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A renewed focus on infrastructure has been welcomed by South African contractors, but the urgency of many projects places significant demands on inputs like readymix.

Michelle Fick, business unit development for concrete aesthetics and key accounts at CHRYSO Southern Africa said, “This is where admixtures play a vital role in ensuring that readymix concrete performs to the highest standards while meeting fast track schedules.” 

Fick noted the importance of durable concrete in giving structures their expected lifespan and delivering value for money for end clients. Large readymix pours are central to many of these projects and speed up construction. 

“For instance, in a recent reservoir project with multiple large pours, CHRYSO was able to contribute to a concrete mix design that ensured low shrinkage while achieving a durable and watertight concrete,” she says. “Our products helped to keep the heat of hydration as low as possible, and to prevent cracks from plastic shrinkage.”

The latter was addressed by using CHRYSO Serenis – a shrinkage inhibitor – in the wall footing, floor slab and roof slab. To help seal possible leaking cracks and construction joints, the cementitious crystalline concrete waterproofing admixture CHRYSO CWA 10 was added to the mix. The dolomitic aggregates used to produce a lower coefficient of thermal expansion also had a low water demand; CHRYSO Omega 178, a high-performance water-reducing super-plasticiser, was therefore used to reduce water content. 

Road building and upgrades rely on a variety of precast concrete components, such as culverts and pipes, where curing time directly affects the pace of production. Here, she says, CHRYSO’s accelerator range speeds up the curing process and reduces the turnaround time of each precast item. There are also superplasticisers to improve the durability and workability of concrete with reduced water and cement.

Fick said these solutions are also important in high-rise buildings where concrete is pumped to great heights, making for rapid progress. For a recently completed skyscraper in Sandton, the readymix included CHRYSO Omega 140AFR, a hybrid plasticiser/super-plasticiser, and CHRYSO Optima 100 super-plasticiser. The result was a mix with a 180 mm slump which could be pumped 200 metres high. 

Curing compounds are another important product range enabling more time-efficient construction, with various bases including wax, resin, acrylic and water for different applications. This ensures effective curing with minimum effort and manpower.

Fick said the company’s research and development laboratory in Johannesburg is crucial to the applying their admixture solutions. “Our resources here include a valuable database of past projects, aggregates and cement types from around the country – allowing us to rapidly develop and apply solutions for contractors and readymix suppliers.” 

Fick notes that this database can provide guidance for a project’s concrete mix, drawing on the experience of previous projects in the same area using the same sources of aggregate and sand. This allows CHRYSO to speed up the identification of the most suitable admixture for that specific application. 

Top Photo: CHRYSO Jet accelerators proved invaluable for Gautrain’s extensive shotcrete tunnel lining