Weak economic conditions in construction have led contractors to find new ways of surviving, and some strategies could undermine the longevity of roads and buildings, says AfriSam Construction Materials Executive Avi Bhoora.

“On the aggregates side, we find that the call for ‘brown’ material – as opposed to the high-value ‘blue’ material like quartzite, tillite and dolomite – is rising,” he says. “While some brown materials can be modified by additives, they cannot match the quality of competent rock.”

In the past, G1 aggregate was the main base course for roads, with G2 as the sub-base, and G4 and G5 used for the selected layers. Bhoora says that recently there are efforts to substitute these, using products with names like G4A or G4A Special, for instance. Specifications are being adapted possibly because of cost pressure, but have not yet stood the test of time.

“During my 40 years in construction, I have been involved in projects building roads that have outlasted their expected 25 year lifespan by a decade or more,” says Bhoora. “It is uncertain whether the new specifications will be as effective, especially with the much heavier loads on our roads today. My personal view is that going this route might be short sighted in the long run.”

In terms of the readymix market, he says the average strength of concrete supplied has been gradually declining. AfriSam has long been known in the sector as a specialist in high strength products for demanding applications like high-rise buildings – with concrete strengths up to 100 MPa for high-rise projects.

“There are fewer projects like this currently, but there are also signs of users ‘buying down’ when it comes to readymix,” he says. “Whereas 35 MPa was the average strength we supplied until recently, that average is now closer to 28 MPa. This is concerning, as skimping on concrete strength is certain to have long term consequences for buildings’ longevity.”

He notes that there is still insufficient work entering the project pipeline throttling, holding back the potential of the construction sector to create jobs and build valuable infrastructure. Contractors and their supply chain remain under pressure, with low margins leading to the demise of amalgamation of important industry bodies.

The use of extenders in AfriSam’s composite cements has over the years resulted in a substantial reduction in its clinker factor without compromising the quality of products. Blast furnace slag, a by-product of the steel industry, remains central to the company’s efforts to substitute clinker in its products. 

Since 2008, the South African cement industry has seen a year-on-year reduction in emissions per ton of cement, largely driven by the increased focus on clinker substitution. According to the Association of Cementitious Material Producers (ACMP), clinker substitution rose from 12% in 1990 to 23% in 2000 and a substantial 41% in 2009. The industry is pressing for a 60% rise by 2030.

Over the years, AfriSam has accelerated its efforts to substitute clinker through the development of composite (extended) cements. In 2000, the company launched Project Green Cement to increase the use of extenders to promote more sustainable products. The use of extenders, says Hannes Meyer, executive cementitious at AfriSam, has resulted in a substantial 20% reduction in the company’s clinker factor since 1990.

Composite cements, he explains, contain not only clinker, but other cementitious materials such as pulverised fly ash (PFA) from coal-fired power stations and ground granulated blast-furnace slag (GGBS) from steel-making plants. 

GGBS has been used in the manufacture of cements since the second half of the 19^th century. Back then, the practice was to intergrind the blast furnace slag with clinker. However, in the 1950s, AfriSam’s slagment operation pioneered the use of separately ground slag for the construction industry. 

The use of this product has grown steadily in South Africa, with AfriSam among the frontrunners. The company’s slagment operation plays a crucial role in the production of its composite cements. Established in 1955, the plant was previously owned by three companies, before AfriSam acquired 100% shares in 2004. The raw material is sourced from steel producer, ArcelorMittal South Africa, which is strategically located some few metres away from the plant. 

Blast furnace slag has good cementitious properties, providing enhanced strength and durability. By evolving its chemical and mechanical activation methods, AfriSam has achieved a more reactive product allowing the company to progressively replace more and more clinker while retaining high cementitious quality and strength performance.

“Re-using waste products from other industries reduces the amount of limestone that we have to mine and clinker that we have to produce, thus reducing carbon emissions from those processes, as well as minimising waste to landfill,” says Meyer. “We are therefore constantly searching for new extenders and additives to further reduce our carbon footprint and our impact on the environment at large. The end result is less clinker produced per ton of each final product, resulting in less CO₂ generated from our operations.”