مجله مهندسی زیر ساخت های حمل و نقل
سال ششم شماره 2 (پیاپی 22، تابستان 1399)

Conservation of natural resources, optimization of energy use, and minimization of environmental pollution are among the core goals of sustainable development that should be duly considered in the development of national infrastructures, including roads and highways. In the case of asphalt mixtures, these goals can be achieved by the reduction of mixing temperature and the use of recycled materials instead of natural aggregates. This study investigated the mechanical properties of asphalt mixtures containing Electric Arc Furnace Slags(EAFS), which were used as partial replacement for coarse aggregates, and also Sasobit, which was used as an additive for Warm Mix Asphalt (WMA) mixtures. This replacement was performed in, 0, 25, 50, and 75% of natural Coarse limestone (>4.75 mm). In WMA specimens, Sasobit was also added at a concentration of 3% by weight of bitumen. After investigating the properties of aggregates and slags, the Marshall method was used to determine the optimum bitumen content of 8 asphalt mixtures (4 HMA+ 4 WMA) with different slag contents. The results of the Marshall Mix Design method showed that because of the high porosity of slags, slag-containing mixtures have a higher optimum bitumen content. Overall, 120 specimens with optimum bitumen content were prepared with a Superpave Gyratory Compactor (SGC). To assess mechanical properties, these specimens were subjected to Indirect Tensile Strength (ITS) test, resilient modulus test at 25°C and 40°C, and dynamic creep test at 40°C and 55°C. The results of these tests showed an improvement in the mechanical properties of the mixtures containing Sasobit and EAF slags. This improvement can be attributed to the increased stiffness resulting from the use of Sasobit, better interlocking of slags, and better adhesion of slags to bitumen.

Permeable concrete or porous concrete, due to its interconnected cavities, allows high-speed ‎water to pass from the surface to the lower layers. Although one of the main characteristics of ‎conventional cement composites is their impermeability, permeable concrete can be used for ‎special applications such as parking and road pavements. According to the issues associated ‎with the use of impermeable surfaces in cities such as storm water runoff and improper water ‎supply to groundwater aquifers, it is anticipated that in near future a rise in permeable ‎concrete applications will occur. In this research, permeable mortar specimens containing ‎different replacement values of silica fume (up to 20%) were fabricated. To evaluate the bond ‎between aggregates and cement paste in permeable pavements, electrical resistivity of ‎permeable‏ ‏mortars cured in two different conditions namely lime-water and NaCl solution ‎was measured. The tests including compressive strength, electrical resistivity and permeability ‎were performed on the specimens. The aim was to find a balance between mechanical and ‎hydraulic properties of permeable‏ ‏mortars and extracting a relationship between compressive ‎strength and electrical resisitivty of such cement composites. Results showed that specimens ‎containing coarser aggregate had better performance in compressive strength and electrical ‎resistivity tests. Also, the processing of samples in salt water greatly reduced the electrical ‎resistance of the samples, so that even after 90 days of processing, the samples rarely showed ‎resistance above 10 Ω.m. A meaningful linear correlation was found between electrical ‎resistivity and compressive strength of permeable ‎mortars.‎

The limitation in the application of pure bitumen for producing asphalt mixtures is due to the increased vehicle load and the effects of environmental factors, which results in the premature deterioration involving the rutting in asphalt layers. In this study, the waste polybutadiene rubber was used in combination with Sasobit to improve thermal resistance and rheology behavior of bitumen. For this purpose, the bitumen samples were prepared with different percentages of additives using the high shear mixer. The results of the study showed that adding waste polybutadiene rubber to the bitumen improved thermal resistance, rutting and fatigue resistance potential, and generally, middle and high temperature performance. Accordingly, the combinations of 2.3%PBR and 2.3%PBR+2.5%Sasobit increase the high-temperature bitumen performance by one and two grades, respectively. The combinations of 2.3%PBR increase fatigue life and add Sasobit, and also adding more than 2.3% PBR reduce fatigue resistance. The results of TGA show that there is good agreement between the results of these technique and other results, which can help assess the results accurately at macromolecular level.

Reinforced concrete bridges are one of the most important structural elements in road and rail transportation systems. The use of cement-based alternative materials that have a better tensile behavior than concrete is always considered. The material of high performance fiber reinforced cementitious composite (HPFRCC) is of more resistance and ductility than normal concrete in tension, due to the strain hardening behavior under tension after formation of first cracking and bridges between the cracks by the fibers present in this material. In this study, the behavior of concrete and HPFRCC columns in bridges, that are under the eccentric load due to the dead load of the bridge deck, using finite element method with ABAQUS software, and theoretical method after validation with based on the experimental approach, have been compared. Also, in reinforced HPFRCC column, the effects of peak compressive stress, ultimate tension strain of HPFRCC and longitudinal reinforcement on variation of axial load-bending moment interaction curve have been investigated. The results show that the load carrying capacity of reinforced concrete and HPFRCC columns in the compression control area of axial load-bending load interaction curve is almost close to each other. But, the amount of balanced eccentricity and load carrying capacity of the HPFRCC column in the tension control area curve is higher than of the reinforced concrete column due to the change of the HPFRCC behavior in the tension compared to the concrete. The value of this increase in load carrying capacity varies and depends on the amount of eccentricity of axial load and is between 5.2% and 42.7%. Also, the amount of increase in balanced eccentricity is equal to 20%.

In recent years, due to the higher cost of pavement construction and environmental considerations, various waste and recycled materials have been used in concrete and Roller Compacted Concrete (RCC) mixtures. This study investigates the effect of partial and full replacement of natural aggregates with steel slag as a by-product of the steel industry and Reclaimed Asphalt Pavement (RAP) as a waste of the road pavement construction industry, on the mechanical and environmental properties of RCC pavements. For this purpose, compressive strength, indirect tensile strength and three-point bending tests were conducted on 7 and 28-day samples. Three-point bending test was used to obtain flexural strength, toughness, and energy absorbency. Also Cantabro abrasion test and Toxicity Characteristic Leaching Procedure (TCLP) were conducted on 28-day samples. The results showed that the compressive strength, tensile strength and flexural strength of RCC pavement reduced by replacing natural aggregates with steel slag and RAP. In the meantime, the effect of RAP on reducing mechanical properties of roller concrete is more pronounced. Increasing the content of steel slag and RAP increases the toughness, as well as the energy absorbency capacity of the specimens despite the decrease in the maximum load. On the other hand, the abrasion resistance of the roller concrete mixture increases, with increasing steel slag. Also, according to the results of this study, the mixtures containing up to 50% steel slag or combined steel slag and RAP, met the regulatory requirements. By incorporating 25% steel slag and 25% RAP as substitutes for natural aggregates, compressive, tensile and flexural strengths decreased and toughness increased up to 24%, 34%, 21% and 13%, respectively. Thus, the waste materials used in this study, are usable in RCC because of their satisfactory results and economic-environmental advantages.

The Markov technique with discrete interval and dividing the PCI into 10 modes and each mode into 10 units, gives the probability of the remaining in a specified mode or declining to the next mode after one duty cycle for the pavement. In this method can change the number of considered modes and extend the method accordingly. By increasing the number of modes, it may be possible to provide a more accurate estimate of the deterioration process and the type of actions needed at the appropriate time to increase road maintenance and preserve capital; Therefore, the purpose of this study is to investigate the division of PCI into 20 modes with 5 units’ width to estimate the pavement collapse process. In addition, the 5-unit segmentation is more in line with the presented qualitative classification. For this purpose, first, the probability matrix of the corresponding transfer is formed by two classifications, and then by a state vector and one family, a pavement performance prediction model based on homogeneous Markovian trend for two 10-digit and 5-digit PCI classifications, based on the data from valid twenty-year-old pavement was developed. The results showed that in the prediction curve obtained from the two segmentations, there is no specific critical point. But given a steep slope to begin to increase the severity of the failures, the 5-unit segment, 4 years earlier than the 10-unit segment, suggests the start of preventive measures. Also, the PCI prediction in the tenth year of these two curves shows the probability of 0.32 and 0.08 for the 10 and 5 unit methods, respectively, with significant differences. In addition, in the 5-unit method the curve slope increases over time, which is more in line with the pavement deterioration process, but in the 10-unit method the slope is almost uniform during the deterioration.

The everyday increase in population, the increase in the activity of industrial factories and workshops, and the expansion of transportation system lead to the release of metal pollutants and acid-forming compounds, such as nitrogen and sulfur, into atmosphere. The presence of these polluted compounds in atmosphere lowers the natural rain pH and gives it an acidic property. Acid rain, as one of the sources of soil pollution, has devastating effects on soil. A variety of natural and chemical materials are used to stabilize different types of soil. In the present study, the effect of acid rain on mechanical behavior of cement-stabilized sandy soil is investigated. Primarily, the cement was added to the sandy soil, with percentages of 3%, 5% and 7%, and then the samples were tested after saturation in solutions with pH values of 1, 3, 5 and 7.8. The results show that the increase in cement percentage enhances the optimum moisture, maximum specific dry weight, shear strength, Secant modulus (E50), and shear strength parameters of samples. Nonetheless, the acidification of environment reduces the Secant modulus, cohesion, and internal friction angle of soil. The results indicate that the decrease in uniaxial compressive strength and Secant modulus, due to the acidification of environment, are more pronounced with higher percentages of cement. According to the results, the increase in shear strength parameters, due to the increase in curing time and decrease in environmental acidity, is more significant in cement-stabilized samples than lime-stabilized ones. Finally, the effect of pH and cement on the cohesion between sand and cement particles was investigated using image processing and getting binary images from samples, the results of which revealed that the increase in acidity and the reduction of cement percentage drastically reduces the cohesion between sand and cement particles.