Table 4.1 in ACI 224R-90, "Control of Cracking in Concrete Structures," lists tolerable crack widths for reinforced concrete under various exposure conditions. Section 4.4 of ACI 224R-90 indicates that a portion of the cracks in a structure should be expected to exceed the values in Table 4.1 by a significant amount, even when other report recommendations for limiting crack width are followed. However, the table's values have been used in court cases to imply that the presence of any cracks exceeding the widths listed--at any concrete age--indicates inferior design or construction practices.
What is the proper use of the values in Table 4.1? Concrete Construction asked Edward Nawy and Randall Poston to share their views. Nawy was the chairman of ACI 224 when "Control of Cracking in Concrete Structures," including Table 4.1, was first published in 1972. The current table is based on a crack-width table from a technical paper written by Nawy. Poston chaired ACI 224 from 1991 through 1997, when revised wording for the table was proposed to clearly indicate that the tolerable crack widths listed are a guide and not to be taken as absolute or misinterpreted as "allowable" crack widths. However, the revision wasn't adopted.