Mahmoud Ameri

Developing a model for estimation of polished stone value (PSV) of road surface aggregates based on petrographic parameters

Micro-texture of road aggregates wears away under traffic action in the course of time and gets polished. Aggregates resistance to polishing and their ability to maintain the micro-texture are measured in the laboratory by polished stone value (PSV). The standard test method for measuring PSV is costly and time consuming. In this study, efforts have been made to develop a model for estimation of PSV. For this purpose, 20 quarries used in road pavements were selected and placed under polishing, physical and mechanical tests. Also, by carrying out the petrographic analysis on thin sections of the rocks, efforts were made to convert the petrographic properties to quantitative variables and use them in inferential modelling. Modelling results showed that PSV can be significantly affected by aggregate hardness and also PSV can be estimated by combination of petrographic parameters.

Laboratory investigation of moisture susceptibility of warm-mix asphalt mixtures containing steel slag aggregates

A number of completed or ongoing studies on warm-mix asphalt (WMA) and steel slag (SS) asphalt mixtures have been conducted all over the world. Moisture damage is one of the major concerns for both WMA and SS asphalt mixtures. This paper presents the results of a laboratory study aimed at verifying moisture susceptibility of WMA mixtures containing SS aggregates. The physical, chemical, and mechanical properties of aggregates and binders were evaluated to identify their effects on moisture susceptibility of asphalt mixtures. The moisture susceptibility of the asphalt mixtures was also evaluated by four different methods, including Marshall Stability Ratio, Resilient Modulus Ratio, Tensile Strength Ratio and Fracture Energy Ratio. The results generally indicated that use of coarse SS aggregate in WMA mixtures enhances the resistance of asphalt mixtures to moisture damage. Hence, use of steel slag aggregate in production of WMA mixture is recommended.

Effect of nanoclay on performance of neat and SBS-modified bitumen and HMA

ABSTRACT The aim of this research was to investigate impact of nanoclay on rutting and moisture damages resistance of neat and SBS-modified asphalt binder and mixture. 4% SBS was blended with 2% nanoclay and 6% nanoclay was used and compared with neat and 4% SBS-modified asphalt binder and mixes. Results of performing rotational viscosity, dynamic shear rheometer, repeated creep recovery, indirect tensile strength, and dynamic creep tests indicated nanoclay has positive impact on rutting and moisture damages resistance of neat and modified asphalt binder.

Evaluation and Performance of Hydrated Lime and Limestone Powder in Porous Asphalt

ABSTRACT Porous asphalt mixture or Open Graded Friction Course (OGFC) has many benefits that resulted in its extensive use and development. OGFC improves the friction of a wet pavement, surface reflection, traffic noise, wet weather driving conditions by allowing the water to drain through its porous structure and reduces the hydroplaning, the splashing and spraying of water in the air (acts as spray reducing surfaces). For achieving the advantages mentioned above, this mixture must have big Voids in Total Mix (VTM). The big VTM reduces durability of the paving mixtures and prone them to raveling. The use of hydrated lime in porous asphalt is an accepted practice for many highway agencies in order to increase mixture strength as well as to improve durability of asphalt pavements. The goal of this study is to evaluate the mechanical properties of lime treated OGFC before and after multiple cycles of freeze-thaw moisture conditioning and also to show that hydrated lime improves stability and durability of the mixture more than limestone powder.

Properties of asphalt modified with devulcanized polyethylene terephthalate

ABSTRACT The objective of this research is to investigate the effectiveness of the devulcanized polyethylene terephthalate in enhancing the performance characteristics of modified asphalt binders. The physical and rheological behavior of four binder samples were investigated using the penetration, softening point, storage stability, rotational viscometer, and dynamic shear rheometer tests. The polymer tends to decrease penetration and increase softening point, viscosity, and permanent deformation resistance of modified binders in comparison with base asphalt binders. However, this processed polymer could not be considered storage stable blend at high temperatures.

Viscoelastic fatigue resistance of asphalt binders modified with crumb rubber and styrene butadiene polymer

ABSTRACT In the present research study, the fatigue behavior of modified asphalt with crumb rubber (CR) and styrene-butadiene-styrene (SBS) are investigated. Each of these additives was mixed with a 85–100 neat bitumen at two different dosages. The time sweep test was used to investigate the viscoelastic fatigue properties of asphalt binders in terms of energy dissipation. Linear amplitude sweep tests were conducted to study the fatigue life of asphalt binders under varying loads based on the concepts of viscoelastic continuum damage mechanics. Results showed that adding CR and SBS can enhance the fatigue resistance of modified asphalts based on the energy approach and viscoelastic continuum damage analysis.

A Phenomenological Fatigue Performance Model of Asphalt Mixtures Based on Fracture Energy Density

In this study the fatigue performance of asphalt mixtures was interpreted based on fracture energy density. Recent studies indicate that the fracture energy from indirect tension tests correlates with the field performance of asphalt concrete. The fracture energy density was obtained from indirect tensile strength tests, and the fatigue performance of asphalt mixtures was evaluated with four-point bending beam fatigue tests implemented at three different strain levels. Two different asphalt mixtures with varying binder contents were tested during this study. Test results showed that the fracture energy density could be an appropriate material property in phenomenological fatigue models. Thus a phenomenological fatigue model based on fracture energy density is presented, and this approach could be advantageous because a simple fatigue model based on fracture energy density does not require time-consuming fatigue tests. For comparison purposes, the various types of fatigue models were evaluated, and fatigue models based on fracture energy density and dissipated energy showed rather high prediction accuracy. In general, fatigue models based on the energy concept have the least dependence on material properties and can predict the fatigue lives of asphalt mixtures without changing coefficients.

Evaluation and comparison of flow number calculation methods

The objective of this research study is to evaluate and compare several methods to be used in calculating the onset of tertiary flow (referred to as flow number (FN) parameter) for asphalt mixtures. The FN indicates the onset of shear deformation in asphalt mixtures, which is a significant parameter in evaluating rutting in the field; however, its variability has limited its implementation. The FN is obtained from the repeated load permanent deformation laboratory test. To evaluate and compare the methods, permanent deformation data from tests performed on 12 mixtures were analysed in terms of within- and between-sample variability and their ability to determine whether a tertiary stage was reached or not. The results showed that for modified and unmodified asphalt mixtures the Francken model has lowest variability and may be used as the final method for calculating FN.

Effects of nanoclay on hot mix asphalt performance

ABSTRACT The purpose of this study was to evaluate of nanoclay effects as an additive on performance of asphalt mixtures. Two types of montmorillonite nanoclay, namely CA and CB, were used at concentrations of 2%, 4%, and 6%. Marshall, indirect tensile strength, resilient modulus, and dynamic creep tests were performed to investigate the effect of additives on moisture susceptibility, structural response, and rutting resistance. The results showed improvement of the asphalt mixture performance by adding nanoclay with respect to all tests. According to the results, samples containing nanoclay CA have better performance in comparison with the samples containing CB.

Finite Element Analysis of a New Test Specimen for Investigating Mixed Mode Cracks in Asphalt Overlays

Cracking is a common mode of deterioration in asphalt pavements. In general, cracks in the asphalt pavements experience a combination of opening and sliding deformation due to thermal and traffic loads. In this research, a new test specimen called ASCB is proposed for mixed mode I/II fracture toughness study of asphalt materials. The ASCB specimen is a semi-circular specimen containing a crack normal to the specimen edge and subjected to asymmetric three-point bend loading. Simple geometry and convenience of testing set up are two primary advantages of the ASCB specimen. In addition, the disc shape of specimen facilitates its preparation using the conventional gyratory compactor machines or using the asphalt field coring devices. The stress intensity factors (K I and K II) are fundamental parameters in order to characterize the load bearing capacity of asphalt failure due to brittle fracture or fatigue crack growth. Hence, in this paper the stress intensity factors of the ASCB specimen are calculated from several finite element analyses and for different mixed mode loading conditions. The numerical results show that the complete mode mixities ranging from pure mode I (opening mode) to pure mode II (in-plane sliding) can be achieved from the ASCB specimen by changing the loading support positions relative to the crack plane. It is also shown that the suggested laboratory specimen is also very suitable for simulating the stress and deformation fields of real cracked pavements which are subjected to the loads induced by the wheels of the moving vehicles.