Building blocks for the future - organic binder for construction materials

Materials World magazine
,
2 Jan 2014

Natural materials could revolutionise the sustainability of the construction industry. Rhiannon Garth Jones talks to Mark Nichols, Chairman, and Dr Stuart Shaw, R&D Manager, at masonry company Encos Ltd, UK, to find out how.

At the dawn of the Stone Age, Paleolithic men created paintings on their caves using pigment made from minerals mixed with vegetable oils such as linseed, which polymerise when exposed to oxygen. Those same paintings have survived until the present day because of the binding agent in the oils. In more recent years, people aware of the hardening properties of linseed oil have used it to coat their cricket bats and now, these oils are being used as a binder to create carbon neutral bricks.

In 2000, scientists at the Universities of Leeds and Nottingham, UK, having noticed that vegetable oils could function as an organic binder, collaborated to investigate if those binders could be used in the manufacture of construction materials. That research could soon be translated into reality, with the impending commercialisation of masonry units made using organic binders that look and perform like their ceramic equivalents.

The science is surprisingly simple. Vegetable oils (including sunflower, rapeseed, linseed, and corn) are composed of molecules called triglycerides. Each molecule has three fatty acid chains attached to a central glycerol molecule. When heat is applied, the reactive sites along these chains are activated, allowing oxygen present in air to bind them together, creating an irregular polymer network that is both solid and durable. The binder is then mixed with an aggregate, where it is absorbed by the fine aggregate particles (less than 63_), which then polymerise with heat and oxygen to form a matrix that encapsulates the larger aggregate particles. A similar encapsulation is performed by cement, but this binder is organic in nature.

Mark Nichols, Chairman of Encos Ltd, UK, which is working with the universities to commercialise the technology, explains, ‘The benefit of using vegetable oils is that their carbon negativity contributes to the calculation of the overall carbon footprint of the material. We looked at various aggregates, both natural and recovered, and found that limestone fines, which are derived from the crushing of limestone rock in the production of coarse aggregates (around 30% of all the limestone crushed in the world), work extremely well with the binder. The grading profile of those aggregates allows effective construction materials to be produced.’

In addition, only a fraction of the energy that the brick industry uses to form their ceramic equivalent units is needed in this process. The organic binder only needs to be in an oven for maximum 24 hours, at a relatively low temperature of around 150-160°C. Dr Stuart Shaw, Encos’ R&D Manager, believes that at a conservative estimate, the embodied energy in an Encos brick is around 0.3kWh compared to 1.8kWh for a conventional ceramic brick. He adds, ‘The process requires a significantly lower curing temperature compared to ceramic brick production, with the resultant carbon emitted by manufacture offset by the biogenic carbon storage in the binder, to create a product that is at least carbon neutral.’ Shaw adds that the process generates zero waste during manufacture and that the products have a neutral pH.

A viable alternative?
Of course, crucial to the success of these alternative construction products will be the ability to compete with their ceramic equivalents. While the industry has increased its focus on sustainability, that cannot come at the cost of performance, or of the products themselves. However, Shaw is confident that the products will stand up. ‘There’s no difference in performance. Once the matrix is set up, it is durable and sturdy, and it won’t be degraded by weather. Unlike cement, which changes over its lifetime, this material stays the same over time. There’s no further reaction within the polymerised binder – not even with sodium chloride or sulphates, which can be detrimental to cement-based materials.

Bricks made with the organic binder do have a slightly higher cost when compared to concrete, particularly the large construction blocks. Against ceramic bricks, though, they compete very well, and have much better thermal conductivity – around 0.3W/mK compared to a clay brick, which is around 0.8 W/mK. However, the crucial difference remains the organic nature of the material. The use of inorganic binders and processes in the manufacture of the other construction materials on the market can sometimes lead to adverse reactions such as the alkali-silica reaction, which is a reaction between cement and reactive silica found in some aggregates, a problem avoided when using an organic binder.

Encos has spent the last seven years working on commercialising the process, and applying it to masonry units that have been rigorously tested to prepare them for market. Nichols elaborates, ‘We have conducted all the tests to comply with BS EN 771. We have also undertaken four accelerated ageing tests designed by BRE, to determine how well the product would last in the field including thermal shock and submersion. About 32 tests were carried out in total including flammability and susceptibility to microbes. Results have indicated that the material is non-flammable, and that the microbial activity on Encos’ products is no different than it is on ceramic or concrete materials.

The production process first developed by the researchers at Leeds and Nottingham Universities and now by Encos is, in many ways, similar to the conventional ceramic brick producing process, which means that conventional factories can be easily adapted to produce the organic equivalents. Very soon, such products could be on the market and before long, we could be building homes with the same materials used by our Stone Age ancestors.

For further information, email Mark Nichols, mark.nichols@encosltd.com