Thermochemical valorisation of sheep manure into bio-oil for asphalt binder modification

Sheep manure is an abundant biogenic residue with potential as a renewable feedstock for producing value-added materials through thermochemical conversion. This study investigates the valorisation of sheep manure by slow pyrolysis to obtain a bio-oil suitable for use as a bio-based modifier in bituminous binders. Physicochemical characterisation showed that the recovered BO had a pH of 4.8, 2.20 wt% water, and 30.33 wt% oxygen, with ketones dominating the GC-MS profile. The sheep-manure-derived bio-oil was incorporated into a conventional B50/70 bitumen at 3, 6, and 9 wt%, and its performance was compared with that of a commercial additive. The modified binders were evaluated using dynamic shear rheometer, multiple-stress creep-recovery, linear amplitude sweep, binder yield energy, and elastic recovery tests, supported by Burgers-model fitting. The bio-oil produced a clear dosage-dependent softening effect, reducing the complex modulus, complex viscosity, and elastic contribution of the binder. At 20 °C, the complex modulus decreased by 56% for the 3 wt% formulation and by 81% for the 9 wt% formulation compared with the base binder. High bio-oil contents increased accumulated deformation and strongly reduced recovery capacity, particularly under multiple-stress creep-recovery conditions, indicating lower resistance to permanent deformation. Intermediate-temperature tests also showed that 6 and 9 wt% bio-oil reduced mechanical resistance and recovery capacity, whereas the 3 wt% dosage provided a more balanced viscoelastic response. Slow pyrolysis of sheep manure therefore represents a promising circular route for producing a value-added bio-based modifier for bituminous binders, particularly at moderate dosages that balance softening efficiency and rheological performance.