What is so different about cold store floors? The flooring is the most important part of a freezer store and should be seen not just as a wearing surface, but also as a foundation for the racking system. James Cunningham, managing director of Barpro Storage SA, explains the technical aspects of flooring in cold storage facilities.
Normal warehouse floors are designed to carry the loads that will be imposed on them, including forklifts, pallet racking systems or bulk products. These concrete floors are reinforced both to carry the load, and to stop unwanted cracking during the curing process and thereafter for the life of the store. Storing new products should be done with care.
Cunningham explains: “I once visited a good friend whose office was on the third floor of an old CMT (cut, make and trim) building. Suddenly his office door wouldn’t close. It didn’t take much investigation to reveal the cause. Twelve pallets of sugar weighed far more than fabric and were forcing the concrete floor downwards.”
Warehouse flooring: managing the cracks
According to Cunningham, all concrete floors will crack. However, this process can be managed with fibre, reinforcing, anti-crack mesh, expansion/contraction joints and saw-cut joints.
If rails are installed in the concrete floor, either for cranes or mobile racking, then increased reinforcing is likely both to assist in carrying and spreading the increased rail-point loads and to prevent the concrete floor from cracking around the rails. This can happen as embedded rails are crack inducers.
Rails installed in a recently cured floor before the Storax mobile bases are installed.
The actual design of normal concrete warehouse floors depends on the supporting ground beneath them. If it is of a variable nature or not supporting the weight, and the imposed loads will be relatively large, then piling may be needed.
Cold storage requirements
Freezer store concrete floors, or wearing slabs, must incorporate all the requirements of normal warehouse floors, with a few extras for freezing. If the temperature of the subfloor approaches freezing, usually +4°C is taken as the danger point – then any water moisture in the subfloor will freeze.
When water becomes ice, it expands in volume and must be accommodated. This normally leads to the concrete floor rising and cracking, as the rise is variable over the floor area. Ice will lift just about any weight, which is particularly important when pallet racking is present. “Lately some cold stores have set the temperature higher to prevent frost heave from starting,” says Cunningham.
Frost heave solutions
In addition to underfloor insulation, all freezer floors should have added protection from frost heave. In South Africa the current standard is the electric heater mat, which is normally laid in three circuits in case there is a circuit malfunction. The mat only uses energy if the subfloor temperatures reach 4°C or less.
Some larger freezer stores are now using a warm piped-glycol/water mixture that absorbs the waste heat given off by the condensers, which run continuously. The Australians favour underfloor 200mm diameter pipes through which warm air should be blown via a fan system. The pipes are laid at a slight angle to prevent moisture from lying in them as this might freeze, gradually closing the pipe.
A heater mat control box; showing the current being used by each circuit.
Cunningham recalls being in a freezer where frost heave had raised portions of the floor by over 800mm. “The store had a good underfloor air ventilation system, but the openings had been blocked with a checker plate to stop rats from entering.”
Mobile racking is especially affected by “frost heave”, as the drive systems are designed to only operate on reasonably level floors. Freezer floors also experience a secondary contraction when cooled to below-zero temperatures, and it’s not unusual to see a 10-15mm gap between the concrete floor and the insulated wall panels. “It is not a good idea to ‘cool’ a new freezer store floor quickly, as it’s more likely to crack – especially around the door, a high-traffic area,” advises Cunningham.
In freezer stores there can be either contraction or construction joints. Cunningham has seen freezer stores up to 1 600m² without contraction joints, where the reinforcing is designed to make the floor shrink inwards. In this situation, one would expect to have about 120kg to 130kg of reinforcing per cubic metre of poured concrete.
Contraction joints should be designed so that both sides of the joint can move, while maintaining the same level. These should be armoured when in high-use areas such as gangways.
“We try and design mobile layouts so that any contraction joints are under fixed racks. In such instances, where a double-fixed rack spans a joint, the one side should only be bolted down once the floor has stabilised at its sub-zero temperature,” says Cunningham. Although tempting in a mobile store, construction joints should not be placed at rails, as this encourages cracking and voids.
“It is worth taking time to get the floor right in a freezer store, as subsequent repairs on a large scale at sub-zero temperatures are extremely difficult,” concludes Cunningham. For those who do have the occasional floor problem, there are cementitious and epoxy-based products available to fix them.
Issue: The unique issues surrounding cold store floors.
Solution: Understanding the impact of weight, reinforcing, frost heave and contraction joints on a cold store floor, reduces the risks of a flooring failure.
Full acknowledgement and thanks go to…
www.barprostorage.co.za for the information in this article.
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