Concrete manufacture is responsible for 8% of global carbon emissions, with the ingredient “clinker” accounting for most of it. Global demand for cement (which hardens into concrete) is expected to increase 48% from 4.2bn to 6.2bn tons by 2050, mainly driven by developing nations. China used more concrete between 2011 and 2013 than the United States did in the entire 20th century. Ben Skinner and Radhika Lalit at RMI look at the materials and engineering innovations that are at the forefront of decarbonisation efforts that target zero emissions by 2050. New engineering methods saved New York’s Freedom Tower and the Shanghai Tower in China 40% and 24% of concrete use respectively. Using less concrete, reusing old concrete, low-carbon concrete, SCMs (similar to clinker), Holcim’s low-carbon ECOPlanet cement, and the new LC3 cement are all reviewed by the authors. Ultimately, the sector needs a multi-pronged approach, targeting reductions in concrete, cement, and clinker. Success won’t come fast nor be total, so alternative fuels, electrification, and carbon capture will have to eliminate remaining emissions, say the authors.
As world leaders convened at the World Economic Forum’s annual conference in Davos to discuss global issues including climate change, they spent the day surrounded by concrete. Houses, skyscrapers, roads, freeways, bridges, sidewalks, water systems, dams, and more rely on concrete for its unrivalled strength properties, durability, versatility, and low cost. It’s no surprise that global demand for cement, which hardens into concrete when mixed with water and minerals, is expected to increase 48 percent from 4.2 billion to 6.2 billion tons by 2050.
In China’s recent massive urbanisation, the nation used more concrete between 2011 and 2013 than the United States did in the entire 20th century. While China’s use of concrete slows down, consumption in India, Africa, and other developing countries will skyrocket amid economic development, with uses split between residential, commercial, and infrastructure.
Concrete: 8% of global carbon emissions
While essential to building the structures that improve our everyday life, concrete is responsible for 8 percent of global carbon emissions; and 90 percent of these emissions come from the production of clinker, the primary strength-contributing ingredient of concrete.
…mostly thanks to “clinker”
In accordance with the Paris Climate Agreement, the global concrete industry must reduce emissions by 16 percent by 2030 and 100 percent by 2050 to stay within the 1.5°C warming carbon budget. This effort will require significant changes across the concrete value chain, but the easiest and most cost-effective measure is to use less material while meeting project requirements. Reducing the demand for carbon-intensive clinker will help put the concrete industry back on track to reaching its climate goals.
…Using less concrete: New York, Shanghai
The first step toward mitigating the sector’s carbon footprint is to use less concrete in each application, even as applications grow. There are several existing and developing methods of ensuring concrete material efficiency that can lead to large carbon savings without changing the material itself. Traditional designs of buildings and other projects aim to minimise cost rather than carbon emissions and layer on excessive design margins. However, recent and ongoing progress in automated design tools allow structural engineers and architects to swiftly explore more structural options for a given project, taking material efficiency into greater consideration.
RMI’s publication Profitably Decarbonizing Heavy Transport and Industrial Heat dives into the concrete and steel savings that can be achieved profitably through better structural design. For example, such engineering methods saved New York’s Freedom Tower and the Shanghai Tower in China 40 percent and 24 percent of concrete use respectively. As automated design software improves, lean design is expected to be cost competitive (in design time) with current methods and become a main driver of demand reduction.
A second lever is not to use new concrete. In some cases, options like reusing concrete elements from old structures can provide CO2 reductions. However, the right answer will vary from region to region and depend on a host of other factors including the type of construction, design requirements, local availability of materials, and more.
At the same time, building codes and market preferences must be adapted to allow the use of low-carbon concrete. As carbon becomes a key consideration of building our infrastructure, we must close the innovation gap between designers’ needs and existing technology. Tools like the EC3 Tool efficiently compare the embodied carbon of project design options alongside rigorous testing will pave the way for the low–carbon structures of the future.
Making lower-carbon concrete
In addition to reducing the total amount of concrete used in buildings, using less cement per unit of concrete is another effective way to reduce the clinker content and carbon intensity of concrete. To reduce binder intensity without increasing risk we should transition toward bulk cement usage such as ready-mix concrete, in which cement wastage is reduced by up to 30 percent, mix specifications and mix creation are more precise, and chemicals called admixtures can be added to improve concrete properties and reduce cement requirements.
In many countries, builders still prefer the use of bagged cement which leads to both waste and overuse. Industrialising a portion of the world’s bagged cement market (currently 42 percent) would yield significant cement savings but requires investment into ready–mix plants and cement trucks and considerable change in local market dynamics. In regions such as the US and EU cement usage is already largely industrialised, whereas the market share of bagged cement in India is nearly 90%, offering a huge opportunity for carbon savings. Existing plants are already incorporating a wide variety of chemical admixtures such as dispersants that reduce the need for water and consequently the amount of cement needed. Other admixtures include accelerants that strengthen concrete more quickly and air–entrenching agents which allow air bubbles to increase volume and displace solid material input for lower strength applications.
Innovation to create new admixtures as well as increase applicability, efficiency, and cost competitiveness of existing solutions will allow for drastically lower clinker and cement content in concrete while maintaining performance in a given application.
Alternatives to traditional Portland clinker cement have also been the subject of much research, but cost, material performance, availability of raw materials, and energy inputs have resulted in limited adoption. While this lever has some merit, large-scale deployment of these niche solutions is unlikely in the short term as they remain relatively customised products, seeking niches in a highly commoditized world.
SCMs, similar to clinker
However, using less ordinary Portland cement has gained ground in another way — substituting limited amounts of supplementary cementitious materials (SCMs) in cement blends to partially displace clinker. SCMs exhibit similar behavior to clinker when mixed with water and contribute to the strength of the cement blend, but in most cases cannot fully displace clinker. SCMs include industrial waste products such as ground granulated blast furnace slag (GBFS) and fly ash, calcined clays, natural pozzolans, and ground limestone. The current clinker–to–cement ratio is 0.72, but the Global Cement and Concrete Association (GCCA) Concrete Future roadmap targets an 18% reduction in average global clinker content of cement by 2050.
Holcim’s low-carbon ECOPlanet cement
Selecting concrete with high clinker substitution rates can immediately reduce related carbon emissions of a traditional five-story building by 32 percent with less than a 0.5 percent increase in total construction cost. The ancient Roman Pantheon is constructed entirely of natural pozzolan cement while more modern examples include The Spheres in Seattle and the Iconic Tower in Cairo, both of which use Holcim’s low-carbon ECOPlanet cement. While many of these SCMs yield performance benefits, increased setting time and reduced early strength can delay project timelines and incur additional cost in some cases.
Improving the accelerating admixtures that improve the setting time and strength is crucial for greater incorporation of the SCMs in blended concrete. Further testing and updating standards are also crucial to improve adoption. It’s important to note, however, that the supply of fly ash and GBFS is expected to decline as their sources, coal power and steelmaking plants respectively, are phased out and decarbonised, making exploration and extraction of other SCMs even more critical to creating greener concrete. Given the global availability of limestone and calcined kaolinite clay, LC3 cement — consisting of 50 percent clinker, 30 percent calcined clay, 15 percent limestone, and 5 percent gypsum — is seen as one promising approach to the future of low-carbon concrete. As new SCMs and improvements to the performance of current blended cements emerge, the clinker factor and carbon intensity of concrete will continue to decrease. However, time is of the essence in this decisive decade of climate action.
A net-zero future
Entities such as First Movers Coalition, ConcreteZero, Industrial Deep Decarbonization Initiative, and others are asking for low-carbon concrete now, and suppliers will need to act to match the increasing demand. Innovation across the concrete value chain can decrease both emissions and costs, pushing the technical limits of carbon intensity and informing policy changes. We need a multi-pronged approach, targeting reductions in concrete, cement, and clinker.
The structural engineers of the future will quickly explore an efficient frontier of design options using state–of–the–art software while ready–mix plants deliver less carbon–intensive concrete to projects. These demand reductions are only part of the equation, and supply–side measures such as alternative fuels, electrification, and carbon capture will have to eliminate remaining emissions.
Through the Mission Possible Partnership, RMI has partnered with Energy Transitions Commission, Systemiq, World Economic Forum, ECRA, and GCCA to explore each of these decarbonisation levers in addition to decarbonisation levers on the supply side in the soon-to-be-released Cement Sector Transition Strategy. The concrete and cement industry is at the cusp of a radical transformation in its journey to the net-zero energy transition.
Ben Skinner is a Senior Associate on the Climate Aligned Industry team at the Rocky Mountain Institute
Radhika Lalit is a Manager with the Buildings Practice at the Rocky Mountain Institute
This article was first published on RMI.org and has been reprinted with permission