High-strength lightweight ECC hollow panels with GFRP reinforcement: Toward superior flexural efficiency and modular construction

Material lightweighting through concrete density reduction and weight-efficient hollow-section design are effective strategies for improving the structural efficiency of prefabricated panels. Glass fiber-reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) offer corrosion resistance and inherent crack-width control, but their integration in hollow modular panels has not been fully explored. This study investigates 15 GFRP-reinforced ECC panels under monotonic four-point bending, using digital image correlation (DIC) for full-field deformation and crack quantification. Twelve monolithic panels incorporated three ECC variants (ultra-high-strength ECC, high-strength ECC, high-strength lightweight ECC) and two section forms (solid and hollow). Three additional high-strength lightweight-ECC hollow panels were tested to evaluate bolted joints and cast-in-place closure strips using ultra-high-strength ECC. All panels exhibited flexure-dominated multiple cracking. The solid panels reached peak nominal flexural stresses of 35.5–39.6 MPa, whereas the hollow panels achieved higher values of 49.0–60.7 MPa. DIC revealed section-dependent crack widening, with diagonal strains accelerating in hollow panels. A simplified sectional model predicted peak loads within 10% error. For modular panels, cast-in-place strips restored stiffness and strength, while bolted joint improved post-peak ductility and energy absorption. These findings guide durable, efficient GFRP-ECC systems for prefabricated panels. ● High-strength lightweight ECC enabled lightweight hollow GFRP–ECC panels with strong crack control. ● Hollow-section design delivered the largest gain in flexural efficiency. ● High- and ultra-high-strength ECC promoted effective utilization of GFRP bars. ● UHS-ECC cast-in-place joints improved stiffness while bolted joints increased post-peak deformation and energy absorption.