Modelling the yield stress of cement pastes and mortars containing heterogeneous and unconventional aggregates like raw crushed wind turbine blade

Determining the yield stress of cementitious materials is crucial for casting and concrete mix design. Fresh concrete possesses yield stress, behaving as a solid with viscoelastic properties below this threshold. When the yield stress is exceeded, concrete flows with a steady-state behavior commonly described by the Bingham or Herschel-Bulkley models. As the construction industry increasingly consumes more and more scarce raw materials, there is a growing need to develop and explore alternative construction materials to replace traditional ones while valorizing waste. Raw Crushed Wind Turbine Blade (RCWTB) has demonstrated interesting results when included in cementitious mixtures. However, a full characterization of rheology including the yield stress of mixtures containing RCWTB is still missing and would be of great practical interest. In this paper, the yield stress of cementitious pastes and mortars containing RCWTB with two different water/cement ratios is measured. Results demonstrate higher yield stress for higher RCWTB inclusion, this is mainly due to the bridge effect of the Glass Fiber Reinforced Polymer (GFRP) contained in the RCWTB. Finally, a physical model is applied for RCWTB to predict GFRP fibers maximum packing fraction based on their geometry, elastic properties, and the rheology of the surrounding cement-based material. This model is then validated with experimental yield stress of cement pastes and mortars.