One of the major contributors to climate change is right under your feet, and transforming it can be a powerful solution to keeping greenhouse gases out of the atmosphere.
The production of cement, the binding element in concrete, accounted for 7% of total global carbon dioxide emissions in 2018. Concrete is one of the most widely used sources on earth, with an estimated 26 billion tons produced annually worldwide. Production is not expected to slow down for at least another two decades.
Given the scale of the industry and greenhouse gas emissions, technologies that can invent concrete can have profound consequences for climate change.
As engineers working on infrastructure and construction issues, we have designed next-generation concrete technology that can reduce the carbon footprint of infrastructure and increase durability. This includes concrete with CO2 application that traps the greenhouse gas and can be stronger and even flexible.
The industry is ripe for dramatic change, especially as the Biden government promises to simultaneously make major investments in infrastructure projects and reduce U.S. emissions. However, in order for CO2 to work in concrete on a wide scale so that the emissions are drastically reduced, all its related emissions must be taken into account.
Reconsideration of concrete
Concrete consists of composite materials – mainly rocks and sand – along with cement and water.
Because about 80% of the concrete’s carbon footprint comes from cement, researchers worked to find substitute materials.
Industrial by-products such as iron slag and coal fly ash are now regularly used to reduce the amount of cement required. The resulting concrete can have significantly lower emissions due to the change. Alternative binders, such as limestone-limed clay, can also reduce the use of cement. One study found that the use of limestone and calcined clay can reduce emissions by at least 20%, while also reducing production costs.
Apart from the development of mixed cement, researchers and companies are focusing on ways to use trapped CO2 as an ingredient in the concrete itself, to block it away and prevent it from entering the atmosphere. CO2 can be added in the form of aggregates – or injected during mixing. Carbonic acid curing, also known as CO2 curing, can also be used after concrete has been poured.
These processes convert CO2 from gas to mineral, creating solid carbonates that can also improve the strength of concrete. This means that structures require less cement, which reduces the amount of related emissions. Companies such as CarbonCure and Solidia have developed technologies to use these processes for concrete that is poured on construction sites and in precast concrete, such as ash blocks and other construction materials.
At the University of Michigan, we are working on assemblies that produce a flexible concrete material that allows for thinner, less brittle structures that require less steel reinforcement, further reducing related carbon emissions. The material can be designed to maximize the amount of CO2 it can store by using smaller particles that react easily with CO2 and then convert it to minerals.
The CO2-based flexible concrete can be used for general buildings, water and energy infrastructure, as well as transportation infrastructure. Flexible concrete was used in the 61-story Kitahama Tower in Osaka, Japan, and bridge slabs in Ypsilanti, Michigan.
The challenge of life cycle releases
These leading technologies may begin to address the carbon footprint of concrete infrastructure, but barriers still exist.
In a study published on February 8, three of us looked at the release of the life cycle of the application of CO2 in concrete and found that estimates do not always take into account the emissions of CO2 capture, transport and use. Together with colleagues, we devised strategies to ensure that carbon curing has a strong emission advantage.
In general, we recommend developing a standard CO2 curing protocol. Laboratory experiments show that CO2 curing can improve the strength and durability of concrete, but the results vary according to specific curing procedures and concrete mixtures. Research can improve the conditions and timing of steps in the healing process to increase the performance of concrete. Electricity consumption – the largest source of emissions during curing – can also be reduced by streamlining the process and possibly by using waste heat.
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Advanced concrete mixtures, especially flexible concrete, are already beginning to address these problems by increasing durability.
Integration of infrastructure and climate policy
In 2020, a wide range of companies announced steps to reduce their emissions. However, the government’s investment and procurement policies are still needed to transform the construction industry.
Local governments are taking the first steps. Legal and low-carbon concrete projects to reduce the amount of cement in concrete have sprung up across the country, including in Marin County, California; Hastings-on-Hudson, New York; and a sidewalk pilot in Portland, Oregon.
In New York and New Jersey, lawmakers have proposed state-level policies that would offer price reductions in the bidding process to proposals with the lowest concrete emissions. These policies can serve as a blueprint for reducing carbon emissions through concrete production and other building materials.
Nationally, the disintegration of federally managed infrastructure has been an ever-growing crisis. The Biden administration can tackle the problems, as well as climate change, and create jobs through a strategic infrastructure program.
The Minister of Transport, Pete Buttigieg, recently stated that “huge opportunities for job creation, equity and climate performance when it comes to promoting America’s infrastructure. Policies that increase low-carbon to a nationwide climate solution can follow.
This article was published from The Conversation, a non-profit news site dedicated to sharing ideas from academic experts. It was written by: Lucca Henrion, University of Michigan; Duo Zhang, University of Michigan; Victor C. Li, University of Michigan, and Volker Sick, University of Michigan
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Lucca Henrion works as a research fellow in the Global CO2 Initiative at the University of Michigan. He is a volunteer at the Open Air Collective.
Duo Zhang works as an assistant researcher at the University of Michigan. He does research on concrete materials that carbon sequestrate.
Victor C. Li receives research funding from the Department of Energy (ARPA-E) and the Aramco Company. He is the James R. Rice Distinguished University Professor at the University of Michigan, Ann Arbor. Professor Li is the leader of the Center for Low Carbon Built Environment (CLCBE) at the University of Michigan.
Volker Sick receives funding from the U.S. Department of Energy and the Global CO2 Initiative at the University of Michigan.