3 Reasons Why Concrete Doesn’t Live Up To Its Environmental Claims
Up to 8% of all global man-made anthropogenic emissions are due to a single material: cement. And our use is increasing.
The cement and concrete industry encourages this use, for example, by claiming that the use of concrete will reduce the “lifetime” carbon emissions of buildings.
The lack of regulation to measure this has allowed these claims to play an important role in persuading designers and specifiers to use certain products. However, research by my colleagues and I shows that these claims are often, to say the least, exaggerated.
We have identified the use of three of these claims. The first is the claim that because concrete has a high thermal mass, allowing it to act as a heat store, it will reduce carbon emissions from heating and cooling a building over the course of a building. of his life.
The second claim is that concrete is more durable than other materials and therefore concrete buildings will last longer, reducing the need to construct new ones. The third is based on the ability of concrete to undergo carbonation, in which carbon dioxide is slowly absorbed from the atmosphere. This means that concrete can be considered a “carbon sink”, and therefore a sustainable choice.
These and other messages are promoted by the Mineral Products Association (MPA), the UK trade association, through their technical advice and industry roadmap for ‘beyond net zero’. Similar messages have been repeated by the European concrete industry.
Our research reveals a very different picture.
Absorbing the heat will not reduce the use of the heater
First, although the thermal mass of concrete does allow it to act as a reservoir of heat or “coolness”, it is unlikely to help reduce carbon emissions from heating buildings. Rather, the ability of concrete to absorb heat is more likely to require increased heating energy consumption, since the concrete must be heated as well as the room space.
This can be illustrated by considering stone churches, which testify to the challenges of heating buildings with high thermal mass. It is true that using exposed concrete can reduce the need for cooling, especially in deep plan office buildings. However, in relatively cool climates like the UK, cooling still uses only a fraction of the energy of heating.
Additionally, cooling is mostly powered by the national power grid, which is rapidly decarbonizing. Our research shows that the calculations for using carbon-intensive building materials, in order to save diminishing amounts of future operational carbon, simply don’t add up.
Buildings are replaced before they need to be
The second argument, sustainability, is also wrong. Our research revealed that few buildings are demolished because they have reached structural obsolescence. Instead, they are being destroyed to make way for “regeneration” in economically booming areas.
There is also little evidence to suggest that concrete buildings are more durable than others. The number of exposed concrete buildings and structures that have “concrete cancer”, in which the steel reinforcing bars have begun to rust and degrade and the concrete to break, suggests quite the opposite.
Meanwhile, millions of ancient buildings around the world constructed from wood, as well as brick and stone, suggest that other building materials can be very durable.
Concrete buildings don’t absorb a lot of carbon
Finally, the capacity of concrete to absorb carbon is generally overestimated. Only the exposed surface of the concrete will carbonate. Thus, concrete located underground, or hidden under plaster or cladding, will not act as a carbon sink.
Reinforced concrete is also designed to minimize carbonation, as this leaves the steel reinforcement vulnerable to rust. Carbonation therefore mainly occurs after the end of the building’s life, once the concrete has been crushed.
If concrete rubble is left exposed to the air, it will slowly reabsorb some of the carbon dioxide emissions emitted during its original manufacture. This is more correctly understood as “partial re-carbonation” and hardly a good argument for using additional high-carbon concrete in new buildings.
Is the tide changing?
In 2021-22, the UK Government’s Environmental Audit Committee carried out an inquiry into the sustainability of the UK’s built environment. In its response to the investigation, the MPA again repeated its thermal mass, durability, and carbonation claims.
However, the report on the results of the investigation does not repeat these assertions. Instead, it encourages the increased use of low-carbon materials such as wood and calls for the measurement of carbon throughout the life of buildings to be included in regulations.
Along with the recent introduction of such regulations in several European countries, this should encourage the move away from high-carbon materials. The accurate measurement and actual reduction of carbon, both embodied in materials and resulting from the operation of a building, is essential to reducing our impact on the environment.