Superplasticisers

Superplasticisers, such as sulfonated naphthalene or sulfonated melamine formaldehyde, when added to a normal 50 mm slump concrete produce a flowing, self-levelling or self-compacting concrete (SCC) which can be placed, even within congested reinforcement, without vibration. Alternatively, significantly reduced water contents can be used to produce early- and ultimately higher-strength concretes. As the effect of superplasticisers lasts for less than an hour, the admixture is usually added to ready-mixed concrete on site prior to discharge and placing. Standard concrete additives, fillers and steel or polypropylene fibres may be incorporated into self-compacting concrete which can be pumped or delivered by skip or chute. Good-quality off-the-form surface finishes can be achieved, especially with timber formwork. Self-levelling mixes for screeds between 3 and 20 mm thick can be adjusted to take light foot traffic after 3 to 24 hours. Renovation mixes, usually incorporating fibre-mat reinforcement, can be used over a range of existing floor surfaces to thicknesses usually in the range 4-30 mm.

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