Dust swirls in the air at a cement factory on the outskirts of Redding as mud-caked tires travel along a wide conveyor belt. The tires are carried up 90 feet into a smoldering-hot incinerator, where they're used as fuel for firing a kiln.
The massive, 2,700-degree kiln at the Martin Marietta, Inc. plant churns more than 2,500 metric tons of pulverized limestone and other materials daily to produce clinker, the jagged lumps of rock that are used to make cement.
The factory needs a constant and steady supply of fuel to sustain its 24-hour operations. Although the burning tires supply some fuel to fire up the kiln, about 80 percent still comes from fossil fuels, including high-polluting coal.
As a high-carbon and energy-intensive product, manufacturing cement, the key ingredient in concrete, takes a heavy toll on the climate. The Redding factory emitted about 282,000 tons of carbon dioxide in 2020 -- equivalent to about 55,000 gas-powered cars.
Under pressure from state lawmakers, California's cement industry is gradually taking steps to reduce its carbon footprint. But experts say the industry is one of the most difficult to decarbonize.
The state's eight cement plants account for about 2 percent of California's total greenhouse gas emissions, 8.2 metric tons of carbon dioxide, in 2017, according to a report from Global Efficiency Intelligence, an environmental research firm. Their emissions declined 20 percent between 2000 and 2015 because of improved energy efficiency and increased use of lower-carbon fuels.
"We are committing to get to zero by 2045," said Tom Tietz, executive director of the California Nevada Cement Association, a trade group representing the industry. "We're unique in how difficult that is and this is why we're striving to collaborate with the state as much as we can to accomplish this."
Cement is difficult to tackle for two main reasons: Fossil fuels are still the main fuel source for kilns and cooking limestone naturally releases carbon dioxide.
Keith Krugh, the Redding plant's director of sustainability and product development, said making the switch to alternative energy sources such as tires, pistachio shells, wood chips and other waste products is just one way that the cement industry is cutting emissions.
The cement industry needs a variety of technologies to cut carbon, he said, some so costly that the industry is seeking state funding and incentives.
"This is what we must do," Krugh said. "So what are all the different kinds of tools that we've got in the box to attack this problem? It's not just a single thing. There are many different avenues that cement producers can use to get to that net-zero."
California is the second-largest cement producer in the U.S. after Texas, producing nearly 10 million metric tons of cement yearly, according to the Portland Cement Association. Large manufacturers in California include Lehigh Southwest and CalPortland.
Cement's outsized carbon footprint is a problem that industry leaders have been working to address as California strives to decarbonize its economy. State lawmakers are increasingly targeting the cement industry because of its large role in contributing to climate change, proposing legislation that could accelerate the pace of eliminating carbon.
A first-of-its kind law passed last year is a prime example. Authored by state Sen. Josh Becker, a Democrat from San Mateo, the law requires the cement industry to offset its greenhouse gas emissions and reach net-zero carbon by 2045. The Air Resources Board must develop a metric to compare the environmental effects of different kinds of cement by July 2023.
Meeting those climate targets will require heavy investments, according to Guarav Sant, director of UCLA's Institute for Carbon Management. The industry will need to switch to more environmentally-friendly fuels, increase energy-efficiency, invest in new carbon capture technologies and produce low-carbon cement blends, he said.
"Decarbonization is hard and it's also really expensive," he said. "In short, you're talking about a significant shift in how we approach these (industry) sectors and how these sectors operate. Fundamentally we need to think about technological innovations."
About 60 percent of the cement industry's total carbon dioxide emissions in California are from heating limestone in the kiln; the other 40 percent is from fuel combustion and electricity use, according to the Global Efficiency Intelligence report.
Most of the fuels used in the cement manufacturing process, such as natural gas, coal and petroleum coke, emit planet-warming gases. Unlike other industries, the cement industry cannot rely on most renewable energy sources to power its operations due to the extremely high temperatures that are needed for production. That's part of the reason why the industry is making the switch to alternative fuels that consist of recycled waste products.
The Redding factory, which produces 635,000 short tons of cement a year, uses a mix of coal, petroleum coke, tires and natural gas to fuel its operations. Fuel sources vary depending on availability and pricing, but on average, about half of its fuel comes from coal, 20 percent comes from petroleum coke, 20 percent from car and truck tires and the rest from natural gas.
Using tires for fuel eliminates only about 5 percent of the kiln's emissions. Krugh said the factory, which will be sold to CalPortland effective July 1, is working to replace at least half its fossil fuels with climate-friendly alternatives within the next 10 years.
About 13,000 tons of used tires a year are burned at the plant, which keeps about a million tires out of landfills. Burning tires reduces the company's greenhouse gas emissions because they contain a large amount of biomass in the form of natural rubber that reduces the carbon dioxide intensity of the process, Krugh said.
He said the fumes created from burning tires are captured in the kiln.
"When people think of burning a tire, they think of these tire piles that catch on fire and make a huge black horrible, contaminated cloud," Krugh said while pointing to the plant's 252 foot- tall smokestack. "In the cement kiln, the entire process is under time, temperature and oxygen control. You don't see a black cloud coming out the top of the stack because all of the combustibles are completely burned due to the extremely high temperatures and process controls."
However, documents provided by the Shasta County Air Quality Management District show that the factory, in addition to emitting greenhouse gases, is a substantial source of dust particles and smog-forming emissions. Residents filed five complaints that dust from the plant drifted onto their property last year, and the district issued a violation notice in December that has prompted the company to step up dust control. The plant also emits 62 toxic air contaminants that total more than two tons a year.
Crushing and heating limestone is a major source of greenhouse gases at cement factories because of its high concentration of calcium carbonate, a compound needed to make cement. For every ton of cement that's produced, about 0.8 tons of carbon dioxide is released through this process. These emissions are an unavoidable byproduct, which means that the industry needs to invest in technologies that capture the carbon so it doesn't spew into the atmosphere.
Some of these technologies aim to use carbon dioxide for cement production, while others involve capture and storage, where the carbon is injected deep underground into rock formations.
The practice is controversial due to its practicality and cost, but also because environmentalists say using carbon capture and storage for enhanced oil recovery will only prolong the lifespan of the fossil fuel industry. Many environmental justice groups, however, are not as opposed to the cement industry using carbon capture because of how difficult it is to decarbonize.
Alex Jackson, senior attorney at the Natural Resources Defense Council, an environmental advocacy group, said public investments in these carbon-capture projects could help the state ensure strong worker protection measures and community health standards that may be more difficult to enforce if companies were solely driven by market forces.
"There's a good case to be made for leaving open the possibility of carbon capture for an industrial sector like cement that has these non-combustion emissions that are going to be difficult to avoid or eliminate entirely," he said.
Jackson said the cement industry has resisted adapting to climate change for several reasons: Global market forces didn't grant companies incentives, and for years there was a lack of political interest and available technology.
"There's lots of momentum and there's lots of promising technologies taking fruit now," he said. "But historically, we haven't seen the same degree of progress."
UCLA's Sant said carbon capture and storage is necessary to attain a net-zero future for the cement industry. But complications include the high cost and lack of infrastructure to capture, transport and store carbon dioxide, he said.
"We need things like pipelines to be able to take carbon dioxide from sequestration sites," he said. "Most cement plants are not sitting on top of geological reservoirs. This infrastructure doesn't exist, which makes geological capture and storage extremely hard."
Vincent Wiraatmadja, a policy advocate at The Climate Center, a climate and energy policy nonprofit, said while carbon capture and storage for cement sounds promising, existing projects "do not have the most efficient technology."
Globally just 27 carbon capture and storage projects are operating so far and many experts vastly disagree on its effectiveness.
"Many of the carbon capture and storage projects that exist in the world I would characterize as failures," he said.
Wiraatmadja said the cement industry is a unique sector where carbon capture and storage could make sense because it will not be used to extract oil from the ground.
But he added,"We should be cautious about how this rolls out and not go down a slippery slope about carbon capture and storage being a silver bullet for every application. We should keep the scope narrow."
Cement companies say they will need public-private partnerships or state and federal funds to help them build carbon capture and sequestration facilities.
Capturing and liquefying carbon dioxide is expected to cost between $45 and $100 per metric ton of carbon dioxide, Krugh said. Since a plant emits hundreds of thousands of tons, that cost alone would reach millions. Plus, the cost of just a pipeline to deliver carbon dioxide to a sequestration site could range between $70,000 and $200,000 for each inch-mile of pipeline (a calculation used to consider diameter and length), depending on whether it passes through open rangeland or a densely populated area.
"To put this in perspective, such incremental operating expenses are in excess of the margin that most cement producers earn per ton of product sold," Krugh said.
A bill introduced in the Legislature could help fund and demonstrate the technology for companies that are hesitant about investing. SB 905, co-authored by Sen. Nancy Skinner, would fund one to five pilot projects at cement plants by 2026 to capture carbon dioxide and store it geologically. The projects would have "unknown ongoing costs, up to the low millions of dollars annually," according to the Senate's analysis.
Skinner, a Democrat from Oakland, said cement is a critical building material so the state should invest public dollars in some of these projects to encourage the industry to keep operating in California. The industry is projected to grow by as much as 40 percent by 2040, according to the Global Efficiency Intelligence report.
"If we don't assist the cement industry in California to become less carbon intensive or emit less greenhouse gases, then, in fact, we'll be driving the industry out of our state," she said. "Then we'll be dependent on cement from elsewhere and that cement will have far more carbon content."
Skinner is hopeful that the bill, which is pending in the Assembly's appropriations committee, will gain enough support to make it to the governor's desk to be signed into law.
Other bills aiming to decarbonize the industry haven't been successful.
At an Assembly committee hearing last week, Becker urged its members to support his bill, SB 778, which would have added concrete to the Buy Clean California Act. The law requires the state to use low-carbon building materials in public works projects.
While the bill received support from the cement industry and environmental justice groups, it faced fierce opposition from the construction industry and failed to receive widespread support from the seven-member committee, with four members voting against it.
Contractors and construction industry representatives said the legislation would have complicated the permitting process for construction, limited the types of cement they could use, increased construction costs and delayed projects.
Assemblymember Tom Lackey, a Republican from Palmdale, said he could not support the bill because of the constraints the construction industry is already facing with supply chain issues and high costs. He said local air quality management districts and the state's cap and trade program already regulate emissions from cement kilns.
"If the industry needs to go to another state to buy the product - that's very problematic," he said. "This bill will increase costs and slow construction."
Becker's effort to include concrete in the Buy Clean California Act has been five years in the making. He said he'll continue to push for it.
"The contractors, they've just been adamantly opposed," he said. "We lost in the committee, but we're going to keep working on this. We have to get there. The industry knows that and that's why they're working with us."
Some companies are trying new technologies to tackle cement's toll on the environment.
The Redding facility is the first cement plant in the state to partner on a pilot project with Fortera, a Silicon Valley-based company that makes low-carbon cement. The project, which broke ground earlier this month, involves building a small operational plant next to the existing facility that would use carbon dioxide to make cement. This process converts carbon dioxide from a gas to a mineral, creating a solid carbonate that could improve the strength and durability of cement, according to Kas Farsad, Fortera's vice president of corporate development.
"What's exciting about us is that we're taking the emissions that would have been emitted by the kiln and remineralizing it," Farsad said. "Trying to get ahead of the curve by reducing emissions and making a new (cement) material that is lower carbon has a more progressive outlook. And that's exactly what we're doing."
Farsad said the project, which is expected to be fully operational by January, could transform the industry.
The plant also has been working on reducing cement's carbon intensity by incorporating other substances into the mix, such as fly ash, which is a byproduct of burning coal, slag, which comes from iron production, or pumice, a type of volcanic ash. Adding these ingredients can replace between 15 percent to 30 percent of the clinker needed to make cement.
Tietz of the California Nevada Cement Association said the industry faces steep hurdles in the coming years as it tries to decarbonize.
"What really hits us is that there's financial and regulatory barriers that we've identified that are going to be challenging for us to reach the state's goals," he said. "And that's what we're actively pursuing - resolving those barriers."
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