Underwater fatigue behavior of cementitious mortar and a countermeasure using a water-dispersible polyurethane ether–Portland cement composite

Abstract

The underwater fatigue behaviors of cementitious mortars are investigated with a focus on the mechanisms contributing to the deterioration of bridge foundations and possible countermeasures. This study analyzes the effects of water penetration during repetitive loading and unloading on the underwater fatigue lives of cementitious materials, highlighting the importance of considering dynamic water motion, in addition to the surface energy mechanism. Water penetration during underwater fatigue occurs even in water-saturated specimens, and water in- and egress within a few millimeters of the specimen surface can significantly reduce the fatigue life. This study proposes a novel approach using a water-dispersible polyurethane ether–Portland cement composite as a countermeasure to improve underwater fatigue resistance. Based on experimental analysis of fatigue in water and microstructural investigations of the composite, the presence of polyurethane compounds within the nano-to-micron-sized microstructures may mitigate water penetration and contribute to a corresponding increase in underwater fatigue life.