Goal crushing

France-based Holcim is one of the largest producers of cement and aggregates products in Europe and North America. When the company directs its attention toward boosting its recycling rates, it can have widespread impacts.

Aggregates operations of the global firm include those of the former Lafarge company, which Holcim acquired in 2015. At least two projects involving Holcim, one in France and one in Canada, focus on “upcycling” concrete recycling methods by isolating materials that can be used as clinker, an intermediate product in cement production.

A separate research project has focused on using steel furnaces as a crucible for purifying end-of-life cement to produce a low-carbon substitute for lime in producing new cement.

At a Holcim quarry site in France, the company has enlisted the help of global aggregates crushing and recycling equipment maker Metso in a project designed to add more value to the concrete crushing process.

At the site in Saint-Laurent-de-Mure near Lyon, France, the Holcim plant combines a variable pressure crushing system (a Metso HRC 8 crusher) with an airflow system (Metso Air Classifier AC30), making it possible to separate and recover the cement paste during the crushing operation without grinding the original aggregate.

With this proprietary processing technology, Holcim says it can upcycle 100 percent of construction and demolition (C&D) materials into new building solutions, from aggregates to decarbonized cement paste. According to the company, it’s an advanced circular system aimed at lowering the carbon dioxide footprint of new buildings while closing the material loop to save virgin resources.

The recycling plant makes it possible to produce a superior quality of recycled construction aggregates for high-end applications, Holcim says, adding that the technology also helps produce cement-rich fractions that can be used to replace limestone in cement making, therefore helping decarbonize cement manufacturing.

The setup, which began operations last September, is focused in part on isolating very fine materials with a high concentration of cement in demolition concrete. This provides carbon-free additions to the manufacturing of new cement, Metso says.

The plant will serve as a pilot for Holcim to deploy this equipment in other parts of France in the future. If the technology goes global, Holcim has a considerable recycled aggregate presence in the United States in the form of facilities formerly operating as the Aggregates Industries brand. In the late 2010s, the company intended to “multiply by four our volume of recycled aggregates from C&D [materials] and reclaimed asphalt paving” as one of its two main circular economy targets to reach by 2030.

In Saint-Laurent-de-Mure, the cementitious materials separation plant consists of two independent lines: the first line receives concrete demolition material as infeed (sized from about one-third of an inch to 1.2 inches) into the HRC 8, which separates the aggregates from the cement paste. A second line helps further separate and refine material, creating the final products.

According to Metso, cement fines, which in most existing crushing processes remain attached to the sand-like residue, is becoming a sought-after alternative source material to supplement clinker, a limestone-rich cement material, making it possible to reduce clinker’s share in the final composition of the cement and therefore reduce its carbon weight.

Concrete is the most widely used construction material in the world thanks to its durability, affordability, versatility and strength, Holcim says, and that’s why the company is working to scale up low-carbon, circular and smart concrete applications to decarbonize construction.

“Construction [materials] generated worldwide represent a great opportunity to accelerate circularity to close the loop in construction, while decarbonizing building,” says Vincent Teissier, head of circular construction at Holcim. “Holcim is a world leader in recycling. Building new from old, we recycle nearly 7 million tons of C&D materials each year into new building solutions. We are working to double down on that as soon as possible.”

Metso, citing the concrete recycling organization Recybeton, based in Paris, says in France, 80 percent of end-of-life concrete currently is recycled, primarily in road applications such as pavement base course. In partnering with Holcim to upcycle and reintroduce these demolition concretes into the cement and concrete manufacturing chain, the company aims to increase demolition material value while helping Holcim to advance its circular ambition.

“This new [plant] is a decisive step in developing the reuse of demolition materials by utilizing all the value they have to offer,” says François Petry, CEO of Holcim operations in France and Belgium. “Recovering the fines from crushed concrete to reuse them as a carbon-free addition to the cement process is a first in Europe and a giant step forward in the ecological project of building the city of tomorrow with the materials of the city of yesterday.”

Closer to home

This May, Holcim and member companies Lafarge Canada and Geocycle Canada completed a pilot program at the Lafarge Brookfield Cement Plant in Nova Scotia.

That pilot effort was designed to produce high-quality clinker made of recycled minerals recovered from waste sources, which the companies say can potentially reduce [the] CO2 level by 60 percent per ton of clinker.

According to the company, each year more concrete is sold globally than all other building materials combined.

“Our teams have been tirelessly working toward finding solutions to decarbonize our business in Canada,” says David Redfern, president and CEO of Lafarge Canada East.

Crushed discarded glass is one component of the recycled content the company used in the pilot while the larger stream is materials otherwise destined for landfill. The goal in Nova Scotia, Holcim says, is 100 percent circular production of clinker at the Brookfield Plant.

“This new clinker product will be used to produce a 100 percent recycled cement during this pilot, which will in turn be employed in ready-mix concrete operations to produce a 100 percent recycled concrete product,” says Andrew Stewart, a vice president at Lafarge Canada East.

New research

An alternative method of making cement more circular is being studied at the University of Cambridge in England. Researchers there say they have developed a method to produce low-emission concrete at scale using steelmaking electric arc furnaces (EAFs) already engaged in the recycling of that metal. The researchers refer to the finding as “an absolute miracle,” saying using the EAFs to simultaneously recycle cement offers a “scalable, cost-effective way of reducing concrete emissions while meeting global demand.”

The Cambridge researchers say used cement is an effective substitute for lime flux, which is used in steel recycling to remove impurities and normally ends up in skimmed furnace slag. But by replacing lime with used cement, the end product is recycled cement that can be used to make new concrete, they say. The cement recycling method, reported in the journal Nature, does not add any significant costs to concrete or steel production and significantly reduces emissions from both concrete and steel, they claim.

“We held a series of workshops with members of the construction industry on how we could reduce emissions from the sector,” says Professor Julian Allwood from Cambridge’s Department of Engineering, who led the research. “Lots of great ideas came out of those discussions, but one thing they couldn’t or wouldn’t consider was a world without cement.”

Although the binding material is a small proportion of concrete, cement is responsible for almost 90 percent of its emissions. Cement made via the clinkering process, where limestone and other raw materials are crushed and heated to about 2,600 degrees in large kilns, releases large amounts of CO2.

“I had a vague idea from previous work that if it were possible to crush old concrete, taking out the sand and stones, heating the cement would remove the water, and then it would form clinker again,” says research report co-author Cyrille Dunant.

He added, “A bath of liquid metal would help this chemical reaction along and an EAF, used to recycle steel, felt like a strong possibility. We had to try.”

Cambridge says its electric cement process has been scaling rapidly, and the researchers say the world could be producing 1 billion metric tons per year by 2050, which represents roughly a quarter of current global annual cement production.

For recyclers of construction and demolition materials, the inclusion of cement recycling and production may soon play a larger role in how they navigate the C&D recycling landscape.

The author is senior editor for the Recycling Today Media Group and can be reached at btaylor@gie.net.