Sounding Bridge Deck for Repairs 2

[umrce]

I sounded a bridge deck a few years ago (we dragged it with chain to look for delamination's) and while visually it appeared to be in good condition it sounded terrible. I probably had 80% of the surface indicating repairs. We later found our from the transportation agency that owned/maintained the structure that it had been resurfaced within the last 15 years. They had hydro-demolished 2" of the original deck and resurfaced it with a concrete overlay of equal thickness.

I'm convinced that the reason for so much of the delaminated concrete we sounded is the horizontal joint between the overlay and the original deck. I've now got a different client that wants to do the same thing on a bridge that was originally built in the 70's with a concrete overlay and I'm worried it's going to reflect the same issue. Has anyone had any experience with this?

 

[bridgebuster]

Surface prep and curing are critical, whether it is a structural or non-structural overlay. I'll dig out some info and details that we use on NYSDOT projets.

 

[wiktor]

I did some soundings years ago with mixed results. It helps to find the areas delaminated, but it only allows for performing repairs immediately required, while leaving already corroding areas undetected.
Measuring and mapping the electro potential of the top rebars could be helpful, as the active corrosion could be spotted and addressed.
As Bridgebuster pointed surface preparation and curing are critical, the main problem being cohesion in between existing concrete and and the new overlay. But when properly done, this could squeeze additional 15-years of service at fraction of the cost of entire deck replacement.

 

[bridgebuster]

link to plan and specs for a project with deck scarification details and patching
Link

hydrodemolition project
Link

another hydrodemolition project
Link

Thin polymer overlay project.
Link

 

[STrctPono]

I will re-affirm the importance for surface prep for bonded overlays. Curing should be standard as it is for all concrete but for some higher performance overlays it can be even more critical. We do a decent amount of structural concrete overlays and a lesser amount of non-structural overlays. For Highway jobs, placing a good Very Early Strength Latex Modified Concrete can have many benefits.

If they hydro demolished the upper 2inches of existing deck, they surely got proper profiling of the concrete surface so I couldn't imagine that that was an issue with that. Achieving SSD (in my opinion) always seems to be one of those things that is very very important, is really easy to achieve, yet it is like pulling teeth with these Contractor's to actually do this. The difference between bond strength between an overlay on a bone dry existing concrete surface and one place on a properly SSD surface is significant and can certainly exacerbate delamination issues due to early bond issues. The mix is also critical. The mixes that I am used to dealing with are site batched in a volumetric concrete truck and getting the mix properly dialed in is necessary.

In the end, I would say that it is definitely achievable to get a good bonded concrete overlay. Past bad experiences with overlay delamination can lead to negative biases but is not indicative of all projects. You should incorporate a Just-In-Time Training requirement into your specifications to make sure the Contractor is sharp and alert just prior to production work.

EDIT: After re-reading your post it sounds like you are saying the new client's bridge ALREADY has an overlay on it NOT that you are going to be putting the overlay on it. In that case, you are wondering about experience with sounding the deck as opposed to placing new overlay... In that case, the question becomes what are they planning on doing with this bridge and what is your responsibility? Does your scope and fee and project budget have room for more in depth non-destructive testing like impact echo? Infrared scanners can also be useful tools but cheap ones are garbage and even expensive ones are questionable about what they pick up. Chain drag sounding really is the most introductory level of non-destructive testing when it comes to sounding for delamination and is really only useful for preliminary assessments.

 

[bridgebuster]

In NY we were using LMC from the late 70's until around 1990. Then it fell out of favor. It was supposed to last 40 years but would often debond much sooner. I know several states still use it. The current trend in NY is a miscrosilica overlay or aflyash overlay. They work work well but they're sensitive to surface prep and curing.

 

[bridgebuster]

A free webinar later this month on LMC

Link

 

[OSUCivlEng]

LMC made some pretty awesome concrete canoes when I was in school.