency repair work:
Admixtures can be added to concrete to improve its properties in certain conditions. In winter, certain admixtures can be used to help the concrete set and cure properly despite low temperatures. These admixtures include accelerators that speed up the setting time and reduce the time required for the concrete to gain sufficient strength. In emergency repair work, admixtures can also be used to quickly restore the integrity of the structure without compromising its durability.
The following paragraph discusses admixtures suitable for use in early removal of formwork:
Admixtures can also be used to facilitate the early removal of formwork. These admixtures are known as form release agents and they prevent the concrete from sticking to the formwork. This allows the formwork to be removed earlier than usual, which can save time and improve productivity. However, it is important to use form release agents properly to avoid compromising the quality and durability of the concrete.
Disadvantages of Accelerating Concrete Admixtures
The first statement suggests that there is an increase in drying shrinkage, which can be problematic for the material being used. The second statement implies that there is a reduced resistance to sulphate attack, which can lead to damage to the material. Both of these issues can negatively impact the quality and durability of the material, which can result in additional costs for repairs or replacement.
The third statement highlights a specific risk associated with the use of CaCl2, which can potentially cause corrosion of steel. This is particularly concerning in reinforced concrete structures, as the corrosion of steel can weaken the overall structure and compromise its safety. Therefore, the use of CaCl2 is not permitted in reinforced concrete applications.
Lastly, the fourth statement suggests that the material in question is both more expensive and less effective than alternative options. This can be a significant drawback, as it may make the material less competitive in the market and less appealing to potential customers.
3. Water Reducing Admixtures
Chemical Types for Water Reducing Admixtures
The two substances mentioned are different types of chemical compounds. One is the calcium or sodium salt of lignosulfonic acid, while the other is a poly carboxylic acid.
The calcium or sodium salt of lignosulfonic acid is a type of chemical compound that is derived from lignin, which is a complex organic substance found in the cell walls of many plants. This salt is commonly used as a dispersant in various industrial applications, such as in the production of concrete and ceramics, as well as in the processing of certain types of ores.
On the other hand, a poly carboxylic acid is a type of organic compound that contains multiple carboxylic acid groups within its structure. These acids are often used as dispersants or water-soluble polymers in a wide range of industrial applications, such as in the production of detergents, paints, and pharmaceuticals.
Both the calcium or sodium salt of lignosulfonic acid and poly carboxylic acids have important industrial uses and are key components in many manufacturing processes. However, they are distinct chemical compounds with unique properties and applications.
Mode of Action
Water reducing admixtures contain long-chain organic molecules that have hydrophobic and hydrophilic ends. These molecules form a film at the interface between cement and water, altering the physio-chemical forces acting at this interface. This film concentration allows the admixture to reduce the interfacial tension and increase the electrokinetic potentials.
The primary role of water reducing admixture is to deflocculate or disperse the cement agglomerates into primary particles or smaller fragments. This deflocculation is a physiochemical effect that occurs when the admixture is adsorbed onto the surface of the hydrating cement, forming a hydration “sheath” that reduces the anti-particle separation. The presence of water reducing admixture in fresh concrete results in a protection sheath of water dipoles around each particle, making the mobility of the fresh mix greater.
The presence of water reducing admixture in a fresh concrete mix reduces the inter-particle forces, making water freed from the highly flocculated system available to lubricate the mixture. As a result, less water is required to achieve a given consistency. Overall, the use of water reducing admixture improves the properties of fresh concrete by enhancing workability, reducing the water-cement ratio, and improving the mechanical strength of the hardened concrete.
Why Water Reducing Admixtures are used?
a) It is possible to produce concrete with higher workability without using additional water. This approach can prevent any reduction in strength and ensure that the concrete remains strong.
b) Another method to increase the strength of concrete is by using a lower water content while maintaining a certain level of workability. This technique eliminates the need for extra cement, which can lead to higher costs.
c) It is possible to achieve the same strength in concrete as the reference concrete by using the same water-to-cement ratio and workability. However, the amount of cement required can be reduced by using this technique, which can result in cost savings.
Effect on durability
The context suggests that the addition of certain types of admixtures does not lead to an increase in permeability. On the other hand, when the admixture is utilized to lower the water-to-cement ratio (w/c), it results in a significant reduction in permeability.
It can be inferred from the given statement that the effect of admixtures on permeability is dependent on their type and intended purpose. When admixtures are added without altering the w/c ratio, they may not have a significant impact on the permeability of the material.
However, when the admixture is employed to lower the w/c ratio, it can lead to a considerable decrease in permeability. This could be due to the fact that a lower water content results in a denser and more compact material, with fewer pores and channels for water to flow through.
Overall, the given context highlights the importance of selecting the appropriate admixture for a given application and utilizing it in the correct manner to achieve the desired outcome in terms of permeability reduction.
Effect on shrinkage
There is a type of admixture that can be used as workability aids on water reducers without negatively affecting shrinkage.
Effect on creep
Admixtures are substances added to concrete to enhance its properties or improve its workability. One important property of concrete is its resistance to deformation under sustained load, which is known as creep. The creep of concrete can lead to structural problems and is a major concern in construction.
There are some types of admixtures that do not have a negative impact on the creep of concrete. These materials can be added to the mixture without causing any detrimental effects on the long-term deformation behavior of the concrete. This is an important consideration for construction projects that require long-lasting, durable structures.
By using these admixtures, engineers and builders can improve the performance of the concrete without compromising its structural integrity. This allows for greater flexibility in the design and construction of buildings and infrastructure, as well as increased longevity and durability of the final product. The use of admixtures that do not affect the creep of concrete is therefore an important aspect of modern construction practices.
Detrimental effect
a) When using water reducing agents, it is important to exercise caution and pay close attention to the air content in the mixture. This is because many water reducing agents tend to entrain air as a result of their surfactant properties. Therefore, proper control of the air content is necessary to ensure that the mixture achieves the desired consistency and strength.
b) In situations where lignosulphonate material is used in high dosages, retardation of the mixture may occur. This means that the mixture may take longer to set and achieve the desired strength. It is important to monitor the dosage levels of lignosulphonate material to ensure that the mixture does not become overly delayed in setting, which can cause issues during construction or other applications where timely setting is important.
Applications of Water Reducing Concrete Admixtures
Admixtures are added to concrete for various reasons. One of the reasons is when concrete pours are restricted due to congested reinforcement or narrow sections. In such cases, admixtures can help improve the workability of the concrete, making it easier to pour and place.
Another reason for adding admixtures is when harsh mixes are encountered, such as those produced with crushed aggregates. Adding admixtures can significantly enhance the plastic properties of the concrete, making it more durable and easier to handle.
Admixtures can also be used when required strengths are difficult to achieve within the specified maximum cement content, or when early lifting strengths are necessary. In such cases, admixtures can improve the strength and durability of the concrete, making it more suitable for the intended purpose.
Finally, admixtures can be added to concrete to achieve cement economics of about 10%. This means that by using admixtures, less cement is needed to achieve the desired properties, resulting in cost savings.
4. Retarding Concrete Admixtures
Retarding concrete admixtures serve the purpose of prolonging the setting time of cement paste in concrete, which can be beneficial in a variety of scenarios. For instance, it can be helpful when concrete needs to be transported over long distances in transit mixers. Additionally, this type of admixture can be particularly useful when placing concrete in high-temperature environments.
In particular, retarding admixtures are commonly employed as grouting admixtures, and can also function as water reducers. In fact, the use of these admixtures has been shown to improve the strength and durability of concrete. By delaying the setting time, concrete is able to maintain its workability for a longer period, ultimately leading to a better end result.
Chemical type for Retarding Concrete Admixture
Unrefined lignosulphonates are known to contain sugar, which is responsible for causing retardation. Hydroxyl carboxylic acid and their salts, carbohydrates including sugar, soluble zinc, and soluble borates are also commonly used components in various industrial applications. These components can have different effects on the performance and properties of the final product. For instance, the presence of sugar in unrefined lignosulphonates can lead to retardation, while soluble zinc and borates can provide additional benefits such as improved durability or fire resistance. Similarly, hydroxyl carboxylic acid and their salts can be used as chelating agents or to modify the pH of a solution, among other functions. Overall, the selection of components depends on the specific requirements and objectives of the application, as well as on the cost and availability of the materials.
Mode of action
Retarding admixtures are commonly used in cement to delay the setting time of the mixture. It is believed that these admixtures are absorbed onto the C3A phase of the cement, which forms a film around the cement grains. This film can then present or reduce the reaction of the cement with water, thereby retarding the setting process.
Although this film is effective at delaying the setting time, it eventually breaks down, allowing normal hydration to proceed. The breakdown of the film can be a gradual process, which is why retardation can be extended for a period of many days.
While the interaction between retarding admixtures and the C3A phase of cement is well established, there is also reason to believe that these admixtures can interact with the C3S phase. This is because retardation can be extended for a prolonged period, suggesting that the admixtures are not just affecting the early stages of the hydration process.
Overall, the use of retarding admixtures is a common practice in the construction industry to allow for more flexibility in the handling and placement of cement mixtures. By understanding how these admixtures interact with the different phases of cement, researchers can further optimize their use and develop new and improved formulations.
Why Retarding Concrete Admixtures are used?
Concrete is a versatile building material that is widely used in construction. One of the challenges faced during the construction process is ensuring that the concrete sets properly within the desired timeframe. However, in some situations, it may be necessary to delay the setting time of the concrete without compromising its subsequent strength development.
To achieve this, it is important to use the appropriate materials and techniques. For example, adding certain chemicals or admixtures to the concrete mix can help to slow down the setting process. These chemicals work by delaying the reaction between the water and cement, which is responsible for the setting process.
It is important to note that delaying the setting time of concrete can also have an impact on its overall strength development. Therefore, it is crucial to select the right materials and techniques that will not adversely affect the concrete’s strength. This may involve testing the concrete mix in a laboratory to determine the optimal combination of materials and techniques that will achieve the desired result.
By delaying the setting time of concrete without adversely affecting its strength development, construction professionals can have greater flexibility in their construction timelines. This can be especially beneficial in situations where unexpected delays or changes in the construction plan occur, allowing the concrete to be used at a later stage without compromising its quality.
Advantage of Retarding Concrete Admixture
Paragraph 1: The use of hydroxyl carboxylic acid type admixture in concrete production typically results in a slightly lower water content compared to a control mix.
Paragraph 2: Some materials belonging to this class, such as those containing lignosulphonate, sugar, and derivatives of hydroxyl carboxylic acid, can have a significantly greater dispersing effect, leading to a higher capacity for water reduction in certain cases.
Paragraph 3: The use of these admixtures can also lead to an increase in the durability of the resulting concrete.
Detrimental effect
a) The use of lignosulphonate based material may lead to a slightly higher air content in the mixture, typically ranging from 0.2 to 0.3%. However, this can be mitigated by adding materials of the tributyle phosphate type.
b) An increase in the amount of water in a mixture can cause the material to experience drying shrinkage. This means that as the water evaporates, the material may shrink, resulting in potential issues such as cracking or deformation. Therefore, it is important to carefully consider the water content when preparing a mixture to ensure that the final product has the desired properties and performance.
Applications of Retarding Concrete Admixture
Retarding admixtures are commonly used in concrete construction to slow down the setting time of the concrete. This type of admixture is particularly useful in situations where long transportation of ready mixed concrete is required, as it helps to avoid premature setting. This is because during transportation, concrete can be subjected to a range of temperatures and conditions that can accelerate the setting process, leading to potential problems with workability and finishing. By using a retarding admixture, the setting time can be extended, giving workers more time to place and finish the concrete.
Another situation where retarding admixtures are useful is when concrete is being placed or transported under conditions of high ambient temperature. In hot weather, concrete can set very quickly, making it difficult to achieve a smooth and uniform finish. By using a retarding admixture, the setting time can be slowed down, allowing workers to place and finish the concrete properly.
Retarding admixtures are also commonly used in the case of large concrete pours, where the sheer volume of concrete can make it difficult to control the setting time. By adding a retarding admixture to the mix, the setting time can be slowed down, giving workers more time to place and finish the concrete.
Finally, retarding admixtures are often used in concrete construction involving sliding formwork. Sliding formwork is a technique used to pour large concrete structures, such as bridges or tall buildings, in a continuous pour. This requires a steady supply of fresh concrete, which can be difficult to maintain without the use of a retarding admixture. By slowing down the setting time of the concrete, workers can ensure that the pour remains continuous and that the finished structure is uniform and strong.
5. Super Plasticizers or High Range Water-Reducing Admixtures in Concrete
The second generation admixture, also known as Superplasticizers, are a type of synthetic chemical product that is made from organic sulphonates. These sulphonates are of the RSO3 type, where R is a complex organic group of higher molecular weight. These products are produced under carefully controlled conditions to ensure their quality and effectiveness.
Superplasticizers are considered to be an advancement in the field of admixtures, as they have superior properties compared to their first-generation counterparts. They are specifically designed to improve the workability of concrete, without compromising its strength or durability. This makes them a popular choice for a variety of construction projects, especially those that require high-performance concrete.
The production process of these superplasticizers is carefully monitored to ensure that they meet strict quality standards. This involves controlling factors such as temperature, pressure, and reaction time to ensure that the final product is of the desired quality. These products have been extensively researched and tested to ensure their effectiveness and safety for use in construction projects.
In summary, the second generation admixture, or superplasticizers, are synthetic chemical products made from organic sulphonates of the RSO3 type, with a complex organic group of higher molecular weight. These products are carefully produced under controlled conditions to ensure their quality and effectiveness, and they are widely used in construction projects to improve the workability of concrete without compromising its strength or durability.
The commonly used superplasticizer are as follows:
The context appears to be a list of three different chemical compounds: sulphonated melamine formaldehyde condensate (SMFC), sulphonated naphthalene formaldehyde condensate (SNFC), and modified ligno-sulphonates and other sulphonic esters and acids.
Sulphonated melamine formaldehyde condensate (SMFC) is a type of polymer that is produced by the condensation of melamine and formaldehyde, with the addition of sulphonic acid groups. This results in a water-soluble polymer that is commonly used as a dispersant and plasticizer in a variety of industrial applications, including coatings, adhesives, and concrete.
Sulphonated naphthalene formaldehyde condensate (SNFC) is another water-soluble polymer that is produced by the condensation of naphthalene and formaldehyde, with the addition of sulphonic acid groups. Like SMFC, SNFC is commonly used as a dispersant and plasticizer in a range of industrial applications, including concrete, ceramics, and textiles.
Modified ligno-sulphonates and other sulphonic esters and acids are a broad category of chemical compounds that are typically used as dispersants and plasticizers in a variety of industrial applications. Ligno-sulphonates are produced by the sulfonation of lignin, a natural polymer found in wood and other plant materials. Modified ligno-sulphonates may have additional chemical modifications to enhance their properties for specific applications. Other sulphonic esters and acids may be produced from a variety of starting materials, including petroleum and other fossil fuels, and may have a wide range of industrial applications depending on their specific properties.
Chemical type
Formaldehyde derivatives, such as melamine formaldehyde and napthalene sulphonate formaldehyde, are compounds that are formed by reacting formaldehyde with other chemicals. These derivatives have various industrial applications due to their properties, such as high strength, durability, and resistance to heat and moisture.
Melamine formaldehyde, for example, is commonly used as a binder in particleboard, plywood, and other composite wood products. It is also used in the production of kitchenware, electrical insulation materials, and textiles. The addition of melamine formaldehyde can improve the dimensional stability, water resistance, and hardness of these materials.
Napthalene sulphonate formaldehyde, on the other hand, is often used as a dispersant in concrete and as a water reducer in cement. It helps to improve the workability and flow of the concrete mix, making it easier to pour and shape. Additionally, this compound can also improve the strength and durability of the concrete by reducing the amount of water needed for the mix.
Despite their beneficial properties, formaldehyde derivatives have been subject to some controversy due to concerns over their potential health effects. Formaldehyde is a known carcinogen, and while the derivatives themselves are not as hazardous, they can release formaldehyde gas over time, especially in poorly ventilated areas. As such, it is important to use these compounds safely and to follow recommended guidelines and regulations.
Mode of action of Super Plasticizer Admixtures
Superplasticizers are a type of admixture that function similarly to water reducing admixtures. When cement is mixed with water, it can sometimes form agglomerates that prevent it from properly dispersing. This is where superplasticizers come in – they help disperse these agglomerates by adsorbing onto the surface of the cement particles.
By doing so, the superplasticizers cause the cement particles to become mutually repulsive. This is due to the anionic nature of the superplasticizers, which means they have a negative charge. As a result, the cement particles are less likely to clump together, allowing them to disperse more evenly throughout the mixture.
Overall, superplasticizers are an important tool in the construction industry as they help ensure that cement mixtures have the desired properties. By helping to disperse cement particles and prevent agglomeration, they can improve the workability and strength of the final product.
Why Super Plasticizer Admixtures are used?
Paragraph A: One of the benefits of using this admixture is that it can increase the workability of concrete at a given water-to-cement ratio. This increase in workability is typically seen by raising the slump measurement from 75 millimeters to 200 millimeters.
Paragraph B: Another use of this admixture is to produce concrete with normal workability but exceptionally high strength. This is achieved by using a super plasticizer, which can reduce the amount of water required for a given workability by 25-35%. This reduction in water content is much higher than that achieved by conventional water-reducing admixtures, which only reduce water content by half of that amount.
Advantages of Super Plasticizer Admixtures
The use of a certain admixture in concrete results in several benefits. One of these is that the concrete can be placed without the need for extensive compaction. Additionally, it is not susceptible to excessive bleeding or segregation. This makes it a practical choice for a wide range of construction applications.
Another advantage of this admixture is its ability to be used in high dosages without causing a significant change in the surface tension of water. This property makes it an ideal choice for situations where large quantities of concrete are required.
The use of this admixture has minimal impact on the setting of concrete, especially when it is used in conjunction with cements that have low C3A content. This means that the setting process of the concrete will not be significantly affected by the admixture’s use.
Furthermore, this admixture does not have any significant influence on the shrinkage, creep modulus of elasticity, or resistance to freezing and thawing of concrete. These properties are important considerations for concrete used in various construction applications, and the use of this admixture does not compromise them.
Disadvantage
Superplasticizers are a type of additive used in the construction industry to improve the workability of concrete. These compounds have several benefits, such as increasing the fluidity of the mixture, reducing water content, and enhancing the strength of the final product. However, the primary drawback associated with superplasticizers is their cost. Compared to other concrete additives, they are relatively expensive.
Despite their higher cost, the use of superplasticizers is becoming increasingly common in the construction industry due to their ability to improve concrete performance. The cost of superplasticizers can vary depending on several factors such as the type of compound, its concentration, and the market demand. However, their effectiveness in enhancing the properties of concrete makes them a valuable investment for many construction projects.
In conclusion, while the cost of superplasticizers may be a disadvantage, their benefits make them a popular choice in the construction industry. By improving the workability and strength of concrete, superplasticizers offer significant advantages that can justify their relatively higher cost. As the demand for high-quality concrete continues to grow, the use of superplasticizers is expected to become even more widespread.
Applications of Super Plasticizer Admixtures
a) In situations where sections require particularly strong reinforcement and are difficult to access, such as in floor or road slabs, specialized construction methods may be necessary. These sections may be subject to heavy loads or other stresses, and require reinforcement to ensure their stability and longevity. However, accessing these areas for construction and reinforcement can be a challenging task, requiring specialized equipment and techniques.
b) In some cases, there may be a need for very rapid construction or placing of materials. This may be due to time constraints or other factors, such as weather conditions. In such situations, specialized methods and techniques may be employed to expedite the construction process. This could include the use of pre-fabricated materials, or the use of specialized equipment to rapidly pour and shape materials into place. However, it is important to ensure that these techniques do not compromise the quality or safety of the final product.
6. Mineral Admixtures for Concrete
Mineral admixtures are used in concrete to enhance its properties. These admixtures are finely divided materials that are added to the concrete in significant amounts, typically ranging from 20 to 100 percent by weight of Portland cement. This means that the amount of mineral admixture added is substantial in comparison to the amount of Portland cement used.
The purpose of using mineral admixtures is to improve the properties of concrete. These materials are added to the mixture during the production of concrete and are mixed with other components to achieve the desired properties. Mineral admixtures may be added to improve the durability, workability, strength, and other aspects of the final product.
Mineral admixtures are typically made from waste materials, which make them environmentally friendly. They can be produced from materials such as fly ash, blast furnace slag, silica fume, and other similar materials. These materials are commonly used in concrete production as they provide significant benefits in terms of cost, sustainability, and performance.
In conclusion, mineral admixtures are a crucial component in concrete production. They are added in significant amounts to improve the properties of the final product. Mineral admixtures are environmentally friendly and can be produced from waste materials. By using these materials in concrete production, we can improve the sustainability, durability, and cost-effectiveness of our construction projects.
Source of Mineral Admixtures
a) Natural minerals can either be used in their raw form or after undergoing a process called calcination, which involves heating them at high temperatures to remove any impurities and improve their properties for various industrial applications.
b) Industrial byproducts, which are the waste materials generated during various industrial processes, can also be repurposed for various applications. These materials can include things like fly ash from coal-fired power plants, slag from metal smelting operations, and even waste materials from agricultural processes. By finding new uses for these materials, we can help reduce waste and create more sustainable industrial processes.
Reasons for using mineral admixtures
In recent years, the cement industry has focused on reducing energy consumption in the production of Portland cement. To achieve this goal, mineral admixtures have been introduced as a partial replacement for Portland cement, accounting for up to 50-60% of the total cementitious material. This approach has resulted in significant energy savings.
The cement and concrete industries have the potential to be classified as environmentally friendly due to their ability to utilize millions of tons of industrial byproducts containing toxic metals. This approach effectively reduces waste and pollution.
Natural pozzolana and industrial byproducts are typically available at substantially lower costs than Portland cement. By utilizing the pozzolanic and cementitious properties of mineral admixtures as a partial replacement for cement, significant economic benefits can be achieved.
In addition to the aforementioned benefits, the use of mineral admixtures in concrete offers several technological advantages. These include enhanced impermeability and chemical durability, increased resistance to thermal cracking, and an improvement in ultimate strength.
Classification of Mineral Admixture
Mineral admixtures are classified into two categories: pozzolanic and pozzolanic & cementitious. Pozzolanic materials have little or no cementitious value but can react chemically with moisture and CalOH2 at ordinary temperatures to form compounds that possess cementitious properties. Pozzolanic & cementitious materials, on the other hand, have some cementitious properties in themselves.
The ASIM specification C618 recognizes three classes of mineral admixtures: Class N, Class F, and Class C. Class N consists of raw or calcined natural pozzolanic materials such as diatomaceous earths, clay and shales, tuffs, and volcanic ashes. Class F is fly ash produced from burning anthracite or bituminous coal. Finally, Class C is ash normally produced from lignite or sub-bituminous coal, which may contain analytical CaO higher than 10%.
7. Silica Fume as Concrete Admixture
The Norwegian Institute of Technology conducted research on the effects of silica fume (SF) on concrete properties in the late 1970s and early 1980s. This research was crucial in realizing the benefits of using SF in concrete, a practice that has seen a significant increase in recent years. Prior to this comprehensive study, the properties of SF in concrete were not well understood. However, the findings from the research shed light on the positive impact of SF on concrete properties, leading to its increased use in the construction industry.
Production of Silica Fume
The production of materials such as silicon, ferrosilicon, and other alloys involves the use of submerged arc electric furnaces. These furnaces are available in two varieties: those with heat recovery systems and those without.
The submerged arc electric furnace is a type of furnace used in the manufacturing of alloys. It is designed to have an electric arc that is submerged beneath the surface of the materials being melted. This process helps to reduce the risk of oxidation and ensures that the alloys produced are of high quality.
In addition to the submerged arc electric furnace, there are two types of electric furnaces available. One has a heat recovery system, which means that the heat produced during the melting process is captured and reused. The other type does not have this system and the heat produced is simply released into the environment.
The decision to use a furnace with or without a heat recovery system will depend on various factors such as the cost of the equipment, the amount of energy needed for the melting process, and the desired level of energy efficiency. Ultimately, both types of furnaces can be used to produce high-quality alloys, but the choice of furnace will depend on the specific needs of the manufacturer.
Types of Alloys Produced in Submerged Arc Electric Furnaces
a) Ferrosilicon is a metal alloy that comes in various Si contents. FeSi-50% contains 43 to 50% Si content, while FeSi-75% has a Si content ranging from 72 to 78%. FeSi-90%, on the other hand, has a higher Si content, ranging from 87 to 96%.
b) Calcium silicon is another type of metal alloy used in various industries. It is made by combining calcium, silicon, and iron. This alloy is known for its ability to improve the castability, fluidity, and machinability of steel.
c) Ferrochromium Silicon is a metal alloy that combines chromium, silicon, and iron. This alloy is commonly used in the production of stainless steel because it enhances the steel’s corrosion resistance, durability, and strength.
d) Silicomanganese is a type of metal alloy made by combining silicon, manganese, and iron. This alloy is used in the production of steel and is known for its ability to improve the strength and toughness of steel. It also has high resistance to oxidation and wear.
Specific Gravity and Specific Surface Area of SF
Silica fume (SF) typically has a specific gravity of about 2.20, which is similar to that of amorphous silica. However, certain SF particles may have a higher specific gravity of up to 2.40 or 2.55, depending on their chemical composition. For instance, FeGSi has a specific gravity within this range.
The specific surface area of SF can be determined by measuring nitrogen absorption.
| SF | Calculated Surface Area (m2/kg) | Measured by Nitrogen Adsorption | Mean Diameter (mm) |
| Si | 20000 | 18500 | 0.18 |
| FeCrSi | 16000 | – | 0.18 |
| FeSi – 50% | 15000 | – | 0.21 |
| FeSi – 75% | 13000 | 15000 | 0.26 |
Supplementary cementitious materials known as SF come in various types, differing in chemical composition, carbon content, and color. Despite these variations, SF shares certain important physiochemical characteristics that make it an effective addition to cement concrete. One such characteristic is the high silica content, which ranges from 35 to 98% and originates from the condensed SiO vapors.
Another characteristic of SF is that it is an amorphous material, meaning it lacks a well-defined crystalline structure. Finally, SF is composed primarily of fine spheres that have a mean diameter of 0.1 to 0.2 mm. These spheres are generally small, but they play an important role in the effectiveness of SF as a supplementary cementitious material.
Overall, these physiochemical characteristics of SF are critical to its ability to improve cement concrete. By understanding these characteristics, researchers and engineers can better utilize SF in their concrete mixtures, resulting in stronger and more durable structures.
Filler and Pozzolanic effects of Silica Fume
Supplementary cementitious materials, such as SF, are known for their unique properties that make them suitable for use in concrete. SF is highly amorphous, fine, and rich in SiO2, which makes it an ideal material to act as a filler between coarser cement grains. By filling the gaps between cement grains, SF can improve the density and gradation of fine particles, resulting in a denser matrix.
According to Bache, when small SF spheres are added to low w/c ratio concrete, they can displace water trapped between the flocculated cement grains. This displacement can increase the amount of free water in the paste, thereby enhancing its fluidity. Numerous studies have investigated the pozzolanic properties of SF, which reveal that the reactions between SF and Ca(OH)2 can increase the volume of CSH while reducing the total volume of capillary pores in the cement paste. By reducing the amount of Portlandite in the hydrate cement paste, SF can also prevent the formation of large, weak crystals of Portlandite and enhance the mechanical properties of concrete.
Moreover, SF can reduce the porosity of the transition zone between the cement paste and aggregate, which can increase the strength and impermeability of the concrete. In conventional concrete, the transition zone may contain large and oriented Portlandite crystals that form weak zones. However, the addition of SF to the concrete can drastically reduce the thickness of the transition zone by reducing bleeding and water accumulation under aggregate. By doing so, SF can decrease the porosity of the transition zone and reduce the concentration of oriented Ca(OH)2 crystals, thereby enhancing the durability and mechanical properties of concrete.
Selection of Concrete Admixtures
Concrete admixtures play a crucial role in enhancing the quality and properties of concrete. It is essential to choose the right admixture as per the specifications and instructions provided by the manufacturer or lab testing reports. The recommended quantity of admixtures for a specific application is also provided by the manufacturer. For larger construction projects, the quantity of admixture required can be determined through testing the concrete mixed with varying percentages of admixtures to understand their impact on the strength and quality of the concrete. Based on the results obtained from these tests, the optimum quantity of admixture can be selected for a particular application.
The selection of admixtures for altering the properties of concrete should be made carefully, based on the specific requirements of the concrete work. The application of concrete admixtures should also be carried out judiciously, adhering to the specified methods and quantities to avoid any adverse effects on the properties of the concrete, both in its fresh and hardened state. It is crucial to select a reliable supplier who can provide quality admixtures, timely service, and competitive prices. The admixture supplier should have a good track record and employ staff with professional experience and expertise to guide on the effective application and use of the admixture.
It is also essential to ensure that the concrete admixture is accepted with a test certificate, clearly stating the manufacturing date and chemical composition, and that it complies with the specifications set by the authorities. Adhering to these guidelines and selecting the right admixture can help in achieving the desired properties and quality of concrete for various construction applications.