# Bond Properties of Steel Bar in Polyoxymethylene-Fiber-Reinforced Coral Aggregate Concrete

## TL;DR

This study explores how adding polyoxymethylene fibers improves the bond between steel bars and coral aggregate concrete, offering a sustainable solution for marine infrastructure.

## Contribution

The study systematically quantifies the effect of polyoxymethylene fibers on the bond performance of coral aggregate concrete with steel reinforcement.

## Key findings

- A 0.6% POM fiber addition optimally enhances peak bond stress and reduces radial cracking.
- A bond–slip model incorporating fiber content and c/d ratio was established and validated experimentally.
- The findings reveal a multiscale coupling mechanism among coral aggregate, POM fiber, and steel reinforcement.

## Abstract

The rapid expansion of island and reef infrastructure has intensified the demand for sustainable concrete materials, yet the scarcity of conventional aggregates and freshwater severely constrains their supply. More critically, the fundamental bonding mechanism between steel reinforcement and coral aggregate concrete (CAC) remains poorly understood due to the highly porous, ion-rich nature of coral aggregates and the complex interfacial reactions at the steel–cement–coral interface. Moreover, the synergistic effect of polyoxymethylene (POM) fibers in modifying this interfacial behavior has not yet been systematically quantified. To fill this research gap, this study develops a C40-grade POM-fiber-reinforced CAC and investigates the composition–property relationship governing its bond performance with steel bars. A comprehensive series of pull-out tests was conducted to examine the effects of POM fiber dosage (0, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0%), protective layer thickness (32, 48, and 67 mm), bar type, and anchorage length (2 d, 3 d, 5 d, and 6 d) on the interfacial bond behavior. Results reveal that a 0.6% POM fiber addition optimally enhanced the peak bond stress and restrained radial cracking, indicating a strong fiber-bridging contribution at the micro-interface. A constitutive bond–slip model incorporating the effects of fiber content and c/d ratio was established and experimentally validated. The findings elucidate the multiscale coupling mechanism among coral aggregate, POM fiber, and steel reinforcement, providing theoretical and practical guidance for the design of durable, low-carbon marine concrete structures.