Enhancement of the concrete-PCM interfacial bonding strength using silica fume

Abstract

Recently, the polymer cement mortar (PCM) overlaying method has gained popularity as a repair/retrofitting technique. The debonding issue at the interface hinders the worldwide application of this strengthening method. Accompanying the occurrence of debonding at the interface, the strengthening effect of the PCM is lost, causing a sudden decrease in the load-carrying capacity. To prevent premature debonding, this study aims to enhance the concrete-PCM interface by using silica fume. The bi-surface shear test was selected as the test method, and three levels of surface roughness (highest level with sandblasting, medium and lowest levels with steel wire brushing) and two different concrete compressive strengths (low strength type (LS) with 16.73 MPa and normal strength type (NS) with 29.59 MPa) were given as experimental parameters. When the surface is roughened by sandblasting, the specimens with 5% silica PCM increase the interfacial strength compared to that of the normal PCM cases by approximately 36.84% and 35.05% for the “LS” and “NS” types of concrete, respectively. The percentage increase is even higher when the surface is roughened by steel wire brushing (high and low), with an increase of approximately 135.35% and 181.12%, respectively. This fact indicates that silica fume inclusions can enhance the chemical bonding at the concrete-PCM interface. The mixing of silica fume in PCM and a higher surface roughness level shifts the pure interface failure (I) mode closer to the concrete cohesion (C) failure mode for “LS” type concrete and to the composite fracture mode (I-P) for “NS” type concrete. Conclusively, it is confirmed that mixing silica fume into PCM strengthened the interface bonding strength.