Mechanical and Moisture Performance of Dense-Graded Cold-Recycled Asphalt with 60% RAP and Cement-Fly Ash Additives

Emulsion-based cold recycling can reduce the demand for virgin aggregate and high-temperature asphalt production, but mixtures with high reclaimed asphalt pavement (RAP) contents often have limited early strength and moisture resistance. This study evaluated a dense-graded cold-mix system containing 0%, 60%, and 70% RAP, combined with a 2 × 3 additive matrix comprising cement (0.5% and 1.0%) and Class C fly ash (0.5%, 1.0%, and 1.5%). The 70% RAP blend fell outside the adopted dense-graded envelope, whereas the 60% blend satisfied that envelope and was therefore selected, not claimed as a universal optimum for the additive stage. Hot-mix asphalt was included only as a benchmark. Marshall stability, indirect tensile strength, Marshall quotient, tensile strength ratio, retained Marshall stability, and retained Marshall quotient were measured under the reported laboratory curing and conditioning procedures. Among the tested cold mixtures, the 60% RAP formulation containing 1% cement and 1% fly ash produced the highest measured stability (13.1 kN), dry indirect tensile strength (1.11 MPa), and Marshall quotient (6.89), with retained-property indices of approximately 87%. These short-term results indicate that gradation control and low-dose cementitious additions can improve strength development and moisture retention in the studied emulsion-RAP system. The contribution of the work is an integrated, formulation-level comparison of RAP screening and a cement-fly ash dosage matrix; the findings remain specific to the materials, gradation envelope, curing regime, and screening tests used.