Rebar-matrix Interface in Extrusion Molded Cementitious Filaments

Abstract

Extrusion molding enables automatic construction through the pattern of material addition. The unique molding would result in several features that are different from those in conventional framework molding, such as weak interlayer bonding and a laminar structure with high anisotropy. To strengthen the interlayer bonding, reinforcement is often implanted to penetrate through the extrusion molded filaments (EMF). However, different from the pre-implantation of reinforcement before concrete casting, the post-implantation of reinforcement in EMF may trigger the problems concerning the interface bonding between reinforcement and material matrix. In this work, saddle stitches, a type of Ushape rebar or fiber, are taken as an example to demonstrate the effect of the post-implantation of reinforcement on the interfacial structure between the rebar and EMF matrix. X-ray computed tomography (XCT) is employed to non-destructively probe the post-implanted saddle stitches as well as the surrounded EMF materials. Regions of interest (ROI) are set on the rebar-matrix interfaces to elaborately analyze the material or defect distributions around the saddle stitches. Results demonstrate that insufficient material filling is observed at the outboard of the U-shape rebar, while material pressing is shown at the inboard. Large defects unevenly form in the rebar-matrix interface. Mechanisms of the observations may be ascribed to the low flowability of EMF materials that can hardly migrate to the rebar-matrix interfacial gaps spontaneously. The findings would deepen the understandings in rebar-matrix interfacial structure of EMF with post-implantation of reinforcement.

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