Bristol Royal InfirmaryBristol Royal Infirmary is a large teaching hospital based in south west England. The structure was undergoing some redevelopment work in 2015 which, following a specialist radar survey, revealed a void under an area of slab. The redevelopment necessitated an additional load to be placed on the existing slab but following load tests the void would compromise the slab integrity to withstand additional loads.

Geobear was contacted to propose a solution which required filling the void with specialist geopolymer material with the compressive strength to withstand additional forces.

The void was identified as a 280m3 area beneath one of the main concrete slabs. The project was made particularly complicated by the presence of asbestos in the original construction.

Geobear proposed the use of a specialist high expansive geo-polymer that could be injected into the area, which subsequently solidifies and fills the void whilst creating additional load bearing strength.

Solution

In order to inject the geo-polymer over 70 16mm holes drilled through a timber subfloor of 50mm over a reinforced concrete slab, Geobear could then phase the geopolymer injections across the site working from the furthest point back to entry.

During the injection process the geo-polymer expands up to 45 times its liquid volume and exerts an expansive force as it quickly fills the void. To ensure an even coverage and fill of the void, the holes were injected in several passes, the number of passes being dependent on how big the void is at each particular hole.

The void was injected in several passes over the whole area until resin emerged from the injection holes providing the visual verification that the void has been filled. In addition to visual monitoring of the geo-polymer injection, we also monitored for possible movement of the floor slab with eye safe lasers. The laser was set up-on a tripod close to the hole being injected and sensored any slab movement to within 0.5mm. Following the injection process the drill holes were filled in with Fosroc cement.

The project was completed within 10 days, and the Geobear teams fully complied with regulatory health and safety for working in asbestos zones.