3 reasons concrete doesn’t live up to its environmental claims

up to 8% All global anthropogenic man-made emissions are caused by just one material – cement. And our use of it is increasing.

The cement and concrete industries are encouraging this use, for example, by claiming that using concrete will reduce “whole life” Carbon emissions from buildings.

The absence of regulations to measure this has allowed such claims to play an important role in persuading designers and specifications to use certain products. Although, Research The work done by my colleagues and myself shows that these claims are often at least exaggerated.

We have identified the use of three such claims. The first is the claim that because the height of the concrete is greater thermal massWhich allows it to act as a heat store, it will reduce carbon emissions from heating and cooling a building over the course of its life.

The second claim is that concrete is more durable than other materials, and therefore concrete buildings will last longer, reducing the need for new construction. 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 seen as a “carbon sink”, and is therefore a sustainable option.

These messages are promoted, among other things, by the UK trade association Mineral Products Association (MPA) through their technical guidance and their area roadmap. “Beyond net zero.” similar messages has been replicated by the European concrete industry.

Our research paints a very different picture.

Absorbing heat will not cut heating usage

First, while the thermal mass of concrete actually allows it to act as heat, or “cool”, it is likely to do little to reduce carbon emissions from heating buildings. It is more likely to require increased use of heating energy rather than the concrete’s ability to absorb heat, because heating the concrete requires room space as well.

This can be illustrated by considering churches made of stone, which testify to the challenges of heating buildings with high thermal mass. It is true that the use of exposed concrete can reduce the need for cooling, especially in deep planning office buildings. However, in relatively cold climates such as the UK, cooling still uses only a fraction from heat energy.

What’s more, the cooling is mainly driven by the national electricity grid, which is being rapidly decarbonized, Our research shows that calculations for using building materials, which take a lot of carbon, simply don’t add up, to save dwindling amounts of operational carbon in the future.

Buildings are replaced before they need to be replaced

The second argument, permanence, is similarly flawed. Our research found that some buildings have been demolished because they have reached structural obsolescence. Instead, they perish to make way for a “resurrection” in areas that are booming economically.

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 steel reinforcement bars have begun to rust and degrade and to break down the concrete, has been suggested.

Meanwhile, the millions of ancient buildings around the world built of wood, as well as brick and stone, suggest that other building materials may be highly sustainable.

Concrete buildings don’t absorb much carbon

Finally, the ability of concrete to absorb carbon is usually over-sold. Only the exposed surface of the concrete will carbonate. Therefore concrete located underground, or hidden under coatings or cladding, will not act as a carbon sink.

Reinforced concrete is also designed to reduce carbonation, as it leaves steel reinforcement vulnerable to rusting. Carbonation therefore mainly occurs after the end of the life of the building, once the concrete has been crushed.

If concrete debris is left exposed to air, it will slowly reabsorb a proportion of the carbon dioxide emissions that were emitted in its original construction. This is more correctly understood as “partial re-carbonation” and hardly represents a good argument for using extra high carbon concrete in new buildings.

Is the tide turning?

During 2021-22, the UK Government’s Environment Audit Committee has check In the sustainability of the UK built environment. In their response To investigate, the MPA again reiterated its claims of thermal mass, durability and carbonation.

Although report good Do not repeat these claims on the outcome of the investigation. Instead, it encourages the increased use of low-carbon materials such as wood, and calls for the measurement of whole-life carbon of buildings to be included in the regulations.

with the recent introduction of such rules In many European countries, it must support a move away from high carbon content. Accurate measurement and actual reduction of carbon, embodied in materials and as a result of the operation of a building, is essential to reducing our impact on the environment.

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