A Concrete Solution
A massive infrastructure buildout and a reduction in CO2 emissions… can we do both?
Key Takeaways
- The world produces an incredible amount of concrete. Global annual production of concrete is about 10 billion metric tons and this number is expected to grow by 10% a year. The number of buildings on the planet is expected to double by 2060 — equivalent to building another New York City every 30 days for the next 40 years.
- Concrete and cement production is responsible for roughly 8% of global emissions. For each ton of concrete produced, 1 ton of CO2 is emitted.
- If Biden’s infrastructure plan passes, will it dramatically increase global CO2 emissions? No. The US is only 2% of the global cement market (and we can only build so many new cement plants per election cycle).
- Still, this is a critical opportunity to scale modern, lower carbon cement technologies through creating voluntary “CarbonStar” standards, grants for demonstration projects, and other strategies.
If the Biden Administration’s $2.3 trillion infrastructure bill becomes law this summer or fall, one thing is clear — we are going to use a lot of concrete. [1]
However, using more concrete is at odds with another one of the Biden administration’s stated goals — reducing CO2 emissions. A whopping 8% of global CO2 emissions come from producing cement, a key ingredient in concrete. For each metric ton of concrete produced, roughly 1 ton of CO2 is emitted to the atmosphere. The US alone produces over 600 million metric tons of concrete each year, or almost 2 tons of concrete per person. [2]
It isn’t just us either. Concrete is the second most consumed material on earth, after water. The world’s annual production of concrete is about 10 billion metric tons and this number is expected to grow by 10% a year. Looking at just one use of concrete, the number of buildings on the planet is expected to double by 2060. This is equivalent to building another New York City every 30 days for the next 40 years. [3]
In this post, we’ll pause to consider concrete. Without it, the modern infrastructure (and brutalist architecture) we enjoy today would not be possible. But perhaps now is a good time to rethink how we make this critical material. Before diving in, I am grateful to Derek Popple for his research which informed this post!
Concrete and Cement Industry Basics
First, a quick note on the difference between concrete and cement. Concrete is the material you see when you look at a sidewalk or a highway overpass. It is a mixture of water, sand, aggregates (rocks), and cement. Cement is the glue that holds everything together. Concrete typically contains about 10–15% cement.
We usually don’t think much about concrete, probably because it is all around us — highways, buildings, airports, bridges, sidewalks, sewer mains, seawalls, the foundation of our homes. Concrete has many wonderful properties: it is strong, durable, fire-resistant, and above all cheap. [4] The main raw materials used to make concrete — limestone, clay, sand, gravel — are readily available all over the country (virtually every cement plant is parked next to a limestone quarry). No wonder concrete is everywhere. So how is this critical material made, and why does it produce so much CO2?
Most of the CO2 emissions associated with concrete are from cement production. To make cement, limestone (CaCO3) and clay are ground up and heated in a furnace ( specifically, a “rotary kiln”) to ~1500 degrees C. Under these conditions, the limestone (CaCO3) turns into clinker (CaO) and carbon dioxide (CO2). This process burns a lot of fuel, but also 44% of the original mass of the limestone is turned into CO2 and released to the atmosphere. This step is why CO2 emissions from cement production (and concrete production as a result) are so high.
After the CO2 intensive “clinkering” step, the clinker is mixed with other minerals to control how fast it will harden. The result is a standardized product called Portland cement. To make concrete, Portand cement is mixed with sand, aggregates, and finally water, which starts the reaction.
Reducing CO2 emissions from this process is a two-part problem. The first challenge is the high temperatures (1500 deg C) needed — it’s hard to reach temperatures this high without burning fossil fuels. (Our portfolio company Heliogen is addressing this challenge by making high temperature process heat from sunlight.) Roughly 40% of the emissions from cement production are the result of these heating requirements.
The second challenge is reducing the “process emissions”, or the CO2 released from the limestone used as a starting material. Even if all cement plants were able to use only renewable energy, we’d still have the 60% of the CO2 emissions to contend with.
Are There Better Options?
The short answer is yes, or at least they are coming. There are several companies and startups with “low carbon” cement solutions (at different levels of commercial readiness). These generally fall into one of three categories:
- Find alternatives to limestone. Start from feedstock materials that don’t release CO2, or find ways to reduce the amount of limestone needed.
- Redesign the cement kiln. Create cement kilns that are more efficient, run on electricity or renewable energy, and/or capture the CO2 coming out.
- Use concrete to sequester (permanently store) CO2. Carbon dioxide can be incorporated into cement by starting with limestone made from captured CO2, by turning it into rocks and using these as aggregate, or by injecting CO2 during the curing process.
Below are a few examples of companies with concrete solutions…
Alternatives to Limestone
Since 50–60% of the CO2 released from cement production comes from the limestone (CaCO3) used as the starting material, several companies have developed processes to make cement from other minerals that don’t release CO2, or reduce the amount of limestone needed. Solidia, TerraCO2, Brimstone Energy and Sublime Systems are each pursuing new pathways to avoid process emissions while producing high quality cement or cement-like materials. Carbicrete is working to turn a material that is currently considered waste — steel slag — into a cement alternative.
Other companies like Biomason and Fortera are drawing inspiration from seashells and coral reefs to create strong, sustainable building materials. While these may take more effort to control quality under existing ASTM standards, there are interesting sub-applications, particularly in marine environments.
Redesign Cement Kilns
Some established cement companies are redesigning traditional cement kilns to use electricity or heat that isn’t produced by non-fossil fuels, eliminating the ~40% of the CO2 emissions generated from burning fuel. For example, Australian company Calix has redesigned cement kilns to capture both the CO2 from burning fuel and the CO2 released from limestone. As part of the EU’s LEILAC program, they have partnered with Heidelberg Cement to complete a demonstration project by 2023.
Use Concrete to Sequester (Permanently Store) CO2
In total, we emit about 35 billion metric tons of CO2 globally. While it would be great to turn the CO2 we emit into products, there are very few materials that we consume on the billion metric ton scale. Cement (10 billion metric tons per year) and fuels (about 15 billion metric tons per year) are the two obvious choices, and several companies are pursuing the logical strategy of turning CO2 sources into CO2 sinks.
Over time, concrete and cement naturally absorb CO2 from the environment. CarbonCure takes advantage of this process and speeds it up by injecting CO2 into cement as it hardens, incorporating the CO2 into the cement. This brings down the carbon footprint of the cement by a small amount, roughly 1–2%. [5] Despite this incremental improvement, I give credit to CarbonCure because they offer a bolt on system that’s easy to implement and is commercially available today.
Blue Planet has developed a technology to store CO2 in the aggregate (gravel and rocks) that make up 60–75% of concrete. They convert CO2 into rocks via a mineralization process, [6] and then uses the mineralized CO2 as the aggregate in concrete. This process could store a significant amount of CO2, [7] though at considerable added cost (as one would expect if replacing natural rocks with synthetic ones).
Is “Better” Cement Viable?
Two things need to be proven for any of these companies to be viable: the unit economics and ability to scale. One of the eternal challenges of hardtech startups is the link between these two: increased production scale drives down unit costs. Without scale, new technologies remain economically infeasible.
Some of the technologies above can reach cost parity with Portland cement on paper by starting from materials that are also inexpensive (or currently considered waste) and/or reducing the heat required. The challenge is getting to the scale where those estimates are valid. If the technology requires an entirely new cement production process, or set of process steps, financing is even more of a barrier.
The scale needed to supply the “ready-mix plants” responsible for most construction projects (roughly 70% of the cement market) is daunting. These plants typically have large silos that hold limestone, clinker and other components that are refilled several times a day. Thus it is extremely hard for a cement producer to justify converting over a silo to a new material or mix. Because of this, many startups target “pre-cast” products, like tile and cinder blocks, that can be sold in small quantities.
For any of these companies or technologies to be successful, they need projects that allow them to get to scale.
If Biden’s infrastructure plan passes, will it dramatically increase global CO2 emissions? No. At the end of the day, the US is only 2% of the global cement market (and we can only build so many new cement plants per election cycle). However, it is a critical opportunity to scale new low-carbon cement technologies, especially as demand for concrete and cement continues to grow.
One idea that I think is interesting is a “CarbonStar” program, modeled after the voluntary “EnergyStar” program. The EnergyStar program was created by the US EPA back in 1992 to identify and promote energy-efficient products. [8] By creating standard tiers for concrete with a recognizable label, concrete suppliers could focus on offering concrete products with specific CO2 reduction targets relative to a 2019 baseline. Companies, business owners and state/local governments could decide which level to purchase based on their budget, ESG and branding goals.
A second type of program that could work uniquely well in the infrastructure sector is federal project grants to qualify new materials. Unlike investing in first-of-a-kind rockets or chemical plants (where the investment could literally blow up in your face), with infrastructure projects there are higher costs associated with qualification testing for the first facility but something will be built that serves the purpose (downside protection). Qualification testing results and project summaries then become tools for later projects.
A final strategy often discussed is creating federal procurement requirements around the carbon intensity of concrete. This is likely an effective way to drive incorporation of innovative lower-carbon materials, because it should effectively act as a marketplace for the bidders able to meet the specifications at the lowest cost.
As an engineer and scientist, I hope we take advantage of the opportunity to practice building things again and improve our aging infrastructure — it needs it. I also hope that we create opportunities for innovations (with sound financial models) in building materials and concrete to prove themselves.
Many thanks again to Derek Popple for his research on this topic. Derek is a PhD Candidate in chemistry at UC Berkeley with interests in sustainable chemistry, project management and consulting, and printmaking.
Comments, questions or something else exciting? Please reach out! As always any mistakes are my own, and I would welcome the opportunity to correct them.
Notes
- Infrastructure projects specifically called out in the American Jobs Act (released 3/31): proposes investment in many concrete-heavy infrastructure projects. Examples include modernize 20,000 miles of highways and roads, fixing bridges, and building Veteran’s Affairs facilities like hospitals. It remains to be seen which parts will actually make it through Congress.
- Per the USGS, the US consumed 102 million metric tonnes of cement in 2020. Concrete typically contains 10–15% cement, so we estimate that this translates to well over 600 million metric tonnes of concrete.
- Per Prof. Yet-Ming Chiang, MIT (2019)
- In the US, concrete costs on average $125 per cubic yard, or $68/tonne ($0.068/kg). Compared to the costs of lumber or steel, this is cheap!
- The fine print: at 25–40 lbs CO2 sequestered per cubic yard (equivalent 13–22 kg CO2/tonne concrete), Carbon Cure’s solution reduces the net CO2 emissions by just 1–2%. Still, 1% of 600 million tonnes of CO2 per year (6 million metric tonnes of CO2) is better than nothing.
- CO2 mineralization reactions are also used by a few CO2 capture companies (e.g. Carbon Engineering) and carbon sequestration efforts like the CarbFix project in Iceland.
- Comparing the potential of Blue Planet’s solution to the US’s annual CO2 emissions: let’s say all 600 million tonnes of concrete the US produced included 60% Blue Planet aggregate, and the aggregate contains 44% captured CO2 by weight. We would sequester 160 million tonnes of CO2, reducing CO2 emissions from the cement industry by 27% and offsetting roughly 2.8% of the US’s net CO2 emissions.
- The EnergyStar program began by labeling computers and monitors. The program eventually expanded to lighting, commercial buildings, and home appliances. (EnergyStar milestones and history)
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