Permeability of Concrete Subjected to Cyclic Loading

The effect of microcracking development and propagation on the permeability of concrete was investigated in this study. Large numbers of single-edge–notched beams as well as unnotched beams were prepared in the laboratory and in the field from different concrete mixes and subjected to dynamic loading at various stress ratios. During the cyclic loading, stress-strain and air permeability measurements were simultaneously recorded using strain gauges and the poroscope apparatus. Obtained strain and the air permeability measurements were used to evaluate the deterioration of concrete during crack initiation and further propagation. After fatigue testing, other sets of samples were cored from the fractured beams for water permeability testing. Results from these samples were used to correlate with the air permeability as well as with the compressive strength of the beams. Findings indicated that at the first stage of cyclic loading the beam samples exhibited large strains along with a rapid deterioration in the permeability values. Scanning electron microscope images on a specimens obtained from cracked sections in Stages I and II corresponded with the severity of the strain measurements and the air permeability values in these zones. It was also found that compressive strength influenced the transport characteristics of concrete. Another relationship was derived for the air permeability ratio versus the ratio of number of cycles. This relationship can be used as a tool to predict the remaining fatigue life of a structure by measuring its permeability.