Products from chemicals solutions company Chryso Southern Africa Group are ideal for the base foundation construction of wind turbines, as well as various other aspects of the country’s proposed extensive wind farm energy projects, says Chryso technical services GM Eddie Correia.
Independent power producers will produce over 600 MW of electricity from wind farms contracted in the first phase of the Renewable Energy Independent Power Producer Procurement Programme, with more wind farms to be erected in the future.
Correia says wind turbines, with their enormous blades, require massive reinforced concrete foundations to keep the towers grounded and secure.
He explains that each concrete foundation has a diameter and height of about 20 m, a portion of which is underground. These massive concrete foundations have high Portland cement contents, which can result in cracking caused by thermal contraction.
“This cracking can be avoided by using supplementary cementitious materials (SCMs), such as fly ash or slag in combination with Portland cement. However, SCMs can impact on the early and late age strength development of concrete. Therefore, water-reducing admixtures, such as the ChrysoFluid Omega range, must be used to reduce water and cementitious materials while boosting concrete mix strengths and maintaining the lowest possible carbon footprint.
“High slump concrete is often required for wind turbine foundations which can lead to segregation and compromised durability. The ChrysoFluid Optima range of products should, therefore, be used to create a cohesive, low viscous, durable concrete mix,” Correia notes.
He says Chryso is exceptionally skilled at matching superplasticisers with cement and aggregate chemistry. Once the soluble alkalis and soluble sulphates within a part- icular cement are assessed, Chryso can choose a suitable product from the range, thus optimising the dosage of superplasticisers for cost purposes. “The most popular product within the extensive Chryso range of super- plasticisers is ChrysoFluid Optima 100, which is not water sensitive and can, therefore, assist in producing robust concrete mix designs that are easy to use.”
The ChrysoFluid Optima range also helps concrete maintain its plastic characteristics for an extended period. This is particularly useful if there are long distances from the batching plant to the foundations, or if the readymix plant is far away from rural construction sites. Chryso retarders can also facilitate the long-haul delivery of the concrete or a slower rate of cure. Both products also allow for concrete to be placed without fear of formation of cold joints and enable concrete to remain plastic long enough to be fully compacted,” Correia adds.
Applying a curing compound from the Chryso Cure range to the foundations and precast products will also reduce the incidence of shrinkage cracks and promote better strength gain characteristics.
a.b.e. concrete repair and general construction product manager Ivor Boddington says that a bed of grout between the tower and its foundation helps in the transfer of loads from top to bottom in a predictable and consistent manner.
“Traditionally, cementitious grouts are used to fill spaces 50 mm and greater and epoxy grouts for spaces smaller than 30 mm. While epoxy grouts can reach high early age strengths and provide a quicker turnaround time, cementitious grouts take longer to reach the required ultimate strength but are less expensive.
“All a.b.e.s’ grouts have a stable volume. Once the grout has filled the space between the tower flange and the foundation, it keeps that space filled without excessive shrinkage or expansion, as this may influence the bearing capacity of the foundation, which, in the case of wind turbines, is usually tied down to the ground with deep embedded anchors and a.b.e.’s dowel or bolt grout assists in bonding the anchor to the foundation and ground,” Boddington adds.
Correia notes that Chryso can also supply products to ensure speed and uniformity in the production of precast concrete elements for wind turbines.
He notes that, globally, precast concrete is increasingly preferred over steel as the construction material for turbine towers. “As the towers increase in height to support higher-powered, longer-bladed turbines, the need for increased structural strength and stiffness to cope with the turbine weights and bending forces is also increasing. This will call for tower segments with larger cross-sectional diameters, which could lead to formidable transportation problems for steel segments. Precast concrete segments, on the other hand, can be produced at a portable concrete batch plant erected on site, which will have the added benefit of job creation for the, sometimes, isolated communities where the turbines are based.
“The ChrysoFluid Premia range of superplasticers is an essential part of the concrete mix used for the manufacture of turbine tower precast elements. The molecules in the Premia range are highly effective water reducers and offer workability retention of between 30 minutes and 45 minutes, while achieving high early strengths. This allows for fast erection and helps the towers to withstand demanding fatigue loads,” explains Correia.
He says the ChrysoFluid Premia range maintains consistency in the manufacturing of reinforced concrete components, as it helps to “reduce the sensitivity of concrete to variations in water content owing to changes in aggregate moisture or production batch tolerances”.
The average concrete wind turbine tower comprises 18 precast segments, each with a height of 1.8 m and a diameter of between 600 mm and 2 m.
Chryso Demoulding Oils facilitate easy stripping of moulds in the production of precast elements for wind turbines. This reduces labour costs and preserves the mould while maintaining the quality of the precast elements. “Most importantly, the Demoulding Oils play a huge role in creating a defect-free surface finish with consistent colour and allow for casting immediately after oiling the moulds, unlike older types of demoulding oils that require a standing period,” Correia adds.
When it comes to bonding the precast elements together, a.b.e. Construction Chemicals can supply an extensive range of adhesives for specific strengths. The company also produces epoxy systems for the moulds used to manufacture the blades.
Boddington says another key durability issue in wind towers is to ensure that reinforcement is covered with sufficient concrete thickness. “With insufficient concrete cover, the reinforcement may corrode, causing spalling and structural failure. a.b.e. has two solutions for this, namely the silocoat and duracoat ranges. The silocoat range is a cementitious coating that is equivalent to 180 mm of concrete cover. It protects wind towers against chloride ingress. The duracoat range is also a protective coating that provides a barrier to chloride and carbon dioxide ingress, which are the main contributors to corrosion, while also offering an attractive finish to the concrete,” he explains.
Correia says Chryso has a presence in 70 countries through 13 subsidiaries and an international network of distributors. “Chryso recently supplied products to two huge wind farm projects in India and France. This resulted in technology transfer with regard to wind farms from Chryso France and Chryso India to Chryso Southern Africa Group.
“Owing to its acquisition of South Africa-based specialised construction products supplier a.b.e. Construction Chemicals, Chryso Southern Africa Group can now offer a full range of solutions from both companies for the construction of wind turbines – from base foundations to blades,” he adds.