Performance of Asphalt Mixtures Hybrid-Modified with Industrial Diatomite By-Products and Different Microfibres

This study evaluated asphalt mixtures incorporating two diatomite types (D1 and D2) at contents of 10% and 15% by binder weight and three fibre treatments added by aggregate weight: polyacrylonitrile (PAN) (0.065%), polyethylene terephthalate (PET) (0.10%), and basalt fibre (0.30%). An unmodified mixture and a mixture containing 5% styrene-butadiene-styrene (SBS) by binder weight were included as references. Performance was assessed using indirect tensile strength (ITS), tensile strength ratio (TSR), Cantabro loss, repeated load creep, and semi-circular bending (SCB) tests. Factorial analysis of variance indicated that diatomite type and content significantly affected ITS, diatomite content governed permanent deformation, and diatomite type was the principal factor affecting Cantabro loss. Significant interaction effects for the SCB parameters showed that fracture performance depended on the specific combination of diatomite and fibre treatments. Among the tested formulations, D1%10-PAN exhibited the highest ITS of 4712.36 kPa, representing numerical increases of 43.8% and 22.4% over the control and SBS-modified mixtures, respectively. D1%10-PET achieved the highest TSR (95.58%), whereas D2%10-PAN exhibited the lowest Cantabro loss (6.76%). Mixtures containing 15% diatomite generally showed lower permanent deformation, while D2%10-PAN achieved the highest flexibility index (14.003). The different performance trends observed for D1 and D2 are likely associated with differences in their physical characteristics, such as particle morphology and binder absorption behaviour, which may influence their interaction with the asphalt mastic and fibre reinforcement. No single formulation provided the best performance for every response. Overall, D2-based treatments improved resistance to particle loss, a higher diatomite content enhanced permanent deformation resistance, and 10% diatomite combined with PAN or PET treatment provided a more favourable balance of tensile, moisture, and fracture performance.