Effects of classes C and F fly ashes on the viscoelastic behavior of cold mix asphalt (CMA)

To promote sustainability in the pavement industry, this study investigates how replacing traditional aggregate filler with Class C or Class F fly ashes impacts the mechanical and volumetric properties of cold mix asphalt (CMA). The mixture design phase involved determining the optimum fluid content, number of compaction gyrations, and residual asphalt binder content using the modified Proctor test, conducting a compaction study, and assessing the resistance to moisture-induced damage, in that order. Once the optimum parameters were established, three different trial mixtures were prepared and tested: a control (100 % traditional aggregate filler), FA-C (100 % Class C fly ash filler), and FA-F (100 % Class F fly ash filler). After determining the mixture volumetric properties, the mechanical behavior of each mixture was analyzed using the dynamic modulus tests. Mixture modeling included detailed analyses through Black space diagrams, master curve development, and model fitting. The findings reveal that incorporating Class C or Class F fly ash increases mixture stiffness, with the Class C mixture achieving up to 3 times, and the Class F mixture up to 1.5 times the stiffness of the control CMA at high temperatures. The 2S2P1D model effectively represents the complex modulus of all three mixtures. However, this is not the case for the mixture phase angles, as the addition of fly ashes adversely affects the model’s accuracy, resulting in greater discrepancies between the modeled and measured values. • Optimum fluid content, number of gyrations, and residual binder content were determined. • Fly ash was used as a total replacement for limestone filler in asphalt mixtures. • Master curves from dynamic modulus results were fitted with the 2S1P1D model. • The use of fly ash increased stiffness in the studied mixtures.