Low Energy House - Insulating Blocks - Lightweight Concrete
Types of Insulating Concrete Blocks
Medium and lightweight concrete blocks are manufactured from a wide range of aggregates including expanded clay, expanded furnace slag, sintered ash and pumice.
Additional insulation can be provided by filling the voids in cellular blocks. Alternatively a layer of extruded polystyrene or foil faced phenolic foam is bonded to the face of the block.
Autoclaved Aerated Concrete Blocks (AAC)
Probably the most effective insulating concrete blocks available are those manufactured from autoclaved aerated concrete. They are produced to the same dimensions and strength standards as conventional medium and dense blocks. They have the advantage of better thermal insulating properties and are lighter and easier to handle on site.
Most AAC blocks are formed by the addition of aluminium powder to a fine mix of sand, lime and pulverised fuel ash (PFA) and Portland Cement. The inclusion of aluminium filings with concrete mix causes a chemical reaction with the lime during manufacture and gives off hydrogen, producing tiny bubbles throughout the material. Steam curing in an autoclave causes a secondary reaction which gives the concrete blocks increased strength.
Autoclaved aerated concrete blocks were first commercially produced in Sweden in 1923. They can be sawn by hand, sculpted and will take nails, screws and other fixings without the use of plugs.
Lightweight Insulating Concrete Block Sizes
Concrete walling blocks generally have a work face size of 440 mm wide by 215 mm high and insulating blocks are available in several different thicknesses from 100 mm to 300 mm.
Higher Thermal Values from Thicker Walls
Higher thermal values in masonry cavity walls, than are currently demanded by the Building Regulations, can be achieved by using a thicker insulating concrete block in the inner leaf. By using longer wall ties, it is possible to increase the thickness of the cavity to accommodate more thermal insulation.
Lightweight Insulating Concrete Block Strength
Although autoclaved aerated concrete blocks have a high strength to weight ratio, care should be taken when using this type of concrete block as they are not always suitable in situations where there are point loads or where high load bearing is required. In order to avoid problems, an architect or structural engineer should be consulted at an early stage in the design.
British Board of Agrément (BBA)
Before they are put on sale, autoclaved aerated concrete blocks are tested and issued with a British Board of Agrément (BBA) certificate. The test certificate lists the physical properties of the concrete blocks, including their crushing strength, thermal properties, and resistance to moisture.