{Ginny} Introducing our guest blogger, Marcus Griswold. Marcus has over 15 years experience working at the interface between the public and sustainability initiatives. He’s spent a large portion of his time helping stakeholders understand, develop and interpret sustainability initiatives. He has experience in climate change and sustainability at the local, state, and federal government levels. You can find out more about him at: www.littlegreenmyths.com.
Concrete is the most popular and commonly used building material worldwide. We use 35 billion tons a year and will use more than 90 billion tons in the next 20 years. In fact, it’s the second most commonly used material after water!
Table of Contents
Environmental Challenges to Concrete
The production of conventional concrete poses several environmental challenges:
- Resource Depletion and Habitat Destruction: The mining of essential aggregates used to make concrete like sand and stone disrupts ecosystems and depletes finite natural resources. This extraction process often leads to habitat loss, soil erosion, and water contamination.
- Waste Generation: The concrete industry generates staggering amounts of waste, exceeding 2 billion tons annually. This figure is predicted to surge to 3.4 billion tons by 2050. In Europe, construction waste, largely composed of concrete, accounts for 450-500 million tons each year. In the US, concrete can constitute up to 85% of construction waste. This massive waste stream burdens landfills and contributes to environmental pollution.
- Climate Change Contribution: The construction sector, with concrete as a major component, is responsible for 37% of global emissions. Concrete production alone accounts for 8% of total global emissions, releasing approximately 2.8 billion tons of CO2 annually. Cement production, the key ingredient in concrete, is the primary culprit, responsible for 90% of concrete’s emissions. The energy-intensive heating of kilns, reaching temperatures over 1,400 degrees Celsius, contributes significantly to these emissions. Transportation and processing of cement further exacerbate the environmental impact.
What is Green Concrete?
Finding a green concrete solution could substantially reduce the environmental impacts. Green concrete includes an array of products from utilizing recycled materials like fly ash and blast-furnace slag to the use of bio-material alternatives like concrete made from bacteria or algae. The hospitality industry and data center industry are making efforts to design buildings that not only reduce carbon emissions, but suck the carbon from the atmosphere.
Benefits of Green Concrete
There is not yet one type of green concrete that has been able to replace what we already use. The benefits of transitioning to alternatives includes:
- Reduced Carbon Emissions: With a far lower CO₂ output, it reduces the overall environmental impact of construction.
- Energy Efficiency: Fewer high-temperature processes are required, conserving energy.
- Resource Conservation: Using recycled concrete and natural alternatives we can reduce impacts on the environment caused by mining and air pollution from concrete manufacturing.
- Reduced Landfill Waste: When concrete is recycled, we can reduce the amount of waste sent to landfills.
- Water Conservation: Uses less water than traditional cement, supporting sustainable production.
- Environmental Certifications and Standards: Helps projects earn certifications like LEED and supports compliance with global green building standards.
Types of Green Concrete and Alternatives
Recycled Concrete
Believe it or not, concrete is recyclable. It’s not as straightforward as tossing an aluminum can into the blue bin. But, when it comes to reducing waste, reuse and recycling of concrete is the best way to reduce our impact on the environment.
Most concrete waste comes from demolition rather than construction. When a structure is demolished, all kinds of building materials will remain in the rubble, ranging from wood and steel to concrete.
The majority of the time this demolition waste is hauled away to a landfill. But, recycling is cheaper and more ecological than trucking rubble to a landfill. Reusing demolished concrete as recycled concrete aggregate can save around 40% compared to making new concrete.
Recycling concrete can immediately reducing carbon emissions by about 1 ton of carbon dioxide per ton of concrete since most of the emissions from concrete comes from its mining, production and transport. It also saves water as recycling one ton of concrete saves about 445 gallons of water.
Recycled concrete has been used for a number of buildings. The Olympic Park of London was constructed for the 2012 Summer Olympics using recycled concrete. In Paris, France, affordable housing development, UpCycle Studios, was built from two thirds recycled concrete from the demolition of the Copenhagen Metro station, saving 45% in carbon emissions. Singapore, connected its city center with the north via the Central Expressway, reusing crushed demolished concrete from old structures.
Ferrock
Ferrock is made mostly from recycled steel dust that would not have been reused, meaning that about 95 percent is recycled. Because it has iron in it, ferrock has a beautiful finish that looks like the color of burnt clay. To harden the mixture, it is exposed to high concentrations of carbon dioxide to create a solid material. Ferrock is up to five times stronger than traditional concrete, and can bend without breaking more than concrete.
When the mixture is poured and reacts with carbon dioxide, it produces an odorless, colourless gas and iron carbonate. That is what binds carbon dioxide from the atmosphere into the ferrock after it solidifies. Essentially it is pulling carbon dioxide from the atmosphere, though a relatively small amount.
Carbon Fiber
Typically to make concrete usable as a building material, cement is poured into layers placed on top of each other, with steel rebar inside to make it stronger. In carbon fiber concrete, steel is replaced by braided mats of carbon threads.
Using carbon instead of steel significantly saves material and reduces environmental impacts. Construction with carbon fiber concrete requires only about half the material costs and releases just under one-fifth of the carbon dioxide of equivalent concrete.
The CUBE building in Dresden, Germany, uses carbon fiber reinforced concrete to reduce material costs and CO2 emissions. This was the first building to use this material.
Fly Ash and Mine Waste
Ancient Romans used volcanic ash to make slow-setting but durable concrete, including the Pantheon, built nearly two hundred years ago. Today, the ash comes from coal power plants and mine waste.
We have plenty of this waste as global coal waste production averages 600 million tons per year and 75–80 percent of that is fly ash. We currently dispose of fly ash in landfills and in waste ponds, placing the environment at risk. There have been many cases where fly ash ponds have overflowed into nearby rivers, polluting the environment and devastating fish populations.
One example was in 2008 when the coal ash pond dam failed at the Kingston coal-fired power plant in Tennessee, sending 1.1 billion gallons of waste into the Clinch and Emory Rivers. The ash contains toxic heavy metals including arsenic, lead, mercury, selenium and chromium, toxic to aquatic life.
Concrete made from fly ash is known as Ashcrete or geopolymer. It requires less energy to produce than traditional Portland cement and emits fewer greenhouse gases. It’s also more resistant to fire and acidity than concrete; making it a good option for locations with wildfires or acid rain caused by pollution.
Eco Material Technologies’s PozzoSlag uses fly ash to produce green cement at 1,000 locations in the U.S., with enough fly ash to produce concrete for decades. Eco Material products have already surfaced at a number of highways across Texas—the I-69 Interchange project in Hidalgo County, and the I-35 project in Travis County, and parts of I-45.
Waste Plastic
We know that plastic is one of the most difficult materials to recycle, with only 5 percent of plastic in the U.S. being recycled. This is, in part, because it is so difficult to separate out the different types of plastics.
Companies and architects are looking at plastic as a building material. The company, D Composites built the world’s first house entirely constructed from recycled plastic bottles in Nova Scotia, eastern Canada. The roof, walls and floor of the plastic beach house are all made from 600,000 recycled bottles which have been melted down and turned into foam panels.
In 2022, a building made from recycled plastic bottles was constructed in the Kyaka II refugee settlement in Uganda. Young refugees use the space to become social entrepreneurs. Around 40,000 bottles were used in the Kyaka refugee camp in Uganda.
You can now buy your own modular homes made from recycled plastic online through Ecoplast. They are conveniently shipped in flat packages to the building site, saving on shipping costs. According to the company, their plastic homes use 60 percent less energy, cut energy bills in half, and reduce greenhouse gases by a quarter.
Bio-Based Concrete
The shift to bio-based materials could lead to emissions savings of up to 40 percent in many of the world’s regions by 2050, even compared to savings from low-carbon concrete and steel, according to UNEP’s 2023 report.
Hempcrete
Hempcrete combines the woody core of the hemp plant with lime to create a lightweight, breathable material that offers excellent insulation. Hempcrete is mostly used for insulating properties and not for structural support, and definitely not for roads. Because it is a good insulator, it can reduce energy costs. One other benefit is that as a plant, it captures and stores carbon dioxide.
Oyster Shells
Oysters are the world’s number one farmed shellfish. In oyster farms large amounts of oyster shell waste is discarded and buried. Oyster shell is a product of oyster production, accounting for about 90% of the total oyster mass, contributing to a large amount of waste.
Concrete created from oyster shells is called Tabby, and has been used for centuries. This type of concrete is made by burning oyster shells to create lime, then mixing it with water, sand, ash and broken oyster shells. Tabby is strong because of the calcium carbonate in oysters. Tabby is also resistant to erosion and is a good material to use in places that flood and along the coast.
Self-healing Bacterial Biocement
Inspired by ancient Roman concrete, self-healing concrete uses microcapsules or bacteria that naturally repair cracks as they appear. The use of quicklime, as in Roman concrete, further enhances its self-healing capabilities and reduces carbon emissions. Several aqueducts built using this innovation since ancient Roman times are still functioning today.
Bacteria can be used to activate minerals, binding soil particles together to form a solid mass. The most common method involves the bacteria Sporosarcina pasteurii, which helps convert urea and calcium into calcium carbonate, resulting in a strong, cement-like material. The bacteria are mixed with sand and nutrients (AKA dinner for bacteria).
This method of producing cement is less energy-intensive compared to traditional cement production and significantly reduces carbon emissions. Biocement can reduce carbon dioxide emissions by up to 70% compared to traditional cement.
Mass Timber
Mass Timber is not concrete, but an alternative to concrete. Mass timber products are created by mechanically bonding various types of softwood from trees to form large, prefabricated wood panels (known as laminated timber). Using mass timber instead of conventional building materials can significantly reduce emissions by as much as 26 percent.
Mass timber is highly durable, surprisingly fireproof, and building components can be pre-fabricated off-site in a modular or serial way, reducing construction waste and speeding up building processes.
T3 (Timber, Technology, Transit) Minneapolis is the first commercial building in the United States to use wood as its main structural element as well as in its interior design. The use of timber not only adds to its beauty but also allows for a faster construction process.
Bamboo
Another sustainable alternative to conventional construction materials, bamboo is highly flexible, allowing builders to use it for both structural and decorative purposes. It’s easy to find and source bamboo, as the tree grows all over the world. The challenge with bamboo is that it can fracture easily and can become moldy if not treated.
Bamboo produces very little waste. A whole stem of a bamboo tree can be used in construction, and any pieces left over are compostable, which means they naturally break down back to the earth. Or you could use them for staking your tomatoes or roasting marshmallows. Bamboo grows very fast and is a highly renewable resource.
Bamboo has been successfully used in buildings, mostly in tropical locations. For example, The Arc and Green School in Bali used bamboo to create an impressive 62 foot long arch as both a roof and walls using bamboo.
Mycelium
Mycelium are the thin root-like fibers of a fungus or mushroom, and when dried, it is highly durable and resistant to mold, water, and fire. Like bamboo, mycelium is organic and compostable, so it leaves little waste and has virtually no negative impact on the environment.
Another critical property of mycelium is its excellent thermal insulation capabilities, which can help lower energy consumption in buildings. These natural insulating properties make mycelium an ideal material for walls, roofs, and flooring in energy-efficient construction.
Mycelium composites are naturally fire-resistant and capable of withstanding high temperatures without emitting toxic fumes, making them a safer alternative for building construction.
Mycelium can be used to create mycelium bricks, which are better for the environment than conventional baked clay bricks. These are grown in molds and customized into various shapes and sizes depending on individual preferences. They are lightweight, strong, and good for insulation. They also make for good sound insulators and can be used in movie houses, recording studios, or your teenager’s bedroom.
When combined with materials like timber, sawdust, and demolition waste, mycelium can be molded into bricks used for constructing buildings and their parts.
Mycelium isn’t used at a massive scale yet, but there are a few notable examples. In 2014, an organic brick structure knowns as Hy-Fi was built in Queens, New York. Created as part of MoMA’s Young Architects Program, the building used organic, biodegradable bricks made out of mycelium.
Algae-grown Limestone
Researchers at University of Colorado discovered that algae could be used to make limestone, while also sucking carbon dioxide from the atmosphere. In fact, researchers claim this concrete alternative could pull as much as 250 million tons of carbon dioxide and save 2 gigatons of carbon dioxide from being emitted.
The algae based concrete blocks were able to achieve ASTM C129-22, Standard Specification for Nonloadbearing Concrete Masonry Units, and C90, Standard Specification for Loadbearing Concrete Masonry Units performance requirements.
Final Thoughts on Green Concrete Alternatives
Concrete is now an everyday item in our life, but comes with large environmental impacts. By thinking creatively we can find alternative solutions to concrete. While the solutions about are intriguing, they need to be picked up and mass marketed to successfully shift the market.
{Ginny} I loved getting to share this guest post from Marcus Griswold—it’s always inspiring to learn of sustainability options that I haven’t had to deal with too much in my day-to-day life. But concrete is everywhere…The foundation of our house. The pavers in our retaining wall. Even sitting in bags in our garage waiting to be used in our berry path (so many projects)!
But it’s important to know that concrete does effect our planet, we have the power to take action, and that there are tons of exciting, viable options out there for us to weigh the pros and cons against.
