No other Earth material usage matches these two. But unlike water which is essential to life on Earth, concrete materials have a Jekyll and Hyde relationship with us. The Jekyll side of concrete is its use in almost everything humans build on the planet. Its Hyde side is the amount of greenhouse gas emissions created when we produce it.
Today’s process of producing concrete begins with the mining of raw limestone and clay which is then crushed, mixed with other materials and then fed into kilns to be heated to 1,450 Celsius (2,640 Fahrenheit) degrees. The output yields clinkers, a greyish chunky output that is cooled, ground, and mixed with additional limestone and gypsum to make the raw cement that goes into concrete. The industrial process produces lots of carbon dioxide (CO2) amounting to 8% of total greenhouse gasses emitted into the atmosphere today.
For those who raise the issue of water vapour being a far more visible greenhouse gas, it should be noted that Earth’s atmosphere long ago accommodated the water cycle. What the atmosphere, in accommodating today’s industrial emissions, is doing is heating up with concrete representing number four in the list of biggest greenhouse gas sources, trailing only coal, oil, and natural gas.
Concrete producers are well aware of the Paris Climate Agreement and the goal of countries and the industry to achieve net-zero emissions by 2050 and to be in negative emissions after that to draw down on existing CO2 in the atmosphere. What that means is a dramatic change in every aspect of the production process. Retrofitting older cement plants to burn blue and green hydrogen as fuel for kilns is one solution. Capturing CO2 is another.
A company based in Canada has made CO2 part of its end product. CarbonCure Technologies’ recipe for concrete turns its finished concrete blocks and pavers into a carbon sink. Another company, HeidelbergCement, a German company recently announced plans to build the first CO2-neutral cement plant in the world to be located in Sweden and operational by 2030.
The alternative to these types of solutions is for architects and builders to stop using concrete materials which would be better for the atmosphere, but for the industry, disastrous.
But what about all those concrete buildings and structures already in existence? Is there something that they can do to contribute to achieving a low-carbon future? Researchers may have come up with just the right idea: to turn concrete into rechargeable batteries.
Using concrete to store electricity is an idea that is gaining ground and although the material is far less efficient in storing electricity than traditional chemical and solid-state batteries, its abundance makes it a very attractive option. What would be great is to be able to turn existing concrete building inventories into battery storage for renewable energy producers. Imagine a building with solar arrays pumping out electricity and its concrete walls acting as battery backup when the sun is no longer shining.
We are not there yet, but Emma Qingnan Zhang and Lu-Ping Tang, of the Division of Building Technology, Department of Architecture and Civil Engineering, Chalmers University of Technology, in Gothenburg, Sweden, have a cement-based battery with energy densities of 7 Watt-hours per cubic metre. To use cement as a battery the researchers have incorporated anodes of iron and zinc, and cathodes of nickel-based oxides along with carbon fibres into the mix. And although their battery doesn’t generate a lot of power when compared to chemical and solid-state ones, with concrete as a primary construction material, turning buildings into storage batteries while serving as living accommodation would be a game-changer.
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The media in the past week has been speculating this very topic. A Time magazine headline from July 1st states, “The Fear Is Very Real. The Surfside Collapse Is Renewing Focus on Climate Change Risks.” A National Geographic article published July 2nd leads with these words, “Miami condo collapse highlights urgent need to adapt to rising seas” even though it immediately concedes that climate change was likely not a factor. A July 1st Rolling Stone headline reads “Miami’s Climate Dystopia Gets Real: South Florida’s real estate is only going to get more deadly if we continue to ignore all the warning signs of a doomed coastline.” Even the Biden administration’s Energy Secretary, Jennifer Granholm, speculated that climate change may have played a part in the building’s structural failure.
Pictures from the building showed corroded rebar in the reinforced concrete found in the basement. An engineering report from 2018 noted cracking and degradation of the concrete. What about climate change would contribute to such physical evidence?
We know that the production of cement and concrete is a significant contributor to greenhouse gas emissions. But how many of us are aware of how reinforced concrete interacts with climate and carbon dioxide (CO2) whether from heat, the atmosphere or seawater?
It turns out that concrete absorbs CO2 in a process called carbonation. You would think that could be beneficial if we were to consider our concrete infrastructure could become a primary carbon sink. But we would be drawing a false conclusion. That’s because reinforced concrete combines two materials, embedded steel rebar and cement. And it is this combination that produces an electrochemical process, which in the presence of air and water containing CO2 produces gradual erosion of both materials. The corrosion proceeds at a rate of up to one millimetre (0.04 inches) per year. In the presence of higher water exposure, the carbonation corrosion rate is faster.
In South Florida, that water exposure comes from two sources, the atmosphere and the ocean. Florida’s high relative humidity contributes to CO2 penetration of reinforced concrete leading to carbonation-induced corrosion at a higher scale. And sunshine-day and high-tide flooding from the Atlantic Ocean, increasingly common occurrences in South Florida, produces chloride-induced corrosion as seawater penetrates the pores in the concrete surfaces and reaches the rebar steel which causes rusting in increasing volumes over time. How much time has to elapse before this can lead to major structural problems? Engineers and material scientists state that the timeline can be as small as 15 years.
And then there is the interaction of concrete structures with heat, a process called heat-induced delayed expansion which can cause swelling and cracking of the materials. Normally this is seen during the making of cement, and not after it has been converted into reinforced concrete. But concrete surfaces get bombarded by sunlight and in Florida, these surfaces are often far hotter than the air surrounding them. A concrete surface can reach temperatures of 60 to 70 Celsius (140 to 158 Fahrenheit), hot enough for heat-induced expansion to corrode surfaces causing cracks that become points for other invasive processes to penetrate the material.
In the case of the Surfside condominium, likely all of the above contributed to what was a growing number of structural deficiencies in the building after standing for 40 years. You can blame climate change for inducing these deficiencies. But it is human failure that ultimately led to the building collapse and a death toll of 28 so far with 117 still unaccounted for.
When buildings are designed and planned, the engineers take into consideration environmental conditions. In the case of the Champlain Towers, in Surfside, this would be no exception. Bud would a building designed more than 40 years ago have taken into consideration saltwater intrusions from sunshine and high tide flooding? And would the engineers have been paying attention to the potential of both atmospheric warming and carbonation?
One thing is certain: those governing South Florida haven’t paid attention. Florida’s state building code is not where it should be in light of the threat from climate change. And county and municipal governments are negligent in regulating building inspections to ensure this infrastructure is resilient. That’s because experience around the world over the last 50 years is clearly demonstrating that ordinary reinforced concrete used in coastal environments is highly susceptible to corrosion.
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