MO Bridge Deck Repair Quantities - Half Sole Repair /vs/ Shallow Deck Repair 1

[Jayburr]

Hello, I am a recent grad from May working my first "real" job (in Missouri), and I have been tasked with putting together plans/quantities for a bridge repair project and am struggling greatly with the deck. We went out and chain dragged the deck to identify delaminated area, and I've attached a screenshot below showing what that looks like. Needless to say, it's a lot, as the bridge is really in horrible condition. There is also significant spalling and slab edge repair that will be needed, as well as existing repairs that will need to be removed and replaced.

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Here's my main question, among many: how can I classify the repairs as half-sole repairs or shallow deck repairs before any demolition or removal is performed? Half-sole repair areas are classified as "deck imperfections exposing the upper layer of the top mat of reinforcing steel 1/4"..." and shallow deck repairs are classified as "deck imperfections deeper than 1/4" to a depth where reinforcing steel is not exposed." So how can I differentiate which repair is needed before I can see how deep/significant the damage is underneath the surface? For areas with just spalling (not shown in the attached image), I have pretty much the same question.

I will also attach a screenshot from the original plans for the bridge (built ~1975) to the post, as well as a profile view from my own CAD drawing, so you can get a better idea of what the structure looks like.

Any advice helps, as would examples of plans from similar projects, as I've pretty much exhausted my searching abilities and have had little success finding any. Apologies for naivety and any formatting errors here. Like I said, I'm brand new to this line of work, and I've also never posted on this site. Thanks so much.

 

[BridgeSmith]

Without doing something more than a chain drag, such as an impact echo, GPR, etc. it will be hard to determine the depth of the delams. Of course, that's assuming this is the original deck without a rigid (concrete) overlay.

If it were one of our bridges, we'd assume all of the delam areas, reduced by the full-depth repair area, are half-depth repairs. For that much area, we would probably specify hydrodemolition to remove a minimum of 1/4" of the deck, and the unsound concrete up to half the deck thickness (anything more than half-depth requires full-depth removal) and specify modified concrete (latex or silica fume) to fill the repair areas and add a 1 1/4" thick overlay (1" finished grade raise).

How does the underside of the deck look? Efflorescence? Map cracking? Any areas of map cracking (and beyond) would likely need full depth repairs. We usually estimate twice map-cracked areas for full-depth repairs.

 

[Jayburr]

BridgeSmith,


Underside of the deck has lots and lots of efflorescence but no map cracking.

This is the original deck; there has not been a rigid overlay, just a lot of mediocre patching attempts. My firm's general plan (other than trying to convince the city to entirely replace the bridge) is to perform the deck repairs and then use an ultrathin bonded wearing surface. We will also perform a lot of slab edge repair, because there is quite a bit of exposed (and even freely dangling) reinforcing steel around the slab edges. For crack repairs in the substructure, we are going have to bid that out as lump sum, because the sheer amount of cracking makes it very hard to get an accurate estimate.

Thank you for the advice, that all is very useful, especially regarding the hydrodemolition and assumed half-depth repair for delaminated areas.

 

[BridgeSmith]

ultrathin bonded wearing surface.

3/8" epoxy overlay, or something else?

We will also perform a lot of slab edge repair, because there is quite a bit of exposed (and even freely dangling) reinforcing steel around the slab edges.

We would typically do larger (deeper) reconstruction areas with concrete removal and normal concrete.

For crack repairs in the substructure, we are going have to bid that out as lump sum, because the sheer amount of cracking makes it very hard to get an accurate estimate.

We would go the opposite, and pay by the linear foot (epoxy resin crack injection), so the contractor gets paid for what they end up doing. That way, the estimated quantity is only for cost estimating purposes. We would never do a lump sum bid for an item where the scope is poorly defined (How would you even define the scope of work?), and especially one where the quantity may change by the time the work is to be performed. IMHO, you're setting yourself (or the city) up for litigation when there's more to fix at construction time than there was when the contractor bid the job.

 

[Jayburr]

BridgeSmith,

Our preliminary engineering report recommended a Ultrathin Bonded Asphalt wearing surface overlay that is ½”-¾” thick.

Can you explain more what you mean by this? Apologies.

That is an excellent point, especially because the quantity will certainly change in the time between making plans and actually performing the work. I will keep that in mind. Thank you very much, I appreciate it.

 

[SlideRuleEra]

Jayburr - What is the as-built thickness of the deck? If it is shown on the attached drawing, I can't read it. Thickness of the deck that does NOT need removal is just as important as how much is replaced. Working on "thin" remaining deck is dangerous... too easy for the Contractor to accidentally punch thru it.

 

[BridgeSmith]

Our preliminary engineering report recommended a Ultrathin Bonded Asphalt wearing surface overlay that is ½”-¾” thick.

Interesting. I haven't heard much about those. Have you had good results with that type of overlay?

Can you explain more what you mean by this? Apologies.

No apology necessary. Outside of top surface of bridge decks, we specify a vertical/overhead concrete repair material for shallow repairs (usually <4"), but for larger depths (>6") and larger volumes (>2 cubic feet) we typically pay for removal of concrete and class A concrete (standard 4ksi mix).

 

[Jayburr]

SlideRuleEra,


Good question. The thickness of the slab on the original plans is a mere 12", and there's never been a wearing surface placed on top. After looking at pictures from one of our site visits, it still seems to be 12" thick (in the areas without severe spalling).

Could you give me any advice on half-sole repairs on a structure of that thickness? Thank you, I appreciate it.

 

[Jayburr]

BridgeSmith,


I am very new to the company, only having worked there since the start of June after I graduated from my undergrad, so I can't speak to the long-term success of that kind of overlay with too much confidence. The vast majority of my firm's bridge projects are rural, county-owned bridge replacements, usually single span and between 40-80 feet. I can say that for our bridge rehab projects, we have used that type of overlay a lot in the past. But my understanding is that such an overlay is usually a short-term fix for bridges that don't quite meet the prerequisites for a federally funded replacement yet.



Right, I've looked over MoDOT's qualified materials list and their standard specs, and that does seem to be the norm here as well. I do have a question however, if you can answer it, about substructure repair and repair materials. First, for some background, MoDOT standard specs classify (non-deck -related) repair types like this: Substructure Repair (Formed), Substructure Repair (Unformed), and Superstructure Repair (Unformed). However, they classify repair materials into two categories: Horizontal & Vertical/Overhead.

So my question is this: am I correct in presuming that such "horizontal" repair materials are for unformed repairs, and the "vertical/overhead" repairs must be formed?

 

[SlideRuleEra]

Jayburr - Twelve inch thick deck should be thick enough to allow a safe working surface if no more than half that depth (6") is removed and the remaining concrete (6") is in good condition.

I agree with BridgeSmith, expect major cost overruns on this project... nor matter how the cost estimate is prepared. Don't "fine tune" your estimate.

My advice to you is do not try to precisely define numerous specific "spots" that need repair (like the "spots" shown in the posted image). Instead, group "spots" together into a reasonable number of "areas". The bridge has a fair number of spans, see if you can find any pattern for damage that is common to many spans. The key to addressing any problem like this (where you have limited data) is to work with what data is available. Keep and open mind and review available data using "fuzzy logic". Don't expect to get a good answer immediately. Just keep working with the data. After a while, you will find that what looked like random information when you started actually makes some sense. This approach does not always work, but you have to start somewhere... otherwise just wring your hands and give up. At worst, you will learn much just by trying.

 

[BridgeSmith]

am I correct in presuming that such "horizontal" repair materials are for unformed repairs, and the "vertical/overhead" repairs must be formed?

Not really. Unformed means they're using a either a vertical/overhead patching material (which is a paste that can be troweled into place), or they're doing the top of a horizontal surface, such as a deck, where forming is not needed to contain the material. Formed repairs would be just what it sounds like - formwork is required to contain the material, which is typically concrete.