Alternative building materials contesting tradition
Ellis Davies takes a look at how alternative building materials are being used around the world.
As part of the modern landscape, we encounter building materials every day. Concrete, brick, glass and tile to name a few, are ever present in structures that adorn the streets, but there are some unusual alternatives being used around the world. ‘As new builds are going up, it's important to look at the ecology of the materials to try and mitigate the environmental impact in all ways,’ Mischa Hewitt, Director at the Low-Carbon Trust, UK, told Materials World. Be it for environmental, cost or decorative reasons, there are a number of examples of unusually constructed buildings, from plastic renewable housing to giant wooden towers.
Plastic for homes
Waste plastic is a much-discussed global issue, with an estimated 297.5 million tonnes of plastic consumed in 2015. Of this figure, America contributed around 10.5 million tonnes, of which only 1–2% is recycled. Biodegradation of plastic materials can take more than 500 years, with multilayer plastics or mixtures often making reuse a complicated process.
With the material in such abundance, Columbian company Conceptos Plasticos, founded by architect Oscar Mendez, aims to use this waste product to combat Columbia’s housing deficit, as well as tackle the issue of plastic waste. Set up to reuse the waste from pipe manufacture, the company uses extrusion to create beams, blocks, jambs and sills. The plastic is first cleaned thoroughly, before being ground into a rough powder to be mixed and melted, then extruded into the range of shapes. The separate pieces slot together like LEGO blocks, and without adhesive.
Conceptos Plasticos also provides training for communities to construct the houses themselves. Mendez claims that four people can build a 40m2 house in five days. A house of this size costs US$5,200, which is considerably lower than traditional systems in both cities and rural areas. The company has built nearly 1,500m2 of housing over several regions of Columbia, using 300 tonnes of waste plastic. In the future, it plans to build 600 homes a year by 2018, impacting 3,000 people.
Wooden structures are often associated with small cabins in the woods or a shed at the bottom of the garden – not tall buildings. At the University of British Columbia (UBC), Canada, however, the latest wooden structure on campus, engineered by Fast + Epp, Canada, is 18 storeys high. At around 53m, it is the world’s tallest contemporary wooden building.
The structure is UBC’s Brock Commons student residence, and is a mass wood and concrete hybrid, with a concrete podium, two concrete cores and 17 storeys of cross-laminated timber (CLT) floors on glue-laminated wood columns. On the topic of CLT, Hewitt said, ‘One of the most important steps forward is through laminated structures, with the combination of timbers making for a really strong structural member.’ In order to avoid a vertical load transfer through the CLT panels, a steel connector is used to direct load transfer between the columns and provide a surface for the CLT panels. Paul Fast, founder of Fast + Epp, told Materials World, ‘We went with concrete cores because the building is located in a high seismic zone, so it would be more costly to go to a CLT core. Equally important, concrete cores helped to get the approvals sooner.’ The building code in Canada currently only permits the construction of timber structures up to six storeys, which meant that a special zone had to be established for the site in order to begin construction.
The roof is made from prefabricated steel beams and metal decking, and the façade is 70% wood fibre. The hybrid construction affords the building benefits such as a lighter weight, which is advantageous in poor soil condition sites, the use of prefabricated elements to speed up construction, long unsupported span distances in design and an increased strength-to-weight ratio. The structure was built in 70 days with prefabricated components, and the building is set to open to students in September 2017, following the completion of the interior.
Fast says the construction of a wooden structure differs from a concrete or steel building most prominently in the amount of design time required. ‘Wood construction is typically more design intensive as you are piecing together more individual components. Concrete structures are pretty straightforward with well-established procedures. Building multi-storey with wood requires considerations such as differential settlement of structure. Dealing with weather issues during construction is also important. The wood is exposed, you're building 18 storeys, how are you going to deal with that?’ In this case, construction was carried out during the summer to avoid the increased rainfall of the autumn and winter months. Fast explained that if construction were scheduled for a rainy season, care would need to be taken to stop the wood from swelling and warping, making sure it was dried properly if it became wet.
UBC claims that taller wood buildings such as the Brock Commons residence offer economic and environmental benefits, with the use of wood providing a 2,432 tonne reduction in carbon dioxide in comparison to traditional construction materials – the equivalent to 500 fewer cars on the road per year or enough energy to power a home for 222 years. Fast said, ‘Wood is a very resource efficient material because it quickly regrows and is regarded as the greenest material, being very low on body energy and being able to sequester carbon. In terms of fabrication, you can build a structure quickly, saving time in the construction period.’ He also mentioned that the process was a lot quieter than the building of a conventional concrete or steel structure, with the lack of cement trucks and pumps, leaving the residential area surrounding the building relatively undisturbed. The building uses 2,233 cubic metres of CLT in its construction – the amount of wood grown in USA and Canadian forests in around six minutes.
UBC may, however, not have the largest wooden building for long. Global architecture company Perkins + Will have proposed a structure that would surpass UBC’s 18 storeys, with 80. This comes as part of the Riverline project along the south branch of the Chicago River, looking to create a new community of 3,600 residents over 566m2 of land vacant since 1971. The structure is currently entirely conceptual.
It would feature a large central atrium with an aluminium veneer over exposed diagonal lattice timber beams. Perkins + Will have claimed that this is structurally possible, but as yet do not have an overall cost for the build.
Fast commented on the proposed project, saying, ‘From an initial concept to following through to an end product in a cost-efficient way, is still a very large step. Is it doable? Absolutely. Things must remain realistic, however – you cannot force a square peg into a round hole.’
Cities of bone
Buildings made of bone may seem more at home in a horror film, but researchers at the University of Cambridge, UK, are developing samples of artificial bone and eggshell that could be scaled up for use as low-carbon building materials. The team sees its artificial bone as an energy-efficient alternative to concrete and steel.
The artificial samples, like the real thing, are composites of proteins and minerals. Dr Michelle Oyen, University of Cambridge, UK, told Materials World, ‘In the case of both bone and eggshell, the materials are a composite of something organic (protein) and something inorganic (biomineral). This combination gives rise to materials that are relatively lightweight and that have properties (strength, stiffness and toughness) that are very good on a per-weight basis.’ The artificial samples also make use of bone’s self-healing characteristics.
During manufacture, the materials can be engineered to have various properties by varying the proportion of the different sub-components of the composite. ‘This can be seen in nature in comparing bone and the exterior hard surface of tooth (enamel). Both are composites with hydroxyapatite (calcium phosphate) as the mineral, but they have very different properties because bone is only about half mineral and enamel is mostly mineral, giving rise to a factor of five or so stiffness difference between them,’ Oyen said.
To make the samples, the mineral components are ‘templated’ into collagen. The bone minerals deposit along the collagen, while the eggshell tends to deposit outwards from the collagen. This holds potential for a lattice-like structure to be created, adding further strength. The samples can be made at room temperature, therefore requiring minimal energy during production.
Currently, the collagen needs to be obtained from natural sources – animals. The team is investigating ways to use synthetic protein or polymer instead to aid the process of scaling up. ‘We’ve been making laboratory-scale (cm) samples that are easy for us to manufacture and big enough for us to be able to test their chemical composition, microstructure, and mechanical properties,’ said Oyen, commenting that a partnership would be required to pursue the project further.
Another obstacle to tackle in design is building standards made with concrete and steel in mind. Using artificial bone in construction would require a major rethink in the industry – one that the researchers feel is justified given the environmental benefits. However, as wooden structures have been successfully constructed – the properties of bone and wood are similar – the team claims that using bone is possible.
Buildings made of alternative materials are on the rise, particularly using CLT, and can bring economic and environmental benefits. It remains to be seen, however, whether the industry will evolve with them.