Aerated blocks are distinguished by their capacity to perform a dual structural / insulation function.
Typical thermal conductivity: 0.25 - 0.60 W/mKįirst produced in Sweden in 1923 and used in the UK since the 1960s (when they were known as ‘cellular’ or ‘gas’ concrete blocks), aerated concrete or ‘aircrete’ blocks are the lightest of the family of concrete blocks. The density of the aggregate is generally proportional to the strength of the block - so for example ‘super-lightweight’ aggregates such as expanded clay and pumice used for their excellent thermal performance, feature a relatively low compressive strength. Lightweight blocks are manufactured from cement together with one of a variety of natural or man-made expanded aggregates including: granulated / foamed blast-furnace slag, expanded clay or shale, furnace bottom ash (FBA), pulverised fuel ash (PFA), or the less common pumice (a volcanic material). The lighter block enables time and material cost savings through easier handling and larger units. Units the same size as other block types. Their main advantage over dense aggregate blocks comes from a combination of higher insulating properties and a lighter unit weight. Produced in greater volume, but less strong than dense blocks, lightweight blocks are used in both internal and external walls where loading is slightly more restricted or as infill blocks in beam and block flooring. Typical thermal conductivity: 0.70 – 1.28 W/mK. Dense aggregate concrete blocks are manufactured from cement, sand and aggregates. Their distinctive properties of durability and strength make them an ideal and cost-effect solution for all types of load-bearing walls. In use from the 1940s onwards, dense aggregate blocks are very much the work-horse of the construction industry. Types of concrete block: 'Dense', 'Lightweight', 'Aerated' Concrete blocks’ advantageous properties are reflected in their myriad of variations of strength, insulating and sound-reducing properties. Today, the immense versatility of concrete blocks is demonstrated in their use throughout a building from its foundation walls, through cavity walls, monolithic walls, partition walls, separating walls and as a component of ‘beam and block’ flooring. Early cavity walls used brick in both leaves, but as the economics of using a cheaper substitute became apparent, concrete block largely replaced brick as the inner leaf from the 1950s onwards. These early lightweight blocks were popular as internal partition walls because of their ease-of-use and cheapness, but it was only as a result of the development of cavity walls and the advent of mass housing programmes of the post-war years that the industry dramatically expanded.Ĭavity walling became adopted in the 1920s (led by house-builders Costains) because, although slightly more expensive to build, the perceived advantage was that the technique successfully overcame the problem of water penetration that traditionally plagued solid masonry wall construction. The earliest blocks manufactured in the UK were made using cement mixed with locally available aggregates – often waste products of industrial processes such as breeze (cinders retrieved from gasworks and coke ovens – from the French ‘braise’ meaning ‘hot coals’) and clinker (blast furnace slag). In the early twentieth century block manufacturing became an established industry. The mix, cast in wooden moulds, consisted of powdered limestone and clay mixed with water. 
In 1827, Joseph Aspidin devised the basic mix that we would still recognise today.
Though history records the use of concrete blocks by the Romans, Greeks and even Egyptians (some of the two-tonne blocks that make up the Pyramids are believed to be a primitive form of concrete), modern-type blocks were first cast, albeit in modest quantities, in around the middle of the nineteenth century. Insulated concrete form (ICF) masonry blocks Aerated masonry concrete or ‘aircrete’ blocks
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