Hello,

I'm working on a drainage project at work which involves a temporary fix on an existing box culvert.  For some reason, the expansion portion of a box culvert was built approx 20" higher than the flowline elevation.  As a result, water ponds due to a "mini-dam".  A temporary solution will require us to fill a portion of the existing RCB with concrete.  We're matching the FL upstream up to the "mini-dam".  I have been asked to provide a detail for this work and I don't know what information to place on the detail.  I have a note stating to "roughen the existing concrete and chip as required for bonding".  Should I include a dowel for the new concrete?  The problem is that on one end, the concrete fill is approx 6" and 0" on the upstream end.  I appreciate any advice.

Are you sure that this mini dam is not an intentional energy absorbing feature to dissipate energy in the system?

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

Yes, that was a possible reason for the "mini-dam", but it was ruled out because the outlet of the RCB flows into a golf course.  During a storm, the majority of the golf course is flooded.    

Good point, Mike.  If that's not the case, then you are on the right track for an overlay patch.  Use dowels, even small ones.  Do not feather the overlay.

you cannot feather your overlay to zero inches using normal portland cement concrete. You might be able to do a fairly thin epoxy overlay. Otherwise, you will have to live with perhaps a 2 or 3" lip at the end. I would suggest some of the following methods of surface prep: sand blast / shot blast / water blast to clean and roughen the surface. Perhaps bush hammer prior to placing the overlay. Your spec should require contractor to submit his methods before construction and engineer approval of the finished surface prep prior to placing any overlay. You may also want to use a bonding agent.

You cannot dowel thin overlays effectively, you will either need to achieve a good bond or place a thicker overlay

Thank you all for the advice / info.  I'll definitely include the method request in our specs.  

 

Cut a section out of the surface of the concrete to increase the minimum thickness of the overlay.