What is the Crack Width in Concrete Structures to Prevent leakage?

Abstract

ACI 318-99 no longer refers to Z factors or crack width formulae as in previous editions of the code. Instead, ACI 318-99 correlates bar spacing with clear concrete cover, indicating that following these guidelines will reduce crack widths at the concrete surface. Field investigations have found leakage at certain type cracks which exhibit widths of .23mm (0.009") or greater. Research and condition surveys completed by the author have found greater potential for concrete deterioration at cracks which extend to embedded reinforcement as compared with low slump, low water/cement ratio concrete having adequate cover over reinforcement. Current codes and standards present considerable variation with regard to recommended maximum crack widths to prevent leakage. Use of ACI 318-99 to design liquid or gas retaining structures could lead to designs that are not conservative, not durable and possibly unsafe, if preventing leakage is an important requirement for the particular facility.