Situated between Vereeniging and Sasolburg is the large coal powered Lethabo Power Station which commenced operations in 1990. By 2011, major concrete repairs had become necessary for which Eskom conducted an initial project proposal. DBI Consulting and C3 Consulting specified Sika’s high performance concrete repair and protection products for the refurbishment of trench walls, floors and pump bases at the power station. The contract was awarded to concrete specialists, Botes & Kennedy Manyano (Bkm), with BKV Holdings as sub-contractor.

With the removal of damaged areas of concrete commencing in February 2012, the estimated completion date for the project was set for May 2012. However, when contractors discovered that approximately double the amount of concrete required removal due to its appalling condition, the completion date for the project was postponed to August 2012.

SikaTop-Armatec 110 EpoCem was applied onto the walls and floors of the trenches as a bonding and anti-corrosion agent. This cement-based, epoxy-modified, three component product provides excellent adhesion to steel and concrete as well as an excellent bonding coat for subsequent application of  Sika’s repair mortars. It acts as an effective barrier against penetration of water and chlorides and provides a high degree of mechanical strength.

This was followed with an application of Sikacrete-214, a one-component, free-flowing, high strength, cement-based concrete with a maximum aggregate size of 9mm. It is ideal for casting sections or members where the volumes required are too large for conventional grouts, and too small and inaccessible for normal concreting procedures. Easy to mix and apply, this economical repair concrete provides rapid strength development, is shrinkage compensated and vapour permeable.

Sika MonoTop-610, a cementitious, polymer modified, one-component primer with corrosion inhibitors, was used for protection on steel reinforcements in the concrete. This user-friendly primer meets ZTV-SIB requirements for corrosion protection, and provides excellent adhesion to steel.

Where thick concrete repairs on overhead and vertical structures were required, Sika MonoTop-610 was used as a bonding slurry for Sika MonoTop-615 HB, a high build, repair and reprofiling mortar, containing silica fume. With its excellent workability characteristics and thixotropic behaviour, Sika MonoTop-615 HB was an ideal mortar for this application. Requiring only water for mixing, both Sika MonoTop products provide adjustable consistency, good mechanical strength with good resistance to water and chloride penetration, and are sprayable by the wet spray method.

Unfortunately the flushing of chemical containment tanks exposed the newly repaired concrete to constant attack from high concentrations of hydrochloric acid, sulphuric acid, ammonia and caustic acid.

To begin the protection process of these areas, a coating of Sikagard-69, a plural component system composed of a proprietary polymeric binder, providing excellent performance in highly corrosive, chemical and abrasive environments. It is designed for industrial use at elevated temperatures and will maintain its physical properties under continued exposure at high constant temperature, both in exposed and immersion conditions. Its fast-curing, trowel grade consistency allows for back-to-service within 24 hours. This product also bonds well to rubber and metals.

To complete the chemical protection of the concrete, Sikalastic-844 XT Plus, a two-part, flexible, modified polyurea spray-applied membrane that is extremely fast-curing, was applied to the pump bases as well as the drainage trenches. It is designed for use on concrete or steel that is exposed to high acidic or alkaline chemical concentrations. For machine application only, Sikalastic-844 XT Plus, which is 100% solids with zero VOC, is suitable for many other applications including primary and secondary containment, waste water and treatment plants, petrochemical storage and food processing plants. This superlative product, with its fast reactivity and cure time, provides monolithic, seamless protection, with high resistance to acid or base chemicals as well as to microbial waste.

Lethabo Power Station was originally built on 11 000 concrete piles, which were sunk 25m deep to alleviate the heaving clay problem after thousands of blue gum trees were removed during site- clearing. At the time, it was the largest piling contract ever awarded to a South African contractor. This design however, posed unique challenges to contractors on this project who had to tunnel underneath the power station and work in confined spaces in order to repair the regent trench floors and walls. Severe chemical exposure was another hazard for workers.

Despite all the challenges encountered, contractors were able to complete the project timeously, due mainly to the ease of mixing, ease of application and exceptional workability characteristics of Sika’s innovative products. With its infrastructure having been repaired, strengthened and protected by Sika, Eskom’s Lethabo Power Station can continue generating electricity for many years to come.