Concrete performance and durability underpin the value to society of water-retaining structures such as water treatment plants and storage reservoirs – and admixtures make all the difference.

Challenges, including cracking and permeability, can undermine the strength and longevity of these structures, according to Michelle Fick of CHRYSO Southern Africa’s Concrete Aesthetics Business Unit.

“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.”

She 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, this admixture helps to 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, like pore blockers such as CHRYSO® Fuge B that further enhance concrete’s resilience against chemical attack and reduce permeability, she adds.

“Another waterproofing agent is crystalline admixture such as CHRYSO® CWA 10,” she says. “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 like reservoirs, adds Patrick Flannigan, Technical Manager of the Concrete Business Unit at CHRYSO Southern Africa.

“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.”

Another aspect of water-retaining structures to consider is their weight, so the ground underneath them must be well drained if they are to remain stable. “To ensure water does not collect, a pervious base layer usually needs to be installed,” he says. “This is constructed from no-fines concrete, which allows water to flow away without eroding the sub-base material.”

He notes that an admixture like CHRYSO® Easy Drain is ideal for no-fines concrete, as it coats the coarse aggregate to ensure a stronger bond between these particles and the cement-water mix.