Construction World September 2016

ALTERNATIVE POWER SOLUTIONS

“We are currently testing an even higher cement replacement formu- lation and hope to achieve the desired strength test results soon,” Khobab Wind Farm has announced the completion of its first foundation pour on 30 June 2016. The foundations are designed using an 89% replacement of cement, one of the world’s lowest carbon wind farm foundation footprints, making use of the same formulation that its sister farm, Loeriesfontein Wind Farm, successfully used in the completion of its foundations. > KHOBABWIND FARM strives for INDUSTRY FIRST

cement per cubic metre. But now scientists working for Murray & Roberts have developed a technology that meets the 30 MPa standard using just 25 kg of cement or even less. Not only does it meet the standard, it far exceeds it. To date strengths of up to 52 MPa have been achieved on other sites using Murray & Roberts’ patented ARC (Advanced Recrys- tallisation) technology and 0 kg of Portland cement per cubic metre. The wind farm capability Khobab Wind Farm will comprise 61 wind turbines each with an output of 140 MW and will generate approximately 563 500 MWh/year of clean, renewable energy to the national grid. The wind farm will avoid approximately 550 000 tonnes of carbon emis- sions each year when compared to traditional fossil fuel power plants and generate enough to power around 120 000 average South African households. The site, which spans a total of 3 200 hectares, was chosen for its excellent wind resource, favourable construction conditions and straightforward electrical connection into Eskom’s Helios substation. The wind turbines will be supplied by world-leading manufacturer Siemens Wind Power, with the blades, hubs and nacelles that compose them arriving from overseas at a nearby port and being transported by road to Loeriesfontein. The majority of the 99 m turbine towers are to be manufactured by GRI, in Atlantis, in the Western Cape. Civil and electrical works are to be completed by a consortium comprised of Murray and Roberts Construction and Consol- idated Power Projects. The Khobab Wind Farm is part of the South African Government’s Round 3 Renewable Energy Independent Power Producer Procure- ment Programme (REIPPP) is expected to be operational by December 2017.

energy intensive process; so by substituting the cement with a by-product the carbon footprint has been considerably lowered,” continued Foster. A 28 day compressive strength test was completed when the formulation was originally tested; it indicated that the 89% replacement ratio achieved an impressive strength of 55 MPa (megapascals), and an expected ultimate strength of 100 MPa, within a 56 day period. “The strength of concrete is measured in megapascals; theoretically a cubic metre of concrete that is rated 30 MPa, is able to with- stand the weight of six bull elephants, whereas these foundations are able to withstand the approximate mass of 20 bull elephants standing on a square centimetre of concrete – a phenomenal feat,” demonstrates Cyril Attwell, Murray & Roberts Construction, group concrete & research manager. A carbon footprint is defined as the total amount of greenhouse gases produced to directly and indirectly support human activ- ities, expressed in equivalent tons of carbon dioxide (CO 2 ). “The achieved reduction in our carbon footprint is phenomenal, especially considering that a standard 30 MPa concrete as supplied by the ready-mix industry equates to a carbon footprint of approximately 300 kgs to 350 kgs of CO 2 per cubic metre,” added Foster. Traditionally, 30 MPa concrete requires between 300 kg and 350 kg of ordinary

explained Kevin Foster, project manager for Khobab Wind Farm. Situated in the Hantam Municipality, 60 km north of Loeriesfontein in the Northern Cape, Khobab Wind Farm is currently employing over 100 local workers on site. All 61 foundations are due for comple- tion by mid December 2016. Khobab Wind Farm is utilising extremely low quantities of Portland cement in the concrete formulation of its wind turbine foundations. “This revolutionary formula has been tested in the adjacent wind farm and we are confident to continue to use it in our foun- dations. The insights gained have allowed us to continue to test lower levels of Portland cement,” says Foster. Environmentally friendly bases The bases use a unique design comprising 35 kg of high grade Portland cement per cubic metre, almost 90% less than a standard concrete mix. This composition means that the wind farm’s carbon footprint is reduced to approximately 90,7 kg of carbon dioxide per cubic metre. Ground Granulated Corex Slag (GGCS), a by-product from the iron industry, is used to replace 89% of the cement. “Cement manufacturing is typically a high

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Khobab Wind Farm is owned by a consortium dedicated to providing clean, renewable energy to the people of South Africa: • Lekela Power: Lekela Power is a pan-African renewable energy platform, which has in excess of 1 300 MW of wind and solar power projects in its portfolio. It is a 60:40 joint venture between Actis, the global pan- emerging market private equity firm, and Mainstream Renewable Power, the global wind and solar company. • Khobab Community Trust: Established by the project company with the objective of carrying out public benefit activities to benefit the local community in the areas of enterprise development, education and health. • Thebe Investment Corporation; one of South Africa’s most established broad based BEE Investment management companies and leading investor in the Energy & Resources sector (advised by Bridge Capital). • The IDEAS Managed Fund, is managed by Old Mutual Alternative Investments, a subsidiary of Old Mutual Investment Group one of Africa’s largest independent investment managers. • Futuregrowth Asset Management, a pathfinder in fixed interest and developmental investing.

CONSTRUCTION WORLD SEPTEMBER 2016

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