How concrete blocks fit into the circular economy

As the focus on sustainability intensifies in the wider construction industry, environmental concerns are increasingly on a par with capital costs as a key design driver. In the future, flexibility will be crucial, whether building from scratch or redeveloping existing sites. Chris Stanley of the Concrete Block Association explains more.

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As Simon Sturgis, adviser to RIBA on sustainability and founder of consultancy Targeting Zero Carbon, recently stated, ‘we should be designing for future retrofit, not future demolition.’ Rightly, the discussion has shifted towards the whole-life performance of buildings. The consensus is that low-energy, sustainable design is the way to future-proofing property assets in the public and the commercial sector alike.

At the Concrete Block Association, sustainability is at the heart of the work we do. However, there are some prevailing misconceptions among architects about how concrete blocks fit into the circular economy model: ‘reduce, reuse, recycle, recover energy’.

It’s no secret that concrete structures are durable, which is naturally fundamental to whole-life performance. However, concrete possesses unique attributes which minimise CO2 emissions, yet many in the industry are less familiar with these.

Correctly specified, concrete blocks can keep the embodied CO2 to a minimum. Therefore the material’s thermal mass qualities should be taken full advantage of, as they can also greatly reduce the operational emissions from heating and cooling required during a building’s lifespan, without compromising on comfort.

The components

CO2 emissions relating to concrete blocks are associated with production, however, their long-term performance virtues can offset these. The carbon intensity of the material has been reduced by a remarkable 13% since 2008, and improvements in the manufacture process are ongoing. Furthermore, the majority of concrete blocks produced in the UK are made in local product plants which means local deliveries to site effectively lowering the carbon footprint.

The most substantial component of concrete blocks are fine and course aggregates, accounting for very little carbon emissions. They reduce the need for processing and transportation, as they occur naturally and are sourced locally. Therefore transport costs associated with concrete blocks tend to be minimal, as the raw materials are all found locally.

Cement accounts for the majority of concrete’s environmental impact. However, while it remains a part of the composition, standard practice in the UK blockmaking industry today is to blend other cementitious materials with it, consequently reducing the overall embodied CO2. These are often industry by-products with ground granulated blast furnace slag (GGBS) and fly ash from the power industry being the two most commonly used.

Taking advantage of thermal mass

As we adapt to a more changeable climate, it is important we build with materials that also make for comfortable homes. Lightweight materials are less ideal, as they do not provide inertia against temperature fluctuations, but instead have a tendency to overheat.

The thermal mass inherent in concrete blocks is one of the most important ways in which the whole-life CO2 performance of buildings can be enhanced. It’s essentially an alternative method of temperature control that allows the building to naturally retain heat and cool, reducing the need to resort to air conditioning or central heating.

Concrete absorbs and stores excess heat during the day, which can be removed overnight passively through ventilation. Buildings made with concrete blocks are therefore comfortable all year round; warm in the winter and cool in the summer.

Lean design and flexibility

The first step in the circular use of concrete blocks is material efficiency and lean design; using less of our resources and using them to better effect. Technology and innovation now enable us to ascertain the optimal thickness of structures needed for best energy efficiency. Key to this is knowing the appropriate U-values required. Concrete can also be incorporated in buildings in a way that enables more environmentally harmful materials, such as plastic, to be designed out.

Concrete is an ideal material to be reused, or kept in use for as long as possible. Structures made of concrete can be designed to be stripped back and repurposed. What’s crucial is that buildings are designed to be adaptable, have generous floor-to-ceiling heights and a well-defined long-term use.

Essentially, flexibility must be built in so the building can assume new uses, incorporating new technologies and changing conditions.

The secondary life of concrete blocks

Concrete blocks have a secondary life in groundworks, piling mats and landscaping. They are crushed and used as recycled aggregate for a range of applications. The CBA’s members have pledged that all blocks produced are 100% recyclable.

The construction industry is responsible for around a third of the UK’s waste, and for most building materials, deconstruction and waste processing at the end of a building’s life results in the release of more CO2. But unlike most materials, concrete absorbs CO2 when it is broken up and reused in other applications. This process is called carbonation.

The CBA encourages manufacturers to introduce measures to reduce energy consumption, eliminate waste and implement environmental and sustainable management systems beyond what is required by the government. This is part of our ‘Raising the Bar’ initiative, where all full members have signed the Sustainability Charter.

Innovation and education

To be sustainable, materials need to be utilised in optimal quantities, and with regard to blockwork, the correct weights and dimensions are crucial. Educating the wider industry has been the purpose of our ‘Better Built in Blockwork’ campaign. To this end, CBA also launched an online U-value calculator, assisting architects and builders with the complex yet necessary calculation.

Masonry materials have seen a great deal of innovation in recent years. But developing new, more sustainable solutions is of little significance when delivered without accompanying education to enable designers and specifiers to make informed choices.

Developers working to stringent sustainability briefs should feel assured by the 100% recyclability of our blocks, and as an industry we need to be more vocal about these qualities. Misconceptions currently surround concrete as a material and its sustainability credentials. As an association, one of our key goals in 2019 and beyond, is to clear these up, and ensure the most resilient and energy efficient materials are used to build for the long term.

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