FRP-Needles as Discrete Reinforcement in Concrete

Abstract

This paper presents a new type of discrete reinforcing element for concrete produced from either waste or new pultruded fiber-reinforced polymer (FRP) composite materials. These elements, referred to as FRP-Needles, are rigid, long, and low in aspect ratio, and have distinct physical and mechanical differences from macrofibers used in concrete. The FRP-Needles used in this study were produced by cutting FRP reinforcing bar (rebar) production scrap with nominal diameter of 6 mm into rod-shape elements with length of 100 mm (aspect ratio of 17). FRP-Needles were incorporated in concrete to replace 5 and 10% of coarse natural aggregate (NA) by volume. The needles did not reduce the workability or stability of concrete. The dispersion and orientation of FRP-Needles in concrete were relatively uniform. The 5 and 10% replacement of NA with FRP-Needles increased the splitting tensile strength of concrete by 22 and 33%, respectively, while reducing the compressive strength by only 5 and 9%. The incorporation of FRP-Needles in concrete resulted in significant increases in postfailure toughness of concrete in both compression and tension. In a parallel study, FRP recycled aggregate (FRP-RA) was produced by cutting scrap rebars into cylindrical pieces with aspect ratio of 1. FRP-RA was incorporated in concrete with the aforementioned dosages to observe the effect of geometrical characteristics of FRP elements on the studied mechanical properties of concrete. The improvements achieved by using FRP-Needles were not observed when FRP-RA was incorporated in concrete.