What is considered an "intentionally roughened surface" per ACI318?

[mkcengr]

ACI 318 states for the purpose of shear friction the interface of hardened concrete should be roughened to an amplitude of at least 1/4". Does this need to be done using a tool? or can the surface be considered roughened if no finishing work is done and it naturally cures such that the aggregate extends out 1/4"?

My feeling is that the statement "intentionally roughened" means it needs to be done with a tool. I'm looking at a case where a concrete corbel is cast separately and "mucked" in to a concrete wall or spandrel pour in a precast plant.

 

[JAE]

I think the idea is that there is a concrete paste & aggregate variation in surface throughout the face with 1/4" amplitude "waves" occurring in a high frequency. I have always viewed this as either done by hand during concrete placement (with a tool) or chipped at afterwards.

 

[Ron]

Can be "raked" with tines just before concrete sets or roughened with scabbling tool after curing.

 

[UcfSE]

The intention with that 1/4" amplitude is that it occurs at a frequency between 1/4" and 3/4", so you don't get the rough protruding parts occuring too frequently or not often enough. In that sense, you're (intentionally) creating a roughened surface with specific parameters instead of just saying unfinished concrete is rough enough.

 

[ToadJones]

I have seen it done with a good ole' garden bow rake.

 

[paddingtongreen]

Ive seen them rake, chip, and in a couple of large jobs, they sprayed retarder and then hosed the loose material off after the rest had set up.

Michael.
Timing has a lot to do with the outcome of a rain dance.