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The influence of laboratory aging on Marshall stability (MS), Marshall quotient (MQ), indirect tensile strength (ITS) at 25 and 60° C, tensile strength ratio (TSR), resilient modulus (MR), modulus of rupture (MOR), cohesion, and aging index (AI) of dense graded asphalt mixes (DGAMs) containing Baiji (B) and Qayyarah (Q) Iraqi asphalt was examined. The results of DGAMs containing B and Q-asphalt showed 46% and 43%, and 37% and 24% higher MS, 132% and 99%, and 111% and 78% higher MQ, 24%, and 20%, and 14% and 10% higher ITS at 25° C, 4%, and 3% and 20%, and 13% higher ITS at 60° C, 27% and 19%, and 26% and 24% higher MOR at 0° C, and 25% and 18%, and 24% and 21% higher MOR at -10° C. For 4 and 8 d aging, TSR was 11% and 7%, and 4%, and 3% higher, MR 52% and 38%, and 38% and 24% higher, cohesion 73% and 58%, and 58% and 44% higher, and AI 1.74 and 1.58, and 1.56 and 1.44 times higher, respectively.

Buses of General Company for Passenger Transport was the primary mode for public transportation in Baghdad City. This system suffers from many problems, part of which were related to bus routes, while the other part was related to the bus and its operators. These problems have a direct effect on the users of public transport buses. The objective of this study was to assess the performance of eight public transport bus routes which they represented by the Al-Tahrir bus network and adopting the level of the transit service method. Seven transit performance measures were selected in this study, such as bus travel time, hours of service during the day, service frequency (headway), total delay on the route, running speed of the bus, bus occupancy, and capacity of the route. The results of this study showed that bus routes No. (72, 36, 13, 114, 11, 30, 37, and 9) were operating at overall Level of Transit Service LOTS (D, E, E, E, E, D, E, and E) respectively, whereas the bus network (Al-Tahrir bus network) was operating at overall LOTS (E); therefore, the performance of Al-Tahrir bus network was not acceptable, and improvements were needed to increase the level of transit service of this network.

Water causes freeze and thaw (F–T) damage on asphalt pavement, and the extent of such damage varies with the water phase. This study describes the F–T damage evolution of asphalt mixtures in differ...

Snow removal is a critical security issue in airports, where heat-pipe technology can be an environmentally friendly and efficient alternative to traditional approaches for snow removal. This study investigated the long-term thermal regime of airfield-runways equipped with a heat-pipe system, using data collected over several recent years from two full-scale snow-melting systems, one located in Beijing, and the other in Harbin, China. The findings showed that the heat-pipe system automatically increases the airfield-runway surface temperatures by up to 17 °C utilizing geothermal energy in winter for preventing icing. Surface temperature levels up to 0 °C were observed to increase by over 25% when a shallow pipe embedded depth and a longer pipe evaporation section were selected. However, the surface temperature was less affected by the diameter of the heat-pipe. Field experiments indicated that, the heat-pipe technology threshold value for the airfield-runway snow-melting performance was an ambient air temperature exceeding −10 °C. Using the heat-pipe technology, the snow-melting rate on an airfield-runway was about 3–8 mm/h within the working range, and there was therefore a decrease in the snow-cover durations. Particularly, the heat-pipe airfield-runway was always free of snow when the average ambient air temperature exceeded −4 °C. The statistical results illustrated that the heat-pipe airfield-runway snow-melting system is applicable in more than 78% of the cities in China, indicating that this technology is feasible and practical in China and can be applied in other countries.

Porous asphalt is a commonly used material for permeable pavement. However, porous asphalt will inevitably result in void structure clogging and affect its drainage function in the road service period. Most studies focus on macroscopic permeability but ignore microscopic seepage behavior in void structure, which is unfavorable for the understanding of the change in the permeability of porous asphalt. In this study, we described the microscopic water migration of the porous asphalt with the seepage depth, seepage velocity, and seepage path, and clarified the void structure evolution and the water migration characteristics variation during the clogging. On this basis, we explored the impact of the size of clogging particles and the void content of porous asphalt on the variation of water migration. The data demonstrate that water migrates and branches along the void structure of porous asphalt under the action of inertia force. The deposition of clogging particles in the void hinder the migration of water and restrict the water distributary. However, the clogging process does not affect the dominant effect of inertia force on water migration. Water migration is more impeded by small particles due to their more significant water absorption effect. The increased void content of porous asphalt can reduce the effect of clogging on the void structure. This research can help us understand the evolution of water migration characteristics at a micro-level.

Heat pipe technology has been demonstrated to melt ice and snow in airfield rigid pavement, and field observations indicate that it achieves satisfactory effects. However, the impacts of heat pipes on pavement responses are unclear. This paper compared the responses of traditional versus snow-melting airfield rigid pavement under aircraft loads, temperature loads, and their coupling effects by the means of field tests and a three-dimensional finite element (3D FE) model. The effects of types of interface contact on pavement responses were also modeled and discussed. The results show that introduction of heat pipe does not change the mechanical-induced responses of pavement. However, it significantly decreases the maximum thermal stresses by reducing the internal temperature gradient of concrete layer. Besides, the maximum principle stress induced by coupling effects of aircraft loads and extremely thermal loads decreases significantly when heat pipe is embedded. Such coupling stress is independent on the type of interface contact conditions. Overall, heat pipe can potentially postpone pavement deterioration and damage extents, such as thermal cracking and fatigue cracking.

To better understand oil modifiers’ effects on the performance of asphalt binders at low and intermediate temperatures and the mechanisms of the modification, laboratory tests including mechanical ...

This study was carried out to investigate the effect of the warm compaction modifier on the physical and rheological properties of High-viscosity High-elasticity modified asphalt and SBS modified asphalt. Three types of asphalt binder with different concentrations (at 0.3%, 0.5%, 0.8% by weight) of the warm compaction modifier were studied respectively. The influence of the warm compaction modifier on the physical and rheological properties was evaluated by penetration, softening point, and ductility and Dynamic Shear Rheometer (DSR) test. It was evident that the addition of the warm compaction modifier had a significant effect on the stiffness and elasticity behavior of the asphalt both at high and intermediate temperatures. It is indicated by DSR analysis that the warm compaction modifier could increase stiffness and fatigue behavior compared with base modified asphalt. Based on the physical and rheological tests, the concentration of warm compaction modifier was recommended to be at 0.3% by the weight of base modified asphalt.

Oils can be used as modifiers to improve low temperature performance of asphalt. However, the relationship between phase transition of oil modified asphalt and their low temperature properties still need more detailed research to reveal the effect of the transition on rheological properties. To investigate this, 9 different oils of bio-base and refined waste oils are used as modifiers in this study. During the study, Modulated Differential Scanning Calorimetry (MDSC) test is used to study the phase transition, and the Bending Beam Rheometer (BBR) test and Single Edge Notched Beam (SENB) test are used to evaluate the rheological and fracture properties of oil modified asphalts, respectively. It is found that the glass transition temperatures of oil modifiers are significantly different but are all much lower than the glass transition temperatures of asphalts. The results show that there is a good linear relationship between glass transition temperature and stiffness of asphalts, but no good correlation with the relaxation parameter (m) measured with the BBR. There is a much stronger correlation of the glass transition temperatures with the fracture properties of asphalts. Considering this strong relationship with the fracture properties, DSC test shows the potential possibility for quickly and accurately evaluating the low temperature fracture performance of asphalts. The combination of BBR and DCS can therefore be used to select the type and amount of oil modifier to meet a specific low temperature performance. The study was limited to one asphalt source and thus validation of the relationships for other asphalts is needed before generalizing the results.

Hydronic heated technology is an efficient and controllable method for airfield-runway snow removal. The heating strategy plays an important role in the application process. Nowadays, the users only consider the snow melting performance of pavement to determine the heating strategy, however the thermal stress of pavement is another considerable but missing aspect for the design of hydronic heated snow melting pavement. This paper investigated the thermal strain distribution of hydronic pavement through the digital-image-correlation and fiber Bragg grating strain sensors in a full-scale field experimental system. Thereafter, the thermal stress field of hydronic heated pavement was analyzed by a two-dimensional numerical model which contains the pavement temperature, thermal strain, and thermal stress distribution. Model validation results indicated that pavement temperature and thermal strain distribution between the experiment and the model were in good agreement. Numerical results showed that the remarkable compressive stress was observed near the hydronic pipe, and the maximum tensile stress appeared in the midpoint between two pipes at the depth of the pipes. The maximum thermal stress of pavement increased with fluid temperature but decreased with air temperature. The comparison results between the maximum thermal stress and mechanical strength of pavement show that the critical heating temperature increased with air temperature. The critical fluid temperature °C = 73 °C + 1.17 × ambient air temperature °C. The obtained results could ensure the security of hydronic heated snow-melting airfield-runway.

Compaction quality control (QC) of asphalt pavement is an important operation, which still lacks of real-time and convenient methods to achieve the controlling goals. Based on the principle of fibre Bragg grating (FBG) sensing technology and hypothesis of relationship between material stable performance and deformation property, a framework for QC of asphalt pavement compaction using FBG sensing technology was provided. Simulation laboratory experiments which included compaction and loading test of a composite rutting plate embedded FBG sensor were carried out. According to monitoring indicator found in laboratory tests, the QC method was practiced in an engineering project. Results indicate that FBG sensing technology can effectively catch rolling response information. When the value of indicator S DI obtained from the response information approaches to zero for the second time in succession, rolling pass number can ensure asphalt mixture meet compactness requirement. Results of laboratory test and data from engineering application are in good conformity. The effective compaction control distance is ±90 m from measuring point. FBG sensors embedded in asphalt pavement not only can identify the weak compacting areas on the basis of different FBG sensor response values, but also can be used for long-term monitoring of pavement structural behaviour.

It is hardly to address the mechanical behavior with the classic measurement techniques accurately, which is very important for asphalt mixture and pavement deign. To obtain more experimental information of the asphalt mixture failure processes to improve the identification procedures for this type of material, DIC technique and IDT test are employed in this study. It is found that the information obtained by DIC system is very useful to investigate the deformation and fracture propertied accurately. It is also found that the distribution of aggregate and asphalt mortar will affect the distribution of strains because the module difference between aggregate and asphalt mortar. So the appropriate length of analysis should be determined to achieve the required accuracy and increase computational efficiency; the Poisson’s ratio of asphalt mixture under 25 °C is not a constant, which is effected by load and gyratory compaction times. And because the formulas for calculating strain suggested in Chinese specification are introduced by the linear elasticity theory, and Poisson’s ratio is a constant, it is not appropriate for the calculation of horizontal deformation, especially in the larger stress conditions.

The laboratory experiment results of diatomite modified asphalt mixtures are inconsistent with the observed results of the trial road. To find the reason of this, Scanning Electron Microscope (SEM), Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (IR), Dynamic Mechanical Analysis (DMA), beam bending test, uniaxial compression test, Thermal Stress Restrained Specimen Test (TSRST) and Thermal Conductivity (TC) tests are employed to evaluate the low temperature performance of diatomite-modified asphalt mixtures and investigate the modified mechanism of diatomite. Three types of mixtures, including diatomite modified asphalt and neat asphalt, are used in this research. The analyses of test results show that Changbai and Linjiang diatomite particles distribute well in asphalt and no new functional group generated after adding diatomite into asphalt, and the thermal physical properties of asphalt mixture are changed. From these mechanical tests results it can be found that diatomite-modified asphalt mixtures have the better low temperature performance than neat asphalt mixture.

To protect the environment and reduce the consumption of energy, warm asphalt has been used widely in recent years. In this paper, Brookfield rotational viscometer test and dynamic mechanical analysis method are employed to investigate the effect of a kind of commercial wax named Sasobit® on the properties of three kinds of asphalt. It can be found that this kind of wax can increase the value of softening point, complex modulus, anti-rutting factor and reduce the value of the penetration and the phase angle; when the temperature is higher than 110 °C, the Sasobit® modified asphalt has a lower viscosity, comparing with the original sample; when the temperature is lower than 70 °C, the complex viscosity of Sasobit® modified asphalt is higher than the original sample, and the higher the Sasobit® content, the higher the complex viscosity. From the statistics analysis, it can be found that the effects of Sasobit® on rheological properties of asphalt are significant.

Because the thermal stress restrained specimen test (TSRST) is recommended by the Strategic Highway Research Program (SHRP) as a test method to evaluate low-temperature cracking resistance of asphalt mixtures, many studies have been carried out to investigate the performance of asphalt mixture with this test using fracture temperature as the indicator. However, few of them focus on discussing its reliability. In this paper, six kinds of asphalts mixtures are evaluated by TSRST, and it is found that the evaluation results obtained by the four indices are contradictory. It is also inferred from the results of each index coefficient of variation that fracture temperature and transition temperature are more stable when they are used to evaluate low-temperature performance of asphalt mixtures. Through the application of principal-component analysis (PCA) and the Boston Consulting Group’s matrix on the TSRST results, it is demonstrated that fracture temperature used as the indicator of low-temperature p...

This study investigates the benefits of modifying asphalt and stone-matrix-asphalt (SMA) mixtures in flexible pavement. 70/100-penetration-grade asphalt cement and 5% styrene-butadiene-styrene (SBS...

This paper investigates the viability of using starch (ST) as a new modifier for asphalt paving materials. Different ratios of ST (2.5, 5.0, and 7.5% by weight of asphalt) were blended with 70/100 paving grade asphalt. Unmodified and modified asphalt binders were subjected to physicochemical, alkali, acid and fuel resistance tests. The performance tests including, Marshall stability, Marshall Quotient (MQ), tensile strength, tensile strength ratio, flexural strength, rutting resistance and resilient modulus (MR) were carried out on unmodified and modified stone matrix asphalt (SMA) mixtures. The analyses of test results show that the performance of ST-modified asphalt mixtures are better than conventional and styrene–butadiene–styrene (SBS)-modified mixtures. The rutting potential, moisture susceptibility and temperature susceptibility can be reduced by the inclusion of ST in the asphalt mixture. The laboratory MR values are lower than the calculated ones using the empirical equations. The results also revealed that this modifier can be used as anti-stripping agent. It also shows resistance to fuels and most common chemicals. A ST content of 5% by weight of asphalt is recommended for the improvement of the performance of asphalt concrete mixtures similar to that investigated in this study.

In the asphalt mixtures, although asphalt is predominantly considered the binder holding the aggregates together, the actual product used to connect aggregate particles is the asphalt-mineral filler mastic which consists of the asphalt and mineral filler. The characterization of asphalt-mineral filler mastic is essential to improve the understanding of the response and performance of asphalt concrete pavements. It is also important to understand the high- and low-temperature properties of asphalt-mineral filler mastic. In this paper, the parameters of the viscous component of the repeat creep stiffness Gv were evaluated using a dynamic shear rheometer; and the creep stiffness modulus S was determined using a bending beam rheometer. The effects of filler/asphalt ratios F/A (on a weight basis) on the high-temperature and low-temperature properties of different asphalt-mineral filler mastics were studied. The results showed that the rheological behavior of asphalt-mineral filler mastics are nonlinear, and fo...

A laboratory investigation of the interactions between granites and asphalts based on rheology is described. In this study of asphalt-filler interactions, the rheological properties of asphalt mastics using different granite powders and different filler-asphalt ratios were measured using a dynamic shear rheometer. Statistically significant relations between the rheological properties of the granite-asphalt mastics and the moisture stability of granite-asphalt mixtures were found. Aggregate factors that influence the moisture stability of asphalt-aggregate mixtures were obtained, and the selection criteria for selecting granite aggregates for use in roads were developed; these could be useful as a reference for practical application.

Styrene-butadiene-styrene (SBS) and starch (ST) have been used by many to modify asphalt cement and to improve the properties of asphalt concrete. In this investigation, SBS and ST were used to modify asphalt cement. The basic properties of modified asphalt binders and stone mastic asphalt concrete (SMAC) containing such asphalt binders were studied and compared with those of asphalt cement. Marshall stability, Marshall Quotient, tensile strength, tensile strength ratio, rutting resistance, flexural strength, and resilient modulus were carried out on the SMAC. A mechanistic-empirical design approach was used for estimating the improvement in service life of the pavement or reduction in thickness of SMAC and base layer for the same service life due to modification the SMAC. In addition, an optimization table was prepared to select the type of SMAC for any field applications. The analyzes of test results show that the performance of SBS-modified SMAC is slightly better when compared to ST-modified SMAC. The temperature susceptibility can be reduced by the inclusion of SBS and ST in the SMAC. The results of multilayer elastic analysis presented herein indicate that the pavement consisting of SBS and ST-modified SMAC as a surface layer is beneficial in reducing the construction materials. Actual savings would depend upon the option exercised by the designer for reducing the thickness of an individual layer.

This paper reports studies of the anti-icing performance of a pavement containing granular crumb rubber asphalt (PGCRAM). In this mixture the granular crumb rubber is used as part of the a...

The present study investigates the benefits of modifying the asphalt and stone matrix asphalt (SMA) mixture in flexible pavement. Fifty/sixty penetration grade asphalt cement and four proportion of pyrolisis polypropylene (PP) were selected. Unmodified and modified asphalt binders were subjected to rheological and homogeneity tests. The performance tests including, Marshall stability, tensile strength and compressive strength were conducted on unmodified and modified SMA mixtures. The regression relationships between the performance tests were obtained. A mechanistic-empirical design approach was used for estimating the improvement in service life of the pavement or reduction in thickness of SMA and base layer for the same service life due to modification the SMA mixtures. The analyses of test results show that the performance of PP-modified asphalt mixtures are better when compared to conventional mixtures. The temperature susceptibility can be reduced by the inclusion of PP in the asphalt mixture. A PP content of 5% by weight of asphalt is recommended for the improvement of the performance of asphalt concrete mixtures similar to that investigated in this study. The results of multi-layer elastic analysis presented herein indicate that the pavement consisting of PP-modified SMA as a surface layer is beneficial in reducing the construction materials. Actual savings would depend upon the option exercised by the designer for reducing the thickness of an individual layer.

The present study investigates the potential use of pyrolysis low density polyethylene (LDPE) as a modifier for asphalt paving materials. Five different blends including conventional mix were subjected to binder testing such as rheological tests, as well as to some other tests related to the homogeneity of the system. Further, its effect on the moisture sensitivity and low temperature performance of stone matrix asphalt (SMA) mixtures was studied. Research results indicate that modified binders showed higher softening point, keeping the values of ductility at minimum range of specification of (100+ cm), and caused a reduction in percentage loss of weight due to heat and air (i.e. increase durability of original asphalt). The results indicated that the inclusion of LDPE in SMA mixtures can satisfy the performance requirement of high-temperature, low temperature and much rain zone. In addition, the horizontal tensile strain at the bottom of asphalt concrete layer (Et) and the vertical compressive strain at the top of subgrade layer (Ec) were calculated using multi-layer elastic analysis program, BISAR under 50KN set of dual tires with 106.5 mm contact radius. These responses were used for estimating the improvement in service life of the pavement or reduction in thickness of SMA and base layer for the same service life due to modification the SMA mixtures.

To evaluate the properties of asphalt accurately, a new index, dynamic viscoelastic index (Dvi), is proposed on the basis of rheological mechanics. To verify this new index, six kinds of asphalt are evaluated with Dvi, and six kinds of asphalt mixtures are tested at high and low temperature with asphalt pavement analyzer and indirect tensile test, respectively. It is found Dvi and temperature shows a good relationship and can be fitted with quadratic function. Also, the slope of the curve changed at around 50°C, and the curve can be fitted with linear model respectively. It is recommended that Dvi be used as the index of high-temperature and low-temperature performance of asphalt since there is a good relationship between Dvi and performance of asphalt mixture.