High strength concrete additive

Superplasticizers (SPs), also known as high range water reducers, are additives used for making high strength concrete or to place self-compacting concrete. Plasticizers are chemical compounds enabling the production of concrete with approximately 15% less water content. Superplasticizers allow reduction in water content by 30% or more. These additives are employed at the level of a few weight percent. Plasticizers and superplasticizers also retard the setting and hardening of concrete.[1]

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According to their dispersing functionality and action mode, one distinguishes two classes of superplasticizers:

1. Ionic interactions (electrostatic repulsion): lignosulfonates (first generation of ancient water reducers), sulfonated synthetic polymers (naphthalene, or melamine, formaldehyde condensates) (second generation), and;
2. Steric effects: Polycarboxylates-ether (PCE) synthetic polymers bearing lateral chains (third generation).[2]

Superplasticizers are used when well-dispersed cement particle suspensions are required to improve the flow characteristics (rheology) of concrete. Their addition allows to decrease the water-to-cement ratio of concrete or mortar without negatively affecting the workability of the mixture. It enables the production of self-consolidating concrete and high-performance concrete. The water–cement ratio is the main factor determining the concrete strength and its durability. Superplasticizers greatly improve the fluidity and the rheology of fresh concrete. The concrete strength increases when the water-to-cement ratio decreases because avoiding to add water in excess only for maintaining a better workability of fresh concrete results in a lower porosity of the hardened concrete, and so to a better resistance to compression.[3]

The addition of SP in the truck during transit is a fairly modern development within the industry. Admixtures added in transit through automated slump management system,[4] allow to maintain fresh concrete slump until discharge without reducing concrete quality.

Working mechanism

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Traditional plasticizers are lignosulfonates as their sodium salts.[5] Superplasticizers are synthetic polymers. Compounds used as superplasticizers include (1) sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate and (2) polycarboxylates ethers. Cross-linked melamine- or naphthalene-sulfonates, referred to as PMS (polymelamine sulfonate) and PNS (polynaphthalene sulfonate), respectively, are illustrative. They are prepared by cross-linking of the sulfonated monomers using formaldehyde or by sulfonating the corresponding crosslinked polymer.[1][6]

The polymers used as plasticizers exhibit surfactant properties. They are often ionomers bearing negatively charged groups (sulfonates, carboxylates, or phosphonates...). They function as dispersants to minimize particles segregation in fresh concrete (separation of the cement slurry and water from the coarse and fine aggregates such as gravels and sand respectively). The negatively charged polymer backbone adsorbs onto the positively charged colloidal particles of unreacted cement, especially onto the tricalcium aluminate ( C3A) mineral phase of cement.

Melaminesulfonate (PMS) and naphthalenesulfonate (PNS) mainly act by electrostatic interactions with cement particles favoring their electrostatic repulsion while polycarboxylate-ether (PCE) superplasticizers sorb and coat large agglomerates of cement particles, and thanks to their lateral chains, sterically favor the dispersion of large cement agglomerates into smaller ones.[7]

However, as their working mechanisms are not fully understood, cement-superplasticizer incompatibilities can be observed in certain cases.[8]

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Common superplasticizer types

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• Sulfonated Naphthalene Formaldehyde
• Polycarboxylate Superplasticizer (PCE), also called water reducer, is an additive used in concrete and mortars. It improves the flowability without increasing the water content. This allows for high-strength, high-performance concrete and mortar with lower water-to-cement ratios. SCE accelerate the early strengthening of concrete or mortar.[9][10]

See also

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• Particle aggregation (inverse process of)
• Peptization
• Plasticizer
• Polycarboxylates
• Rheology
• Surfactant
• Suspension (chemistry)

References

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Further reading

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Using Superplasticizer Additives in Concrete

A superplasticizer is a chemical additive used in concrete mixtures to enhance its flowability and workability without sacrificing strength. It achieves this by dispersing cement particles more effectively and reducing the water-to-cement ratio needed for a given level of workability. Superplasticizers are often added to concrete mixes where high strength, high durability, and improved placement characteristics are required.

Superplasticizers are typically sulfonated melamine formaldehyde (SMF), sulfonated naphthalene formaldehyde (SNF), or polycarboxylate-based. These chemicals work by dispersing cement particles and reducing the surface tension between particles, thereby allowing them to flow more freely. This improved flowability leads to better compaction and reduced need for water, which can result in higher strength and durability of the concrete.

Superplasticizers are commonly used in a variety of concrete applications, including high-strength concrete, self-compacting concrete, and in situations where concrete needs to be pumped long distances or placed in congested reinforcement areas.

Advantages of Using Superplasticizer:

Using superplasticizers in concrete offers several advantages:

1. Improved workability: Superplasticizers enhance the flowability and workability of concrete, making it easier to place and compact. This allows for easier handling during construction, reducing labor and equipment requirements.
2. Increased strength: By reducing the water-to-cement ratio while maintaining workability, superplasticizers can lead to higher compressive strength in the hardened concrete. This results in stronger and more durable structures.
3. Enhanced durability: Superplasticizers improve the homogeneity and density of concrete, resulting in reduced permeability and improved resistance to chemical attack, abrasion, and freeze-thaw cycles. This leads to longer-lasting concrete structures.
4. Better finish: The improved flowability provided by superplasticizers allows for smoother concrete surfaces with fewer voids and imperfections. This results in better surface finishes, reducing the need for additional surface treatments.
5. Increased flexibility in design: Superplasticizers enable the production of concrete mixes with varying water content while maintaining desired workability. This flexibility allows engineers and architects to design concrete mixes tailored to specific project requirements, such as strength, durability, and aesthetic considerations.

Disadvantages of Using Superplasticizer:

While superplasticizers offer several advantages, there are also some potential disadvantages associated with their use in concrete:

1. Cost: Superplasticizers can be relatively expensive compared to traditional concrete additives. The cost of superplasticizers may outweigh their benefits for certain projects, especially those with tight budget constraints.
2. Set time control: Superplasticizers can extend the setting time of concrete, especially when used in higher dosages or in combination with certain cement types. This may require careful monitoring and adjustment of the concrete mix to ensure proper setting and finishing times.
3. Retention of workability: Depending on the specific type and dosage of superplasticizer used, there may be limitations on the duration of workability retention. Concrete mixtures with high doses of superplasticizers may lose workability more rapidly, requiring faster placement and finishing.
4. Compatibility with other admixtures: Superplasticizers may interact with other chemical admixtures in concrete, affecting their performance or causing unintended consequences. Careful testing and compatibility evaluations are necessary when using superplasticizers in combination with other additives.
5. Potential for air entrainment: In some cases, excessive use of superplasticizers can lead to entrainment of air in the concrete mixture, which may compromise its strength and durability. Proper dosage control and mix design optimization are essential to prevent air entrainment issues.

How Do Plasticizers Differ from Superplasticizers?

Plasticizers and superplasticizers both improve the workability of concrete, but they achieve this through different mechanisms and have different effects on water reduction, dosage rates, and chemical composition. Plasticizers and superplasticizers are both types of chemical additives used in concrete, but they serve different purposes and have distinct effects on concrete properties:

1. Purpose:
   • Plasticizers: Plasticizers, also known as mid-range water reducers, are additives that improve the workability of concrete by reducing the amount of water required for a given slump or consistency. They help increase the flow of concrete while maintaining a constant water content.
   • Superplasticizers: Superplasticizers, on the other hand, are high-range water reducers primarily used to enhance the flowability and workability of concrete without significantly increasing its water content. They achieve this by dispersing cement particles more effectively, reducing the water-to-cement ratio needed for a given level of workability.
2. Water reduction:
   • Plasticizers: Plasticizers reduce the water content in concrete by dispersing cement particles more efficiently, allowing for increased workability without compromising strength.
   • Superplasticizers: Superplasticizers also reduce the water content in concrete, but they achieve this by dispersing cement particles more effectively and dramatically decreasing the water-to-cement ratio. This results in much higher flowability and workability without sacrificing strength.
3. Dosage rates:
   • Plasticizers: Plasticizers are typically used at lower dosage rates compared to superplasticizers. They are effective in improving workability while minimizing the risk of segregation and bleeding.
   • Superplasticizers: Superplasticizers are used at higher dosage rates compared to plasticizers. They are particularly useful in applications requiring high-strength concrete, long-distance pumping, or where very high flowability is necessary.
4. Chemical composition:
   • Plasticizers: Plasticizers are often based on lignosulfonates, hydroxylated carboxylic acids, or other organic compounds.
   • Superplasticizers: Superplasticizers can be sulfonated melamine formaldehyde (SMF), sulfonated naphthalene formaldehyde (SNF), or polycarboxylate-based. They are chemically designed to disperse cement particles more effectively and reduce water demand in concrete mixes.

Your Ready-Mixed Concrete Supplier Can Help

Talk to your ready mixed concrete supplier about selecting the most suitable superplasticizer for your project’s specific requirements. Consider factors such as the desired level of workability, strength requirements, and environmental considerations. Discuss the available options, including sulfonated melamine formaldehyde (SMF), sulfonated naphthalene formaldehyde (SNF), or polycarboxylate-based superplasticizers, and their respective dosage rates and effects on concrete properties. Your supplier can provide valuable guidance on choosing the right superplasticizer to optimize concrete performance while ensuring cost-effectiveness and sustainability. Collaborating with your supplier ensures that you make informed decisions tailored to your project’s needs, ultimately resulting in successful concrete applications.

Read about admixtures for ready-mixed concrete and other helpful information on our Concrete Resources page at TriangleReadyMix.com/edu. We also have a convenient Glossary of Ready-Mixed Concrete Terms. Triangle Ready Mix is a proud member of L&L Construction Group, along with our sister companies L&L Concrete and East Coast Civil Group.

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