Concrete pumpability is an essential factor in the construction industry, and any admixture that improves its workability is advantageous. Chemical admixtures are commonly used to achieve this goal, and their selection and application depend on the concrete mixture’s properties.
One type of chemical admixture that enhances concrete pumpability is the air-entraining agent. This admixture improves concrete cohesiveness and reduces segregation and bleeding. The air-entraining agent introduces tiny air bubbles into the concrete mix, which improve its ability to flow and reduces the risk of blockages during pumping.
Another chemical admixture that can improve pumpability is the high-range water-reducing admixture. This type of admixture reduces the amount of water required to achieve a specific level of workability, which improves pumpability by reducing the likelihood of blockages and increasing the flowability of the mix.
Finally, mineral admixtures can also improve the pumpability of concrete. By reducing the rate and amount of bleeding in the mixture, mineral admixtures improve the overall workability of the mix and make it easier to pump. Finely divided admixtures are an example of mineral admixtures that can improve concrete pumpability.
In conclusion, the selection and application of chemical admixtures in concrete are crucial for improving pumpability. The air-entraining agent, high-range water-reducing admixture, and mineral admixtures are some examples of chemical admixtures that can improve the workability of concrete and enhance its pumpability. The choice of the admixture depends on the specific characteristics of the concrete mix.
Types and Roles of Admixtures in Pumpable Concrete
Air-entraining Admixture
Concrete is a widely used construction material, and ensuring its cohesiveness and workability is crucial for its effectiveness. One of the ways to achieve this is by using air-entraining admixture. By incorporating such admixtures, the likelihood of segregation in pumpable concrete is significantly reduced. Additionally, air-entraining admixture decreases the tendency of concrete to bleed, which is another significant concern in the construction industry.
Another benefit of using air-entraining admixture is that it makes the start-up of the pipeline after shutdown easier. This is because the admixture reduces bleeding, which in turn decreases the chances of pipeline blockage. In contrast, non-air-entrained concrete is more susceptible to bleeding, making pipeline start-up more challenging.
Table-1 presents the recommended dosage of air-entraining admixture based on the maximum aggregate size. These values are established based on the resistance of concrete against freezing and thawing cycles. It is important to note that these recommended values should not be violated during the production of pumpable concrete. By adhering to these dosage recommendations, the desired properties of air-entrained concrete can be achieved while ensuring its effectiveness in construction applications.
Table-1: Recommended air contents for concrete resistant to freezing and thawing*
| Nominal maximum aggregate size, mm (in.) | Average air content for moderate exposure, % | Average air content for severe exposure, % |
| 9.5 (3/8) | 6 | 7-1/2 |
| 12.5 (1/2) | 5-1/2 | 7 |
| 19.0 (3/4) | 5 | 6 |
| 25.0 (1) | 4-1/2 | 6 |
| 37.5 (1-1/2) | 4-1/2 | 5-1/2 |
| 50 (2) | 4 | 5 |
| 75 (3) | 3-1/2 | 4-1/2 |
Mineral Admixtures
Mineral admixtures play an essential role in improving the properties of concrete. These admixtures are generally categorized into three types based on their chemical properties. The first type of mineral admixture consists of materials that are relatively chemically inert, such as ground limestone, ground quartz, and hydrated lime. These materials do not have a cementitious effect but can improve the workability and pumpability of the concrete mixture due to their smooth and dense surface texture.
The second type of mineral admixture includes materials that are cementitious, such as natural cement, ground granulated blast furnace slag, hydraulic lime, and slag cement. These materials contribute to the strength and durability of concrete and can replace a portion of cement in the mixture.
The third type of mineral admixture comprises pozzolan materials, such as class C and F fly ash, diatomaceous earth, volcanic glass, heated shales and clays, and silica fume. These materials react chemically with calcium hydroxide in the presence of moisture and form additional cementitious compounds, resulting in improved strength, durability, and reduced permeability of concrete.
The particle size of these mineral admixtures is typically smaller than that of cement, and their spherical particle shape and smooth and dense surface texture improve the pumpability of concrete. When a concrete mixture lacks an adequate amount of fines, the addition of finely divided mineral admixtures can enhance its workability and pumpability and reduce the rate and amount of bleeding. In summary, mineral admixtures are valuable additions to concrete that can improve its properties and make it more suitable for various applications.
Normal and High-Range Water-Reducing Admixtures
Water-reducing admixtures are a type of additive that can be used in concrete to enhance its workability. When added to the mix, these admixtures either increase the workability of the concrete for a constant water-cement ratio or reduce the water-cement ratio at a constant slump.
In addition to improving workability, some water-reducing admixtures can also entrain air in the concrete. This feature further enhances the pumpability of the concrete by reducing pumping pressure and allowing for the concrete to be pumped over greater distances. However, it is important to note that if high-range water-reducing admixtures, also known as superplasticizers, are used for pumping concrete, it must be placed before any loss in workability occurs.
High-range water-reducing admixtures are particularly useful in producing flowing concrete, which is a type of concrete that is highly workable and suitable for pumping. By using this type of admixture, the rate and distance up to which concrete can be pumped is significantly increased. This makes it easier to transport the concrete to its intended location and reduces the time and effort required for placement.
Anti-Washout Admixtures
Anti-washout admixtures play an important role in enhancing the cohesiveness of concrete that is pumped underwater. These admixtures are designed to prevent the separation of the constituents of the concrete mix during the pumping process, ensuring that the material stays intact and well-structured.
Natural or synthetic gums and cellulose-based thickeners are commonly used as anti-washout admixtures. These materials help to bind the concrete particles together, reducing the likelihood of segregation and sedimentation. By improving the stability of the concrete mix, they make it easier to pump the material over long distances underwater without losing its quality.
In essence, anti-washout admixtures serve as a safeguard against the risks of washout that can occur when concrete is pumped underwater. They help to ensure that the material retains its strength and consistency, even in challenging conditions. Through their use, construction professionals can achieve a higher level of control over the placement and quality of concrete, making it easier to build durable, long-lasting structures that can withstand the test of time.
FAQs
What are the benefits of air-entraining agents in pumpable concrete?
The following paragraphs have been rewritten based on the given context:
- To enhance workability, it is necessary to optimize the operational efficiency of the system. This can be achieved through the use of advanced technology and streamlined processes that eliminate unnecessary steps and reduce the likelihood of errors. Regular maintenance and cleaning of equipment can also improve workability by preventing malfunctions and ensuring that components are functioning as intended.
- Segregation and bleeding are common issues in systems that handle multiple materials or fluids. To reduce these problems, it is essential to ensure that the system is designed and operated with the correct parameters in mind. This includes selecting appropriate materials that are compatible with one another and adjusting flow rates and pressures to minimize the risk of segregation or bleeding. Regular inspections and maintenance can also help to identify and address these issues before they become more significant problems.
- The risk of pipeline blockage can be reduced through proper design and maintenance of the system. This includes selecting appropriate pipe sizes and materials, as well as ensuring that the system is operated within the specified parameters. Regular cleaning and inspection of the pipeline can also help to prevent blockages by removing debris and identifying potential problem areas. In addition, the use of sensors and monitoring equipment can help to detect blockages early, allowing for prompt action to be taken to address the issue.
How do air bubbles work in pumpable concrete?
When an air-entraining admixture is added to a concrete mixture, it can create small and stable bubbles. These bubbles serve an important function as they act as flexible ball bearings within the mixture. This allows sand particles to move more freely, which in turn increases the plasticity of the mix without the need for extra water.
One key benefit of these air bubbles is that they supplement the grading of the sand in the mixture. This is especially important when it comes to pumping concrete, as the bubbles help to reduce the gap grading effect. Essentially, the bubbles help to fill in any gaps that might exist between the sand particles, making it easier to pump the concrete.
Overall, air-entraining admixtures can play an important role in the performance of concrete mixtures. By creating these small and stable bubbles, they can help to increase plasticity and supplement sand grading, making it easier to work with and pump the concrete.
How do anti-washout admixtures improve concrete pumpability?
Anti-washout admixtures play an important role in maintaining the quality of concrete placed through pumps under water. These admixtures are specifically designed to increase the cohesiveness of the concrete, which is a critical factor for its successful placement.
When concrete is placed through pumps under water, it is subject to several challenges, such as segregation and loss of cement particles due to the pressure of the water. These factors can cause the concrete to lose its structural integrity and fail to meet the desired standards. Anti-washout admixtures work by reducing the risk of segregation and improving the stability of the concrete mix.
By using anti-washout admixtures, the concrete mix becomes more cohesive, which means that its particles are better able to bond together. This cohesiveness improves the ability of the concrete to resist the pressure of the water and maintain its shape and structural integrity. As a result, the concrete is better able to meet the required standards for strength and durability.
In summary, anti-washout admixtures are essential for the successful placement of concrete through pumps under water. They work by increasing the cohesiveness of the concrete mix, thereby improving its stability and resistance to the pressure of the water. This helps to ensure that the concrete meets the required standards for strength and durability, and maintains its structural integrity over time.
Do retarding admixtures aid concrete pumpability?
Concrete pumping is a common method of placing concrete in construction projects, but it can be challenging in hot weather conditions. The high temperatures can cause the concrete to set too quickly, making it difficult to pump and resulting in a weaker final product. To address this issue, retarding admixtures can be added to the concrete mixture.
Retarding admixtures are specifically designed to slow down the setting time of concrete. By delaying the setting process, the concrete remains fluid for a longer period, making it easier to pump and place in hot weather conditions. This is important because it ensures that the concrete is properly placed and consolidated, resulting in a stronger and more durable final product.
Overall, the use of retarding admixtures is an effective solution to the challenges posed by hot weather conditions in concrete pumping. It allows construction projects to proceed smoothly and efficiently, while also ensuring the quality and durability of the final product.
What is the role of mineral admixture in pumpable concrete?
The materials mentioned above have a particle size that is predominantly smaller than cement. This is due to their spherical shape and smooth, dense surface texture. These characteristics make it easier to pump a concrete mixture. However, if the concrete mix lacks sufficient fines, adding finely divided mineral admixtures can help improve its workability and pumpability. Additionally, the use of mineral admixtures can reduce the rate and amount of bleeding in the concrete.