Construction World December 2023

COVER STORY

Concrete’s durability plays a central role in reducing the structure’s carbon footprint.

AFRISAM PAVES THE WAY TO GREENER CONSTRUCTION

With every tonne of ordinary Portland cement produced, the environment must deal with around a tonne of carbon dioxide emitted by the manufacturing process; with its commitment to more sustainable construction, AfriSam is offering contractors opportunities to move in a greener direction. Amit Dawneerangen, AfriSam Executive Construction Materials: Sales & Product Technical.

A mong the sustainability efforts are initiatives to use less ordinary Portland cement, which is high in energy intensive clinker, as well as to improve on water usage, waste management, material sourcing and the final durability of construction materials. According to Amit Dawneerangen, Executive Construction Materials: Sales and Product Technical, there has been a concerted drive in recent years to reduce the proportion of Portland cement in concrete – by replacing it with supplementary cementitious materials. This is part of global efforts among many players in the industry to reduce the carbon footprint associated with cement, concrete and the buildings and structures they create. “The two common cementitious supplements in South Africa are pulverised fly ash from our coal-fired power stations, and ground granulated blast furnace slag from the steel making process,” says Dawneerangen. Using slag has a further value in environments where chlorides can attack concrete and even start oxidizing the reinforcing steel – a common challenge in coastal areas. Slag has the ability to bind chloride, enhancing the long term durability of concrete. Being a very fine material, fly ash also offers additional

benefits, such as helping to create a dense and less permeable concrete. The spherical shape of its particles also gives concrete better workability and aids with reducing the water requirement. He explains that geo-polymers are also attracting attention as a potential cement alternative. While slag and fly ash need cement to activate them, there is research underway based on the polymer’s ability to fulfil this activation function. “Over the next few years, the use of polymers is likely to grow as these mainly inorganic materials find their way into specifications for projects,” he said. Current construction codes are based on the use of Portland cement, he notes, so it will take some time before the industry feels comfortable using these kinds of alternatives. To reduce the carbon emissions associated with the energy used in conventional cement manufacturing, industry is also looking at Limestone calcined clay cement (LC3). South Africa, however, is not as well endowed with clay as many countries, especially in Europe. Recycling of concrete aggregates is an important theme in making construction more sustainable. In the Green Star ratings from the Green Building Council South Africa, for instance, recognition is given for the use

2 22 nd Best Projects Awards 2023