Self compacting concrete and admixtures

Self compacting concrete is a type of concrete that is highly fluid allowing it to self-level, penetrate into complicated areas and formwork, through complex reinforcement and much more. Despite its increased fluidity, self compacting concrete maintains the high quality demanded by today’s building industry, presenting both flexibility as well as incredible strength. Its flexibility lies in the fact that there are multiple admixtures that can be added when designing the mix to create a final product that is suitable for the end result.

When working on residential or commercial projects the goal is to create an aesthetical pleasing result which is strong as well. For example driveways in residential areas or floors in high traffic commercial zones need to present a good looking finish while also being strong enough to take the weight of multiple vehicles on a daily basis. The advantage of using self compacting concrete in this case is that is requires no vibration and also dries to a shiny finish which requires little extra water.

Some admixtures that can be used in such an application include:

High water reducer – superplasticizer. This is an admixture that is used in all types of self compacting concrete because it is what gives it its flowability. Essentially, this admixture reduces the quantity of water needed to achieve the same consistency as traditional concrete meaning that if the same quantity of water is used then the resulting material will be much more fluid and easy to work with.

Generally, polycarboxylate ether superplasticizers are used in self-compacting concrete, despite the fact that they are quite expensive. However, they are extremely strong so a lower dose will achieve the same result as other products.

Retarding admixtures. These admixtures prevent the self compacting concrete from setting too soon. The concrete will then require an additional 90 to 360 minutes to set after it has been poured. Retarding admixtures can be made from gluconate, sucrose or phosphate, depending on the application.

Retarders are useful because rarely is concrete poured in a single batch, and if the first batch has had too much time and has begun to set it may not bond properly with the second batch. No matter how great the plan is, delays are bound to happen and retarders can help extend the setting period of the self compacting concrete to allow all the batches to bond properly.

Air-entraining admixture. This is used to entrain the air within the concrete while mixing to obtain a uniform distribution of the air pockets within the concrete. Air entrainment helps protect the self compacting concrete from the damaging effects of freezing and subsequent thawing, it also increases the level of cohesion as well as the stability of the final product.

Water resisting admixtures. These reduce the permeability of self compacting concrete which protects from the corrosive action of water. However, these admixtures only prevent absorption through surface pores and not if cracks are present in the concrete.

There are a wide range of admixtures that are used to improve self compacting concrete, with more being developed constantly with the rise in popularity of this concrete.

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