Effects of Cyclic Loading on Chloride Permeability of Plain Concrete

This paper describes an empirical study of the effects of high amplitude (stress ratio) cyclic flexural loading on chloride permeability in concrete. Third point cyclic loading is applied to notched concrete beams at 1Hz, using a closed-loop control system based on deformation at the notch mouth (CMOD). The work addresses two types of fatigue: conventional constant load per cycle and constant deformation per cycle. Both compliance (CMOD/load) and chloride permeability (K_cl) using the "Rapid" test (ASTM C1202-94) are monitored with progressive deformation. The measured K_cl is a composite measurement through the 3.75" diameter, 2" thick cores recovered from beam sections bracketing the distressed area. Comparisons are made between the distressed K_cl and that measured on cores of "intact" concrete obtained at the non-loaded sections of the same beams. A relationship between chloride permeability and compliance (inverse of stiffness) is indicated, showing that fatigue cracking affects both mechanical and diffusive behavior.