264 / 2022-08-26 16:08:50

Mechanical properties of concrete containing macro fibers recycled from GFRP waste: Effects of fiber length and volume fraction

GFRP waste; Mechanical recycling; Macro fibers; Concrete; Mechanical properties

Fiber-reinforced polymer (FRP) composites have been widely used in many sectors such as the aerospace, wind energy, and construction industries due to their excellent mechanical performance, durability, and lightweightness. Inevitably, the increasing use of FRP composites led to an accumulation of FRP waste that needs to be disposed of. A new mechanical recycling method has recently been explored by the authors’ group to process waste GFRP into “macro fibers” with their aspect ratios being close to those of steel fibers, which are then incorporated into concrete, resulting in what is referred to as macro fiber reinforced concrete (MFRC). This paper presents an experimental program on the mechanical properties of MFRC, in which the effects of fiber length and fiber volume fraction were examined through a series of compression, splitting, and bending tests. In particular, the load-deflection responses of the beam specimens obtained from the tests were used to derive the tensile constitutive law of the MFRC using a point-by-point double inverse analysis approach. The results indicate that the splitting tensile strength, flexural tensile strength, and toughness (i.e., Area under the load- net deflection curve 0 to L/150) of the concrete can be significantly enhanced through the incorporation of macro fibers.



The experimental compressive strengths of all MFRC cylinder specimens tested in the present study are shown in Fig. 1. The differences in compressive strength among the specimens are in the range of -5% to 4%, indicating that the fiber addition has a minor effect on the compressive strength. The incorporation of macro fibers has a significant effect on the splitting tensile strength of MFRC (Fig. 2), which is seen to be more significantly enhanced when a higher volume fraction or longer fibers are used. More specifically, the splitting tensile strength increased from 3.19 to 3.87, 4.12, and 4.86 MPa when the volume ratio of 90-mm long macro fibers increased from 0.5% to 1.0%, and 1.5%, representing an increase in splitting tensile strength of 21.3%, 29.3%, and 52.2% respectively.



The key results of bending tests are given in Figs. 3 and 4. Compared with the corresponding plain concrete, the incorporation of 90-mm long macro fibers into concrete led to significant increases in the flexural tensile strength and toughness: there are increased by 1.3 and 230 times respectively when macro fibers of 1.5% in volume fraction were added to the mix. The tensile stress-strain curves of MFRC were obtained from the bending test results through point-by-point double inverse analysis. All the tensile stress-strain curves exhibit a strain-softening phenomenon, and the slope of the descending portion reduces with an increase in the length and volume fraction of incorporated macro fibers.



In summary, the results from this study show that the incorporation of macro fibers significantly enhances the tensile properties of concrete. As a result, this new mechanical recycling method is expected to be both technically feasible and economically attractive.