Why is concrete so damaging to the environment?

As urbanisation accelerates, can we afford to keep paving over nature? Or is it time to build smarter, greener solutions before concrete solidifies its place as one of the planet’s biggest threats?

Climate experts at COP29, the UN's global climate conference held in Azerbaijan this year, called for a reduction of greenhouse gas (GHG) emissions from the construction sector, comprising the concrete, iron and steel industries, which collectively generate 27 per cent of the world’s industrial carbon emissions. Of these, concrete is responsible for over 7 per cent of the world’s carbon emissions.

What is concrete? 

Concrete is created by mixing a binding mass, either cement or lime, with fine or coarse aggregates (like stone, gravel or sand) and water.

The cement is a manufactured mixture of materials that includes calcium, silicon, aluminium and iron, among other ingredients. While concrete has been used since ancient civilisations, like the Mayans, the Ancient Egyptians and the Romans, who used different ingredients like limestone and volcanic stone, modern concrete mainly relies on Portland cement. 

Why is concrete bad for the environment? 

Greenhouse gas emissions 

The creation of cement is the most carbon-intensive portion of the concrete process. This comes down to two main activities: the calcination of limestone and the heating of cement kilns. 

To create Portland cement, limestone undergoes a calcination process, which releases large amounts of CO2 from the chemical reaction. This is the concrete industry’s dirtiest activity, releasing up to 50 per cent of the cement industry’s carbon emissions.

Additionally, to transform raw materials into clinker, cement's intermediate product, large amounts of energy are required to heat, mix and cool the ingredients in giant kilns.

It is estimated that, in traditional kilns, one tonne of cement produces one tonne of carbon dioxide, although modernised factories have found ways to reduce these emissions.

Water Use 

Cement creation is also highly water intensive, particularly during cooling after materials are baked at extremely high temperatures.

Nature Magazine estimates the concrete industry is responsible for nine per cent of all water withdrawals from the sector. Approximately 16.6 km squared of water is used annually for concrete production, and this figure is expected to soar as the demand for concrete continues to rise.

By 2050, most of the water withdrawals for concrete production will be in geographical areas that already face water stress, found a 20188 study published in Nature.

Reduces Biodiversity

The rapid urbanisation of the past century has resulted in drastic biodiversity loss, as animals, plants, and fungi have found themselves and their ecosystems smothered under tonnes of concrete. As much as 80 per cent of urban spaces are covered by pavement or buildings, leaving little land for green spaces. 

Not many species can adapt to the urban environment, which leaves many without mating grounds, food sources or homes.

The result is a homogenisation of species, which disrupts food chains and ecosystems - including our food systems. The endangerment of bee species is a key example, as the loss of hive habitats and pollen-producing flowers has caused bee populations to plummet. 

Read more about the risks and dangers of bee extinction

How concrete contributes to environmental injustice

Air Pollution

Cement production emits large amounts of toxic substances into the air, worsening air quality and leading to respiratory diseases.

For example, cement factories have been known to release Sulphur dioxide and Carbon monoxide, which can cause or aggravate respiratory issues like asthma or cause damage to the central nervous system.

Heat Island Effect

Concrete is notorious for magnifying heat on hot days, creating what is known as the heat island effect. Concrete paving can increase urban temperatures by up to seven degrees Fahrenheit (3.9 degrees Celsius).

This is significantly magnified in lower-income areas of cities, which have fewer green spaces and plants and more pavement - leading to sweltering heat and pronounced environmental racism. 

Concrete Solutions 

Despite the various hazards that concrete and its production generate, humanity is far from phasing it out since concrete offers many benefits that are hard to beat. No other material can yet compete with its value for low-cost production, durability and strength.

For this reason, concrete was widely adopted to reconstruct war-torn nations after the Second World War. Its ease of creation from widely available natural resources has helped spur urbanisation in the Global South. 

Understanding this impact, scientists and engineers globally have worked to come up with solutions to this issue, the implementation of which could ensure that construction does not lead to destruction.

An Energy Change opportunity

During cement-making, materials are heated at very high temperatures, requiring large amounts of energy - mostly powered by fossil fuels. In fact, up to 40 per cent of the industry’s carbon emissions come from heating cement kilns for this process.

These emissions could be drastically reduced by decarbonising the energy sources for kiln heating and switching instead to renewable energies. 

Many cement manufacturing plants are already switching to green energy or improving the efficiency of these kilns to optimise energy consumption and reduce costs. 

Alternative clinker 

As mentioned, the calcination process to create Portland cement is the most polluting activity of the concrete industry, generating 50 per cent of its carbon emissions.

Portland cement is widely used due to its reliability and its low-cost, abundantly available ingredients. However, replacing Portland clinker with an alternative blend of materials - waste materials from production, for example - could reduce emissions by up to 60 per cent without compromising the product's strength. 

Governments and environmental institutions could focus on regulating the use of Portland clinker, subsidising alternative blends or taxing the carbon emissions from clinker production to incentivise a change in materials.

Carbon Capture

There is potential to prevent carbon emissions released during the kiln-heating process from entering the atmosphere by using carbon capture and sequestration (CCS) technology. However, due to the high cost of CCS, it is not widely adopted and may be challenging to incorporate in smaller cement plants, especially in the Global South. 

Concrete manufacturers have figured out how to inject carbon dioxide captured during CCS into concrete through carbonation curing - therefore locking CO2 into our solid structures and preventing emissions from heating the atmosphere.

Picture by Uve Sanchez