145 / 2022-04-29 12:28:53

Hybridization effect on the mechanical properties of recycled waste GFRP and PET fibers reinforced concrete

Hybrid Effect; Waste GFRP and PET Fibers; Mechanical Properties; Bond Behavior; Microstructure

The widespread use of glass fiber reinforced polymer (GFRP) and polyethylene terephthalate (PET) may generate a large amount of waste, therefore the recycling of waste GFRP and PET is of great importance. In this study, mechanical cutting technique is adopted to process waste GFRP and PET. The obtained GFRP and PET fibers are added to concrete to improve its mechanical properties. Experimental studies were conducted for specimens with recycled fiber (RF) of 0%, 0.5%, 1.0% and 2.0% in volume fractions. The proportion of GFRP in the hybrid fibers are 0%, 25%, 50%, 75% and 100% respectively for different specimens. The results of the study are as follows:

(1) The addition of hybrid fibers has little influence on the compressive strength of concrete, but can significantly improve the splitting tensile strength and flexural strength of concrete (Fig. 1). The test results indicate that the specimen with the addition of 0.375% GFRP fiber and 0.125% PET fiber shows the best strengthening effect. Compared with plain concrete, the splitting tensile strength and flexural strength increased by 26.2% and 24.2% respectively. More importantly, owing to the bridging effect of fibers, hybrid fibers greatly improve the flexural toughness (Fig. 2) and ductility (Fig. 3) of concrete.

(2) According to the reinforcement pullout tests, the addition of hybrid fibers to concrete can inhibit the expansion of cracks and improve the bond strength of concrete. The free-end slip (Fig. 4) at peak load of concrete increases significantly after fiber addition. Compared to that of the reference concrete, the free-end slip at peak load of the specimen G0.25P0.25 increased by 241.9%. Fiber-reinforced concrete still has a large residual bond stress after reaching the peak bond stress, indicating a better ductility (Fig. 5).

(3) SEM result shows that a fiber is firmly connected to cement paste (Fig. 6). The fiber act as a bridge in cement paste, which can inhibit the occurrence and development of concrete cracks. When the concrete is subjected to external loads, fibers are micro reinforcement in concrete and sustain external loads with the concrete matrix, thus improving the mechanical properties of the concrete.

1	2
3	4
5	6

Fig. 1 Splitting tensile strength and flexural strength at different fiber volume fractions; Fig. 2 Flexural toughness index I₅ at different fiber volume fractions; Fig. 3 Load-deflection curves for a total fiber volume fraction of 2.0%; Fig. 4 Free-end slip at peak load of concrete; Fig. 5 Bond stress-slip curves for a total fiber volume fraction of 0.5%; Fig. 6 SEM image of a crack in the transition zone



Acknowledgment



The authors would like to acknowledge the funding support from the National Natural Science Foundation of China (Grant number: 51708361).