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High Quality Foundation System

Step 6 – Installation and Finishing of Steel Fibre Reinforced Concrete

  • The steel fibre reinforced concrete should be fresh and no older than 60 minutes from batch time with a maximum temperature of 25┬░C
  • The concrete should be delivered at a constant and consistent rate throughout the pour. Concrete delays should be avoided where possible and when they do occur the condition of the previously placed concrete should be monitored closely
  • The concrete slump on arrival at the job site should be constant and consistent within a tolerance of +/- 25mm of the specified slump
  • During installation, the free flowing and stable mix should not require any poker vibration. The concrete raft form shall be carefully braced along the edges to ensure that the hanging part of the form above the footing will be rigid
  • First stage pour can then be commenced by placing the steel fibre reinforced concrete (SFRC) by a pump or the bucket on a machine. It is important that this is done carefully as hydrostatic pressure can build up if due care and attention is not applied. In the event of a polystyrene pod lifting, a board (such as a scaffold board) should be introduced across the front of the unaffected pods in order to stop the SFRC continuing to spill into the ribs. The pod should then be removed, and the spilled SFRC shovelled back in to the perimeter beam. The pod should then be replaced and the scaffold board removed (Photo 1)
  • Pre-bent H12 Z bars at 250 mm centres, as approved by the structural engineer, are to be introduced into the first stage pour to provide a shear connection between the two pours (Photo 2)
  • Sacrificial bar or blocks may be introduced to support the second stage pour shutter
  • Once set, the lower shutter can be stripped and installed to form the second shutter. The foundation is then ready for the internal ribs, slab, beams and remaining external beam to be completed
  • If the placement is completed, level carefully and finish by bull float or skip float (Photo 3) in order to improve flatness and to hide visible fibres under the superficial mortar. If required the slab may be finished by power-trowelling
  • The DPM is then lapped up the outside vertical face of the toe. The horizontal and inside vertical face of the toe is painted with bitumen emulsion in accordance with (BS3940)
  • The vertical insulation is then placed against the outside face of the toe and backfilled against
  • Alternatively, the face brickwork can be used as the second stage shutter (Photo 4). If this is the preferred option, then the horizontal face of the toe must be painted with bitumen emulsion in accordance with BS3940, prior to the brickwork being commenced. A sacrificial insulation is used to form the cavity. Once the second stage pour is completed, the sacrificial insulation is removed and the vertical face of the toe is painted with Sealocrete ALLPRUFE
  • Poker vibrating is prohibited in order to avoid fibre segregation. ┬áVibration in some zones is permissible to encourage the concrete to completely fill the formwork e.g. hanging shutters. In that case poker vibration should be moderately used locally to allow for full consolidation of the concrete
  • Pumping is easy when the above concrete mix design guidelines are followed. It is advisable to suggest to the pump company that only pumps with operational vibrators installed on the grills of the pump hopper should be considered for use. The hopper must not be covered by a mesh or screen that prohibits the steel fibre reinforced concrete from easily flowing into the hopper
  • The pump line diameter should be at least 125mm. Reductions along the pump lines create less favourable conditions which require extra attention. It is advisable to avoid any reduction in the diameter of lines, hoses and pipes when pumping.
Photo 1

Photo 1

Photo 2

Photo 2

Photo 3

Photo 3

Photo 4

Photo 4

 
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