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Of all the questions The Concrete Centre receives from architects, the majority concern how to specify low-carbon without having to go in-depth on concrete technology or supply chain dynamics. Designers are keen to move beyond business as usual, but they’re struggling to know what good actually looks like.

There are a number of reasons for this. First, as our collective knowledge and proficiency increases, we start to look more closely, find more carbon and understand the implications of the design decisions and specifications we make. Secondly, the data available to us is increasing in quantity, granularity and, hopefully, accuracy.

EPDs are updated as a minimum every five years, reflecting the changing performance of products, as well as refinements in the rules to calculate emissions. Finally, the solutions themselves are evolving, with new multi-component cements and various innovations at different stages of development.

Against this backdrop, designers could be forgiven for throwing their hands up in defeat. Not so fast. There are some simple rules of thumb that will continue to hold true. The first is not to get bogged down in the concrete composition. Specify a carbon aspiration and a performance category, but not particular constituents. There are many possible ways to achieve the desired end result, and the right one will depend on many factors – from construction conditions to local supply chains – that are outside the designer’s control or knowledge.

Well-intentioned targets or limits can easily backfire, forcing a specification that’s higher carbon than necessary. Designers’ most important role is to establish the carbon aspiration at the outset and thus not hinder the adoption of an innovative, or particularly appropriate alternative solution.

The next rule of thumb is not to miss carbon-reduction opportunities that are within your grasp. The amount of concrete that is used is just as significant as what’s in it – and material efficiency sits squarely with the designer. With our free Concept structural comparison tool, you can see how even small changes can add up to massive reductions (see CQ 289).
 
Our feature on 3 Chamberlain Square shows this approach in action. By shrinking the grid from 9m to 7.5m, structural engineer Cundall reduced the amount of concrete required by 25%. When it came to the concrete specification, it set a strict limit for embodied carbon and a stretch target, leaving the contractor to determine how best to meet it. In the end, it beat the target by 5%.

But how to set project goals? The third rule of thumb is to lean on established standards and benchmarks. The Embodied Carbon Market benchmark from the Low Carbon Concrete Group in the UK and the Global Cement and Concrete Association’s Global Low Carbon ratings system enable specifiers to see what current practice looks like, and set targets for their project, whether that’s a slight improvement or a deep green exemplar.

An enormous amount of work has already gone into agreeing how to measure whole-life carbon – we’re not in the Wild West anymore. Today’s standards and benchmarks will inevitably change. But that’s what progress looks like.

Elaine Toogood, senior director, MPA Concrete and The Concrete Centre