Concrete creations

Materials World magazine
,
3 Nov 2013
Concrete Canvas being used for slope protection in Spain

Rhiannon Garth Jones talks to Phill Greer of Concrete Canvas Ltd and Tom de Saulles of the Minerals Products Association, both UK, about exciting innovations in one of the most ancient building materials.

Although concrete had already been used for building in Ancient Greece and Assyria, the Romans’ use of it centuries later led to an architectural revolution. More than 2,000 years on, we are well accustomed to thinking of concrete as a permanent fixture, an unchanging material. But in the past few years, concrete has had a makeover that could lead to a materials revolution of our own. From Doreen Lace’s beautiful, high-performance lace concrete structures to a self-healing smart concrete invented in the Netherlands last year, and Hungarian architect Áron Losonczi’s light emitting concrete, the innovations are exciting.

One such development with potentially huge significance beyond its original intended function is Concrete Canvas (CC). Developed by Will Crawford and Peter Brewin, engineers and founders of CC, it initially served as a rapidly deployable emergency shelter made from a concrete-impregnated fabric. However, the material has proved to have many further applications.

CC comprises a roll of canvas that can be laid in position and hydrated to form a thin, durable, waterproof and fire-resistant concrete layer. While the concept is simple, the science is a little more complex. The material consists of a 3D fibre matrix that links two faces, one porous and one impermeable. Between the fibre lies a dry concrete mix that separates the two faces and reinforces the concrete once set. A critical water/cement ratio is controlled by the material structure of the mix, which prevents over-hydration and ensures it can be installed in the rain or even underwater.

The environmentally friendly material uses low-carbon technology and up to 95% less material than conventional concrete. However, recent studies by the Mineral Products Association (MPA) suggest that traditional concrete has less environmental impact than previously supposed, and in fact absorbs CO2 from the air during its lifecycle.

Tom de Saulles, Senior Manager of MPA’s Building Sustainability project, says, ‘The building sector hasn’t talked much about this in the past, with the focus lying on timber’s ability to sequester CO2, but increased focus on sustainability has made the issue much more topical’.

The cement used to make concrete accounts for most of its embodied CO2. Around 60% of CO2 emissions from cement production comes from the thermal decomposition of calcium carbonate (CaCO3) and these emissions are reversible through the process of carbonation. The rate of carbonation during the service life of medium/highstrength concrete is slow and will only occur to a depth of a few millimetres below the surface. At end-of-life, however, when the concrete is crushed, the rate of carbonation accelerates due to the significant increase in exposed surface area. Furthermore, carbon sequestered by concrete is never released back into the atmosphere, as it is with materials such as timber. While de Saulles does not see a greater awareness of carbonation alone driving sustainability in terms of concrete, he does believe it has an important contribution to make.

Concrete Canvas: around the world


Chile

Glacial melt water threatening to flood a copper mine in the Atacama Desert 1,200 metres above sea level was successfully diverted by channels lined with CC. Two five-man teams cut the CC to size using hand tools, and used pegs to hold the canvas in place across the ditch. To account for the water flow, adjoining layers were overlapped by 100mm and held together with screws. The CC was hydrated by water mixed with an accelerant, to take the cold temperatures into account.

Canada

At Willow Creek Mine in British Columbia, CC was used to line 39,000m2 of carrier ditch to direct contaminated industrial wastewater to a settling pond. The canvas was cut to size on-site to minimise waste, and layers were directly laid transversely across the width of the ditch. Each layer was overlapped by 100mm, beaded to create watertight joints and then attached to the work sections using standard fixings and adhesives.

For further information, contact Phill Greer, phill.greer@concretecanvas.co.uk, or Tom de Saulles, tdesaulles@concretecentre.com