As construction strives to meet emissions standards, a persistent obstacle is the carbon-intensive process that produces cement. But the emergence of low-carbon solutions to help change the calculus of cement’s creation seems to have hit a tipping point.
In January, the California Dept. of Transportation approved low-carbon alternatives to portland cement for use on its projects. The top replacement, portland-limestone cement (PLC), reduces the amount of carbon emissions as part of its production by about 10%. The new agency standard has brought one of the largest U.S. transportation departments in line with the majority of others across the country, according to the Portland Cement Association.
The production process for cement requires grinding and heating limestone in industrial kilns at temperatures as high as 2,800° F. That creates “clinker,” which is the base element of most types of cement. The process also releases tremendous amounts of carbon dioxide. Globally, production of portland cement is estimated to be responsible for as much as 8% of the total CO2 released into the Earth’s atmosphere by human activity.
PLC reduces this environmental impact—as much as 10% to 15% more than ordinary cement—by using less clinker, replacing it with limestone. In addition, the cement replacement does not sacrifice performance or affordability in comparison with its predecessor. That has made it a relatively straightforward alternative to the higher-carbon version.
Commercial production of PLC began in the U.S. in 2005, with initial demand driven by privately developed building projects. Some state DOTs, notably Colorado, Oklahoma and Utah, began experimenting with using PLC on projects in the late 2000s.
Although limited in scope—by 2018 only 900 miles of roadway had PLC concrete—those efforts provided information regarding its durability and effectiveness in the field. By 2007, the cement trade group had begun championing its use.
As recently as 2018, only 27 states had adopted standards to allow use of PLC on their projects. That group has now grown to 44. With adoption by CalTrans, the state agency responsible for the second-highest number of lane miles in the U.S., some cement manufacturers have begun modifying their plants to produce the low-carbon material exclusively as they anticipate further growth in market demand.
Last November, LafargeHolcim, the largest cement manufacturer in the U.S., fully converted its plant in Midlothian, Texas, to produce portland-limestone cement. The facility, which began operation south of Dallas in the mid-1980s, has a production capacity of 2.35 million metric tons of cement per year.
Since then, LafargeHolcim has converted two other plants, in Missouri and Michigan, to exclusively produce PLC. The manufacturer’s Ste. Genevieve, Mo., plant is the largest cement-producing facility in North America with a capacity to manufacture 4.5 million metric tons of cement annually. The company’s Alpena, Mich., plant produces 2.4 million metric tons of cement each year. Another six LafargeHolcim U.S. plants are also slated to be converted this year to exclusively produce PLC.
“Instead of waiting for the market to ask and demand low-carbon cement, we decided to take the lead and produce a cement that performs as good as, if not better, than the cement base that the market is currently utilizing,” said Patrick Cleary, LafargeHolcim senior vice president of sales.
In 2021, portland-limestone cement products made up approximately 12% of LafargeHolcim’s U.S. sales. “In 2022, I’m estimating that will be somewhere closer to 70%,” Cleary said.
Other major U.S. cement producers are also making the shift. Last year, Titan America announced that PLC production comprised half of its manufacturing output. The company said that it plans to have its plant in Medley, Fla., converted to 100% PLC production in 2023. Argos USA also said that it intends to have all of its plants producing PLC by the end of next year.
The first commercial production of PLC in the U.S. started in 2005 and, initially, the demand for the product was driven by buildings and projects handled by private developers. Some state DOTs—notably Colorado, Oklahoma and Utah—began experimenting with using PLC on various projects in the late 2000s. Although limited in scope—by 2018 only 900 miles of roadway in those three states featured PLC concrete—those efforts provided information regarding PLC’s durability and effectiveness.
By 2007, the PCA began championing PLC and worked to increase awareness of the material in the industry. PLC gained its own blended cement specification in 2012, which spurred greater acceptance by state and local agencies. PCA launched a dedicated website to promote PLC in 2020 and included PLC in its “Roadmap to Carbon Neutrality,” released last year.
A part of the PCA’s effort has been directed at building a “comfort level” in industry for using the lower-carbon alternatives.
“We have focused our efforts on speaking to the people who use cement, and design with it and build things with it, so that they understand [PLC] can be used every place they can use ordinary portland cement,” said Jamie Farney, PCA's director of environmental measurement and metrics.
The gradual acceptance of PLC standards by DOTs across the country was critical for fostering the demand for the material within the transportation industry.
“What these agencies want to see is that they can use this cement in specific applications and that’s where we've really been able to make strides over the last 10 to 15 years,” said Jason Weiss, professor of civil and construction engineering at Oregon State University. “People now understand that this has a similar performance to conventional ordinary portland cement. It's designed to be directly substituted for ordinary portland cement.”
Caltrans launched the effort to evaluate PLC as an alternative for contractors to use in 2017. The agency contracted with Weiss and his team at OSU to conduct a three-phase research project to address whether PLC would negatively impact the performance of concrete materials that are specific to California.
Caltrans officially published its revised standard specifications in October 2021, adding portland limestone cement as one of the accepted types of cement on the department’s materials authorization list. Contractors now may replace all type II and type V cement with type IL cement (portland limestone cement) in concrete mixes that are used in Caltrans projects.
“Using low-carbon cement can cut Caltrans’ concrete-related carbon dioxide emissions annually by up to 10%. This is a big step in supporting California’s efforts to achieve carbon neutrality by 2045,” said Caltrans Director Toks Omishakin in a statement.
Caltrans oversees more than 50,000 miles of highways and roads in the state. In 2017 alone, Caltrans used 325,000 tons of cement to upgrade the state highway system. The agency says switching to low-carbon cement has the potential to reduce carbon dioxide emissions by 28,000 tons a year—the equivalent of removing more than 6,000 cars off the road.