As part of the survey four 50mm diameter cores were taken at each floor level, which provided information on the quality of the clinker concrete, its make-up and any voids that existed. Owing to the condition of the concrete, some of the cores broke up when being removed. The steel filler joist was exposed in 16 locations, four on each floor, and was found to be in good condition with minimal corrosion evident. The only exception being the exposed openings at ground floor level, where light corrosion was evident due to poor quality, shallow depth, voided clinker concrete.
Resitech Limited consulted material manufacturer, Mapei, for a material that has the correct mechanical properties, and is capable of being injected into fine cavities. Mapei Stabilcem, a cementitious consolidating grout, was recommended and proposed for use by Resitech Limited, and by using their specialist injection techniques and bespoke in-house pumps, this material would fill the voids and cracks, bind the clinker concrete, and introduce structural integrity back to the clinker concrete infill.
These proposals were approved by engineers at MLM Consultant Structural Engineers prior to the work being carried out. The work involved a cementitious sealing slurry being applied to the top surface of the localised areas to be grouted, as well as the underside. Holes were drilled in a 1m staggered grid pattern across the areas to be consolidated, and injection ports inserted. Resitech Limited then injected 450 x 20 kg bags (9 tonnes) of Mapei Stabilcem, an expansive super-fluid cementitious binder with special admixtures, which filled the voids within the clinker concrete.
Cores were taken once the injection process was complete with each of them demonstrating where Mapei Stabilcem had flowed and filled voids to consolidate the slab, proving the correct and best choice of material was used.