Concrete solutions

Analyzing tipping floor composition is likely far down the list of priorities for transfer station operators focused on the day-to-day tasks of managing and moving waste. However, ensuring proper upkeep through proactive repair and replacement is essential for protecting the integrity of these floors, avoiding unnecessary shutdowns, and helping save money.

Dealing with the issues

Between constant heavy equipment traffic and the composition of the waste itself, transfer station floors are subject to a tremendous amount of abuse.

Jim Andrews, CEO of Huntington Beach, California-based American Restore Inc., has been repairing and resurfacing floors in waste facilities for close to 40 years. According to Andrews, there are several common reasons why these floors suffer aggressive wear.

According to Andrews, the busier the facility and the greater the traffic, the greater the wear. This wear occurs when waste is dumped on the floor, excavators and material handlers—especially tracked machines—traverse the floor, and buckets create friction against the ground when moving trash.

Specific to the buckets used to move waste, Andrews says that those affixed with rubber edges can accelerate wear due to added friction placed on the floor.

Then there is the issue of the operator. Andrews says that older, more experienced operators tend to exercise more caution and care. Younger and more inexperienced operators, conversely, may be more likely to exert force on the floor or slam attachments since they are not as skilled at maneuvering the equipment. Similarly, facilities that are able to retain their workforce tend to have more disciplined and seasoned operators compared to transfer stations with more turnover.

Beyond the equipment used, the material being dumped at these sites is a catalyst for floor damage. Glass and metal tend to gouge floors, accelerating wear. Additionally, decomposition from organic waste generates a caustic liquid that can speed up concrete wear issues.

“Waste has highly concentrated amounts of organic acid from food waste, restaurant waste—any waste that is decomposing,” Andrews says. “That creates ‘off pH’ liquids. This is particularly true in warm environments where these organics deteriorate faster. In the summer months or the warmer months, or in facilities located in warmer environments, those acidic materials accelerate and wear on the concrete more.”

Andrews says that these organics-derived liquids would formerly seep out of waste trucks during transport, but public pushback and environmental legislation resulted in waste trucks being designed to retain these liquids. The result is these waste byproducts end up on the bottom of a transfer station floor during dumping.

Another factor that can influence floor wear is how wet or dry the floor is kept, Andrews says.

“Wetter facilities wear out faster than dry facilities,” he notes. “People think that in a wet facility, there’s a lubricating factor of the water that helps protect the floor, but it’s not true. If it’s a wet facility, the floors are remaining cleaner. If the floors are cleaner, they’re more subject to exfoliation from abrasion. In dirty facilities, the dirt will stick to the floor. And now you’ve a protective membrane between the concrete and the environment above it.”

Repair vs replacement

With all the variables that influence floor wear, it is difficult to ballpark repair or replacement intervals. That’s why relying on a trusted third party to assess floor composition can be a prudent strategy for operators.

RRT Design & Construction in Melville, New York, is an engineering and construction company that specializes in solid waste processing and recycling facilities.

According to Nat Egosi, president of RRT Design, his company routinely gets called to help operators assess what floor repair or replacement work might be needed.

“We have proactive customers that ask us to survey their tipping floors on a regular basis, as well as their push walls. This is part of how we inspect their entire facility. They’ve made a capital investment and they want to be proactive in understanding how their facility is being operated and how it should be maintained,” Egosi says. “These individuals want to plan their capital projects and repairs ahead of time and not have to face the potential of an emergency shutdown.

“We have other clients who suddenly run into a problem, and they need us to come out and do an evaluation of their floors. Usually in those cases, what we’re finding is the floor itself not only has worn down, but they’ve lost structural integrity. In those cases, structural engineering work is usually required. You have to put together drawings; you have to put together fit packages; panels or sections need to be removed and other sections might need to be redone, so it becomes a much larger kind of project that wasn’t necessarily planned.”

To avoid the latter scenario, operators need to be mindful of the stages of typical floor wear.

Andrews says that operators should look for worn aggregate as the first stage of decomposition. Everyday use can wear anywhere from 1/4 to 1 inch of concrete away from the floor every year. More severe cracking and signs of rebar underneath the concrete can point to immediate need to look into repair options. When concrete integrity has been compromised, rebar has been torn out or damaged, or dirt is becoming visible, complete replacement might be necessary.

“If there’s enough integrity left in the slabs, then we can overlay concrete,” Andrews explains. “If there are evidentiary signs that the slabs are weak, have lost a lot of strength from cracks and erosion, and there is slab pumping where water is shooting up from the soil below the floor due to compression or there is movement in the concrete, you really have to take a closer look because you might need to consider replacement.”

"A lot of times, people’s view of the world is, ‘Well, we got this far without spending money to repair our floor and nothing happened. Why don’t we just go six months longer?’ Inevitably, six months becomes 12 months, and 12 months becomes 24 months. Meanwhile, things are just getting worse and worse until their floor is just dirt.” –Nat Egosi, president, RRT Design

Egosi says that his teams put steel wear-bar indicators into the concrete during floor construction. Once these bars become uncovered through regular wear, it is a sign that the operator should begin to plan for repairs before the structural rebar underneath is exposed and integrity begins to get compromised.

Despite the warning signs of floor degradation, Egosi says operators often put off repair because of budgetary concerns, which can compound the problem.

“A lot of times, people’s view of the world is, ‘Well, we got this far without spending money to repair our floor and nothing happened. Why don’t we just go six months longer?’ Inevitably, six months becomes 12 months, and 12 months becomes 24 months. Meanwhile, things are just getting worse and worse until their floor is just dirt,” Egosi says.

Refusing to heed the warning signs of a floor that needs repair or replacement can have significant ramifications for operators.

Egosi says that letting a floor degrade to the point it is unsound can cause structural issues beyond the floor itself.

“The concrete slab floor actually provides structural integrity to the walls in some transfer stations. In these cases, engineers are needed to come in to evaluate whether the loss of structural integrity in a floor affects just the floor or if it also affects the walls,” he says. “What would’ve cost you maybe $100,000 to repair is now going to cost you $300,000.”

In addition to alleviating additional construction challenges, taking proactive measures to repair a floor before a full replacement is needed can also be instrumental in helping prevent environmental contamination that can occur when the liquid waste stream leaches into the soil. When this happens and there are remediation issues, operators can end up spending significantly more time, energy and money addressing the issue than what would have been necessary by tackling the issue early on.

“These transfer stations, particularly the older ones, have a lot of waste material that has gone through the building over the years. And these slabs, even though they’re supposed to act as primary containment to the waste stream, they have cracks, they’ve joints, stuff goes through the slab and gets into the dirt, and that can be an enormously risky scenario,” Andrews says.

Specific to negating environmental risks, Andrews says that a concrete overlay design can be a safer bet for operators as opposed to new concrete construction, which can open up a facility to environmental contamination problems due to the exposure of the soil.

In the mix

One thing that both Andrews and Egosi stress is that not all concrete is created equal. Because concrete is made from aggregates derived from quarries, the strength and integrity of this material differs based on the geography from which it is mined.

“You want to select an aggregate that has a wear index property that’s very suitable for crushing, degradation and disintegration. That really does make a difference in the longevity of the floor,” Egosi says.

For Andrews, he says that the concrete mix his company uses has evolved over time.

“We have used a lot of different mix designs over the years, but what we always come back to is a slightly altered version of a Department of Transportation bridge mix. It’s a federal standard concrete that’s used in bridges because bridges are built in the desert, they’re built in the mountains, they are built in all these different types of environments. ... What we’ve done at American Restore is we’ve started with that mix and then we’ve altered it over the years where we’ve added some silica fume and fly ash to reduce the porosity of the concrete, and maybe we add some more cement to the mixture depending on where we are in the country since not all the aggregate is the same.”

To negate the variables of using different aggregate with different qualities, Andrews says that most of the engineered overlay American Restore uses for its concrete floor restoration is made in the same plant with the same ingredients to ensure a consistent product.

“Because of our quality assurance and quality control measures, we can do a job in New York; Seattle; Texas; or Casper, Wyoming and it’s the same exact formula. It’s the same material. So, now we can tell the owner and the engineer [of a site] with certainty what their performance expectations can be.”

Because cost can be an issue, especially for municipal clients, Andrews says that the company offers two different grades of concrete that are priced accordingly.

He says that for those on a tighter budget, companies often opt to use the tougher material in high-wear areas and use the other mix where there is less traffic and potential for wear.

Regardless of the mix, transfer station floors inevitably degrade over time. Making facility assessment a routine part of the job can help transfer station managers identify problems before they lead to significant costs—and even bigger headaches.

The author is the editor of Waste Today and can be reached at aredling@gie.net.