FEATURED PROJECT:

Auto Parts Warehouse / Distribution Center

Tstrata TR Installation

Many facilities across America utilize and depend on multi level, elevated slabs for manufacturing and warehousing their raw and finished products. The effects of increasingly heavier material handling equipment such as fork trucks combined with the long term effect of the dynamic loading caused by this equipment can tax floors beyond their capability. Typical construction of these facilities involves a steel column, beam and joist system for the main framing. Stay-in-place steel pans are used to form the reinforced concrete slabs. Although the ultimate load carrying capacity of these systems is sufficient to handle the day to day service loads, the long term effects of the dynamic loads, excessive flexing and vibration in the slabs when a fork truck drives by can be quite pronounced. Over time, this level of dynamic movement seems to create distress in the form of cracking, deterioration and spalling of the concrete slabs. This flooring deterioration process can also occur on other types of construction. Slab on Pile construction can have the same signs of distress as the elevated slab.

In both of these cases, the main mechanism for this distress is related to the typical deterioration process of a crack in a concrete surface that sees repetitive heavy wheel loads. After a wheel crosses over a crack many times it eventually begins to break off a very small piece of the front edge of the crack. As traffic continues over time, the damage to the front edge of the crack gets larger. When the crack gets large enough, the wheel dropping down into the crack begins to break off the back wall of the crack (See Figure 1). This crack deterioration process known as “un-raveling” eventually turns the crack into a small hole... and eventually into a “pothole”. Repairing these potholes creates a unique challenge as the continual slab flexing and vibrations create the same dynamic as trying to keep an ice cube in a flexing ice tray.

This type of surface deterioration creates very difficult driving conditions for the equipment and the operator. Extra wear and tear on the fork truck, operator injuries and product falling off the truck can follow. From a structural failure perspective, these potholes can eventually decrease the slab thickness to the point where its structural load carrying capacity is so compromised that a wheel may literally punch through the slab.

In the past, repair options for this condition have been limited. Considering that repairs usually involve the traffic aisles, it is difficult to achieve repairs with minimal disruption the facility operations. Repair strategies have traditionally involved one of two scenarios- total removal and replacement or bonded reinforced concrete overlays.

For both options-a new slab or bonding additional concrete to the existing slab – the repairs require some form of additional reinforcement to limit future cracking and must offer a durable, smooth driving surface.

For the removal option, the slab must be totally removed down to the structural steel framing and replaced. The new slab would incorporate enough steel rebar to accommodate the static and dynamic loads. Although simple in concept, this creates many difficulties in demolition, and protection of operations below. Overall cost of repair is very high and there is a long period of downtime to the repair area.

The second option is installation of a reinforced bonded concrete overlay. The overlay needs only disrupt the top surface during installation but usually adds 2-3 inches of concrete (See Figure 2). The new additional dead load and complicated transitions to be able to get on and off of the overlay usually limit the viability of this option.

Typical thin epoxy overlays, although used extensively as new durable resurfacing systems, are not capable of incorporating additional reinforcement in them to limit future cracking. When these polymer overlays installed on slabs with the problems described above, the high level of stresses created by movement in old and new cracks in the concrete substrate create future problems. Typically the cracks will “Reflect” completely through the these standard polymer overlays... and the same “Un-Raveling” process will repeat itself.

Such was the case for a heavily trafficked elevated slab in a multi-story warehouse/distribution facility operated by a large automotive parts distributor in Illinois. The long-term dynamic loading of fork trucks, as well as the increase in size of such trucks since initial design of the facility, had resulted in myriad distress scenarios in the concrete. The long term flexing of the concrete floor resulted in numerous cracks and eventually crack un-raveling and deep spalls as noted above. Previous repair attempts would only last for a few weeks at best. Fork truck maintenance was on the increase due to damage caused by the rough floor surface. A flooring solution was needed that not only would serve as a new durable driving surface, but would also add an structural reinforcing component to the more than 10,000 square feet of busy truck aisles.

Total removal was not a viable option for the client. The cost and the major disruption that would occur on and below the elevated slab during tear out and replacement was unacceptable. Instead, the solution utilized would involve the application of the Tstrata TR Reinforced Flooring System. This unique system uses some of the most durable thin polymer based overlay materials cast over very small, high strength twisted steel reinforcement. In concept, this is very similar to a reinforced concrete overlay- but much thinner. In place of large 60,000 psi tensile capacity rebar used in a concrete overlay, very thin sheets of 500,000 psi capacity Hardwire® are used. Basically, by using a thinner equivalent steel reinforcement, the overlay could be reduced to a mere 1/8”-1/4”.

Tstrata TR was developed by Structural Preservation Systems featuring Hardwire® reinforcement technology. Hardwire® is made from ultra-high strength twisted steel wire cords manufactured into reinforcement sheets (See Figure 3). The product can be molded into or on virtually any structure or part and provides high strength (up to 8,000-pounds/inch width of sheet) and a high modulus. Although Tstrata TR with Hardwire does not replace today’s polymer flooring systems, the addition of Hardwire reinforcement dramatically strengthens today’s retrofit flooring design capabilities. The level of preparation depends upon the amount of work which needs to be done prior to the application of the Tstrata flooring.

To minimize the downtime to operations, the project was broken down into multiple phases and all work was completed on a weekend schedule. Badly deteriorated sections of the concrete floor were completely removed and recast with high strength, rapid setting concrete. The floor surface was prepared using enclosed abrasive shot blast equipment. Once the surface was prepared, the concrete was coated with a primer. The Hardwire material, providing 1,400-pounds/inch width of sheet in is installed in a two ply, two direction orientation (0º and 90º). A color tinted polymer base coat is then applied over the reinforcement to lock it down to the floor as well as create an attractive new driving surface (See Figure 4). Because the Hardwire sheets create an open mesh type surface, the base coat easily flows through the reinforcement. Having the consistency of a self leveling slurry, the base coat leaves a level, smooth surface without trowel marks or irregularities. After a rapid cure time to traffic, the color tinted base is then coated with a, high wear UV protective clear topcoat.

This topcoat has two very unique properties. First, it is a no VOC, no HAP Vinyl Ester based system. Vinyl Esters have long been recognized for their high resistance to chemicals, abrasion and marring (from tire marks, etc). Unfortunately, typical vinyl esters also contained enough solvents in their base chemistry that it made them almost impossible to install indoors because of the odors and other hazards to the surroundings during installation. Recent breakthroughs in chemistry now offer the same benefits without the hazards. Second, this system is roller applied and then rapidly cured using innovative technology that almost instantaneously cures the coating when a high intensity UV light unit is rolled over it (See Figure 5). This topcoat allows for immediate foot traffic and heavy wheel traffic within 1-2 hours compared to the 24-hour cure time of most topcoat systems. The flooring system’s high level of reflectivity also offers brighter work area.

The new floor was ready for traffic with little or no disruption to plant operations and access to each phase was returned before weekday operations were to begin. The process was repeated on following weekends until the entire aisle system was completed. The result is a durable, smooth, easily cleaned floor that added very little new deadload. Depending on the condition of the concrete and level of preparation required to assure a sound substrate, the Hardwire™ reinforced floor system thickness can range from 1/8” to 3/16”.

To ensure quality and structural soundness a few simple, but unfortunately not used enough concepts, were used on this project. The first relates to performing bond pull tests on the floor and or system prior to installation (See Figure 6). This is helpful in determining the level of bond achievable to the existing substrate before jumping into the entire area of repair. This process should also be repeated during the installation of a flooring system for QA/QC feedback.

Another strategy to seriously consider for flooring projects is a Pilot Project area. If long term performance in your specific working environment is something you would like to “test drive before you buy”, then you should consider a Pilot program. It will allow you to see how a flooring system is installed and how it will effect your operations during installation. You will also see first hand how it will perform with the typical daily traffic and exposures. You will experience how it will perform, clean, and hold up under real world conditions. It will also give you the opportunity to experience how your specialty contractor and material supplier perform- two key components to successful floor repairs. On the other hand, it allows for the specialty contractor and material supplier to also experience first hand the many key issues related to the floor, your plant operations, true production rates and plant specific safety. Knowing these items usually leads to a more accurate proposal estimates and a better installation once the full size project is done.

Not all flooring projects require a product with internal reinforcement to repair existing conditions. Many cases require only a thin or high build coating. Using the same polymer technologies, this system may also be used as a thin or thick film coating (10-50 mils). All the features of the system such as high wear, aesthetics and rapid UV curing can be incorporated using the same polymer systems in the Hardwire™ reinforced floor, but without the reinforcement. The Tstrata Engineered Flooring System can be used to create an attractive, yet durable solution for many challenging flooring situations.