Focus: Characterful


After hundreds of years as the keystone to building, functional—not beautiful—concrete is changing its character


Words by Francis Pearce

The appreciation of bare-faced building materials that flourished in the mid-20th century may have waned briefly, but concrete has made a come-back since the Millennium; particularly within buildings.

One form of concrete or another has been in use since about 700BC. Although sometime between the Roman era and the Georgian period important alchemical secrets of ‘liquid stone’ were lost and rediscovered, it is still an evolving technology.

At the pilot plant for additive manufacturing at the Techical University of Munich student Bettina Saile fills a test extruder with fresh concrete ready for 3D-printingAt the pilot plant for additive manufacturing at the Techical University of Munich student Bettina Saile fills a test extruder with fresh concrete ready for 3D-printing

There’s a treatise waiting to be written on why slave owning imperialists mainly preferred to dress concrete with brick or stone, while the more democratically inclined egalitarians of post-War Europe learned to like theirs raw.

In common with most ideas, though, greater currency has knocked the rough edges off brutalism so that polished concrete rather than beton has become ubiquitous in interiors: marble for the masses is as likely to be found on a foyer floor as on a kitchen top. In the age of ‘fake news’ and safe spaces, new concrete facades are often softened with sandblasting and older buildings are clad – including, of course, the ill-fated Grenfell Tower in London. Not that bare concrete has disappeared altogether; it just tends to be less honestly brutal.

At the pilot plant for additive manufacturing at the Techical University of Munich student Bettina Saile fills a test extruder with fresh concrete ready for 3D-printing

Inside AHMM’s White Collar Factory in Old Street, London, the exposed concrete beneath its 3.5m-high ceilings wears its timber markings and tie holes like ritual scars. But while the office complex, whose main tower ‘takes its cue from the multi-level factory typology’, keeps it real, it does so comfortably. Traditional concrete looks cold, but half the concrete used there is granulated, blast furnace slag that makes it appear warmer, more forgiving.

Changing the mix of the concrete had the added benefit of reducing its carbon content but, in addition, GBFS is a by-product of steel-making, and the manufacture of concrete and steel together account for about a tenth of greenhouse-gas emissions.

BFDO Architects in New York used polished concrete and Caesarstone lit with hidden LEDs in this retail space for the Dermalogica skincare brandBFDO Architects in New York used polished concrete and Caesarstone lit with hidden LEDs in this retail space for the Dermalogica skincare brand

Enormous research efforts are being channelled into making concrete more planet-friendly. Counter-intuitively, Massachusetts Institute of Technology students recently found a way to strengthen cement using discarded plastic bottles. Concrete is composite material comprising a fine aggregate such as sand, a coarse aggregate like gravel and a fluid cement that hardens over time in an exothermic (energy exhausting) reaction. Including even small amounts of plastic tends to weaken the material’s internal structure, but the students found that pulverising and then irradiating the bottles with gamma rays before adding them to standard concrete actually made it 15 per cent stronger.

There’s no shortage of raw material, either: at an average of 1.5 bottles per household a day, some 13 billion plastic bottles are used each year in the UK, according to the Recoup UK Household Plastics Collection Survey, and most end up as pollution.

Other attempts to finesse sustainability include the development of C-Fix by Shell and the University of Delft.

This carbon-based organic cement is produced as waste when crude oil is cracked and historically burned to avoid waste-handling measures, putting CO2 into the atmosphere.

Shell claims that using C-Fix could produce concrete with a carbon footprint up to 3.5 times lower than that of the traditional material based on Portland cement. It softens when heated and hardens when cooled so that within concrete it is temperature and pressure-sensitive and could also help create one of the new generation of smart materials. These include electrically conductive concrete made by adding materials such as steel fibres and carbon black to traditional cement. They are used for applications such as indoor heating, health monitoring, and electromagnetic shielding.

Atelier Barda used concrete to create a deliberately raw aesthetic when it renovated the Montreal headquarters of fashion curator SsenseAtelier Barda used concrete to create a deliberately raw aesthetic when it renovated the Montreal headquarters of fashion curator Ssense

Researchers at the Technical University of Munich (TUM) are finding ways to 3D-print intricate concrete structures. They have been experimenting with additive processes to make tiny pipes that biomimick bird bones, but by mid to late 2018 it hopes to have a machine capable of making concrete parts with volumes of up to 10 cu m. ‘That’s enough to create freely shaped, storey-high components,’ says TUM’s Dr Klaudius Henke.

The TUM team has also created an extrusion system for processing lightweight wood-concrete, which is as resilient and as good at insulating as conventional gas-aerated concrete and is also easy to saw, mill and drill. It has a rough surface texture: the strands that make up the wall are readily visible. ‘This structure can be used as a design element or can be post-processed,’ says Henke.

Cement-bonded wood products have been around for more than 100 years, but they were only used for non-load bearing purposes, such as insulation. Researchers at the School of Engineering and Architecture of Fribourg, Switzerland, though, have been trying out concrete blends that include up to 50 per cent sawdust instead of gravel and sand. These can be formed into slabs or walls capable of bearing large weights, show good flame retardance and act as thermal insulation, but ‘they weigh at most half of what normal concrete weighs – the lightest of them even float,’ says Daia Zwicky, head of the Institute for Building and Environmental Technologies at Fribourg. At the end of a building or interior’s life, it could also be burned to give back some of its embedded energy, he notes.





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