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Book: Building your own Home by George Wilkie

What's just arrived and what's coming over the horizon
Dick Clarke, Director, Envirotecture

There are some exciting developments in progress in the realm of new and reinvented materials. Some are brand new and hi-tech, others very low tech, but all have a high performance outcome with reduced eco-impacts.

Geopolymer cement and concrete

Pre-cast geopolymer concrete panels

Geopolymer concrete uses no Portland cement, instead using a geopolymer binder to chemically activate two industrial wastes – blast furnace slag (waste from iron production) and fly ash (waste from coal fired power generation). This alternative eco-friendly binder technology reduces the carbon emissions associated with normal Portland cement by 80-90 percent. High early strength is usually achieved within 24 hours. However, they set slowly enough that they can be mixed at a batch plant and delivered in a concrete mixer. A world first was recently achieved on a project in Queensland, with Bligh Tanner Consulting Engineers using a geopolymer concrete supplied by Wagner in Brisbane to create precast floor and ceiling panels. These have an extremely low carbon debt, while combining an extraordinarily high visual finish with excellent structural performance.

Precast hempcrete panels

Hempcrete is a kind of concrete made from chopped industrial hemp stalks, lime and water, and in its traditional form of in-situ placement similar to rammed earth (albeit not yet common in Australia) is the subject of chapter 3.02 and 5.07. It is a low eco-impact material, being grown and processed locally, and requiring no pesticides or irrigation. It has good acoustic, fire rating and thermal properties, and outstanding humidity and condensation control, some of the properties most needed for multi-unit construction – where speed is also of the essence. Hempcrete also offers the potential to be precast, in much the same way as traditional concrete; that is, formed in horizontal formwork with reinforcement and service conduits in place, and after curing, taken to site for high speed construction. Because hempcrete is a low strength concrete, it is likely that panels will be somewhat smaller and thicker, but the trade-off there is a single element monolithic wall element which meets or exceeds all fire, acoustic and thermal regulations, yet still provides high speed on site.

Recycled content concrete

Several manufacturers are working on reducing the embodied energy of their concrete through replacing some or all of the Portland cement content with alternatives, or using recycled aggregates and sand, even mix water. Boral have been marketing ‘Envirocrete’ for some years, which replaces virgin aggregates with up to 40% recycled aggregates, while maintaining all the usual performance and workability characteristics. Recently Boral announced a significant reduction in carbon footprint with ‘Envisia’, a high early strength, low shrinkage concrete that has 65% less Portland cement than a similar traditional concrete. Fifty percent less shrinkage would be reason enough to specify it, but it is also less permeable, has lower chloride diffusion and is Green Star MAT-4 compliant. Initially available in NSW, then available across the country. Fairfield City Council in Sydney’s west, working together with Metromix, have created a 95% recycled concrete by volume. Using recycled sand, aggregates and batch water from council’s Sustainable Resource Recovery Centre, and still using Portland cement, a slow-curing and very plastic concrete results. While the slow cure is a disadvantage in winter, for most of the year it is an advantage, especially when placing concrete in 35° heat, when traditional concrete can suffer fatal shrinkage cracking even before it is finished.

Magnesium cements

Magnesium oxide is a very common mineral on planet Earth, and makes a strong cement with very little embodied energy, which then absorbs CO2 during curing, resulting in net negative emissions. Tec-Eco in Tasmania has been researching these for many years, and produces small commercial quantities, which can be purchased on the mainland as well.

Magnesium oxide boards

Magnesium oxide can also be formed into flooring, wall cladding and lining. It has all of the advantages of its core cement (described above), plus a hard surface finish with firm edges, and extremely high fire ratings. There are several Australian distributors, and although the sheets are manufactured mainly in China at this point in time, the Ubiq Co (Inex products) are planning for local production (refer to page 170).

Structural insulated panels (SIPs)

SIPs are formed from three components: two stressed skins bonded to a non-stressed core. Essentially the same structural concept as a fibreglass surfboard or foam-sandwich racing yacht, in buildings they are usually flat panels, such as Bondor make, although Ritek Custom Roofing panels can be curved about the transverse axis. SIPs have been around for a while, but there are some new developments in the components, which avoid the problems associated with expanded polystyrene (EPS) foam cores, such as the difficulty in recycling, and the little white balls that inevitably escape during cutting on site and their impact on waterways and livestock. Ozone is a SIP with skins made of oriented strand timber (OSB3), which is high stress and FSC certified. The core is a fire rated polyisocianurate foam, which at 120mm thickness gives R4.0 insulation. It is fully recyclable, and is zero VOC. It is normally clad and lined, although the OSB pattern may be acceptable to some aesthetics. eSIP takes the renewable content of SIPs to a new level. Currently being developed by Tasmanian architect/builder Warren French, the panels use plywood skins and an innovative PVA-bonded sawdust core. The core provides both the structural bridging between stress skins in the usual way, as well as insulation, but unlike foam cores it sequesters carbon and has no hazardous or recycling problems.

Cross-laminated timber panels (CLT)

CLT is essentially massive plywood, typically around 100m thick. It is generally made from fast-growing softwoods, yet is so strong that it can be used as loadbearing elements in multi-storey construction. Panels are bolted or screwed together as floors, walls and roof, then lined and clad in the usual choice of materials. Advantages are speed of construction, carbon sink, relatively lightweight, flexible in design and can be altered on site. Rice husk insulation As bulk pump-in insulation, risk husks offer worthwhile advantages over produced materials. It is otherwise a waste product, with good performance in situ. However, even though Australian rice growers are the most water efficient in the world, it is still largely an irrigated crop, with associated river health and climate change implications for broadacre cropping.

Photovoltaic glass

Using windows or glazed roofs as photovoltaic (PV) to make electricity makes a lot of sense; it means the glass is doing three jobs at once: keeping out wind and rain, controlling heat flow and making power. Obviously care needs to be given to aspect and location, and at this stage it is still relatively expensive. Mushroom fibre boards and insulation Mushrooms in buildings are usually a sign of serious problems, but here is a horizon material that will change that. The mycelium fibres have some amazing properties, and current R&D is working on making those practical for building boards and also for insulation. It will probably be more than five years before we see this in local production.

Mushroom fibre boards and insulation

Mushrooms in buildings are usually a sign of serious problems, but here is a horizon material that will change that. The mycelium fibres have some amazing properties, and current R&D is working on making those practical for building boards and also for insulation. It will probably be more than five years before we see this in local production.

Sawdust

Usually an irritating waste product on site, it has many potential uses. Hyne Timber (amongst others) use it to fire their timber drying kilns. Timbercrete blocks contain 65% sawdust by volume, resulting in a useful dynamic mix of insulation and thermal mass. But it has found a higher value end use as aggregate supplement in concrete.

Contour crafting

Essentially 3D printing on a whole-building scale, contour crafting is being pioneered by Dr Khoshnev at the University of Southern California. It enables whole buildings to be ‘printed’ in many different materials, on site, in high speed, with infinitely variable designs and finishes. It therefore offers the potential for truly site-responsive ‘local’ designs, colours and textures, while also providing good thermal performance and affordability. Site access constraints need to be considered.

Celluform - 'Zeoform'

Celluform is a process whereby cellulose at its most elemental level is combined with water to reform into any shape or design. ‘Zeoform’ is a patented proprietary process that does this to make a huge variety of products, including doors and joinery, furniture – almost anything. The formula duplicates nature’s ‘glue-free’ process where cellulose fibres stick together in water, to make a moulding material that sets as strong as ebony. Cellulose is the most common organic compound on Earth, contained in one third of all plant matter (cotton 90 percent, wood 50 percent, hemp 75 percent). Henry Ford built a hemp-bodied car in the 1940s using a primitive version of the same technology, and hemp is once again proving to be a raw material of choice. Zeoform can be sprayed, poured, moulded, pressed or shaped into flat, curved, cylindrical or spherical forms. Forms are then dried, worked, finished and coated to create beautiful and functional products and objects of all kinds. It can be coloured, stained, or blended with substrates. Virtually any surface and texture can be formed to create unique aesthetics and can also be formed to provide additional specific functional properties. The material is extremely versatile once it has been formed and has dried solid. Standard tools can be used to machine it. Natural or synthetic coatings can also be applied. Revolutionary surface treatments provide opportunities like programmable surfaces, UV protection, heat dissipation, water absorbing or water repelling, etc.

More about this article

This content in this article was taken from the book "How to rethink building materials" which can be purchased online as a hard copy or soft copy.