An experimental and simulation study on the wet-dry action to crack cause of pier concrete in a tidal river bridge

An inspection of a tidal river concrete bridge in the Mekong River Delta discovered a large number of map cracks in most piers within the tidal range. These map cracks distribute nearly vertically and horizontally with a distance of about 15 and 20 cm. Many of them have a width over 1 mm and a depth exceeding the thickness of the reinforcement protection concrete layer.Considering the location and the pattern of cracks, the most acceptable hypothesis on their cause was the strain gradient in concrete induced by the change of moisture content during tide rise and fall, i.e. by the effect of wet – dry action. To verify this hypothesis, experiments on the time dependent change of concrete moisture content and volume were conducted. Based on the results of these experiments, a computer simulation was performed. The simulated crack map and pattern agreed very well with the observed ones. With the obtained results, it is reasonable to conclude that strain gradient in pier concrete induced by the wet – dry action may one of main causes of cracks in such bridge piers