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Secret combination

Aarsleff Piling's 600mm by 600mm piles, used in the CTRL cyclic, lateral pile tests, are believed to be the largest square section continuously reinforced precast concrete piles ever installed in Western Europe.

The self-compacting C50 concrete test piles were heavily reinforced with 8 longitudinal T20 bars and 10mm links and factory cast in special high slump, fluid concrete, which Aarsleff developed in a partnering arrangement with ready mix concrete supplier RMC.

Like thin custard the concrete flows into the moulds and around the reinforcing without the need to use noisy poker vibrators. It is believed to be the UK's first use of self-compacting concrete in precast pile production.

The special mix uses a blend of ordinary Portland cement and pulverised fuel ash to give Class 4A sulphate resistance combined with a high range water-reducing admixture, producing good workability at very low water/ cement ratios.

Aarsleff, which has spent a lot of time and money developing the self-compacting concrete, is naturally reluctant to divulge the exact recipe.

Managing director Terry Bolsher says: 'The mix is completely selfcompacting and the strength gain is significantly better than our original conventional sulphate resistant Portland cement mix, which we have used since we began pile production in this purpose built factory in 1993.

'At 16 hours, when the moulds are stripped, compressive strengths range from 26-28N/mm 2and at nine days the 50N/mm 2mark has been passed and the piles are ready for driving.'

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