SUSTAINABILITY - CARBON MANAGEMENT | INSIGHT, BTS


the worst exposure case, or alternatively doing the opposite and creating management complexity by applying different concretes in many places, are extreme scenarios. He said there is need to optimise for the sweet spot between them, and simply giving freedom to use lower-carbon mixes. It was noted that cement replacement with Ground


Granulated Blast-furnace Slag (GGBS) is common in many places but not so in Denmark, which has no steel industry. While it is permitted by the Danish national annex to EN 206, there has been limited awareness about being able to do so. Interestingly, Denmark has calcined clay as a low-carbon alternative. Clay is abundant and calcining certain clays uses less energy. The embodied carbon can be around 500kg/t versus nearly 900kg/t for typical Portland cement. Alun highlighted the age of concrete in evaluations,


noting they are using 56 days as the evaluation age and emphasising there is “nothing magic” about 28- day strength requirements, and often structures are not loaded until the concrete is more mature. Further, 56 days can allow a concrete strength grade to be dropped, saving carbon. Wrapping it all together, the working assumption


is that structural concrete for M5 will have an embodied carbon of around 160 kg/m³.


CARBON IN PROCUREMENT AND CONSTRUCTION STAGE Procurement needs reform. Contracts are often evaluated on quality and price, but it is still a cost-optimised industry, faced with challenge is all bidders score high on quality in the pre-qualification stage. This risk needs mitigated against and to make greener options decisive, Alun said. Price could be evaluated on the carbon saved, or a score made on the footprint of the tender design, he added. Incentives – with bonuses and penalties – could help. A further option is a client innovation fund for good ideas, although its use would need some caution. In procurement, there need to distinguish between


‘hard’ and ‘soft’ requirements was highlighted — the former setting specifics (e.g., strength by a certain time, say 56 days), the latter being more of a suggested intent. Alun said he is not a fan of soft requirements.


Above: Pie charts of metro carbon footprint – life- cycle perspective.


Far left: Running tunnel in the existing metro line.


Left: Pie chart showing breakdown of carbon footprint distributed over all of the M5 Base scheme.


Contract form matters too, he said. Metroselskabet


uses different forms, generally D&B. Early Contractor Involvement (ECI) can help influence design as project development progresses. He noted that the UK has done a lot with NEC contracts, and NEC X29 provides a useful template for sustainability targets. Contract interfaces are worth considering too, as


small decisions can help carbon management, e.g., put all Permanent Way track bed concrete into the Civil Works contract. It means first-stage concrete could be precast. On current contracts, there are requirements for


emission-free equipment, EPDs, and the competence of people handling sustainability issues, and carbon appears to some degree in tender evaluation, he noted. For carbon monitoring, advantage can be gained


from existing processes to monitor financial spend, under the WBS, as discussed. Also, on site, data already being collected can help carbon monitoring, such as electricity usage, fuel delivered (diesel or biodiesel), etc, which can be mapped to relevant needs. EPDs a should provide a reliable basis for embodied-carbon information but because something looks green does not mean that it is good. Transport to site, or ‘material miles’, also need consideration. During construction, caps on materials can


help counter ‘carbon creep’, again highlighting the valuable weight of early choices in the face of programme pressures. For the metro, caps were tested on smaller civil works projects.


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