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It is safe to say that the strength of a floor is largely dependent upon the quality of the base on which it rests. Preparation of the sub grade is therefore vitally important.

Construction of a commercial or industrial floor isn’t different than a residential slab, the only thing is it just more of everything – more time spent levelling the side forms, more time spent straightening and restraightening the surface, more care taken with the curing.

The best way for a building owner who needs a concrete floor to meet flatness and levelness requirements for this equipment is to specify the floor tolerance requirements at the very beginning, at the conception phase of the project.

Concrete for floor construction should be made with hard, well-graded aggregates and should contain only sufficient water to insure good workability.

The accepted modern way of assuring that quality concrete is used is to purchase it from a well equipped and competently staffed ready mixed concrete plant.

Water content is important – the less the better for a strong, wear-resistant and watertight surface.

Setting the side forms and screeding has the greatest impact on floor levelness and getting the surface at the specified elevation.

For very level floor requirements, like F-min floors, the side forms will be set then checked with surveyor’s instruments and planed to precise elevations.

F-min is a floor industry standard measuring system for very narrow aisle (VNA) traffic floors.

It is expressed as a unit less number for both the longitudinal and transverse axis for the exact wheelbase configuration of a VNA forklift or truck or order picker crane in high-stack warehouses.

The higher the number, the more flat and level the floor. As an example, it may be expressed at F-min L 85/F-min T 100 (L = longitudinal; T = transverse).

The primary reason for developing the F-min system was to quantify the threshold of mastsway for preventing lift truck payload racking strikes and analyze the bumpiness of VNA floors.

The system allowed contractors to expedite floor repairs and ultimately paved the way for development of construction techniques to manufacture this type of floor.

Some owners and contractors prefer to get high-tolerance F-min floors using the “strip pour” method.

This method is specific to post-tensioned structures. It is typically located at the mid-span or quarter point of the bay. To provide any crack control benefit, the slabs on each side of the pour strip have to be completely separate when the tendons are stressed.

Any reinforcement extending from one slab into the other will act as a tension tie, restrain the relative movement of the two slabs, and most likely cause cracking. All rebar and post-tensioning must be lap spliced inside the width of the pour strip only after the tendons have been stressed.

This placing and finishing method uses forms set to rigid tolerances of plus or minus 1/16-inch, milled wood form tops or thin steel edge forms, and vibrating truss screeds with hand tools (check rods and bump cutters) used for strike-off.

Floors installed this way usually require little or no remediation, as tolerances are more stringently controlled with the narrow strips.

Source : Concrete Construction, Concrete Network

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