مجله مهندسی زیر ساخت های حمل و نقل
سال هشتم شماره 2 (پیاپی 30، تابستان 1401)

With the increasing use of asphalt roads, it is necessary to design and produce asphalt pavements that can withstand various damages such as rutting damage, cracking, and moisture damage. The use of nanomaterials due to their excellent and unique features in the asphalt pavement industry to improve the mechanical properties of asphalt has welcomed broad attention in recent years. This study examined the impacts of Nano Reduced Graphene Oxide (RGO) on the mechanical properties of stone mastic asphalt mixture (SMA). In this study, indirect tensile strength test, static creep test, and Pull-off adhesion test were used to investigate the effect of Nano reduced graphene oxide on the mechanical properties of SMA mixture. The pure asphalt binder was modified with three different percent of Nano RGO (0.2 %, 0.4 %, and 0.6 % by weight of bitumen used in asphalt samples in this study). The experiments performed on modified bitumen in this study show that the addition of Nano reduced graphene oxide in pure bitumen raises the viscosity, softening point, and specific gravity and reduces the ductility and penetration of pure bitumen. The mechanical tests showed that augmenting the percentage of Nano reduced graphene oxide leads to increased indirect tensile strength, pull-off adhesion resistance, accumulated strain, reduced creep stiffness, and improved moisture sensitivity in stone mastic asphalt mixture. In general, 0.6% of this nanomaterial caused more significant changes in the mechanical properties of SMA mixtures than other amounts of Nano-reduced graphene oxide. So that adding 0.6% of this additive in the asphalt mixture has increased the TSR index by 23%, increased the pull-off adhesion resistance in the wet condition by 48%, and reduced the creep stiffness by 43% compared to the control mixture.

WMA mixes, compared with HMA mixes, are environmental friendly mixes that produce little air pollutants and greenhouse gases. Their high energy saving costs resulted in their extensive use in construction projects. However, these warm mixes recognized to be susceptible to moisture damage that results in stripping distress in pavements. In this research, WMA mixtures were prepared applying two different methods; namely, application of an organic additive (Sasobit) and adoption of foam bitumen technique. In this latter, small amount of water is inserted together with high pressure air into Wirtgen, WLB-10 machine One of the methods of solving moisture damages is to use anti-stripping additives to increase adhesion properties between bitumen and aggregate particles. In this research, two types of additives; namely, hydrated lime (at 1.5, 2 and %2.5 by weight of aggregates) and Zycotherm (at 0.1, 0.2 and %0.3 by weight of bitumen), were used to reduce moisture sensitivity of Warm Mix Asphalt (WMA). To evaluate moisture susceptibility of WMA mixes, Indirect Tensile Test, boiling water, and Pull Off testing were preformed. The experimental results showed positive effects of hydrated lime and zycotherm anti-stripping additive in reducing moisture sensitivity of WMA mixes. The testing results showed that WMA mixtures that were prepared applying foam bitumen techniqe were more sensitive to moisture damage than WMA mixtures that were prepared by organic additive (Sasobit). As conclusion, results indicated that the mixes containing %2.5 hydrated lime (by weight of aggregates) and %0.3 zycotherm (by weight of bitumen) are the optimum contents of addetives for reducing moisture sensitivity. Moreover, the results indicate that zycotherm additive has a greater effects on redusing moisture sensitivity compared to hydrated lime.

 Due to aging, reclaimed asphalt mixtures are composed of more heavy molecular components, reducing molecular mobility and asphalt repair ability. The use of rejuvenating materials that have light molecular components can be effective in improving the fatigue properties and healing of asphalt mixtures. To control the performance of such mixtures at high temperatures, using polymers can effectively prevent the phenomenon of rutting. This research evaluated fatigue behavior and recovery of reclaimed asphalt mixture using waste oil and styrene butadiene styrene polymer.The chromatography method for the chemical analysis and a four-point bending beam (4PBBT) test to investigate the fatigue behavior and heal the asphalt mixture are used. The results of fatigue tests have shown an increase in the fatigue life and healing ability of the asphalt mixtures rejuvenated with oil and polymer, so that the oil and the combination of oil and polymer have increased the fatigue life of the recycled mixture by 6 and 3.5 times, respectively. Correlation analysis between chemical components and fatigue life and healing of asphalt mixtures shows a significant relationship between the healing rate and the values of asphalt chemical indices. In this regard, the correlation of chemical parameters, including the colloidal index Ic, the sum of heavy bitumen molecules, i.e., asphaltene plus resin, as well as the ratio of light components, i.e., the ratio of saturated to aromatics, and also the amount of recovery at

Today, in the research of researchers, the use of waste materials with heat transfer capability in various asphalts, especially warm mix asphalt (due to environmental benefits) has been considered. Obtaining the modulus of elasticity is very important in determining the efficiency of asphalt, which can be achieved by various methods. Also, the sound absorption of this type of asphalt has been studied using ultrasonic waves. In this study, asphalt samples containing fillers of zinc slag, iron slag, converter sludge, copper slag and earth filler reducing electrical resistance each with 35%, 70% and 100% weight replacement of lime filler (normal) in asphalt. Through SCB three-point bending test, the amount of modulus of elasticity was obtained and then on Marshall samples using underwater method and using ultrasonic waves, the amount of longitudinal modulus and the amount of sound absorption of the samples were investigated. The results show the fact that on average, in the mixtures containing BOF, steel slag, GIM and copper slag, it can be said that mixtures containing BOF by 7% and mixtures containing steel slag, GIM and copper slag by 4, respectively. , 20 and 6% have more impedance than the control sample (WMA). Furthermore, the results showed that the longitudinal modulus obtained by ultrasonic wave method for the samples has the same trend of modulus of elasticity by three-point bending method. The results also showed that statistically, although the type of filler is effective on the performance of the longitudinal modulus, but the percentage of conductive filler (replacement of lime filler) is not effective on the performance of asphalt.

The non-renewability of natural materials and the prevention of environmental degradation for the production of stone materials, has increased the tendency to use waste materials in asphalt mixtures in recent decades. Several research studies were conducted to assess WMA mixtures' mechanical properties containing Reclaimed Asphalt Pavement (RAP), Electric Arc Furnace Slag (EAFS), and waste plastic (WP) separately. However, very scarce studies assessed the influence of the simultaneous presence of RAP, EAFS, and waste plastic on the mechanical properties and moisture susceptibility of WMA mixtures. This research investigates the effects of simultaneous recycling of RAP, EAFS, and waste plastic into the WMA mixtures to remove these barriers. Mechanical properties of WMA mixtures containing different percentages of RAP (0%, 35%, and 55%, fine aggregate replacement), EAFS (0%, 20%, and 40%, coarse aggregate replacement), and waste plastic (0%, and 10% bitumen weight) were evaluated using compressive strength, resilient modulus, static creep, Marshall quotient, and moisture susceptibility tests. Sasobit uses 1.5% of the total asphalt mass to prepared WMA mixtures. The results of this study were shown to improve the moisture sensitivity, rutting resistance, and resilient modulus by increasing the percentage of RAP and also reduce the resistance to moisture sensitivity and improve the compressive strength of mixtures by increasing the percentage of EAFS and decreasing the compressive strength and resilient modulus by increasing waste plastic. The simultaneous use of EAFS, RAP, and waste plastic seems to produce an environmentally-friendly mixture with minimum mechanical properties.

Determining the bearing capacity of the soil and its subsidence is one of the most important parameters that must be carefully evaluated when designing a safe foundation. In the present study, using a physical model, the behavior of the foundation located on sandy soil under static loading and the effect of various factors on soil behavior have been investigated. In this laboratory study, the effect of foundation width, sandy soil density and amount of overhead on strip foundation subsidence has been investigated. The soil material used in this study is poorly grained medium sand (SP). The foundation model has a width of 5, 7.5 and 10 cm and its length is 34 cm. The sand raining technique has been selected to obtain a homogeneous sample with a definite relative density and repeatability of laboratory conditions. The loading system is compressed air that has the ability to apply a uniform and static load. The relationship between the final relative settlement and the width of the foundations located on medium-density sandy soils is linear, and as the foundation width increases, the final relative settlement reaches less than its final ultimate bearing capacity. At the same pressure, the settlement of the foundation located on medium-density sandy soils is about 10 % higher than the foundation located on dense sandy soils. Soil behavior up to a pressure of about 50% of the final bearing capacity is linearly elastic. The pressure- settlement relationship of the strip foundation is linear up to about 5% of the foundation width. General shear failure occurs at a relative settlement of about 12 to 14%. For this reason, it is suggested to determine the ultimate bearing capacity of the strip foundation located on sandy soil, the amount of pressure such as 12% .

Soft and loose soils have always been the focus of attention due to their high settlement and insufficient bearing capacity. The foundations on soft soils and soil slopes containing this type of soil should be modified for high probability of failure. There are various ways to improve these soils, which vary greatly depending on the environmental conditions, site priority, the degree of softness, cost of materials used. Stone column is one of soft soil modification and soil slopes safety factor improvement methods which is economical and easy to implement. The aim of this study is to conduct a numerical study to investigate the effect of stone columns on the bearing capacity of the clay slope and its stability using the FLAC3D finite difference software. the slope is modeled in three dimensions with appropriate dimensions and boundary conditions. The bearing capacity was obtained by stress control procedure and slope safety factor was calculated by shear strength reduction method. In general, two types of failures observed in stone columns. The columns were Located under the footing Were exposed to phenomenon of bulging and the columns were Located outside the footing Were exposed to phenomenon of lateral displacement. The results showed that in general, the stone column will improve the stability of clay slope and its bearing capacity. The use of stone column below the foundation will affect the most on increasing bearing capacity and the effect will decrease by increasing center to the center distance of foundation and columns, so that at 4 times the diameter of stone column it will not have much effect on the bearing capacity. In the case of group columns, the arrangements are along the length of footing is preferred over the arrangements are along slope due to the higher replacement area.