The complex interactions between soil and additives such as lignin, glass powder, and rubber tires were investigated using principles of material and soil mechanics. Previous research has mainly focused on individual additives in clay soils. In contrast, this study investigates soil improvement with two different types of waste materials simultaneously. The improvement of soil properties by hybrid waste materials was evaluated using several laboratory tests, including the standard Proctor test, the unconfined compressive strength test, the California Bearing Ratio (CBR) test, and cyclic triaxial tests. The aim of this research is to identify key parameters for the design and construction of road pavements and to demonstrate that improving the subgrade with hybrid waste materials contributes significantly to the sustainability of road construction. The mechanical and physical properties were evaluated in detail to determine the optimal mixtures. The results show that the most effective mixture for the combination of waste glass powder and rubber tires contains 20% glass powder and 3% rubber tires, based on the dry weight of the soil. For the combination of waste glass powder and lignin, the optimum mixture consists of 15% glass powder and 15% lignin, based on the dry weight of the soil. These results provide valuable insights into the sustainable use of waste materials for soil stabilization in road construction projects.

This paper presents the design of geosynthetic reinforced flexible pavements and their modification by incorporating waste materials into bonded and unbonded layers of the pavement structure. The optimal design of flexible pavements was achieved by minimizing the construction cost of the pavement. The incorporation of waste materials into the pavement structure affects the material properties. Therefore, along with the traffic load, the effects of the material properties of the asphalt concrete, base layer, sub-base layer, and subgrade were analyzed in terms of pavement structure costs and CO₂ emissions of materials used in pavement construction. In addition, a comparison was made between pavements with and without geosynthetic reinforcement in terms of design, optimum construction cost, and CO₂ emissions. The use of geosynthetics is even more effective in pavement structures that contain waste materials in an unbound layer, both in terms of cost and CO₂ emissions. The minimum value of the California Bearing Ratio of the subgrade was determined at which the use of geosynthetic reinforcement for pavement structure with and without the inclusion of waste materials is economically and sustainably justified. The use of geosynthetics could result in a 15% reduction in pavement structure cost and a 9% reduction in CO₂ emissions due to the reduced thickness of unbound layers. In addition, reducing the CBR of the unbound layer from 100% to 30% due to the inclusion of waste materials implies a cost increase of up to 13%. While the present study is based on an empirical pavement design method in which pavement thickness is limited by the pavement thickness index, the same minimum thicknesses are obtained in the optimization process regardless of whether the objective function is the minimum construction cost or minimum CO₂ emissions.

In recent years, many studies on the prevention of icing on highways and airports through the use of electrically conductive asphalt pavements have been carried out. However, although electrical conductivity in asphalt mixtures has been extensively investigated, the gradation in conductive stone mastic asphalt (SMA) mixtures has not yet been studied in detail. The main purpose of this study was to investigate, for the first time, the effect of aggregate gradation variation on the electrical resistivity and temperature change of electrically conductive SMA. Samples of conductive SMA were produced using three different aggregate gradations (series 1A, 2A and 8S) and 5 mm long carbon fibres (0.2% by weight) as the conductive component. Marshall mix design was performed on series 1A, 2A and 8S. The samples were tested for volume resistivity, temperature change under constant electrical voltage and ultrasonic pulse velocity and the results were compared. The results showed that a change in aggregate gradation had a significant effect on the electrical conductivity properties of the conductive SMA, with a denser gradation of the SMA mixture leading to higher electrical conductivity.

Due to advantages like abrasion resistance, increased operating and service life, high coarse aggregate content and high resistance to deformation, increased fatigue life, and others, stone mastic asphalt (SMA) mixtures have recently become a popular asphalt pavement type in road sections such as highways, tunnels, and bridges. There hasn't been much research on the topic, despite the fact that gradation significantly affects the performance of SMA combinations. In this study, the experimental findings of three distinct gradations of SMA mixtures with hybrid materials (basalt coarse aggregate, limestone fine aggregate) and carbon fiber were compared. As a result, it was concluded that the hybrid aggregate used with carbon fiber, maximum aggregate size, and coarse aggregate % had a positive impact SMA mixtures.

With the dramatic increase in the world population, the demand for transportation and, accordingly, energy is also increasing. Clean and renewable energy sources are one of the most important research topics in all countries. The word piezo-electric that, means energy from pressure, is the ability of the material to change an electric field or electric potential as a result of mechanical pressure applied to some materials. This effect is directly related to the change in polarization density inside the material. If the material is not short-circuited, the applied loading and stress creates a voltage in the material. Energy production with materials that provide piezoelectric energy harvesting placed within asphalt pavements is one of the topics that road pavement engineers have been researching in recent years. This study was carried out as a preliminary study. In this study, experiments were made using different sensors to improve energy harvesting from asphalt pavements. The difference of this study from other studies was that different piezoelectric sensors were placed in the asphalt mixture samples and the measurements of the resulting voltages were made. As a result of the experimental study, voltages up to 0.210 V were obtained in the asphalt samples. The obtained results showed that this method is encouraging for energy harvesting and might be the answer for highway transport demand in the future.