Sharif Digital Repository

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... 

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... 

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... 

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... 

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... 

Low temperature cracking is the most important type of asphalt pavement distress that occurs in cold climates. Up until the development of performance grading (PG) based binder specification, there was no irect indication of low temperature suitability of asphalt binders. PG specification was mainly developed for and validated by neat binders.
With increased use of modified asphalt binders in recent years, some of the limitations and shortcomings of the original PG specifications have surfaced.Considering that low temperature cracking is a fracture failure, it was hypothesized that tests based on the fracture mechanics and fracture energy parameter can lead to better classification of... 

It is widely recognized today that excess moisture in pavement layers, when combined with heavy truck traffic and moisture-susceptible materials, can reduce the service life. Temperatures below freezing can also contribute to durability problems of saturated materials. A major objective in pavement design is to keep the base, subbase, subgrade, and other susceptible paving materials from becoming saturated or even being exposed to constant high moisture levels over time. The use of subsurface drainage has gained popularity over the past two decades, and many pavement agencies now routinely specify drainable pavement structures to reduce moisture-related problems in avements. In this... 

Early failure of pavement is one of the most important problems. As the research conclusions in Iran, Non-conformancity is the most important cause of this problem.Quality management system, Audits and expert systems are the solutions. This research provides an Audit system for quality management system of batch-type asphalt plants as the preliminary solution.A state survey conducted and useful part of state programs had been considered. After developing software, The system functionality has been tested  

Fatigue is one of the most common failure modes that reduce the structural integrity of asphalt pavements. Dynamic tests are used as fatigue performance indicators for asphalt mixture. However, these tests are expensive and require special equipment and set up. At this research, the main goal is to develop a fuzzy model which is more efficient than the existing regression model for prediction of the fatigue life. A database from the available data from various research was compiled. For each model, a comparison between Fuzzy and regression output by actual outputs was done and it was seen that the fuzzy modeling can predict fatigue life very closely. Finally, the required software for this... 

Accurate prediction of pavement performance is essential to a pavement infrastructure management system. Selection of the prediction model is based on the extent of available data, assumptions used in performance modeling, ease of use and management purposes. Therefore, two methods were proposed in this thesis based on the assumptions of availability and unavailibility of accurate data. The first method presents a two-stage model to classify and accurately predict the performance of a pavement infrastructure system. Sections with similar characteristics are classified into groups using a support vector classifier (SVC). Then, a recurrent neural network (RNN) is utilized to predict... 

Modification by crumb rubber is a useful means of improving the resistance of asphalt binders and mixtures against rutting, fatigue cracking, and low temperature cracking. Increase binder viscosity and decrease stability at high temperatures are accompanied by most modifiers, and crumb rubber is no exception. Recent research efforts have shown that development of cross bonds across polymer chains and sulfur can improve the storage stability of modified binders. Also, WMA additives can considerably decrease the binder viscosity. This research showed that addition of small amount of sulfur during the crumb rubber modification can improve the workability and storage stability of this binder.... 

Asphalt concrete is a heterogeneous and multi-phase material that consists of aggregates, asphalt binder, and pores. These components create a complex microstructure. There is no consensus on how to quantify the microstructure and the required parameters from two-dimensional images. The load transfer can be managed by aggregate-aggregate or aggregate-mastic interactions that depend on the gradation, aggregate internal structure, and asphalt binder viscoelastic properties. The most important internal structure indices affecting the behavior of HMA are aggregate orientation, contact orientation, contact length, and number of contact points. In this research, the influence of aggregate...