Precast concrete products important in power generation

19th April 2013

  

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Products from admixture producer Chryso Southern Africa can play a vital role in ensuring speed and uniformity in production of precast concrete elements for the turbines which are expected to become a major source of power generation in South Africa in the future, says Chryso technical services GM Eddie Correia.

Globally, precast concrete is increasingly preferred over steel as a construction material for turbine towers. As the towers increase in height to support higher-powered, longer-bladed turbines, the need for improved structural strength and stiffness to cope with the turbine weights and bending forces also increases.

This calls for tower segments with larger cross-sectional diameters, which can 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 facilitates job creation for the sometimes isolated communities where the turbines are situated.

The Chryso Fluid Premia range of superplasticers is an important part in the concrete mix used for the manufacture of turbine tower precast elements. The molecules in the Fluid Premia range are highly effective water reducers and offer workability retention between 30 and 45 minutes while achieving high early strengths. This allows fast erection and helps the towers withstand demanding fatigue loads.

“The Chryso Fluid Premia range ensures consistency in the manufacturing of reinforced concrete components. It aids in reducing the sensitivity of concrete to variations in water content due to changes in aggregate moisture or production batch tolerances,” Correia explains.

The average concrete wind turbine tower comprises 18 precast segments; each with a height of 1.8 m and a diameter between 600 mm and 2 m.

In the production of precast elements for wind turbines, Chryso demoulding oils facilitate easy stripping of moulds, thereby reducing labour costs and preserving the mould while maintaining the quality of the precast elements.

“Most importantly, the demoulding oils play a great 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, Chryso Southern Africa group member a.b.e. Construction Chemicals can supply an extensive range of adhesives that cater for specific strengths. a.b.e. also produces epoxy systems for the moulds used to manufacture the blades.

Wind turbines must be able to perform in harsh environments and that is why durability is a vital requirement for the concrete mixes.

“Plastic shrinkage cracking and settlement cracking can penetrate the full depth of a slab and/or precast unit, resulting in the need for expensive remedial measures and even greater cost should the slab and/or precast element have to be replaced. Chryso fibres form a three- dimensional bond with the concrete matrix that holds the matrix together. This prevents early microcracks from turning into serious, slab threatening cracks,” Correia adds.

a.b.e. concrete repair and general construction product manager Ivor Boddington says another key durability challenge regarding wind towers is ensuring 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 remedies for this; the Silocoat and Duracoat ranges. Silocoat is a cementitious coating that is equivalent to 180 mm of concrete cover. It protects the tower against chloride ingress. The Duracoat range is also a protective coating that provides a barrier to chloride and carbon dioxide ingress – the main contributors to corrosion – while also offering an attractive finish to the concrete,” he explains.

Edited by Tracy Hancock
Creamer Media Contributing Editor

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