The concrete chemical pit which served as both secondary and tertiary bunding in an electroplating plant was suffering from significant degradation as a result of prolonged exposure to aggressive chemicals such as Chromic Acid and Sodium Hydroxide.
As part of a significant refurbishment project of the area, in which the tanks which usually prevented access to the pit were being removed and replaced, the opportunity was taken to repair and protect the concrete structure.
Due to the chemicals and temperatures which they are present, the only viable lining solution was a vinyl ester resin based lining. We proposed the application of a fully reinforced vinyl ester lining from Atako for improved impact resistance and tensile strength.
Initially the tank was thoroughly decontaminated and the concrete prepared by method of ultra high pressure water jetting.
During this process water ingress into the tank was observed. This was resolved by injecting the areas where present using Normet Tampur 130 Hydrophobic polyurethane resin.
To minimise the risk of osmotic blistering – a phenomenon that can occur in buried structures where the concrete/primer serves as a semi permeable membrane and to extend the life of the concrete, all surfaces were treated using Aquron 7000 and 2000.
Aquron 7000 contains anti corrosive agents which protect the steel reinforcing and Aquron 2000 waterproofs the concrete. Both materials are colloid silicates which form a hydrogel within the concrete up to 200mm deep, filling pores within the concrete matrix. Both materials are applied by method of airless spray.
During this process a phenomenon called ‘purging’ occurred, where contaminants within the concrete are driven out by the penetrating action of Aquron materials.
The process to address this is to high pressure wash to remove the now surfaces contamination and repeat the application until the purging action ceases. As a result four further application of Aquron materials was undertaken, evidencing the heavy contamination of the concrete which had occurred.
Once satisfied that this had ceased all exposed steel reinforcing was prepared to ST3 as per ISO8501-1. Given the pits location within the factory environments it was no practicable to abrasive blast in order to prepare the steel to SA2.5.
The exposed steel reinforcing was then treated using Sika MonoTop 1010 – a polymer modified primer and steel reinforcement protector.
Previously broken out repairs were then reinstated using Sika MonoTop 630 rapid to match the original profile. To ensure a suitable surface to apply the pit lining to a fairing coat of SikaTop 586 Seal was applied by method of render pump and trowel.
The floor was severely degraded and the falls ran away from the sump. We conducted a level survey of the slab which identified the volume of materials required. The floor was to be reinstated flat to provide maximum support for the tanks and the decision was taken to use a flowable levelling compound.
A new sump was formed using shutters and all surfaces to be treated primed using Don Construction Products Strong Coat primer. This was applied at a heavy application rate by brush and roller. Whilst uncured this was fully blinded with quartz aggregate to provide a mechanical anchor for the subsequent flowable screed.
Loose and unbound quartz was removed using soft brooms and vacuums, prior to the application of Don Construction Products Cemflow Renovation fibre reinforced screed to pre determined levels.
Unfortunately some cracking did occur in the screed, so these were expressed using vacuum controlled diamond saws and consolidated using a low viscosity epoxy resin.
Throughout all application processes the temperatures, relative humidity and dew point were tested and recorded to ensure compliance with the manufacturers recommendations as per our standard quality assurance.
All cementitious materials were tested for their moisture content post hydration and prior to coating application, again as part of our standard quality assurance.
Repairs to the top edge of the pit were made using a high strength epoxy mortar to support the mezzanine flooring that was to be installed. As per best lining practice a fillet detail was installed to all internal corners in order to isolate the points of greatest potential for movement from the new pit lining.
To ensure excellent adhesion of the new pit lining all surfaces were primed using Atako ATB primer applied by method of brush and roller.
Prior to the application of the tissue layer the pit lining was tested for porosity using a DC holiday spark tester. A single pin hole in a chemical demanding environment is a point of lining failure, which will allow attack of the concrete structure to recommence.
Any pin holes identified were made good using the same resin material prior to the application of the tissue layer.
The works were completed either side of the Christmas Shutdown, with the shutdown period used to allow the hydration of the cementitious materials. The additional unexpected Aquron applications put pressure on the completion of the cementitious material phase of the works to facilitate this curing window, however our team worked additional hours and weekends to ensure the successful delivery of this pit lining project.
