مجله مهندسی زیر ساخت های حمل و نقل
سال نهم شماره 4 (پیاپی 36، زمستان 1402)

Efforts to mitigate and control global warming have led to the consideration of warm-mix asphalt technology in the asphalt industry. Warm mix asphalt, compared to hot mix asphalt, offers advantages such as reduced energy consumption and lower production of toxic gases. However, it does have certain weaknesses, including susceptibility to moisture and premature rutting. Therefore, it is crucial to develop warm mix asphalt mixtures with excellent mechanical performance. One potential solution is to carefully select the appropriate filler. The objective of this research is to examine and explore the impact of limestone powder, cement, fly ash, and micro lime as fillers on the performance of warm mix asphalt mixtures. Additionally, an organic additive called Ethylene bis estearamide was utilized to create the warm mix asphalt mixture. To evaluate the mechanical performance of the asphalt mixture, various tests were conducted, including indirect tensile strength tests, dynamic creep tests, and semi-circular bending tests. In the indirect tensile strength test, the force required to break the samples was measured under a constant loading rate of 50.8 mm/min. In the dynamic creep test, the sample was subjected to a haversine loading of 200 kPa at a temperature of 40 degrees Celsius. In the semi-circular bending test, the energy required to fracture the sample at -22 degrees Celsius was calculated. When making a warm mix asphalt mixture using Ethylene bis stearamide additive, although it increased resistance to rutting by 10%, it reduced resistance to low-temperature cracking by decreasing fracture energy by 7%. The semi-warm asphalt mixture containing fly ash with a TSR equal to 80% exhibited good moisture resistance. The addition of cement increased resistance to rutting by 25%. The use of micro lime improved moisture sensitivity, resulting in a 140% increase in rutting resistance and a 17% increase in fracture energy.

The constraints such as altering soil acidity and environmental concerns stemming from the use of traditional soil stabilizers like cement have justified the exploration of environmentally friendly, cost-effective materials with fewer secondary risks, such as biopolymers. This study focuses on examining the effect of adding Persian gum and calcium chloride to two types of soils, silicate sand from Firoozkooh and carbonate sand from Hormuz. For this purpose, initial parameters such as the weight percentage of Persian gum and the molarity of calcium chloride were evaluated through an unconfined compressive strength test, identifying optimal additive percentages. Then, the impact of factors such as curing time, curing place, and wetting-drying cycles on the compressive strength and durability of the optimized treated specimens was investigated. The results of this research indicate that the compressive strength of Persian gum-treated Firoozkooh and Hormuz sands increases up to 2.75 and 3 MPa, respectively, after a 28-day curing period at 40°C with the optimal Persian gum percentage (2.5% and 3%). Under dry conditions, Persian gum and calcium chloride-treated Firoozkooh and Hormuz sands at the optimal percentage (1.5% Persian gum and 3 molar calcium chloride for Firoozkooh sand and 2.5% Persian gum and 2 molar calcium chloride for Hormuz sand) achieve compressive strengths of 6.2 and 5.1 MPa, respectively, after 28 days, representing a 125% and 70% improvement compared to specimens treated with Persian gum. Persian gum exhibits acceptable durability against wetting and drying cycles, demonstrating initial dry and wet uniaxial compressive strengths (after immersion in water) for Firoozkooh and Hormuz sands treated with Persian gum, which were initially 2200 and 200, 2250 and 240 kPa, respectively. After undergoing 10 wetting and drying cycles, these strengths decreased to 750 and 110, 600 and 80 kPa, respectively, and will maintain this resistance in subsequent cycles.

In recent years, in order to improve the functional properties of asphalt binder, researchers have turned to modify asphalt binder using various materials such as chemicals, polymers, nanomaterials, etc. Rutting is one of the most important and common failures that occur in asphalt pavement. In order to investigate the effect of additives on rutting failure, two types of modifiers including gilsonite (natural mineral bitumen) and high dense polyethylene (HDPE) have been used in this study. For this purpose, pure bitumen 85/100, with three amounts of 4, 8, and 12 percent by weight of bitumen with gilsonite and three amounts of 2, 4, and 6 percent by weight of bitumen with HDPE, has been mixed with a high shear mixer. By conducting a dynamic shear rheometer (DSR) test at 4 temperatures of 58, 64, 70 and 76 degrees Celsius, the effect of additives on asphalt rutting behavior has been investigated. Based on the DSR test results, it can be said that the short-term aging of modified asphalt binder has a significant effect on the amount of rutting based on the G*/sinδ parameter. The results show that the lowest amount of rutting parameter (G*/sinδ) at temperatures of 58, 64, 70 and 76 degrees Celsius in pre-aging conditions is related to asphalt binder modified with 4% HDPE. But among the aged samples, the asphalt binder sample containing 6% HDPE had better rutting behavior. The rutting behavior of asphalt binder modified with gilsonite also shows that with the increase of gilsonite percentage up to 12%, the rutting resistance rate of bitumen has also increased and its effectiveness is more significant in aged samples.

Today, surface treatments have become extensively popular for pavement maintenance and repair around the globe. A major environmental problem of the present age is the ever-increasing generation of construction wastes (CWs). Application of recycled CW in pavements can contribute to preservation of non-renewable materials while reducing the environmental problems. The present research seeks to investigate possible usage of recycled waste travertine stone powder (RWTSP) as an alternative to mineral filler (MF) in thin-layer surface treatment mixtures (slurry sill). For this purpose, wet cohesion test, wet abrasion test, loaded wheel – displacement test, and loaded wheel – sand cohesion test were performed on mixtures in which the MF was replaced by the RWTSP at 0, 25, 75, and 100 wt.% (by total weight of filler). Then, FESEM-EDS, XRF, and FTIR analyses were performed to check for the particle geometry and surface analysis, chemical composition, identification of organic compounds and their structures, chemical bonds, and recognition of functional groups and their molecular structure. Results showed that the mixture containing RWTSP at 100 wt.% with a residual bitumen content of 9% provided for improved wet cohesion, abrasion, and vertical and lateral displacements by about 27.2, 24, 28, and 20%, respectively. Indeed, thanks to irregular particle geometry with uneven and rough surfaces coupled with higher contents of CaO and SiO2, the RWTSP filler replacement enhances the performance of the thin-layer surface treatment.

In this article, one of the solutions to reduce greenhouse gases in block concrete pavements, i.e. the use of recycled materials investigated. concrete pavers blocks containing micro silica gel, fly ash, macro and micro polymer fibers, as well as reclaimed asphalt pavement (RAP) were made and in terms of compressive strength, bending resistance, durability against periods of freezing and thaw, skid resistance by the British pendulum method and wear resistance, by wide wheel abrasion method, were tested. The results showed that micro silica gel has the greatest effect in improving the compressive strength of the samples. The result of the flexural strength test was that micro silica gel increase the flexural strength by nearly 20%. Although polymeric fibers did not affect improving the compressive strength, they improved the modulus of rupture by about 5%. Meanwhile, two other materials, i.e. fly ash and RAP were not able significantly increase the flexural strength. The evaluation of the results of the durability test showed that the presence of three-tenths volume percent of macro polymeric twisted fibers preserves the compressive strength before and after 50 cycles of freezing and thawing. overall, the comparison of the ratio of the compressive strength of the samples after freezing and thawing to the strength of the samples before the test showed that the use of high percentages of micro silica gel, fly ash and macro polymer fibers is more than RAP and fibers and Micro polymers affect improving durability. The results of the abrasion and sliding resistance test also showed that different types of polymer fibers were more effective in improving the skid resistance of the samples. The test of abrasion resistance with wide wheel abrasion method also showed that micro silica gel plays a more effective role in keeping the surface of the sample blocks unified

The signaling system as one of the main components of the railway network, has a decisive role in the capacity of the lines and the headway of the trains as two major indicators in evaluating the performance and safety of the railway networks. The dynamic safety distance in the moving block signaling system and its adjustment based on the position and speed of trains is a suitable approach to optimally use the capacity of railway network lines and reduce the headway of trains. In this article using the fuzzy Petri net, a model of block in the railway signaling system and the simultaneous dispatch of several trains in a fixed block has been presented. In fact, by using the fuzzy Petri net, a moving block structure is considered next to the existing fixed block. For this purpose, a decision is made by defining control variables and fuzzy membership functions for them and defining fuzzy rules, taking into account the safety requirements regarding the permission or lack of permission for the follower train to enter a block. The main innovation of this method is to provide the possibility of benefiting from the benefits of the moving block system without the need to change the previous system and as a result increase the reliability compared to the moving block. From the results of this method, we can mention the increase of network capacity and reduction of headway train.

In this study, mechanical properties of roller compacted concrete pavement (RCCP) containing metakaolin (MK) with or without polypropylene fibers (PP) are experimentally and analytically investigated. For this purpose, sixteen different mixes were designed and tested in the lab. The effect of using polypropylene fibers in 0, 0.05, 0.1 and 0.2 percent of cement volume with metakaolin powder in 0, 7.5, 15 and 22.5 percent of cement weight was investigated. Compressive strength, tensile strength and water absorption were evaluated. The results showed that the highest compressive strength occurs in the combination of 0.1% of PP and 15% of MK that increases the compressive strength of 7 and 28 days respectively, by 51% and 25% compared to the reference sample. The tensile strength using the above combination increased 42%, which is the highest increase in the tensile strength. With using of 0.1% of PP and 22.5% of MK, maximum decrease in water absorption was observed by 11% compared to the reference sample. In this research, analytical formulas predicted properties of the RCCP and estimated optimal combination of the PP and MK.