A minimum of 75 mm of concrete cover is required all around the steel foundation beams. This coating provides a surface for the beam and block floor and also prevents corrosion for the lifetime of the building by sealing against the oxygen and water necessary for rust to form. It is the only wet process in the build and unfortunately the 2 month project delay by the frame supplier pushed this into the period with the highest risk of adverse weather. This was not what we had planned!
The weather forecasts were checked to find a window of opportunity where low temperatures would not drop below 3 deg C. Week beginning 28/01 showed a sharp drop in temperatures and likelihood of snow, but long range forecasts showed that this was likely to be followed by by a week of temperatures suitable for concrete setting. Labour, concrete supply and overhead pump equipment were provisionally booked for Monday 4/02, but this was reviewed on Thursday 31/01 when the sharp drop in temperature went below forecasts and the transient snow forecast as slush proved to be sufficient to lie and turn into ice. The decision was taken to continue as planned and a constant clearing of the steels took place over the weekend to make sure no ice built up on surfaces. As everything is above the ground, any melt water flows away to ensure that the underside coating is not compromised by standing water,
The temperature started rising overnight on Sunday 03/02 and the thaw set in. Total Concrete arrived with their overhead concrete pump at 9am on 4/02 whilst the road outside of the site was still ice covered and difficult to walk on. First on site volumetric mix delivery of C30 concrete arrived at 10am. The required 20.5 cu metres was made in 3 deliveries direct into the stationary pump, which was able to reach across the site without the truck having to be moved. All equipment had left site by 1pm and the concrete was left to set.
The braced shuttering has been released today and the concrete is not showing any differential drying cracks and the temperatures are set to not drop below 6 deg C for the rest of the week.