In 2021, Byrne Bros published an analysis of the concrete it had used between 2015 and 2020 - a study that meticulously assessed the carbon intensity of every load received by strength class and structural application, resulting in the most detailed, reliable baseline of concrete ECO_2e seen in the industry to date. From this, the company identified its average and lowest ECO_2e/m~3 for each application (now its baseline and target compositions), but this was data from a period when carbon reduction didn't feature in its mix designs. We analysed the data and forecast how far we could push the mix compositions within current Codes with no impact to cost or programme - our 'stretch' targets. The challenge from Lend Lease provided an opportunity to try to prove what the company had been loudly exhorting - that better use of existing materials can significantly reduce concrete's carbon footprint. There was nothing to lose by trying and everything to gain. There are many ways we could decarbonise our works, but the immediacy of the physical start on-site limited the options. Embarking on a design assisted by testing (DABT) regime to trial geopolymer concretes, graphene or similar would take many months to execute and there was no time to influence the design, so the best option was to work with the tools, materials and Standards already in place to deliver a better outcome. Maximising cement replacements and pushing for theoretical 'stretch' targets was the best option. We also used maturity strength assessment for some structural elements, as this gives a far more accurate representation of live in-situ strength compared with the highly conservative data achieved from crushing cubes. In turn, this would allow more flexibility in mix selection to ensure striking/stressing strengths were being achieved within working hours.
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