Experimental Study of the Effects of Grout Filling Completeness on the Performance of Grouted Sleeve Connections

Grout filling completeness (GFC) is the primary factor affecting the mechanical properties of grouted sleeve connections. To investigate the influences of vertical top void defects on semigrouted sleeve connections, two groups of samples with different rebar diameters (14/16 mm) were designed, incorporating five levels of grouting fullness gradients (GFGs): 60%, 70%, 80%, 90%, and 100%. A total of 60 semigrouted sleeve connection samples were prepared and subjected to uniaxial tensile tests and high-stress cyclic loading tests. The changes in the failure modes and mechanical responses under varying loads were systematically analyzed. The results indicated the following: (1) GFC Threshold Effect: When the GFC was less than 90%, both groups of connections failed to maintain reliable performance, with failure modes transitioning from rebar tensile fracture to interfacial bond-slip failure. Under cyclic loading, interfacial bond-slip failure occurred six times more frequently in the 16 mm-diameter samples than in the 14 mm-diameter samples, indicating significantly reduced reliability for larger diameters. (2) Uniaxial Tensile Behavior: The strength metrics of both joint groups exhibited consistent correlations with the GFC. The yield limits were weakly correlated, whereas the ultimate tensile strengths were significantly strongly correlated. The residual deformation and grout damage depth were not uniformly correlated with the GFC. As the GFC decreased, the yield phase elongation and elongation in the experimental curves generally increased. (3) High-Stress Cyclic Loading Behavior: The mechanical parameters of the 14 mm-diameter samples were not significantly correlated with the GFC. Conversely, the 16 mm-diameter samples exhibited dual dependencies on strength and deformation, with the ultimate tensile strength and grout damage depth showing strong correlations. Under cyclic loading, yield phase elongation and overall elongation decreased inversely with decreasing GFC—a trend opposite to that under uniaxial tensile loading. This phenomenon provided critical theoretical support for the ductility design of prefabricated structural joints under seismic conditions.