Tough Problem: Waste Transfer Station Suspended Slab 1

[James Hornett]

Hi,

My company is currently dealing with a difficult problem.

We recently reviewed a waste transfer station (built late 1990s). The station consists of a metal framed structure over a concrete foundation. There are two levels. At the upper level trash is dumped onto a slab-on-grade. The trash is loosely sorted and then pushed to a openings in the floor below where transport trailers are positioned to take the trash. At the openings the slab on grade transitions to a suspended slab. Due to the original slab becoming damaged, a few years after the building was constructed, a topping layer (approx. 6") was added to the slab. The drawings from that project indicate that additional rebar was added to help support the suspended slab.

Problem: moisture is visible at the underside of the suspended slab and corrosion of the rebar is beginning. Spalled concrete was not observed though. Although covered by the metal structure above, moisture from the trash and from equipment moving into and out of the building renders it effectively an outdoor space. During original construction and at the time of repairs it does not appear that a waterproof membrane was applied to protect the suspended slab. We have considered removing a portion of the topping, applying a membrane and adding a topping back over. The amount of concrete that needs to be removed would likely mean a significant shutdown which the client would like to avoid. We also looked at removing a small portion of concrete (approximately 3/4"), applying a membrane and installing metal panels over. Heavy equipment including equipment with tracks are used to move the trash. The client felt that there would not be enough grip with the steel plates.

We briefly looked at applying a robust traffic membrane directly to the concrete however we doubt it would last long given the nature of the work.

If anyone has seen a similar situation or knows of a possible solution, please let me know.

Thank you

 

[HTURKAK]

Apparently the concrete is not compact and moisture from the trash and from equipment migrating in to concrete.

I will suggest the waterproofing of concrete with crystalline technology and epoxy flooring for the surface hardening and wearing resistance.
I do not like to define any commercial name . You may contact with local suppliers of;

- XYPEX single-step Xypex Megamix

- jotun epoxy flooring or SIKA epoxy flooring.

or look similar products.

 

[Enable]

Conventional Thoughts: Talk to Tremco about their Puma System (see here:

https://www.tremcosealants.com/mark...em-ews-for-traffic-coatings/vehicular-puma/).

It is a methacrylate based thin system that we use to turn around commercial projects in the same day/night.

We use it for airports and other heavily trafficked areas. Since it's a thin system it is probably not ideal for this application, but it is a very strong product that can be turned around in a night(shot-blast, prepped, installed, and turned back to the client for morning use). It's worth calling to see if Tremco thinks it will stand up. I know I've run bobcats and excavators on the stuff and I have yet to see a dent in it.

Otherwise on the coating front you are stuck with more durable epoxies, which take several days for a total a turnaround. Or if the slab can handle the additional weight and elevations are not a concern, you can just add another topping without removing the existing. Shot-blast existing surface, waterproof, and add say another 4" of concrete. Same effect as getting back to the top of the suspended slab.

Although you would likely phase the project in that case to minimize total disruption (i.e. facility always open just some area restricted for slab/coating application).

I think that's it unless you do the shutdown on the conventional front. Maybe a sealer if you just want to extend the service life some.

Unconventional Thoughts: What I mean is, if a shutdown is truly impossible (owners will always say that until they see the price of staying open but I digress), then there are oddball ways of doing this. Here is one such procedure:

1. Form and pour slabs of a size that is easily moveable by the type of excavator that can fit into the facility. Cast them with eyelets for lifting. Roughen the sides of the forms to provide a nice CSP profile for epoxy bonding later. These are going to be to replace our existing topping.

Note: topping thickness is likely to vary so cast the slabs for what you anticipate to be the minimum thickness and we will build up as needed to make things flush when we install them.

2. Saw cut and remove a panel of the existing topping via lifting (epoxy in some eyelets). Make the removed panel marginally bigger then the pre-cast replacement panels.

3. Clean the surface via an approved abrasive. Ideally have the contractor use a small shot-blaster in the main area, and grinding discs at the perimeter. Have reglets cut along the perimeter.

4. Have a small kettle on-site and apply conventional 2-ply hot applied waterproofing w/asphalt protection board (don't stagger joints keep flush)

5. Lift our pre-cast panel into place. Shim as necessary. Once shim heights are established, remove panel and apply some rapid-setting concrete/cement in-between shims to desired height (to achieve even bearing once panel is lifted on-top). Place panel back.

6. Rinse and repeat. At joints between panels use EP350 or some other approved epoxy binder.

Additional Note: If you want to be assured of panel interactions (that is they work together) then make two types of panels. One with bar that sticks out and one that has voids at bar locations. That way when you pour the epoxy into the joint the bars will become encapsulated in the epoxy and bind everything together.

 

[miningman]

If the CAT backhoe in the photo is typical of the tracked equipment that will be used going forward, none of the earlier post suggestions will stand up to the repeated abrasion induced by the heavy point loads from the tracks. The only technique that I am aware of that will withstand this is to cast railway rails into the concrete. This could be done without ripping out the entire existing floor but it will be time intensive and not cheap. If this is unacceptable to the owner, he must be willing to change out to rubber tyred equipment.

 

[Enable]

If the CAT backhoe in the photo is typical of the tracked equipment that will be used going forward, none of the earlier post suggestions will stand up to the repeated abrasion induced by the heavy point loads from the tracks. The only technique that I am aware of that will withstand this is to cast railway rails into the concrete. This could be done without ripping out the entire existing floor but it will be time intensive and not cheap. If this is unacceptable to the owner, he must be willing to change out to rubber tyred equipment.

How do cast-in rails help with the moisture migration issue from garbage on the topping? The issue isn't abrasion of the slab surface it's the deterioration of the suspended slab reinforcing steel due to bulk water / chlorides. Or is your suggestion to cast in rails to elevate tracks off of the slab to allow for waterproofing application within the railway system and then fill with some light-weight material to make flush? That might work in a staged fashion. Probably cheaper than my slab replacement idea above.

 

[epoxybot]

You could talk to Master Builders or possibly Euclid Chemicals, both out of Cleveland, OH. They produce cementitious-malleable-iron filled abrasion & impact resistant toppings for waste transfer stations, paper mills, etc.
These sacrificial toppings are often placed at 3 inches but the thickness is based on the harshness of the service condition and future maintenance planning. The toppings are bonded with an epoxy bonding agent, which will give you, your waterproofing membrane. The product is delivered in bulk bags and mixed on-site in transit mixers and screened with a roller screed. It is generally a good idea to install steel pins before topping. The toppings are designed for a short turn around. Both companies should have a long list of transfer stations on their projects list.

 

[Enable]

Thanks epoxybot. Didn't know about those.