Article - Issue 57, December 2013
Located in the Andes mountains, in the southern reaches of the Chilean Atacama Desert, is a highly profitable open pit mine. However, meltwater erosion, high UV levels and wind speeds of over 100km/h had degraded the existing water channels surrounding it over a number of years. Different thicknesses of Concrete Canvas were used to match variations in ground quality and profile at different sections of the channels to successfully line them
Concrete Canvas provides a quick, cost-effective method of laying concrete that is revolutionising the construction industry. A material that started life as a way of creating rapidly deployable concrete shelters for humanitarian aid purposes has evolved to become a mainstream civil engineering solution for stabilising slopes and lining ditches. Following the company’s nomination as a finalist for the 2013 MacRobert Awards, Ingenia asked one of its inventors, Will Crawford, how Concrete Canvas developed, and to describe a few of the many applications for this versatile product.
It was high in Chile’s Atacama Desert that Concrete Canvas came of age. The concrete-impregnated geotextile that hardens when water is sprayed onto it was being used on a project at the Minera Lumina copper mine. It was the largest application of the product to date.
Over 53,000m³ of Concrete Canvas was used to line water channels. The work was undertaken in a remote and challenging environment, with temperatures ranging from -10°C to 20°C. The bulk of the installation took place at over 4,000m above sea level, an altitude where working for more than three hours at a time becomes problematic. Its quick-setting benefits were more than ably demonstrated in Chile, providing an easy and rapid way to lay a thin, durable, waterproof layer of concrete. Water channels were dug and lined to successfully divert glacial meltwater that was threatening to flood the copper mine and carry contaminants down to agricultural land below.
How it works
The material itself consists of a three-dimensional fibre matrix linking two faces: a porous face that retains the dry concrete powder but allows water to pass through it, and an impermeable PVC face. The dry concrete mix is trapped within the fibre matrix that controls the separation of the faces and provides paths for water to trickle through by capillary action. The fibre matrix also acts as reinforcement for the resulting set concrete.
The composition, particle size distribution and density of the concrete mix within the fabric are carefully controlled to define a void ratio – when water is sprayed on to it, the water fills the voids. Because the fabric controls the internal volume, the resulting concrete cannot expand, so the critical water to cement ratio required to create sound concrete is controlled by the material. This means Concrete Canvas cannot be overhydrated, allowing the product to be installed by non-specialist contractors with minimal training. With a very low wash out rate and a low alkaline reserve, it can even be installed safely in live water courses. The result is a concrete solution that can be laid anywhere – in the rain, underwater and even in high-altitude desert conditions.
Concrete Canvas comes in thicknesses of 5mm, 8mm or 13mm, and the material can be supplied in batched rolls that can be carried by two to four workers. It is also available in larger rolls that can cover up to 200m2. For the Chilean project, 5mm-thick material was delivered on bulk rolls and dispensed from a crane truck using a spreader beam – a piece of equipment conventionally used for laying geotextiles.
Lengths of 6.4m were cut on site (to allow it to be laid across the width of the ditch), and held in place with ground pegs before being buried in an anchor trench situated at the head of the ditch sides. Adjoining layers were overlapped by 100mm in the direction of water flow and joined together with screws.
A sprayer truck then dispensed water containing an accelerant to help the material set faster in the cold environment. Once hydrated, the Concrete Canvas was covered in plastic sheeting for three days to protect the setting material from freezing temperatures.
By using this method, two five-person teams were able to install the material at an average rate of 144sqm/hour without the need for specialist equipment or heavy plant.
Concrete Canvas provides excellent resistance to chemical attack and has passed acid (ph4) and alkaline (ph12.5) immersion tests to BSI standard 4414
This high-altitude activity is a long way from the purpose for which the fabric was originally developed. Back in 2003, engineers Will Crawford and Peter Brewin were students in their mid-twenties when they met on an industrial design engineering postgraduate course run by the Royal College of Art and Imperial College London. Both had worked in industry and felt ready to create their own products and run their own company. The course gave them the freedom and support to use their technical knowledge and experience to develop ideas for commercial projects.
Both were short of money, so they pooled their ingenuity and resourcefulness to win student design competitions offering cash prizes. One of these was run by what was then called the British Cement Association, which challenged students at the art college to come up with new ways of using concrete.
As their starting point, the pair brought together the basic properties of concrete –it sets hard with water and it is strong when compressed – with a fascination with the eggshell shape which also is strong under compression. They realised that a similar parabolic shape to an egg is created when a balloon is inflated. As tensile forces are oppositional to compressive forces, they saw a way to use tension to create the optimum surface for compressive loads and, in the process, invented a low-tech, low-cost method of erecting instant structures.
Crawford and Brewin’s eye-catching concept for a rapidly-deployable, inflatable emergency shelter made of concrete-impregnated fabric won the pair top prize in that competition and others that followed. By the end of their campaign, they had £40,000 with which to launch their own company and develop the product.
The shelter is still produced today. It consists of an inflatable plastic inner tube with 13mm-thick dry concrete-impregnated fabric bonded to the outside and steel doors fixed at both ends. It comes sealed in plastic airtight packages that can be delivered along with a fan to inflate the structure and pegs to hold it in place.
Once deployed in a refugee camp or disaster zone, all that is needed is for the sack to be cut open, the fan plugged into a generator and, 20 minutes later, the resulting structure is ready to be sprayed with water from a borehole or the sea. After 24 hours, it will both set hard and be structurally sound. There are two shelter sizes available, one measuring 25m² and weighing 1.8 tonnes, the other 50m² and weighing 3 tonnes: far lighter than comparable conventional hard- skinned structures and well within the lifting capability of military equipment.
In December 2010, Concrete Canvas was chosen to address years of erosion and instability issues affecting the entrance of Alcobendas tunnel station in Madrid. The material was delivered to site in bulk rolls and a crane with spreader beam was used to position the fabric. The project’s first phase, covering 800m², was completed in three days
The engineers visited a refugee camp in Uganda and spoke with UN field workers and other non-government organisations to establish that there was a demand for their buildings-in-a-bag. Full-scale development of the shelters took two years, and in the process opened the eyes of the Concrete Canvas business team to new markets and uses for their ground-breaking material technology.
Funding was key in order to commercialise the idea, and the pair took their idea to various investor groups. They even went on to BBC TV’s Dragon’s Den where they were offered money by two of the investment Dragons, offers which they turned down as too big a share of the company would have been released in return. By 2006, investment from business angels and a government grant allowed them to concentrate on developing the products and pilot production line.
A large proportion of the early R&D work focused on developing the material, which was achieved by working with core suppliers and specialist manufacturers. The team came up with the patented 3D fibre matrix design that would prevent the dry concrete mix from moving while being transported. Evolving the production process to carefully control the density of the concrete mix within the fabric had been a major challenge and the solution remains a closely guarded secret.
Almost from the start, it was the material and not the shelters that became the main attraction to potential customers. In 2008, the first big sale for the young business was to the British Ministry of Defence to upgrade front line protection in Afghanistan, using the fabric to harden sandbag walls. This order was a great demonstration of the potential of Concrete Canvas, and gave the team the confidence to widen their search for other markets.
Concrete Canvas has a wide range of applications, from protecting slopes from surface erosion and slip, to lining drainage ditches and repairing existing concrete. It is typically used to replace conventional concrete (in-situ, precast or sprayed) for erosion control, remediation and construction applications
One major application was in the construction of drainage channels, and a major breakthrough came with a contract to line a 140m-long ditch beside a Network Rail high-speed line. The job was virtually completed in minutes, and both the contractor and client could see that Concrete Canvas offered huge benefits in terms of speed, reduced risk of possession overruns and better health and safety when compared to traditional sprayed concrete. Network Rail is now a major customer.
Concrete Canvas can be installed 10 times faster than other methods of laying a thin layer of concrete. Because it can be supplied at around a tenth of the 100 to 150mm thickness achieved with poured, pre-cast and sprayed concrete, it can also offer impressive savings on materials and consequent CO₂ emissions.
The material also does away with many of the complex logistical and health and safety issues associated with shotcrete (wet mix sprayed concrete) and gunite (dry mix sprayed concrete), something international rail operators have been quick to appreciate.
It was these benefits that saw the product taken up by ADIF, the Spanish railway infrastructure management authority, as slope protection for a railway station in Madrid. The steep slope marking the entrance to the Alcobendas rail tunnel had been affected by years of erosion and instability and previous attempts to remedy the problem with shotcrete had failed. The debris and rebound associated with sprayed concrete also meant that the rail line needed to be closed during installation, should the same method be adopted again.
For this job, the company supplied 2,500m² of material to site in bulk rolls and dispensed them from spreader beam and crane. The material was fixed to the top of the slope using galvanised steel pegs, while adjacent layers were screwed together. A shallow surface runoff ditch to help with drainage was formed at the toe of the slope before the material was hydrated using onsite equipment. Installing at a rate of over 450m²/day, the project was completed in under a week. Train traffic was not affected during the works, and the station was able to remain open, as there was no risk of debris landing onthe tracks.
In 2012, an award-winning installation was set up outside Rome’s Maxxi Museum. The benches were made from ribs of marine-grade plywood, with sections covered in a Concrete Canvas material. Photo by Urban Movement Design, Courtesy of MAXXI Museum
Culvert and outfall lining, irrigation, bund protection (barriers intended to contain leaks or spillages), concrete remediation, gabion protection and weed suppression have now been added to the Concrete Canvas portfolio as well as lining mine vent walls. Around 90% of the business is for civil engineering applications, with the mining industry a growing source of custom. In the last year, over 250,000 square metres of the material were sold, with 85% exported to 40 countries around the world. The company turnover has doubled every year for the last five years, an increase in demand that is predicted to continue in the coming years.
There is also still significant demand from the aid sector for the Concrete Canvas shelters as field hospitals and command and control centres. In November 2013, Concrete Canvas carried out a large deployment in the Middle East.
An early appreciation of the wider potential of the product played a significant role in the rapid expansion of the company. A healthy research and development culture means that Concrete Canvas is constantly being developed for new applications. It has recently been installed to provide hard armour capping for containment bunds at a UK marine terminal and as an erosion control solution in a limestone quarry where it performed successfully under blast conditions. Research into new material variants will also mean Concrete Canvas will no longer be limited to external projects but can be specified for internal and specialist applications such as wall cladding, flooring, basement lining and waterproofing.
The company believes that the use of its material will have far-reaching consequences throughout the construction industry for many years to come, providing innovative solutions to logistical, environmental and cost problems in a wide variety of applications.