The influence of recycled polypropylene fibre and lime-pozzolana cement on the swell response of clay–marl samples

Ground heave is known for its strong sensitivity to moisture changes, which often leads to volume variations responsible for damage to foundations, pavements, and light structures. While cement stabilization and fibre reinforcement have been widely studied, the combined use of recycled polypropylene (PP) sweeper brush filaments with lime–pozzolana cement (LPC) remains relatively unexplored, particularly for marl–clay soils. This study examines how this combined stabilization approach influences both the swelling behavior and mechanical response of two high-plasticity expansive soils. PP were added at contents ranging from 0.1 to 1.8%, with fibre lengths between 12 and 48 mm, while the LPC content varied from 1 to 18% by dry weight. A series of laboratory tests was carried out to evaluate performance. The findings show that adding fibres and binder decreased swelling. Additionally, fibres tend to alter the stress-strain response. However, in some cases, peak compressive strength dropped, most likely due to interactions of the fibres and the cemented soil. The results imply that, when paired with cementitious stabilization, PP can function as a substitute reinforcing material. However, further study is needed to enhance the combination and assess long-term performance before genuine field applications can be completely addressed.