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Currently, Egypt is using the [AASHTO, 1993. Guide for design of pavement structures. Washington, DC: American Association of State Highway and Transportation Officials] guide for the flexible pavement structural design. In this method the resilient modulus (MR) of the unbound granular base/subbase materials and subgrade soils is a measure of material stiffness used for characterisation. It is considered one of the major factors affecting the pavement layerthicknesses. However, in Egypt, California Bearing Ratio (CBR) is the main strength parameter used for characterisation of the unbound materials and subgrade soils due to its availability and simplicity. In this research, a comprehensive experimental testing programme was conducted on different unbound granular base/subbase materials typically used in pavement construction projects in Egypt. The testing programme includes MR, CBR, and basic material properties. The effect of aggregate gradation on MR is investigated. A model predicting MR as a function of the basic material properties is proposed. The MR–CBR relationship adopted in the current Egyptian Code of Practice is verified based on the testing results. The experimental data warranted the calibration of the current model. The calibrated model has reasonable goodness of fit statistics and yields rational MR estimates for the local materials. [ABSTRACT FROM AUTHOR]

International Roughness Index (IRI) is a pavement performance indicator which reflects not only the pavement condition but also the ride quality and comfort level of road users. The aim of this paper is to develop an accurate IRI prediction model for flexible pavements using both multiple linear regression analysis and artificial neural networks (ANNs). The models were developed based on the Long-Term Pavement Performance Database. The data were collected for both original and overlaid flexible pavements from the general pavement studies (GPS-1, GPS-2 and GPS-6) and the specific pavement studies (SPS-1, SPS-3 and SPS-5). The final database consisted of 506 sections with 2439 observations. The proposed models (regression and ANNs) predict IRI as a function of pavement age, initial IRI (IRI just after pavement construction), transverse cracks, alligator cracks and standard deviation of the rut depth. The regression model yielded a coefficient of determination (R2) value of 0.57 while the ANNs model resulted in a much higher R2 value of 0.75. [ABSTRACT FROM AUTHOR]

This paper mainly aims at investigating the effect of using multi-wall carbon nanotubes (MWCNTs) as an additive on the rheological properties of asphalt. Pristine (P-MWCNTs) were mixed at 120 °C with control asphalt at contents of 0.5%, 1.0%, 2.0% and 3.0% by asphalt weight. The empirical and rheological properties (using the Superpave testing) of the control and modified asphalts were evaluated at different aging conditions. The rheological properties of the modified asphalts were found to improve with increasing the percentage of P-MWCNTs. The high failure temperature and rutting resistance of both unaged and rolling thin film oven aged (RTFO) modified asphalts increased with increasing P-MWCNTs percentage and became suitable for the Egyptian climatic conditions as required by the Superpave binder characterization. At a given temperature, the fatigue cracking resistance and low temperature cracking resistance decreased with increasing P-MWCNTs percentage. [ABSTRACT FROM AUTHOR]

Highlights: [•] NCHRP1-37A yielded better E * values compared to NCHRP 1-40D model at all binder characterization input levels. [•] NCHRP1-37A E * model with Level 3 binder characterization produced the most accurate and the least biased estimates. [•] Because of the hot desert climate in KSA, care should be taken when using such models for E * predictions. [Copyright &y& Elsevier]

The newly Mechanistic-Empirical Pavement Design Guide (MEPDG) allows engineers to design pavement structural layers to sustain predefined limits of distress levels due to traffic loads and environmental conditions based on nationally/locally calibrated performance models. Users are required to input variables related to traffic, environment, and materials. In addition, reliability and limiting values of the distresses are required inputs. MEPDG in its current version is an analysis procedure rather than a design tool. However, it is intended to be also used as a design tool. Thus, the design process of the pavement structure in MEPDG is a trial process. It starts with assuming a structure and material properties and then performing the analysis. If the proposed trail did not meet the criteria, then the material properties and/or layer(s) thicknesses are changed until the design meets the criteria. This paper presents a reference document to assist pavement designers in identifying the most important MEPDG key inputs to modify such that the predicted distresses meet predefined design criteria. Results showed that, pavement structural design should be coupled with the mix design and selection of material properties in order to achieve an economic design complying with the criteria. [ABSTRACT FROM AUTHOR]

Flexible pavement structure design is a complex task because of the variability of design input parameters and complex failure mechanisms. Therefore, the aim of this study is to develop and implement a simplified Mechanistic-Empirical (M-E) pavement design method based on the 1993 American Association of State Highway and Transportation Officials (AASHTO), the National Cooperative Highway Research Program (NCHRP) 9-22, and NCHRP 1-37A and 1-40D projects. This simplified methodology is implemented into a computer code and a user-friendly software called "ME-PAVE". In this methodology, only two equivalent temperatures, as per the NCHRP 9-22 project, are estimated to adjust the dynamic modulus of the asphalt layer(s) for Asphalt Concrete (AC) rutting and AC fatigue cracking prediction instead of using the hourly climatic data, as in the AASHTOWare Pavement ME. In ME-PAVE, the structural responses at critical locations in the pavement structure are determined by a Finite Element Module (FEM), which is verified by a Multi-layer Elastic Analysis (MLEA) program. To ensure that the simplified methodology is practical and accurate, the incorporated transfer functions in the proposed simplified methodology are calibrated based on the Long-Term Pavement Performance (LTPP) data. Based on statistical analyses, the built-in FEM results exhibit very similar trends to those yielded by MLEA, with a coefficient of determination, R2 of 1.0. For all practical purposes, the proposed methodology, despite all simplifications, yields acceptable prediction accuracy with R2 of 0.317 for the rut depth compared to the current practices, NCHRP 1-37A and 1-40D (R2 = 0.399 and 0.577, respectively); while the prediction accuracy for fatigue cracking with R2 of 0.382 is comparable to the NCHRP 1-40D with R2 of 0.275. Nonetheless, the standard error for both distresses is in good agreement based on the investigated data and the developed methodology. Finally, the conducted sensitivity analysis demonstrate that the proposed methodology produces rational pavement performance. [ABSTRACT FROM AUTHOR]