Concrete is rated for strength by its ability to maintain shape and rigidity under crushing pressure. The results are measured in pounds per square inch of pressure, or “psi”.
Average driveway concrete often has a compressive strength of around 4,000 psi. This supports the weight of cars, SUVs and two-axle box trucks without cracking or crumbling.
In comparison, Agri-Rok has a compressive strength of about 10,000 to 12,000 psi when poured as an overlay over existing concrete.
This puts Agri-Rok into the realm of what the American Concrete Institute defines as High Strength Concrete. High-Strength Concrete is usually found in building projects such as skyscrapers rather than flooring applications – even floors intended to have semi-truck traffic are often made from concrete with no more than a 5,000 psi compressive strength.
For perspective, a grown man of average weight jumping up and down exerts about 80 psi on a surface, but that’s because his weight is spread out through his two feet measuring approximately twelve inches long each. If you could focus that man’s weight onto a square inch, you’d get pressure of about 3,000 psi every time he landed. An 80,000 to 100,000 pound truck obviously creates far more pressure but it’s spread out across a much greater area, allowing concrete to maintain it’s shape as long as the truck is simply driving or parking on it.
However, a nagging problem with concrete floors in an industrial setting occurs when forklift drivers turn the same corner on a steadily repeated basis. The specific stress of this activity ends up calling for a much denser, stronger floor than usually necessary.
Industrial floors are recommended to be poured using 4,000 psi concrete occasionally reinforced with bars or mesh, making it strong enough to handle most activity in a manufacturing setting. A common axle weight for an industrial forklift is about 10,000 pounds; when in use, the forklift often carries another 12,000 pounds of cargo, spreading 22,000 pounds across four wheels that connect to the concrete in about a 1’ x 1’ strip each. This spreads the weight of a loaded forklift to about 38 psi, which sounds completely reasonable.
However, this doesn’t factor in what happens when the forklift brakes and turns a corner, especially while loaded.
Cornering causes the truck to bear down far more heavily on the tires to the inside of the turn while braking, creating a grinding effect that basically stretches the concrete and makes it begin to crumble quickly.
Agri-Rok is well-suited to correct this problem since it bonds quickly and easily to previous floors and has the strength to withstand both the stretch and wear of even heavily-loaded forklifts. At 10,000 psi, it's well above the recommended concrete compressive strength even without the addition of re-rod or wire mesh to support it.
One of our most successful applications of Agri-Rok to date has been inside the loading area of a busy manufacturing facility where forklifts load and unload shipments from docked semis. The floor in this area had become eroded to rough aggregate and riddled with cracks, making it both unsightly and unsafe. After resurfacing with Agri-Rok, plant maintenance personnel tried using a sledgehammer on the new overlay to test its comparative strength against more normal concrete. Where the former concrete would’ve cracked and chipped under the hammering, Agri-Rok shrugged it off without even a dent…as it’s continued to do under the daily grind of forklift traffic that destroyed its predecessor.
That's what a "high compressive strength" ultimately means.