Admixtures help manage effects of extreme weather

15th February 2024

 Admixtures help manage effects of extreme weather

CHRYSO plasticisers used for concrete

Extreme weather conditions such as very hot or cold ambient temperatures can affect both strength and open time, when working with concrete.

CHRYSO Southern Africa technical manager Patrick Flannigan 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, he explains.

The Chryso Tard range of plasticisers are designed to ensure enough open time, helping users deal with very hot weather. “This retarder slows down the hydration of cement by momentarily blocking the surface of the cement particles and delaying the time of initial setting,” says Flannigan.

For cold weather, the CHRYSO XEL range of chloride and non-chloride accelerators 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 in the Lesotho Highlands.

“Another form of extreme weather leading to challenges with concrete is heavy rainfall that causes flooding,” notes Flannigan. “Protection of concrete in rainy conditions is of the utmost importance, as this will eliminate surface blemishes on exposed concrete areas.”

He explains that concrete that is in contact with standing or flowing water needs to be protected, especially with regard to its finish. CHRYSO Aquabeton allows concrete to be cast in standing or flowing water, making it an ideal solution for concrete that needs to be placed underwater.

Flannigan points out that the company develops admixtures specially for certain types of cement and construction material, which allows for a wider range of material to be sourced close to site, even if it is high in clay content, for example. This helps reduce transport distances, helping to minimise vehicle carbon emissions.