Mechanical Processing of GFRP Waste into Large-Sized Pieces for Use in Concrete

Abstract

Recycling glass fiber reinforced polymer (GFRP) composite materials has been proven to be challenging due to their high mechanical performance and high resistance to harsh chemical and thermal conditions. This work discusses the efforts made in the past to mechanically process GFRP waste materials by cutting them into large-sized (cm scale) pieces, as opposed to pulverization, for use in concrete mixtures. These pieces can be classified into two main categories-coarse aggregate and discrete reinforcement, here referred to as "needles." The results from all the studies show that using GFRP coarse aggregate leads to significant reductions in the compressive strength and tensile strength of concrete. However, GFRP needles lead to sizable increases in the energy absorption capacity of concrete. In addition, if the glass fibers are longitudinally aligned within the needles, these elements can substantially increase the tensile strength of concrete. Processing GFRP waste into needles requires less energy and time than that for producing GFRP coarse aggregate. Also, compared to pulverized GFRP waste, which consists of broken and separate particles of glass and resin that at best can be used as low-quality fillers, GFRP needles are high strength composite elements.Recycling 2018, 3, 8 2 of 11 fibers [8]. These techniques are very costly and are justifiable only for carbon fiber reinforced polymer composite materials because of the high price of carbon fibers.Low-impact processing of GFRP into products which can be used in built infrastructure can have a significant beneficial impact on the environment, as it reduces the demand for natural resources and the need for landfilling. Mechanical recycling of GFRP is an attractive option in terms of lower energy demand and the avoidance of chemical processes. The energy required for mechanical recycling is between 0.5% and 5% of that required for chemical recycling and between 0.4% and 16% of the energy used for thermal recycling (pyrolysis) [9]. One issue with traditional mechanical processing (pulverizing or shredding) is that the processed GFRP is no longer a composite material. It consists of separate pieces of broken damaged fibers and resin particles and therefore has a negative impact on the mechanical properties of the new material in which it is incorporated [8,[10][11][12]. Cutting GFRP waste into relatively large pieces for use in new products, as opposed to grinding and shredding, is an attractive potential recycling option for two reasons: (1) the energy demand for cutting GFRP to large pieces is less than that required for grinding and shredding (since less surface is generated) and (2) cut pieces of GFRP are composite materials, rather than separate damaged fibers and resin particles, with mechanical properties the same as those of the GFRP before being processed.This work presents the main investigations performed in the past on the incorporation of coarse processed GFRP waste in concrete. In those studies, different types of GFRP products were processed into ele...

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