Improving concrete, one of the world’s worst materials

Solving the problem that is concrete—the second-most-used substance, after water, and a candidate for the most harmful to the planet—has inspired a wave of start-ups to develop less harmful alternatives. Representatives of many of these firms gathered in Paris recently to compete for €100,000 (about $107,000) and become the cleantech start-up champion at Hello Tomorrow’s Global Summit.

The multibillion-dollar concrete industry is a particularly rich target but one that has proven slow to change. The start-up founders in Paris seemed undaunted.

“We can turn buildings into carbon sinks,” said Steff Gerhart, cofounder and chief commercial officer of ecoLocked, as she pitched her company. The firm and others gathered in Paris claim to have alternative chemistries the world’s concrete industry could adopt to fulfill its pledge to cut its annual carbon dioxide emissions of approximately 3 billion metric tons (t)—roughly 8% of total anthropogenic greenhouse gas emissions—to zero by 2050.

ecoLocked’s product is a concrete additive featuring biochar, a carbon-rich material made by heating biomass in low-oxygen conditions. ecoLocked calculates that its approach has the potential to store about 4 billion t of CO₂ annually in concrete and other building materials. The company opened a lab in Berlin in 2022, and in the past year released its first product, for nonstructural concrete.

Rather than trying to offset concrete’s CO₂ emissions, other start-ups at the Paris meeting are seeking to reduce the amount of concrete needed in a structure by enhancing its strength. Yet others want to replace cement—the adhesive component of concrete—with lower-carbon alternatives.

Portland cement makes up 12% of concrete but accounts for 85% of its carbon emissions. Traditional Portland cement is made by combining calcium carbonate with clay minerals and heating the mixture to 900 °C in a kiln to form calcium silicates known as clinker. The clinker is then ground into a powder, and calcium sulfate is added to form cement. CO₂ is generated in the heating step of this process and also during the chemical transformation of calcium carbonate.

In a bid to reduce the amount of concrete a given structure requires, the French start-up Blackleaf has developed a graphene material that, when added to concrete at a concentration of between 0.02% and 0.04%, increases its compressive strength by more than 10% and bending strength by more than 20%.

“This enables the use of less concrete for the same application,” said Camila Rivera Cárcamo, a business development manager at Blackleaf. While other firms have developed graphene powders for concrete, Blackleaf says it is unique in offering a water-based graphene additive, which is easier for concrete makers to mix in. “It’s a huge advantage,” Rivera Cárcamo said. The company is now doing construction-site testing on the strength of concrete made with its additive.

A potential secondary benefit of graphene-containing concrete is that it can form buildings that block electromagnetic waves such as those used by cell phones. This feature is especially useful for buildings handling sensitive information, Rivera Cárcamo said.

The Austrian start-up ParaStruct has taken a more radical approach to cutting concrete’s carbon emissions: removing cement altogether. It has developed an algorithm that selects combinations of low-cost, low-carbon raw materials for making cement-free concrete. The algorithm targets local mineral and biogenic waste, said founder and CEO Georg Breitenberger.

ParaStruct is testing versions of its cement-free concrete, including a wood-based compound, to form internal features such as soundproof walls. To make this product, it has partnered with the German 3D-printing firm Voxeljet.

Producing 1 m³ of concrete releases 564 kg of CO₂, according to Breitenberger. ParaStruct’s cement-free compound has a CO₂ footprint that is “looking pretty good” at 308 kg, he said. ParaStruct is set to begin a seed funding round later this year to raise money to build a pilot plant that can produce 6–7 m³ of low-carbon concrete per day.

While ParaStruct’s wood-containing concrete has not been designed for use as a weight-bearing material, there are no such limitations when it comes to a geopolymer binder that the US start-up Ultra High Materials (UHM) claims can completely replace Portland cement.

“It reduces the embodied CO₂ by 80–90%,” CEO Jonathan Cool said in his pitch to judges at the Paris event. “It also performs much better. It’s stronger, faster to strength, much more durable—and we can make this at up to 65% lower cost when compared to the raw material cost of Portland cement.”

Depending on the local availability of materials, UHM’s binder consists of components such as blast furnace slag, fly ash, fumed silica, and metakaolin, a clay derivative. While Portland cement uses water as an activator, UHM uses a stoichiometrically optimized activator consisting of silica, water, and an alkali like sodium hydroxide.

UHM’s binder can be made with local materials anywhere in the world, Cool claimed. The company is running field trials and has about 50 customers lined up, he said.

To extend the life of concrete—and thereby avoid the release of CO₂ emissions created by rebuilding or repairing a structure—the Cambridge University spin-out Mimicrete is commercializing a technology that enables concrete to self-heal when cracks appear. Inspired by the human body, the technology involves 3D-printing concrete with a vascular system.

Emulating human arteries, tubes in the concrete contain a liquid-polymer-based material that can find its way into any crack, CEO Arta Selmani said in her pitch. Mimicrete’s approach costs 20% more up front but promises a 40–70% reduction in the lifetime cost of a concrete structure by doubling its life-span and avoiding maintenance costs, Selmani said.

Already building some projects with low-carbon cement, the European construction firm Vinci was at the Paris event to share its strategy for cutting its worldwide carbon emissions by 40% by 2030. “Concrete is great—and probably the best construction material—as long as we reduce its carbon footprint,” said Bruno Paul-Dauphin, head of sustainable concrete solutions for Vinci.

The company’s approach is to reduce carbon emissions by substituting standard cement clinker with a clinker generated in steel mill blast furnaces or with fly ash from coal-fired power plants. As the steel and energy industries transition to cleaner production, the availability of this substitute clinker will decline, Paul-Dauphin acknowledged. Consequently, Vinci is already trying out another family of low-carbon materials, including metakaolin, limestone filler, and pozzolanic ash.

Vinci is already using its low-carbon cement in projects such as the construction of the athlete’s village for this summer’s Olympic Games in Paris. “The lesson is that when using low-carbon concrete, there is no impact on method, no impact on materials, no excuse not to use low-carbon concrete,” Paul-Dauphin said.

Other major European concrete producers have also started trying out alternatives to standard Portland cement, Paul-Dauphin said. They include Holcim, which is using a clay derivative to make cement at its plant in Saint-Pierre-la-Cour, France. And the cement firm Vicat is using clay derivatives to reduce the carbon emissions of concrete from its plant in Xeuilley, France.

Meanwhile, Germany’s biggest cement maker, Heidelberg Materials, has launched what it says is the world’s first net-zero carbon emissions cement, based on carbon capture and storage technology, at its facility in Brevik, Norway. Heidelberg says in an email that it is also in a dialogue with start-ups and university research groups “to examine cooperation and investment opportunities” in the field of low-carbon concrete.

The good news for many of the start-ups at the Paris meeting is that, according to a study by Boston Consulting Group, funding for deep-technology innovations, such as low-carbon concrete, has been growing in several European countries, including France.

Judges at the Paris event, however, did not consider the alternative concrete technologies on show to be prizeworthy solutions for reducing carbon emissions. Neither ecoLocked nor any other concrete- related innovator walked away with an award. Instead, the winner of Hello Tomorrow’s Sustainable Construction and Infrastructure challenge was the Chilean start-up Photio. It has developed a coating made of nanomaterials that simulates photosynthesis to passively cool any building.

The grand winner across all segments and the recipient of the €100,000 prize was Tozero, the German developer of a hydrometallurgical process for recycling lithium-ion batteries. But as ecoLocked and other construction technology firms are aware, the sheer scale of the carbon emissions resulting from concrete means that bigger prizes await.