Slaking characteristics and rock–mortar interface durability of red-bed mudrock subjected to wet–dry cycles: a case study in the Three Gorges Area, China

The red-bed mudrock of the Middle Triassic Badong Formation in the Three Gorges Area of the Yangtze River is prone to slaking and failure when exposed to wet–dry cycles, resulting in frequent bank collapse in the Three Gorges Reservoir and the failure of artificial slope in the immigrant new town. To better understand the slaking process of this rock type and the factors influencing its failure in contact with concrete support structures, the typical mudrock of the second section of the Badong Formation in the Badong County seat was studied. The results indicate that the slaking process of siltstone samples was significantly affected by the drying temperature and water pH value. The failure process was observed to occur in three stages: cracking, the peeling, and finally, the stabilization stages, with the mass-particle size fractal dimension of samples reaching 2.2. Simulation test on rock–mortar contact durability revealed that bidirectional roughening of the rock surface and appropriate sand–cement ratio of mortar can significantly enhance the bonding strength of rock–mortar interface, while the application of a cementing agent on the rock surface was found to be ineffective, as the interface failure primarily arose from the disintegration in one side of the mudrock during wet–dry cycles.