Concrete Bonding Agent

[MHSpurs]

We are investigating the bond of a thin high strength concrete screed 2" to existing concrete floor using an SBR. Prep includes saturating the floor and grit balsting to expose aggregate.

using pull off testing, can anyone tell me what bond strengths should be achieved?


Also, at what strength would concrete (original slab) failure be expected? The original slab is 35N, 10 years old and in relatively good condition.

Thanks

MH

 

[Ron]

Bond strength does not need to be quantified. When you do the pull off test, it should fail in the original concrete, not at the bond interface.

 

[Duwe6]

Even if it fails in the bond, anything much over 1000 psi should fill the structural needs. Your loads are down, thus in the original slab. The topping pour is not part of the tension load. All that needs to be achieved is a bond sufficient that wear & tear will not break it loose from the existing slab.

 

[Ron]

Duwe6...I've tested lots of toppings and coatings...have never had one go to 1000 psi. Most fail at under 300 psi, even if failure occurs in the concrete. Concrete tensile strength is usually less than 10 percent of its compressive strength.

 

[MHSpurs]

hi

what i have been told is that for an epoxy agent the concrete will fail first but not necessarily so for an sbr.

we are doing QA pull off tests and only achieving 150 psi. i'm looking for vales of pull off where we should expect the original slab to break.

any ideas? is it just the tensile strength of the slab? if so that is approx 3-4 times stronger than the SBR bond.

Confused!

 

[Ron]

It appears that your concrete is relatively high strength. Assuming you are using the SBR as an admixture in the topping, it is unlikely you'll get failure in the base concrete. As you note, the strength of an SBR modified concrete in tension is not all that high. Epoxies are much higher but that process is one of "glueing" the topping to the underlying slab.

Yes, it is just a simple tensile failure consideration. 150 psi is no bad, but it likely won't withstand the stress if you are have the need for a high strength topping.

You might consider a full polymer modified topping such as SikaTop or similar.