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Self-compacting concrete admixtures

With careful mix design, self-compacting concrete (SCC) admixtures produce a concrete that is fully flowing and self-compacting and which can be placed with no vibration. SCC functions in the same manner as superplasticised, flowing concrete but does not need any compacting effort. It is alos less susceptable to bleed and segregation normaly associated with high workabilities.

Fluidity is obtained from traditional superplasticisers or from the new polycarboxylate ether co-polymers. The latter are particularly effective as they give fluid but cohesive concrete with high flow retention.

The lack of bleed and segregation come mainly from careful mix design including the use of fine fillers or additions but may also require an admixture to control rheology or segregation (viscosity modifying admxiture VMA). This can be added separately or form part of a dual function admixture with the superplasticiser. Two of the most effective chemicals are nanometric colloidal silica and polysaccaride biopolymers.

Acknowledgement: The Concrete Society

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TR18 A guide to the selection of admixtures for concrete

TR62 Self-compacting concrete- a review

Guide to the use of self-compacting concrete in bridge construction