Sharif Digital Repository

Today convolutional neural networks (CNN) are very popular due to their high accuracy and robustness. As the size and complexity of CNNs grow, the demand for larger on-chip memories also increases. Given that off-chip access memory has a high cost, one solution is to enlarge on-chip caches by employing emerging multi-level Cell (MLC) STT-RAMs. This memory provides higher capacity at the cost of lower reliability. The root cause of low reliability of MLC STT-RAM is failure of read and write operations. However, MLC STT-RAM and CNNs are perfect matches in the sense that in one hand MLC STT-RAM provides higher capacity, on the other hand CNN can tolerates moderate level of inaccuracy and low... 

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... 

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... 

Asphalt binders are known to exhibit an inherent ability to repair damage. Such selfhealing potentially affects the fatigue damage performance of bituminous materials. There is no consensus about the effect of aging and polymer modification on cohesive healing. Also, the effectiveness of rejuvenating agents have not been addressed in previous studies. In the current study, three healing indices are presented to precisely quantify the healing capacity of various binders. These indices have been defined using the damage characteristic curves derived from interrupted linear amplitude sweep (LAS) tests. Instantaneous healing (IH) describes immediate reduction in accumulated damage after the rest... 

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... 

Recycled materials have been very much taken into consideration in recent years due to economic issues and the preservation of natural resources. Warm Mix Asphalt (WMA) is also of particular importance due to less energy use in construction and environmental compatibility. This study examines the compressive workability and resistance to low temperature crackings of warm mixt asphalt containing reclaimed asphalt pavement (up to 30% by weight of aggregate). Sasobit was used as an organic additive in 1.5% by weight of bitumen in warm mix asphalt. Two additives of crumb rubber modifiers (9, 15 and 18% by weight of bitumen) and hydrated lime (1.5 and 2% by weight of aggregate) were also used to... 

Master curves describe the behavior of asphalt binders over a wide range of temperatures and loading frequencies which are utilized by various predictive models in design and analysis procedure of asphalt mixtures. Frequency sweep test is extensively used for construction of master curves within the temperature range of 4 ̊C to 82◦̊C and frequency range of 0.01 to 30 Hz. There is a concern that master curves are unable to accurately represent the low temperature (below 4 C) behavior of binders. In this study a new cyclic loading pattern for the bending beam rheometer (BBR) test was utilized to conduct the low temperature tests and generate an isotherm compliance curve for incorporating the... 

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... 

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... 

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... 

Preventive maintenance strategies have been considered by highway agencies in order to increase pavement service life and to reduce the costs associated with pavement maintenance. Due to the increasing concern regarding promoting sustainable pavements, consideration of the environmental, economic and performance factors in devising preventive maintenance strategies is of great importance.This study contributes to developing a multicriteria decision-making tool for sustainability evaluation of pavement preventive maintenance strategies. The developed tool, PaveSAT, considers the greenhouse gas emission, net present value, and pavement performance to rank preventive maintenance schemes using... 

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... 

Utilization of RAP in HMA reduces the initial costs, conserves natural sources and avoids disposal problems. Aged binder from RAP will have some effects on resultant binder. To date, solvent extraction and recovery is the only method that physically separates the RAP binder from the RAP aggregate for characterization. Time consuming for recovery, altering the physical properties of the recovered asphalt binder like binder hardening and the possibility that Asphalt binder is not completely extracted from the aggregate are the weak points of this method. Addressing the need for non-solvent based RAP binder characterization; procedures for low temperature characterization of RAP binder... 

Asphalt concrete exhibits viscoelastic and viscoplastic behavior which is dependent on rate and temperature. To model this behavior, various mechanical modelshave been presented in which total strain, as the response of the applied stress, is decomposed by various researchers to recoverable and permanent strains.Accumulation and expansion of permanent response result in rutting which is a dominant and prevalent distress in hot mixed asphalt (HMA) in hot climates. The available models are not capable of accurately calculate the viscoplastic strain under cyclic loading.
To close this gap, recovered viscoelastic strain at rest (unloading) period was introduced. This parameter accounted for... 

Increased environmental concerns and high oil prices have encouraged highway agencies to maximize the use of recycled materials like Reclaimed Asphalt Pavements (RAP) in pavement construction. However, utilization of RAP has limited to low percentage, generally less than 25%. This is due aged, stiffer, and less strain tolerant asphalt binder in RAP. As the RAP proportion increases, a large amount of the aged binder will be introduced into the mixture. The excessive stiffness of HMA mixture tends to lead to less workable mixture. Studies were conducted to examine the effect of Sasobit on the workablility of high RAP mixtures. The results indicated while the utilization of Sasobit had improved... 

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.... 

Composite nature of asphalt mixtures necessitates a micromechanical scheme which depends on distinctive characteristics of various constitutive phases. In this regard, discrete element method was utilized to predict the creep behavior of asphalt mixtures and strain response in primary, secondary and tertiary stages. In this research, a modified mixture modeling procedure was considered to better simulate permanent deformation response of asphalt mixtures under creep loading. A random distribution of mastic and aggregate particles with respect to a typical dense gradation was implemented to reconstruct cylindrical specimens. A bonding model represented the cohesion effect in mastic...