Designing 3D-Printed Concrete to Absorb More CO2

Concrete’s Environmental Limits: Sand Use and CO₂ Emissions

Concrete has become the central material for construction over the past few decades, especially in dense urban environments. It has progressively replaced bricks, stone, and wood, thanks to its low cost, ease of use, and scalability.

But it is not without issues.

First, it is far from a sustainable product when it comes to resource consumption. It uses tremendous amounts of sand, to the point that reports suggest the world is “running out of sand.”

Source: Visual Capitalist

The production of cement is also a very energy-intensive activity. It is almost exclusively powered by fossil fuels, resulting in cement production being responsible for 8% of the world’s CO₂ emissions.

This is comparable to the emissions from cars and vans, which are responsible for 10% of global emissions. Consequently, making concrete more sustainable would be as impactful as transitioning all of the world’s cars to EVs and powering them only with green energy.

However, these emissions can also be partially compensated by a phenomenon called carbonation, in which cementitious materials absorb CO2 from the atmosphere.

A new study by researchers at ETH Zurich (Switzerland), University of Bath (UK), and University of Manchester (UK) investigates the potential for 3D-printed concrete to have a lower carbon footprint than ordinary concrete with faster carbonation. For the printed concrete assessed in Tor Alva, the researchers estimated that carbonation could offset approximately 21% of its initial carbon footprint over 50 years.

They published their findings in Cement and Concrete Research¹, under the title “(Re)carbonation: A new opportunity for sustainable 3D-printed concrete”.

Concrete & CO2

The main reason for concrete to be a large segment of global carbon emissions is the calcination of limestone (CaCO3), which decomposes into CO2 and calcium oxide/quicklime (CaO). The quicklime then immediately fuses with silica (SiO₂), alumina (Al₂O₃), and iron oxide (Fe₂O₃) from clay or shale to form the final cement.

“The main share of these emissions (typically 60% [2]) is due to the calcination of limestone (CaCO3), which decomposes into CO2 and calcium oxide (CaO), prior to the clinkerization process that takes place in the kiln. The rest of the cement’s CO2 emissions are mainly linked to fossil fuels required for thermal energy.”

These carbon emissions can be somewhat compensated by the next step, once the cement is used to make concrete structures.

In the hardened cement paste, the Ca-bearing hydration products will slowly react with CO2 in the air, forming calcium carbonates, thereby sequestering CO2.

“From a sustainability perspective, the same reaction of binding CO2, can be referred to as (re)carbonation. This amount corresponds to approximately 43% of the CO2 emissions associated with cement production.”

This process of carbonation is, however, not without downsides. It reduces the alkalinity of concrete’s pore solution, which in turn can destabilize the passivation film present on the steel reinforcement. This can result in steel corrosion, reducing the service life of ordinary reinforced concrete structures.

This can be a serious issue for low-carbon concretes, as they tend to carbonate faster than ordinary Portland concrete.

3D-Printing Concrete

Using A Real-Life Example

In the context of new construction methods using digital fabrication with concrete, 3D-printed concrete is the most widespread and promising technology.

To evaluate the real carbon footprint of this technique, the authors of this study developed a methodology to evaluate its dynamic Life Cycle Assessment (LCA). They used the 3D-printed “Tor Alva” tower in the village of Mulegns, in the Swiss Alps, as a real-life case study, with a focus on the 3D-printed branched columns and the cupola.

Source: Cement and Concrete Research

They first measured carbonation with three different approaches, one using accelerated testing (using a carbonation chamber maintained at 4% CO2, 67% RH, and 20 °C) and two using natural carbonation results: direct carbonation depth measurement and quantifying carbonates/CO2 via thermogravimetric analysis.

Finding Real Carbonation Rate

When projecting the effect of the observed carbonation, the researchers used a 50-year time horizon. They also compared the results of the 3D-printed concrete structure with a cast-in-place structure with a similar outside geometry and produced with a similar cement composition.

They found that in the area of the concrete carbonating, all the available material was reacting and absorbed CO2.

“In the carbonated region, the amount of bound CO2 lies between 44.16 and 51 g CO2/100 g of hydrated binder. The latter corresponds to having enough CO2 to decalcify all available calcium silicate hydrate.”

Source: Cement and Concrete Research

Then, the next question is to figure out how much of the 3D-printed concrete will actually capture carbon over its lifetime. By analyzing the penetration of the carbonation process with accelerated testing, they determined that within 50 years, 86% of all printed mortar used in the tower would be carbonated, totaling 32 m3 of printed carbonated concrete.

Source: Cement and Concrete Research

When comparing these results with natural carbonation measurements, direct carbonation depth measurement gave a similar number (89%). The methods produced different estimates of carbonation extent, but those percentages do not directly measure total CO₂ uptake. The researchers explain that pH indicators can overlook substantial absorption before the material changes colour. Thermogravimetric analysis measures uptake directly and supported an estimated 21% reduction in the printed concrete’s carbon footprint, compared with 14% using natural-carbonation pH measurements.

Source: Cement and Concrete Research

When compared to the cast-in-place structure, Tor Alva’s carbon footprint is superior, thanks to 25% less concrete used, as well as better carbonation.

“Despite having 25% less cementitious material, the 3DPC structure can bind 2.5 times more CO2 than the cast-in-place reference (4.6 tCO2 for the printed structure and 1.9 tCO2 for the cast one).”

Improved Carbon Capture

This study indicates that quick carbonation can lead to higher capture of carbon by concrete, greatly reducing the total carbon emissions in the lifecycle of a building. This is especially true for concrete structures without steel rebars and for 3D-printed concrete thanks to quicker carbonation.

It should also be noted that cycles of freeze-thaw, like in the example studied (Swiss Alps), likely affected both the boundary conditions and the internal transport properties governing moisture and CO2 movement.

Source: Cement and Concrete Research

In practice, this could mean that 3D-printed concrete in warmer climates could act as an even better carbon sink, but this requires further study to be proven.

“Freezing of pore water could partially obstruct the pore network and thereby reduce effective transport and slow carbonation. These results suggest that low-temperature effects—whether through partial pore blocking, changes in moisture state, or a combination of both—should be considered when describing carbonation under such environmental conditions.”

This also opens a new perspective on how to optimize concrete 3D printing. Optimizing carbonation could become an additional parameter in the geometric optimization of 3D-printed concrete structures, exposing surface to carbonation as much as possible.

This is not to say that 3D-printed concrete is a carbon-free construction method. Even with optimized carbonation, the emissions during calcination when producing the cement are still significant. And of course, carbon reabsorbed over 50 years will significantly contribute to climate change in the meantime.

However, if these carbon emissions were to be captured at the cement factory level, the later carbonation of the concrete building could truly turn such infrastructure into a net carbon sink, despite being made of concrete.

3D-printed concrete is much more likely to reach that goal first, by combining optimized geometry, low-carbon binders, and suitable reinforcement. In turn, this could turn into an opportunity for providers of construction materials.

Investing In Advanced Concrete Technology

CRH

As one of the world’s leaders in cement production, CRH will be instrumental in turning cement construction into a more sustainable industry. It ranks #1 in total volume of construction material provided in both the US and European markets.

Source: CRH

The company is active in 28 countries and 3,390 locations, employing 78,500 people, with CRH Americas making 65% of its global sales. It is also by far the largest cement company, a leadership further consolidated with its recent acquisition of Arcosa.

“The transaction reinforces CRH’s position as the leader in U.S. aggregates, as well as globally, and increases exposure to some of the fastest-growing Metropolitan Statistical Areas (MSAs) in the U.S.”

Source: CRH

CRH expects robust spending by Western governments on infrastructure to help grow its business. The trends of re-industrialization and on-shoring high-tech manufacturing should also help.

CRH has made serious progress in sustainability with a series of initiatives:

• It is the largest recycler in North America, with 43.9 million tons of waste and by-products from other industries recycled in 2023.
• It reduced its CO₂ emissions by 8% in 2023, thanks to using 36% alternative fuels in its cement plants.
• It is aiming for a reduction of emissions by 30% by 2030 (compared to 2021 emissions).

CRH is also a driver of more fundamental changes to the sector. Notably, it has invested $75M in low-carbon cement company Sublime, together with the European concrete giant Holcim.

Sublime Systems was spun out of MIT in 2020 to utilize an electrolyzer to produce cement at ambient temperatures, replacing energy- and fossil fuel-intensive kilns. It also enables the use of calcium sources as an input material, avoiding the release of CO₂ from limestone input.

Sublime’s first commercial facility in Holyoke is expected to open as early as 2026. If proven successful, it could be the real game-changer for the cement industry, and it could open the way to scalable low-emission concrete.

CRH also invested in other decarbonization and sustainability startups:

• €23.7 million in Cool Planet Technologies, developing carbon capture solutions for industries that have traditionally been difficult to decarbonize.
• $34.7M by CRH and other investors in Carbon Upcycling Technologies, using an all-electric mineralization solution to permanently store CO₂ in industrial by-products and minerals, like cement, plastics, consumer products, fertilizers, and pharmaceuticals.
• AICrete, a ‘recipe-as-a-service’ platform that works with local concrete producers, optimizing local materials and minimizing the amount of cement used using AI analyses, reducing both the CO₂ footprint and the cost of concrete production.
• FIDO AI’s Series B funding is for a startup using AI to reduce water consumption and increase water savings.

Lastly, CRH is also investing in 3D concrete printing (3DCP) through its subsidiary Amerimix.

Overall, CRH is a profitable leader in the concrete and construction industry and is very actively preparing for the decarbonization of the industry, both directly in existing facilities and by being a prime provider of capital to innovative startups creating the next generation of cement and concrete production technology, including decarbonization and 3D printing.

Latest CRH (CRH) Stock News and Developments

Study Referenced

^{1. Lucas Nascimento de Lima. (Re)carbonation: A new opportunity for sustainable 3D-printed concrete. Cement and Concrete Research. December 2026. Article: 108411. Volume 210. 10.1016/j.cemconres.2026.108411}