Question about repair of concrete with exposed rebar

[GreenJug]

Hello,

I was reading ACI RAP bulletin 4 titled "surface repair using form and pour technique". At one section it states the following:

"Maximum aggregate size should not exceed 25% of the space between the formwork and the substrate, or 50% of the distance between the reinforcing steel and the substrate."

The first part saying 25% of the space between formwork and substrate makes sense to me. However, the second part stating 50% of the distance between reinforcing steel and the substrate does not make sense to me. I always have the habit of chipping 1 inch or 5mm + the largest repair mix aggregate size behind the bar to allow proper encapsulation around the bar and to allow the aggregate to find its way behind the bar.

Needing to chip double the max aggregate size behind the bar seems excessive and unnecessarily risky due to further weakening of the concrete member.

Am I misunderstanding this piece of text?

What do you guys think about this?

 

[Tomfh]

Seems a bit onerous. Is this perhaps just a roundabout way to get you to use small aggregate in repair jobs?

 

[GreenJug]

Seems a bit onerous. Is this perhaps just a roundabout way to get you to use small aggregate in repair jobs?

You would think so... but the next sentence states "in general, the largest practical maximum size aggregate should be used to minimize drying shrinkage and reduce the potential for cracking of the repair" !

 

[HTURKAK]

I always have the habit of chipping 1 inch

Good habit. At least concrete should be removed until sound concrete is reached. My interpretation is the ACI RAP bulletin 4 is for repair of deteriorated concrete resulting from reinforcing steel Corrosion.
-Assuming a minimum (1 inch repair + reinf. bar size + clear cover ) 60 mm , max . aggregate size makes 15 mm.
- chipping behind the reinf .25 mm , makes max aggregate size 12 mm .

Use the smaller and 12 mm would be max. agg. size.