“When disaster strikes and permanent structures are leveled, as they were recently by earthquakes in Japan and New Zealand (and more distantly in Haiti), they are usually replaced in the short term by tent cities. Two engineering students thought they could do better and invented Concrete Canvas, a fabric impregnated with concrete that can turn a tent into a hardy, permanent structure in 24 hours. Just add water”
Concrete Canvas (CC), is a flexible, cement impregnated fabric that hardens when hydrated to form a thin, durable, waterproof and fire resistant concrete layer. CC allows concrete construction without the need for plant or mixing equipment. Simply position the Canvas and just add water. CC consists of a 3-dimensional fibre matrix containing a specially formulated dry concrete mix. A PVC backing on one surface of the canvas ensures the material is completely waterproof. The material can be hydrated either by spraying or by being fully immersed in water. Once set, the fibres reinforce the concrete, preventing crack propagation and providing a safe plastic failure mode. CC is available in 3 thicknesses: CC5, CC8 and CC13, which are 5, 8 and 13mm thick respectively. Figure 1 shows a typical concrete canvas section.
The technology for concrete canvas was invented at Imperial College London in 2004. Concrete Canvas Ltd was incorporated in 2005 to manufacture both concrete canvas and concrete canvas shelters. Concrete canvas has been used for roofing and building cladding, although the main applications are in civil engineering; including ditch lining, slope protection, pipe protection, and retaining walls.
Concrete canvas can be laid into ditches and drains by simply rolling out the fabric. If the ditch is narrow then the fabric is rolled longitudinally along the length of the channel. Alternatively, if the ditch is wide, the fabric is laid transversely with overlaps that can be sealed to form a waterproof lining. In either orientation the fabric will mould to the shape of the channel. After laying, the fabric is pinned to the ground and wet.
Once hydrated the fabric remains workable for 2 hours and hardens to 80% strength within 24 hours.
Concrete canvas comes in rolls 1.0m or 1.1m wide. Available lengths are 4.5m (weighing 60kg) or 200m (weighing over 1.5t). Rolls come in three thicknesses: 5mm, 8mm and 13mm. Refer Figure 2.
Concrete Canvas Key Facts:
Easy To Use: CC is available in man portable rolls for applications with limited access or where heavy plant equipment is not available. There is no need for mixing or measuring, the concrete is premixed and cannot be over hydrated. It will set underwater and in sea water.
Rapid: Once hydrated, CC remains workable for 2 hours and hardens to 80% strength within 24 hours. Accelerated or retarded formulations can be produced to meet specific customer requirements.
Environmentally Friendly: CC is a low mass, low carbon technology which uses up to 95% less material than conventional concrete for many applications. It has minimal impact on the local ecology due to its limited alkaline reserve and very low wash rate. The impact on the environment is further decreased by reducing the need for plant equipment.
Flexible: CC has good drape characteristics allowing it to take up the shape of complex surfaces including those with a double curvature. Unset canvas can be cut or tailored using basic hand tools.
Strong: The fibre reinforcement prevents cracking, absorbs energy from impacts and provides a stable failure mode.
Durable: CC is chemically resistant, has good weathering performance and will not degrade in UV.
Water Proof: The PVC backing on one surface of the canvas ensures that the material is completely water proof and chemically resistant.
Fire Resistant: CC is fire-safe, does not contribute to the surface spread of flames, has a low level of smoke development and minimal hazardous gas emissions. CC has achieved Euroclass classification B-s1, d0.
Concrete Canvas Applications:
Ditch Lining: CC can be rapidly unrolled to form ditch or channel lining. It is significantly quicker and less expensive to install than conventional concrete ditch lining and requires no specialist plant equipment. The 30m ditch shown above was lined in 45min. Refer Figure 3.
Slope Protection: CC can be used as slope stabilisation and other erosion control applications such as temporary and permanent slope protection, retaining walls, boulder fences, low level bunds and river bank and dam revetments. Refer Figure 4.
Bund Lining: Secondary containment bunds can be quickly lined with CC to provide an efficient, chemically resistant alternative to concrete walling. Refer Figure 5.
Cable Protective Covering: CC can be installed in-line with existing cable laying equipment to provide protection against impact damage at a rate of 1000m/day. 200mm wide CC13 has been tested to BS 2484:1985 Impact resistance for straight concrete and clayware cable covers. Refer Figure 6.
Pipeline Protection: CC can be used as a coating for overland or underwater pipeline protection, providing a superior tough rock shield. In remote areas it can be used to coat steel pipe on site without expensive wet concrete application plants. CC will set underwater and provide negative buoyancy. CC13 meets the requirements of ASTM G13 . Refer Figure 7.
Ground Resurfacing: CC can be secured with ground anchors to rapidly create a concrete surface for flooring, pedestrian walk-ways or dust suppression. CC8 and CC13 have been tested to EN 1991-1-1:2002 (Resistance to Imposed Loads on Vehicle Traffic Areas). Refer Figure 8.
Mining Applications: CC can be used as an alternative to poured or sprayed concrete or as a quick way of erecting strong permanent or temporary blast and vent structures and spall lining. Refer Figure 9.
Concrete Canvas benefits- General:
– An 8mm thick roll can in some applications replace up to 100mm of reinforced insitu concrete.
– Very low or zero wastage in application.
– Around 90% less material usage.
– Up to 95% less embodied carbon.
– Less water is required to hydrate Concrete Canvas than is contained within insitu concrete.
– Fewer vehicle movements due to material volume and weight reductions.
Concrete Canvas benefits- Contractors View Point:
Whether laid longitudinally or transversely concrete canvas offers value for money for ditch lining projects.
– The installed cost is typically less than the cost of conventional concrete ditch lining, particularly if the roll is laid longitudinally.
– A 100m2 section of drain lining can be laid transversely by three men in one day.
– Concrete canvas can be laid in wet conditions. This can reduce programme disruption typically caused by bad weather.
– The rolls are easy to transport using standard vehicles.
– No handling of wet concrete or formwork.
– Chemically resistant with good weathering performance.
– Fire safe (Euroclass classification B-s1-d0).
– The fibre reinforcement prevents cracking and absorbs energy from impacts.
A bag weighing 230 kilograms inflates into a shelter with 16 square meters (172 square feet) of floor space. Cost is estimated at $2,100, while an equivalent-size Portacabin costs about $7,700. The same-size tent costs about $1,150.
Concrete Canvas is a revolutionary product that has come into the market. In a country like India where the natural calamities are very frequent, concrete canvas allows aid teams to construct solid structures in emergency zones quickly and easily as it is a fabric shelter that, when sprayed with water, turns to concrete within 24 hours. concrete canvas replaces 150mm of poured concrete with just 8mm for many surfacing applications, resulting in material saving of 95%for a typical construction project. This directly reduces the CO2 footprint of construction in both material savings and reduced road transport. The material is also ideal for rain-screen cladding, greatly increasing the thermal efficiency of buildings. concrete canvas has been material, environmentally and fire tested by several or organisations, including theBBA. The material has already been used for many major projects around the world.