Composite reinforced concrete (RC) elements, such as those combining cast-in-place slabs with precast girders, are widely used in bridge construction. The shear transfer at concrete-to-concrete interfaces is critical for structural integrity. This transfer is typically facilitated by reinforcement acting as shear connectors. This study evaluates glass fiber-reinforced polymer (GFRP) headed-end bars as a corrosion-resistant alternative for shear friction reinforcement in untreated concrete cold joints. Three large-scale push-off specimens were constructed and tested to failure. The specimen consisted of two L-shaped blocks, each measuring 1,050 mm × 600 mm × 300 mm. For all specimens, the interface surface of the cold joints was left untreated, replicating typical construction practices. Two specimens were reinforced with GFRP headed-end connectors at reinforcement ratios of 0.33% and 0.66%, while the third specimen was unreinforced, serving as a reference. Results demonstrated that specimens reinforced with GFRP headed-end bars achieved higher shear friction capacities compared to the unreinforced specimen. Increasing reinforcement stiffness across the shear plane resulted in higher pre-cracking loads and enhanced post-peak behavior, highlighting the distinct phases of the shear friction mechanism. CSA S6-19 predictions were overly conservative (up to 71.7% underestimation), while ACI CODE-318-19 overestimated capacities by up to 90.7%, highlighting the need for tailored GFRP models.