Experimental and Life Cycle assessment of RAP modified with Fe2O3 and Waste Cooking Oil Admixtures

Technical Summary: Experimental and Life Cycle Assessment of RAP Modified with Fe2O3 and Waste Cooking Oil Admixtures

Problem Statement
Asphalt pavements frequently suffer from distresses such as thermal cracking at low temperatures, rutting at high temperatures, and moisture damage, driven by heavy traffic, construction deficiencies, and environmental factors. While asphalt additives can improve performance, single modifiers rarely enhance all properties simultaneously. Furthermore, the road construction industry relies heavily on natural resources and energy-intensive processes, contributing significantly to environmental pollution. Although Reclaimed Asphalt Pavement (RAP), Waste Cooking Oil (WCO), and Nano Fe2O3 have been investigated individually, there is a lack of research regarding their composite application in RAP mixtures and the systematic quantification of their combined mechanical and environmental impacts.

Methodology
This study employed a dual-additive modification approach to evaluate RAP asphalt mixtures. Five distinct mixtures were prepared and tested:

1. Control mix (virgin asphalt).
2. RAP mix (20% RAP).
3. RAP mix modified with Waste Cooking Oil (WCO) at varying dosages (5%, 7%, 9%).
4. RAP mix modified with Nano Fe2O3 at varying dosages (2%, 3%, 4%).
5. RAP mix with a composite of Nano Fe2O3 and WCO.

Experimental Evaluation:

• Specimen Preparation: A dry mixing method was used. Aggregates were heated to 175°C, blended with additives, followed by virgin bitumen (60/70 grade) at 160–170°C, and finally filler.
• Mechanical Testing:
  • Marshall Test: Determined optimum binder content, stability, flow, density, and air voids.
  • Wheel Tracking (Hamburg): Assessed rutting resistance at 60°C under 0.7 MPa pressure.
  • Marshall Immersion: Evaluated moisture damage resistance (Moisture Susceptibility Ratio - MSR).
  • Indirect Tensile Strength (ITS): Measured low-temperature cracking resistance at -5°C.
• Life Cycle Assessment (LCA):
  • Functional Unit: 1 km length × 1 m width of wearing surface layer (15-year design life, 20,000 vehicles/day).
  • System Boundaries: Included raw material production, bituminous mix manufacturing, transportation, and wearing surface construction. Excluded design, use, and end-of-life phases.
  • Tools & Data: SimaPro 9.1.0 software with the Ecoinvent database (V 3.6) and the CML2001 impact assessment method.
  • Impact Categories: Assessed 10 categories including Global Warming Potential (GWP), Acidification (AP), Eutrophication (EP), Ozone Depletion (OLD), and various toxicity potentials.

Key Results

• Mechanical Performance:
  • Rutting Resistance: Nano Fe2O3 significantly improved rutting resistance. The composite mixture (M8) achieved the greatest improvement, reducing rutting depth by 38.60% compared to the control. WCO alone slightly increased rutting depth.
  • Low-Temperature Cracking: WCO demonstrated a superior effect on thermal cracking resistance compared to Nano Fe2O3. The composite mixture (M8) recorded the highest Indirect Tensile Strength (ITS), improving by 30.21% over the control.
  • Moisture Resistance: Nano Fe2O3 showed a greater effect on moisture damage resistance than WCO. The composite mixture (M8) achieved the highest Moisture Susceptibility Ratio (MSR), increasing by 8.24% over the control.
  • Optimal Dosages: Based on Marshall test results, 4% Nano Fe2O3 (M4) and 9% WCO (M7) were identified as the optimal dosages for single-modifier mixes.
• Environmental Performance (LCA):
  • Single Modifiers: The RAP mix (M1) improved environmental impacts across all categories compared to the control. The Nano Fe2O3 mix (M4) showed the best overall environmental profile among modified mixes, though it exhibited minor negative impacts in EP, GWP, TETP, and OLD categories. The WCO mix (M7) also improved the profile but showed negative impacts in similar categories.
  • Composite Modifier: The composite mixture (M8) generally improved the environmental profile compared to the control but displayed the highest negative impacts in several categories (TETP, AP, EP, OLD, GWP) relative to other modified mixes.
  • Process Contributions: Bitumen production was the primary driver for AP, EP, GWP, HTP, FWETP, MAETP, and POFP. Asphalt mixture manufacturing drove OLD impacts, while transportation drove ADP and TETP.
  • Weighting: Using a Canadian panel weighting method, all modified mixes displayed lower overall environmental impacts than the control mix. The Nano Fe2O3-modified mix (M4) had the lowest overall environmental impact, followed by the composite mix (M8).

Significance and Claims
The authors claim that this study provides the first systematic investigation into the composite modification of RAP asphalt using both WCO and Nano Fe2O3. The research demonstrates that while single additives have specific strengths (Nano Fe2O3 for rutting and moisture; WCO for low-temperature cracking), a composite approach yields the best overall mechanical performance, significantly enhancing rutting resistance, moisture stability, and thermal cracking resistance simultaneously.

Regarding environmental sustainability, the study concludes that while the composite mixture offers superior mechanical properties, the single Nano Fe2O3 modification offers the most favorable overall environmental profile when considering weighted impact categories. The paper asserts that composite admixtures are a viable strategy to improve the overall efficiency and service life of asphalt mixtures without compromising environmental sustainability, providing data to support decision-making for road construction policies in Egypt and similar contexts. The authors emphasize that no single additive can enhance all mixture properties, justifying the need for composite solutions.