The spill gulleys at a COMAH site were allowing water egress, meaning that in the event of a spill it may not be contained. The water normally present in the gulleys prevents the stored chemicals changing form a liquid to a more hazardous gaseous state, meaning that the water was constantly having to be replenished.
The slab when in service is extremely heavily loaded, with heavy plant traversing to move the stored vessels.
A sealing solution for a concrete tank or bund lining would be a fairly conventional lining application, however the extremely restricted access for this application presented a unique challenge that would mean normal lining techniques could not be employed. The narrowest gulley was only 130mm wide and nearly 1 metre deep.
Initially a previously applied bitumen layer had to be mechanically removed from the base of the gulley – an extremely awkward task. Because of the width and depth of the gullies we elected to prepare all surfaces by method of high pressure washing at 500 bar to remove surface laitance and contaminants.
The dynamic cracks in the gulley were then sealed using an elastomeric bandage system. How this works is by partially securing a polyolefin elastomer at the perimeters, remaining unbonded over the area subject to potential movement. This means that if movement does occur in the future the bandage can expand and contract with this movement akin to an elastic band without cracking or splitting, thus maintaining fluid tightness.
The next challenge to overcome was to create a concrete surface suitable for a lining application. Conventionally to deal with blow holes in concrete which cannot be filled with coatings alone we would apply a cementitious fairing coat. Given the extremely restricted access this would not be possible. The solution we developed was to prime the vertical surfaces using Remmers Epoxy MT100 and into this embed and saturate 300gsm chopped strand mat. This served to bridge to blow holes and provide surface suitable for linings to be applied to, as well as providing additional strength to further mitigate against future cracking.
Amazingly a much larger national contractor had proposed that they would completely ignore this essential stage in the lining process and just apply a tank lining system directly to the concrete.
As per our standard quality assurance all climatic conditions were tested and recorded throughout the lining application. An additional important consideration for this project is that it would not be possible to abrade the coating properly if the overcoat window was exceeded. This meant that we had to carefully plan the works around wet weather, to ensure that once the coating sequence had commenced each stage could be completed within the required overcoat window.
Remmers Epoxy Universal was then applied to all primed surfaces, taking care not to coat the bandage details previously installed. Remmers Epoxy Universal is a versatile material in that it offers both good chemical resistance as well as crack bridging. This made this lining material particularly suitable for this application given the history of cracking in the concrete susbtrate.
Where possible we spark tested the lining to check for pin holes as part of our standard quality assurance. However in the deepest and narrowest sections of the channels this was not possible, so we had to rely on a thorough visual inspection using telescopic mirrors to check the inaccessible areas of the gullies. The light grey colour significantly aided in the identifying of defects.
Following a drop test our client was able to confirm the 100% effectiveness of the works, satisfying their own internal standards and the requirements of the relevant regulatory authorities.
