Recycling of Grape and Olive Pomaces as Renewable Antioxidant Additives for Asphalt Pavements

Abstract: Each year, over 150,000 tons of olive pomace (OP) and 450,000 tons of grape pomace (GP) are generated as byproducts from the olive oil and winery industries in California. The disposal of these vast amounts of waste pomaces in landfills may lead to environmental pollution to soil and water. The current uses of grape/olive pomace include compost for fertilizers, animal feed additives, and extraction of bioactive compounds for food and cosmetics as valorization venues. However, these options are restricted for large-scale applications as pomaces may adversely affect the quality of soils and meat products. In this study, these waste pomaces were processed and used as renewable antioxidant additives for asphalt binders, aiming to enhance the long-term anti-aging performance of asphalt pavements. This study developed three types of OP (whole, pulp, and finer than 0.3 mm) and three types of GP (whole, seed, and skin) as antioxidant additives for an unmodified PG 64-22 asphalt binder. The antioxidant performance of pomace-modified asphalt binders was compared with asphalt binders modified with conventional antioxidant additives of Zinc Diethyldithiocarbamate (ZDC) and Kraft Lignin (KL). The dosage of bio-based additive was 15% by binder weight, while ZDC and KL were added at two dosages of 3% and 5%. The performance tests included the viscosity, high-temperature performance for rutting resistance, low-temperature cracking resistance, short-term and long-term aging properties of these binders using the Rotational Viscosity (RV) test, Bending Beam Rheometer (BBR) test, Dynamic Shear Rheometer (DSR) and Fourier Transform Infrared (FTIR) spectroscopy. The results indicated that GP and OP were effective antioxidant additives, with GP-seed and OP-pulp showing the most promising results. Additionally, the total phenolic contents in GP additives had a strong correlation with the anti-aging performance of modified asphalt binders. This could be attributed to the work that phenolic compounds serve as free radical scavengers to retard asphalt aging. The anti-aging property (e.g. Glover-Rowe Parameter) of OP-modified asphalt binders have a strong correlation with residue oil contents in OP additives. The OP-pulp fraction was found to contain the highest oil content among the processed OP. The carbonyl index (Ic), as an index of oxidative aging, was higher for these pomace-modified asphalt binders initially than the unmodified binder, but lower after PAV aging. This indicated that GP and OP could effectively delay the oxidative aging rate.