Efficient manufacturing could slash cement-based greenhouse gas emissions

May 4, 2021
Making cement more efficiently could lead to reductions in greenhouse gases, and using fewer of these familiar vehicles is part of the plan. (Pixabay/Oknesanofa)

Making cement more efficiently could lead to reductions in greenhouse gases, and using fewer of these familiar vehicles is part of the plan. (Pixabay/Oknesanofa)

With more energy-efficient methods for production and use, Brazil's cement industry can more than halve its carbon dioxide emissions in the next 30 years while saving nearly $700 million, according to a new analysis — and the reductions could be much deeper, when accounting for cement products' absorption of carbon dioxide from the air.

In a paper published April 5 in the Journal of Industrial Ecology, Brazilian researchers crafted a new roadmap for the greenhouse gas emissions-heavy industry that they said can also be adopted in many other countries. It includes a higher use of filler materials when making concrete and a larger reliance on ready-mix concrete and mortar.

The group also suggested that Brazil should alter its tax incentives and create a carbon tax to spur these changes more quickly, as limited time remains to decarbonize society fast enough to limit the extent of climate change.

The production of cement, the stone-based powder used to create construction materials such as concrete and mortar, is one of the largest sources of greenhouse gases on the planet. The cement industry emitted 4.1 billion metric tons of carbon dioxide in 2019, about 8% of global emissions, and Brazil is home to the 12th-largest market. Most of the carbon dioxide is produced when limestone and clay are heated in a calcination reaction to create clinker, which is used as a binder in cement.

The new study expands on two emissions scenarios through 2050 that were created by Brazilian cement trade associations: a business-as-usual scenario and a low-carbon scenario. The latter focused on the production of cement and included improving the energy efficiency of cement plants, using alternative fuels and reducing the use of clinker.

But the low-carbon roadmap did not consider the carbon-dioxide emissions that occur when cement is used in products such as concrete and mortar, sources that are explored less often, said Daniel Reis, an author of the study and a postdoctoral researcher of civil engineering at the University of São Paulo.

"Most of the solutions to decarbonize the cement industry are focused on the material level; this means to reduce the CO₂ per unit of cement produced," Reis said.

In addition to the preexisting low-carbon scenario, the researchers created a second low-carbon roadmap with a focus on reducing emissions when cement is used to make other materials. The scenario includes higher industrial production of concrete and mortar rather than mixing them on-site, as these "ready-mix" products require less carbon-dioxide emissions. It also involves substituting as much as 70% of cement with filler materials during mixing and using efficient planetary concrete mixers at concrete production plants.

Combining both low-carbon scenarios — efficiency improvements in cement production and use — would reduce up to 56% of the carbon-dioxide emissions expected under the business-as-usual scenario, according to the analysis. The new set of cement-use improvements accounted for a 22% decrease.

The researchers also noted that the reductions could be brought to 82% when considering the carbon dioxide absorbed by cement-based products through 2050, which happens when the greenhouse gas enters pores and reacts with the material.

This process is not normally included in industry emissions roadmaps given the relatively little research behind it, the researchers said, but it could be accelerated in cement products with a high proportion of filler, as proposed in the second low-carbon scenario.

Reis said the solutions in the second low-carbon scenario are much cheaper than other options such as carbon capture and storage, which removes carbon dioxide directly from the air. Between 2018 and 2050, the combined measures would save $695 million, or $1.36 per ton of carbon dioxide, making them more viable and easily scalable, Reis said.

The authors said that public policies are important for promoting low-emission measures, and that changes in Brazil's policies could incentivize them more effectively. The current tax structure discourages the use of planetary mixers in favor of on-site concrete trucks, and most environmental policies don't take into account the usage side of cement captured in the second scenario, they said. 

According to Reis, a tax on carbon can also encourage emission-reducing solutions in the industry, although he recommended a careful introduction so that the tax does not increase cement costs in a way that impacts developing nations with a preexisting housing deficit.

Emissions from the cement industry account for less than 1% of Brazil's overall emissions of 2.2 billion metric tons of equivalent carbon dioxide, which it has pledged to reduce 37% below 2005 levels by 2025. But the country has been increasing emissions in recent years, especially as Amazon rainforest fires have intensified.

Although the analysis was constrained to the Brazilian cement industry, many of the methods included in the roadmaps can be adopted elsewhere, according to Reis. Global cement use and associated emissions are dominated by China, followed by India and the U.S.

"Practically all the measures explored in this article can be applied in other countries, except the industrialization of concrete and mortar, since in developed countries most of concrete and mortar is already industrialized," he said. 

The study "Potential CO₂ reduction and uptake due to industrialization and efficient cement use in Brazil by 2050," published April 5 in Journal of Industrial Ecology, was authored by Daniel Reis, Marco Quattrone, Sergio Pacca and Vanderley John, National Institute on Advanced Eco‐Efficient Cement‐Based Technologies and University of São Paulo; Jhonathan Souza, University of São Paulo; and Katia Punhagui, Universidade Federal da Integração Latino‐Americana.

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