Admixtures ensure concrete quality in fast-track projects

Concrete mix treated with crystalline waterproofing admixture on site for the Vlakfontein Reservoir.
Concrete mix treated with crystalline waterproofing admixture on site for the Vlakfontein Reservoir.

Growing pressure on government to roll-out infrastructure projects and create jobs is likely to add to the fast-track culture in the construction sector. According to Michelle Fick of construction chemical specialist CHRYSO Southern Africa, this trend will increasingly rely on a wide range of purpose-designed admixtures to facilitate quality outcomes – even under tight deadlines.

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

Fick emphasises the importance of durable concrete in giving structures their expected lifespan, thereby delivering value-for-money for end-clients. Large readymix pours are central to many of these projects, and enhance the pace of 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 assist with the healing of possible leaking cracks and construction joints, the cementitious crystalline concrete waterproofing admixture CHRYSO® CWA 10 was added to the mix. The dolomitic aggregates that were 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 offers its accelerator range to speed up the curing process and reduce 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 explains 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, as well as CHRYSO Optima 100 super-plasticiser. The result was a mix with a 180 mm slump which could be pumped 200 m 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 a minimum of effort and manpower.

“Key to the application of our admixture solutions is our research and development laboratory in Johannesburg,” says Fick. “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.”

She 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.

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