CONCRETE'S EVOLUTION AS A CONSTRUCTION MATERIAL

Still the second-most used substance behind water, global concrete consumption is showing no signs of falling. However, as Mitchell Keller reports, the material isn’t what it once was, as the industry races to create more sustainable products

Concrete pours from a mixer on-site

IMAGE: ADOBE STOCK

The population of the world keeps growing, people keep on building, and – therefore – concrete will keep pouring. Concrete’s permanence in the construction industry has long been solidified, but the secor is changing, following intense research and scrutiny, with its binder – cement – blamed for 5% to 10% of carbon-dioxide emissions worldwide.

Citing pressure from governmental regulations, public interest, and a steady rise in green investing, the concrete industry will need to find a way to reduce its cement use and carbon footprint, and the plan is in motion.

Dr Chamila Gunasekara of RMIT holds a sample of low-carbon concrete

IMAGE: MICHAEL QUIN, RMIT

To deliver on expectations, the industry is using an all-hands-on-deck approach in the pursuit of delivering a lower-emissions product. “Not one-size-fits-all,” says James Chambers, director of global industry development for Nemetschek Group, a German-based software vendor for the design, build, and construction industries.

As in, there won’t be a singular so-called unicorn product or process that suddenly puts global carbon-reduction plans into hyperdrive. Instead, there will be multiple innovations where “everyone has to be involved to make an impact,” adds Chambers.

Especially considering climate variables – a pour in South America will not be the same as one in far-north Norway – it’s likely better for the industry that a host of different products floods the market from multiple continents. Manuel Toro, commercial chief officer for sustainability, digital strategy, and sales with Mexico-based building materials company Cemex, notes that, ultimately, customers want less carbon-emissions and the industry is due to deliver as quick as possible. “For 2024, I think that I am excited about the speed that the industry is gaining towards a more sustainable one,” he says. “Many countries with high volumes of concrete are now more engaged in the sustainability trend and that’s something that definitely will impact our customers.”

Replacing and altering cement

In finding a substitute for cement, it’s important to note that the industry means to replace, specifically, traditional Portland cement made from limestone, which is the most common type of cement used globally.

The calcination of limestone to make cement is also the biggest single releaser of carbon emissions during the process, with up to 50% of the industry’s emissions coming from this procedure. Eventually, it’s estimated that this traditional Portland cement blend will become extinct, but the term ‘cement’ and its basic purpose in the creation of concrete will remain.

Two of the most common materials replacing limestone are fly ash (a powdery byproduct from burning coal) and slag (a byproduct of smelting). Using both can limit the need for other high-cost materials and substances (like water and clinker) but also has some nuances that builders will need time to adjust to – literally.

What if you could construct one of the world’s first carbon prestressed concrete buildings and achieve significant CO2 and material savings, then dismantle its components for reuse elsewhere?

Sara Neff, head of sustainability in America at Lendlease (an Australia-based construction and real-estate company), inferred that knowledge is power for planning projects with novel mixtures.

“We were told correctly the slag and fly ash would cause the concrete to cure more slowly,” she notes, referring to finished projects in the US.

It’s one component that can throw off even an experienced crew more familiar with conventional concrete. Weaker strength at initial placement for fly ashand slag-based cement can extend a workday and lead to increased costs; a potential hinderance to universal adoption.

Render of Lendlease’s 1 Java building project in Brooklyn, New York, US, which is using pozzolan concrete in construction

IMAGE: LENDLEASE

36-HOUR CONTINUOUS CONCRETE POUR

The immense developing skyscraper, Okan Tower, located in Miami, Florida, US, had a 36-hour continuous concrete pour to lay the foundation for what will be a 70-storey mixed-use high-rise in the city’s downtown.

Starting at 9pm local time on 29 March, a fleet of 1,200 concrete trucks, 160 drivers, and 300 workers cooperated throughout the day-and-half straight of pouring concrete.

They filled the base hole, which measured 234 by 140 ft (71 by 43m) and 14 ft (4m) deep.

In addition, crews installed more than five million lbs (2,300 tonnes) of highstrength reinforcing steel.

The collective worked at a rate of 400 cubic yards (306m3 ) per hour and finished on 31 March.

Lead contractor Jacob Companies (US) oversaw the project in a joint venture with Okan Construction. US American Concrete served as the scheme’s concrete contractor, and the mixture was from Mexico-based construction materials producer Cemex.

A row of Cemex trucks line up for the 36-hour continuous concrete pour for Miami’s Okan Tower foundation

IMAGE: OKAN GROUP

But Neff adds the additional time is nominal, and it doesn’t have to be wasted if contractors and builders know how to manage it. “It’s maybe a little bit disconcerting for a little bit,” she acknowledges. “[But] we incorporated that into the schedule. We planned for it.”

Neff also notes strength and emissions-reduction successes with pozzolan – ground and recycled glass added to concrete mixtures – on several projects in the US.

“On our 1 Java project in Brooklyn, we replaced 40% of the cement in the foundation with a recycled glass product called ground glass pozzolan at no added cost to the project,” she said. “We worked with our concrete subcontractor and batch plant to procure, batch, and pour foundation concrete with Pozzotive, a ground glass pozzolan product made in the greater New York City region.”

Raising reduction rates

In the last few years, carbon-emission reduction rates advertised up to 30% appeared to be the high end for emerging concrete products. In 2024, the bar has been set higher, with some products advertising 60% emissionreduction.

One product in Cemex’s Vertua line of concretes and mixtures uses a proprietary geopolymer cement solution, which the company believes can reduce CO2 emissions by more-than or equal-to 60%. Davide Zampini, head of global research and development for Cemex, says more gains could be in the works.

“There are clear indications that we can go above and beyond what we what are targeting,” he tells International Construction.

Just reducing or removing cement, too, is not enough, says Zampini. The whole process should be reconsidered with the goal of reducing emissions. “For example, the grinding efficiency, the grinding energy,” he notes. “We can improve the level of substitution of clinker with supplementary symmetries and materials as we develop new technologies.”

What Zampini is describing is essentially a means to measure embodied carbon, which Neff adds has been underreported through the years. Measuring embodied carbon, she says, tracks carbon emissions created from making materials used in construction.

A large concrete pour in Kuala Lumpur, Malaysia

IMAGE: ADOBE STOCK

“We are measuring embodied carbon consistently on all our projects and in conceptual design,” she says. In this measurement, there is still a long way to go in terms of reductions, however. She says embodied carbon reductions on projects is levelling out with current products and processes around 30%.

“We’re just treading water,” Neff notes at 30% reduced embodied carbon, because concrete consumption increases every year – for example, around 3% in the US, alone.

CUTTING CONCRETE WITH WATER AT A CEMENT PLANT

Despite being hard as rock, concrete doesn’t last forever, and when the material needs to be removed or recycled, it’s often an invasive and dangerous project. Modern hydro-demolition – using water to demolish or cut through construction materials – is a popular method.

Workers in Spain use the Aquajet Ergo robotic hydro-cutter to remove decaying concrete from a silo

(IMAGE: AQUAJET)

Roger Simonsson, managing director at US-based hydrodemolition company Aquajet, says, “Applications such as concrete removal and repair on roads and bridges continue to be a primary use, [but] contractors use it for a variety of applications, such as coating removal, tank cleaning, tunnel repair, and even airport runway repair.” One project utilising Aquajet’s Ergo robotics system is in Spain – at a cement plant. “Fixen Structural Services used the Ergo to restore a 100m (328 ft) tall, 16m (52 ft) diameter silo in a cement plant,” explains Simonsson. “The walls of the vessel were held together with rebar on the outer and inner layers of its concrete. But nothing was there to connect the two, and with age, it resulted in deteriorating and falling concrete.”

Ergo uses a controller unit and can attach to standard scaffolding, which allows the highpressure cutter unit to access remote locations on a site.

“The Fixen team connected the Ergo to an electrical hoist to reach the areas of repair. They first used the Ergo to cut and remove the silo’s deteriorating concrete and then installed stirrups to anchor the existing horizontal rebars and attach them to the concrete,” says Simonsson. “The final step of the repair was to fill the open spaces with fluid mortar to complete the section.”

The team achieved a production rate of 1m per-minute, removing two 45m vertical sections of concrete each day and the project removed 1,440m of material in 26 days.

A construction worker lays Holcim’s prestressed, reusable concrete slabs for the Grüze Innovation Laboratory

IMAGE: HOLCIM SWITZERLAND

Reusing concrete

The industry has been focused on reducing on a large scale, and has always had a market for recycling concrete, but what about reusing? A major hinderance to the substances’ carbon output is that the reuse of concrete has been highly limited.

However, Switzerland-based Holcim – a construction materials and aggregates company – believes its prestressed concrete solution could be a path forward.

“What if you could construct one of the world’s first carbon prestressed concrete (CPC) buildings and achieve significant CO2 and material savings, then dismantle its components for reuse elsewhere?” asks Holcim rhetorically. It’s exactly what Holcim did in construction of its 120m2

Grüze Innovation Laboratory, a company information centre and sustainable construction workshop. The building is constructed with Holcim’s ‘delicate but reusable’ concrete panels, which can be dismantled and reused.

The building – believed to be one of the first CPC buildings in the world – was constructed using a new method developed by CPC and Zurich University of Applied Sciences.

Coupled with a ‘sharing’ programme (wherein a customer can loan the individual concrete panels), Holcim says the process lowers construction costs by up to 75%.

“It reduces the cost of a new development – since they don’t have to buy materials outright or dismantle the building,” explains the company. “Secondly, it gives them the option of assembling the structure elsewhere. Finally, the client can ask Holcim to disassemble the structure when it is no longer needed, so we can prepare the components for reuse.”

Eyes on this sector

If there is any major takeaway regarding the concrete sector, it’s that it is no longer operating in the shadows. From corporate transparency to scientific data, there is no escaping concrete’s relevance and emission challenges. It simply must evolve.

Partanna CEO and former NBA basketball player Rick Fox with his company’s concrete block

IMAGE: PARTANNA

WORLD’S LONGEST STEEL-REINFORCED CONCRETE ARCH BRIDGE COMPLETED IN CHINA

The Tian’e Longtan Bridge in Guangxi, China, opened to traffic earlier this year, and the structure now holds the record for the world’s longest steel-reinforced concrete arch bridge, with a 600m main span.

Chinese contractors Guangxi Road and Bridge Engineering Group started construction of the 2,500m-long bridge in 2020 as part of the Nandan-to-Tian’e Expressway. Spanning a reservoir over the Hongshuihe River, which is up to 900m wide and 130m deep, the bridge deck sits 140m above the water. The bridge features a box-ribbed, steeltubed arch structure supported by 13 horizontal struts, carrying four lanes of traffic. Utilising a cantilever construction method with stay cables, the construction avoided the need for falsework support. The project relied on vacuum-assisted graded pumping, non-shrinkage concrete, and instantaneous stress load regulation for the arch rings. The bridge’s steel structure, weighing more than 8,000 tonnes, was divided into 44 segments, with the largest measuring 23.35m long, 9.91m high, and 5.2m wide.

The Tian’e Longtan Bridge in China’s Guangxi Zhuang Autonomous Region. It opened to traffic earlier this year and is the longest steel-reinforced concrete arch bridge in the world

IMAGE: XINHUA NEWS AGENCY

Investment in the sector isn’t just coming from inside the industry; celebrities and professional athletes have been putting money down for a more sustainable product, which could lead to increased public attention, overall.

Take Partanna, the US-based sustainable concrete producer, which was co-founded by three-time National Basketball Association (NBA) champion Rick Fox, who also serves as the company CEO.

The Canadian native and current Bahama resident formed the company after a hurricane battered The Bahamas in 2019 to see if a more weather-resistant material could be made.

Rory Anderson, chief growth officer for Partanna, said Fox was then inspired to lean into innovations that reduced the environmental impact, as well. “He was looking for hurricaneproof housing solutions,” Anderson says, noting the mission has now doubled-down on being “nature positive.”

While much of the biopolymer is proprietary, Partanna concrete uses brine as an additive and can be cured at room temperature, which it believes reduces its CO2 emissions. The product, Partanna says, also exhibits the ability to absorb CO2 from the atmosphere during the production process.

Fox isn’t the only celebrity intrigued by the concrete industry. Actor Dennis Quaid – through his digital content program Viewpoint – announced a series of episodes will feature sustainable technology innovations in building and architecture. The opening programme (titled 'Green Building Materials') is expected to highlight new eco-friendly construction products.

“Sometimes innovation has to come outside of the field,” says Anderson on why Hollywood and the pro sports community is suddenly actively involved in the industry and discussion. “And this is a huge problem. “Up until recently, there haven’t been enough commercially scalable solutions to be able to create impact.”

He says the public, too, can see technology transform before their eyes from gas-powered cars of yesterday to electric/automated dump trucks of today. “But we’re still using the same materials to get to concrete,” Anderson adds. “People, I think, are feeling that frustration and that there haven’t been solutions.

“There are massive pressures on the construction sector to decarbonise from a policy perspective, and I think that is driving a lot of the demand for innovation. People have looked at this as a sector and said, ‘What can I do?’”

For now, contractors and builders should keep building a diverse network of material and aggregates providers and continue their education on new concrete products. The best advice is to keep up with the evolution of the sector, as it’s showing no sign of slowing down anytime soon.