4 ways to reduce carbon footprint in dry mix mortar

For the past century, cement has been the backbone of the construction sector. As the basis for concrete and mortar, cement has a widespread presence in our buildings and infrastructure.

But cement-making is an energy-intensive activity — for every one kilogram of cement produced, 0.5-0.7 kilograms of CO₂ are emitted, pushing its share of global emissions to nearly eight percent. 

In response to the rising demand for low-carbon products, manufacturers are working to reduce the carbon footprint of dry-mix products.

In this article, we will investigate four different ways to decrease the CO₂ emissions within the dry-mix sector, while connecting it to the Scopes concept, and gain insights from Manuel Baumann, Director Global Construction, IMCD Coatings & Construction.

Carbon capture is a catch-all term for several technologies that, rather than avoid CO₂ generation at cement plants, aim to stop it from being released into the atmosphere. The focus on emissions within the plant puts carbon capture firmly in Scope 1.

Most CO₂ emissions in cement manufacturing — 60 percent in total — occur as a by-product of clinker production, as calcium carbonate is calcinated inside the kiln. Carbon-capture plants paired with the kiln would collect the CO₂, compress it into a liquid and transport it to permanent storage underground.

Alternatively, collected CO₂ could be made useful as a supplementary cementitious material — up to 20% of the final blend — or by injection into concrete, creating a stronger final mixture. 

In theory, these technologies could fully decarbonize calcination, or even make it into a carbon negative process, trapping more CO₂ than what is generated.

“While there are ongoing projects and great interest by cement manufacturers in carbon capture, we are still at a stage where existing technology is only applicable in pilot projects and seems commercially difficult for widespread adoption,” explains Baumann.

 
The kiln is the heart of the cement factory. It is where the limestone is heated to 1,450 ºC, producing the clinker that is then ground to create cement. 

Achieving that temperature absorbs 90% of all the energy consumed in cement manufacturing. The fossil fuel used to power the kilns, as well as the precalciners, is responsible for 40% of all emissions during cement production. 

While cement manufacturers can make incremental improvements in energy efficiency, clinker production will remain an energy-intensive process. Switching to alternative fuels, such as biomass, or treated municipal waste would instead directly reduce the CO₂ emissions from burning fossil fuels.

Some manufacturers opt for electrifying the kiln, instead of burning fuel on-site. Returning to the Scopes framework, this option uses electricity procured for the plant in order to reduce Scope 2 emissions.

“Like carbon capture, most manufacturers already have programs to improve their energy efficiency and to study the feasibility of using alternative fuels,” explains Baumann. However, obstacles remain, such as the price and availability of biomass.

 
Another effort to lower CO₂ emissions in cement production is to reduce its amount of clinker by using supplementary cementitious materials (SCM). Clinker reduction falls into Scope 1, as we try to reduce CO₂ emissions from the kiln by bypassing and reducing the use of calcination.

SCM can be obtained from several sources: industrial waste, such as blast furnace slag from iron production and coal fly ash from electric power generation, or natural-occurring materials such as pozzolans. 

Blended cement of this type can result in a 10-30% reduction in the carbon footprint compared to cement Type I.

New types of cement are appearing in the market, as in the case of Limestone Calcined Clay Cement (LC3). Using limestone and calcined clay is an alternative for when the availability of slag is low. At the same time, LC3 uses less energy, resulting in a reduction of CO₂ emissions by up to 40%. However, this option requires manufacturers to adapt the production process to include a second production line.

With the existing technology, clinker reduction is the most promising approach for all cement-based products. However, the transition is easier for the concrete business than for the dry-mix one. For context, it may be possible to bring down the clinker content of cement by 30 to 40% without compromising durability, strength and setting time of the final product.

“Dry-mix products such as grouts, tile adhesives or self-levelling compounds have quality requirements that may be compromised by lower clinker content,” describes Baumann. “Cement Type I produced with biofuel combined with secondary raw materials can lower clinker content while allowing for flexibility in formulation. However, when using blended cements, it’s a challenge to keep performance at the same level when it comes to durability, porosity, and chloride resistance, among other indicators. For example, clinker substitution impacts the hydration process, which might negatively impact the final strength. Achieving the right formulation often requires extensive re-formulation efforts and testing.” 

 
Finally, the mass balance approach is a proven strategy to support the replacement of fossil-based raw materials with more sustainable ones based on biomass or waste. 

Thanks to this approach, manufacturers can add renewable and recycled feedstock to the process without changing the existing production method and deliver a final product that requires no changes in application. Such seamless integration requires an exact calculation of feedstock inputs during formulation.

“Redispersible powders, which usually account for a small percentage of the final product, is a component of dry-mix products that could benefit from this approach,” explains Manuel Baumann.