A new ecoefficient cement is developed

The formula for the cement allows the cement industry to reduce CO2 emissions, increase efficiency and reduce the concentration of cement in the composition of concrete and mortar.

By Elton Alisson

Agência FAPESP – A technology developed by researchers from the Universidade de São Paulo’s Polytechnic School (Poli-USP) could help the cement industry to reach its objectives: doubling cement production to meet global demand and reducing the carbon footprint, as the sector is among those most responsible for emitting carbon dioxide (CO2) into the atmosphere.

The researchers created a formula to substitute the majority of the material responsible for CO2 emissions in the product’s manufacturing process, decreasing the concentration of reactive material produced at high temperatures in the composition of cement and, consequently, concrete and mortar coating, while maintaining the resistance of the material.

The formula was tested in the laboratory and has sparked interest among companies that are analyzing the feasibility of its use on an industrial scale, where cement is the second-most produced and consumed product in the world, behind only foodstuffs.

“In some laboratory experiments, we managed to reduce the quantity of binder [a fraction of the cement capable of reacting with water] in high-resistance concrete with the product made with this formulation,” said Vanderley Moacyr John, professor at the USP Polytechnic School’s Department of Civil Construction Engineering and one of the coordinators of the project. “Recently, we managed to adapt the formulation for lower-resistance concrete with half the binder used in a conventional product.”

According to the researcher who conducted the FAPESP-funded project, traditional cement — so-called Portland cement — is basically composed of clay and limestone. These materials are extracted from mines, ground and then forged in furnaces at 1,500 degree Celsius, transforming them into small clinker pellets. The clinker pellets are mixed and ground with gypsite — the prime material for plaster — until they become cement.

To produce a ton of clinker, however, the cement industry emits between 800 and 1,000 kilos of carbon dioxide, including CO2 generated by the decomposition of limestone and the fossil fuel burned to keep the furnaces working.

With a view to reducing CO2 emission in clinker production, the cement industry in the last few decades has begun to replace part of the material with blast furnace slag — a steelmaking residue — and, more recently, fly ash — a residue of coal used in thermo-electric plants.

The problem with these two solutions, however, is that the steel industry — also a high CO2 emitter — and the generation of fly ash are not growing at the same speed as cement companies, making long-term planning impossible. “The strategies used today by the cement industry to mitigate CO2 emissions are insufficient,”considers John.

“Because the scale of cement production is 3.5 billions tons per year and the global production of this material will reach an estimated 5.5 billion tons by 2050, the cement industry could be responsible for 30% of total global CO2 emissions, surpassing that of many countries,” he said.

Limestone powder

According to the Poli-USP professor, because of these limitations the cement industry has, since the 1970s, used another candidate material to partially replace clinker in the cement formula as filler: raw limestone powder. This filler is a prime material that does not require thermal treatment (calcination) — a process that is responsible for more than 80% of the energy consumption and 90% of CO2 emissions in cement manufacturing.

The quantity of filler in the cement formulation, however, has been limited to a maximum of 10% in Brazil and up to 30% in some cases in Europe. This is because the limestone is ground along with the cement and, because there is no way to control the size of material particles, the additive limit is low.

The Poli-USP researchers used granulometry control techniques, which are used in the foodstuff and pharmaceutical industries. They showed in laboratories that by combining the granulometry of limestone powder it is possible to increase the proportion of the material to 70% and to reduce the quantity of clinker in the composition of cement to 30%.

“Currently, the level of filler in cement sold around the world is 6%, and in Brazil it reaches a maximum of 10%. In Europe, in some situations, a ton of cement has 700 kilos of clinker and 300 kilos of filler (including other types of filler in addition to raw limestone],” noted Bruno Damineli, one of the authors of the study, who is pursuing his doctorate at Poli-USP as a part of the project.

“We showed that it is possible to invert this composition and produce a ton of cement with 300 kilos of clinker and 700 kilos of limestone powder,” he said.

In addition to a controlled standard on the size of grains, according to the researcher, the limestone powder filler particles and clinker must be treated with chemical dispersants, such as polycarboxylates, which impede agglomeration and the formation of clumps in the water.

Consequently, the dispersant reduces the quantity of water and cement needed to mix the sand and stone to produce the “glue” in the concrete used in the civil construction industry.

“Generally, the least efficient cement presents clumps. Because of this it is less reactive and efficient and requires a much greater quantity of water flow because it is more porous,” explained Rafael Pileggi, professor at Poli-USP and one of the authors of the project.

“Because cement with more ground filler needs more water flow, it is possible to make concrete that is more resistant and less porous than conventional cement,” said Pileggi.

The researchers obtained similar results with other cement-based products. Through a project conducted with FAPESP funding, the Poli-USP research group found that the level of cement in stucco could be reduced while maintaining resistance to adherence of the material.

“We determined that it is possible to reduce the quantity of mortar cement by using cement with a higher proportion of ground filler and that the resistance of the material does not decrease. We are showing that the resistance does not depend on the cement,” John commented.