Appraising the synergistic use of Nano Fly Ash and Cold Bituminous Emulsion Mixes

Abstract: Cold Bituminous Emulsion Mix (CBEM) is advantageous in terms of lesser energy consumption, better workability, and lower greenhouse gas emissions than hot mix asphalt. However, its poor mechanical performance and strength characteristics are major concerns. This study incorporates Nano Fly Ash (NFA) with bitumen emulsion to evaluate its influence on the strength of CBEM. The research focuses on assessing volumetric characteristics, along with stability under both wet and dry conditions, as key performance indicators within the Marshall mix design framework. In the bitumen emulsion, NFA was added at varying dosages of 0% (control sample), 1%, 2%, and 3% by weight of residual bitumen content (RBC) using a high-shear mixer at 4000 RPM for 25 minutes at 25°C to prepare CBEM. As the bitumen emulsion began to break down at NFA dosages > 3%, the maximum dosage was restricted to 3%. For each NFA dosage, the optimum residual bitumen content (ORBC) was calculated by varying the RBC at 4, 5, 6, and 7%. The result of this study indicates that incorporating NFA up to 3% exhibits comparable characteristics to the control sample regarding air void and moisture content, regardless of RBC concentration. The Voids in mineral aggregate for the control sample observed a peak at 7% RBC; however, in NFA-modified samples, no such peaks were observed, and its value increases with increasing RBCs. While NFA-modified samples show improved strength, the 3% NFA modification exhibited the maximum stability value of 12.1 kN at 7% RBC. In the case of the control sample, the highest stability of 9.6 kN was observed at 4% RBC. The ORBC was evaluated based on maximum wet stability, or factors such as percentage moisture absorption, loss of stability, and total voids. For the control samples, the ORBC was attained at 6%, corresponding to a maximum wet stability of 7 kN. In the case of the 1% NFA-modified sample, the ORBC remained at 6%, with an improved wet stability of 7.1 kN, along with 0.7% moisture, a stability loss of 0.3%, and total voids of 12.1%. However, for 2% and 3% NFA-modified samples, the ORBC value was 7%. The wet stability values were 8.8 kN for the 2% sample and 9.3 kN for the 3% sample. Moisture absorption rates were 0.11% and 0.09%, with stability losses of 0.28% and 0.23%. Total voids were 9.6% for the 2% sample and 9.1% for the 3% sample. In conclusion, the incorporation of NFA enhanced the strength of CBEM. The findings advocate for the adoption of NFA in CBEM formulations, paving the way for more resilient and environmentally friendly pavement solutions.