Civil Engineering January-February 2022 | Vol 30 No 1

Civil Engineering January/February 2022 35 loading of the turbines and to withstand the wind forces. This strength allowed Nordex engineers to opt for lighter concrete sections which added a further eco-friendly dimen- sion to the project through lower material usage and transport costs. Moreover, the tower sections were man- ufactured with self-compacting concrete (SCC). Without it, the project would have been much more complex, involving ex- ternal vibration and more expensive moulds. SCC was supplied by Megamix, which has a batching plant close to Concrete Units. The SCC mix was one of the critical components of the whole manufacturing process. Rainy weather can affect the mix because the amount of water used is critical. Even a slight water overdose can cause segregation and a loss of strength which is why the slump flow of every batch was tested at Concrete Units before being pumped into the moulds. In most instances, the higher one goes, the better the wind, and for heights above 80 m, concrete towers tend to be less expensive than steel towers, thus positively impacting on the cost of the electricity gen- erated. To date, most wind turbines in South Africa have been mounted on steel towers, the majority of which are imported and therefore carry a comparatively low local labour and job creation component. By contrast, concrete wind towers come with high local content inputs and by default carry a much higher job generating capacity. For example, over 95 % of the raw materials for Roggeveld’s concrete towers including the reinforcing steel, was sourced locally. All the IPPs have submitted tenders for Bid Round 5 and the notices to proceed are expected to be published in March 2022. With greater heights and different designs, Round 5 towers will be able to generate up to 5.6 MW each. When completed, Round 5 will generate up to 1 600 MW from onshore wind energy and 1 000 MW from solar photovoltaic power plants. “Against the backdrop of global steel price increases over the last two years, it seems a safe bet that during the coming years precast concrete will play a major role in wind-tower construction,” con- cludes Coetzee.  Text by David Beer on behalf of the Concrete Manufacturers Association (CMA) david.bigsky@gmail.com A tower prior to the installation of the wind blades