Bio-cement from Algae

Prometheus Materials outlines a novel approach to cement production, using CO₂, sunlight and microalgae...

Global Cement (GC): Please could you introduce Prometheus Materials and its products?

Loren Burnett (LB): Prometheus Materials was founded in March 2021 to develop new biomimetic technologies that will enable low-CO₂ building materials. The company was built on research by the Living Materials Laboratory, based at the University of Colorado Boulder and led by Prof. Wil Srubar. Wil and his colleagues had been working on ‘living materials’ with both biological and structural function since receiving a Department of Defense grant in 2017. The breakthrough was to harness bio-mineralising organisms that precipitate calcium carbonate to produce ‘bio-cement’ that can then be used in ‘bio-concrete.’

Wil Srubar (WS): Macro-organisms like oysters and clams often come to mind when thinking of natural calcium carbonate structures. However, there are also aquatic micro-organisms that precipiate calcium carbonate on a smaller scale. They are fast growing and, if you grow enough of them in one place, the mass of calcium carbonate builds
up quickly.

GC: So how do you build macro-structures with micro-organisms?

WS: The first step of the process is to make bio-cement. To do this, we culture naturally-occuring biomineralising micro-algae in water that also contains a proprietary bio-polymer. The micro-algae are photosynthetic, so we just feed them CO₂ and sunlight at ambient temperatures. They precipitate calcium carbonate onto the biopolymer, which acts as a scaffold, similar to forming a seashell.

After several hours, the water is removed for re-use. The bio-cement is then pressed into blocks of bio-concrete using conventional machinery, sand and aggregates. The blocks cure via dehydration over seven days, an important difference to Ordinary Portland Cement (OPC) concretes, which cure via hydration.

GC: How does the embodied CO₂ emissions of this process compare to OPC-based concrete?

WS: Bio-concrete production has no need for heat, nor does it release CO₂ from the decomposition of limestone, dramatically reducing direct emissions. There is no grinding, which reduces CO₂ emissions from electrical power use. As the input materials are readily available, there is no need to transport, process and transfer heavy materials, reducing emissions even further.

In addition, the CO₂ precipitated within the bio-concrete itself is sequestered. This means that the embodied CO₂ of mass-produced concrete masonry units (CMUs) are just 10% of that of a functionally-equivalent OPC-based CMU. By combining this process with solar or wind power, the embodied energy and CO₂ of the bio-concrete could be negligible.

GC: How do the products themselves stack up?

WS: There’s no market for products that aren’t up to the job, so our bio-concrete has undergone extensive testing for compressive and tensile strength, comfortably meeting or exceeding recognised norms. Indeed, its tensile stength is particularly high, thanks to its relatively low density. This means that it will be possible to make pre-cast elements in shapes and sizes that cannot be obtained conventionally. Bio-concrete also exhibits higher fracture toughness and crack resistance.

Thanks to its very low water content, we have also found that bio-concrete mortars have 90% lower thermal conductivity than traditional ones. This will likely improve the energy efficiency of buildings made using bio-concrete, reducing the cost and CO₂ emissions from heating and cooling over a building’s lifespan.

GC: What do you estimate the production cost and price of the initial CMUs to be?

LB: We anticipate marketing our products at prices that are close to the current industry standard. We don’t want to rely on policy incentives to be profitable, as these are likely to be removed over time. Indeed, it may be that our products become more competitive than OPC-based material, if fuel, electricity and CO₂ emission prices continue to rise.

GC: How close are you to production?

LB: Following successful scale-up in the lab and extensive testing, Prometheus Materials received US$8m of Series A funding in March 2022. We are now building a pilot production facility in Longmont, Colorado, with CMU production anticipated by the end of 2022. Pilot production will begin in stages, with an eventual early pilot capacity of 250,000 units/yr. This will precede large scale, geographically dispersed manufacturing operations.

GC: So you will sell CMUs directly to users?

LB: Direct sales are the first part of our strategy, but we will also licence the technology to pre-cast element producers and global cement and concrete players. Very often with start-ups it can be hard to sign that first contract. However, interest has been very strong. Multinationals are acting on decarbonisation mandates and we are already in advanced discussions with several parties.

GC: Will this work for ready-mix?

WS: Yes. We are currently developing a ‘just add water’ mixture that will act just like regular cement. This can be used at job-site and as a feedstock for pre-cast elements.

GC: OPC-based cement has a relatively short shelf-life. Is it the same for bio-cement?

WS: We have conducted a series of tests that show shelf-lives in excess of six months, which was the duration of the test. This is not dissimilar to OPC. We will run longer tests in due course but we don’t anticipate any issues.

GC: Where do you think your materials will be most popular?

LB: We are marketing to the demand side, specifically to architects, engineers and large construction firms, to educate them about the advantages of bio-cement and concrete. Once our bio-cement starts to be included in their specifications, suppliers will follow suit.

Location-wise, it makes sense for us to start in North America, simply so we can be close to those projects. However, one of our major shareholders is based in Paris, France, so we would like to move into Europe soon. Both regions have high building standards that will help us demonstrate the benefits of bio-concrete. After that, I am confident that our track record would allow us to move into many other global markets.

GC: What do you see as the biggest barriers to development of bio-cement and concrete?

LB: A year ago, I would have said resistance from the industry. However, that is no longer the case. Cement and concrete manufacturers have become far more receptive to new chemistries and methods. OPC is increasingly seen as old fashioned.

To return to the question, we know that the process and materials are ripe for scale up. I cannot pin-point any particular challenge that keeps me up at night. That said, there are inherent risks to the development of any new business.

GC: What impact would you like bio-cement and concrete to have over the period to 2030?

LB: It is our aim to be mitigating around 1Bnt/yr of CO₂ emissions. Even in the precast concrete products market, we have the potential to go a long way towards that target. We know we won’t reach our target overnight, but we want to make meaningful change to the global cement and concrete sector, and to the planet as a whole.

GC: Thank you for a very interesting discussion.

LB/WS: You are very welcome indeed.