“Cement is, after water, the second most consumed material in the world and its use will continue to increase as it is essential to satisfy the construction needs that will be generated on a planet that will gain two billion inhabitants by the year 2050” . The statement is made by Elena Guede, senior vice president of sustainability at the multinational construction materials company CRH. The expert, who was at the time the first woman to run a cement factory in Spain, also warns that “70% of the urban infrastructure necessary to accommodate this population growth has not been built to date” and that cement It is an “irreplaceable material due to its durability, resilience, flexibility, low maintenance, recyclability, thermal efficiency and carbon dioxide (CO?) absorption capacity.”
However, not all benefits. Cement production is responsible for between 7% and 8% of global greenhouse gas emissions. In the roadmap of the Spanish cement industry to achieve climate neutrality in the year 2050, published by Oficem, the use of waste and its recovery or recycling play an important role in the decarbonization of the sector. The latter was, precisely, the topic of a conference organized in September by the Repsol Foundation Energy Transition Chair at the Comillas Pontifical University.
In the session, the use of fuels derived from waste was proposed, among other measures. Currently, in Spain, only 26.5% of the heating value of cement kilns comes from this type of fuel, a percentage much lower than the European Union average (46%) and far from that of countries like Austria. , Sweden, Germany and Norway, where the rates of substitution of fossil fuels for fuels derived from waste are greater than 60%.
Another proposal consists of the use of raw materials from waste to obtain clinker, the intermediate product with which cement is manufactured and which is generated from the calcination of limestone. The chemical reaction that causes clinker is responsible for between 60% and 65% of the CO? emissions from cement manufacturing (the rest is due to the burning of fuels to heat the kilns). The use of waste and byproducts from other industrial processes can be used to replace part of the limestone. These include, for example, recycled concrete from construction and demolition waste, air-cooled slag and waste from lime production.
Finally, another proposed solution is the use of biochar, a type of charcoal made from organic waste that absorbs CO? from the surrounding air. Two researchers from Washington State University have developed a formula to create concrete (the main derivative of cement) composed of 30% biochar. The concrete that the scientists obtained not only has a strength comparable to ordinary cement, but it absorbs up to 23% of its own weight in CO?.
It should be noted that, as Elena Guede pointed out and independently of biochar, cement structures act as a CO? sink. That is, they naturally capture carbon dioxide. On the other hand, the cement sector is one of the main recyclers in the country. The Spanish cement industry has recovered nearly 60 million tons of waste since 2004, which are used as raw materials, according to the Observatory of the circular economy in the cement industry.
