All About Concrete: The History, Data and Details

The Wonder of Concrete, Starting 2,000 Years Ago!

Concrete has, by some accounts, done more for humanity that almost any other material ever invented. It is the foundation of modern development, putting roofs over the heads of billions, fortifying our defenses against natural disaster and providing a structure for healthcare, education, transport, energy and industry. And, it's been around since the dawn of human civilization. (source)

Thousands of years ago, Egyptian people burned limestone to make lime, which they then mixed with clay to create mortar, a precursor to cement. They used this mortar to build the pyramids. Later, the Romans combined lime with volcanic ash from Mr. Vesuvius and sand (along with animal fat, milk, and blood) to make an early version of Concrete. They used this concrete to build the Appian Way, Roman baths, the Coliseum and Pantheon in Rome, and the Pont du Gard aqueduct in south France. The volcanic ash made their concrete so strong that many of their buildings, bridges, and roads still exist today, 2,000 years after they were built! (source)

In 1824, Joseph Aspdin of England invented portland cement by burning finely ground chalk with finely divided clay in a lime kiln at 2,500°F until carbon dioxide was driven off. He called it portland cement after the high quality building stones quarried at Portland, England. 

The invention of reinforced concrete gave the material a new life. It was pioneered in France in the mid-19th century, but was popularized by a California-based engineer named Ernest Ransome, who poured it over iron (and later steel) bars to improve its tensile (side-to-side) strength. (source)

What makes concrete so useful?

• Concrete has a very high compression strength -- it can support the weight of a whole building. We put rebar in it to make up for it's relatively weak tensile strength (side-to-side), making it a strong, affordable and easy-to-use material for all modern construction. 

• Concrete has a quick set time, meaning when you can pour it, it will set quickly so you can build faster. Since 90% of the cost of concrete construction is labor, having a quick set time is critical to keeping costs down.

• Concrete is easy to work with - it can be mixed, transported and placed into its final position with ease. A high degree of workability is essential for achieving the desired shape and finish of the concrete.

• Concrete can be made aesthetically pleasing. It can be stamped, textured, colored, even molded into artwork, making it both beautiful and practical. 

• Concrete is fire-resistant, doesn't burn, and increases the safety of building inhabitants. It is an inert material, so it doesn't give off gases, attract mildew or feed rot.

• Concrete is strong and durable almost immediately, so it's an obvious choice for almost any construction job. 

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The Scale and Problems of Traditional Concrete

Concrete is everywhere. 

Look around and you'll see concrete in sidewalks, driveways, foundations, patios, bridges, parking lots, water channels, retaining walls, high-rise buildings,, dams, sewer systems, pools, playgrounds, and much more. 

• Concrete is the most massively produced material in the world, by volume. (source)

• Concrete is the second most consumed material in the world, 2nd only to water. (source)

• Worldwide, 30 billion tons of concrete is used each year. On a per capita basis, that is 3 times as much as 40 years ago — and the demand for concrete is growing more steeply than that for steel or wood. (source)

• Global annual production of concrete is forecast to grow from 14 billion m3 (cubic meters) today to 20 billion m3 by mid-century, as human societies urbanize and demand for infrastructure grows.  (source)

However, concrete and cement have a huge carbon emissions problem.

The key problem, from a climate change perspective, is the carbon emissions from the production of cement, which is the binding agent and main ingredient in concrete.

• On a per-dollar basis, concrete generates more emissions than any other product we manufacture at scale. (source)

• The production of cement accounts for 6-8% of global CO2 greenhouse gas emissions. That's larger than aviation, shipping, or deforestation. (source)

• Producing 1 metric ton of cement releases about 1 ton of CO2 emissions. (source)

• If the cement industry were a country, it would be the third largest carbon dioxide emitter in the world with up to 2.8 billion tons, surpassed only by China and the US. (source)

• CO2 emissions from concrete will soar from 2.8 billion tons to 3.8 billion tons per year, in the next 20 years. (source)

• The cement manufacturing process starts with the extraction of raw materials – mainly limestone, which gets transformed into clinker in a rotary kiln heated up to 2,600°F. Clinker, which represents almost 95% of cement’s composition, is responsible for 88% of its overall emissions, related both to the energy input for heating (35%) and the CO2 chemically separated from the crushed limestone (53%).  (source)

And cement is a very "hard-to-abate" sector.

• Unlike other sectors, where the largest share of emissions is energy-related, in cement and concrete production, more than half are process emissions, requiring either novel solutions to a millennia-old industry, or strong reliance on carbon capture.  (source)

• Moreover, it’s a complex “value chain” with multiple causes of emissions all along the way from getting the limestone to delivering it to customers. And since cement plants tend to generate a lot of local pollution, communities attempt to shut them down, requiring cement to be transported from other places, further increasing the total emissions. (source)

• Cement is cheap (<$125/ton) which means a replacement would need to be extremely cost effective, and that's difficult for new technologies to achieve quickly, especially since cement has many unique properties.

• Most of cement’s emissions are created because of chemical reactions needed to make cement.

• We have centuries of construction experience with Portland Cement, which is the most widely used type of cement. Strict building codes often mandate the use of Portland Cement and specify concrete composition or performance standards, which heavily favor traditional practices. 

The Science and Chemistry of Cement and Concrete

The basic steps of making concrete and associated carbon emissions:

1. Mine and Grind Limestone: Limestone, or calcium carbonate, are mined from quarries and then crushed in to a powder called raw meal. CO2  emitting fossil fuels are used in the machinery at the quarry and production facilities.

2. Convert Raw Meal into Clinker: Raw Meal is burned to make lime, which is then heated in a kiln to 2,600°F to make clinker with silicate additives. This step produces the most CO2 from the fossil fuels used to heat the raw materials to the CO2 driven out of the materials by chemical reaction.

3. Turn Clinker into Portland Cement: After cooling, the clinker is combined with gypsum and ground into Portland Cement. CO2  emitting fossil fuels are used in the production process.

4. Distributing Cement: Cement is then shipped all over the world to concrete suppliers who mix it with water, aggregate and sand to make concrete (10% cement, 90% aggregate and sand).

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Deep dive into the chemistry:

• • Summary: The overall process leading to Portland cement involves the calcination of limestone, the reaction of the produced calcium oxide with other materials to form clinker, and finally, the grinding of clinker into cement. Here’s the steps:

  • Put limestone rocks into a long rotating kiln, at a 5 degree angle, and they tumble to the other end which is very very hot: around 2,600OF. 

  • As this happens there are two basic chemical reactions:

    • Conversion of limestone (calcium carbonate) into calcium oxide (quicklime) and carbon dioxide (greenhouse gas). Like this:
      CaCO3 → CaO + CO2

      • Note: limestone is CaO3, which is calcium bound to CO2. So it’s chemically inert and can’t react with anything. But, when you heat it up to 2,600OF, it releases CO2 into the air. 

      • Once the CO2 is released, you’re left with calcium oxide CaO which then goes into the second phase of production, second chemical reaction, as it tumbles down the kiln: 

    • The calcium oxide (CaO) reacts with added silicates (clay or shale) to make “clinker.” So, it reacts with stuff in clay or shale: silicon dioxide (SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), and other minor components present in the raw materials. Like this:
      CaO+SiO2,Al2O3,Fe2O3, etc.→Clinker

      • During this step, the most important phase of reaction is called tricalcium silicate, or 3CaO⋅SiO2, often abbreviated as C3S. This phase is responsible for the early strength development of Portland cement. It’s why you can pour it and it will set quickly and very strong

      • The clinker is then grinded into a fine powder to make Portland cement. A little gypsum is added to control set time.

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Sustainability in Concrete is Taking Off

The concrete industry has long recognized that it has a carbon emissions problem and has committed to fixing it by 2050. Here are the current top 4 paths to decarbonizing concrete, and a bonus 5th alternative:

1. Replacing Limestone
   The fossil fuels used to heat limestone to produce clinker (the key ingredient in cement) accounts for 50% of the emissions in cement production. Several companies are using alternative chemistries and processes to replace limestone. 

2. Cut Down on Clinker with SCMs
   90% of emissions in cement come from clinker, from both the heating of limestone and the chemical reaction to make clinker. Replacing some clinker with supplementary cementitious materials (SCMs) that are less carbon intensive can reduce CO2 by up to 40% compared with traditional cement.

3. Fuel Switching and Electrification
   The fuels used to make concrete are half the problem. Partially heating up the kiln used to make clinker with decarbonized eletricity source and replacing fossil fuels with low-carbon fuel alternatives for the remaining part can help phase out coal.

4. Capturing and Injecting Carbon
   Point-source carbon capture, where CO2 is trapped and stored to prevent it from being released into the atmosphere, is a key method for cutting emissions. Carbon can be injected into concrete during the production process where it's stored forever.

5. Replacing Concrete All Together (source)
   Many companies are working on low-carbon or no-carbon replacements for concrete. These include Hempcrete, self-healing concrete, ashcrete, fiber cement, Ferrock, and bamboo concrete. 

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Who's Who in Low-Carbon Concrete: Companies & Start-ups

As more and more companies explore solutions to the concrete CO2 problem, there are key considerations that must be taken into account. The solution has to be as strong and fast setting as traditional concrete. Moreover, the most efficient (lowest energy) solution will win, so it has to use less energy than other solutions. Finally, low-carbon concrete can't be more expensive than traditional concrete as it scales up. 

Some of the key companies making progress in low-carbon or zero-carbon concrete:

• Blue Planet System's mineralization technology captures and permanently sequesters CO2 into aggregate, the largest component of concrete.

• Brimstone has developed a new process to make industry-standard cement using basalt and other calcium-bearing silicate rocks, in lieu of limestone.

• CarbonCure Technologies creates technologies that introduce captured CO₂ into fresh concrete to reduce its carbon footprint, without compromising performance.

• Cemvision has begun piloting the production of fossil-free cement made entirely from recycled materials.

• CoolBrook, SaltX and Rondo Energy have all developed electric or thermal-based alternatives to fossil-based kilns and calciners – a stage that preheats limestone before entering the kiln.

• Ecocem recently received a European Technical Assessment for their groundbreaking ACT technology—low carbon cement technology that combines SCMs with limestone filler and novel admixtures. 

• Fortera uses a mineralization process to capture carbon dioxide from existing Portland cement facilities and dissolves them in a proprietary solvent. The end result is a form of calcium carbonate called vaterite.

• Minus Materials’ cultivated algae produces renewable limestone that performs the same as traditional limestone, but without the embodied carbon. When heated, it only releases carbon dioxide that was previously sequestered from the atmosphere during the algae’s lifetime.

• Sublime Systems uses an electrochemical process that can turn non-carbonate rocks and industrial waste (that don’t release CO₂) into cement at ambient temperature — eliminating the need for fossil fuels entirely.

• Synhelion – in collaboration with Cemex – and Heliogen are testing the use of concentrated solar to achieve the high temperatures required to heath the kilns.

• Terra CO2 Technologies is developing a ​“supplementary cementing material” (SCM) made from the world’s most abundant and commonly used minerals.

Who's Who in Low-Carbon Concrete: Associations & Nonprofits

The concrete industry is taking climate change seriously. However, it won't be easy to transform this 2,000 year old technology with policies, business models and behavior set in stone, so to speak. There are several important associations and nonprofits that are working to helping us get there:

• American Concrete Institute encourages and establishes criteria related to enhancing the sustainability of the built environment.

• Concrete Advancement Foundation builds a better world by funding projects that advance decarbonization, resilient and affordable communities, and world-class sustainable infrastructure.

• Concrete Sustainability Council develops a global responsible sourcing certification system, to help the concrete industry operate in a environmentally, socially and economically responsible way.

• Global Cement and Concrete Association (GCCA) is committed to building a bright, resilient and sustainable concrete future for our industry and for the world.

• Portland Cement Association is working with cement and concrete manufacturers on innovating new processes and products to meet the industry goal of carbon neutrality by 2050.

• World Cement Association supports a sustainable cement industry, encouraging technical development and innovation by its members to achieve full decarbonisation, in line with the UN’s Sustainable Development Goals and the 2015 Paris Agreement.

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