With the growth of crossdocking (see – Crossdocking Continues To Play An Important Role In Increasing Supply Chain Efficiency), and emphasis on shorter cycle time (for inventory), DC floors must be able to withstand the abuse of 24-hour traffic. In addition, the floor must be an integral part of high throughput logistics typical in today’s DCs. A floor that is not flat enough will forever keep the DC from reaching optimum performance.

To emphasize how important a flat floor is – some lift truck manufacturers will not warranty new lift trucks unless the floor meets certain flatness and levelness specifications. Why? Because most lift trucks do not have a suspension system or pneumatic tires to absorb the bumps. Therefore, warranty repair costs will naturally be higher (and in some cases significantly higher) with inferior floors. Any sudden height change in the floor (even as little as 1/16 of an inch) can cause wheels to become airborne when running at optimum speed. This can lead to excessive stress on the entire unit and premature failure. It’s not so good on the operator either contributing to operator fatigue and injury over time.

Three Ways to Gauge Floor Flatness

Because so much depends on a level floor, contractors use three measurements to gauge floor flatness:

FF = (Face Flatness or bumpiness) measures curve over two feet of floor, and is a good indicator of how well (smoothly) a vehicle will travel over a floor.

FL = (Face Levelness or tilt/pitch of the slab) measures elevation difference or slope over 10 feet of floor, and indicates how equipment like tall storage racks will rest on the floor.

The third metric, Fmin, is used to measure levelness of a specific aisle (in super-flat floor application) that support defined traffic (wire or rail guidance).

Requirements Differ Within the Facility Depending on Operation

The following metrics provide important guidelines for floor specifications in today’s DCs:

• Random traffic in conventional DC = FF35/FL25 (Good - for most lift truck/pallet storage applications)
• High throughput DC receiving/shipping area = FF45/FL35 (Flat - for crossdocking and AGVs)
• High performance DC with random traffic patterns = FF65/FL40 (Very Flat - for high bay order picking)
• Very Narrow Aisle (VNA) high bay application (6 pallets high or more) = Fmin50 *or Fmin100 (Super Flat - for high speed Turret Truck operation)
  
  

*Note: There is no reason to specify anything between Fmin50 and 100 because it would cost as much, or almost as much, as Fmin100.

Most “Spec” facilities being built today will have 6” fiber mesh reinforced (4,000 psi) FF35/FL 25 concrete floors, which are suitable for basic storage and logistics operations. However, for high throughput DCs a better specification is FF45/FL35. Although this will increase the initial construction cost, the flatter floor will lower truck maintenance cost, and improve truck performance especially in crossdocking applications.

In DCs with high ceilings (capable of 6 high or more pallet storage), the Very Flat floor FF65/FL40 specification allows for maximum putaway and retrieval performance. For example - in order picking applications even minor variations in the floor will force operators to lower the load to reduce mast sway when moving to another location, thus wasting valuable time. Depending on activity level - a Very Flat floor should provide an acceptable ROI when compared to a Good or Flat floor.

Upgrading Conventional Floors

When a change of floor use is planned, an F-Number measurement is essential in evaluating an existing floor’s ability to support the new operation. As mentioned above, it may be required to obtain a lift truck warranty, or a new AGV system, for example, may require a higher degree of floor flatness/levelness.

In older facilities often the concrete floor was poured with no flatness and levelness specified, probably striking off each slab by hand and bull floating. This method could produce FF20/FL15. Even with a skilled craftsmen, wet screed, highway straightedge, and machine troweling, you may only get FF25/FL20.

Existing floor flatness and levelness can be improved by:

• Applying a self-leveling, synthetic material (for low-wear applications mostly foot traffic or light vehicles.
• Topping the floors with concrete (in high-wear applications)
• Corrective spot grinding (for minor or localized problems)
• Wheel-track or aisle grinding for correction up to Super-Flat tolerances (required for VNA Turret Truck operations and some AGV applications)

Stabilizing Loose Floor Joints

Loose joints that shift when vehicles cross them can really slowdown an operation. Unfortunately, no standard way of dealing with this problem has been developed. While common in older buildings, the problem can occur in relatively new buildings. First, lift truck drivers will begin to notice bumps and knocking sounds as they cross the joints forcing them to reduce speed to avoid damage to the vehicle. Then, joint edges begin to chip, requiring patches that don’t last very long.

Options like sub-slab grouting and doweling rely on chemical reactions that take many hours to cure and come with severe drawbacks that are costly and disrupt operations.

In the last few years many companies are relying on a relatively simple mechanical method to stabilize the joint. The device, referred to as a SD7 Joint-Saver, consists of a seven-inch-long, three-inch –diameter aluminum cylinder, split lengthwise. The device fits into a drilled hole centered on the joint. A screw pushes the two halves apart, locking them into the hole with 8,000 pounds of force. Springs maintain the clamping force if the joint should open wider, which could be caused by normal drying shrinkage of thermal contraction. In addition to being affordable, the floor can accept traffic right after repair.

Repairing Cracking That Typically Occurs In Industrial Floors

Floors are the foundation of a well-run operation. They must bear the traffic in a variety of ways: steel-tipped boots, pallet-laden metal racks, lift trucks, conveyors, as well as many other types of heavy industrial equipment and vehicles.

Is it any wonder that over time these industrial floors crack, crumble and shrink? Based on our somewhat limited research we found some basic do-it-yourself steps you can take to repair the most common problem - cracks:

• Don’t Make The Condition Worse – If it’s just a hairline crack, it’s usually best to leave it alone. For extra protection against deterioration, apply an epoxy coating over the crack.
• Cut Only When Necessary – If the crack snapped cleanly with no islands, and if the edges of the crack have not *spalled, fill the crack with a proper semi-rigid epoxy.

*Note: Spalling is a result of water entering concrete and forcing the surface to peel, pop out or flake off. Check for proper drainage.

• Cut Out As Narrow A Section As Possible – Don’t fix a 1/8-inch wide crack with a tool that will make a 1/2-inch repair furrow.
• Cut Deeply Enough – When cutting out cracks, always go at least 1/2-inch deep to provide enough area along the joint walls for the epoxy to adhere. Epoxy's strength and its bond to concrete are stronger than the concrete itself. Epoxy crack filler does not necessarily fill the full depth of the crack but provides a strong surface for heavy traffic. Narrow cracks have to be routed out first with a grinder before pouring in the Epoxy filler.
• Don’t Weld – Welding the slab together at the crack may result in another stress crack next to the first.
• Don’t Feather-Edge Repairs – To feather means to taper to zero thickness. Instead, create a vertical edge (trough) of at least 1/2 inch deep on all crack repairs so that the epoxy attaches firmly to the concrete.
  

Final Thoughts

It can be challenging determining exact FF & FL specification, type of grinding needed, costs and time to remedy a bumpy and/or deteriorating floor. There are on-going consequences to operating in a facility with an inferior floor. Therefore, regardless of whether you are considering new construction or upgrading the floor in your existing facility, your first step should be to consult a qualified expert for advice on how to obtain a floor that will serve your long term needs.

Brad Helminem is head of technical sales for Somero Matson Group LLC, U.S. distributors of the SD7 Joint-Saver device for stabilizing joints and cracks in concrete floors. Contact him at 800 584-5553 brad@someromatsongroup.com. George Garber is a concrete floor consultant, a partner in the firm Face® Consultants, and the author of Design and Construction of Concrete Floors, published by Elsevier Press. Contact him at ggarber@floorconsultants.net.

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