Patrick Flannigan, Technical Manager at CHRYSO Southern Africa
When ambient temperatures become very hot or cold, concrete users can struggle to achieve the required strength and workability – but there are admixtures for those challenges.
Patrick Flannigan, Technical Manager at CHRYSO Southern Africa, explains that high temperatures cause concrete to develop higher initial strength, but reduce the strength development over the long term. Very cold weather creates the opposite effect, causing lower strength gain initially but higher strength gain later.
When temperatures drop below 5°C, the slower hydration process could even cause extended bleeding. At temperatures lower than that, there is a risk that the water in the concrete will freeze. Water expands by 9% when it freezes, so it could even cause cracking if the concrete has not reached sufficient strength.
“To deal with very hot weather, customers use our CHRYSO® Tard range of plasticisers, which ensures enough open time,” he says. “This retarder slows down the hydration of cement by momentarily blocking the surface of the cement particles and delaying the time of initial setting.”
For cold weather, he recommends the CHRYSO® XEL range of chloride and non-chloride accelerators, which help with early strength gain of concrete. To deal with the risk of water freezing in the concrete, CHRYSO® Air helps by adding extra air to the mix. Instead of cracking the concrete, the freezing water will expand into the capillary openings that the air entrainer has created. These low temperatures are not that common in South Africa, but more relevant to higher elevated areas such as the Lesotho Highlands.
“Another form of extreme weather leading to challenges with concrete is heavy rainfall that causes flooding,” he says. “Protection of concrete in rainy conditions is of the utmost importance, as this will eliminate surface blemishes on exposed concrete areas.”
Flannigan explains that concrete that is in contact with standing or flowing water needs to be protected, especially in terms of its finish. “CHRYSO® Aquabeton is the ideal solution for concrete that needs to be placed underwater, and this allows concrete to be cast in standing or flowing water.”
Flannigan points out that CHRYSO’s solutions are driven not only by functionality but by a global commitment to sustainability. The company develops admixtures specially for certain types of cement and construction material. This allows a wider range of material to be sourced close to site, even if it is high in clay content, for example.
“This reduces the distances that material needs to be transported and therefore keeps vehicle carbon emissions to a minimum,” he says.