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Marginal hard asphalt possesses high stiffness and modulus; however, due to poor ductility at low temperature, it was seldom applied into road structures. Increasing asphalt content seemed to be an effective way to minimize the thermal cracking problem of hard hot-mix asphalt (HMA). Therefore, three types of methods (Groups 2–4) aiming to improve hard asphalt content were designed and compared with the traditional method (Group 1). Specifically, Groups 2 and 3 were designed with coarser gradation and lower gyration levels (Ndes), respectively, and Group 4 was designed following the enrobé à module élevé 2 (EME2) method. The high- and low- temperature, fatigue, modulus, and cracking performance were then conducted for each group. It can be seen that with the increase of asphalt content, the low-temperature strain increased in all three groups, of which Groups 2 and 3 improved more significantly. In addition, with the coarser gradation or lower Ndes , the high-temperature and cracking resistance of hard HMAs was lost to some degree; however, they can still compete with traditional neat HMAs. The hard HMAs designed with EME2 method performed excellent dynamic modulus and rutting resistance. Moreover, the hard HMAs designed with EME2 method and lower Ndes showed a surprising improvement in the fatigue life. These results may contribute to the better use of hard HMAs. [ABSTRACT FROM AUTHOR]

Using recycled materials in construction of asphalt pavements yields both economic and technical advantages. Recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) are two major sources to serve this purpose for which proper design and characterization are key elements. In this study, engineering properties of asphalt concrete containing RAP and RAS under dynamic loading were investigated. Three asphalt mixes were designed and included in this research: a conventional mix with no RAP/RAS as a control, a mix with 35% RAP, and finally a mix with 35% RAP and 5% RAS. A conventional resonant column (RC) apparatus was retrofitted and used for testing the specimens in torsional mode. Testing was conducted at five temperatures ranging from 10 to 45°C. Damping ratios and moduli of the mixes were analyzed and compared to assess the effect of the recycled materials on dynamic properties of asphalt concrete. Results clearly show the impact of RAP and RAS in increasing the mix stiffness. The study also included uniaxial dynamic modulus (DM) testing of the control mix to compare the moduli measured at high frequencies through RC testing to those estimated by the DM master curve through extrapolation. Results show that the modulus obtained from RC testing correlates well with that extrapolated from DM tests. Results also indicate that the accuracy of such correlation is significantly increased once dependency of Poisson's ratio on modulus is incorporated. [ABSTRACT FROM AUTHOR]

Polymers are commonly used to modify asphalt binder in order to satisfy the performance-grade binder's rheological properties, such as shear, storage, loss, and bending stiffness. However, it is not known what types and percentages of polymers affect these properties under conditions of aging. To this end, base asphalt binders were modified with styrene-butadiene and styrene-butadiene-styrene polymers at 3, 4, and 5% and then aged in the laboratory using a rolling thin film oven for short-term aging, a pressure aging vessel for long-term aging, and a draft oven for intermediate aging. The stiffness properties of the modified binders were determined using dynamic shear rheometer (DSR), multiple-stress creep recovery (MSCR), Brookfield rotational viscometer (RV), and bending beam rheometer (BBR) tests. Comparison of aging indexes for storage and loss modulus indicated that aging increases the elastic or storage component more than the viscous or loss component of the complex shear modulus. It was shown that increasing the percentage of polymer results in a decrease in aging for both SB- and SBS-modified binders. Those modified with SB are more resistant to aging than are those modified with SBS. [ABSTRACT FROM AUTHOR]

The measurement of shear modulus at small strains in unsaturated soil is critical to evaluating the deformation behavior of soils at working loads. However, little has been done to determine if the small-strain shear modulus surface is unique during variation in either net mean stress or matric suction. In this context, uniqueness is defined as similar samples subjected to different stress paths that converge to the same stress state. Research is presented herein in which a unique constitutive shear modulus surface was established by independently controlling mean net and matric suction stress in a modified resonant column apparatus. Uniqueness was also investigated using data extracted from literature studies. Uniqueness of the shear modulus surface was shown for single-direction stress and hydraulic paths, by the convergence of modulus and by the agreement between predicted and measured modulus. The presence of a unique shear modulus surface allows for the use of a constitutive relationship based on soil type that describes the small-strain shear modulus in terms of the stress state variables. [ABSTRACT FROM AUTHOR]

Traditionally, deflection data from a falling weight deflectometer (FWD) test and thickness data from pavement coring are used to backcalculate layer moduli. In this study, instead of coring, a neural network (NN) model is developed to determine layer thickness from FWD time-deflection histories. Using the NN predicted thicknesses, layer moduli are backcalculated using a commercially available backcalculation software. For validation, backcalculated moduli are compared with the laboratory determined moduli. Results show that backcalculated moduli are nearly equal to the laboratory moduli. Thus, the inclusion of NN-based thickness data has the potential to replace pavement coring, which is very expensive, and/or to enable a backcalculation method to run with a reasonable assumption of thickness whenever coring information is not available. [ABSTRACT FROM AUTHOR]

The amount of particle breakage of Tacheng rockfill material (TRM) in the process of shearing was quantitatively measured by a relative breakage index. The fractal dimension of TRM at the final state of the tests was found to be linearly related to the void ratio and logarithm of the confining pressure. The influences of the relative breakage index on the friction angle, modulus, and deformation were investigated based on a series of large-scale triaxial compression tests on TRM. An increase in the relative breakage index leads to an increase in the volumetric strain and to decreases in the peak state friction angle, critical state friction angle, deviatoric strain, and critical state void ratio. The test results were used to propose simple formulations pertaining to the relative breakage index for the strength and deformation indexes (e.g., peak state friction angle, critical state friction angle, initial elastic modulus, secant modulus at 50% of the peak strength, volumetric strain, deviatoric strain, and critical state void ratio). [ABSTRACT FROM AUTHOR]

A series of large-scale triaxial compression tests were conducted to investigate the strength and deformation behaviors of Tacheng rockfill material (TRM) in relation to the initial void ratio and initial confining pressure. The critical state friction angle of TRM was expressed as a linear function of the logarithm of the initial confining pressure. The excess peak state friction angle and excess characteristic state friction angle of TRM were formulated as linear equations of a revised relative dilatancy index to capture the influences of density and pressure on the peak state and characteristic state friction angles. The initial elastic modulus, tangent modulus, and secant modulus of TRM were dependent on the initial void ratio and initial confining pressure. In addition, a formulation incorporating density and pressure was proposed to simulate the initial elastic modulus of TRM. The volumetric and deviatoric strains of TRM at the critical state were also dependent on density and pressure. The critical state line of TRM in the space descended with a decrease in the initial void ratio. [ABSTRACT FROM AUTHOR]

The falling weight deflectometer (FWD) testing develops a deflection basin on the pavement surface. Depths of this deflection basin from the center of the falling weight are measured at different radial offsets. These deflections are used for the backcalculation of the pavement layer moduli. Most of the available backcalculation software uses the layered elastic theory and static load to calculate moduli from known pavement surface deflections. However, the FWD test load is dynamic, and layer materials may show nonelastic behavior. Layered elastic theory in these types of software cannot characterize dynamic response of the pavement. Also, elastic theory is unable to accurately predict the surface deflection whenever stress developed in any pavement layer exceeds the yield point. For this reason, this study has performed a finite-element analysis of the airport pavement under the FWD test considering the dynamic load and materials plasticity. The analysis presented here includes elastoplastic behavior of pavement layer materials. Both axisymmetric and quarter cube models have been developed in ABAQUS. Time-deflection histories are simulated to match the FWD test data. A comparison is made between the dynamic, static, and field deflection basins. Contours of vertical deflection and strain are also plotted to observe their distribution on both the axisymmetric and quarter cube models. Analysis results show that the time-deflection histories are in close agreement with the field data. The axisymmetric model yields better results than the quarter cube model. Deflections from the static analysis are greater than the dynamic analysis for an identical set of the layer modulus of elasticity. A uniform distribution of strain is observed from the static analysis in both of the geometries. However, the dynamic analysis does not show similar distribution because of the time-dependent response. [ABSTRACT FROM AUTHOR]

An analysis is presented of a database of 67 tests on 21 clays and silts of undrained shear stress-strain data of fine-grained soils. Normalizations of secant in terms of initial mean effective stress (i.e., versus ) or undrained shear strength (i.e., versus ) are shown to be much less successful in reducing the scatter between different clays than the approach that uses the maximum shear modulus, , a technique still not universally adopted by geotechnical researchers and constitutive modelers. Analysis of semiempirical expressions for is presented and a simple expression that uses only a void-ratio function and a confining-stress function is proposed. This is shown to be superior to a Hardin-style equation, and the void ratio function is demonstrated as an alternative to an overconsolidation ratio (OCR) function. To derive correlations that offer reliable estimates of secant stiffness at any required magnitude of working strain, secant shear modulus is normalized with respect to its small-strain value , and shear strain is normalized with respect to a reference strain at which this stiffness has halved. The data are corrected to two standard strain rates to reduce the discrepancy between data obtained from static and cyclic testing. The reference strain is approximated as a function of the plasticity index. A unique normalized shear modulus reduction curve in the shape of a modified hyperbola is fitted to all the available data up to shear strains of the order of 1%. As a result, good estimates can be made of the modulus reduction across all strain levels in approximately 90% of the cases studied. New design charts are proposed to update the commonly used design curves. [ABSTRACT FROM AUTHOR]

The response of a laterally loaded pile is normally dominated by the limiting force per unit length profile (LFP, ) mobilized along the pile to the depth of the plastic zone (e.g., maximum slip depth, max ) and depends on pile-soil relative rigidity (via the subgrade modulus of elasticity ). The values of and the shear modulus (, thus ) were deduced extensively against the measured response of 32 and 20 piles tested in situ in clay and sand, respectively. In this paper, simplified closed-form solutions are presented for the design of laterally loaded piles. The parameters of the and the obtained previously are utilized to examine the impact of loading eccentricity on piles and to assess the validity of existing -profiles. Expressions are also explored and provided regarding determinations of the -profiles, the modulus of the subgrade reaction (via ), the ranges of the plastic zone (max ), and the depth of elastic influence (via the critical pile length ), along with the correlations between the shear modulus of soil and undrained shear strength () and/or the standard penetration test blow count (). It is noted that the popularly adopted LFPs (such as Matlock's LFP, Reese's LFP, and American Petroleum Institute code methods) are not sufficiently accurate for 60-85% of the 52 piles investigated herein, especially for those with a diameter >1.5 m. [ABSTRACT FROM AUTHOR]