JOURNAL OF TRANSPORTATION INFRASTRUCTURE ENGINEERING (JTIE)
Year:2024 | Volume:10 | Issue:4|Papers Count:6

In this study, effects of adding ground granulated blast furnace slag, Type II Portland cement, and glass fibers on the performance of recycled cold asphalt mixtures were investigated. Based on the previous studies, the additive content in the mixture was set at 2% by weight for cement and ground granulated blast furnace slag, and various percentages of glass fibers were considered, specifically 0.2%, 0.3%, and 0.4% of the aggregate weight in the asphalt mixture. Results indicated that recycled cold asphalt mixtures without additives do not possess sufficient durability. The use of glass fibers leads to an increase in Marshall stability up to a maximum of 10.3% compared to the base mix design. By increasing the percentage of emulsion bitumen in the recycled cold asphalt mixture, and in the worst case, it causes a decrease in indirect tensile strength in dry condition by at least 78% and 17.7% at the age of 7 and 28 days of the samples, which indicates a decrease in the moisture resistance of the recycled cold asphalt mixture containing glass fibers. Results also indicate that cement and ground granulated blast furnace slag increase the Marshall stability by 50% and 40%, respectively, increase the indirect tensile strength in dry conditions by 36.3% and 16.4% at the age of 28 days, also significantly increase the flow number at the age of 28 days and increase the fatigue resistance at the age of 42 days compared to the base mix design. From the results obtained, it can be understood that due to the functional and economic parameters, the use of cement as an additive in recycled cold asphalt mixtures is justifiable and useful.

The present study analyzes and measures the vertical stiffness of ballasted railway track based on the beam on the elastic foundation method by focusing on the effects of dynamic stabilizer machine. Investigating the effects of this machine on the vertical stiffness of ballasted tracks can help the railway engineers in track maintenance planning and cost reduction. One of the methods for maintaining ballasted railway tracks is using the mechanized track maintenance trains to adjust longitudinal leveling, track alignment, and stabilize the railway. While the tamping machine has advantages for quickly correcting the track geometry, it also has disadvantages such as a reduction in the lateral resistance and stiffness. These disadvantages result from the penetration of tamping tines into the ballast layer, and lack of coherence in the ballast grading. The dynamic stabilizer machine, based on available technical literature, can reduce some of the deficiencies caused by the tamping machine. To examine these effects, a field experiment was conducted in Line No. 1 at Karaj Railway Station. Results of the tests performed in three steps including before tamping, after tamping, and after using the stabilizer machine indicate that, due to the absence of tamping for five years, the vertical stiffness was at its maximum level before tamping. After employing the tamping machine, the vertical stiffness decreased by approximately 69%, mainly due to the penetration of tamping tines into the ballast layer, which reduced the compaction and the contact surface between ballast particles. Following the passage of the dynamic stabilizer machine and application of horizontal vibrations and static vertical loads, which enhanced the compaction and proper interlocking of ballast particles, the vertical stiffness increased by approximately 47% compared to the step after tamping operation.

The use of Reclaimed Asphalt Pavement (RAP) in Stone Mastic Asphalt (SMA) mixtures offers environmental and economic advantages. However, incorporating RAP into SMA can introduce challenges related to rutting, particularly under heavy traffic and high temperatures. This study investigates the influence of different RAP gradations (fine and coarse) and percentages (0%, 15%, and 30%) on the performance of SMA mixtures. Additionally, the effects of waste engine oil (WEO) and rubber process oil (RPO) on the penetration, softening point, bitumen bleeding, and resistance to deformation of RAP-modified SMA mixtures were examined. Results indicated that increasing RAP content directly decreased bitumen bleeding. The resistance to deformation ( ) value was higher in mixtures containing fine RAP due to the uniform distribution of smaller particles and increased surface area, which enhanced bitumen-aggregate bonding and reduced vertical deformation. Conversely, coarse RAP, owing to its more robust structure, exhibited a higher capacity to withstand applied loads, resulting in increased maximum resistance. The combination of these two mechanisms provided nearly equal performance in terms of ultimate strength. Furthermore, WEO exhibited a positive effect, with an average improvement of 11.1% compared to RPO, which could be attributed to the chemical and structural properties of WEO that enhance bitumen-aggregate cohesion and bonding in the presence of RAP.

Predicting the budget for road construction and maintenance has been one of the most significant issues in government budget allocation. Early identification of road problems through preventive measures increases their lifespan and reduces maintenance costs. This study focuses on a 35-kilometer stretch of the Sabzevar-Shahrood road, located in a hot and dry region and serving as a transit path from east to west, where asphalt damage is frequently observed. To forecast the Pavement Condition Index (PCI) based on pavement age (AGE), systematic random sampling of asphalt was conducted at designated locations using GPS, followed by spectral analysis in a physics laboratory with a spectrometer. Optical images from Sentinel-2 were processed, utilizing green, blue, red, and near-infrared bands due to their 10-meter resolution and wavelengths ranging from 440 to 900 nanometers, which correspond closely to the asphalt response spectrum. Subsequent analyses involved extracting pixel values from the corresponding bands at the asphalt sampling sites within the Sentinel-2 satellite images and conducting statistical evaluations. The inverse relationship between AGE and PCI indicates that field analyses and calculations of distress indices were performed accurately, with their extension in band analysis as dependent variables being appropriately selected. In examining the relationship between the PCI and satellite imagery spectroscopy for predicting distress indices, the near-infrared band (B8) exhibited superior performance with a coefficient of determination (R2 = 0.48) compared to other bands, demonstrating relatively high accuracy that can be extended to other distress indicators such as the Pavement Serviceability Index (PSI). Given the average spatial resolution of 10 meters for the selected bands from Sentinel-2, a relatively low convergence coefficient  (R=0.323) was observed in this analysis concerning pavement distress dimensions. Furthermore, in assessing the relationship between pavement age (AGE) and satellite imagery spectroscopy for predicting pavement age, the near-infrared band (B8) outperformed other bands with a coefficient of determination R2= 0.55. In this analysis, higher convergence coefficients (R=0.56) were noted, suggesting that higher wavelength numbers in spectroscopy indicate younger pavement conditions. Traffic load significantly influences pavement distress; additionally, employing existing criteria for random sample selection plays a crucial role in determining distress indices and final analytical outcomes. Therefore, Sentinel-2 satellite images in the near-infrared band with a resolution of 10 meters demonstrated better correlation with age and distress indices of roads. However, these images will perform more effectively on roads wider than 10 meters.In examining the relationship between the PCI and satellite imagery spectroscopy for predicting distress indices, the near-infrared band (B8) exhibited superior performance with a coefficient of determination (R2 = 0.48) compared to other bands, demonstrating relatively high accuracy that can be extended to other distress indicators such as the Pavement Serviceability Index (PSI). Given the average spatial resolution of 10 meters for the selected bands from Sentinel-2, a relatively low convergence coefficient (R=0.323) was observed in this analysis concerning pavement distress dimensions. ،he near-infrared band (B8) outperformed other bands with a coefficient of determination (R2= 0.55). In this analysis, higher convergence coefficients (R=0.56) were noted, suggesting that higher wavelength numbers in spectroscopy indicate younger pavement conditions. Traffic load significantly influences pavement distress; additionally, employing existing criteria for random sample selection plays a crucial role in determining distress indices and final analytical outcomes. Therefore, Sentinel-2 satellite images in the near-infrared band with a resolution of 10 meters demonstrated better correlation with age and distress indices of roads. However, these images will perform more effectively on roads wider than 10 meters.

Due to extensive construction activities in urban areas, the generation of construction waste has been increasing significantly. Among these wastes, recycled concrete aggregates (RCA) are notable, as they can serve as alternative natural materials in various road construction projects. Utilizing such materials in road construction projects can mitigate the environmental hazards associated with their disposal. This study investigates the clay from Kazem Abad region of Qazvin, Iran, which exhibits low plasticity characteristics. The RCA materials used in this research were obtained from laboratory concrete samples. A series of laboratory tests, including compaction tests and uniaxial compressive strength (UCS) tests, were conducted on stabilized clay samples incorporating 25% and 50% RCA, and the effect of curing durations of 7, 14 and 28 days on UCS was investigated. Also, the effect of freezing and melting cycles on the uniaxial compressive strength of the stabilized clay was investigated. Results indicated that incorporating RCA into clay soil reduces maximum dry density (MDD) and optimum moisture content (OMC). Moreover, due to the higher proportion of unhydrated cement particles in the 50% RCA mixture compared to the 25% RCA mixture, the UCS values exhibited greater growth over time. Additionally, UCS values for all RCA percentages declined as the number of freeze-thaw cycles increased, with the most significant strength reduction occurring in the initial cycles. Overall, the findings suggest that incorporating RCA can enhance the geotechnical properties of clay subgrade layers, making them a viable option for sustainable road construction.

Construction of embankments on soft soil is considered as one of the common challenging topics in the field of geotechnical engineering and transportation infrastructure. These challenges arise from unfavorable ground conditions, such as high compressibility, significant settlement, and low strength of the subsoil. Therefore, the use of innovative methods in the construction of embankments using geosynthetic layers and piles is increasingly gaining attention as a technical and economical option. This paper examines the reinforcement mechanism in the performance of embankments reinforced with geosynthetics and supported by piles in soft soils. The key areas of focus in this study include the performance of geosynthetic reinforcements (such as geogrids or geocells), the role of platform layers, and a comparison of design methods in the guidelines of the United Kingdom (BS8006), Germany (EBGEO), and the Netherlands (CUR226). In addition, the results of nine field studies are also considered in this research. The findings indicate that for calculating the effectiveness of the BS8006 method, the results are closer to the measured field values. Furthermore, for stress concentration ratios, differential settlements, and maximum tensile forces in geosynthetics, the values calculated using the CUR226 method are closer to the measured field values. Finally, based on the obtained results, recommendations for advancing future studies are presented.