Rock Village Hall was constructed between 2004 – 2006, it’s a flagship building that demonstrates best practice in sustainable construction.
The hall uses recycled materials to a considerable degree, including the use of recycled hemp for insulation, and recycled plastics for the underground drainage. Rainwater is collected and used in the lavatories, and a ground source is used to heat the whole system. Additionally, recycled aggregates were used in the foundations.
Following a flood, the local arrangement committee became aware of movement between the floor and internal/external walls. Gaps had begun to appear below the skirting boards and between the door frame and timber threshold strips; over time, these gaps increased.
A CCTV survey in October 2012 identified drain defects, but these were not considered significant enough to cause movement. Monitoring of the floor confirmed the movement was active and ongoing.
The cause of movement was extensive flooding that occurred in October 2007. Rock Village Hall was directly in the path of a flash flood where water ran off adjacent fields following torrential rain.
Swathes of water ran into the building via an external door overnight but had drained away by the morning. A tidemark on the exterior door to the kitchen was approx 250mm above floor level.
An engineering report indicated structural movement was ongoing and flooding, resulting in washout of the soils was the likely cause. A site investigation revealed that two layers of rock wool insulation were saturated with water. This rock wool insulation had significantly deteriorated from its original specification, with the water causing it to lose its original compressive strength. The report later suggests that this deterioration could have contributed to the movement occurring.
The primary alternative solution was to commission a full slab replacement. With the village hall in regular use, this would have resulted in weeks of work and would have necessitated the complete replacement of the underfloor heating system. Furthermore, with such emphasis on sustainability in the original design, a low carbon solution was also preferred.
Geobear was selected to deliver the stabilisation and releveling works due to the non-disruptive method of geopolymer injection and the and speed of the programme. We could also to complete work without damaging the underfloor heating system that was built into the existing slab. Furthermore, our geopolymer injection method is a low carbon solution, which is in keeping with the ethos of the original design.
The repair work was instructed via insurance claim, and ultimately the loss adjuster considered the Geobear solution to be the most suitable for the project.
The floor of the village hall was constructed of multiple layers situated on a hardcore base. Above the hardcore was the polypropene membrane followed by rock wool insulation, with a concrete slab above that; this was followed by a further layer of rock wool, before the top slab which also housed the underfloor heating. The finish was made from recycled timber.
Our solution was to inject an expansive geopolymer at two depths at 1metre centres across the entire floor space. The injection depths were beneath each of the concrete slabs, where the geopolymer material would expand to fill any voiding left as a consequence of the saturated Rockwool. The expansive force of our material would also provide the lift to relevel the floor.
The process for the works was to drill out an area at the two depths in line with the work plan and then insert two injection tubes in each location. We then injected our geopolymer material in the two points, using laser monitors to ensure accuracy of upward movement.
With the upper concrete slab housing the heated flooring, we had to be careful not to drill into the pipework. To prevent against this before any drilling took place, we switched the heating on and using thermal imaging cameras could mark out the exact pattern of the heating system.
The Geobear process was a complete success and took one week to complete. The floor was returned to its datum level, and the village hall returned to use many weeks faster than anticipated.