Samer Dessouky

Accuracy of Current Complex Modulus Selection Procedure from Vehicular Load Pulse: NCHRP Project 1-37A Mechanistic-Empirical Pavement Design Guide

The Mechanistic-Empirical Pavement Design Guide (MEPDG) uses the complex modulus to simulate the time and temperature dependency of hot-mix asphalt (HMA). To account for the time dependency of HMA, MEPDG recommends calculation of the frequency of the applied load as a function of the vehicle speed and the pavement structure. By this approach, the Odemark method of thickness equivalency is first used to transform the pavement structure into a single-layer system, and it is then assumed that the stress distribution occurs at a constant slope of 45° in the equivalent pavement structure. Concerns were raised that the current MEPDG methodology may be overestimating the frequency, which would result in underconservative distress predictions. Therefore, to evaluate the MEPDG methodology for calculation of the loading time, the results of the MEPDG procedure were compared with those of an advanced three-dimensional (3-D) finite element (FE) approach that simulates the approaching-leaving rolling wheel at a specific speed. The model developed accurately simulated actual tire rib sizes and the applicable contact pressure for each rib. In addition, laboratory-measured viscoelastic properties were incorporated into the FE model to describe the constitutive behavior of HMA. Comparison of these two methods shows that the frequencies calculated on the basis of the MEPDG procedure are greater than the ones determined by the 3-D FE method, which indicates that the loading time determined from MEPDG is not conservative. Ultimately, this would result in underestimation of the pavement response to a load and, therefore, greater errors in calibrations of the pavement response to field distress. Correction factors are thus presented to ensure the correctness of the loading time calculation in MEPDG. Adoption of the proposed factors within the MEPDG software does necessitate a recalibration of the performance models.

Asphalt Mixture for the First Asphalt Concrete Directly Fastened Track in Korea

The research has been initiated to develop the asphalt mixtures which are suitable for the surface of asphalt concrete directly fastened track (ADFT) system and evaluate the performance of the asphalt mixture. Three aggregate gradations which are upper (finer), medium, and below (coarser). The nominal maximum aggregate size of asphalt mixture was 10 mm. Asphalt mixture design was conducted at 3 percent air voids using Marshall mix design method. To make impermeable asphalt mixture surface, the laboratory permeability test was conducted for asphalt mixtures of three different aggregate gradations using asphalt mixture permeability tester. Moisture susceptibility test was conducted based on AASHTO T 283. The stripping percentage of asphalt mixtures was measured using a digital camera and analyzed based on image analysis techniques. Based on the limited research results, the finer aggregate gradation is the most suitable for asphalt mixture for ADFT system with the high TSR value and the low stripping percentage and permeable coefficient. Flow number and beam fatigue tests for finer aggregate asphalt mixture were conducted to characterize the performance of asphalt mixtures containing two modified asphalt binders: STE-10 which is styrene-butadiene-styrene (SBS) polymer and ARMA which is Crum rubber modified asphalt. The performance tests indicate that the STE-10 shows the higher rutting life and fatigue life.

New Approach to Recycling Asphalt Shingles in Hot-Mix Asphalt

AbstractThe objective of this study is to introduce a new approach to recycling asphalt shingles in asphalt paving construction in which recycled asphalt shingles (RAS) are ground to ultrafine particle sizes and blended with asphalt binder through a wet process. In the proposed wet process, the ground recycled material is blended with the binder at a high temperature prior to mixing with the aggregates. Two unmodified binders that are classified as PG 64-22 and PG 52-28 were blended with two contrasting sources of RAS at a modification content ranging from 10–40% by weight of the binder. The use of RAS modification through the proposed wet process was successful in the laboratory. Based on the results of the experimental program, the use of RAS modification through the proposed wet process would generally improve or not influence the high temperature grade of the binder, but it may reduce the low temperature grade of the binder. As demonstrated in this study, an optimum shingle content may be identified t...

Energy Harvesting from Roadways

This paper presents a preview of an ongoing study to develop an energy harvesting system based on piezoelectric elements embedded into the pavements structure. The system development involved designing and testing a number of prototypes in the laboratory under controlled stress conditions. In addition, it involved numerical modeling of the stress distribution in the power generation module and economic analysis of the value of the electric power generated, under a given traffic composition scenario. The results available to date suggest that this technology shows promise in powering LED traffic lights and wireless sensors embedded into pavement structures.

Thermal properties of asphalt mixtures modified with conductive fillers

This paper investigates the thermal properties of asphalt mixtures modified with conductive fillers used for snow melting and solar harvesting pavements. Two different mixing processes were adopted to mold asphalt mixtures, dry- and wet-mixing, and two conductive fillers were used in this study, graphite and carbon black. The thermal conductivity was compared to investigate the effects of asphalt mixture preparing methods, the quantity, and the distribution of conductive filler on thermal properties. The combination of conductive filler with carbon fiber in asphalt mixture was evaluated. Also, rheological properties of modified asphalt binders with conductive fillers were measured using dynamic shear rheometer and bending beam rheometer at grade-specific temperatures. Based on rheological testing, the conductive fillers improve rutting resistance and decrease thermal cracking resistance. Thermal testing indicated that graphite and carbon black improve the thermal properties of asphalt mixes and the combined conductive fillers are more effective than the single filler.

Low-Temperature Characterization of Foamed Warm-Mix Asphalt Produced by Water Injection

This study evaluated the low-temperature performance of foamed warmmix asphalt (WMA) produced by water injection and compared it with that of hot-mix asphalt (HMA). Two asphalt binders (PG 70–22 and PG 64–28), two aggregate types (limestone and crushed gravel), and two aggregate gradations [nominal maximum aggregate size (NMAS)] (12.5-mm NMAS and 19.0-mm NMAS) were used in this study. The low-temperature properties of the asphalt binders were measured with the bending beam rheometer, and the low-temperature behavior of the asphalt mixtures was evaluated with the thermal stress restrained specimen test after being subjected to short-term and long-term aging. As expected, the fracture temperatures obtained for the short-term aged specimens were lower than those obtained for the long-term aged specimens. This was the case for both foamed WMA and HMA mixtures. The HMA mixtures exhibited colder fracture temperatures than did the foamed WMA mixtures for the short-term aged specimens, but fracture temperatures comparable to those for the long-term aged specimens. This comparison suggests that the traditional HMA mixtures may have better resistance to low-temperature cracking than foamed WMA does during the initial service life of the asphalt layer, but may have similar resistance to low-temperature cracking at later stages. This study also showed that the low-temperature binder grade had the most significant effect on fracture temperature, whereas the aggregate type had the most significant effect on fracture stress.

Laboratory Evaluation of the Workability and Compactability of Asphaltic Materials prior to Road Construction

AbstractAsphalt mix compaction is dependent on many factors, particularly gradation, asphalt grade and content, aggregate size, temperature, and compactor manufacturer. The new development in polymer-modified asphalt has a major impact on asphalt pavement compaction in the field. Although it leads to improving overall mechanical characteristics, there are concerns that mixes become drier and more difficult to compact. This paper aims to develop compaction indices using the Superpave gyratory compactor to evaluate the workability and compactability of the mixes during the routine mix design process and prior to laydown operations. Workability is reflected in the ease of blending the mix components using construction equipment. Compactability is reflected in the mixes’ stability and resistance to densification under traffic loading. To identify adequate thresholds for the compactability indices, performance testing is required to validate the long-term behavior of these mixes. This was accomplished in two p...

Simulation of snow melting pavement performance using measured thermal properties of graphite-modified asphalt mixture

Chemical melting agents are traditional methods for snow-removing applications. Due to their adverse environmental impact, thermo-snow melting pavements with conductive fillers are becoming frequently used. In this study, the thermo-physical properties of graphite-modified asphalt mixtures (GMAM) and the sensitivity of snow melting pavements were investigated. The microstructure of GMAM was analysed at extremely high magnification to observe the distribution of conductive fillers in the mixture. Two different mixing processes were adopted to mould asphalt mixtures: dry mixing and wet mixing. The conductivity was compared to evaluate the effects of asphalt mixture preparing methods and the quantity of graphite on the thermal properties of GMAM. A one-dimensional finite difference analysis was performed to determine the efficiency of GMAM for snow melting processes. Microstructure analysis was conducted on scanning election microscope (SEM) images of the fractured surface of specimens. Thermal testing and analysis results indicated that graphite improves the conductivity of asphalt mixtures and shortens the time required for snow melting. The numerical analysis results showed that environmental factors have significant effects on pavement surface temperature, and adjusting the heat source temperature can substitute the changes in environmental conditions. According to the micro-analysis, graphite particles form clusters throughout the asphalt mixture.

Full-depth flexible pavement responses to different truck tyre geometry configurations

Pavement stresses and strain responses due to tyre loading are essential data for design and performance analysis. The magnitude and distribution of these responses are primarily affected by the tyres configuration geometry. This study investigates the longitudinal strain responses at the bottom of a hot-mix asphalt layer for full-depth medium-volume flexible pavement under different truck tyres design. Pavement testing was carried out with a user-control accelerated pavement facility at various speeds and tyre inflation pressures and loading. Three truck tyre configurations: dual-tyre (11R22.5) and two wide-base tyres (425/65R22.5 and 455/55R22.5) widely used in the truck industry were examined. A 3D finite element model was developed to quantify surface stresses to loading at various critical locations in the pavement after being calibrated with the field-measured strains. Field measurements showed that the 455 wide-base tyres yield 7% more longitudinal strain than a dual-tyre assembly at the same tyre pressure.

Harvesting thermoelectric energy from asphalt pavements

The goal of this study was to develop a prototype for harvesting thermoelectric energy from asphalt pavement roadways. This emerging research field encompasses technologies that capture the existing thermal energy in pavements to generate electricity without depleting natural resources. In lower latitudes, such as south Texas, the asphalt pavement surface temperature in the summer can reach 55°C because of solar radiation. Soil temperatures below the pavement, however, are roughly constant (i.e., 27°C to 33°C) at relatively shallow depths (150 mm). This thermal gradient between the surface temperature and the pavement substrata can be used to generate electrical power through thermoelectric generators (TEGs). The proposed prototype collects heat energy from the pavement surface and transfers the energy to a TEG embedded in the subgrade at the edge of the pavement shoulder. Evaluation of this prototype was carried out through finite element analysis, laboratory testing, and field experiments. The results suggest that the 64- × 64-mm TEG prototype can generate an average of 10 mW of electric power continuously over a period of 8 h in the weather conditions in south Texas. Scaling up this prototype by using multiple TEG units could generate sufficient electricity to sustainably power low-watt LED lights and roadway and traffic sensors in off-grid, remote areas.