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Reasonable Crack Width in a Concrete Slab

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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 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?


Larry Reynolds, P.E.