مجله مهندسی زیر ساخت های حمل و نقل
سال هشتم شماره 4 (پیاپی 32، زمستان 1401)

Recycling and reusing materials have received much attention from researchers in recent decades. Today, environmental issues have become very important due to the limitation of available resources as well as the increase in the cost of new materials. Since most of the existing roads in Iran have flexible pavements, using reclaimed asphalt pavement (RAP) and using fewer new materials can be considered an environmentally friendly solution. In recycling asphalt pavements, there is a major concern related to low-temperature cracking. The purpose of this research is to investigate the low-temperature cracking properties of asphalt mixtures containing RAP along with other additives to introduce a mixture with performance characteristics equivalent to the new asphalt mixture. For this purpose, asphalt mixtures with two different contents of RAP (25% and 50%) were considered. Also, to improve their adhesion properties, the addition of a rejuvenator (10% by weight of RAP binder as the optimal percentage) and to improve the resistance of the mixture against cracking, crumb rubber (10% by weight of new binder) was considered. An indirect tensile strength test and a semi-circular bending test (SCB) were performed to investigate the properties of the mixtures. Also, the crack mouth opening displacement (CMOD) during the SCB test was measured through imaging. According to the SCB test, adding RAP to the base sample reduces the fracture energy. But adding rejuvenator and crumb rubber to the recycled samples improves the properties of the mixture against crack growth. The results showed that the asphalt mixtures containing RAP and additives, according to the tests used in this research, presented equal or even better performance than the new asphalt mixture. Also, the combined index of fracture energy - CMOD can be used as a suitable criterion to investigate the effect of RAP, rejuvenator and crumb rubber in asphalt mixture.

An effective measure of protective road maintenance is the application of slurry seal surface treatment. In this research, a cellulosic nanofiber solution was used at 0 (i.e., control), 3, 5, 7, and 9 wt.% by solid weight of asphalt binder to modify bitumen emulsion. First, the modified polymeric bitumen emulsion samples were evaluated by their physical properties like Saybolt FUROL viscosity, softening point and penetrability. Next, the modified polymeric bitumen emulsion samples were used in slurry seal mixtures. The asphalt mixtures were then evaluated through wet cohesion test, wet track abrasion test, loaded wheel – displacement test, and loaded wheel – sand adhesion test. Results of the asphalt binder tests showed that the use of the cellulosic nanofiber solution could improve the asphalt binder characteristics in terms of reduced penetrability, increased softening point, and enhanced viscosity. With increasing the percent dosage of the cellulosic nanofiber solution from 0 to 5%, significant changes occurred to the penetrability and the softening point. In the meantime, further increase in the percent dosage of the cellulosic nanofiber solution from 5 to 9% imposed significant changes neither in the penetrability nor the softening point. Results of asphalt tests on the samples showed clearly that the asphalt mixtures containing the modified asphalt binder make better-performing slurry seal surface treatments. On average, the slurry seal containing the cellulosic nanofibers at 5% exhibited higher wet cohesion, resistance to abrasion, and resistance to displacement by 23.1%, 42.7%, and 42%, respectively, as compared to the control

Soil frost in cold regions is the most important factor in the deterioration and reduction of pavement efficiency of roads and other soil-based structures. The present work aims at introducing a novel method to reduce the adverse effects of frost in the soil. In the proposed method, a moisture-compatible thermal insulation was prepared to prevent the penetration of cold air in the subgrade. Silica aerogel nanomaterial with extremely low thermal conductivity and high hydrophobicity was mixed with soil to provide the thermal insulator. Silica aerogel was mixed with soil in ratios of 0.5, 1 and 2% and the properties of these mixtures such as thermal conductivity, hydrophobicity, permeability, moisture content in saturated state and durability against freeze-thaw cycles were studied. In this study, it was observed that due to the hydrophobicity of silica aerogel, soil-aerogel mixtures also become significantly hydrophobic. For this reason, their water absorption is significantly reduced; So that the moisture content in the saturated state in the soil without silica aerogel is about 4 times the moisture content in the soil-aerogel mixture. As a result, wetting soil-aerogel mixtures do not have much effect on increasing their thermal conductivity. On the other hand, it was observed that the permeability of the soil without silica aerogel is about 21 times the permeability of the soil-aerogel mixture, which indicates a significant decrease in the permeability of the soil-aerogel mixtures. Moreover, wetting-drying and freezing-thawing cycles as well as exposure to water flow had no effect on the thermal conductivity of the soil-aerogel mixtures. Considering the set of the thermal and hydraulic characteristics of the soil-aerogel mixtures, they can be introduced as a suitable choice for use on the soil surface as a moisture-compatible thermal insulation in order to deal with the adverse effects of frost in the soil.

Today, the use of plastic waste in highway and geotechnical engineering, especially in subgrade stabilization, is extensively examined. This study investigated the effect of using disposable high-density polyethylene (HDPE) chips in stabilized sandy subgrade. The impact of adding HDPE to the sand was investigated through the one-dimensional consolidation, the modified standard proctor (MSP), the California bearing ratio (CBR), and the direct shear test (DST). Adding HDPE to the sand reduced the maximum dry density of the mixture because of its low specific gravity, but the optimum moisture content did not markedly change. The incorporation of HDPE in the sand also promoted the shear strength of the mixture because of the frictional resistance and interlocking between the particles and enhanced the CBR of the sand-HDPE mixture up to 48.7%. Therefore, using HDPE chips in sand-HDPE mixtures for subgrade stabilization can significantly improve the shear strength characteristic of sandy subgrades and, thus, reduce road construction costs.

The demand for using industrial waste has increased significantly due to their environmental impacts and limitation of natural resources. Copper waste (CW) is among those that are known to cause environmental problems. Categorized under waste materials, it causes various environmental problems, especially those related to waste disposal. The main purpose of the present study is to investigate the application of CW, as compared to mineral aggregate (MA), in surface treatment. For this purpose, various tests, including wet cohesion test, wet track abrasion test, loaded wheel – displacement test, and loaded wheel – sand adhesion test, were performed on five different mixtures designated as CW0+MA100, CW10+MA90, CW20+MA80, CW30+MA70, and CW40+MA60, with the designations defined based on total aggregate weight. Results showed that, thanks to its unique physical and chemical characteristics, the replaced CW could improve the treatment performance, especially in the CW30+MA70 sample, in terms of abrasion, wet cohesion, and vertical and lateral displacements by about 23, 22, 39, and 33%, respectively, at a residual asphalt of 8%. Also, regarding the analysis of variance, the copper slag is a more effective factor with respect to residual bitumen in increasing the cohesion and reducing the vertical and lateral deformations due to traffic loading

Concrete pavements are commonly used in some areas of airfields such as aprons. Repairing these pavements is costly and time-consuming, and it also disrupts flight operations. The use of concrete block pavement is a more suitable option at aprons. Fewer studies have been done on this type of pavement in the airfields than on roads. For further studies, the performance of this pavement was examined by making a 3D model and a test track with dimensions of 2m×2m. This sample was composed of subgrade, subbase, base and Cement-Treated Base(CTB) layers, with 15cm thickness, for each layer, bedding sand with 3cm thickness and a Unipave-shape (zig-zag) concrete block pavers with 8cm thickness and herringbone pattern. Then their quality was controlled, based on Federal Aviation Administration(FAA) regulation. At the next step, Plate Load Test (PLT), was conducted on this sample. For this purpose, a setup including a concrete foundation and a reaction beam was built. For the first time in related research, several 3D models of concrete block with all its angles and corners representing their actual dimensions were made using ABAQUS software. Then the force-deflection curve, as a guidance chart was presented. The 3D model analysis result showed that the elastic modulus of the concrete block surface could be taken into account at 2000 MPa to achieve the most coordination between finite element analysis and PLT results. Also the Pull-Out test results showed that using Portland cement in the jointing sand improved its performance against the Pull-Out force by about 2 times as the sample with lime in the jointing sand mixture.

The use of fiber-reinforced concrete in various industries is developing due to the desired mechanical properties, light weight of the structure, good energy absorption capacity and high initial strength under impact loads. a new generation of fiber-reinforced concrete with excellent ductility and exceptional crack control capability. Although fibre concrete is suitable for structures exposed to impacts and other extreme loads, In this study, the energy absorption and initial strength of reinforced concrete with Forta, basalt and barchip fibers under penetration impact loading were investigated. To investigate the effect of fiber percentage on impact properties, 8 specimens were subjected to experimental tests hybrid groups. Also, the fracture surface and the adhesion of fibers to fiber-reinforced concrete with degradation modes were evaluated. The results showed that the initial strength and energy absorption in hybrid-fiber reinforced concrete increased by 292.8% and 212.3%, respectively, compared to Net conceret. Also, by examining the fracture surface of the specimens, it was found that the adhesion between the two basalt and forta fibers to the base concrete is very desirable. However, the separation between barchip fibers and concrete is high and reduces the efficiency of these fibers in reinforcing concrete.