فصلنامه مهندسی حمل و نقل
سال چهارم شماره 1 (پیاپی 13، پاییز 1391)

Moisture is one of the most important causes of asphalt stripping. The removal of moisture effect on hot mixed asphalts is a major problem in pavement engineering. One solution to reduce this problem is using different kinds of additives during mixture procedure. Portland cement can be used as a substitute of filler in hot mixed asphalt. In this paper, results of a research program conducted to evaluate the effect of cement in reducing the moisture sensitivity of asphalt are presented.The experiments of this research are designed to assess the effect of long term humidity conditioning on hot mixed asphalt. Results indicate that the effect of cement in reducing the water susceptibility of asphalt strength is time dependent and anti-stripping effects in early stages after mixture are not considerable. Results also reveal that cement has a suitable long term moisture sensitivity reducing effect which can be attributed to the time dependence of chemical reactions.

Experimental research was concluded to the fact that resilient modulus is the best parameter to illustrate structural strength of unbound pavement materials. Resilient modulus was used to be determined by expensive and complex cyclic triaxial test and obtained by dividing the deviator stress by pure elastic strain. Thus use of simple tests that do not require complex equipment and are performed by site technicians, has been used as an appropriate alternative in these years. One of the methods for determining the strength properties of pavement layers used in recent years is DCP test. This device is simple and inexpensive and evaluates the structural strength of unbound pavement layers in a relatively short period of time. This method is rarely used in Iran and there is no enough knowledge about it. In this research, the DCP device and test methods have been introduced.The CBR and cyclic triaxial test were performed along DCP and the correlation between the results were presented. Thus all three tests were conducted on 15 subgrade samples and after analysis it was concluded that there is a good correlation between results, especially those of DCP and resilient modulus.

Cold in place recycling is one of the widely used rehabilitation techniques in different countries. Although many research works have been carried out on these mixes, no universally accepted mix-design method has been proposed for cold-mix recycling. In this research, two mix design methods, namely modified Marshall Method and a proposed mix design method were verified on specific cold mixes. Bulk specific gravity and air voids determination are used in Modified Marshall Method and Indirect Tensile Strength (dry and soaked), Marshall Stability and Tensile Strength Ratio (TSR) were used in the proposed mix design method. Also, two types of active fillers, namely cement and lime, have been substituted with part of the mix filler as the stabilizing agents. The results showed that there are some ambiguities in Modified Marshall method. Results also indicated that with the proposed mix design method, the optimum bitumen emulsion content was lower than the case of modified Marshall Method. However, ITS and Marshall Stability values in proposed method show enhanced properties of the mixes that were designed using the Modified Marshall method.

The lateral stability of the railway track is one of the most important parameters that must be considered during operations. In the life time of railway track, the different lateral forces are applied on it. These forces are perpendicular to the main axis of the track and caused by the lateral component of the lateral frictional forces between wheels and rails, the applied lateral force from the edge of the wheel to the rails and rail buckling due to the variation of axial force of the rail. During the applying of the lateral force to the track, many factors such as rails, sleepers, ballast and fasteners will prevent the lateral deformation of track. In order to prevent the undesired lateral deformation of the track and also reduce the high maintenance costs, the lateral stiffness of the track should be increased.In this field investigation, the frictional concrete sleeper was first introduced and then lateral stiffness was studied through the panel displacement method of railway track of an actual curve with a radius of 250 meters by using the simple mono-block concrete sleepers and frictional concrete sleepers.Results show that the lateral stiffness of railway track increases approximately by 179% using frictional concrete sleepers instead of standard mono- block concrete sleepers. According to the field test results, in order to increase the lateral stiffness and thus reduce the lateral deformation, the frictional concrete sleepers can be used instead normal mono- block concrete sleepers.

Prediction of the fatigue life of asphaltic concrete is required for design and management of pavements. The prediction of the fatigue life of asphaltic concrete using Artificial Neural Network has been investigated in this research. Sufficient experimental data containing fatigue test conducted on asphaltic concrete over a wide range of conditions was needed for modeling. Therefore, reviewing the literature, the results of the fatigue tests on Kansas State asphalt mixtures were found to be appropriate for this research. The parameters of asphalt viscosity, strain level, stiffness of mixture, asphalt content, air voids content and gradation were selected as input variables, while the fatigue life was set as the only output variable. Progressive multilayer perceptron Artificial Neural Network modeling has been used for prediction of the fatigue life, with back propagation training algorithm and numerical optimization technique of Levenberg-Marquardt. Modeling was performed using the neural network tool box and programming in MATLAB, and the results have been compared. It is shown that the programming, can better predict the fatigue life than directly utilizing the tool box. It is also found that Artificial Neural Network can predict the fatigue life of the asphaltic concrete than the regression equation.

In this study the economic factors affecting road accidents are investigated through the environmental Kuznets hypothesis (EKC) framework. Based on the hypothesis, the road mortality rate increases in the early stages of economic growth and ultimately because of technical progress, increase in the related investments, and improve in medical care, the road mortality rate decreases as the economic growth increases.Therefore, in this study the relationship between road mortality and economic growth is analyzed in econometric methods framework, OLS, for the time period 1971-2009. Results obtained from this study show that there is a relationship between economic growth and traffic fatalities, so that traffic fatalities have increased along with economic growth till reaching to a critical point, and after that will reduce. In other words, the same relation to the Kuznets inverted U- is shaped for traffic fatalities and per capita GDP relation for Iran.The other results obtained in this study indicate that there is a negative relationship between traffic fatalities with investment in transport infrastructure, improvement of health care and cultural indicators, and also a positive relationship with the number of vehicles per capita rate.

Due to high expenditures, maintenance of road networks has always been one of the main concerns of pavement engineers. Effective use of Nano materials in industry, was a good reason for authors to study the capability of these kinds of materials in order to increase the service life of asphalt pavements.Considering the fact that applying Nano clay in polymers, modifies polymers characteristics e.g. stiffness, tensile strength, thermal stability, increasing flash point and resistance against moisture and vapor, also as bitumen is a thermoplastic material, the bitumen was modified by adding 20% nano clay and tested for increasing the fatigue life of asphalt pavements. The effect of nano clay additive on performance of flexible pavements is investigated through the repeated constant stress, in indirect tensile test for the core samples prepared by conventional mix and asphalt mixed with 2% of nano clay in four stress levels from 200 – 500 KPa (Steps of 100). The primary results indicated that nano core samples have almost double or even more fatigue lives in most of stress levels with less variability than conventional ones.

Selecting mode choices on the basis of different behavior of passengers creates selection of different modes of transportation. Since the human being as an agent selector of mode choice has a different and random behavioral characteristics, the non-probability of mathematical models, can’t completely express the human behavior at mode choices of suburban trips. The aim of this study is to import whatever more behavioral characteristics on mode choices of suburban trips and more reliability the results of models with the use of fuzzy logic in them. In this regard for the mode choices of suburban trips a nested logit model was used. In order to consider the obscure behavior of the human in this model, variables of utility functions of each nest with using fuzzy subtractive clustering algorithm have been fuzzificated. Then calibration of the model with using the method of the maximum probability has been done. The results of this model with the data from the selected cities have been compared, clarifying the process modeling is satisfactory.