Combining strength, versatility, and economy, concrete is the foundation of modern infrastructure. It is the world’s second-most-used material next to water.
However, concrete relies on cement, a pollution-intensive component.
For every ton of cement produced, approximately a ton of CO2 is emitted. This process contributes up to 8% of global CO2 emissions annually.
The CO2 and NOx emissions associated with cement make finding an alternative to current solutions a climate imperative.
Terra CO2 products are poised to disrupt the cycle of CO2 and NOx pollution in the cement industry.
Challenge
Limestone is a carbon-intensive ingredient
The problem with Portland cement is the limestone feedstock that makes up 85% of the raw material.
A ton of limestone-rich feedstock goes into the cement kiln, but only about 2/3 leaves the kiln as cement precursor. Nearly half the weight of limestone is lost to the atmosphere as CO2. That’s unfortunate for both the atmosphere and cement economics.
This “fossil CO2” released from limestone accounts for almost two thirds of Portland cement’s CO2 emissions, with the remaining third coming from burning fuel for heat.
Solution
Terra CO2
Unlike Portland cement, which relies on carbon-intensive limestone, Terra’s technology leverages affordable, abundant, and local raw materials including silicate-based igneous rocks (such as granite, basalts), unconsolidated sediments (such as sands and gravels) and clays.
These types of raw materials are not only abundant and attractive from the mineralogy perspective, but the equipment and infrastructure to extract these rocks already exists, and sites are located everywhere that concrete is needed.
Challenge
Fly ash is going away
Fly ash, a byproduct of burning coal in power plants, is used beneficially in concrete – a better alternative to ending up in landfills. It was first used as a cheap filler, but engineers learned quickly that ash can give concrete important engineering properties, such as higher long-term strength, reduced heat of hydration, resistance to alkali-silica reaction, and more.
However, a global transition to cleaner energy sources is underway. Coal-fired power plants are closing (or switching to natural-gas and renewable energy) at a record pace, creating an unintended problem for the concrete industry.
As these materials become inaccessible and there is no viable cost-effective substitute for fly ash, more Portland cement will be used in concrete, further increasing CO2 emissions and cost and decreasing performance.
1. WHAT ALTERNATIVES CAN FILL THE FLY ASH VOID?
Fly ash has been especially useful to the concrete industry because quality ash has traditionally been available near many concrete markets at a low price. Existing alternatives to fly ash include metallurgical slags, natural pozzolans such as volcanic ash, and metakaolin. Unfortunately, existing products cannot replace fly ash at large scale due to limited supply volume, geographical constraints, and most concisely: higher delivered price.
2. ARE NEW TECHNOLOGIES AVAILABLE TO REPLACE FLY ASH?
Many new technologies are being deployed that could help address the fly ash gap. For example, CO2 injection during concrete mixing can provide extra strength (leading to 10%+ reduction in cement content). Portland Limestone Cement achieves about 10%+ reduction in cement content by partial replacement with unheated limestone.
These, and other new technologies, have their place, but the performance and environmental impact of fly ash as an SCM is arguably larger than alternatives since it routinely replaces 10-30% of Portland cement content in modern concrete, an impressive and underappreciated fact.
3. COULD WE KEEP BURNING COAL TO MAKE FLY ASH?
Yes, but we shouldn’t. “Manufacturing” a ton of fly ash requires burning about 14 tons of coal, which causes 31 tons of CO2 emissions1!
The value of electricity produced by burning coal is worth several times more than the ash produced (supposing it is suitable quality for concrete), so the fly ash is traditionally considered a by-product.
It may be more useful to think of fly ash as a co-product of coal energy because fly ash has become a market commodity in its own right with distributors, resellers, and a formerly robust supply chain. The concrete industry demand for fly ash has never been higher, yet supply is dwindling. Our response to this problem is the development of OPUS SCMTM: a “synthetic fly ash” that can be produced locally without burning coal.
1 Calculation assumes: i) a coal ash content of 9% (typical of bituminous and subbituminous coal, the most frequently used coal in the US), ii) the use of a furnace (dry bottom) that produces the highest percentage of fly ash (80%), iii) carbon emission estimate for burning 1 ton of bituminous and subbituminous coal: 2.21 ton CO2/ton coal.
Solution
Terra CO2
Terra CO2 first mills raw materials and then our proprietary, patent-protected, low-carbon and low NOx reactor vitrifies them into a glassy powder. This produces a supplementary cementitious material (OPUS SCMTM) that looks and performs like traditional Type F fly ash, and is suitable for replacing cement in concrete products. Because the materials we use are the most abundant rock materials on Earth’s surface, we eliminate the supply problem currently faced by fly ash.
Challenge
Transportation across markets
With the fly ash shortages in many markets, what is left is being transported across great distances across North America – distances that are only poised to grow. Because existing Portland cement and fly ash sources are centralized for production, haul distances over 100 miles can be common.
Solution
Terra CO2
Our plants are located on or near our partners’ operation sites, found broadly across large urban centers, reducing transportation costs and leveraging existing infrastructure. This eliminates the need to permit new mines for sourcing raw materials and the expense of transporting raw materials across long distances.
Environmental Bulletins
Concrete's CO2 Problem: Cement
DownloadTo the future of cement
From source to deployment, Terra is catalyzing full-system changes in concrete production, not just incremental improvements over existing processes and technologies.