The Dot-Com extension at Tesco Mansfield Jubilee Extra was completed in September 2013 involving a building extension approximately 3,000 ft²
Due to the nature of the external levels, the extension was built with a suspended floor slab comprising of a steel deck/concrete composite structural slab spanning between main steel beams at up to 6m centres. A 60mm thickness of insulation was placed on top and, on top of that, a 100mm thickness non-structural floating slab up to finished floor level with a power-floated finish.
The floating slab had been cast without any saw cut crack inducer joints but cast as a single monolithic pour. Over the following months, this resulted in the floating slab developing cracks at approx. 5-7 meters spacing as the concrete has experienced drying shrinkage as well as the thermal movement to the slab.
Engineers from ISG contacted Restek to discuss the severity of the cracks and to come up with proposals for the remedial actions that should be taken to ensure the area remains serviceable.
Restek proposed that the most effective action would be to apply an epoxy resin using a specialist pressure injection system for its ability to seal, bond and stabilise building components. Nitofil LV resin chosen for its low viscosity with both high internal strength and adhesive tensile strength so that it can be injected into cracks of 0.25mm and reach the finest of micro-cracks through the use of Restek’s pressure injection procedure. This enabled the resin to permeate into the concrete and bind the particles together restoring the slab back to its original design specification.
The work was separated into three zones;
There were two fractures to the cold store that required sealing. The store was to be handed over to our team of resin injection operatives at 4pm with Tesco Dot Com taking back the cold store by 7am the following day. All works were to be carried out over the one shift therefore the temperature of the cold store would have to be raised as the core temperature of the slab was reading 0.6ºc. With these conditions, the resin would be left in a liquid state so the core temperature of the slab needed to be raised with the assistance of our heated floor mats to allow the resin to cure. It took over 3 hours before the slab could receive the application. Once the application had been made and cured, work progressed to grind the slab surface down to a smooth finish and was handed over to Tesco Dot Com as not to disrupt their works programme.
"A successful structural repair project needs more than just a good contractor"