INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

highway questions

highway questions

(OP)
I looked for a highways forum, figured this'd be close enough.

A couple questions ...
1) why, when resurfacing a highway, do they skip over overpasses ? They've "munched" the road surface on both sides of the overpass, but left the overpass decking. This noticed on the 401 in Toronto.

2) why do they use concrete as the top surface on highway on ground level, but bitumen for overpasses ? This noticed on the 407, north of Toronto.

another day in paradise, or is paradise one day closer ?

RE: highway questions

rb1957...
bridge decks are reinforced concrete. Milling into those can intersect the reinforcing steel...not good. Putting a thin overlay after milling will not last as the stresses at the interface are quite high from traffic loading.

Milling the ground supported pavement is usually a no-brainer....usually not heavily reinforced if at all and not detrimental if impinged. When asphalt is the surfacing, milling and overlaying is a common remediation.

RE: highway questions

different types of pavement, both rigid and flexible are used where appropriate and economical, and usually based on local preferences. The local preference is different in Toronto than it is in Arizona. You can find a lot more information in the link below

http://www.pavementinteractive.org/category/paveme...

RE: highway questions

When the wearing surface of a bridge needs to be replaced, it is milled. One of the reasons asphalt is used is that the operator of the milling machine can visually see when he hits concrete and knows when to stop milling. This is useful because often the thickness of the wearing surface is unknown or varies. Its kind of similar to the practice of dyeing paint of subsequent coatings. When you apply a second coat, its a different color than the first coat so that you can areas you missed.

RE: highway questions

(OP)
thx MC ... makes sense, and very practical.

why do you think they'd leave the overpass wearing surface unmilled when they've milled the ground supported wearing surface ?

another day in paradise, or is paradise one day closer ?

RE: highway questions

I would guess because the contractor is waiting for approval of the local DOT to use the milling equipment on the bridge due to its weight.

RE: highway questions

around here, most local roads are asphalt and bridge decks are usually (but not always) concrete without blacktop. freeways are nearly allways concrete with blacktop rubberized asphalt for sound reduction. the bridges are only milled if they have a blacktop.

attached photo shows a photo with black topped and un-black topped bridge decks, side by side. you can see that the black top is peeling where it was placed over the concrete deck in a thin layer.

RE: highway questions

I think that re-surfacing bridges is not as cut and dry as regular roadways; if you mill off an extra 1/4 inch every time, the bridge potentially becomes weaker over time, while roadways can tolerate cracks better.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: highway questions

concrete and asphalt behave completely differently so their use depends on the situation. Bridges are almost always concrete but can have asphalt surface for ease of maintenance. Concrete is 4x more expensive and takes 50x longer to cure. Asphalt expands and contracts and concrete only shrinks and hardens. Gotta take into consideration the materials behavior as a designer to make the best choice about which material to use.

RE: highway questions

Also bear in mind that the surface often fails due to deflection of the subgrade, which will be less (usually) with a concrete subgrade such as a structure. So maybe no remedials required?

Cheers,
Chris

RE: highway questions

They skip over the bridges usually for a couple of reasons. The asphalt adds additional dead load to the bridge and some aren't designed for that weight. An asphalt overlay will trap water beteeen the asphalt and concrete deck which usually deteriorates the deck at a much faster rate. In my area we don't do asphalt overlays for the 2nd reason, it's a huge maintenance nightmare.

RE: highway questions

Quote (why do they use concrete as the top surface on highway on ground level, but bitumen for overpasses ? This noticed on the 407, north of Toronto)


It's possible that the bridge deck has a waterproofing membrane below the black top. In some environments this is an economical way of preserving the bridge deck.

Here in NY, we sometimes pave bridges when the deck is still in good structural condition but the wearing surface has become "polished" over time.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close