Concrete – it’s literally the foundational material of the building and construction industry.
It’s strong, it’s durable, it’s affordable, it’s versatile and it’s readily available. But what are the environmental impacts of concrete and cement, especially considering the sheer scale of its production and use in the built environment?
It’s a tricky question to answer, since concrete can be considered relatively environmentally-friendly, or somewhat environmentally harmful, depending on your perspective.
On the plus side, the efficient passive thermal design of concrete buildings means less energy is required to heat or cool them. Concrete materials are also well suited to recycling, and their durability means concrete lasts longer in comparison to other materials, meaning less wastage.
Concrete is incredibly easy to work with, capable of being moulded into almost any shape, and has a unique versatility that makes it a very popular material for architects.
From a manufacturing perspective, however, concrete and cement products can be environmentally damaging, with a whole range of potential impacts.
Many of the raw materials required for cement production, such as limestone, silica, aluminium oxide, iron oxide, and gypsum, require some form of mining or quarrying (except for where concrete is recycled). These activities can create environmental and social issues such as threatening biodiversity and ecosystems in adjacent areas, erosion in coastal and river banks, or pollution of waterways, as well as generating noise and dust pollution. These impacts can be lessened with appropriate management plans in place.
Concrete (of which cement is a component, along with aggregates and water) has similar environmental impacts associated with its production, in addition to the impacts from cement manufacturing. The sand and gravel used for concrete are typically obtained by mining, and while the impacts of mining these may be small in comparison to those involved in cement production, they can still cause significant problems at a regional scale. Concrete also tends to use large quantities of water, often resulting in high wastage of water that would otherwise be fit to drink.
Cement manufacture is known for its large energy and raw material requirements, and for contributing to global warming through significant CO2 emissions. On a global scale, impacts include the use of energy (such as kiln usage, in grinding operations or through transportation), consumption of fossil fuels, and the release of CO2. Regional and local impacts would include the emission of pollutants such as nitrogen oxides, sulfur oxides, and dust.
Admixtures are ingredients (mostly organic compounds, and sometimes heavy metals) added to the concrete mixture to improve or change properties such as setting times, workability and durability. They are mostly and conventionally added in amounts less than five per cent by weight. However, they can still prove problematic if leaching occurs into the area surrounding the concrete. Polished concrete floors or certain types of architectural/decorative concrete may also use colours with ingredients potentially harmful or with a potential impact on the environment.
To reduce all these impacts, research has focussed on improving processing technologies to reduce energy and fuel use, usage of alternative fuels in the kiln, and replacing portions of cement clinker with supplementary cementitious materials (SCM). Using recycled concrete and developing alternative cement chemistries can also reduce overall environmental impacts of cement production.
Compared to other materials (such as steel, for example), concrete has a much lower amount of embodied carbon content – it’s the sheer scale and volume of concrete usage throughout the industry that makes it an issue. After fossil fuels, production of Portland cement is the largest emitter of CO2 globally, and we’re using 22.4 billion tons of it across the world each year. This number is predicted to rise dramatically over the next few decades, particularly in the developing world. It’s clear that for better or for worse, cement and concrete are definitely here to stay.
So what are the options?
Dr Shaila Divakarla, standards and technical manager for Good Environmental Choice Australia, acknowledges that dealing with the environmental impacts of cement production involves accepting that we’re going to be producing and using the material for a very long time.
“We need to focus on encouraging best practice cement and concrete products, rather than tell people that they shouldn’t be using it, because there are still some advantages to using concrete over other materials,” she said. “We should move towards developing more alternative cement chemistries that don’t have such a large environmental impact, and encouraging their uptake in the building industry over conventional Portland cement.
“Alternative cement chemistries, such as geopolymer and geopolymer-like materials and other blended cements, are a comparatively recent development. They make use of materials that would otherwise go to waste, such as fly ash and furnace slag, and incorporate these into the final product. That definitely helps reduce the overall impact of cement production.”
With all the new technologies and techniques available to us, cement production can have a much lower impact on the environment. Let’s continue to explore new ways of reducing that impact and encouraging those manufacturers who manage to achieve it.