Civil Engineering Reference
In-Depth Information
Table 6.3
Permissible Crack Widths
Permissible crack widths
Members subjected to
(in.)
(mm)
Dry air
0.016
0.41
Moist air, soil
0.012
0.30
De-icing chemicals
0.007
0.18
Seawater and seawater spray
0.006
0.15
Use in water-retaining structures
0.004
0.10
Definite data are not available as to the sizes of cracks above which bar corrosion be-
comes particularly serious. As a matter of fact, tests seem to indicate that concrete quality,
cover thickness, amount of concrete vibration, and other variables may be more important
than crack sizes in their effect on corrosion.
Results of laboratory tests of reinforced concrete beams to determine crack sizes
vary. The sizes are greatly affected by shrinkage and other time-dependent factors. The
purpose of crack control calculations is not really to limit cracks to certain rigid maximum
values but rather to use reasonable bar details, as determined by field and laboratory expe-
rience, that will in effect keep cracks within a reasonable range.
Lake Point Tower, Chicago, Illinois.
(Courtesy of Portland Cement
Association.)
