The Superpave mix design system integrates material selection and mix design into procedures based on the project's climate and design traffic. Superpave uses a completely new system for testing, specifying, and selecting asphalt binders. While no new aggregate tests were developed, current methods for selecting and specifying aggregates were refined and incorporated into the Superpave mix design system. Performance testing uses new equipment and procedures to ensure that Superpave mixtures exhibit acceptable amounts of the distress types considered by Strategic Highway Research Program (SHRP) researchers: permanent deformation, fatigue cracking, and low temperature cracking. Moisture damage is weakens the adhesiveness and cohesiveness of the Asphalt Concrete (AC) due to the following attributes: (1) The material properties of the aggregate in terms of mineralogy, external compounds, moisture content, and surface roughness. (2) The material properties of the binder in terms of permeability and chemical composition. (3) The mixture properties in term of void structure, aggregate gradation, and binder content. (4) Additional causes such as environmental conditions, traffic volume and loads, pavement design, and construction practices (Sebaaly 2007). Surface Free Energy (SFE) is a method to evaluate asphalt concrete’s susceptibility to moisture damage. Liquid anti-strip agents and chemical lime additives have been used to reduce the susceptibility of the asphalt concrete to moisture damage. Chemical, wax or other organic additives, and foaming technologies obtained by means of special bitumen modifiers, represent a promising technical solution to reduce the temperatures required for warm mixtures asphalt production and pavement construction. Nanotechnology has the potential to create many new materials and devices with wide-ranging purposes. Nanomaterials are generally important modifiers in improving pavement performance, nanoclay, carbon nano tubes, nanosilica, nano-hydrated lime, nano-sized plastic powders, or polymerized powders, and nano fibers.

This research focused on predicting the performance of modified asphalt mixtures with high contents of nano-silica fume (NSF) using AASHTOWare Pavement ME Design software, which is the production version of the Mechanistic-Empirical Pavement Design Guide (MEPDG). The NSF was completely mixed with the virgin asphalt using a high-shear mixer at 160 °C and a speed of 2000 rpm for 1 hr. The physical- rheological properties of the control binder, as well as the binders modified with 30, 40, and 50% NSF by asphalt weight, were determined. The asphalt mixtures were prepared using control and NSF-modified binders by the conventional Marshall method. The predicted field pavement performance of both the control and NSF-modified asphalt mixtures in terms of rutting, longitudinal cracking, alligator fatigue cracking at three different climatic locations in Egypt (Aswan, Cairo, and Alexandria), and three design speeds (10, 55, and 95 kph) was evaluated. The simulations indicated that the NSF-modified mixtures outperformed the control mixture.

 prepared using modified asphalt binders with various contents of nano-silica fume (NSF). The modification to virgin bitumen is done by shear mixing with NSF at low contents (2, 4, 6, and 8%) and high contents (20, 30, 40, and 50%) with bitumen weight. The homogeneity of the modified asphalts was assessed using Scanning Electron Microscopy. The rotational viscosity, softening point, and penetration tests were used to evaluate the rheological-physical properties of the modified asphalt binders. The stiffness, moisture damage, rutting, and fatigue of the hot mixes prepared with NSF-modified binders were evaluated using Marshall, indirect tensile strength, and double punching tests. The results showed a significant improvement in the rheological-physical properties of the modified binders with high content compared to low content of NSF. Therefore, the modified binders with 30%, 40%, and 50% of NSF were selected to prepare NSF-modified mixtures. The results showed that asphalt mixtures incorporating 30, 40, and 50% NSF-modified binders were more resistant to moisture damage, rutting, and fatigue cracking compared to the control mixture. The novelty in this research is to produce a modified asphalt mixture with two-thirds a quantity of bitumen while achieving a high performance compared to the control mixture

This paper aims to evaluate the possibility of using nanosilica fume as an economic and a viable alternative to high-cost nanomaterials as a prelude to the large-scale use of nanomaterials in the pavement. Therefore, nanosilica fume (NSF), as an industrial waste material, was employed at low contents (2, 4, 6, and 8%) and high contents (20, 30, 40, and 50%) by asphalt weight as modifying additives to asphalt binder. The chemically prepared nanosilica (NS), as a high-cost nanomaterial, was employed at the contents of 2, 4, and 6% by asphalt weight for comparison purposes. Transmission electronic microscopy was used for scanning the nanostructure particles, and scanning electron microscopy was utilized to assess the homogeneity of modified binders. Changes in the chemical bonds of the modified asphalts were investigated using Fourier transform infrared spectroscopy. The modified binder's physical–rheological properties, temperature susceptibility, aging effect, and economic benefit were investigated. Prediction models were utilized to estimate the rutting parameter (G*/sinδ) for the modified asphalts. The results revealed that significant improvements in physical–rheological properties, temperature susceptibility, and rutting resistance of the modified asphalt with high contents of NSF were attained. It was found that the NSF additive significantly decreased the short aging acceleration compared to NS. Predictive equations with high correlation have been inferred to correlate NSF content with both the rutting parameter and the rotational viscosity of the modified asphalt, thus enabling the designer to select the appropriate NSF content to achieve specified binder characteristics in the mix to serve pavement performance conditions.

Construction of twin tunnels in crowded urban cities compels the designer to select a suitable configuration and the associated railway alignment. Therefore, the estimation of optimum clear distance between tunnels, then vertical and horizontal curves of rails is significant for twin tunnel projects to obtain the optimum design of tunnels, safety and passenger comfort. A case study is the Greater Cairo metro line No. 4, Phase 1. The configuration of twin tunnels includes vertical, horizontal and diagonal alignment. Two cases for diagonal alignment, one of them tunnels pass under the River Nile. Also, two cases for horizontal alignment, one of them tunnels running above bottom clayey soil. Proper clear distance between twin tunnels has been identified according to internal forces and displacement in tunnels. Vertical and horizontal displacements have been presented for twin tunnels and for the surrounding soil. Moreover, induced internal forces in tunnel lining have been computed. Two-dimensional numerical models are employed by using PLAXIS program to perform the analysis. Also, the procedures of construction of the twin tunnels have been discussed. Based on the calculated result, the clear distance between tunnels has a major effect on soil movement and internal forces in tunnel lining. It shows that the construction procedure affects the soil displacement and internal forces. Construction of the bottom tunnel at first reduces bending moment in top tunnel lining and results in small changes in bending moment in the bottom tunnel lining after the construction of top tunnel. On the other hand, the results have also shown the influence of twin tunnel configuration on railway track alignment.

The deformation within soils is commonly observed to concentrate in narrow zones called shear bands. In the recent years, the localization of strain in geomaterials has been the subject of extensive research. Localization is a physical phenomenon in which the nearly homogenous deformation of the body is abruptly changed into a highly concentrated deformation mode, usually in the form of a single or multiple narrow shear bands. Strain localization is a very significant phenomenon because it is likely to correspond to the actual types of failure in geomechanical engineering practice. The Critical State Models in soil mechanics are widely used in many geotechnical applications involving numerical predictions of stability and deformation behavior of soils such as clay, silty clay and sandy clay. The present work aims to develop these models with a simple, efficient and reliable technique to accurately predict the deformation field, stress distribution, strain softening and shear band formation in soil structures, especially the stability of slopes for the different boundary value problems. Firstly, an attempt is made to review the loading criteria, flow rule and hardening rule in plasticity. Critical State Models have been converted into convenient forms for use in the finite element analysis. An attempt has been made to generalize the Critical State Model in perfectly plastic and strain hardening associative and non-associative flow rule. The hardening behavior of the clay soil always has a higher load-carrying capacity than perfectly plastic behavior. The collapse in both perfectly plastic, strain hardening associative and non-associative flow rule is of approximately the same value. Secondly, the Critical State Model, with additional softening non-associative flow rule has been discussed. This considers the beginning and development of shear bands. The structural softening begins at the ultimate load. The necessary condition for the beginning of localization depends on current values of the stress components. The material softening is related to the reduction of the cohesion and friction angle from the peak to residual values, based on the second invariant of the deviatoric plastic strain. According to this approach, strain softening is interpreted in the constitutive model as a particular type of elastic-plastic behavior with negative hardening. An application of the Critical State strain localization softening model to slopes has been presented. The results of this study show that a numerical analysis accounting for the effects of softening can provide an estimation of the non linear effects. It should be observed, however, that the possible use of this procedure for the assessment of stability of actual slopes would require a more refined characterization of the mechanical parameters. In fact, the gradual concentration of strains into shear bands, which governs the development of failure, is strongly influenced, even by minor local variation of mechanical parameters, such as the residual friction angle or the parameter governing the rate of loss of the mechanical resistance. Key words: Elasto-plastic Critical State Model, perfectly plastic, isotropic strain hardening, associative and non-associative flow rule, strain localization.

A study of the structural behavior of rigid pavement jointed slabs and the effect of the different parameters such as soil support, slab thickness and the number and diameter of dowel bars for jointed slabs on their behavior is considered one of the complex subjects which does not have satisfactory solution yet.

In the past some empirical and semi-empirical expressions were used for design purpose. At present, the analysis using the finite element method makes an assumption for the dowel bars; that the dowels transmit shear force only between the connected slabs. Thus there is shortcomings in studying the real behaviour of the jointed slabs and the efficiency of the dowel bars in transmitting the loads.

In the present study, the finite element method is used for the analysis considering the slab to be divided into plate elements resting on winkler foundation. Each element has six degrees of freedom at each node and the dowel was considered as a three dimensional beam element continuous and embedded in the slabs.

A finite-element programme was developed for studying the structural behaviour of jointed concrete pavement slabs under the effect of vertical and horizontal loads. The computer programme deals with the cases of partial contact between the slabs and the soil by iterative technique. The presented method is based on the classical theory of thin plates on Winkler foundation.

The slabs considered in this research were square of twelve feet length, some of them were joined by dowel bars in transverse direction and the others were isolated (separated). The structural behaviour of rigid slabs under the effect of some parameters such as : Modulus of subgrade reaction (k),  thickness of slab (H),  dowel bars diameter (D) and number of dowel bars (N). Were investigated and better understanding of structural behaviour was reached. This study presents also some important recommendations for rigid pavement design purposes

In this article, we deal with enhancing the accuracy of the sampling instant of micro phasor measurement units ( μ PMUs) used in distribution grids. The pulse per second (PPS) signal of the global positioning system (GPS) synchronizes the start of each second of all μ PMUs in the grid. The internal clock of each μ PMUs then takes over and determines the sampling instants till the next PPS. Due to the inaccuracy and drift of the clock and the unavoidably needed fractional count of the clock pulses, accumulation of error leads to excessive phase error. A lightweight algorithm is proposed for the correction of the sampling period. The algorithm fine-tunes the timer count used to determine the sampling instant. As the proposed algorithm aims at correcting the sampling instant, it can be applied by any other platform, but it needs an accurate time reference like that of the 1 PPS of the GPS. The performance evaluation shows that the maximum phase error is lower than the accepted phase error by about two orders of magnitude. The theoretical results are confirmed by implementing the algorithm on a prototype μ PMU.