Pete Walker is a Professor in the Department of Architecture and Civil Engineering at the University of Bath, a chartered civil engineer, a fellow of the Institution of Structural Engineers, and member of both the Institution of Engineers Australia and The Institution of Civil Engineers (UK).
The Guardian recently ran a series of articles on concrete highlighting its importance to humanity as a construction material, but also its impact on climate change and the wider environment.
If the global cement industry was a country it would be the third highest emitter of carbon dioxide after China and the USA; equivalent to around 8% of humanity’s annual carbon emissions. Cement is mainly used as a binder in concrete, mortars and plasters, which also consume vast quantities of other mineral resources, including sand and aggregates. These resources are in increasingly short supply, and their extraction leads to other environmental impacts, such as loss of wildlife habitat, pollution and noise. At the same time globally, only a fraction of concrete is recycled for other uses, much of it ending up in landfill. Naturally the cement and concrete industries have in response defended their positions, outlining that concrete continues to provide safe housing, resilient infrastructure, and (some) delightful buildings.
Indeed, humanity has been using concrete for at least two thousand years, though in its current forms for little more than 100 years. Precast into concrete blocks, as well as in-situ cast frames, concrete has largely replaced many traditional building materials around the world, including masonry, earth, timber, and bamboo. The concrete industry has been very effective at promoting the strength and durability of its product, and its ability to be cast and moulded into many different forms, used together with steel, has led to remarkable bridges, dams, and many buildings from modest single storey homes, to the world’s tallest sky scraper. Despite centuries of architecture using loadbearing masonry, timber and earth, it seems we have come to expect our buildings to be built from concrete.
However, our addiction to this remarkable material remains a problem for the environment. The way we use buildings, and the materials we use to make them, are responsible for nearly 50% of the greenhouse gas emissions contributing toward our changing climate. Yes, concrete is relatively cheap to buy, easy to use at different scales, and incredibly resilient, but we use too much of it, and we use it unwisely.
The problem with concrete
Concrete structures in hot and humid climates often rely on energy intensive air conditioning systems to provide liveable spaces. Similarly, poorly insulated concrete buildings in colder climates suffer from damp and mould growth indoors. Additionally, modern concrete buildings can often lack the thermal mass benefits and natural ventilation of traditional buildings that do not rely on active cooling systems.
Efforts to reduce the environmental impact of such buildings has led to energy efficiency measures including improved insulation, and low energy heating and cooling systems. However the drive to reduce energy consumption through more air-tight envelopes has led to poor indoor air quality, with build ups of carbon dioxide, volatile organic compounds and, in some cases, high humidity levels - leading to health and well-being problems for building occupants.
As northern European’s spend around 90% of their lives indoors, measures to improve indoor environmental quality through better materials, and building design, has been recognised with growth in materials such as moisture responsive clay plasters and photocatalytic finishes. Similarly, in many low and medium rise buildings loadbearing masonry or structural timber solutions to insulation would be much better, and non-loadbearing in-fill wall panels could very easily use sustainable bio-based materials rather than concrete blockwork.
The benefits of bio-based materials
Used either structurally or as insulation materials, the greater use of bio-based materials has a significant role to play in the future of modern sustainable buildings. Plants photosynthesise carbon dioxide in their growth, and as such provide a means of storing carbon. Trees consume around 1.8 kg of carbon dioxide for every 1 kg of timber grown, and other plant based materials - including bamboo, hemp, and straw - do so likewise. However, challenges remain when implementing the use of bio-based materials. The Grenfell disaster has led to a government ban on the use of combustible materials in buildings above 18 metres high; recent proposals for up to 40 storey, and even higher, timber buildings will have to address regulatory as well as wider public concerns. The opportunity where bio-based construction can make greatest beneficial impact seems to be in lower rise buildings, which indeed is where the mass housing market is.
Mud (adobe) blocks, rammed earth, cob, wattle and daub, and other forms of earth building, remain an important vernacular building material around the world, where around one third of humanity are estimated to live in buildings made from earth. In the UK alone, there are over 500,000 earth based buildings, many in the South-West of England. Compared to concrete, earth has remarkably low environmental impact, as soils are often used with little processing following their extraction. Modern earth builders are using the environmental benefits of the material, together with the beneficial moisture responsiveness of clay, to develop new uses, including clay plasters and prefabricated wall panels.
The future of building
Building materials and products are increasingly seen within the context of a circular economy, with uses beyond the 30-100 year life span of the building to be considered during design and construction. Buildings can provide banks of materials for future use, as well as stores for carbon in bio-based materials. There is even now a greater use of waste materials from other walks of life in construction, such as recycled cotton jeans and bedding materials for very effective insulation.
However globally, the construction industry still relies primarily on in-situ construction methods using human labour. A Roman mason transported to the earliest twenty-first century will perhaps be likely as surprised by the similarities, as well as the differences, to construction two millennia ago, especially when compared against how much other aspects of human technology and society has changed. In recognition of this, governments are supporting the construction industry to adopt greater pre-fabrication and digital technologies in modern building processes, to improve productivity, quality, and buildings’ environmental impact. It is time for more sustainable construction materials and technologies to take on and adapt to these modern transformations, and perhaps eventually leave concrete as a material of the past.