Concrete and its reinforcement


Admixtures shall only be used to enhance the performance and durability of concrete.

Issues that should be taken into account include:

  • improved workability
  • waterproofing
  • foaming agents
  • accelerated strength
  • retardation
  • chlorides.

Admixtures should comply with BS EN 934-2 Admixtures for concrete mortar and grout - Concrete admixtures - Definitions, requirements, conformity, marking and labelling, should be used in accordance with BS EN 206 and should be:

  • specified only with full knowledge of their limitations and effects
  • used only where permitted in the specification
  • tested in trial mixes, where necessary
  • added to the mix water to ensure complete dispersal
  • dosed correctly
  • used strictly in accordance with the manufacturer’s instructions.

Accelerators produce early setting of the concrete, and plasticisers can improve concrete cohesion and the bond with reinforcement.

Air-entraining agents should not be used as an anti-freeze for fresh concrete. Though they can increase the frost resistance of cured concrete and are recommended for paths, drives and pavements which are likely to be exposed to freezing conditions.

Retarding agents can increase the risk of frost damage.

Admixtures containing chlorides can cause metal corrosion and should not be used in reinforced concrete.