Search

Automobile industries produce more than 5.2 million tons of scrapped tires each year in the United States. Disposal of such a huge amount of waste scrapped tires has become a serious environmental issue. Scopes to use scrapped tires in the form of Ground Tire Rubber (GTR) in pavement industry have been analyzed in recent years. The GTR has potential to improve hot mix asphalt’s performance from the view points of stiffness, resilience and shock absorbance properties. On the other hand, in recent years, researchers have attempted to explain performance of asphalt in terms of its nanomechanical characteristics. In this study, the PeakForce Quantitative Nanomechanical Mapping (PFQNM™) mode of an atomic force microscope has been employed to find basic nanomechanistic properties and the morphology of GTR-modified asphalt binders. A performance grade (PG) binder (PG 64-22) modified with two different grades of GTR (Mesh #30 and Mesh #40) samples have been evaluated in this study. Nanomechanical properties such as adhesion, energy dissipation, deformation, and DMT (Derjaguin, Muller, and Toporov) modulus for the GTR-modified binders have been quantified. Each sample was scanned for three different (5 × 5, 10 × 10, and 20 × 20 µm) areas. The PFQNM™ analyses revealed distinct microstructures and grain distributions among tested additive modified binder samples. Two distinct phases, namely Catana and Peri-phase, were observed in GTR-modified samples, although the DMT moduli were found to be in a close range in these areas. The neat binder showed another phase, named Perpetua, which was missing from the GTR-modified samples. It was observed that modification of asphalt by addition of GTR considerably changes the mechanistic properties of the base binder.

A mechanical calculation model of tunnel composite pavement was established using finite element software ABAQUS. The shear stress and horizontal tensile strain in the asphalt layer, the horizontal tensile stress in the concrete layer as well as the interlaminar shear stress were selected to be the key indexes. The mechanical calculation results show that with the increase of the thickness of the asphalt layer, its maximum shear stress increases and its tensile strain increases first and then decreases, while the interlaminar shear stress decreases. The maximum horizontal tensile stress in the concrete layer decreases with the increase of the thickness of concrete layer and the modulus of bedrock. Besides, the maximum horizontal tensile strain in the asphalt layer decreases when increasing its thickness. The thickness design methods of the asphalt layer are put forward based on the shear stress index and horizontal tensile strain index as well as interlaminar shear stress index. The thickness of an asphalt layer between 8cm and 10cm is verified to be reasonable. The thickness of the concrete layer is mainly to meet the functional requirements. In order to improve the service life, a minimum thickness of 40cm is recommended.

Different characteristics of aggregates have significant impact on the high modulus mixture properties of hard asphalt (such as high temperature properties, modulus, and fatigue resistance). This paper chooses two kinds of aggregates (basalt and limestone) with obvious differences. Based on the Aggregate Image Measurement System (AIMS), this paper made detailed comparison and analysis on all characteristics of the two kinds of aggregates. Referring to the French high modulus mix design process, the various performance indicators coordinated design methods were tested on the high modulus mixture of hard asphalt. Results show that, it can be achieved a balanced design of high temperature performance, modulus, and fatigue resistance properties on the mixture thronging the gradation and the hard asphalt dosage adjustment, for different properties aggregate.

The microstructure of bitumen is responsible for the rheological properties and pavement performance, the change of microstructure had a significant impact on the bitumen behavior. Atomic Force Microscopy (AFM) technology has a great advantage on microstructure analysis and the microstructure had been proven to be a unique and reproducible property of a bitumen, but the challenge in applying AFM technology is to obtain samples which can reflect the true microstructure of bitumen. The paper mainly investigated the sample preparation, probe selection, and the structural characterization of the bitumen at the nanoscale by AFM. The results showed that molding method can guarantee the reproducibility and stability of sample and the AFM images obtained could reflect true microstructure of bitumen. According to basic modulus principle, nominal spring constant of AFM probe should be lower than 5 N/m at room temperature in tapping-mode. In addition, AFM cantilever material with back coating was recommended as results of the opacity of bitumen. “Bee-shaped” structure with several micrometers in length and 47–55 nanometers in height randomly distributing presented in base bitumen and SBS modified bitumen, the results were in agreement with previous studies. Although many studies reported the component of bee-shaped structure, it still remained unclear at present.

Crumb rubber modifier (CRM), made from scrap tires, has been introduced into the production of different types of hot mix asphalt (HMA) in either wet or dry process. There has been few research about the interaction between asphalt and the crumb rubbers added in the dry process. In the study, dynamic shear rheometer (DSR) and atomic force microscopy (AFM) were used to explore the interaction between the asphalt binder and CRM in dry and wet process. The results indicated: (1) rubberized binder in dry process have similar modulus, phase angle and complex viscosity with wet process, regardless of unaging or short-term aging, (2) rubberized asphalt in dry process has lower roughness of topographical image than wet process before short-term aging. However, the short-term aging may decrease the difference of the microstructures of the binders in two processes, i.e., wet and dry processes.

The objective of the paper is to investigate the influence of bitumen nature on complex modulus and fatigue resistance of bituminous mixtures produced with reclaimed asphalt pavement (RAP). Eight distinct mixtures were produced with eight different modified and unmodified base binders. RAP content was fixed equal to 20% for all mixtures. For each mixture, the corresponding binder blend was produced by mixing the base binder with RAP-extracted binder, in the same proportions. A total of 16 binders (eight base binders and eight binder blends) were therefore used in the study. Both advanced and classical tests commonly used by road paving industry in Europe were performed. Complex modulus (at 15°C and 10 Hz) and fatigue (at 10°C and 25 Hz) DSR tests were carried out on all binders. Two-point bending complex modulus (at 15°C and 10 Hz) and fatigue (at 10°C and 25 Hz) tests were carried out on trapezoidal samples of mixtures. Complex modulus and fatigue resistance of mixtures appeared to vary significantly depending on the nature of the base binder. However, clear correspondences between values obtained for mixtures and corresponding binders could not be found.

The typical structures of frequently used semi rigid base, asphalt treated macadam laying on semi-rigid base and graded broken stone laying on semi-rigid base in Guangzhou-Heyuan Expressway were analyzed on structural stress. Comparative analyses on the load response characters with asphalt pavement structure layers with different base were carried out. Combined effects of gradation, modulus, and thickness of Asphalt treated macadam layer with field investigation of composite base, design schemes of asphalt pavement with rigid-flexible composite base were proposed for expressway in Guangdong.

Pavement performance in cold temperature regions is a concern to highway agencies. Laboratory methods need to be established to test the cold temperature performance of asphalt mix designs. Research conducted at the University of Utah has shown that testing asphalt concrete mixtures using the bending beam rheometer (BBR) is a viable method to measure low temperature performance. Data collected from field cores were used to develop performance relations. However, testing field cores from already constructed roads does not prevent poor performance mixes from being placed on the road. A better approach is to use laboratory-compacted samples from field mixes that are already used for volumetric quality control. While this still relies on material obtained at the time of construction, it is closer to the ultimate goal of evaluation of materials at the mix design stage for cold temperature performance. Typically, volumetric cylinders are gyratory compacted to an air void content of 4% by mass, while field cores target an air void content between 6% and 7%. The question arises in the variability of BBR results from air content ranging between 4% and 7%. For this research, gyratory cylinders were compacted at varying levels of compaction in order to achieve a range of air voids to evaluate stiffness measurements with the BBR. Different binder contents were also tested, with compaction level held constant and binder content varying. For varying air voids, the 60 and 120 second creep modulus was seen to decrease by as much as 30% within the 6% air void range. The m-value for varying air voids was not affected. Results also showed that, at binder content levels close to optimum, no noticeable change was observed in beam measurements. In addition, the m-value was seen to be independent of binder content.

The purpose of this research was to assess the residual structural capacity of the cement-treated base (CTB) layer on Interstate 84 in Weber Canyon following premature fatigue cracking of the overlying asphalt layer. Field testing included falling-weight deflectometer (FWD) testing by Utah Department of Transportation personnel and portable falling-weight deflectometer (PFWD) testing, dynamic cone penetrometer (DCP) testing, and coring by research personnel. The results of the testing indicated that the average modulus and unconfined compressive strength (UCS) values measured in the wheel path were consistently lower than the corresponding values measured between the wheel paths; reductions in structural capacity in the wheel path probably occurred as a result of asphalt cracking, water ingress, freeze-thaw cycling, and continued trafficking of the pavement in these conditions. Despite these effects, the average CTB modulus, California bearing ratio (CBR), and UCS values were still considerably higher than those of typical unbound granular base materials. Specifically, the average CTB modulus values measured during the spring using the FWD in the eastbound and westbound lanes were determined to be 1699 and 852 MPa (246.4 and 123.6 ksi), respectively, while the average CTB modulus values measured during the fall using the PFWD in the eastbound lane were 2609 and 3378 MPa (378.5 and 490.0 ksi) in the wheel paths and between the wheel paths, respectively. Furthermore, based on DCP testing, the average CBR value in the wheel path of the eastbound lanes was determined to be 198. Finally, the average UCS values were determined to be within or just above the range of 2070 to 2760 kPa (300 to 400 psi) recommended by the Portland Cement Association for the 7-day design strength of CTB.

Based on the Bailey-Norton elastic-plastic constitutive model to the asphalt mixture, Mohr-Coulomb plastic constitutive model to the unbounded granular material, and the ABAQUS finite element platform, resistance ability to rutting of 4 typical pavements are studied. Results reveal that: the existence of unbounded granular material between asphalt layer and cement treated material appears negative effect to rutting resistance ability; factors such as temperature, tire-road contact pressure, traffic volume, modulus and thickness of asphalt layers have significant effects on asphalt pavement rutting resistance; rutting prediction models which can be used in new construction design are obtained by regression from orthogonal experiment design.

Berming is a common nationwide practice for pavement shoulder maintenance. Quality berming improves the capacity of pavement shoulders and prevents traffic accidents. Results of a nationwide survey show that there is a major desire to improve the safe and effective berm compaction. Emerging new equipment is being developed by Ohio DOT in-house and private industry that uses self-weight and vibratory plate to compact berm materials. An experimental study was conducted on four types of berm materials to evaluate the compaction effects using proctor or vibratory compaction. The effects of compaction energy level were evaluated by measuring the physical, mechanical and electrical properties. Particularly, NDTs were conducted to identify the best indicator on the quality of compaction. The experimental results indicate that vibratory compaction is effective for crushed limestone berm. The asphalt coating on RAPs might reduce the effectiveness of vibratory compaction. Natural soil berm is not well compacted by vibratory compaction. Heat treatment of RAPs up to 60°C did not significantly increase the material compaction or inter-particle adhesion. Wave speeds and Young’s modulus are found to be sensitive indicators for compaction energy levels. The electrical properties, which Ground Penetrating Radar is based on, are not sensitive to different compaction energies.

The long-term performance of a flexible pavement largely depends on the compaction level achieved in different layers during construction. Traditionally, the compaction level of the subgrade is monitored through spot checking of moisture content and dry density at some discrete points. However, this type of quality control work does not cover the entire pavement and may leave under-compacted areas. These under-compacted areas could likely lead to early failure of the pavement structure. Therefore, it is necessary to develop a real-time compaction monitoring tool that can provide an accurate measurement of the compaction level of the entire pavement. Such measurements could be used to identify and remediate under- compacted areas and provide adequate support to asphalt layers constructed on top of the prepared subgrade. The application of the Intelligent Compaction Analyzer (ICA) for real-time monitoring of compaction of a stabilized subgrade is addressed in this paper. Four case studies demonstrating the successful application of the ICA are included. The compaction level of the stabilized subgrade was monitored in terms of ICA density and modulus. In each case study, it was found that ICA could estimate the compaction level with a reasonable accuracy. It was also found that the ICA modulus and nuclear density gauge (NDG) measured density exhibits a good correlation with R 2 equal to 0.73.