SUSTAINABLE INFRASTRUCTURE
Restoring an iconic reservoir Constructed in 1971, Durban Heights Reservoir 3 is one of the largest concrete structures of its kind in Southern Africa. With a storage capacity of 350 Mℓ, it supplies potable water to over 500 000 people in the surrounding area. This makes optimising its design life a key priority. Durban Heights Reservoir 3 was recently restored following an approximately 14-month refurbishment programme
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haped like a circus tent, the reservoir’s design is unique, with the roof made up of 120 steel post-stressed cables that radiate from the centre roof to the outer base support. In 2003, a full diagnostic survey of the concrete roof panels was done. A variety of issues were identified, but of interest was the existence of a microclimate within the reservoir. This microclimate, with wet-dry cycles, creates a favorable environment for contaminants to be absorbed into the reinforced concrete panels, causing corrosion of the reinforcing. Umgeni Water appointed Royal HaskoningDHV as the project engineer for the rehabilitation programme, with the works carried out by Smart Civils Construction. Based on the original diagnostic survey, rehabilitation proposals and the subsequent product trials, Sika’s solutions and products were deemed optimal for the project. To gain access to the underside of the reservoir’s roof, Smart Civils erected some 550 tonnes of scaffolding
An internal view of the reservoir
Repair process To gain access to the underside of the reservoir’s roof, Smart Civils erected some 550 tonnes of scaffolding, in a bird-cage configuration, from the floor to just under the soffit. The scaffolding provided access to a quarter of the roof at any given time, before being dismantled and re-erected as the works progressed. A decision was made to use SikaTop Armatec-110 EpoCem as the primary rebar protective coating for the concrete repair to protect the reinforcing of steel and inhibit corrosion. Due to the difficult conditions, Sika MonoTop-610 was used as a primer to the concrete substrate. The decision to use Sika MonoTop-412 NFG as a repair mortar was due to its unique properties as an excellent wet spray mortar. This application method improved the compaction of repair mortar and increased the application rate of the product. Sika MonoTop-412 NFG also differentiates itself
as a one-component, polymer-modified, fibre-reinforced, low-shrinkage, structural repair mortar with Sika’s world-renowned Sika FerroGard-903 Plus corrosion inhibitor. Sika FerroGard-903 Plus delays the start of corrosion and reduces the corrosion rate when it occurs. It also increases the service life of a reinforced concrete structure Sika’s carbon fibre fabric, impregnated with structural epoxy resin SikaWrap-230C, was used due to the age of the structure and minimal concrete cover. The perfect product for refilling the ducts was Sika Injection-307 – a low-viscosity, elastic, polyacrylic injection resin that can be adjusted to set at a predetermined time, forming a passivating, permanently elastic matrix.
Panel coatings Two protective coating systems were applied to the panels, namely Sika FerroGard-903 Plus and Sikagard-705 L, as the final protective coating. The latter is a singlecomponent, low-viscosity, solvent-free and reactive impregnation product for concrete and cementitious substrates based on silane. Its unique properties allow for moisture vapour to escape from the concrete panels, ensuring that they stay dry – thus preventing further ingress of contaminants. The end result of all these interventions is a fully functional reservoir with a new lease on life.
IMIESA November/December 2020
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