Bur Dubai and Al Karama concrete for infill and mid-rise

Holding the neighbours up

On an infill plot the first concrete is often not part of the building at all. It is the shoring: a line of bored piles around the plot that lets the contractor dig a basement while the adjacent foundations stay put. The shoring mix has to flow into a bored hole, displace water or slurry, and set predictably.

Bearing piles under the building follow, in the piling mix, then a raft that ties them together.

Pile tops are trimmed back to sound concrete before the raft goes on, so the first metre of each pile is designed to be broken off. Ordering a little extra per pile allows for it.

Salt, sulphate and a shallow water table

This part of the city is coastal. The groundwater sits close to the surface and contains chlorides and sulphates, which corrode reinforcement and break down cement paste. A basement here is a box in that water.

So the substructure mix uses a GGBS blend for low permeability and sulphate resistance, with a low water/cement ratio. The consultant sets the exposure class and the cover to the reinforcement; the waterproofing system works with the concrete, not instead of it. In summer, pour rafts at night so the concrete does not exceed the placing-temperature limit in the specification.

The frame on a tight site

Mid-rise frames here are columns, cores and flat slabs, often with a transfer level above shops. There is rarely space for a truck to wait, so we time loads to the pump. A 57 m boom placed on Sheikh Khalifa Bin Zayed Street or Al Mankhool Road can reach most floors of a mid-rise block. The plant is about 15 km away, and refurbishment pours of a few cubic metres are planned the same way.