Water-retaining structures such as water treatment plants and storage reservoirs depend on the strength and durability of concrete and admixtures can help enhance the performance of concrete, making it last longer.

Challenges in the construction of water infrastructure include cracking and permeability, which can undermine the strength and longevity of the structures, says CHRYSO Southern Africa concrete aesthetics business unit representative Michelle Fick.

“Cracking of concrete, for instance, often calls for urgent and costly maintenance of water-related infrastructure,” says Fick. “In addition to leakage, cracks can undermine the strength of a structure due to corrosion of the steel reinforcing.”

Fick highlights the importance of reducing shrinkage in concrete to avoid cracking, using admixtures such as CHRYSO Serenis. By reducing the volume changes that occur during the curing process, the admixture helps prevent cracking. It works by decreasing capillary tension, protecting concrete against moisture transmission, chemical attack and corrosion of reinforcing steel.

There are also waterproofing agents such as CHRYSO Fuge B pore blockers that further improve concrete’s resilience against chemical attack and reduce permeability, she adds.

“Another waterproofing agent is crystalline admixture such as CHRYSO CWA 10,” Fick notes. “This reacts with moisture to form crystals deep within the pores and capillary tract of the concrete structure.”

Admixtures such as plasticisers and super plasticisers are critical in ensuring workability of concrete, which is especially vital to heavily reinforced structures such as reservoirs, adds CHRYSO Southern Africa concrete business unit technical manager Patrick Flannigan.

“Water in the concrete mixture must be kept to a minimum to ensure strength and density, which could hamper its workability,” says Flannigan. “However, admixtures allow the concrete to continue to flow into the cavities between the steel reinforcing, which is often extensive to ensure strength in these large water-related structures. Secondary reinforcing can be achieved through the application of macro-fibres and micro-fibres, which can reduce the amount of steel while also further reducing the risk of cracking.”

Weight is also an important consideration in the construction of water-retaining structures, and the ground underneath must be well drained to ensure stability. “To ensure water does not collect, a pervious base layer usually needs to be installed,” explains Flannigan. “This is constructed from no-fines concrete, which allows water to flow away without eroding the sub-base material.”

Flannigan asserts that an admixture like CHRYSO Easy Drain is particularly suitable for no-fines concrete as it coats the coarse aggregate to ensure a stronger bond between these particles and the cement-water mix.