With mounting pressure from end users to reduce concrete’s carbon footprint, the entire industry is responding and looking for new strategies to reduce its relatively large footprint. These strategies can include new materials, technologies and processes to minimize carbon dioxide (CO2) emissions during production or approaches to actually absorb CO2 into the material. Let’s start by discussing the source of carbon emissions in the industry, and then address some of the solutions.
Cement: an Ingredient in Concrete The majority of concrete’s carbon footprint is actually attributed to CO2 produced during cement production. Cement acts as the glue that holds concrete products together. It is a critical ingredient. The production of one tonne of cement creates up to 0.8 tonne of CO2, making the carbon intensity of cement production the biggest environmental impediment for the concrete industry. There are two main sources of CO2 emissions associated with cement production:
- Fuel combustion – required to heat the raw materials of cement to high temperatures, and
- Calcination – CO2 is released during a chemical reaction that takes place during cement production.
For chemistry buffs, here is the science behind the reaction:
• When cement is produced, the raw material (limestone) is heated to produce lime (CaO), a precursor to cement – this reaction is known as calcination and releases a molecule of CO2 CaCO3 (limestone) CaO (lime) and CO2
Cement production is ultimately responsible for about 5% of global carbon dioxide emissions. These emissions might not be a problem if there weren’t so much cement and concrete manufactured globally. According to the International Monetary Fund (IMF) database world economic outlook1, worldwide cement consumption reached a record estimated 3.6 billion tonnes in 2012. Future forecasts show that production will increase even higher owing to growing demand in developing markets. This also translates into increased demand for concrete. In fact, concrete is the world’s most widely used building material with about one tonne of concrete used per person every year.
The good news is that strategies are available to reduce the CO2 footprint of concrete masonry, grout and mortar. In fact, a recently published paper2 by Licht and colleagues in Chemical Communications entitled STEP cement: Solar Thermal Electrochemical Production of CaO without CO2 Emission3 hints of a future where cement can be produced with zero carbon emissions and therefore potentially yield carbon negative concrete products. This would be an important development for the industry and for the environment, given that cement and concrete production is on the rise.
Strategy to Reduce Carbon Intensity
Options are available today to make lower-carbon concrete products. Most of the efforts have been in developing lower-carbon cement, which in turn would yield concrete products with lower carbon footprints. The cement industry has three realistic avenues to reduce the carbon intensity (and thereby improve the sustain ability profile of concrete):
- Thermal and electrical efficiency – Deploy best available technology in new cement plants (while pursuing retrofits where economically viable) to lower the energy requirements for producing cement
- Alternative fuels – Use less carbon intensive fuels and/or alternate fuels to supply energy for cement production
- Clinker substitution – Substitute clinker (a precursor to cement) with other low carbon materials with cementitious properties, for example fly ash or slag, byproducts of coal combustion and smelting or refining of ore, respectively.
To contextualize these efforts, currently clinker substitution can help achieve LEED points since it contributes to the recycled content credit of the Materials and Resources category. Other cement and concrete industry carbon intensity levers currently do not provide additional LEED points. Luckily, recently released LEED v4 rewards environmental efforts within the cement and concrete industry by issuing points for manufacturers who provide Environmental Product Declarations (EPDs). EPDs are tools used to measure the environ mental impact of a product throughout its entire life cycle. Like nutritional labels, EPD documents communicate a building material’s environmental impact, transparently identifying ingredients and quantified data for preset categories.
Sequestering Carbon in Concrete Products
A unique idea developed by Canadian innovator CarbonCure Technologies involves taking waste CO2 collected from final emitters, like refineries, fertilizer plants, power plants, and injecting it into concrete during production. The concept is to use a new mineral carbonation technology for beneficially reusing waste CO2 in the concrete products’ manufacturing process – or simply put, recycling waste CO2 to make greener concrete. The idea of sequestering CO2 in concrete production to make concrete stronger and greener was developed from understanding earlier uses of CO2 in concrete production in the 1940s. CO2 was used then primarily to protect against freeze-thaw and efflorescence. CMU was placed in a space filled with CO2; the reaction between the two created a protective calcium carbonate coating. Today’s technology has overcome engineering challenges of early technologies and has taken the approach that economic drivers are necessary for industry to get involved in combating climate change.
This technology’s success to date can be attributed to a strong team and extensive list of industry partners. CarbonCure is not a producer, but a clean-tech company, so its ultimate goal is to work with other material and technology innovators to bring affordable low-carbon concrete products to market. Building durable partnerships with concrete products manufacturers across North America, including Shaw Group, the largest concrete products company in Atlantic Canada, that has been working with CarbonCure for the past five years, is paramount.
There are several environmental advantages to using carbon-sequestering technology in the manufacturing process. Waste CO2 is added at an early stage of production – when the materials are being mixed. The CO2 gas is an accelerated curing agent. It induces a chemical reaction whereby cement undergoes carbonation to create limestone. It is converted into a solid – calcium carbonate – within the concrete. This means that CO2, which would have otherwise become a harmful greenhouse gas, now becomes safely and permanently embedded in the concrete.
The introduction of CO2 can also create other material advantages for the manufacturer, such as higher early strength of the concrete, as a result of the carbonation process. This higher early strength can translate into lower cement and energy requirements, reduced defects (solid waste) and other manufacturing benefits. The best part is that the products, which look and act like typical CMU, don’t have a significant cost premium – low-carbon products cost about the same as regular concrete products. The products also meet all required ASTM and CSA standards. The bottom line is that products made with carbon sequestering technology are green without the environmental or material tradeoffs.
Says Don Gordon, CEO of Atlas Block, “I have been in this industry many years, and this is easily the most exciting technological improvement I’ve seen. This process will be industry-transforming!”
CarbonCure works with concrete products manufacturers to introduce its CO2-injecting technology into their plants. Currently it is working with several manufacturers to bring low-carbon concrete products to market. These forward thinking companies include Shaw Group (Eastern Canada), Atlas Block (Ontario), Northfield (Illinois) and Basalite (Northern California). CarbonCure also engages with end users to encourage adoption of green concrete in the market. Several architects, engineers and construction firms (AECs) have already specified low-carbon products for construction projects. (see sidebar) Designers are seeking sustainable products that meet all performance criteria. Some are now specifying low carbon concrete masonry across all construction projects at their firms.
Leading the Challenge in Green Building Programs
The building sector continues to push the limits on green, with the emergence of LEED v4, the Living Building Challenge and Architecture 2030. For instance, Architecture 2030 is challenging manufacturers to reduce their products’ carbon footprint by 50% by the year 2030. By combining several innovative approaches such as carbon sequestration technology, the concrete industry will be well positioned to meet the growing demand for low-carbon building materials.
Atlas Block has issued the first EPD for a CMU in North America. The CarbonCure by Atlas Block EPD covers their 20 CM Unit. Northfield an Oldcastle Company has issued the first Health Product Declaration (HPD) for a CMU for their Trendstone Sandstone unit made with CarbonCure technology. HPDs transparently communicate a products’s human health impacts, much like an EPD communicates environ mental impacts. Construction projects using at least 20 building products that have issued EPDs and/or HPDs will be awarded points under LEED v4 Materials and Resources: Building Product Disclosure and Optimization credit.
Moving forward, CarbonCure is looking for partners to help transform the built environment by manufacturing and building with low-carbon concrete wherever possible. Imagine a future where concrete absorbs more CO2 than was emitted during its production. While we aren’t there yet, we certainly are headed in the right direction. With a commitment to continued innovation, this technology is the company’s first step toward integrating and developing affordable, regenerative concrete at scale.
Robert Niven, is a cleantech entrepreneur inspired to find profitable and sustainable solutions for the cement and concrete sectors. He is part of the global race to develop affordable carbon-negative concrete at scale. As Founder and CEO of cleantech developer, CarbonCure Technologies, in 2007, Niven has earned a reputation of uncovering innovative ways to raise profits, lower greenhouse gases and improve the material performance of concrete. His passion for developing solutions that combine sustainability and innovation has led to the development of the CarbonCure technology. He holds an MSc in Environmental Engineering from McGill University and a BSc in Chemistry from the University of Victoria. firstname.lastname@example.org | 902.442.4020
Jennifer Wagner, vice president of marketing at CarbonCure Technologies, Halifax, Nova Scotia, addresses architects, engineers and developers. She has helped company licensees issue the first Environmental Product Declarations (EPD) and Health Product Declarations (HPD) in the industry. She is on the National Concrete Masonry Association’s EPD Task Force where she is helping to guide the development of an industry-wide strategy to issue EPDs. She is a Canadian Standards Association-certified GHG (greenhouse gas) inventory quantifier, LEED Green Associate and sits on the board of the Atlantic Chapter of the Canada Green Building Council. Wagner holds a BSc from McGill University, an MSc in Chemistry and an MBA in Finance and Sustainability from Dalhousie University. email@example.com | 902.442.4020