Performance analysis of waste cooking oil granulate modified bitumen and asphalt mixtures

The global demand for non-renewable resources like bitumen in flexible pavement construction is a significant concern, prompting researchers to seek alternative solutions like bio-modifiers. Waste cooking oil (WCO) has shown promise in enhancing bitumen and asphalt properties, yet its use is limited due to its oily nature affecting high-temperature bitumen performance. Therefore, a pre-modification of the WCO was proposed using the Styrene Butadiene Styrene (SBS) to change its phase from liquid to a rubbery solid state. Conversely, a significant difference in molecular weight in SBS modifiers and bitumen is the reason for their limited thermal compatibility with each other. The introduction of SBS directly into the bitumen results in significant segregation issues and high energy consumption to produce modified bitumen. Whereas its utilisation in conjunction with the WCO improves overall performance and mitigates these challenges. This study aims to explore the impact of modified waste cooking oil on bitumen and asphalt mixture performance. The characterization of the raw materials i.e., bitumen, WCO, and aggregates was followed in the study's first objective. The preliminary raw materials assessment suggests that the results are within the specification and suitable for further testing and analysis. The filtered WCO was modified by blending the SBS: WCO at 20:80, 30:70, 40:60, 45:55 and 50:50. The Modified WCO Granulates (MWCOG) were blended with bitumen by weight at various ratios with concentrations of 5%, 10%, 15%, 20%, and 25%. These blended modified bitumens underwent testing for rotational viscosity and rutting parameters and were analysed for their suitability. Hence, the key finding is that the optimum ratio suitability for the bitumen modification is MWCOG-45:55 and MWCOG-50:50. The second objective of the study was to evaluate the effectiveness of the MWCOG-45:55 and MWCOG-50:50 on bitumen's rheological, physical, morphological and chemical properties. Based on the viscosity results, the increasing content of the MWCOG has increased the stiffening of the base bitumen. Adding 5–25 wt.% of MWCOG-45:55 improves the viscosities in the range of 513–3512.2 cp at 135 ℃. However, the MWCOG-50:50 displayed a slightly higher viscosity with values of 562.1–2988.2 cp. It is noteworthy that the performance grading (PG) of the base bitumen is improved from PG64 to PG76 whilst adding the 10% of MWCOG-50:50. Moreover, the Black space diagram curves have shifted towards the lower phase angle (δ) with smooth curves indicating the improvement in the performance of the modified bitumens, and 45:55-25% and 50:50-25% curves are not desirable, indicating the marginal change in δ at higher and lower temperatures. The master curve of 45:55-15% has higher stiffness at a lower frequency than other bitumen curves and is less stiff at a higher frequency. The microstructure analysis showed that there is no such difference in homogeneity between 45:55-10% and 50:50- 10% which further clarifies the principle of the rapid dissolvement of SBS particles in WCO. The third objective's findings for the selective Marshall mix design are derived from the process of elimination established in the second objective, which assesses the optimum bitumen content (OBC). The results suggested that the increasing content of the MWCOG for the bitumen modification eventually decreases the OBC of the asphalt mixtures. The control mixture OBC is 5.04% which is slightly higher than 45:55-10% and 50:50-10% with 4.92% and 4.89% respectively. The study's fourth objective evaluates the mechanical characteristics of the opted asphalt mixtures. There is no notable enhancement in the overall stiffness of asphalt mixtures. However, the 45:55-5% and 50:50-5% have demonstrated an improvement of 13.5% and 0.33% compared to the control mixture respectively. Additionally, the permanent deformation evaluation showed a significant decrease in the cumulative strain of modified asphalt mixtures. The 45:55-5% and 50:50-5% have a strain value of 0.46% and 0.54% respectively which is lower than the 0.63% of the control mixtures. However, the control mixture has demonstrated a lower creep modulus of 239 Mpa compared to the 45:55-5% and 45:55-10% with values of 323 Mpa and 277 Mpa respectively. The integration of the mixture test showed an average loss of 2.50% of the control specimens which is higher among all the modified mixtures. However, the MWCOG-45:55 demonstrated an overall lower average loss compared to the MWCOG-50:50. Thus, the study outcomes suggested that the modified WCO with a concentration of up to 10% has a significant impact on the properties of the bitumen and modified asphalt mixtures and possibly be an economical and sustainable modifier in pavement construction.

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