Construction World April 2022

CEMENT & CONCRETE TECHNOLOGY

ADMIXTURES PROMOTE LOCAL SOURCING AND SUSTAINABILITY

Admixtures have become an integral aspect of concrete production in the modern economy, especially as the construction sector looks for ways to chart a low carbon future while supporting local supply chains in projects.

Patrick Flannigan, Technical Manager in the concrete business unit at CHRYSO Southern Africa.

A ccording to Patrick Flannigan, technical manager in the concrete business unit at CHRYSO Southern Africa, contractors at one stage used admixtures mainly to reduce the amount of water in a concrete mix. “Much has changed, with a new generation of admixtures now playing a vital role in cement chemistry and aggregate selection,” says Flannigan. “As the world becomes more careful in its use of natural resources like river sand, admixtures are coming into their own for companies concerned with sustainability.” To reduce the environmental footprint of concrete, admixtures allow a wider range of material resources to be used in the mix, including sands with high clay content, as well as challenging aggregates. CHRYSO® Quad, for instance, gives contractors more scope to source their aggregates locally, which supports local suppliers while reducing the cost and carbon dioxide impact of transporting aggregate. “Our CHRYSO Clear ® Technology targets the challenge of having an excess of fines – and the problem of swelling clay – by helping to disperse binders and reduce viscosity, thereby improving placeability and finishability,” he says. “Where there is a lack of fines or unfavourable shape factors, our CHRYSO Graft® Technology improves concrete cohesiveness and simplifies finishing work.” The increased use of extenders has also been an important theme in the evolution of lower carbon concrete, allowing less cement to be used

while still retaining the quality and the results. He notes that South Africa, with its large resources of fly ash from power stations and slag from steelmaking plants, has been a leader in the innovative use of extenders. “This process was given a boost in the lead up to the 2010 Soccer World Cup in South Africa, when our infrastructure growth led to a shortage of cement,” he says. “CHRYSO worked closely with customers to ensure that concrete performance was maintained even as extenders were increasingly used.” One of the key contributions of admixtures is to improve early and late strengths, and enhance the overall durability of the concrete. While accelerators increase early setting, retarders can extend the open time and setting duration. The use of admixtures has been very important to high specification infrastructure projects in remote rural areas, adds Flannigan. “We have been very involved in wind farm construction in the Western, Eastern and Northern Cape, for example,” he says. “The bases and towers of wind turbines must be built to exacting standards, but they are located far from most of the traditional sources of construction materials.” He highlights that CHRYSO’s admixtures have allowed projects to use locally sourced material without compromising on the contractor’s requirements for concrete performance. 

Left: To reduce the environmental footprint of concrete, admixtures allow a wider range of material resources to be used in the concrete mix. Right: CHRYSO Clear ® Technology targets the challenge of having an excess of fines and the problem of swelling clay.

24 CONSTRUCTION WORLD APRIL 2022