Drainage-Controlled Cellulose-Fiber Stabilization and Skeleton-Mastic Response of Polymer-Modified Stone Mastic...

Stone mastic asphalt (SMA) derives its performance from the coupled action of a load-bearing coarse aggregate skeleton and a binder-rich mastic phase. This study evaluates polymer-modified SMA using an integrated drainage-skeleton-mastic framework that combines drainage-based cellulose fiber selection, controlled gradation variation, aggregate-type comparison, binder-content sensitivity analysis, pre-compaction laboratory conditioning, and FTIR-SEM-EDX characterization. A 50/70 penetration-grade bitumen modified with 4.5% SBS was used with basalt and limestone aggregates, limestone filler, and Viatop cellulose fiber. The fiber dosage was selected using the Schellenberg binder-drainage test, while a separate preliminary load-deformation series was used to examine the response sensitivity to higher fiber contents. Increasing fiber content from 0.30% to 0.35% reduced mean binder drainage from 0.27% to 0.18% and decreased the standard deviation from 0.020% to 0.006%, supporting 0.35% as a drainage-based design dosage rather than a mechanical optimum. Higher fiber contents increased the maximum recorded load within the fixed test window; however, these results were interpreted only as preliminary load-deformation sensitivity rather than as conventional Marshall stability or MQ responses. The binder-content series showed that lower- and upper-limit gradations followed different volumetric and Marshall response patterns; therefore, these results were interpreted as binder-content sensitivity rather than complete optimum binder content determination. Aggregate-type comparisons showed the mechanical advantage of basalt, while the non-replicated post-extraction gradation results were directionally consistent with greater skeleton preservation in basalt mixtures. FTIR, SEM, and EDX observations indicated that cellulose fiber acted mainly through physical mastic stabilization rather than chemical binder modification. Overall, the results demonstrate that SMA response is governed by the combined contribution of drainage-controlled fiber dosage, SBS-modified binder, aggregate skeleton configuration, and limestone-filler mastic integrity.