A recent article published in the Journal of Materials and Technology Research explored the application of recycled glass fiber (rGF) derived from pyrolysis of waste wind turbine blades (WTB) in the manufacture of rGF-reinforced mortar (rGF/M) as a sustainable construction material.
Background
WTB waste has become a global concern due to its large quantity (50,000 tonnes in 2020) and its non-degradable composition consisting of fibre-reinforced resin composites. Being difficult to recycle, it usually ends up in landfills and causes serious environmental consequences.
Several management solutions have been proposed to recover textile industry waste and reduce its environmental impact. Among these, pyrolysis technology has successfully recycled several tons of textile industry waste. It also applies to waste containing fibers (glass and carbon) and resins (epoxy and unsaturated polyester).
Recycled fibers (RFs) are widely reused as fillers to improve the mechanical properties of lightweight construction materials, including cementitious matrices, concrete, and mortar composites. However, the performance of short fibers extracted from WTB waste is still poorly explored, although they account for about 70 wt% of RFs.
Thus, this study investigated the performance of rFs obtained from pyrolysis of WTB waste in improving the properties of mortar composites.
Methods
The experiments were conducted on rGF derived from locally sourced WTB panels (1.5 m2), which were shredded into small pieces (5–25 mm) using a granulator. Subsequently, the WTB waste was subjected to pyrolysis at 550 °C for one hour to obtain short rGFs.
The rGF was subjected to subsequent pretreatments (sieving, washing, and oxidation) for further purification and efficient binding with cement matrices. The resulting rGF (sieved rGF), rGFw (washed rGF), and rGFo (oxidized rGF) had a size distribution of 2–25 mm.
The chemical resistance of rGF, rGFw and rGFo was studied in a strongly alkaline cement solution (pH 14) for 90 days. Their morphology and diameter were observed using a scanning electron microscope (SEM) to determine the degradation rate of rGF by diameter reduction.
A control mortar sample (M) was made using ordinary Portland cement (OPC), sand and water (weight ratio 1:3:0.5) for comparison. Subsequently, the rGF-reinforced mortar composites (rGF/M) were prepared with 1 wt% of rGFs, rGFw and rGFo.
Cubic and prismatic mortar samples were prepared for compressive and flexural strength tests, respectively, with 28 and 90 days curing. Finally, the effect of subsequent rGF pretreatments on the morphology, mechanical strength, water absorption, and sorptivity coefficient of the mortar composites was analyzed.
Results and discussion
The rGFs differed significantly in morphology and structure with various pretreatments. SEM images showed that the fibers of the rGF sample were densely covered with agglomerates representing undecomposed and carbonized resin particles after pyrolysis.
However, the rGFw samples appeared smoother, with the undecomposed resin forming a thin laminated layer over the entire fiber surface, with all carbon particles and debris removed. On the other hand, the rGFo samples exhibited bare fiber strands with only a few undecomposed resin particles.
The mortar fraction of all composites exhibited a rough surface composed of uniformly distributed soluble OPC grains and inert quartz particles. SEM images also showed complete incorporation between the rGF and the cement hydration products. However, the hydration products did not cover all the rGFs due to their irregular shape and composition.
In contrast, the bare rGFo fibers allowed the hydration products to cover all their surfaces, thus creating strong bonds with them. This interaction of rGFs with the cement matrix influenced the mechanical properties of the mortar samples.
The flexural strength of the mortar samples did not change significantly by adding rGF at the shortest curing time (28 days). However, it was greatly improved by increasing the curing period to 90 days. Such a change was not observed for the control sample. Moreover, the compressive strength of the rGF/M samples increased while their mortar sorptivity and water infiltration decreased after 90 days of curing.
The rGFo/M sample showed the best performance in these experiments. However, all rGFs showed similar performance after a long curing period. This was attributed to the decomposition of organic components (resin and carbon) of rGF and rGFw in the very harsh environment of cement after prolonged exposure.
Conclusion
Overall, rGFo derived from WTB waste by pyrolysis significantly improved the properties of mortar when used as fillers after subsequent sieving, washing and oxidation. In particular, the rGFo/M sample showed a 15% improvement in compressive strength, 38% in absorption coefficient and 32% in cumulative water content compared to the control mortar.
This study highlights the use of recycled short fibers from WTB waste as a cheap and competitive source for short fiber production. Moreover, these sustainable fibers can be used to improve construction materials. However, the authors suggest conducting a life cycle assessment to verify the environmental impact of the proposed WTB waste management approach for practical applications.
Journal reference
Yousef, S., & Kalpokaitė-Dičkuvienė, R. (2024). Sustainable mortar reinforced with recycled glass fibers from pyrolysis of wind turbine blade waste. Journal of Materials and Technology Research, 31879–887. DOI: 10.1016/j.jmrt.2024.06.134, https://www.sciencedirect.com/science/article/pii/S2238785424014467