Concrete bridges

New bridges?

Old bridges?

Design defects?

Construction defects?

Maintenance issues?

Weathering issues?

Location?

Hi

I am referring to both new and old bridges which I want to inspect in Mauritius.

I want to inspect all the defects on some major existing concrete bridges, identify the causes of defects (design defects/ weathering/ poor maintenace)

I intend to carry out a visual inspection on the bridges and propose appropriate remedial measures to the local authority.

Consider adding construction defects to your list. All of these causes will contribute to the bridge rehabilitation (you call it "remedial measures") program for your area.

I suggest during the visual inspection for each bridge, you make notes and take photos for documentation leading to a preliminary report.

Later funding will need to be secured and possibily field work and testing before proceeding to final design and implementation of the remedial program.

Good luck!

One failure mode of concrete bridges is rebar corrosion causing cracking and spalling of the concrete. This comes about normally when the rebars are within about 100mm of the surface and moisture penetrates the concrete causing the rebars to corrode. As the rust is larger than the solid steel material, it effectively expands the size of the rebar causeing cracks and eventually causing sections of concrete to fall away. Early signs are cracks running along the concrete and brown staining where the rust is leaching out of the porous concrete.

It is not acceptable to just expose these areas, blast off the rust and re-patch the concrete as this creates accelerated corrosion of the rebars next to the repaired patch. You should ideally repair the damaged sections and then install some form of cathodic protection.

One option for cathodic protection that is gaining in popularity is metal spraying a pure zinc or alloy of zinc and aluminium onto the surface of the repaired concrete structure, creating an anode where the rebar then becomes the cathode. Depending on the environment, you may benefit from having an impressed current to 'assist' the corrosion cell.

This process has been very popular in the USA for many years and is gaining popularity in Europe.

I have some articles on the subject which I can email upon request.

Hello

Thanks to all those who have helped me.

Thanks for the valuable info Milty. Could you please e-mail the articles to me on : kesweena@yahoo.com

See Jardenzinc.com for the bridge corrosion section. Thanks.

Check out contecus.com

If you e-mail me a jbaker@highwaymaterials.com

I will send you the USGS Bridge inspection manual, Scour calculation manual, and scour protection manual.

Thanks

John

I have read the other posts and I find them to be well on target. However I notice something that is often missed and is " at least in my opinion the first issue to check. " That is the original drawings, including all change orders. I bring this subject up from having experienced a significant issue that occurred when repairs were being made to the rail transit decks on the Ben Franklin Bridge between Philadelphia and Camden N.J.. I was running the crew that was replacing whole sections and smaller areas of defective concrete decking that carried the rail tracks from the underground up to the anchorages. About half way up on one side we had to remove an entire 50 ft long section. Replacing the deck was not an issue, however when it came to replacing the end dams at an expansion joint a problem surfaced. The end dam was supposed to be constructed with an 18' deep surface on the face of the gaps between the upper and lower girts, with a 6" high curb to prevent the trap rock , ties and rails from shifting down hill from vibration. The lower end dam was not damaged and there fore was not being R&R'd. How ever it quickly was noticed that the upper end dam could not be constructed according to the specifications and drawings provided. If an adjustment was not made we would have a 4" high difference between the upper and lower tops of the two end dams. When I brought this up to the Consulting Engineer, He was adamant that I must follow his drawings. I was just as stubborn that it would be physically impossible. I asked to see the original bridge drawings that were being referenced to create the repair drawings. I first looked at the detailed drawings regarding that particular expansion joint, and noticed that both the upper and lower girts were shown to be the same size. The asbilt was different, with the upper girt being 4" deeper, therefore 4" higher at the surface. I then looked at the original dates on the drawings and noticed that they were certified 15 years after the bridge had been constructed. I new this from the brass dedication imblem on the anchorage that had been dedicated to all of the men who lost there lives during the construction of said bridge. I pointed this out to the Consulting Engineer and restated that his detail did not match the field condition. The engineer checked with the Port Authority and found that the original drawings had been lost in a fire and the original engineering firm reproduced the reference drawings. Clearly some where along the way there had been a change in the steel drawings that was not reproduced on the replacement drawings.

We resolved the problem by adding larger bars and additional support in the area and re designed the end dam area to be of a different profile.

I bring this up because often plans are adjusted to meet existing un anticipated conditions, and often the same bridge plans are used repeatedly where possible with adjustments made in the foundation plans to accept the "standard drawings". This is what happened in Minniapolis where the joining plates that were originally called out to be 3/4" thick but were replaced with 1/2" plate material. It might have been satisfactory if the bridge did not get over loaded and life expanded. Whether it be a bridge or roadway, they are all designed with a limited amount of cycles per "time period" vs estimated weight. For me, the first thing I want to look at is the design performance vs the actual effective use that the bridge has under gone in the years that it has been in service.

TMF

Hi TMF,

Thank you for the info. In fact I am doing this for my degree project. I am still a student. I have planned to get the drawings of the bridges from the local Authorities. I will just elaborate on the actual state of the existing bridges, the defects, their causes, etc...

In the future am convinced that the government will work on the maintenance of the bridges. This will help me if i actually get to work on the projects.

Regards,

Kesweena

Hello Kesweena,

I was pleased to touch on the hidden issues like the reproduction of lost or for what other reason the current plans may not be the original drawings for a particular project. There several other areas that you should investigate. The Consulting Engineers always keep detailed record about the evolving history of the work. Issues like weather, rain , freezing or very hot conditions can effect the cure of concrete. Under these circumstances a retarder or an excellerator may be added to the mix that can ultimately effect the ability for a long term bond to the reinforcing steel by increasing the possibility of hidden electrolic activity. These examples would likely not show up on the available drawings, but would be found in places such as the Engineers daily records, the field drawings used by the contractor and his diary, as well as the production delivery tickets that are provided from the concrete batch plant. Though most of the work may have been accomplished according to plan, scheduling that includes work in cold as well as hot times of the year can adversly effect concrete performance over a lengthy period of time. Sometimes the reinforcing steel that is called out on the drawings will not be available and a substitute grade may be approved. This too can have an overall effect on the designed life span of the structure. It is not unusual for an owner to be provided with an after the fact discount from the original contract price because the finished product is judged by the Engineer to have an estimated shorter life span than was originally called out in the Specifications. Comparing the drawings against the Specs. and any other change orders and field memos can turn up the likely hood of future defects in the finished project. These subjects tend to show up years later as Scientific and Engineering knowledge increases. Often this kind of info doesn't show up with out extensive investigation, But for example a bridge that was design to have a 50 year life span, may have its life span extended at a later date through the efforts of "best maintenance practices" and budget constraints, and at the same time have hidden issues that do not support the extended life estimate provided by Engineering inspections.

Good Luck!

TMF

Thanks for the info TMF

I will take that into consideration.

have a look at these articles:

http://www.corrpro.com/pdf/CP48.pdf

http://www.pwri.go.jp/eng/ujnr/tc/g/pdf/19/3-1hooks.pdf

http://www.fhwa.dot.gov/bridge/pubs/07039/07039.pdf

corrosion prevention | corrosion control

S