Assessing the role of recycled tyre polymer fibres (RTPFs) on the key hydration processes governing autogenous shrinkageDidulica, Katarina (Drugo) Baričević, Ana (Avtor) Zalar Serjun, Vesna (Avtor) recycled tyre polymer fibrehydration kineticsself-desiccationautogenous shrinkageThe incorporation of recycled tyre polymer fibres (RTPF) in cementitious composites provides an effective and sustainable approach in tyre waste management while offering potential benefits in mitigating early-age volume deformations. This study evaluates the influence of RTPFs, used in dry (RTPFd) and pre-wetted (RTPFw) states, on key hydration processes governing autogenous shrinkage in cement pastes with w/c of 0.4 and 0.22. The results show that RTPF reduced workability and altered the setting process due to the fibre–matrix mechanical interactions. Incorporation of RTPFs induced changes in water distribution at the fibre surface, delaying self-desiccation and maintaining higher internal relative humidity. While RTPFs offer a beneficial reduction in autogenous shrinkage by 12–41% in mixtures with w/c of 0.4 and by 15–34% in mixtures with w/c of 0.22, RTPFs also increased porosity, which contributed to a reduction in 28-day compressive strength of up to 16%. These findings highlight the dual effect of RTPF on early-age performance and provide insight into their potential application in sustainable cementitious composites.MDPI AG20252026-01-13 11:12:20Neznano25178sl© 2025 by the authors