Solution 2: Decarbonizing Concrete

💡 This blog is meant to assimilate all my readings and solve the crisis of articulation. Each post will address one technology, theory or idea that reduces climate change. It's important to note that all of these solutions need to work in tandem to actually solve the crisis. The blogs will be brief but should provide the opportunity to dive deeper. There may be some gaps in my writing so please validate my musings with external sources. Occasionally, we may have some actual experts and climate tech pioneers who will be writing guest blogs! Please feel free to comment below or reach out.

For my second (and abysmally delayed) deep dive, we're going to be talking about the most used material after water - cement. Since this topic has more than meets the eye, I decided to interview a couple of experts from the Center of Science and Environment, New Delhi: Parth Kumar (Programme Manager) and Manas Agarwal (Research Associate). They have authored the discursive report called "Decarbonizing Cement in India" (from which I base most of my writing on).

The Problem

Concrete production alone accounts for 8% of global CO₂ emissions. This is significant, considering it racks up along with broad categories of emissions (see below).

Share of Global CO2 emissions by sector. Source: McKinsey

For every ton of cement produced (to make the concrete), a ton of CO2 is released into the atmosphere. That means, with the 4.4 billion tonnes of cement produced globally last year, 4.4 billion tonnes of Co2 were released.

In context of India - we’re the second largest producer of cement after China and our production capacity has nearly tripled in 15 years from 209 million tonnes in 2008 to 600 million tonnes in 2023. Ultratech, ACC (subsidiary of Ambuja), and Ambuja are the top 3 companies in this sector.

Adding more gloom to the story, we will face abhorrent degradation of concrete structures in the 21st century due to the deviation in durability of concrete across regions. This means most of the concrete in the world will need to be replaced in the next few decades, leaving aside the concrete required to build underdeveloped and developing countries.

How is concrete currently made?

Cement is an essential ingredient to concrete. It acts as the glue (binder) which holds water, and a mix of crushed stone and sand together. 

Concrete = Cement + Water + Crushed Stone & Sand

What exactly is cement then? It is a powdery substance made from a mixture of limestone, clay, and other minerals. There are different stages to how it’s produced, which is essential to know for understanding why it emits so much CO2. 

• First, limestone, clay and other minerals are mined using heavy-duty machinery. 

• After each raw material is crushed individually, they are blended according to a formula which makes limestone the majority in the composition. 

• Now comes the culprit - the blend is passed into a large furnace (kiln) to produce clinker (the main component of cement which allows it to harden when coming in contact with water, resulting in concrete). To produce clinker you need to convert limestone (calcium carbonate) to lime (calcium oxide), in a process called calcination which takes place in the kiln. This kiln is at a towering temperature of 1450*C enabling the calcination process to take place to produce. Double trouble - carbon dioxide is released to heat the kiln and released as a waste product during the conversion. 

• At last, the clinker material is ground and shipped as a powder to be utilized in construction. 

Now let’s look at the breakdown of the sources of CO2 emissions from cement production processes visually. 

Share of Global CO2 emissions by sector. Source: McKinsey

Clearly the Kiln and precalcinator are the highest producers of CO2. 

Solutions

We can approach decarbonizing cement production from various sources and perspectives. This can be divided into three categories: Material Substitution, Electrification, and CCUS. 

Alternative Product Mix and Material Substitution

Something that we did not hit on earlier is the different types of cement in regard to their ingredient mix. Pozzolana Portland Cement (PPC) is the most commonly produced cement in India, whereas Ordinary Portland Cement (OPC) is the most produced in the world. The difference? OPC has 95% clinker. PPC has fly ash (31%) and less clinker (64%). 

These variations in product mixes mean variation in CO2 released. As a rule of thumb, the less clinker the better (as less CO2 will be released during clinker production).

In regards to this, Portland Slag Cement (PSC) and Composite Cement (CC) are the best variations of cement to produce as they release the least amount of CO2 per ton produced. Here is a table from the report which makes it easy to understand.

Different Cement Blends. Source: CSE India

Short Glossary:

• Fly ash: powder which is a by-product of burning coal. Sourced from coal power plants.

• Slag: stone-like by-product of smelting ores. Sourced from steel plants.

• Gypsum: is a mined mineral made of calcium sulfate dihydrate, which is used in fertilizers, drywalls and chalk mainly. 

While conversing with Parth and Manas, they regarded switching to blended cement as the fastest way to marginally reduce CO2 emissions in India. This can be easily done if regulations are brought on by the government. The main challenges faced with this: the mandatory modifications to production processes by the cement plants and procurement of fly-ash (no government portal made to solve the procurement issue).

In regard to material substitution of cement, there are some visionary start-ups:

• Brimstone: developed a process to produce carbon-negative ordinary Portland cement - carbon-free calcium silicate rock as the raw material instead of limestone

• CemVision AB -  startup that has developed a process to produce near-zero emission cement by utilizing industrial residual products instead of virgin limestone
  

💡 As a comical honorable mention (suggested by a friend studying architecture in a Yale classroom): Hempcrete - A high performance, lightweight, carbon-negative building material made from hemp hurds that insulates and absorbs CO2 from the atmosphere. However, it does not have the same compression strength as cement.

Hempcrete. Source: UW Madison

Electrification and Alternative Fuels

As mentioned before, the Kiln needs to be really hot (1450 degrees Celsius) for calcination to take place. Kiln is powered by thermal energy - coal or petroleum. Thus, we need to either electrify the kiln or use alternative fuels to decarbonize this production process.

Heftier challenge is electrification as it requires a complete innovation of more than a century old technology. Only one company - Coolbrook - has been able to solve it.  It is a startup that has developed a novel industrial electrification technology  - their patented RotoDynamic Reactor utilizes green electricity and is a direct replacement to the thermal power kiln. However, they're still in the early stages and have not reached commercial viability yet.  A glimmer of optimism: Ultratech has signed an agreement with Coolbrook to jointly explore the use of Coolbrook’s Roto Dynamic Heater (RDH) in India for the future.

Illustration of Coolbrook's Electric Kiln Source: Coolbrook

A more doable solution to reducing thermal carbon emissions is using Refuse Derived Fuel (RDF) and biomass as alternative fuels for kilns. All types of industrial waste can be used to make RDF. This is more formally called the Thermal Substitution Rate (TSR). In fact, all companies in India have at least 5% TSR rate in their plants, with some reaching up to 10-13%. This is a main component of the report by CSE written by Parth and Manas. They predict if the government introduces a minimum TSR regulation of 50%, the emissions would halve by 2030 with the same level of production. They also label this challenge of circularity as the main source of start-up opportunity.

Carbon Capture, Utilization and Storage (CCUS)

This solution is pretty straightforward, capturing the carbon from its release points in the production process. There already exists a slew of huge carbon capture machines that can be installed on the exhausts of factories. However, these are expensive and not efficient (Aker Carbon Capture is a great company, which has a viable solution for this). Instead, we need a carbon capture solution that is embedded into the cement production process that reduces the marginal costs to keep up the cheap economics of cement production. 

Parth and Manas state that CCUS is currently inefficient and too expensive for India. Additionally, the lack of viable uses for the captured CO2 makes it commercially unfeasible.

Leilac and CarbonCure are both visionary companies that have developed carbon-capture technologies specifically for this field. They both capture CO2, and repurpose it to directly or in-directly be used in cement production.

Carbon Capture Technology by Carbon Cure. Source: CarbonCure

Moving Forward

A combination of the aforementioned solutions must work in concert to make a significant impact on decarbonization. As highlighted by Parth and Manas, the government is not enforcing regulations vigorously enough in the cement sector and they need to do more. They also propose a valuable idea: incentivizing low-carbon cement by reducing GST on it compared to the standard rate.

Hopefully, these solutions will not remain theoretical, and all stakeholders will take action before it’s too late.

I’d like to thank Parth and Manas for generously providing their time for an interview. Their report, "Decarbonizing Cement in India," delves deeply into the subject and outlines clear pathways for decarbonizing this sector.

Link to all sources and references used in the post