مجله مهندسی زیر ساخت های حمل و نقل
پیاپی 3 (پاییز 1394)

The large volumes of coal usage, and the low efficiency of the coal washing plants in Iran; induced a high percentage of refused coal in the production process, deposited as waste. Destructive environmental impacts stem from waste discharges into the natural environment, if it could be possible to replace this residue as a partial replacement of cement in order to produce concrete, damaging effects of this residue would be reduced. In this research, after pulverizing and conveying the grain size of regulation range of Coal Waste (CW) (of Mazandaran Central Alborz Washing Plant); this waste was replaced with 5, 10, 20 and 30 wt.% of cement in Roller Compacted Concrete Pavement (RCCP) mixture. Mechanical properties (compressive and tensile strength) of RCCP mixtures containing blended cement (composition of cement and Coal Waste Powder (CWP)) at the curing periods of 7, 28 and 90 days were investigated. Results show that 5% CWP replacement, will improve the strength properties of concrete mixtures up to 90 days, but declined compressive and tensile strengths was observed for RCCP mixture with CWP replacement content of 10% and 20% at different ages. Also, by increasing the percentage of CWP replacement, Ve-be time of mixture was declined.

In previous studies on the use of steel slag in asphalt mixtures, no comparison has been made between different types of slags produced in steel factories in Iran. In this research, in order to evaluate the mechanical properties of asphalt mixtures containing different amounts of steel slag and to compare their effects on mixture behaviors, two types of slags – BOF and EAF – were replaced with 25, 50, 75 and 100 percent of coarse part of aggregates. After characterization of limestone aggregates and steel slags using X-ray fluorescence equipment (XRF) and scanning electron microscope (SEM), Marshall mix design method was used to determine the optimum bitumen content. Moreover, the mechanical properties of mixtures using resilient modulus testing at different temperatures and indirect tensile strength testing in both dry and saturated conditions were evaluated. The results showed that the use of steel slag in asphalt mixtures could result in a significant improvement of asphalt mixture properties. Furthermore, moisture sensitivity of mixtures containing steel slags was less than the control mixture.

The static modulus of elasticity from the load-settlement line of a second load cycle in a plate load test (PLT), Ev2, is a key parameter to control embankment bearing capacity, settlement and track quality in general. Because of the greater sensitivity in bearing capacity and settlement of high speed understructure, more strict limitations in this issue should be concerned in high speed rail codes so as each individual layer of fill should satisfy a special amount of Ev2. The PLT, as a test to determine Ev2, is expensive and time consuming. But, tests like Light Weight Deflectometer (LWD) that determines the dynamic modulus of elasticity could be economically more efficient. In this study, field data from several PLT and LWD tests, which have been performed over different layers of embankment in the Qom-Isfahan high speed railway, were analyzed. Then, linear and non-linear regression methods were used to extract the best-fit equations among the results. Similary, the relationship between these field data and laboratory tests of California bearing ratio was extracted. Furthermore, back-calculation was used to determine the static and dynamic elastic moduli of each layer individually.

Construction, maintenance and rehabilitation of highway infrastructures are the most essential issues for developing and improving a sustainable transportation industry. Besides high costs of these issues, improper performance of some aspects such as safety and security creates some problems which will threaten the reliability of a transportation system. Crash prediction models (CPMs), as safety analysis tools, have a specific role in analyzing the contributing factors in occurrence of traffic accidents. This study aimed to evaluate the effects of pavement distresses on the frequency of run-off-road accidents which are the most frequent and severe accidents in Iran and around the world. In doing so, about 150 km of Semnan-Tehran divided rural highway was examined and its pavement condition indice (PCI) was calculated. Then, using GENMOD and NLMIXED procedures in SAS software, two generalized linear models and 39 nonlinear negative binomial regression models were developed. After evaluating the goodness-of-fit of the models and estimating their error, comparison of these models leads to the most proper model. To estimate the goodness-of-fit of the models and select the best-fitted model, several criteria were implemented including standard deviation/scaled deviation, Pearson χ2, -2LL, AIC, AICc and BIC. Moreover, two criteria of mean absolute error and root mean squared error were used to estimate the validity of model results. In analyzing of residuals by standardized residuals method, the mean error was about -0.1048 and the variance was 0.9259, which are close to the assumptions of zero mean and variance equal to 1. CPMs showed that nonlinear negative binomial regression model fits significantly better with the available data, which demonstrates the association between PCI and frequency of run-off-road accidents. Sensitivity analysis of the model indicates that for nonlinear CPM, a unit increase in PCI results in around 1.93% reduction in frequency of run-off-road accidents.

Nowadays, warm mix asphalt (WMA) technology is known as an efficient way to reduce costs of asphalt production, fuel consumption and environmental pollution. In contrast to its numerous advantages, stripping phenomenon comes as a disadvantage for this industry. One way of improving the resistance of asphalt concrete and adhesion between bitumen and aggregates is to use chemical and organic additives. Zycotherm, as a nano-chemical additive, plays a bilateral part: as an anti-stripping agent and as an additive for the production of WMA. To better understand the phenomenon of stripping as a result of weak adhesion, several mechanisms have been used to describe the adhesion between the components of asphalt mixture. Since adhesion between two different phases depends on mechanical and chemical reactions, molecular attraction and theory of free surface energy, the mechanisms controlling adhesion failure between the components of asphalt mixture are complicated. The main objective of this laboratory study is to evaluate the effect of aggregate type on functional properties of WMA modified with a nano-chemical additive, named Zycotherm,  as a warm mix and anti-strip agent in terms of water susceptibility tests according to the newest national and international codes such as modified Lottman test and boiling water test. To do this, indirect tensile test was also carried out. Image processing of boiling water test and analyzing the results of water susceptibility tests showed that on one side, Zycotherm had a poor performance as a warm mix additive on both limestone and silica materials; but on the other side, had a remarkable effect on improving resistance to moisture damage of silica materials.

Since the proper performance of infrastructures requires a careful design, an accurate evaluation of key parameters by using new methods is of particular importance. In design process of soil structures and transportation systems, as a part of the most important technical buildings and substructures, which provide essential services for humans, it is very important to have a more accurate assessment and prediction of soil behavior, especially under dynamic load conditions. Dynamic properties of soils, including shear modulus and damping ratio, are crucial parameters to both fundamental understanding of dynamic behavior and modeling of these materials. Reliable and accurate dynamic properties of soils are necessary for the solution of many soil dynamic problems or soil-structure interaction. Up to now, the dynamic properties of soils have become the scope of many studies in the field of geotechnical earthquake engineering, using various laboratory methods. In this study, two models were developed for evaluation of shear modulus and damping ratio of cohesive soils using group method of data handling (GMDH). Validation of these models was carried out using centrifuge tests results. A parametric analysis was carried out to evaluate the sensitivity of the proposed models to variation of the influential parameters. Finally, the proposed models were compared to available relationships and charts. Results indicated that GMDH-based models could provide more accurate predictions of dynamic properties of cohesive soils, than those obtained by using previous studies.

Seismic performance evaluation of bridges requires the use of natural recorded ground motions or artificially produced records to be used in non-linear time history analysis. Due to the complexity related to energy dissipation characteristics of bridges and dynamic characteristics of earthquakes, the quality and adequacy of inelastic dynamic analysis results are highly dependent on the universality of selected seismic records, numerical modeling of the bridge, and material behavior. These factors unveil the need to consider appropriate criteria in earthquake records selection and to assess the damage potential to connect seismic loading and structural response more than ever. Based on the seismic-response studies of bridge piers, it is well known that among the other factors, the earthquake frequency content increases structural damage. Hence, in this paper, earthquake frequency content is considered as the main factor which affects inelastic response of reinforced concrete (RC) bridge piers. Different methods are presented to determine the earthquake frequency content, and the best method is selected to determine the frequency content. Using the selected method, the frequency content of seven selected records was determined based on the respective index. The influence of this index was also examined on seismic performance of RC bridge piers as well as formation process of plastic hinges. The results showed that due to different characteristics of earthquakes, plastic hinge patterns, which are derived from seismic excitation, indicate the changes among earthquake records. Results also showed that an earthquake with high frequency content causes extended length of plastic hinges at the base of the piers. For earthquakes which have been scaled to the same peak ground acceleration, low frequency content forms long plastic hinges.