Cement production’s long-term Co2 emissions can be dramatically decreased!

Two major public debate subjects are global warming and affordable housing. Climate protection is achieved by lowering carbon dioxide emissions, which are greenhouse gas (CO2). The construction of more housing creates houses. Concrete, the essential building material in our modern world, is required for this. Concrete appears to be unproblematic at first glance. It is non-toxic, does not include any fossil fuels, and does not float in the oceans as plastic debris.

However, this idea is false because cement production is the world’s greatest industrial emitter of CO2, accounting for around 8% of global CO2 emissions, or 2.7 billion tonnes per year. It is due to the burning of fossil fuels—mainly coal—at roughly 1,000°C and sintering at around 1,450°C. Cement is a handy material that can be cast into practically any shape, affordable and complex. In concept, it is made up of merely sand, gravel, water, and binder cement.

The latter is formed by calcining lime, clay, and other ingredients, and when hardened, it creates stable calcium silicate hydrates, which are responsible for concrete’s characteristics. The difficulty, however, is that when lime (CaCO3) is calcined, one molecule of the greenhouse gas CO2 is released for every molecule of calcium oxide (CaO) generated, often known as “burnt lime” or “quicklime.”

It translates to 2.7 billion tonnes of CO2 for roughly 4.5 billion tonnes per year for global cement production. It is around half of all transportation’s annual CO2 emissions. China is responsible for about half of the emissions from cement manufacture, while Germany is responsible for around a quarter of the emissions. Calcination of lime, which is damaging to the environment, is avoided by grinding raw lime with sodium silicate.

Chemists from Germany’s Johannes Gutenberg University Mainz (JGU) have devised a technology that, in the long run, might dramatically reduce CO2 emissions from cement manufacture. In this procedure, the raw lime (CaCO3) is milled with solid sodium silicate rather than transformed into burnt lime in coal-fired kilns (Na2SiO3). This milling stage generates an “activated” intermediate that has a homogenous distribution of cement ingredients.

When calcium silicate hydrates are treated with sodium hydroxide solution, a structurally similar substance to calcium silicate hydrates is generated. A complex chemical cascade carries out the creation of cement paste and its setting with water. The basic processes of which have been explained analytically utilizing high-tech methods. The milling step is done at ambient temperature, but the lime calcination requires 1,000 to 1,500 degrees Celsius. The mechanical energy input for grinding ordinary cement is only around 10% of the energy consumed in the calcination process, at 120-kilowatt hours per tonne.

However, this is only comparable to the energy saved — and accompanying CO2 emissions — by burning fossil fuels in the cement manufacturing process. More crucially, avoiding lime calcination, CO2 emissions in the gigaton range might be avoided. Because grinding is a standard procedure in the cement industry, it is possible to scale up the method from the lab to the industrial level.

Professor Wolfgang Tremel of Mainz University and Dr. Ute Kolb of Mainz University share the following viewpoint: “The technique has the potential to produce cement for large-scale processes,” claimed the JGU Department of Chemistry two group leaders. “However, implementing it on a technical scale would take many years, and hence would not provide a short- or medium-term CO2 emission solution.”

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