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New cement made with plant fibers captures air pollutants and offers greater durability
Cement production uses a compound that “captures” carbon dioxide, a greenhouse gas; the goal is to help reduce emissions from ethanol production
Boards produced with cement reinforced by plant fibers; the use of magnesium oxide reduces alkalinity and allows the fibers to maintain their structural function for longer – Photo: Provided by researcher Adriano Galvão de Souza Azevedo
Researchers at USP’s School of Animal Science and Food Engineering (FZEA) in Pirassununga have developed a new type of cement with plant fibers that can absorb 100 kilos (kg) of carbon dioxide (CO₂) per cubic meter (m3). The new binder replaces calcium-based compounds with magnesium oxide (MgO), incorporating CO₂ — one of the greenhouse gases (GHGs) — into the material and obtaining a more resistant and durable cement.
The research aims to use the CO2 generated during the production of sugarcane ethanol to help reduce emissions of the pollutant, estimated at 11.3 million tons in the state of São Paulo alone. The results of the tests with the new cement are detailed in an article in the scientific journal Construction and Building Materials.
“Each ton of ethanol produces approximately 956.5 kg of CO₂. However, the carbon in ethanol comes from plants, mainly sugarcane, in the Brazilian context. It is captured from the atmosphere during photosynthesis,” Adriano Azevedo, a chemist and researcher at FZEA participating in the project, told Jornal da USP. “Thus, part of the CO₂ emissions generated in the industrial process, as well as all the CO₂ emitted during the combustion of ethanol, can be offset by plant biomass growth. In an ideal cycle, net emissions would be close to zero, making ethanol a low-carbon biofuel.”
Adriano Galvão de Souza Azevedo - Photo: Lattes
According to data from the National Agency of Petroleum, Natural Gas and Biofuels (ANP), the state of São Paulo was Brazil’s largest ethanol producer in 2020, with 14.7 million cubic meters (m³), around 45% of national production. Of the 360 units authorized by the ANP to produce ethanol, 149 are located in São Paulo, with an installed capacity of 169,400 m³/day. “It is estimated that this production results in the annual generation of approximately 11.3 million tons of CO₂,” says the researcher. “Therefore, developing complementary technologies for reusing and capturing carbon in this context can make a decisive contribution to decarbonizing the national energy matrix, strengthening the sustainability of the biofuels sector, and collaborating with global efforts to mitigate climate change.”
According to Azevedo, the cement proposed in the research differs from traditional ones, such as Portland, mainly because it uses magnesium oxide (MgO) as its primary raw material, instead of calcium-based compounds. “They have a high pH [alkalinity], usually between 12.5 and 13, which accelerates the degradation of the plant fibers incorporated into the cement matrix, compromising the material’s durability,” he says. “Cements formulated with MgO have a more moderate pH, between 10 and 10.5, which significantly reduces the alkaline attack on the fibers and allows them to maintain their structural function for longer.”
Cement block reinforced with plant fibers is subjected to a four-point bending test; the production process not only retains the carbon but also reduces the alkalinity, reinforcing the preservation of the fibers and durability of the material - Photo: Provided by researcher Adriano Galvão de Souza Azevedo
CO₂ capture
“In addition, the curing process adopted in the project involves accelerated carbonation, which not only contributes to the capture of CO₂, but also further reduces the pH of the composite,” Azevedo adds. “This reduction in the alkalinity of the environment reinforces the preservation of plant fibers, improving the durability and eco-efficiency of the final material.”
CO₂ capture by cementitious materials occurs through the reaction between alkaline species present in the matrix and carbonic acid (H₂CO₃), formed from the dissolution of CO₂ in the water in the system. In the case of magnesium oxide (MgO)-based cements, the main alkaline species generated is brucite (magnesium hydroxide). “The magnesium carbonates formed as a product of carbonation tend to precipitate in the pores and voids of the material’s structure,” the chemist says. “The formation of these secondary products fills the microstructure, increasing density, reducing water absorption, and improving mechanical properties.”
In addition to anhydrous magnesium carbonate, without water in its composition, other carbonation products can be formed, such as nesquehonite, hydromagnesite, and dypingite, depending on the temperature, humidity, and CO₂ concentration. “These hydrated carbonates contribute not only to the increase in density, but also to chemical stability over time,” the researcher points out.
“As the carbonation reaction consumes alkaline species, there is a progressive reduction in pH as the reaction progresses. In addition to improving mechanical properties, it also promotes durability, especially when vegetable fibers are present, by reducing their degradation over time” – Adriano Azevedo
The test results indicate that the cement developed in the research captured approximately 100 kilos of CO₂ per cubic meter of material. “Based on this, the project moved on to a new stage, aimed at increasing the rate of CO₂ capture and mineralization, by modifying the initial chemical reactions of magnesian cement, which is suggested by the change in the heat released during hydration,” Azevedo notes. “The next step is to subject the composite to an atmosphere enriched with CO₂ to observe in detail how magnesium carbonates are formed through the mineralization of carbon dioxide, an essential stage for improving the material’s technical and environmental performance.”
Carbonation test of the material; the lighter regions indicate places where CO₂ has been captured and mineralized, the parts with an intense pink color are associated with a lower presence of carbonation products (HMCs) – Photo: Provided by researcher Adriano Galvão de Souza Azevedo
According to the researcher, as this is a significantly different technology from the one used by industry, some stages of the production process will need to be adapted to enable it to be implemented on a large scale. “In addition to evaluating production on a bench scale, the project also includes a technical and economic study on the feasibility of using the CO₂ generated by the plants to carbonate the materials,” he emphasizes. “In this way, the project seeks not only to improve cement composites technically, but also to promote a more sustainable business model with a lower carbon footprint,” the chemist points out.
Professor Holmer Savastano Junior from the FZEA and orofessor Cise Unluer from the Department of Mechanical, Aerospace, and Civil Engineering at the University of Manchester (UK) participated in the research. The project is supported by the São Paulo Research Foundation (Fapesp). The results of the tests with the new type of cement are presented in the article Assessment of carbonation as a complementary strategy to increase the durability of Magnesium Oxysulfate (MOS)-based fiber cement boards.
More information: adrianogalvao@usp.br, with Adriano Azevedo
*Intern supervised by Moisés Dorado
English version: Nexus Traduções, edited by Denis Pacheco
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A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.
A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.