Concrete Overlay 1

[martin888888]

We have a small (150ft) length of roadway that is being used as a wet crossing. It is a 12" culvert will the 150ft length of concrete driveway pured over top of it. We want to raise this roadway max 2' and install 2-15" culverts. Before concrete is poured on old concrete is a bonding agent normally needed?

 

[JedClampett]

I'm not sure I understand the culvert raising issue. But if your question is just pouring new concrete on old, I'm not a believer in bonding agents. Clean loose material from the surface, dampen it and pour concrete on it.

 

[martin888888]

Thanks, that is my main question regarding bonding agents.

 

[Ron]

Agree with JC...bonding agents for such applications are useless.

 

[oldestguy]

I don't agree. If you roughen the surface, clean off the loosened material, leave if BONE DRY and then apply a cream made from Portland cement and a little water, brushed (with a broom) on just ahead of concreting, it will bond very well. I have cored these treatments at parking garages and then take a chisel at the bond and try to break the core. They never break at that bond. DO NOT ADD WATER TO THE ROUGHENED SURFACE. The dry surface soaks up the cement cream into the dry pores. That is the trick.

 

[cvg]

maybe you can get a bond, maybe you cant. But, I think the main point is there is no need to bond the old to the new. as long as the new overlay is not "thin" than structurally, it does not need to be bonded. It will not perform any better if it is bonded but it will be more costly. Recommend that you do not make the overlay thin.

 

[Ron]

oldestguy...there's a big difference between a neat cement paste and the snake oil "bonding agents". I agree with you that a properly done neat cement paste provides bond.

 

[SlideRuleEra]

I've used both "bonded overlays" and "unbonded overlays". There are advantages and disadvantages to both.

IMHO, bonded overlays are a nightmare - I would not use them unless the overlay has to be "thin". In fact, for a small project, I would consider removing the existing concrete and replacing it with new instead of using a bonded overlay... but that is just my opinion (based on experience).

Download the 145 page American Concrete Pavement Associations "Guide To Concrete Overlays" and decide for yourself.
Here is the link: Guide To Concrete Overlays - Third Edition - May 2014

http://www.SlideRuleEra.net

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