In September last year, the Gouda Wind Farm, owned in partnership by the South African company, Aveng, and the Spanish renewable energy company, Acciona Energia, began operations with a generating capability of 423 gigawatt hours of electricity through which 200 000 homes will be powered per annum. It is estimated that the clean energy generated by this wind farm will prevent the emission of 406 million metric tons of carbon dioxide per year.

Chemicals in construction

Speciality chemicals company Sika AG, with a head office in South Africa, has been particularly proud of its involvement in the build as a number of company’s products were used in large quantities for the construction of the towers. These included Sikadur-31 CF (one ton per tower), Sealing Backing Cord (22km) and SikaGrout-295 ZA (30 tons per tower). Due to the extreme height of the towers, each tower is comprised of three precast concrete segments joined on site, one on top of the other. In turn, each segment comprises four sections that were sealed and grouted together.

Horizontal joints on the tower segments were sealed with Sika EVA Backing Strip. This semi-rigid, closed cell cross-linked construction foam is designed as a tough, flexible and resilient back-up support material for surface seals in load bearing joints. It can also be used as a bedding seal under precast concrete panels and to prevent loss of grout when joining precast concrete components.

Once joined together, the vertical and horizontal joints of the precast segments were sealed with Sikadur-31 CF and Sikadur-31 DW. Both products are moisture tolerant, thixotropic, structural two-part adhesives and repair mortars based on a combination of epoxy resins and special fillers. Sealing Backing Cord was placed into the expansion joints to regulate the depth of seal and to provide a solid backing onto which the sealants were placed.

Weathered concrete areas were repaired with Sika MonoTop-620, a cementitious, polymer modified, one-component pore sealer and leveling mortar containing silica fume. With an adjustable consistency, it can be applied by the wet spray method and provides excellent adhesion with good resistance to water and chloride penetration.

Grouting of all vertical cavities using SikaGrout-295 ZA, was completed by Derman Construction who used local labour trained by Jacques Reinecke and Anthony Webster, Sika Technical Sales Consultant. SikaGrout-295 ZA is a one-component, ultra-high strength, cement based grout, specifically designed for use in the renewable energy field, under metal bases, between concrete segments and to fill cracks, gaps and large voids. Due to its good flow properties this is a pumpable grout that provides rapid strength development.

To ensure that SikaGrout-295 ZA could reach the horizontal joints on the 100m high towers, a pumping trial became necessary. The trial necessitated sending the South African manufactured grout to Acciona Spain where it was successfully pumped to a height of 120m on an actual tower. SikaGrout-295 ZA not only passed the pumping trial, but was also awarded a fatigue test certificate for durability – the ultimate test on a product. The results of these tests now validate SikaGrout-295 ZA for worldwide use, a noteworthy achievement.

Award winner

As a result of Sika SA’s massive contribution towards this project, the company won the coveted Fulton Award for Innovation in Concrete.