Moisture Susceptibility in Cold Mix Asphalt: A study of Aggregate and Filler Modifications

Abstract: This study investigates the use of quartzite aggregates in cold mix asphalt (CMA), focusing on improving moisture resistance through surface modification of coarse aggregates and filler modification. Quartzite aggregates, known for their high silica content and susceptibility to moisture damage, were sourced from three river-based locations in the Jammu region of India. The research employed two powder-based and three liquid-based anti-stripping agents for surface modification, along with various filler modifications including stone dust, lime, and cement.
The experimental program was conducted in two stages. The first stage evaluated the effectiveness of surface modifications using a modified boiling water test and image analysis technique on loose asphalt mix. This was performed at different durations (6 hours, 1 day, and 3 days) and two curing temperatures (20°C and 40°C). The boiling water test results determined that the optimum concentration for hydrated lime was 1.0% by weight of the aggregates, while for Zycotherm, it was 1:200 (one part in 200 parts of water). Calcium carbonate and saline coupling agents showed unsatisfactory performance.
In the second stage, compacted mixes were prepared using the results from the first stage, incorporating surface-modified aggregates and different filler modifications. These mixes were subjected to various tests including Marshall stability, retained Marshall stability, indirect tensile strength, and tensile strength ratio to assess moisture susceptibility.
Key findings include:
1. Zycotherm-coated (ZTC) aggregates and hydrated lime-coated (HLC) aggregates showed superior coating retention compared to other modifications.
2. Higher curing temperatures (40°C) significantly improved coating retention, achieving in 24 hours what took 72 hours at 20°C.
3. Cement filler exhibited the highest dry and wet stability across all aggregate sources, followed by HLC aggregates, mixes with 2% hydrated lime, ZTC aggregates, and control mixes.
4. Mixes with cement filler showed the highest indirect tensile strength (ITS) values, with some mixes achieving tensile strength ratios (TSR) greater than 1, indicating improved strength even after conditioning.
5. Shaar aggregates consistently showed higher ITS values but failed to maintain this advantage after conditioning, likely due to higher air voids and voids in mineral aggregates (VMA).
The study concludes that surface modification of aggregates and the use of active fillers can significantly improve the moisture resistance of CMA made with quartzite aggregates. Cement as a filler proved most effective in enhancing stability and tensile strength, while hydrated lime coating and Zycotherm treatment also showed promising results. These findings have important implications for the use of locally available, potentially inferior aggregates in road construction, offering a more cost-effective and environmentally friendly approach to pavement design.
Future research directions include exploring these treatment methods under varying curing conditions, investigating different aggregate types and mix design gradations, and conducting comprehensive laboratory performance studies to address potential pavement distress factors. The integration of these findings into field trials is recommended for practical validation and refinement of pavement design practices.