Sharif Digital Repository

Crumb rubber, produced from shredding of scrap or refused tires, is one of the most commonly used modifiers of asphalt. Asphalt rubber, in addition to mitigating some of the environmental problems of disposing scrap tire, improves the flexural strength of pavement, extends the life of pavement and reduces the maintenance costs. The properties of asphalt rubber are highly dependent on the type and composition of base asphalt, type and amount of crumb rubber, and the production method.The goal of this research is to investigate the performance properties of asphalt rubbers produced from Iranian asphalt and crumb rubber, using an industrially feasible method. The Superpave testing procedure was... 

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... 

Although there are several popular and standardized mix design methods for hot-mix asphalt, there is no universally accepted mix design method for cold in-place recycling (CIR). The varieties of recycling machinery, materials, quality control limitations, etc. have contributed to this problem. Most of CIR laboratory mix designs are based on 4-inch molds and maximum aggregate size of 1inch. The use of single unit train, which is the most common machinery used for CIR, results in poor control of aggregate gradation, especially when distresses such as fatigue cracking exist. This may lead to presence of aggregate sizes larger than 1 inch. In this case the use of 4-in mold is no longer... 

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... 

Porous Asphalt or Porous Friction Courses (PFCs) are mainly recommended as surface drainage layers on rainy runway pavements and roads with medium traffic. Characteristic features of porous asphalt mixes are improved permeability, skid resistance and sound attenuation. The purpose of this research is to evaluate the effect of mixture parameters such as binder content, amount of modifier and aggregate gradation on the performance and durability of the porous mixtures. In this research ground tire rubber was used as the modifier. Mechanical properties of these mixes were assessed by determining stone-on-stone condition, Marshall stability, unaged abrasion loss, and aged abrasion loss tests.... 

Binder modification, to improve the rheological properties and meet the standard requirements, is a common practice. The modification is usually done by adding polymers like Ethylene Vinyl Acetate (EVA) and Styrene Butadiene Styrene (SBS), waste materials like crumb rubber, or acids like Poly phosphoric acid (PPA) or by air blowing techniques. High temperature rheological properties of modified binders are usually improved by using polymers while the low temperature rheological properties mostly depend on the original binder. Therefore, the rheological properties at low temperatures do not show clear improvements in the modified binder compared to the original binder. This indicates that a... 

Asphalt concrete is a composite mixture of three phases; aggregate, bitumen and air void. Stress and strain distributions obtained from macroscopic modeling yield different results due to distinctly different mechanical properties of the above-mentioned phases. In this study a more exact analysis of the stress and strain, were carried out by considering the mixture as a two-phase composite; aggregate and mastic phases. Asphalt concrete was considered a composite material consisted of sand mastic and aggregate. Aggregate and mastic phases were separated and response of the loaded asphalt mixture was investigated. Aggregates finer than 2.36 mm in diameter, filler and bitumen consist 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... 

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... 

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... 

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... 

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... 

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... 

Open graded asphalt mixturesareasphaltic mixes used in flexible pavements and the mainadvantages of them are increased permeability and noise reduction. Conventional application of these mixtures in flexible pavement is like that fluids infiltrate into porous asphalt layer that places over a dense graded asphalt layer and then draintoward ditches along the two sides of the road. Another usage of these mixtures, considered in recent years, is in porous pavements that the structure permits water on the surface topass freely through it and to infiltrateinto thesubsoil. In this research, second application of open graded asphalt mixtures is considered, i.e., porous asphalt pavement. In this type... 

Form and angularity of aggregates are two important shape characteristics that have a significant effect on the performance of hot-mix asphalt. The first step toward the study of the effect of these characteristics on pavement performance is their proper measurement. Current test methods used in practice have several limitations in measuring these characteristics. In this thesis, a method based on image processing called “Sharif Aggregate Imaging System (SHAMS)” has been introduced which is capable of directly measuring aggregate dimensions and determining angularity index for aggregates classification. Calculated results related to the form and angularity of aggregates measured by SHAMS... 

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... 

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... 

Hydrated lime has been used as an anti-stripping agent with acceptable performance. Numorous studies have been conducted to evaluate hydrated lime as an anti-stripping agent, however effect of hydrated lime on performance properties of asphalt mixture has not been fully addressed. In the present study, the effect of hydrated lime was investigated. In this study, three methods of adding hydrated lime were evaluated. These methods consist of a) adding dry hydrated lime to dry aggregates, b) adding hydrated lime to the binder to form mastic, and c) adding slurry lime to dry aggregates.
More uniform distribution of hydrated lime on aggregate surface in the slurry method improved performance... 

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...