Lightweight and strong cellular concrete can reduce the time required to build various elements of buildings and houses in South Africa, although it is currently mostly limited to fill-in applications, says cellular concrete firm Lightbuild Technologies Paul Drozdov.

Cellular concrete is manufactured in conventional or specialised mixers where the chemically treated concrete is aerated, or premanufactured foam is used, to produce concrete densities from 150 kg/m³ to 1 400 kg/m³.

The cellular concretes have very low thermal conductivity, with ratings typically between 0.05 Watts per metre Kelvin (W/m.K) to 0.38 W/m.K, and are often used for insulation in residential and industrial use cases, such as an insulating lining for pipes.

The lightest concretes are typically used in insulating applications, while the medium densities of between 600 kg/m³ to 1 200 kg/m³ are usually used to produce precast blocks and panels, roof and floor slabs, and used as fill-in material as part of light gauge steel-frame construction methods. Densities above 1 200 kg/m³ are used as a wall structural element in removable steel-frame construction.

“We provide the additives, admixtures and equipment to produce light-weight cellular concrete. An East London client achieved densities of 1 400 kg/m³ to 1 600 kg/m³ using a concrete truck. Densities below 1 400 kg/m³ are typically achieved using specialised mixers.

“The most advanced specialised plant in our range can produce up to 30 m3/h of lightweight concrete with average costs from R400/m³ to R900/m³.”

A common use of cellular concretes in Europe is the manufacture of prefabricated blocks for use as wall elements, or floor and roof insulation. The use of premanufactured panels can reduce the time to build by about seven times and cost savings, mostly in lower labour cost, are about 30%, says Drozdov.

“Cellular concrete is a very good filler and the technology is widely used in Europe and the Middle East, especially in steel- or concrete-frame construction methods. A specialised mixer used on a construction site is able to produce a wide spectrum of densities for wall cavity fills, and roof and floor slabs,” says Drozdov.

Cellular concrete densities of between 300 kg/m³ to 1 200 kg/m³ have compressive strengths in the range of between 0.4 MPa and 9 MPa. Cellular concrete densities above 1 400 kg/m³ have compressive strengths well above 5 MPa, up to 14 MPa for the higher densities.

Further, no local standards exist for use of prefabricated cellular concrete blocks, although engineers can use the local standards for autoclaved lightweight concrete and autoclaved aerated concrete blocks, he says.

Additionally, the fire-rating of cellular concrete is typically between 1.5 hours and 3 hours, but Lightbuild Technologies only holds non-South African fire-ratings certificates for cellular concrete.

In most cases, cellular concretes significantly outperform typical South African construction materials in terms of thermal conductivity.

“A wall built according to South African standards would have to be 1.5 m thick to meet the Russian thermal conductivity regulations,” he highlights.

“Two companies in South Africa use cellular concrete fill for light-gauge steel-frame construction and a Cape Town-based company is setting up a production line for large wall panels using high-density cellular concrete.”

Lightbuild Technologies used cellular concrete with densities between 400 kg/m³ to 800 kg/m³ for a geotechnical fill in Boksburg and for a project at the Medupi power station, in Limpopo.

“A competitive use for cellular concrete in South Africa is for trench back-fill, where densities of between 300 kg/m³ to 1 200 kg/m3 are used. A novel use for lightweight material of densities between 150 kg/m³ and 400 kg/m³ is to insulate industrial hot water pipes. Steel shuttering is placed around the pipes and the concrete pumped in the void around the pipe,” he adds.

Cellular concrete can be air-cured, chemically cured or autoclaved as the need dictates, he adds.

“Lightbuild Technologies focuses only on foam and aerated cellular concrete technology, providing site services and consulting, alongside its range of equipment and chemicals,” he concludes.