Researchers at Bydgoszcz University of Science and Technology in Poland have investigated cement composites reinforced with fibres recovered from wind turbine blades. The exploratory study combines this recycled material with polypropylene fibres. It also examines how ultrasonic testing could support the development of more circular construction materials.

Repurposing Composite Blade Waste

Wind turbine blades contain durable composite materials that are difficult to recycle after use. For this research, the team shredded blade material into irregular fibres measuring 10–40 mm long and 1–5 mm wide and thick. They combined these with 25 mm polypropylene fibres.

The experimental mortar contained cement, sand and water. Both fibre types represented 5% of the cement weight, resulting in a total fibre content of 10%. The researchers compared this mixture with a reference sample containing no fibres.

Monitoring Cement Without Damaging It

The team used ultrasonic pulse velocity (UPV) measurements to follow the material’s development for 22 days. Transducers positioned on opposite sides of each sample continuously recorded how quickly ultrasonic waves travelled through the composite.

This non-destructive method can provide information about cement hydration, setting time, internal homogeneity and dynamic Young’s modulus. It can also help researchers estimate strength development. Unlike destructive compression tests, UPV monitoring allows repeated measurements on the same sample. This reduces both material use and the number of test specimens required.

Such real-time monitoring could prove relevant to manufacturing processes that depend on precisely controlled setting times. These include sprayed cement mixtures and 3D printed concrete.

Preliminary Material Performance

The fibre-reinforced samples showed a slightly earlier increase in ultrasonic velocity than the control sample. However, the fibres had only a limited effect on the overall hydration process.

After 21 days, ultrasonic velocities in the reinforced samples approached 3,500 m/s and exceeded those recorded in the control sample. According to the researchers, this may indicate a more consistent internal structure with fewer micropores or air voids. Calculations based on the UPV measurements also produced a higher dynamic Young’s modulus for the fibre-reinforced composite.

The results remain qualitative and exploratory. The small number of specimens prevents statistical generalisation, while the study could not yet establish a reliable relationship between ultrasonic velocity and compressive strength. Further testing will therefore be necessary.

Nevertheless, the research indicates how recovered wind turbine blade fibres could replace part of the conventionally manufactured reinforcement in cement composites. At the same time, non-destructive testing may reduce waste during material development and help assess recycled feedstocks with variable properties.

Source: Nature.com
Photo: Vadym Alyekseyenko