Green Cement

Learn about the impact of cement and concrete on greenhouse gas levels worldwide. Concrete is currently the most widely produced substance in the world, and it will soon outweigh all living matter. Concrete accounts for 70 percent of coastal and marine infrastructure worldwide. More than half of China’s coastline is concrete, as is 14,000 miles of the U.S. coastline. Between 2002 and 2021, the cement industry’s global emissions doubled from 1.4 billion tons to 2.9 billion tons, faster than most other carbon sources. Cement is used in almost every structure, including buildings, sidewalks, roads, bridges, and foundations.

• The production of Portland cement, the most common type, relies on baking limestone at high heat in kilns, often powered by fossil fuels, which releases carbon dioxide that otherwise would remain locked within the limestone for hundreds of millions of years. Producing a single kilogram of Portland cement releases a kilogram of CO₂ into the atmosphere.
• The cement sector constitutes 7 percent of industrial global energy use, making it the third-largest industrial energy consumer.
• The cement industry produces an estimated 2 billion tons of carbon dioxide, three times the amount produced by the aviation industry. Burning coal accounts for 40 percent of the CO₂ emissions, while limestone breaking down into lime within kilns accounts for the remaining 60 percent.
• In addition to carbon dioxide, cement plants emit more than 500,000 tons of sulfur dioxide, carbon monoxide, and nitrogen oxide annually.
• Each year the world produces about 4 billion tons of cement—1,200 pounds per person—with the potential to increase to 5 billion tons annually by 2050. 30 billion tons of concrete are used worldwide each year—triple the per capita demand compared to forty years ago. The demand for concrete is also increasing faster compared to other building materials such as steel or wood.
• Global concrete production could increase as much as 26 percent by 2050 based on projections that the number of buildings worldwide is expected to double by 2060. 

Learn about green cement and its potential to lower greenhouse gas emissions worldwide. Green cement refers to cement that is either manufactured with the help of a carbon-negative process and/or made with alternative or recycled materials with lower embodied carbon emissions. It is designed to last longer than conventional concrete, reducing the need for replacement and repair. Some recent innovations in green cement include:

• Replacing the limestone in the traditional mine and grind concrete-making process with basalt or carbon-negative limestone, including algae-grown limestone, could reduce emissions by over 60 percent.
• Experiments using alternative cement materials have found that replacing cement with biochar, bioplastics (bio-based plastic polymers), agricultural waste, and animal wool not only lowers carbon emissions during production but also increases the soundproofing, water absorption, tensile strength, and carbon sequestration of concrete. See Biochar Nexus and Carbon Architecture Nexus.
• Researchers have prototyped cement that eliminates the CO₂-releasing chemical reaction by using fly ash, a low-cost volcanic ash.
• Scientists from Harvard and MIT rediscovered the process behind the making of ancient Roman concrete, whose distinctive hot mixing step creates a final product that requires significantly less setting and curing time than modern concrete, a functional life span of thousands of years, and the ability to be used underwater. 
• Researchers have created a type of living concrete that utilizes bacteria and sunlight, through photosynthesis, to create calcium carbonate that can cement sand particles together as it dries. The mixture can be poured into any shape, including bricks. The process absorbs carbon dioxide from the atmosphere and the resulting product is both durable and green.

Raise awareness about the negative environmental impacts of cement and the benefits of cement alternatives. Spreading the word about how current cement production accelerates global warming can help spur demand for cement manufacturers to invest in alternative cements and technology that lowers emissions.

• Connect with green cement advocates. Many green building forums provide opportunities to share resources and knowledge among those interested in using cement alternatives. See examples here and here.
• Contact your representatives. The Citizens’ Climate Lobby provides a step-by-step tutorial on how to write a letter to Congress as well as information on the benefits of clean energy that could power cement plants.
• Speak up. Write an op-ed for a newspaper or a social media organization advocating for green cement.

Use less cement or use alternative materials that emit fewer greenhouse gases. The amount of cement within concrete can be reduced by 50–60 percent without affecting the strength of the concrete. In addition, the material within the cement can vary up to threefold without affecting performance. Replacing part of cement’s content with substitutes such as fly ash, slag, and rice hull ash, aerated mixes, biocements, and alternative cementitious materials like calcined clays reduce emissions by 50 percent. Find out more about the specific strengths of cement alternatives here and here. 

• In Japan, Taiheiyo Cement Corporation has been developing “eco-cements” that replace large quantities of limestone with ash in order to limit carbon emissions. 
• In Austria, Rieder has replaced 50 percent of the cement in its concrete panels with natural pozzolana (a material derived from volcanic ash), leading to a 30 percent reduction in CO₂ emissions. By 2027, the company hopes to make its facade panel products cement-free.

Reuse concrete. Adapting circular construction, or the recovery and reuse of elements from past projects for new construction, could lead to reductions of up to 61 percent of greenhouse gas emissions emitted across buildings’ life cycles. In nonstructural applications, recycled concrete on-site also reduces costs by 50 percent in addition to reducing the volume of new concrete needed. If concrete cannot be reused and must be demolished, grinding it and spreading it thinly to maximize surface area and exposure to air allows it to absorb as much as 17 percent of the carbon dioxide emitted when its cement was manufactured. 

• University of Tokyo scientists invented a concrete-making process that lowers greenhouse gas emissions by reusing old concrete products, using lower temperatures for manufacturing, and capturing carbon dioxide. 
• Austrian cladding company Rieder opted for circular construction for its new headquarters by renovating a former bus garage and reusing concrete columns, recycled steel, and wooden walls, saving around 1,000 tons of CO₂ in the process. 

Invest in innovative cement that reduces embodied emissions. 

• CarbiCrete replaces the cement in its concrete with steel slag and injects carbon dioxide to produce calcium carbonates with higher compressive strength and better freeze resistance than traditional concrete. 
• Solidia and LaFarge have developed a concrete mix design and curing process that mixes cement powder with sand and cures the mixture with carbon dioxide to create concrete with a 70 percent lower carbon footprint. 
• CarbonCure has developed technology that injects captured carbon into wet cement, strengthening the material and locking in carbon dioxide. Using CarbonCapture’s technology, Amazon has saved an estimated 1,600 metric tons of carbon dioxide emissions thus far. 
• Brimstone Energy is developing zero-carbon cement that replaces limestone with calcium silicate, which releases magnesium that absorbs carbon dioxide from the air. 
• Cement manufacturer Block-Lite is partnering with climate tech startups Aircapture and Carbonbuilt to replace cement with an alternative mixture consisting of locally sourced industrial waste materials, which then will be cured with carbon dioxide pulled directly from the atmosphere. 
• Colorado-based Prometheus Materials has developed a low-carbon cement alternative that replicates the structure of coral reefs by biomineralizing cyanobacteria grown using sunlight, seawater, and CO_2, and has the potential to be mass-produced. 
• Terra CO2’s technology partially replaces Portland cement with silicate from aggregate mines already in operation, leading to a 70 percent reduction in CO₂ emissions for every ton of Portland cement replaced by the blend. The company is aiming to be able to completely replace Portland cement as well as transition to renewable energy within the next five years.

Join an industry-led initiative to lessen the environmental impact of cement and concrete production. Industry-led initiatives offer opportunities for cement companies to share important resources and knowledge about the development of green cement. Examples include: 

• The Concrete Action for Climate (CAC) Initiative is a coalition of organizations, including forty Global Cement and Concrete Association members, working toward the goal of producing net-zero concrete by 2050. It aims to develop a sector-specific road map to net-zero emissions by 2050 by increasing demand for low-carbon cement and concrete and minimizing climate impacts. 
• The Cement Sustainability Initiative is an international effort by twenty-four major cement producers that collectively account for 30 percent of the world’s cement production to minimize the impact of cement production and accelerate progress toward sustainable development. 
• The ConcreteZero Initiative, a coalition of seventeen global businesses in the built environment sector, is aiming to accelerate the adoption of low-carbon concrete among concrete users. Businesses within the initiative have committed to using 30 percent low-carbon concrete by 2025, 50 percent by 2030, and 100 percent by 2050. 

Support the research and development of cement alternatives. Academic research has played a key role in the development of lower-carbon cement alternatives. Examples include:

• University of Tokyo researchers have developed the first process for cement made entirely from food waste such as tea leaves, orange peels, and coffee grounds. The cement, produced via a “heat pressing” used to make construction material from wood powder, has three times the tensile strength of existing concrete. 
• In 2019, researchers at the National Taipei University of Technology and the Indian Water Resources Department discovered that agricultural and aquaculture farming waste could partially replace coarse and binding materials in concrete. 
• Funded by a grant from ETH Zurich, Gnani Landrou developed a process that turns clay-based excavation materials into an alternative concrete that does not require cement. Inspired by homes in his native Togo, the mixture is two and a half times less expensive than cement and can be used to build floors and non-load-bearing walls. 
• Researchers at the University of California, Irvine, and the University of Southern California have invented a process that grows minerals within a 3-D-printed structure inspired by the mantis shrimp, which could be scaled up to develop 3-D-printed, self-repairing concrete. 
• Scientists at ETH Zurich have designed a 3-D-printed formwork made from recyclable mineral foam to create a precast concrete slab that uses geometry to preserve strength while reducing the amount of concrete needed by 70 percent.
• Worcester Polytechnic Institute researchers are using an enzyme found in red blood cells to create self-healing concrete that is four times more durable than traditional concrete, extends the life span of concrete-based structures, and prolongs the duration between repairs or replacements.

How to Make Concrete Green! by Just Have a Think (13 mins.)

How We Could Make Carbon-Negative Concrete by Tom Shuler / TED (5 mins.)

What Is Green Concrete? How to Make Concrete Green by The Structural World (6 mins.)

“Can the World’s Most Polluting Industries Decarbonize?” by Fred Pearce / Yale Environment 360

“Concrete” by Jeremy Gregory / MIT Climate Portal

“How Is Green Cement Better Than Regular Cement?” by Furqan Kabir / The Carbon Herald

“Solving Cement’s Massive Carbon Problem” by Mark Fischetti, Nick Bockelman, Wil V. Srubar / Scientific American

A Concrete Proposal: The Future of Eco-Friendly Architecture by Francisco Camacho / Planet Forward (15 mins.)

Researchers Are Trying to Find a Way to Cut Concrete’s Carbon Emissions by Nathan Rott / All Things Considered, NPR (3 mins.)

The Concrete That Helps the Climate by Martha Henriques / Future Planet (5 mins.)