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For architects and specifiers, concrete is the literal and figurative foundation of countless structures. Its versatility and strength make it a go-to material but, in many cases, increased performance is required to meet specific project demands. This is achieved by the inclusion of performance-enhancing concrete additives, and this article will concentrate on the chemicals that are added at the batching plant under fully controlled and regulated conditions.
Concrete additives, or admixtures, are precisely engineered materials incorporated during the concrete mixing process. These admixtures can be used to modify the characteristics of the concrete both during the placement and in terms of its cured performance, offering a powerful tool to address a wide range of challenges.
The world of concrete additives is vast, with each admixture offering unique benefits. Here&#;s a closer look at some of the key functionalities:
Waterproofing is a crucial consideration for below-ground concrete structures. Whilst well-designed and well-placed concrete is already inherently waterproof, concrete additives that improve or extend the workability can result in better compaction of the concrete, resulting in a structure that offers a greater level of resistance to water.
The main benefit of concrete additives for waterproofing though, is the ability to enhance the self-healing properties of concrete when it is used to provide a Type B form of waterproofing to British Standard :.
Achieving this requires the concrete to be designed to the relevant parts of BS EN . All concrete shrinks during the curing process, and if reinforcement steel was not included the concrete would develop a low number of large cracks, leading to potentially catastrophic volumes of water ingress. BS EN is therefore used by structural engineers to design the reinforcing steel to restrict concrete shrinkage and limit cracking to a high number of cracks that are so small that water is unable to pass through the concrete.
It is understood that concrete cracks of 0.2 mm in width have autogenous (self-healing) properties. When water attempts to squeeze through these cracks, it reacts with calcium hydroxide and microsilica to form a crystalline structure that effectively seals the crack. However, a large volume of expensive steel is required to control cracks to just 0.2 mm.
Instead, BS EN allows crack widths to be controlled to 0.3 mm, which requires approximately 50% less steel volume and so provides substantial cost savings.
However, 0.3 mm cracks are not considered to be self-healing, and this is where a concrete additive is most beneficial. By adding a crystalline admixture to the concrete, the self-healing properties of the concrete are enhanced, ensuring that even 0.3 mm cracks will be sealed just as effectively as 0.2 mm cracks would be.
Essentially, when considering waterproofing admixtures, there are two main types:
An effective Type B waterproofing strategy that includes additives must also specify measures to seal the construction joints, tie-bolt holes and service penetrations through the concrete.
With such a diverse range of concrete additives available, selecting the right one requires careful consideration.
For more construction additivesinformation, please contact us. We will provide professional answers.
Concrete additives are a powerful tool in the hands of architects and specifiers. By understanding their functionalities and collaborating with a specialist, you can unlock the full potential of concrete in your projects. From enhanced workability and setting times to superior strength, durability, and waterproofing, concrete additives can help you achieve lasting results.
We are dedicated to providing high-quality waterproofing services and technical support throughout the UK, and our team of experienced professionals and specialist contractors have the expertise to tackle even the most challenging projects and can assist with the specification of the concrete additive regardless of the performance requirement. We adhere to industry standards and use proven methods, ensuring long-lasting results and peace of mind, so contact us today to get started.
Concrete additives are usually liquid and are only added in very small amounts whilst mixing the concrete. They have a physico-chemical action and are classified into so-called efficiency groups depending on their effect in freshly mixed or hardened concrete.
These concrete additives depressurise the water, improving workability while at the same time reducing or maintaining the prescribed water-cement ratio.
These concrete additives are advanced deflocculants. They have a particularly strong deflocculant action and enable efficient concrete installation with very soft to liquid consistencies. Plasticising admixtures are usually treated as deflocculants and are added in the transport concrete mixer. Plasticising admixtures based on polycarboxylate ether usually have a high consistency and no longer need to be added at the construction site
Concrete with high resistance to frost and thawing salt must have a minimum content of micro air voids (smaller than 0.3 mm) which can be obtained by adding air entraining agents. Ice has a larger volume than water. If the expansion of the frozen water is prevented in the concrete, then the concrete may burst. The additional air voids offer the necessary space for this extension.
These are used to improve the water imperviousness of the concrete. Water resisting admixtures are designed to protect the structure from penetrating substances that may be harmful to water.
These delay the setting time of the concrete, which may be required for several reasons, e.g. hot weather or jointless components with a large mass (e.g. bridge superstructures, strong base plates, concrete for kerb stones). Over-metering can, however, have the opposite effect and turn the setting retarder into a setting accelerator agent!
These chemically accelerate the setting of, for example, shotcrete or sealing mortar up to just a few seconds after spraying or placing. An alternative, without the disadvantage of considerable reduction of the 28 day- and final strength is physically-active micro silica dust.
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