The soon-to-be-iconic new V&A Museum in Dundee was beset by delays before construction began. But the complex concrete structure is now being built, requiring a bespoke mix.
The troubled backstory to the Dundee V&A Museum project is a well-known one. Lengthy delays, a near-doubling of the original budget from £45m to £80m, and calls for a Scottish parliamentary inquiry over the entire process dogged the scheme before construction even began.
Some of the delays and cost inflation were blamed on the building’s complex structure, designed by Japanese architecture practice Kengo Kuma & Associates.
This tricky structure finally got under way last year, with Bam Construction taking the role of main contractor and PJ Carey overseeing the concrete works. Supplying the concrete for the building’s sweeping curved walls is Breedon Aggregates.
Breedon technical manager Brian Lumsden describes the project as a “one-off”. “There are lots of things here that defy what normally happens on a construction site,” he says.
Breedon worked closely with engineering consultant Arup to translate the building’s concrete designs into reality. The firm started supplying concrete for the piling phase in October last year, as well as temporary fill material for the piling that needed to be carried out in the River Tay, next to which the new museum will sit.
“The target strength of the concrete is high at 70 N per sq mm, which posed a challenge for the team when combined with the high flowability needed to create the walls”
Kengo Kuma’s design is such that the building will look like a ship jutting out into the river, with a man-made moat sitting around it to give it the impression of floating on water.
The mix it has supplied needed to be bespoke in order to construct the complex shapes called for in the design. The target strength of the concrete is high at 70 N per sq mm, which posed a challenge for the team when combined with the high flowability needed to create the walls.
Go with the flow
“The biggest technical challenge was to get the strength we required hand in hand with the ability to flow into position,” Mr Lumsden says.
To achieve this, the team used a 14 mm limestone aggregate alongside limestone fines to improve the flowability. Breedon also used pulverised fuel ash for the same reason, as well as to help achieve the dark grey colour and enhance the high-class finish specified.
Breedon Aggregates Dundee V&A Museum 2
In addition, Breedon worked with Grace Construction Products to come up with a tailor-made superplasticiser, which enhanced the flowing properties of the concrete again – and reduced its water content, allowing the team to use less cement.
“It was for cost-effectiveness – and we also had a restriction on the maximum amount of cement we could use,” Mr Lumsden explains.
“Any excess cement content can cause thermal cracking within the structure, microscopic cracking.”
“Rather than formwork being removed as the build progresses, it will remain in place until the entire structure is complete”
Microsilica powder was also included in the mix, again decreasing the cement content required but also acting as a ‘densifier’ to in-fill microscopic pores that occur in normal concretes, helping to increase the concrete’s long-term durability.
“This means there is less likelihood of water ingress into the structure through these microscopic pores. The microsilica wasn’t specified – we introduced it and Arup agreed it should go in as well,” Mr Lumsden says.
The structure did not just pose challenges for the mix: when it has come to pouring it on site, the team has had to work in unusual ways, too.
Firstly, rather than formwork being removed as the build progresses, it will remain in place until the entire structure is complete – a period of one year. This means there is no margin for error.
Breedon Aggregates Dundee V&A Museum 1
“There is no symmetry at all and nothing is re-usable,” Mr Lumsden says. “It’s a massive jigsaw, they can’t take sections out as they go.”
This sacrificial formwork is being supplied by Peri at a cost of £5m.
Secondly, the curved sections have meant that the team have been unable to vibrate the concrete in the normal way, hence the high flowability requirements.
“Usually in a normal structure you’d get vibrating pokers right down to the bottom and vibrate the whole section. In this case, they can only get them in a small way, which means the rest has to free flow into position,” Mr Lumsden says.
The project has been progressing smoothly so far, despite the delays before construction began. The team created a full-scale mock-up on site after extensive testing and Carey is now pouring the concrete into the congested and twisted shapes that will make up the external walls.
Breedon’s involvement supplying concrete will continue until the end of this year.
“It’s all worked really very well,” Mr Lumsden says. “It’s a one-off – we haven’t done anything exactly like it before.”