A recent article published in the Journal of Materials Research and Technology explored the application of recycled glass fiber (rGF) derived from pyrolysis of wind turbine blade (WTB) waste in the manufacturing of rGF-reinforced mortar (rGF/M) as a sustainable building material.
Background
WTB waste has become a global concern due to its large quantity (50,000 tons in 2020) and non-degradable composition comprising fiber-reinforced resin composites. Being difficult to recycle, it mostly ends up in landfills and causes serious environmental burdens.
Several management solutions have been proposed to valorize WTB waste and reduce its environmental impact. Among these, pyrolysis technology has successfully recycled several tons of WTB waste. It also applies to the waste containing fibers (glass and carbon) and resins (epoxy and unsaturated polyester).
The recycled fibers (rFs) are widely repurposed as fillers to enhance the mechanical properties of lightweight construction materials including cementitious matrix, concrete, and mortar composites. However, the performance of short fibers extracted from WTB waste is still little explored despite being ∼70 wt.% of the 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 to 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 effective bonding with the cement matrices. The resulting rGFs (sieved rGF ), rGFw (washed rGFs), and rGFo (oxidized rGF) had a size distribution from 2 to 25 mm.
The chemical resistance of rGFs, rGFw, and rGFo was studied in a strong alkaline cement solution (pH 14) for 90 days. Their morphology and diameter size were observed using a scanning electron microscope (SEM) to determine the degradation rate of rGF through diameter reduction.
A control mortar sample (M) was fabricated using ordinary Portland cement (OPC), sand, and water (1:3:0.5 weight ratio) for comparison. Subsequently, the rGF-reinforced mortar composites (rGF/M) were prepared with 1 wt.% of rGFs, rGFw, and rGFo.
Both cubic and prismatic mortar samples were prepared for compressive and flexural strength tests, respectively, with curing for 28 and 90 days. Finally, the effect of subsequent pretreatments of rGFs on the morphology, mechanical strength, water absorption, and sorptivity coefficient of mortar composites was analyzed.
Results and Discussion
The rGFs differed significantly in morphology and structure with various pretreatments. SEM images depicted the fibers in the rGFs sample as densely covered with agglomerates representing undecomposed and char particles resin after pyrolysis.
However, the rGFw samples appeared smoother with the undecomposed resin forming a thin laminated layer over the entire fiber surface, with all char particles and debris removed. Alternatively, the rGFo samples exhibited bare fiber threads with only a few undecomposed resin particles.
The mortar fraction in all composites exhibited a rough surface comprising soluble grains of OPC and uniformly distributed inert quartz particles. The SEM images also depicted complete incorporation between rGF and cement hydration products. However, the hydration products did not cover all rGFs due to their irregular shape and composition.
Alternatively, the bare fibers in rGFo allowed hydration products to cover all their surfaces, creating strong bonds with them. This interaction of rGFs with the cementitious matrix influenced the mechanical properties of the mortar samples.
The flexural strength of the mortar samples did not change significantly by adding rGFs at the lower curing time (28 days). However, it was greatly enhanced by increasing the curing period to 90 days. Such a change was not observed for the control sample. Additionally, the compressive strength of the rGF/M samples increased while their mortar sorptivity and water ingression decreased after 90 days of curing.
The rGFo/M sample exhibited the best performance in these experiments. However, all rGFs exhibited a similar performance after a long curing time. This was attributed to the decomposition of organic components (resin and char) of rGFs and rGFw under the highly harsh environment of cement after long-time exposure.
Conclusion
Overall, the rGFs derived from WTB waste by pyrolysis significantly enhanced the properties of mortar when used as fillers after subsequent sieving, washing, and oxidation. Especially the rGFo/M sample exhibited a 15% improvement in compressive strength, 38% in absorption coefficient, and 32% cumulative water content compared to the control mortar.
This study underscores the application of rGF from WTB waste as a cheap and competitive source for short-fiber production. Moreover, these sustainable fibers can be used for improving building 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 fiber derived from pyrolysis of wind turbine blade waste. Journal of Materials Research and Technology, 31, 879–887. DOI: 10.1016/j.jmrt.2024.06.134, https://www.sciencedirect.com/science/article/pii/S2238785424014467