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    Australian-developed carbon nanotube concrete approved for US infrastructure

    Nathan Johnson

    Perth-based Eden Energy Limited has announced that its special admixture for concrete with incorporated carbon nanotubes (CNT) has been approved for use on roads in the United States.

    EdenCrete has been permitted for use by the Georgia Department of Transportation (GDOT) for construction and maintenance projects within their jurisdiction.

    The decision was based on results achieved in a full depth slab replacement field trial of EdenCrete on Georgia’s Interstate Highway 20 in August 2015.

    The product, which incorporates super-strength, highly conductive (thermal and electrical) nano-carbon particles that have a flexural strength 200-300 times stronger than steel, showed a 45.8 per cent improvement in compressive strength over a control mix through a 56-day trial as well as a 57 per cent improvement in the rate of abrasion.

    ABOUT THE PRODUCT

    EdenCrete first grabbed media attention back in 2014 when the manufacturers announced that they would be conducting commercial trials of CNT enriched concrete aimed at high abrasion resistant applications such as roads, which do not carry the same risks as concrete used in high rise construction.

    According to Eden back then, the commercial application of CNT also had significant potential to enrich the capabilities of building concrete – a key ingredient for domestic, industrial and commercial projects.

    Since late 2005, Eden and the University of Queensland have been developing a low cost pyrolysis technology to produce CNT from natural gas, with the only by-products being hydrogen and CNT, and no carbon dioxide.

    This proprietary technology is a modular system able to be installed at gas fired power stations or fertiliser plants, and used to produce the CNT from the natural gas feedstock, whilst using the hydrogen by-product to produce cheaper electricity or the fertiliser.

    Eden then developed a process to mix its CNT into cement paste in conjunction with Monash University, achieving an increased compressive strength of up to 30 per cent by using only half of one per cent (by weight) of CNT, and 99.5 per cent of cement.

    Helium ion microscope analysis by Monash University showed Eden’s CNT in cement paste acted as “nucleation points for cement hydration, rather than acting solely as nano-scale fibre reinforcement (like larger-scale fibres), resulting in a denser, stronger and potentially more durable composite”.

    “CNT-enriched concrete should significantly reduce the quantity of concrete required for structures and reduce or even perhaps eliminate the need for re-enforcing steel, resulting in cheaper, lighter, stronger structures, far more flexible designs and far lower Greenhouse Gas footprints,” Eden’s executive chairman, Greg Solomon said.

    “10,000 tonnes p.a of CNT would be sufficient nanotubes for 17 million tonnes of concrete, or nearly 70 per cent of the annual Australian concrete supply, so that gives you an idea of its future potential.”

    He adds that current competitive concrete additives, such as high performance fibre reinforced concrete, fly-ash and blast furnace slag, increase the flexural strength of concrete but require significantly greater quantities of additives and finer crushed aggregates. They generally also do not increase compressive strength – a factor necessary for abrasion resistance.

    Eden has worked in US laboratories in the last three years to bring its nanotube production capability up to a commercial scale, and to develop applications for the CNT, including as an additive into concrete and plastics. It is now taking steps towards potential commercialisation of its CNT by bringing an ‘off the shelf’ concrete product to the market via its US subsidiary, Hythane Company.

    “Our forward strategy is now to test our CNT-enriched concrete over the next 12-24 months in both the US and Australia, and prove up the markets before possibly licensing suitable admixture manufactures to produce Eden’s admixture made with Eden’s CNT,” said Solomon.

    “Eden’s CNT enriched admixtures will be sold to concrete manufactures or selected joint venture partners as the case may be and added into the concrete during production in the same manner that other admixtures are presently introduced to produce stronger concrete.”

    However CNT concrete, while promising, still need to complete tests and satisfy the required standards. The shelf life of Eden’s admixture must also be extended from three months to six to 12 months.

    “For most applications, long-term testing of the CNT-enriched concrete against international standards will be necessary and this will be part of our trial work over the next year or so,” Solomon said.

    “Whilst the current shelf life is not considered to be a project stopping issue, it will require far tighter management of the distribution chain but we are confident that a suitable solution will be found.”

    Another issue related to the product is occupational health and safety. Similar to asbestos fibres, CNT are many times longer than they are wide. This has resulted in concerns that CNT may cause lung and respiratory problems.

    In 2012, Safe Work Australia and the CSIRO recommended that CNT be kept in solution and embedded in a suitable matrix. Additionally, a product containing CNT must carry warning if it contains more than 10 per cent of the nanotube particles. However Eden’s proposed admixture, in which the CNT are mixed in a liquid surfactant, is expected to have a concentration of less than one per cent.

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