Composite Action on Epoxy

[KimWT]

Hi!


CONCRETE LAYER-2 (4" THK)
----EPOXY----
CONCRETE LAYER-1 (4" THK)

I apply epoxy to fix cracks on concrete layer-1 and they are completely bonded.
10 days later I pour topping concrete layer-2.
And then, can I expect perfect bonding between layer-1 and 2?
So, can this whole section work composite action?
I wonder how bonding between hardened epoxy membrane and layer-2 works.
Though I could find many papers about the bonding between layer-1 and epoxy,
I could not remember any reference on the reaction between hardened epoxy and layer-2.

Thanks!

 

[BridgeSmith]

I would not count on any bond between concrete and hardened epoxy - there really isn't any. I'd even be hesitant about counting on the bond with epoxy resin bonding compound that is applied according to the directions, where the concrete is poured almost immediately - before the epoxy even gels, especially if the design stress on the concrete is high.

 

[Canuck65]

No you cannot count on the bond between the cured epoxy and concrete layer 2. In fact I would consider it a bond breaker.

If the proper bonding agent (epoxy or otherwise) was selected, and the concrete surface were prepared properly, and the work was completed properly, it is possible to achieve very high bond strengths. This assumes the 2nd layer is poured within the very short open time after the bonding agent is applied. I have bond tested many repair patches and concrete toppings that were bonded using an epoxy or similar bonding agent. In almost all of the cases the bond strength exceeded the tensile capacity of the parent and repair/topping concrete (>1.0 MPa). For example, this is done in situations where the entire top half of an 8" thick structural 2 way slab is removed via hydrodemolition and then the top half is replaced with a bonding agent at the interface.

 

[epoxybot]

A hardened Epoxy Resin has a relatively low surface energy (45 Dynes/cm). It would be mildly repellent to water and thus concrete bonding. Throw in some minor exudation from carbamation (amine blush) and numerous examples of failed concrete toppings because the epoxy bonding agent's open-time had expired and the answer is No.