Effects of Fibers on the Interfacial Shear Strength of a Two-Layer Bi-Material Polymer Concrete System

Articles in Press

Document Type : Research Article

Authors

Department of Civil Engineering, GKM.C., Islamic Azad University, Gonbad Kavoos, Iran

10.22060/ajce.2026.24923.5960

Abstract

This study presents a comprehensive experimental investigation into the enhancement of interfacial shear strength at the bond interface between old and new concrete layers using polypropylene (PP) fibers and acrylic resin. Given that weak interface performance is a persistent challenge in multilayer concreting and repair operations, particularly when casting delays are unavoidable, this research addresses the necessity of developing material-based solutions capable of improving bond integrity under practical construction conditions. Three placement configurations were examined: monolithic casting (Type A), cold joint with initial set (Type B), and construction joint with final set (Type C). Unlike previous studies that typically evaluated modifiers independently, this work introduces an integrated fiber–polymer strategy and quantifies its performance across varied execution scenarios, thereby emphasizing its innovative and application-oriented contribution. Key variables included PP fibers (12 mm) at 0–1.2% and acrylic resin at 0–7% by weight of cement. Cubic specimens (150×150×150 mm) were tested in direct shear at 7, 14, and 28 days. Results indicated a strong dependence of modifier efficiency on placement conditions. In Type A specimens, the use of 0.7% fibers increased shear strength by 23%. In Type B, while 3% resin alone had negligible effect, its combination with 1.2% fibers improved strength by 11%. Most notably, in Type C, the synergistic application of 0.4% fibers and 3% resin produced a remarkable 71% improvement in interfacial shear strength. These findings demonstrate that the hybrid fiber–polymer system, through crack bridging and enhanced adhesion, provides a robust enhancement mechanism.

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AUT Journal of Civil Engineering

Articles in Press, Accepted Manuscript
Available Online from 02 March 2026

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