Sharif Digital Repository

The ever increasing usage of modified binders in road construction requires that the effect of different modifiers on the performance characteristics of the asphalt binder be determined through laboratory testing. The current Superpave protocol for performance grading asphalt binders has proven to be insufficient to properly characterize modified binders, thus researchers have searched for other testing methods to complement or possibly replace some of the Superpave tests. Most notable are the time sweep test for fatigue resistance, the multiple stress creep and recovery test (MSCR) for rutting resistance and the direct tension test (DTT) for low temperature cracking characteristics. In the... 

Liquefaction of gases is one of the applications of cryogenic science. Among the gases, Helium has the lowest boiling point, which at a pressure of 1atm is approximately 4.2K. Liquid helium can be used to cool superconductors in transportation equipment, military radars, and medical imaging equipment. For helium liquefaction, various cycles are used; these cycles have different parameters in their structure such as of input mass fraction to expanders, heat exchanger effectiveness, expander arrangement and ... which their analysis for improving the performance of the cycle is important. In this research, the aim is to study 2, 3 and 4 expander cycle with various parameters and structure. For... 

Estimation of demand, for example, for transportation is an important issue for the planning and programming of various systems. Thus, enhancing the predictability power of such models is of high value. Demand stems from choices of individuals, and choice is subject to uncertainty and fuzziness. Uncertainty comes from many factors including incomplete information of decision-maker, and fuzziness comes from many other factors including personal perception regarding the value of the variables affecting choice. This study tries to introduce a new approach in building choice models, in which variables are transformed into another variable by the help of a global wisdom. This wisdom shows the... 

As the crowded cities require public transportation and because of lack of space on the ground, Subway and boring underground tunnels encountered. In this thesis the interaction of boring the line 7 of Tehran metro with the existing station of line 1 of Tehran metro (Molavi station) is studied. By changing the soil specification, The surface settlement is significant so the soil specification is one of the important parameters of the interaction. For comparinf the effect of these parameters, the soil settlement and bending moments is investigated in different parts of station while the lower tunnel is passing beneath it. The 3D Abaqus software is used for modeling this interaction. In... 

In Persian language, there are some special uncertainties and complexities regarding the extraction of phonemes due to its flexible structure. In this work, we try to solve two problems caused by this issue, homographs disambiguation and Ezafe recognition in Persian text to speech systems.
In this work, two methods are presented for solving the two problems. The first one is a pattern recognition method based on Aho-Corasick algorithm that has the best performance according to the execution time. The second method is a hidden Markov model tagger based on Viterbi algorithm that uses bigram and trigram statistics. These methods are run on 10 million word corpus and the results are compared... 

Airplanes usually experience minor position change and height loss during cruise flight, but under normal circumstances the aircraft total energy is adequately acceptable to maintain the trajectory and the desired performance without severe oscillations. On the other hand, if the airplane encounters a wind-shear or microburst during take-off or landing phases, it would be a dangerous situation, as the aircraft kinetic and potential energy levels are not as high.
In this research, a model predictive controller is designed and investigated to allow a transport category aircraft to either escape or penetrate the microburst. In this regard, initially a DMC controller is designed for 6-DoF... 

This investigative study intends to identify and characterize bitumen from seven Iranian bitumen production plants according to the Superpave Performance Grading (PG) system, conventional classic tests, and chemical separation tests. The study then compares the identified performance grades with the thirteen performance-grade binders required for specific climatic zones in Iran. It is observed that the variety of available binders is not adequate to fully cover the required PGs. Blending was initially considered as a suitable and economic method for production of the missing performance grades. However due to similar rheological properties of bitumen samples, resulting in nearly identical... 

Rutting is a primary cause of premature deterioration of asphalt pavements and modifying asphalt binders is a common way to improve binder characteristics and field performance. Two types of parameters are used to characterize asphalt rutting. One type includes binder parameters such as zero-shear viscosity and the Superpave rutting resistance index (G*/sinδ) derived from oscillatory loading tests such as the dynamic shear rheometer. The other type is derived from static and repeated loading creep tests on mixtures and binders. Researchers have pointed out that these parameters can rank modified binder and mixture rut susceptibility differently. In this study the rutting resistance of... 

Bitumen ageing is one of the principal factors causing the deterioration of asphalt pavements. Ageing is a complex process that is affected by different parameters.With the rapid growth of modified binders in road paving applications over the past twodecades, it is important to study the ageing properties of these binders. A number of laboratory methods are used tosimulatethe bitumenageing at various stages of the production and service of hot mix asphalt.Recent studies have shown that Superpave testing protocol does not fully address the ageing of modified binders. To study the ageing properties of modified binders, three different types of binder modifiers, plastomer, elastomer, and ground... 

Warm mix asphalt has received considerable attention over the past decade particularly due to its potential environmental benefit such as lower energy consumption and emission, its ability to be placed at lower ambient temperatures making it a suitable material for areas with short construction season. There are three warm mix asphalt (WMA) techniques are available; organic additive, foaming, and chemical additive. This study examined Sasobit, a micro crystalline wax which is an organic additive. The concentrations tested were 1.5, 2.5 and 3.5 percent of the base binder. A PG 64-22 asphalt binder from an Iranian refinery (Tehran refinery) was used as the base binder. Superpave binder... 

The deleterious effect of moisture on the structural integrity of asphalt mixtures has been recognized as one of the main causes of early deterioration of asphalt pavements. This phenomenon, usually referred to as moisture damage, is defined as the progressive loss of structural integrity of the mixture. Moisture damage is associated with the development of different physical, mechanical and chemical processes occurring within the microstructure of the mixture at different intensities and rates. Although there have been important advancements in identifying and characterizing this phenomenon, there is still a lack of understanding of the damage mechanisms occurring at the... 

With a surge in consumption of modified binders in recent years, different methods have been used to evaluate the properties of modified binders with relative success. None of these methods are able to fulfill all the requirements for evaluation and intrerpretation of the physical, chemical and rheologocal properties of modified binders. Since rheological master curves can present a mechanical interpretation of the binders in a wide range of times and temperatures, in conjunction with other evaluation metheods, they are considered a promising means of evaluating the suitability of modified bindrers. The available master curve models do not possess the sufficient diversity for this purpose.... 

Pavement preventive maintenance methods such as slurry seals are cost-effective treatments that enhance pavement longevity. Incorporation of recycled materials such as reclaimed asphalt pavement (RAP) into asphalt pavements helps further reduce costs and energy consumption. Because the use of emulsions and pavement preventive methods is uncommon in Iran, there is little experience with the technology in this area. The present study designed and developed slurry seal and emulsion test devices at Sharif University lab to study the feasibility of incorporation of RAP into slurry seal mixtures while respecting the limits specified by the ISSA and ASTM. Two slurry seal mixtures in which cement... 

The objective of this study was to develop an approach for incorporating techniques used to interpret and evaluate deflection data for network-level pavement management system applications. Because it disrupts traffic flow, is a potential safety problem and because of the expense of data collection and analysis, structural capacity is not currently evaluated at the network level by many agencies. A national pavement management system is being developed in Iran and the use of falling weight deflectometers (FWDs) at the network level was deemed necessary to compensate for the lack of vital construction history data in the pavement inventory. It was imperative to increase the interval between... 

In this study performance of tack coat (thin layer bonding asphalt concrete layers) was evaluated. The shear strength of tack coat layer was considered as its measure of performance. Direct shear tests were conducted on two layered HMA specimens. The test variables included the type of tack coat material, application rate (amount of residual bitumen per unit area), substrate condition, normal stress and shear loading rate. Four types of liquid asphalt (CSS, CRS, modified CRS and MC-250) were applied as tack coat. Three substrates conditions were used in the tests. These were 3-days old, 17-days old and long term aged substrates were used. It was found that optimum application rate depends... 

Tack coat is a layer of asphaltic materials, which is used for binding the surface layer to the current asphalt layer. The appropriate interlayer bonding condition will help different layers form a monolithic structure to resist traffic. The lack of proper interlayer bonding result in slippage between pavement layers, decrease the capability for transferring the load to the underlying layers, rutting, crescent cracking and decreasing the life of the Overlay. This study intends to model a pavement system in three dimensions with ABAQUS software in order to evaluate the amount of shear stress at the interface of asphalt layers. In order to prove the validity of the model, the results of the... 

One of the major challenges in construction of rubber modified asphalt mixtures is determination of mixing and compaction temperature (MCT). In order to estimate MCT according to Superpave volumetric mix design procedure, a temperature-viscosity relationship for the binder should be developed using ASTM D2493. This approach provides reasonable temperatures for unmodified binders which are Newtonian fluids at high temperatures and their viscosity is independent of shear rate. However, this method often yields excessively high temperatures for modified binders which exhibit non-Newtonian pseudoplastic behavior. The reason is that viscosity of modified binders depend on not only temperature but...