Requests for Paebbl's carbon-storing cement substitute far outstrip what it can produce

Paebbl's Rebond 300 requires no changes to a producer's equipment and stores captured carbon dioxide in the finished structure. Ana Luisa Vaz, Paebbl's VP of products, told Construction Outlook senior editor Lily Sawyer that requests for Rebond 300 far exceed what the Stockholm- and Rotterdam-based company, founded in 2021, can produce. She said closing that gap, rather than persuading the market, is now its main challenge.

Vaz described performance as a gate the industry is right to guard: a material that cuts carbon but misses on strength, workability or durability won't be adopted, however good its climate case looks. Paebbl's claim is that Rebond 300 has cleared that gate under commercial conditions. If that holds, the person most affected is the concrete buyer, whether at a precast plant, a contractor bidding European infrastructure or a data center owner chasing Scope 3 targets. Their questions shift to allocation, price and how much of the mix to commit.

Reading the Rebond 300 numbers together

Rebond 300 follows its predecessor, Rebond 200. Vaz calls the new product "a significant improvement on our second-generation material" and "a tenfold improvement in carbon efficiency." The headline figures are best read as a set rather than one at a time.

The 30 and 40 look odd side by side at first. A material that displaces at most 30 percent of the cement yet cuts embodied carbon by up to 40 percent implies it is subtracting carbon on top of the cement it replaces. That is the negative footprint at work. The 40 percent is a ceiling, and real results will depend on the mix design and the rest of the ingredients.

Color is the second detail on the spec sheet. Vaz said Rebond 300 is near-white, whereas most supplementary materials come in grey or dark tones. In architectural and design projects, she said, concrete has to look right as well as perform, and the lighter shade finally puts the material within reach of that bar. That could open up exposed architectural work, where a darker binder would likely fail on appearance before anyone checked its strength.

Vaz's wider case for these materials starts with volume. Concrete is the most widely used human-made material on Earth, she noted, and the world's building stock is expected to double by 2060, so construction cannot shrink its output to shrink its footprint. Her conclusion is that the industry has to change what it builds with.

She adds a commercial pressure alongside the climate one. Cement is energy-intensive by design, which leaves producers and contractors exposed to supply chain shocks and energy price swings, and Vaz said those costs tend to stay elevated long after the disruption passes. In her view, supplementary materials answer both problems: they cut embodied carbon and let the industry flex across feedstocks depending on regional and commercial viability.

From filler powder to cement replacement

Paebbl laid out its chemistry in a May 2023 input it submitted on carbon removals under the Paris Agreement's Article 6.4 mechanism. The process copies natural rock weathering but speeds it up with energy-efficient equipment: CO2 reacts with abundant silicate minerals, water and organic accelerants, locking the carbon into a solid mineral powder. The company said then that the process works with any CO2 source and aimed to scale it for both direct-air-capture and flue-gas CO2.

The interesting part is the job the powder was meant to do. In that 2023 filing Paebbl described its goal as storing carbon in durable filler materials for uses such as concrete, and called the resulting mineral powder a carbon negative substitute for calcium carbonate. Rebond 300 is sold as a supplementary cementitious material, a partial replacement for cement, and Vaz says cement production alone accounts for around 8 percent of global carbon emissions. Moving from filler to binder puts the powder in the part of the mix where most of that carbon sits.

Vaz now describes it as an entirely new category: a material that takes in CO₂ as a raw input instead of treating it as a problem to handle later. She said every structure built with it turns into a permanent carbon store. It counts toward Scope 3 targets because of the material's physical chemistry, she said, and not because of accounting adjustments made after the fact. For the data center owners and contractors mentioned above, that distinction matters, since the claimed benefit travels with the tonnes delivered.

The same filing pointed regulators to a 2020 study by Ostovari and colleagues that assessed seven mineralization pathways and found reductions of 0.44 to 1.17 tonnes of CO2e per tonne of CO2 stored. That range is measured per tonne of CO2 stored, while Rebond 300's -149 kg figure is per tonne of product, so the two are useful context for the method rather than a direct cross-check.

For sustainability teams, the practical question is documentation. Paebbl describes the -149 kg figure as verified, and anyone reporting against it will want the verification report and lifecycle boundaries in the submittal package.

Five projects, five different tests

Vaz says each of Paebbl's projects shows the material's strength in a different application, and that together they give a fuller picture of what it can do in real conditions.

• Structural load, Netherlands: a pedestrian bridge led by Heijmans, with HCM Cement, Van der Kamp B.V., CarStorCon Technologies (biochar) and Urban Mine (recycled aggregates). The material replaced 30 percent of the Portland cement in a mix that was 75 percent circular raw materials, and the concrete met its structural requirements.
• Standard supply chain, Germany: a commercial floor slab trial with Holcim and Goldbeck, using a standard ready-mix design and conventional placement.
• Maritime exposure: work with Hakkers on maritime infrastructure, a demanding environment Vaz said few low-carbon materials have entered.
• Stiff mixes: slipform concrete with AGILIS, a subsidiary of NGE Group, a dense mix that Vaz said has historically resisted modification.
• Data center construction, Spain: Amazon Web Services, one of Paebbl's first commercial collaborators, used the material in what Paebbl calls the world's first carbon-storing data center.

The German floor slab trial was designed to see if the material could move through an ordinary industrial value chain without any changes. Paebbl supplied the material, Holcim's plant batched it into a standard ready-mix design, and Goldbeck placed it using standard methods. Workability, setting time and finishing all matched the reference mix. The concrete reached the full C30/37 strength specification, and construction timelines stayed the same.

From initial concept to completed pour, the trial took less than six months. For a ready-mix producer weighing a first batch, that may be the more telling number. It suggests a qualification pour can fit inside a single project calendar.

The bridge answers a different worry. Vaz noted that much of the early enthusiasm for new low-carbon binders went into decorative or non-structural uses, where underperformance costs little. A pedestrian bridge carries no such tolerance. Vaz said the 30 percent substitution was the highest rate achieved in any structural application at that point, and that the concrete in the bridge met its structural requirements in full.

The bridge also relied on several partners. Heijmans led the project and construction, HCM Cement supplied an optimised cement formulation, Van der Kamp managed concrete production, CarStorCon integrated biochar and Urban Mine provided recycled aggregates. Vaz said the consortium set a new benchmark in the Netherlands for structural concrete that is circular and carbon-neutral. Because the mix also contained biochar and recycled aggregates, the bridge's carbon result reflects the whole formulation and not Rebond alone.

Across roughly 20 customer projects, Vaz said, the materials have performed to industry standards in a wide range of applications using the industry's existing infrastructure. The five above are the ones she singled out because each tested a different risk.

Capacity, cost and who is buying

Vaz sees the backlog as a supply problem, not a confidence problem. She said Paebbl increased production capacity a hundredfold in its first 18 months of operations, partly with help from data and AI tools it uses through its AWS partnership. Using AWS cloud infrastructure, the company gathers data from all its reactors and lab equipment in a single place so it can be analysed quickly. She said this saves time on work that a large team would normally need most of a year to complete.

That AWS sits on both sides of the business is worth noticing. It is a customer for the Spanish data center and a contributor to how Paebbl runs its reactors. That demand still outruns supply after a hundredfold increase suggests allocation will stay tight for buyers in the near term.

Price is the second lever. Vaz said Paebbl aims to close the cost gap between its product and conventional cement within the next 10 years, following a path similar to renewable energy's route to cost leadership, and that the progress will be tightly coupled with holding and improving technical performance. The stated goal implies Rebond 300 currently costs more than conventional cement, so early buyers are paying for carbon performance rather than savings.

On who is buying, Vaz pointed to three forces. The first is the data center buildout. She called hyperscalers a driving force of a new building "supercycle" that needs materials offsetting embodied carbon without slowing construction, and argued that efficiency gained in construction becomes capacity freed up elsewhere. A drop-in material, she said, shows lower-carbon concrete can be used at scale without adding a day to the build schedule.

The second is rising spending on resilient infrastructure, including concrete works such as breakwaters and military installations. New sustainability conditions tied to that funding shift demand toward materials with lower carbon. Third, Vaz pointed to the EU's carbon border adjustment mechanism, which she said is slowly wearing down the price advantage that cheap, high-carbon imported materials have enjoyed in European markets. She describes Rebond 300 as a "sovereign material" built for that demand.

The last two forces connect to the cost target. If border pricing narrows the advantage of high-carbon imports, the gap Paebbl has to close in Europe could shrink from the other side as well as from its own scale-up. Once a Holcim plant can batch it and a Goldbeck crew can place it at C30/37 with no change to the schedule, the number that decides adoption is how many tonnes Paebbl can ship.

Before the first order

Vaz said closing the gap between demand and Paebbl's production capacity is now the company's primary challenge. For buyers, that makes the supply conversation the place to start.

Watch for a production figure in tonnes or a named new plant. Either would show whether supply is catching up with the demand Vaz describes, and it would tell specifiers whether Rebond 300 belongs in a single flagship pour or in a standard mix design.