Integrating waste materials into road infrastructure is essential for environmental sustainability and resource efficiency. This study addresses the modification of short-term-aged 50/70-penetration-grade bitumen using two sustainable additives: waste toner powder and lignin. Waste toner was added at weight percentages of 4%, 8%, 12%, and 16%, while lignin was added at 15% and 20%. Since these modifiers have individual uses, this study examines how they may strengthen the oxidized binder. It focuses on extending the lifespan of the mixture by combining industrial and bio-based polymers. The main aim was to delineate the impact of these modifiers on the physical consistency, low-temperature flexibility, and microstructural morphology of the binder. The results show that both modifiers increase binder stiffness by reducing penetration at all modification rates. The resins in the waste toner enhance the polymer matrix, and the lignin’s aromatic structure increases the elastic components, improving high-temperature stability. However, ductility tests showed a reduction in elongation capability, suggesting a brittle state at lower temperatures. Also, waste toner additive is identified as the ideal modifier for high-temperature applications. SEM analysis illuminated the mechanisms underlying these performance modifications. Both additives had homogeneous distribution and good bitumen matrix interfacial bonding at lower concentrations.

Globally, sustainability is an important issue. Bitumen is obtained from crude oil, is solid at ambient temperature, almost completely soluble in toluene, is in a non-volatile, sticky form, and is defined as a waterproofing material. In terms of low carbon dioxide emissions, the asphalt industry is looking for more sustainable options. Lignin is one of the most common natural polymers on earth. Its role is to hold the chemical components, which is the wall material, together in the matrix structure in plant cells and to provide resistance. Millions of tons of lignin are released after pulp production which is considered waste material. Depolymerized fractions cause significant environmental problems due to toxic chemical structures. In this study, short-term aged bitumen was modified by lignin at the rates of 15% and 20% to bitumen weight, and conventional Penetration Test, Ductility Test, and Scanning Electron Microscope (SEM) analysis were carried out to determine the rheological effect. In addition, it was aimed at determining the effective rate of lignin usage. In conclusion, the current research aimed to demonstrate that lignin, as a value-added modifier, is a promising solution with both environmental and engineering values. Also, as the lignin rate increased, the hardening rate of short-term aged bitumen increased in both penetration and ductility tests. Furthermore, SEM data revealed that particles with irregular surfaces are homogeneously distributed in aged bitumen. However, with the increase in usage rate, the distribution of lignin particles in bitumen became irregular.

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.

The rise in the surface temperatures of flexible pavements, driven by climate change and urbanization, increases the need for materials with a modified thermal response while retaining acceptable mixture properties. In this study, a previously developed n-nonadecane capsule system with a polyurea (PUA) shell was incorporated into bitumen at 1, 3, and 5% by weight of the binder, and the resulting asphalt mixtures were evaluated at the capsule/binder and mixture scales. The capsule system was characterized by SEM and FTIR, and its thermal behavior by DSC and TGA; the effective thermal conductivity of compacted mixtures was measured between 20 and 40 °C with a KD2 Pro thermal analyzer using a KS-1 transient needle probe, and Marshall volumetric and mechanical responses were determined on three replicate specimens per group. DSC showed melting at 34.5 °C for pure n-nonadecane and at ~33.8 °C for the capsule, with total endothermic enthalpies over the 20–40 °C interval of 212.2 and 92.8 J/g, corresponding to an enthalpy-based encapsulation ratio of ~44%. TGA showed no appreciable thermal decomposition up to the asphalt mixing temperature, but this measurement does not establish mechanical capsule survival during mixing and compaction. The measured effective thermal conductivity decreased with both temperature and capsule content, from 1.76 W/m·K for the neat mixture to 1.31 W/m·K for PCM-5 at 40 °C. Marshall stability was higher than the control at all tested dosages and reached 14.01 kN at PCM-3 versus 10.42 kN for the control; however, the volumetric response also shifted with capsule addition, and the modified mixtures were not independently optimized at each dosage. Accordingly, the present results are interpreted as formulation responses under a common 6.0% binder-content condition rather than as proof of an optimized pavement design or field-scale thermal regulation.

A localized landslide that occurred on a specific section of the road to the Uluyazı Campus of Çankırı Karatekin University seriously threatened road safety and disrupted transportation continuity. In this study, the ground conditions of the landslide area were examined in detail. Soil parameters were determined through field observations, drilling, Standard Penetration Test (SPT) data, laboratory experiments, liquefaction potential, bearing capacity, and consolidation behaviour were analysed. The analyses showed that the soil was safe in terms of liquefaction and that the bearing capacity was at a level suitable for road construction and use. However, consolidation settlements and dissolutions in gypsum levels were identified as critical factors that could trigger landslides. To prevent landslides and ensure road safety, double rows of bored piles with a diameter of ∅120 cm, a length of 35 m, and spaced at 1.4 m intervals were connected with a cap beam. This engineering measure cut the landslide surface, limited road deformations, and ensured transportation safety. The study demonstrated the effectiveness of bored pile applications in formations where soil-water interaction was significant and offered an applicable solution for critical areas in highway engineering.