Incorporation of Shredded Wind Turbine Blade Waste in Concrete Using a Packing Approach

Wind energy plays a vital role in sustainable energy production. However, the end-of-life (EoL) management of wind turbine blades has emerged as a critical environmental challenge. Wind farms built in the late 20th century have started to generate large quantities of composite waste due to the 20–25 year service life of wind turbines. This waste generation is expected to accelerate in the following decades, posing a significant challenge for sustainable waste management.

EoL solutions for the two main components of wind turbines: the metallic body (including the motor) and the wind turbine blades (WTB), should be considered separately. The motor and the metallic body of wind turbines can be recycled and reused. However the composite structure of the WTB, which consists of thermoset polymers and glass or carbon fibers, presents challenges in recycling. This leads to an accumulation of WTB waste (WTBW) in landfills at their end of life. With its production capacity and significant raw material demand, concrete provides a valuable opportunity for the sustainable utilization of rapidly accumulating WTBW. To utilize WTBW in concrete, a suitable recycling process must be implemented. Various recycling approaches are available for WTBW, including thermal, chemical, and mechanical methods. Among these, mechanical recycling is generally preferred due to its lower energy requirements and practicality. This method involves cutting the blades into smaller pieces and subsequently crushing them into finer particles. However, shredded wind turbine blades (SWTB) exhibit a highly heterogeneous particle size and morphology, consisting of a mixture of fine powders, micro- and macro-sized fibers, and irregular flakes. SWTB can be utilized in concrete for fiber reinforcement or partial substitution of cement or sand. However, this requires detailed sorting of the waste, limiting the usable portion to specific fractions.

In this research SWTB is used as an overall component in concrete. For this, a new concrete mix design is created using two methods. The Anderson and Andreasen (A&A) model, that is based on particle packing and as a complementary approach, the American Concrete Institute (ACI) method is also applied. The SWTB is a material composed of both powder and fibres, and it also has a high water absorption. Thanks to the new approach with modifying the A&A method, all of these characteristics are taken into account during the concrete design. The model is modified to optimize whole mixture including aggregate and powder replacement and fiber reinforcement with utilizing the SWTB.
The SWTB, ranging from 0.63 µm to 10 cm in size, is composed of 51% granular particles and 49% micro to macro fibers and flakes, enabling its dual role as both an aggregate replacement and a fiber reinforcement. Concrete mixtures were prepared with 0%, 1%, 3%, and 5% SWTB by its total mass, corresponding to 0–2.7% fiber content, 0–10.2% aggregate replacement, and 0–4.4% cement replacement by volume.

The prepared samples were evaluated based on both their fresh and hardened properties, including slump, air content, and density, as well as compressive strength, splitting tensile strength, elastic modulus, and flexural performance with crack mouth opening displacement (CMOD). The use of SWTB, especially at higher dosages, led to a decrease in slump. As the amount of SWTB increased, the air content of the concrete slightly decreased; however, the fresh density also dropped. This reduction in density is mainly due to the low specific density of SWTB.

With the use of the modified A&A method in the mix design, the concrete retained a high level of strength even with increased SWTB content. The 28-day compressive strength of the control sample was 57.2 MPa, while the mixture containing 5% SWTB still achieved 50.8 MPa, indicating that the reduction in strength was relatively small. Elastic modulus at 28 days is also decreased relatively from 39.6 GPa to 30.9 GPa. The effect of fibrous part of SWTB also assessed by the split tensile and CMOD tests. The 28-day splitting tensile tests showed that the control sample had the highest strength at 4.2 MPa. For the SWTB mixtures, strength tended to increase with higher SWTB content, and the 5% SWTB sample reached 3.7 MPa, with only a limited reduction compared to the control. Although the irregular and damaged surfaces of SWTB fibers limit their bonding with the cement matrix, CMOD flexural tests confirmed that SWTB contributes to fiber reinforcement in concrete.