Specifying Adhesives for Strengthening of RC beams 1

[IJR]

My friends

How does one specify epoxy adhesives for use to strengthen RC beams with steel plates? Sikadur -31 is popular in such applications among other adhesives, even used in post-tensioned girders. But what is the design parameter? Bond strength? Tensile strength to match that of concrete? Any literature?

Your time appreciated in advance.

respects
IJR

 

[Ingenuity]

Probably best to reference "ASTM C881-15 Standard Specification for Epoxy-Resin-Base Bonding Systems for Concrete" and provide type and grade. "Type" representing the physical requirements (like Type IV for structural/load bearing) and "grade" representing the flow/viscosity characteristics.

Also, adhesive bonded steel plates can be installed using typically two techniques:

The first technique is installed plates, perimeter sealed and cured (with non-structural paste resin), then injection ports used to inject the finite space between the plate/concrete interface. This requires a low viscosity resin.

The second technique uses a paste epoxy pre-applied to the steel plates and installed and secured to the prepared concrete substrate. Similar to 'buttering-up' carbon FRP pultruded strips, that are common today. Often an epoxy resin primer is used/specified on the concrete substrate.​

Assuming you are in a design/specifying role, (without 'means-and-methods' responsibility), I would simply spec ASTM C881 Type IV (load-bearing, hardened surface to hardened surface).

 

[Agent666]

Talk to sika, they can do a pull off test (forget exact name of test, but they glue a standard test piece to the beam and pull it off a number of times) which determines the bond strength for the substrate. I have used sikadur 32 previously to glue a baseplate of a barrier to a beam where anchors just wouldn't work and by all accounts it seemed to work ok.

Sika rep came out early in the project and confirmed the parameters for the design to take the guess work out of it for our design.

Talk to sika or a contractor familiar with the type of strengthening work about what they might need you to specify to get it done right if you are delegating the design.