Recycling of Mechanically Ground Wind Turbine Blades as Filler in Geopolymer Composite

A comprehensive review of sustainable solutions for reusing wind turbine blade waste materials

By 2050, approximately 43 million tons of wind-turbine blade (WTB) waste materials will have accumulated, emphasizing the critical importance of effective waste management strategies for WTBs at the end of their life cycle to ensure sustainability. Comparing current WTB waste management methods, reuse emerges as a highly-sustainable method that can also serve as a sustainable solution to environmental challenges, including global warming and natural resource depletion associated with civil engineering activities. This paper presents a comprehensive review of sustainable solutions for reusing WTB waste materials in civil engineering applications. Repurposing WTB waste materials as structural elements in housing, urban furniture, recreational facilities, and slow-traffic infrastructure can be a viable option. WTB waste can also be utilized in powder, fiber, and aggregate forms as an eco-friendly material for construction and pavement (e.g., mortar, concrete, asphalt) to replace cement and natural resource aggregates while meeting necessary strength and performance standards. Through a detailed analysis of reusing WTB waste materials, economic and environmental challenges are also discussed. According to the findings, the properties of mortar, concrete, and asphalt can be affected by the type, shape, and content of fibers, polymers, and impurities present in the blades, as well as the cutting direction. Furthermore, while reuse is considered a sustainable end-of-life (EoL) option for WTB waste management from both economic and environmental perspectives, further research is required to fully understand the environmental consequences of this method.

Effects of temperature and moisture fluctuations for suitable use of raw-crushed wind-turbine blade in concrete

Raw-crushed wind-turbine blade (RCWTB), a waste from the recycling of wind-turbine blades, is used as a raw material in concrete in this research. It contains not only fiberglass-composite fibers that bridge the cementitious matrix but also polyurethane and balsa-wood particles. Therefore, concrete containing RCWTB can be notably affected by moisture and temperature fluctuations and by exposure to high temperatures. In this research, the performance of five concrete mixes with 0.0%, 1.5%, 3.0%, 4.5%, and 6.0% RCWTB, respectively, is studied under moist/dry, alternating-sign-temperature-shock, and high-temperature-shock tests. Two damage mechanisms of RCWTB within concrete were found through these tests: on the one hand, micro-cracking of the cementitious matrix, which was verified by microscopic analyses and was dependent on concrete porosity; on the other, damage and degradation of the RCWTB components, as the polyurethane melted, and the balsa-wood particles burned. Both phenomena led to larger remaining-strain levels and reduced concrete compressive strength by up to 25% under temperature and humidity variations, although the bridging effect of the fiberglass-composite fibers was effective when adding RCWTB amounts higher than 3.0%. The compressive-strength loss after the high-temperature-shock test increased with the RCWTB content, reaching maximum values of 8% after an exposure time of 7 days. Statistical analyses revealed that effect of the RCA amount in the concrete was conditioned by the exposure times in all the tests. The accurate definition of those times is therefore key to set an RCWTB content in concrete that ensures its suitable behavior under the environmental conditions analyzed.

Optimizing the L/S Ratio in Geopolymers for the Production of Large-Size Elements with 3D Printing Technology

Geopolymer concretes can be a viable alternative to conventional Portland cement-based materials. In their design, it is important to maintain an appropriate liquid-to-solid ratio (L/S), which affects several properties, such as the compressive strength, water absorption, and frost resistance. The objective of this paper is to analyze the influence of the fly-ash and metakaolin precursor types for three different L/S ratios: 0.30, 0.35, and 0.45. The results of the physical and mechanical properties, including the apparent density and compressive strength, as well the durability parameters, including frost resistance and water penetration depth, are presented in this paper. It was found that as the L/S ratio decreased, the average compressive strength increased for all materials. After freeze–thaw cycles, decreases in the compressive strength properties were observed for all types of materials—metakaolin- and fly ash-based—irrespective of the L/S ratio. Moreover, the frost resistance of geopolymers increased with the increase in the L/S ratio. The printability of the mixes was also verified in order to confirm the application of the developed materials to additive manufacturing processes.