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Last edited 26 Dec 2020
High-density floating track slab
Can you pump heavyweight concrete through 500 m of 125 mm pipeline? Andrew Turner discusses the challenges of pumping heavyweight concrete for use in high-density floating track slab (FTS) at Crossrail.
That question was asked at the design stage of the Crossrail project when Arup was trying to solve the potential problem of noise and vibration being transferred from the track slab to the Barbican performing arts centre.
Fast forward to 2015, and we were asked a very similar question. Can you pump heavyweight concrete through 900 m of 125 mm pipeline? This time we were a bit more confident in our reply: we think so and we’ll be more than happy to try.
Concrete pumping trials:
After extensive laboratory and batching plant trials the material was put to the test in a series of three pumping trials. These were conducted through increasing pump line lengths: 130 m, 500 m and finally 900 m.
Each of the trial pours was a success with the equipment being equal to the task and the material holding together under pressure without segregating or settling out in the pipeline during delays in the pumping.
Also tested during the pumping trials was Camfaud’s water washout system. On the 900 m pumping trial the pipeline contained 11 m3 of heavyweight concrete weighing 40 tonnes. We aimed to use as much of this concrete in the pour to minimise waste, reducing environmental impact and also the overall cost of the contract. The water washout worked as planned and so was adopted into the pumping scheme.
Concrete pumping at Crossrail:
Each of the pump set-ups was different due to the size and configuration of the pumping station. At each site we worked with the temporary works engineers to design the pumping station configuration and particularly to install and secure the high pressure concrete delivery line.
Each pumping station included the water washout system with a dedicated washout pump to push the line clear of material, most of it being used to finish the pour with only a small amount pumped to waste. The water was then blown back to recycling tanks on the surface, treated and used for the next cleaning cycle.
Due to programme changes the operation at Bond Street was extended. This led to the question: can you pump heavyweight concrete through 1,000 m of 125 mm pipeline? Without hesitation, we replied: of course we can.
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