Environmental Product Declarations can help measure the use of embodied and operational carbon used in the construction of tunnels such as tunnel segments used at the SR-99 tunnel in Seattle, WA. Photo by Catherine Bassetti.
By Philip Matisak
An Environmental Product Declaration (EPD) is a tool for assessing the environmental impact of building products. EPDs publish environmental effects of building products that may be an influencing factor on ozone depletion, acidification, freshwater usage, and global warming potential (GWP, also known as CO2 equivalent).
There are many challenges in today’s tunnel construction industry, including an increased demand from the market for products that:
- Consume fewer valuable resources.
- Install faster, last longer, and will protect the environment.
- Have the potential to reduce impact on human health.
- Consume less energy during their use.
- Are reusable, recyclable and can be repurposed at the end of their life.
Ultimately, the industry is looking for products that are lower in embodied carbon and reduce the structure’s carbon footprint.
What is embodied carbon? To answer this question, we need to understand the total carbon equation:
Total carbon (TC) = Embodied carbon (EC) + Operational carbon (OC)
There are two types of carbon emissions in the built environment: embodied carbon and operational carbon. Embodied carbon is the carbon dioxide (CO2) that is emitted during the extraction of raw materials or carbon dioxide that is emitted during the transportation of those raw materials to a manufacturing site, as well as the manufacture of those raw materials into a building product or material. Embodied carbon also encompasses the carbon dioxide that is emitted during the installation and the deconstruction of that building material. On the other side of the carbon emissions equation is operational carbon. Operational carbon encompasses all the emissions during the in-use operation of a building or structure. Operational carbon reduction, common for decades, may focus on more efficient lighting, heating and air conditioning system, and more efficient insulation as ways to reduce carbon emissions.
Embodied carbon is everything until the point that the structure has been put in place and the building’s life has been turned on. Once the building product is made, and in place, all the embodied carbon emissions have taken place, and further reduction of those emissions is impossible. So, if it is possible to reduce the emissions from that product during the extraction, transportation phase or manufacturing phase, the overall carbon footprint of the product can be lowered, and the overall embodied carbon footprint of the building or structure that the product is being used in will be lowered as well.
What are the driving forces behind reducing embodied carbon? Influencers to the market such as the architects, engineers, owner-developers and many of the large owner-developers continue to push the conversation toward lower embodied carbon products in buildings and structures. These are market influencers like Lendlease, Apple, Facebook/Meta, Amazon and others, who have been pursuing green building for many years. Additionally, the federal government has been pushing for lower embodied carbon products in all federal infrastructure purchases. Last year, the U.S. General Services Administration (GSA), the largest purchasing group in the world, put into place embodied carbon targets for concrete on all U.S. federal projects. The GWP limits for concrete are based on compressive strength and application for specific federal projects that contain, at least, 10 yd³ of concrete, and an EPD submittal for the concrete is mandatory.
This is not just in the United States. Canada has a similar provision, and the Canadian Treasury Board Secretariat has issued embodied carbon standards for federal projects budgeted at C$10 million, using a minimum of 100 m3 of concrete. The standards involve GWP targets for ready-mix concrete and EPD submittal for federal infrastructure projects. However, some other groups and agencies in the United States and Canada are using carbon dioxide targets for concrete, including various municipalities, states and other federal groups, such as the U.S. Federal Highway Administration.
What is so special about concrete? Why are all these influencers and federal agencies looking to lower the embodied carbon of concrete? One must consider concrete’s place in the built environment. Concrete is the most used human-made material in the world and since 1980, its use has increased over five-fold. The benefits of concrete include durability, strength and ease of processing and placement. It can be produced in almost unlimited quantities, and it can be produced anywhere in the world. This year approximately 2 m³ of concrete will be produced for every human on the planet; with that volume, one can easily see why reducing the embodied carbon of concrete is so essential to attaining various emission goals around the world.
Understanding the ingredients that make up the volume of a standard concrete mixture. Approximately 70 to 75 percent is aggregates: the sand and stone that make up the bulk of concrete. Concrete also contains water, approximately 10 percent, and about 7 percent air and concrete admixtures, which is potentially 1 percent or less, and 10 percent cement.
In contrast, when we look at the embodied carbon of those ingredients that make concrete, we see a completely different picture. When looking at the embodied carbon associated with the aggregates, we see a much smaller make-up of approximately 7 percent. So, in terms of volume, the aggregates make up 70 to 75 percent of the mixture, and in terms of embodied carbon, they are approximately 7 percent of the mixture. In looking at concrete admixtures, they are still 1 percent or less, water is approximately 4 percent, air is zero, and cement is anywhere between 80 and 90 percent of the CO2 emissions of a concrete mixture. Therefore, controlling cement emissions is a very effective way of reducing the carbon footprint of concrete. Cement has high emissions due to the process by which the cement is manufactured. There is a tremendous amount of energy and processing emissions that are involved in creating the cement clinker, and then grinding that clinker, to make portland cement.
Are there any solutions to reduce the carbon footprint of cement and concrete? The answer to this question is Yes. There is a focus in two areas. The first is to reduce carbon emissions associated with the production of portland cement. Cement producers are diligently working on solutions, some of these include:
- Use of lower carbon footprint fuels–we are seeing a transition from coal to natural gas in cement production. In the United States, less than 5 percent of the kilns used natural gas in 2000 and today that number is more than 25 percent.
- Reducing the clinker-to-cement ratio–another option is to produce more cement blends. These portland-limestone blends take limestone and gypsum and blend them with the finished cement to provide lower embodied carbon options. These cement blends are known as Type 1L in the United States and Type GUL in Canada.
- CCUS–deploying innovative carbon capture, use and storage technologies, especially at the point of the clinker production, provides the greatest impact in CO2 reduction. These are highly complex and expensive systems to implement, but many cement producers are working on these right now.
The second area of focus is concrete production. Today, we have many options that can reduce the CO2 in concrete by as much as 80 percent.
- Concrete producers are also focusing on carbon emissions; many are focusing on the delivery of their concrete. They are switching to lower carbon footprint fuels in ready-mix trucks. Producers are also looking at raw material sources and looking to get more local sources for stone and sand and to reduce the amount of transportation emissions associated with concrete.
- Producers are also focusing on using recycled aggregates, which have a lower carbon footprint and divert material from the waste stream.
- Increased use of supplementary cementitious materials (SCM) – the use of SCM is gaining in popularity. Slag, fly ash, silica fume and others provide the ability to reduce the cement content of the mix and lower the embodied carbon of the concrete.
- Increased use of strength-enhancing admixtures (SEAs) – the newest push is to use SEAs, which provide the ability to reduce cement content, and increase the supplementary cementitious materials even further, without sacrificing strength, durability or workability.
- Water-reducing performance enhancers, superplasticizers, are great tools for reducing embodied carbon in concrete. It has long been known that lowering the amount of water in concrete increases the strength of the mixture, and with the increase in strength you can lower the amount of cement, which also reduces the overall carbon footprint of the product.
Concrete admixtures play an ever-increasing and important role in the sustainability of concrete by allowing the use of greater amounts of SCMs and lowering the amount of cement while maintaining strength, durability and performance.
How do we quantify all of these benefits? The best way to quantify these benefits and validate the carbon footprint of concrete is using an an EPD. The EPD is a multipage, third-party verified document that provides material transparency and shows the carbon footprint of a product. As mentioned earlier, the EPD is like a nutrition label, instead of listing calories, fat, carbohydrates and so on, the EPD lists environmental factors such as GWP, ozone depletion, acidification, net freshwater and so on.
EPDs are documents provided by the manufacturer as an assessment of the environmental impact of the specific product. This includes emission assessments of everything from mining and extraction to transport, to manufacturing processes.
EPDs are becoming more mainstream as institutions push for supply-chain transparency and environmental accountability among manufacturers. The EPD process is backed by the rigor of the International Organization for Standardization (ISO), and before creating an EPD specific elements must first be in place. These elements include a set of guidelines, the completion of an analysis, and the formal document for communicating results. The guidelines are the product category rules (PCR) (ISO 14025), which are the requirements for developing an EPD. The PCR is created by a program operator, and that program operator is typically a standard governing body such as the American Society for Testing and Materials (ASTM), National Sanitation Foundation (NSF) or Underwriters Laboratories (UL).
Once the guidelines are available, a lifecycle assessment (LCA) can be completed to generate the potential environmental impacts following ISO 14040 guidelines. The LCA results are then used to create the communication document, also known as the EPD (ISO 14025). Within the formal process, the LCA will need to be validated for compliance with the PCR and the final EPD will need to be reviewed and registered with the program operator.
Verification is via an independent third-party verifier that is approved by the program operator and the final EPD can then be used to communicate the potential environmental impacts associated with the product.
An interesting thing about the EPD is that the resulting document lists several environmental impacts; however, the impact that most people focus on is the GWP impact, which is stated as kilograms of CO2 equivalent (CO2e). EPDs publish impacts and material ingredients, but they do not publish mixture proportions or mixture designs.
Value and limitations
There is great value in being able to provide EPDs for your product in the market:
- Environmental transparency of these public documents that anyone can view.
- Standardized method for reporting that the value chain understands.
- Mechanism to prevent greenwashing — Greenwashing is the act of stating your product has environmental benefits, such as low embodied carbon, without proof.
- Differentiation of products by concrete manufacturers — showcasing capabilities to win more business.
Additionally, there are some interesting limitations to using EPDs:
- EPDs do not provide a comparison in the results. There is no way of understanding if the result is good or bad, it is just a result.
- There is a time consideration and a cost to producing EPDs — in gathering data, going through the lifecycle assessment, getting a third-party verification, and with that time, comes cost. There is the cost of gathering all that information, dealing with third-party providers, and dealing with potential consultants or software programs.
- Other limitations include the fact that the results, initially, are difficult to understand and interpret. However, once the format is familiar, the results are easily and quickly understood.
- EPDs focus on only one of the pillars of sustainability, GWP, which is the only measurement that gets attention and is measured as the kilograms of CO2 equivalent (CO2e) of the product.
How are concrete producers using EPDs to help lower the GWP of their mixtures? While difficult to improve what cannot be measured, many producers are using EPD generation software systems that allow the ability to measure the GWP of the concrete mixture before it is batched. The software allows the concrete producer to enter in a mix design, and in a few clicks, they can see the GWP of that concrete mixture. At that point, the concrete producer can choose to move forward with that concrete mix design or can rework the design and optimize for carbon reduction.
What can EPDs do for you as an engineer, specifier, constructor or supplier in the tunneling industry? EPDs can help you market your business. EPDs can be used as marketing tools, and many companies are using these documents to help them market their business and showcase their capabilities to an ever-growing list of customers — customers that are looking for lower embodied carbon structures, tunnels, mines, and so on. Many companies are finding out that as they work to optimize their mixtures for carbon reduction, they are reducing the cement in their mixtures, extending their cement supplies, and decreasing overall costs. What the industry is learning is that these low-carbon mixtures are saving money, and as a result, are more profitable after going through the EPD exercise.
How long does it take to get set up to do EPDs? The typical time commitment can be as little as 8–10 weeks or as long as many months. The amount of time is highly dependent on the data collection process, the lifecycle assessment (LCA) creation, and the third-party verification. Many concrete producers are opting to use EPD generation software products that can generate EPDs “on-demand” and publish documents in as little as 30 seconds once the producer’s data has gone through the third-party verification process.
Additionally, the cost of doing EPDs has come down over the past few years as these self-service EPD generation software systems have become more mainstream and third-party verification costs have decreased. However, some manufacturers may find it beneficial to partner with EPD-generation specialists (consultants) that take on the role of data collection, lifecycle assessment creation, EPD creation and third-party verification submission. The additional services can cost a bit more; however, these third-party specialists act as project managers and can ensure that the process runs smoothly and efficiently with minimal time delay.
Are EPDs right for your business? Only you can answer that question. However, by making measurable sustainable choices, engineers, contractors, concrete producers and manufacturers are reducing costs, increasing efficiencies, and providing solutions that minimize the carbon footprint, decrease resource consumption, and reduce waste.