Lightweight concretes

Lightweight concretes can either be lightweight aggregate concrete, foamed concrete or autoclaved aerated concrete (AAC). Such lightweight concrete blocks are often used in house construction.

Lightweight aggregate concrete

Lightweight aggregate concrete can be produced using a variety of lightweight aggregates. Lightweight aggregates originate from either:

  • Natural materials, like volcanic pumice.
  • The thermal treatment of natural raw materials like clay, slate or shale i.e. Leca.
  • Manufacture from industrial by-products such as fly ash, i.e. Lytag.
  • Processing of industrial by-products like FBA or slag.

The required properties of the lightweight concrete will have a bearing on the best type of lightweight aggregate to use. If little structural requirement, but high thermal insulation properties, are needed then a light, weak aggregate can be used. This will result in relatively low strength concrete.
Lightweight aggregate concretes can, however, be used for structural applications, with strengths equivalent to normal weight concrete.
The benefits of using lightweight aggregate concrete include:

  • Reduction in dead loads making savings in foundations and reinforcement.
  • Improved thermal properties.
  • Improved fire resistance.
  • Savings in transporting and handling precast units on site.
  • Reduction in formwork and propping.

Foamed concrete

Foamed concrete is a highly workable, low-density material which can incorporate up to 50 per cent entrained air. It is generally self-levelling, self-compacting and may be pumped. Foamed concrete is ideal for filling redundant voids such as disused fuel tanks, sewer systems, pipelines, and culverts - particularly where access is difficult. It is a recognised medium for the reinstatement of temporary road trenches. Good thermal insulation properties make foamed concrete also suitable for sub-screeds and filling under-floor voids.

Autoclaved aerated concrete (AAC)

AAC was first commercially produced in 1923 in Sweden. Since then, AAC construction systems such as masonry units, reinforced floor/roof and wall panels and lintels have been used on all continents and every climatic condition. AAC can also be sawn by hand, sculpted and penetrated by nails, screws and fixings.

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Aircrete Products Association