Civil Engineering January-February 2022 | Vol 30 No 1

34 January/February 2022 Civil Engineering three blades, each weighing 12 tonnes. Therefore, each tower bears a total weight of 176 tonnes.” The precast sections were assembled at the tower sites. Individual segments were lifted off truck beds and then lowered vertically into position by a giant mobile crane. They were joined to matching segments using bowtie con- nections. This was achieved by inserting reinforcing into hollow slots formed by the segments’ two opposing vertical chan- nels. A proprietary high-strength grout was then pumped into the joint to create a permanent seal. “The 20 m sections were attached to each other in a horizontal plane using starter bar and ducting joints which were sealed with grout. The flawless execution of this process required extremely ac- curate casting and very tight tolerances,” says Coetzee. The Roggeveld towers were designed to bend and during strong winds can move up to 700 mm at their apex. This flexibility was facilitated by the use of steel reinforcing inside the tower walls. This lateral movement was counterbal- anced by the installation of six 90 mm steel cables, which attach the inner wall of T5 sections to the concrete base and provide additional strength to the overall structure. Once installed, they were post- tensioned by Nordex. The precast segments, 799 in all, were cast at Concrete Units’ factory using five moulds which were imported from Italy by Nordex. 2 m long, the mould sections were attached to each other using precision-based laser technology. Moreover, to ensure the accurate layout of the steel reinforcing, Concrete Units used special reinforcing jigs. A maximum of five segments were cast daily. Various types of inserts and sockets were cast into specific positions to accommodate the mechanical (ladders, lifts and landings) and the electrical equipment (cable trays, etc.) required inside the towers. Spaces for doors were cast into every fourth T1 segment. Mould stripping took place either late into the night shift or first thing every morning by which time the segments had reached a minimum compressive strength of 25 MPa. Segments T1 and T2 sections were 5.5 m and 5 m respectively and their transportation on extendable trailers required police escorts. Because of their abnormal loading, the trucks weren’t able to use the Du Toits Kloof tunnel on the N1. Instead, they were routed via Tulbach, over a distance of 350 km and the journey took up to two days. The smaller segments were transported using normal escorts. EXCELLENCE IN CONCRETE In terms of concrete manufacture, the Roggeveld Wind Farm project is cutting edge and is one of the country’s largest wind farms to date. The tower segments were designed ac- cording to European as opposed to SANS codes. This allowed the team to design up to 115 MPa cube strength rather than the 60 MPa which forms part of the SANS structural concrete code. The Roggeveld tower segments were manufactured to 75 MPa, the strength required to bear the A giant mobile crane lifted the tower segments into position Wind blade installation