Part A - Structure

What is aircrete?

This article is provided by H+H

Aircrete is a lightweight masonry material, combining the strength, durability and thermal efficiency of concrete with the ease of use that comes with a lightweight material; it is easy to handle, cut and work with on site.

What is aircrete made from?

The materials used in the manufacture of Aircrete in the UK are sand, pulverised fuel ash (PFA), cement, lime and water. 

About 70 per cent of the volume of each Celcon Block manufactured in the UK by industry leader H+H is PFA. This is a waste material that is a by-product of coal-fired energy generation and aircrete blocks are therefore hugely sustainable, making use of a material that would otherwise be sent to landfill. The use of PFA gives the blocks their distinctive grey colour.

Celcon Blocks also contain a percentage of sand and this percentage can vary depending on the availability of PFA. Some European plants manufacture aircrete using sand entirely in place of PFA. The resulting block will have the same performance characteristics but will be a pale milky colour.

What makes aircrete so light?

The main difference between an aircrete block and a dense concrete block is in its weight, and this is determined by the way it is made. The basic ingredients of aircrete (sand, PFA, cement, lime and water) are mixed into a slurry and a small amount of aluminium oxide is added to the mix. This causes a chemical reaction in which air bubbles are formed – it’s a very similar process to adding yeast to a flour mix to make bread. 

Once all the bubbles have been formed, the aircrete mix sets into a soft block which is then cut to size. These cut blocks are transferred into autoclaves for high pressure curing to produce rigid blocks with the strength to carry the weight of an entire building.

What are the benefits of aircrete?

The air pockets, or cells, trapped within the concrete give aircrete blocks their distinctive performance benefits.

As the cells are not interconnecting, aircrete offers excellent sound insulation, superb thermal insulation and air-tightness. They are also entirely waterproof and resistant to sulfate – important when using aircrete below ground level.

For builders using aircrete on site, the main advantages are to do with ease of use. Because they are lightweight, aircrete blocks can easily be moved around and are much easier to lay. They can also be cut with a hand saw, allowing for standard block sizes to be cut down to fit the precise dimensions of details such as door and window openings.

Aircrete is also fire resistant, making it an ideal product for use in residential properties. Available in a range of thicknesses - 75-200 millimetres (mm) - and strengths (2.9N mm2 up to 8.7N mm2), the blocks can be used from below DPC level right up to the eaves of a house and include both internal and external cavity walls; solid walls; party walls; and beam and block floors.

Aircrete’s load-bearing capabilities are often underestimated, meaning the product can be overlooked for foundations, but it does in fact support up to a three-storey residential building with ease.

Aircrete in action

The significantly quicker build speeds achieved when using aircrete can be of particular benefit for modular housing projects where speed of construction is key.

Aircrete experts H+H have collaborated with SIG Offsite to create the innovative ‘I-House’, which delivers a complete water-tight shell of a standard house on-site within a week, fully-wrapped and ready for follow-on trades.

The improved efficiency achieved when using aircrete helps keep final project costs under control without compromising on build quality.

Find further information on how aircrete can help with your next project,

Contact the H+H technical team.