Reasonable Crack Widths in a Concrete Slab

[roy835]

Our office is involved in a project in which shrinkage cracks, varying in width from 0.003” to 0.009,” have developed in a new 3” exposed-aggregate topping slab. The topping slab was placed over an existing, exterior structural slab.

This project is located in a mid-Atlantic state and the slab is adjacent to a seawall. This seawall forms the edge of plaza area that is adjacent to a pool of brackish water. The plaza is not subject to overtopping from the brackish water.

We are trying to determine which exposure condition from ACI 224, Table 4.1 is applicable to our situation, so we can determine which cracked sections need repair/replacement. We have narrowed it down to the following:

1) Humidity, moist air, soil - reasonable crack width 0.012”
2) Seawater and seawater spray, wetting and drying – reasonable crack width 0.006”

I was not able to find any information in ACI 224 or from other sources that would provide additional insight on how the exposure conditions are defined. For example, does wetting and drying mean wetting and drying in the tidal zone, or wetting and drying due to weather? Or both?

We are having a robust debate here in the office as to which exposure condition applies. My personal opinion is that our project falls somewhere between the two exposure conditions described above.

Does anyone have any insight to offer?

Thanks,

Larry

 

[a2mfk]

What is the end goal? Are you going to chase and seal the cracks with an epoxy or ??

 

[Teguci]

Is there rebar in the topping slab?

Wetting and drying is for any concrete exposed to rainfall.

 

[MiketheEngineer]

Were there any control joints?? Those seem like very minor cracks to me....what did you use to measure - a feeler gauge?? But some people are very picky.

Before I do any concrete job - I SPECIFICALLY spell out the some cracking will likely to occur. IF the customer is hesitant - then I tell them go find another engineer. Invariably, they get the same answer.

Seal them and put a good heavy coat of paint on it and be done.

 

[IRstuff]

"2) Seawater and seawater spray, wetting and drying – reasonable crack width 0.006""

If you have narrowed your choices to include this one, then you must be close to sea water, and the implication should be that you adhere to this clause's requirements.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize