## 2 Proposed Closure Strip Details  
Three details for the joints between precast panels were proposed incorporating GFRP bars, as depicted in Figure 1. The first proposed joint has a 200-mm-wide closure strip, as shown in Figure 1a. In this joint, the top and bottom GFRP bars in the precast slab project into the joint with a 175-mm anchorage length. The precast panel has a projected slab of 90 mm in length at the bottom of the joint to hold UHPFRC within the closure strip during casting. A foam-type packing rod is inserted in the 20-mm gap between the two projected slabs at the bottom of the closure strip to avoid material leakage. This joint is called the \"Angle-shape\" joint or \"A-joint\" in this research. Figure 1b shows a view of the angle-joint cast for testing.  
The second proposed joint has a 200-mm-wide closure strip, as shown in Figure 1c. This joint is identical to the proposed joint but without the 90-mm projecting slab. The top and bottom GFRP bars in the precast slab project into the joint with a 175-mm anchorage length. It is assumed that temporary formwork will close the bottom of the closure strip to hold UHPFRC materials before hardening. This joint is called \"C-shape\" or \"C-joint\" in this research. Figure 1d shows a view of the C-joint cast for testing. The vertical shear key is expected to provide vertical shear friction resistance between the precast concrete and the UHPFRC filling, allowing for vertical shear continuity of the slab across the joint.  
Figure 1e depicts the trapezoidal zigzag-shaped panel-to-panel connection with a vertical female-to-female shear key. The slab thickness of 200 mm is divided vertically into equally four layers. The clear joint width between the ends of the jointed panels is 100 mm, while the zigzag shape (i.e., trapezoidal tooth shape) allows for an extension of the joint width of the other 100 mm into the precast panel. So, a GFRP bar from the end of one panel at its wide width of the trapezoidal shape will project into the joint with a length of 175 mm in 200 mm joint width in the same bar direction (i.e., 100 into the closure strip and 75 mm into the grooved trapezoidal shape in the adjacent panel). The pullout strength of the embedded GFRP in the joint will be resisted by the bond between its surface  
Figure 1: Details of GFRP bars joints. (**a**) Concrete dimensions and reinforcement detailing of A-joint; (**b**) Image of A-joint before adding transverse bars for slabs S1 and S2; (**c**) Concrete dimensions and reinforcement detailing of C-joint; (**d**) Photo of C-joint with projecting GFRP bars for slabs S3 and S4; (**e**) Arrangement of GFRP bars projecting into the Z-joint; (**f**) Arrangement of GFRP bars projecting into the zigzag-joint (Z-shape) for slabs S5 and S6.  
and the surrounding UHPFRC filling, in addition to the bearing pressure between the UHPFRC filling and the precast concrete at the included surface of the trapezoidal shape at the interface between the two concretes. Such bearing pressure is expected to be resisted by the concrete surface normal to the joint at the narrow end of the trapezoidal shape and the GFRP bar projecting through it from the adjacent panel. A vertical shear key is introduced along the side of the precast panel, while the expanded polystyrene foam is cut and used to form the zigzag connection. Figure 1f shows the GFRP bar arrangement in the zigzag joint and a view of the joint cast for testing. More details about the new connection details can be found elsewhere [56]