{"id":661,"date":"2019-12-22T12:31:41","date_gmt":"2019-12-22T11:31:41","guid":{"rendered":"https:\/\/wpethzprd.ethz.ch\/energy\/?p=661"},"modified":"2025-03-27T16:06:25","modified_gmt":"2025-03-27T15:06:25","slug":"concrete-1-5c-world","status":"publish","type":"post","link":"https:\/\/blogs.ethz.ch\/energy\/concrete-1-5c-world\/","title":{"rendered":"Concrete – the building material of a 1.5\u252c\u2591C world?"},"content":{"rendered":"\t\t
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By Johannes Tiefenthaler<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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Bridges, tunnels, buildings – concrete plays a key role in our daily life. How is it manufactured? Can it be recycled? What is its climate impact? Read on and you\u2019ll find out how we can decarbonize concrete. <\/b><\/p>

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From limestone to concrete<\/b><\/h3>

Switzerland has 450 concrete plants and uses 14 million m\u00b3 of it every year; making it the most widely used building material. Being such a heavy and large product, transport distances have to be short to remain competitive \u2013 making it a local and regional business. In addition to sand and gravel, which can be found in nature, concrete manufacturing requires cement, which is an energy- and CO2 <\/sub>emission-intensive industrial process. Cement is obtained by grinding limestone with so-called clinker, which is the \u201cmagic\u201d binder responsible for the strength of the concrete. To produce 1 ton of clinker, 1250 kg limestone are required, which when heated to above 600\u00b0C (necessary for the production of clinker), decompose and release 550 kg CO2<\/sub> (fig.1). From an energy requirements perspective, producing 1 ton of clinker requires 115 kg of coal, which emit around 290 kg CO2<\/sub><\/a>. 1m\u00b3 concrete (equal to 2.5 tons) contains on average 320 kg cement, 160 kg water, 2000 kg sand and gravel and emits 230 kg CO2<\/sub>.<\/p>

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Figure 1: The plot puts the raw materials for clinker and cement in perspective with the CO\u2082 <\/span>emissions. <\/em><\/span><\/p>

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Renewable energies alone<\/em> cannot stop climate change<\/b><\/h3>

Cement manufacturing in responsible for 85% of the overall concrete manufacturing emissions. 3 million tons CO2<\/sub> or 6% of Swiss inland GHG emissions are accounted to the concrete sector in 2017. In a world with only CO2<\/sub>-free energy, emissions from coal and concrete operations can be mitigated. However, the calcination of limestone to create clinker still releases 1.7 Mt CO2 <\/sub>in Switzerland. Reducing emissions by 45% (from 3 Mt CO2<\/sub>) is a big achievement \u2013 but it is not good enough to stop global warming.<\/span><\/p>


In Paris, 195 countries agreed on limiting global warming to well below 2\u00b0C. This implies that all anthropogenic emissions with a global warming effect have to go to zero between 2040 and 2060. But here comes the problem: using renewable energies does not allow decarbonizing the cement industry, because the problem is not the energy, it is the emissions due to the thermal decomposition of limestone!<\/span><\/p>

What does the sector do to reduce emissions?<\/b><\/h3>

Today, the cement sector has two major emission reduction strategies.<\/span><\/p>

      1. Incineration of waste: By replacing coal by car tires, solvents and plastics, CO2<\/sub> emissions are reduced since these wastes emit up to 50% less fossil CO2<\/sub> than coal.<\/span><\/li>
      2. Use of less clinker in cement: different types of cements require different amounts of clinker. This approach effectively reduces emissions \u2013 however, every cubic meter of concrete requires at least 160 kg clinker, therefore there is a limit to the CO2 <\/sub>emission reduction.<\/li><\/ol><\/li><\/ol><\/li><\/ol>

        All other emission reduction measures, like energy efficiency measures or waste heat recovery have a very limited effect on the CO2<\/sub> balance of cement.
        <\/span><\/p>

        Does cement recycling reduce emissions?<\/b><\/h3>

        In addition to reducing the clinker amount in cement, recycling cement could be an option to reduce the CO2<\/sub> emissions related to the decomposition of limestone. However, cement cannot be recycled as cement. But concrete (containing cement) is recycled as a replacement for gravel and sand in recycling concrete. Recycling concrete is concrete with a recycling material content of more than 40% by weight. There are quality issues associated with the use of recycling materials. EMPA realized with interviews to over 10 concrete plant owners<\/a>, that there is 5-10% more cement in recycling concrete to overcome quality issues – effectively increasing CO2<\/sub>\u00a0<\/sub>emissions.<\/p>

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        Figure 2: \u00a0A concrete crushing operation on a Swiss concrete recycling plant. <\/em><\/span><\/span><\/p>

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        How can a future, climate neutral cement and concrete sector look like?<\/b><\/h3>

        The only way to stop emitting CO2 <\/sub>is by using carbon capture and storage (CCS) technologies in concrete production. CCS is in operation at full scale since 1996 in Sleipner, Norway. All components are proven technologies. CCS technologies were specifically developed to mitigate CO2<\/sub> emissions from large industrial point sources like cement manufacturing. The first component in the technological chain is the CO2<\/sub> capture step, where CO2<\/sub> is removed from the cement flue gas. The purified CO2<\/sub> is afterwards liquefied for transport per truck, train, ship or pipeline to a storage place. There is basically one main option to store CO2<\/sub> permanently at the required scale:<\/p>

            1. Geological CO2<\/sub> storage<\/li><\/ol><\/li><\/ol><\/li><\/ol>

              CO2<\/sub> is stored in saline aquifers or exploited oil and gas fields. Aquifers that qualify for CO2<\/sub> storage need to show the following characteristics:<\/p>