A 1.3km long concrete pumping operation carried out by specialist sub-contractor Kelly Formwork on the Crossrail C310 project tunnel is being claimed as a new British record.
The concrete was pumped from Plumstead to Woolwich to complete the formation of the invert of the 6.2m internal diameter tunnel, and the final 112m3 pour took nine hours to complete.
Readymixer Hanson supplied the concrete from its Silvertown depot to a Schwing 3500 static pump connected to a 125mm diameter pipeline. Concrete journey time was 90 minutes, and at any one moment there would be 16m3 of concrete weighing 38t in the pipeline.
Design of the specified grade C32/40 concrete mix was critical. CEMI Portland cement was blended with ground granulated blastfurnace slag in a 60%:40% ratio, and long term durability was enhanced by the addition of a calcium carbonate filler and a Sika admixture containing silica fume.
This blend complied with the BS 8500: 2006 specification for CEM III with SR classification. Coarse aggregate was 10mm and 4mm limestone, coupled with marine sand. Two further Sika admixtures were also used: a high range superplasticiser and a retarder.
Kelly started work at the Plumstead tunnel mouth and carried out 18 pours in total, extending the pipeline as necessary. Although concrete has been pumped greater total distances in the UK, this involved multiple stages, and both Kelly and pump supplier Schwing Stetter are convinced this is the longest single ‘push’ in the UK to date.