Citi-Con’s waterproofing expertise is being successfully deployed to build watertight reservoirs.

This is an extremely specialised and complex aspect of new reservoir construction that Citi-Con has perfected over many years. For this reason, the company is the preferred provider of these specialist services for many principal contractors tasked with constructing these structures. A case in point is the recent successful waterproofing of a new 5ML reservoir in Langebaan, Western Cape, that was built by Rawucon. Citi-Con executed this aspect of the work scope with high precision.

Leaking reservoirs compromise water security. Even a small amount of water lost from a reservoir can be costly especially in a water-scarce country such as South Africa. This is also a significant risk during times of drought which recently affected many areas of the Western Cape, again emphasising the need to use scarce water resources efficiently. The country ranks as one of the 30 driest countries in the world with an average rainfall of about 40% less than the annual world average rainfall. Moreover, leaking reservoirs are expensive and time-consuming to correct. Bear in mind that many South African municipalities are cash strapped and, therefore, have to use limited resources efficiently. Downtime while reservoirs are being repaired can also seriously inconvenience large areas at a time.

Meanwhile, in the same way that these structures need to retain drinking water, they also need to keep contaminants out to ensure a reliable and clean supply of water.

The challenge is that most concrete eventually cracks due to curing, shrinkage, settling and seismic activity, among other factors. This can result in the leakage and contamination of concrete water-retaining structures.

“The best way to reduce the likelihood of these problems occurring in the future is to select the best waterproofing system for concrete reservoirs. Research and plan ahead to avoid future problems or simply deal with an expert right from the outset. There is no reason that a well-designed and built reservoir that is also appropriately maintained

should not continue functioning as intended for at least 100 years,” Andre Vermeulen, Managing Director of Citi-Con, says.

39m in diameter and 5,5m deep, the new Oliphantskop reservoir was constructed using a conventional reinforced-concrete design. It operates alongside a 2ML reservoir on site with matching top and bottom levels to significantly augment water-storage capacity in the town. The pipework also makes provision for a second 5ML reservoir for future needs. Bear in mind the rate at which Langebaan is expanding. It is currently one of the largest growing parent towns in the country.

The state-of-the-art waterproofing system consists of among the best products on the market, of which Citi-Con is an approved applicator. This enables the company to guarantee its workmanship for the maximum term available. Citi-Con is a proud approved applicator of Sika South Africa; Mapei; a.b.e Saint Gobain; StonCor Africa; Pro-Struct; and Urochem Trading’s quality waterproofing products.

Based on plasticised polyvinylchloride and manufactured in specific profiles, quality waterstops were used to seal joints. These particular waterstops were selected because they provide long durability when installed by a skilled and experienced contractor.

As Vermeulen notes, joints between pours are some of the most vulnerable areas of reservoirs. If these products have not been installed correctly, water-retaining structures will leak. A competent waterproofing contractor will avoid common mistakes such as installing waterstops too close to steel reinforcement; misalignment; and roll ends overlapping but not welded or spliced together. Issues also arise when waterstops have been installed adjacent to poorly consolidated concrete and when it extends on flanges that have not been removed before the second concrete pour.

Curing to form a durable rubber like seal, a two-component sealing compound based on a polysulphide polymer blended with fillers and chemical curing agents was used as a joint sealant. Citi-Con selected a sealant that is resistant to ultra-violet light and ozone making it particularly well suited for sealing drinking water reservoir joints.

He explains that joint design is critical. For water retaining structures and where shear movement is anticipated, a 2:1 width to depth ratio should be maintained. This ratio provides the optimum geometry to allow movement to occur within joints without placing excessive force on their faces. These should be parallel and their width at least four times the maximum anticipated movement. When placing the sealant, Citi-Con made sure that joint openings were central to their maximum compression/expansion cycles.

Surface preparation and priming must also be undertaken correctly. All surfaces need to be clean, sound and dry, as well as free of all laitance before being primed. Citi-Con also pays particular attention to voids and hollows and allows for at least 30 minutes for the solvent to evaporate before applying the sealant. Repriming is undertaken where primer has lost tack after three hours. Furthermore, the primed surface is protected from dust and dirt which can interfere with sealant adhesion.

To complete the process, the company then installed a high quality Hypalon bandage system over the sealed joints to reinforce the waterproofing.

“For this application, we selected a high-performance joint and crack sealing system. It allows variable and high levels of movement in one or more directions, while maintaining a high-quality watertight seal. The product consists of a modified flexible Polyolefin waterproofing tape with advanced adhesion properties,” Vermeulen says.

Various quality waterproofing systems were also used to waterproof the reservoir’s internal wall and floor slab.

This included a high two-component cementitious mortar that seals hairline cracks already present on substrates.

Also approved for use in potable water systems, a flexible slurry based on a special synthetic resin dispersion and a blend of selected cement mixed with carefully graded aggregate was then deployed.

In addition, an additive was used to waterproof the cement mixes, improving bond of subsequent treatments. The various waterproofing layers were also reinforced with alkali-resistant glass fibre mesh and associated textiles.

A high-quality bituminous membrane was applied to the concrete floor slab to complete the process.

Again, Citi-Con followed the recommended techniques for bitumen waterproofing. This included the use of the appropriate tools to ensure an even and consistent coverage. The company also applied the membrane according to the recommended thickness and overlapping requirements to achieve optimal waterproofing results.

“Bitumen is highly valued for its excellent waterproofing capabilities by forming a durable and impermeable barrier. The material’s inherent durability makes it an ideal choice for this and other water-proofing applications. It can withstand extreme weather conditions; temperature variations; and heavy loads, providing long-lasting protection,” Vermeulen concludes.