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Moisture susceptibility is one of the most important distresses that affects the life of the flexible pavement. Various methods, such as adding the appropriate additive, have been proposed to improve the asphalt mix properties. Some of these additives have environmental, and some have economic characteristics. In this study, three additives were used to study the moisture susceptibility and rutting of Hot Mix Asphalt (HMA), including rubber powder (RP), Tire Reclaim (TR10), and Butyl Reclaimed (BR120). For this purpose, the Marshall Stability test, Marshall Ratio (for determining the rutting), and Indirect Tensile Strength (ITS) were performed on the samples. Also, the economic analysis of the additive's effects on HMA was evaluated. The results of the Marshall test showed that adding all three additives increased the Marshall Stability and the Marshall ratio. As a result, adding TR10 and BR120 improved the Marshall ratio or rutting more than rubber powder. Indirect tensile strength test results also showed that the addition of rubber powder and TR10 led to improved HMA performance against moisture susceptibility. However, the use of BR120 as an additive reduced HMA moisture susceptibility. On the other hand, the economic analysis showed that adding 20% of rubber powder and TR10 would make the project much more economical. Further, adding BR120 to the asphalt mix provided economic benefits in every percentage. Consequently, based on the presented arguments, adding 20% of rubber powder and TR10 for technical and economic reasons leads to the best result. [ABSTRACT FROM AUTHOR]

A linear elastic fracture mechanics method is proposed to investigate the fracture behavior of hot mix asphalt and warm mix asphalt; this method was used in this study to calculated the fracture toughness of hot mix asphalt and warm mix asphalt containing 3% Sasobit at low temperatures (0, - 10, and - 20 °C) and two types of bitumen (60/70 and 85/100). A semi-circular specimen with an edged crack under three-point bending load mode was used to create different loading modes, including pure mode I and pure mode II, to test the fracture toughness. The critical stress intensity factor was calculated using the critical load obtained from the failure test. The shape factor was determined from finite element analysis. The results show that hot mix asphalt has a higher fracture toughness against crack growth than the warm mix asphalt containing Sasobit. In addition, the fracture toughness of asphalt mixture with a penetration grade of 85/100 against crack growth is more than that of the mixture with a penetration grade of 60/70. The minimum fracture toughness of hot mix asphalt and warm mix asphalt occurred in pure mode I loading condition. [ABSTRACT FROM AUTHOR]

The sight distance at night is one of the most important driving safety factors. Sag vertical curves are one of the important elements of roads, which require a sufficient sight distance at night. The headlight sight distance is used for determining the length of the sag vertical curves. Presently, the parabolic curve is mainly used in symmetrical sag vertical curves. The present study aimed to propose the elliptic curve as a new alternative for the parabolic curve. An elliptic equation is developed for use in vertical curve and sight distance of the sag elliptic vertical curve in nighttime is calculated based on the characteristics of the road geometry. Results indicate that contrary to the parabolic curve, the sight distance of the elliptic curve varies depending on the vehicle location and increases as the vehicle moves forward on the curve; therefore, driver sees the end of curve in elliptic curves much earlier than parabolic curves. The results also indicate that the sight distance of the parabolic curve is more than that of the elliptic curve in the shortest length after the curve beginning (up to 8% of the curve length) while the sight distance of the elliptic curve is more than that of the parabolic curve at the rest of the curve (at least 92% of the curve length). Based on the obtained results, for S > L, the stopping sight distances of the elliptic and parabolic vertical curves are equal. [ABSTRACT FROM AUTHOR]

Vehicle related safety is the principal focus of many agencies and organizations targeting road safety issues. There are many conflicting factors contributing to safety in motor vehicle operations. Unfortunately, the lack of reliable crash data makes it extremely difficult to evaluate the crash causations associated with defective vehicles. Furthermore, clarifying the interrelationships among vehicle related factors causing accidents is very complicated when the conventional decision techniques are used. This study aims to employ a hybrid decision method based on DEMATEL (decision-making trial and evaluation laboratory) and ANP (Analytic Network Process) to construct an Influence Relations Map (IRM) as well as obtain the influential weight of vehicle-related criteria. An empirical case study is provided to demonstrate the implementation process. This paper also employs an Evidential Reasoning algorithm (so-called ER) for assessing the inter-city buses in terms of vehicle safety in order to deal with the uncertainties associated with incomplete input data. The ER improves decision making process by using a belief decision matrix and the Demspster-Shafer theory of evidence. The results and findings reveal that the braking system is the most important criterion impacting vehicle safety, followed by fuel supply and electrical systems. [ABSTRACT FROM AUTHOR]

The use of fibers and polymers in asphalt mixtures leads to improved quality, higher lifespan, and lower maintenance costs by making mechanical, physical, and chemical changes. This results in eliminating or reducing the weaknesses of mixtures in the production, implementation, and service phases. In this study, the Stone mastic asphalt mixtures with the same gradation curve, but different additives are evaluated. In the first, second, and third groups of experiments, SEBS elasto-plastomer polymer (SEBS), SEBS elasto-plastomer polymer with cellulosic fibers (SEBS-CF), and SBS elasto-plastomer polymer with cellulosic fibers (SBS-CF) were added to the mixture in various weight percentages, respectively. Also, Stone mastic asphalt mixtures without any additives (SMA-S) and SBS-modified mixtures (SBS) as the most common modifiers were considered as the control mixtures. To evaluate the designated mixtures related to moisture sensitivity, several tests including saturated marshal, indirect tensile strength, resilient modulus, and drain down tests were applied. The results showed that the designated asphalt mixtures meet the requirements for the moisture sensitivity and resilient modulus tests successfully, and it is concluded that among these samples of mixtures, 4% SEBS has the best performance compared to other mixtures; it had even better performance than the SBS mixtures, which are the most common modifiers. Therefore, this issue can be a great help considering the advantages of this polymer over other modifiers to select and use it to modify asphalt mixtures among the mixtures although SEBS-CF had a higher percentage of optimum bitumen achieved less drain down, which shows that the bitumen of these mixtures has become more behaviorally stable due to modification with polymer and fiber at the same time. [ABSTRACT FROM AUTHOR]