Repeated Shear Test Research Articles

Laboratory Evaluation of Dynamic Characteristics of a New High-Modulus Asphalt Mixture

With the rapid increase in traffic volume and heavy-duty vehicles, rutting has become one of the most serious problems threatening the service quality and life of asphalt pavement. High-modulus asphalt concrete is a promising method to overcome this problem, contributing to the sustainable development of asphalt pavement. In this study, a new composite high-modulus agent (CHMA)-modified asphalt binder and mixture were prepared, and their dynamic mechanical characteristics were investigated by the dynamic shear rheometer, dynamic modulus test, wheel tracking test, frequency sweep test at a constant height (FSCH), and repeated shear test at a constant height (RSCH) to comprehensively evaluate its high-temperature stability. Test results showed that the rheological property of the CHMA-modified asphalt binder was similar to that of low-graded asphalt binder, implying that it had a strong potential in resisting deformation. The dynamic modulus of AC-20(CHMA) was 19,568 MPa at 15 °C and 10 Hz condition, meeting the requirement for the high-modulus asphalt mixture (higher than 14,000 MPa). The dynamic stability of AC-20(CHMA) was 8094 times/mm, lower than that of AC-20(20#), but remarkably higher than that of AC-20(SBS). AC-20(20#) and AC-20(CHMA) both showed strong shear resistance according to the FSCH test results. Under the repeated shear loadings, the growth rate of the shear strain increased rapidly in the primary stage, and then slowed down gradually, finally reaching a constant growth rate. The shear slope of AC-20(CHMA) was between that of AC-20(20#) and AC-20(SBS), demonstrating that its resistance to repeated shear loadings was superior to AC-20(SBS), although slightly weaker than AC-20(20#). The findings in this study provide references for alleviating rutting problems and improving the lifespan of asphalt pavement.

Shear accumulated equilibrium compliance as permanent deforamtion susceptibility parameter

Described procedure summarizes the derivation of accumulated creep compliance in the sequence of the creep and recovery cycles that can be easily fitted to experimentally measured data. The local minima in each measured cycle after the recovery were selected and combined into a set that characterized the irreversible deformation of the specimen during the test. Further, the interval fitting procedure was utilized. The estimation of the discrete retardation spectrum from the used 4-modes standard Kelvin-Voigt model was discussed and the accumulated compliance calculated. It was proved that the accumulated compliance may be used as the pavement rutting criterion (expressing the performance of asphalt in terms of its susceptibility to permanent deformations). The proposed theory was demonstrated on experimentally measured asphalt properties in the two test devices. Repeated Shear tests were performed in the Superpave Shear Tester and the Uniaxial Shear Tester. It was found that the accumulated equilibrium compliance correlates with the asphalt mix rutting parameters. As it is presented and in the view of the general principles showing that long-time processes are revealed in more detail in the retardation spectrum, the use of the accumulated equilibrium compliance can be useful as a criterion for the long life rutting potential.

Repeated shear test on cold forged material

Repeated shear test on cold forged material

Failure Mode and Bonding Evaluation at the Interface between Asphalt Surface and Semirigid Base

AbstractIn this paper, two interface treatments were applied to improve the interface condition, and the shear failure test and repeated shear test were conducted to evaluate the bonding conditions...

Progressive failure mechanism of a large bedding slope with a strain-softening interface

The present work is primarily concerned with the progressive failure mechanism of a large bedding slope with a strain-softening interface. Both the laboratory tests and finite difference method (FLAC software) are employed to fulfill our purpose. Firstly, the shear properties of the interface (the mudded weak interlayer) are investigated through groups of repeated shear tests. According to the test results, all kinds of the interfaces share the characteristics of strain softening. To simulate the shear behavior of the interface in FLAC, a contact constitutive model with strain softening is built and verified against experimental results. The modified constitutive model of the interface is later applied to the numerical simulation of the bedding slope. Through investigating the response of the strain-softening contact elements to the stress characteristics among the rock layers, the chain action law of the bedding slope stability can be obtained. Finally, the progressive failure mechanism of the bedding slope is determined based on the chain action law. A typical case is investigated to validate the feasibility of the strain-softening contact element and the progressive failure mechanism of bedding slopes.

Uniaxial Shear Tester – new test method to determine shear properties of asphalt mixtures

The main focus of the paper is to present the concept of a newly developed Uniaxial Shear Tester (UST) and to investigate the correlation between results from the UST and the Superpave Shear Tester (SST), a tool broadly recognised for asphalt mix design and rutting susceptibility evaluation. In this study, the UST testing principles, finite element analysis of stresses and comparison of measured data are presented. The correlation was assessed on the basis of two tests, the repeated shear test and the small amplitude oscillation test also referred as the shear frequency sweep test. It was shown that the material characteristics determined from UST and SST are highly correlated. The dependencies are discussed in the sense of linear correlation and correlation coefficients. Test variability is discussed in the paper.

Characterization of Permanent Deformation Using AMPT Repeated-Load-Triaxial and RSCH Tests for Mechanistic-Empirical Design and Practical Considerations

AbstractCaltrans is currently implementing a California version of the superior performing asphalt pavements (Superpave) mix design procedure for hot-mix asphalt (HMA) to replace the long been used Hveem mix design process, and is interested in including performance-related tests for mix design and quality assurance. The objective of this study was to compare the repeated load triaxial (RLT) rutting test using the asphalt mixture performance tester (AMPT) and the repeated shear test at constant height (RSCH) using repeated simple shear tester (RSST) for characterization for Caltrans mechanistic-empirical (ME) pavement design in terms of usefulness of the results, difficulty, and time required to obtain results. The results indicated that there is potential to use the unconfined RLT test as a substitute for the RSCH test for mix design and quality assurance, and to use the confined or unconfined RLT for ME characterization. However, the preliminary results regarding shift factors to convert results from RL...

Repeated shear behaviors of geotextile/geomembrane and geomembrane/clay interfaces

Because the normal stress applied to landfill liner systems increases with the volume of waste during the construction of engineered landfills, traditional shear tests do not adequately describe the loading process on the liner system because only one shear test is performed on a single sample. In this study, a series of laboratory tests using a new test method that differs from traditional shear tests were performed to investigate the repeated shear behaviors of geotextile/geomembrane (GT/GM) and geomembrane/clay (GM/clay) interfaces under various normal stresses. The test results indicated that increasing shearing times decrease the peak and residual shear strengths of both GT/GM and GM/clay interfaces. Additionally, the strength parameters obtained from traditional and repeated shear tests were both used to analyze global stability along the liner system of a typical landfill. The results of repeated shear tests and limit equilibrium analysis were determined to be significant for landfill liner system anti-slide design. The limitations of the tests were also discussed.

Study on Permanent Deformation of Asphalt Mixtures by Single Penetration Repeated Shear Test

The problem of asphalt pavement rutting is getting worse, which affects driving safety seriously and reduces pavement life greatly. Through comparative analysis, a single penetration repeated shear test (SPSFT) for a research on asphalt mixture permanent deformation was put forward. Many SPSFT tests on different load levels were did with four kinds of most commonly used asphalt mixtures in the upper and middle layer of asphalt pavements. Some conclusions were the followings: (1) The three-stage permanent deformation behavior of asphalt mixtures on loads could be got by SPSFT. (2) The bigger the load, the faster the permanent deformation of asphalt mixtures increases, and the smaller the fatigue life. (3) Mixtures with modified asphalt had a greater ability resistance to shear deformation than with conventional asphalt. (4) Large load (≥1.3MPa) made the large deformation with not large load cycles and the mixture broke; but the smaller load (≤1.1MPa) got very slow increase of the deformation, which was stably in the second stage of three-stage permanent deformation and didn’t broke. (5) The asphalt mixtures with bigger shear strength had a greater ability resistance to shear deformation. (6) Load stress levels had an equivalence to load cycles.

Performance Assessment of Asphalt Mixtures Using Frequency Sweep Test at Constant Height and Hamburg Wheel-Tracking Device

The study presents the comparative evaluation of mixture performance of the Superpave and dense-graded mixtures using the results of repeated shear test at constant height (RSCH), frequency sweep test at constant height (FSCH), and Hamburg wheel-tracking device (HWTD) test. The results of HWTD testing displayed the Superpave mixtures I and II were less susceptible to permanent deformation than the dense-graded mixture. The results of RSCH testing showed the cumulative shear strain and the predicted rut depths of the accumulated shear strain of the dense-graded mixture was about six times as large as those of the Superpave mixtures I and II. Compared with the test results of HWTD testing, the Superpave mixture II was less susceptible to permanent deformation and the dense-grade mixture was the most prone to rutting among these three mixtures. The normalizing frequency parameter of the dense-graded mixture was about one and half to five times as large as those of the Superpave mixtures I and II. The larger value the specification parameternormalizing frequency parameter, the less that the mixtures could exhibit performance ranking. The use of specification parameter obtained from FSCH test, normalizing frequency parameter, for assessing mixture performance was consistent with the findings from HWTD and RSCH tests. Therefore, the Superpave mixture II ranked first and the dense-graded mixture ranked third based on the overall mixture performance.

Impacts on Asphalt Mixture’s High Temperature Performance with PR Series Additives Added

AbstractImpacts on asphalt mixture’s high temperature performance with PR series additives added by means of rutting test and Repeated Shear Test (Constant Height) (RSCH) were investigated. The analytic results of the two tests show that (1) rutting test is not suitable for the high temperature performance evaluation of asphalt mixture with PR series additives added for the reason of the conflict between dynamic stability and rut depth; (2) the results of RSCH, such as K1 K2, N and γ, show very well consistency which is suitable for the high temperature performance evaluation of asphalt mixture with PR series additives added. The results of RSCH show that asphalt mixture with PR PLASTS (PR.S) added has the best performance, the PR FLEX MODULE (PR.M) one is the next and the original one is the worst for the high temperature anti-shear performance.

A STUDY OF RESISTANCE TO AGGREGATE FRETTING OF POROUS ASPHALT PAVEMENTS

We conducted horizontal repeated shear test in order to appreciate the resistance to aggregate fretting of porous asphalt pavement. Test results showed that the mixture which used the binder with higher bending work (the binder with lower stiffness) had good effect on the resistance to aggregate fretting. However, according to compare the test result with the calculation value of the shear stress acting on the surface layer, we recognized that using high quality binder was not always sufficient to control aggregate fretting. In addition, it suggested that the method to combine the technology to lower the surface temperature of porous asphalt layer with the high quality binder was better for aggregate fretting.

Post-failure mobility of saturated sands in undrained load-controlled ring shear tests

The undrained shear behavior of soils with progress of shear displacement is essential to the understanding of liquefied slope failures with long travel distance. In this paper, using a newly developed ring shear apparatus, a series of ring-shear tests were conducted on a silty sand to examine the undrained behavior of sand subjected to long shear displacement. Based on the test results, the undrained shear behavior of sands with a wide range of densities is discussed. A very low effective stress corresponding to liquefaction was observed at the steady state in all of the tests on loose, medium, as well as dense sand. The effects of stress state and shear history on the undrained shear behavior were examined by performing tests on a sample with different initial stress states and shearing the same specimen repeatedly (three times) at each initial stress state. The tests at different initial stress states proved that the initial stress state has an influence on static liquefaction resistance but has no effect on the steady-state shear strength. Repeated shear tests on the same specimen showed that with increasing shear times, both the peak shear strength and the steady-state shear strength for each specimen became greater. Detailed examination of the shear deformation revealed that the liquefaction phenomena in ring shear tests are localized in the shear zone, irrespective of the initial state of the sand. Grain crushing within the shear zone was examined. Finally, it was found that there was an optimal density at which the undrained brittleness index had a minimum value; meanwhile, the undrained brittleness index became greater with increasing initial normal and shear stresses, but decreased with shear times. These findings offer some basic understanding in assessing the postfailure mobility in landslides.Key words: excess pore pressure, localized liquefaction, shear resistance, ring-shear tests, grain crushing, silty sands.

Effect of Mix Gradation on Rutting Potential of Dense-Graded Asphalt Mixtures

A study was conducted to evaluate the effect of mix gradations, both complying with and violating the Superpave restricted zone, on rutting potential of hot-mix asphalt. Superpave gyratory samples of mixes with granite, limestone, and gravel aggregates were used. The following gradations were used: gradation above the restricted zone, gradation through the restricted zone in close proximity to the maximum density line, and gradation below the restricted zone. Rut tests were conducted at 64°C with the asphalt pavement analyzer under 689-kPa contact pressure and 45.2-kg wheel load. Rut depths were measured at the end of 8,000 cycles. Repeated shear tests at a constant height were also conducted with the Superpave shear tester. Statistical analysis of rut data generally indicates a significant difference between rut depths obtained in mixes using different aggregate types and gradations. The gradations violating the restricted zone did not necessarily give relatively higher rut depths compared with the gradations in compliance with the zone.

Volumetric and Mechanical Performance Properties of Superpave Mixtures

This investigation studied the volumetric and mechanical performance properties of the Superpave mixtures SP-1 and SP-2 and a typical Taiwan mixture (TTM). Both the Marshall and the Superpave mix design procedures were used to produce these mixtures, and the Superpave gyratory compactor was used for realistically compacting specimens to densities achieved under actual pavement conditions. The three mixtures were tested using the Superpave shear tester for conducting a simple shear test at constant height, frequency sweep test at constant height, and repeated shear test at constant height. Volumetric analyses of specimens showed that the TTM mixture hardly met the Superpave volumetric requirements and it contained less than 1% air voids at the number of gyrations for design compaction, which strongly suggests that this mixture might be highly prone to rutting. The design asphalt content of each mixture was found very close to the peak of its compaction slope-asphalt content curve. Mechanical test results indicated that the Superpave mixtures were more resistant to permanent deformation than the TTM mixture.

Low-Temperature Evaluation of Kentucky Performance-Graded 70-22 Asphalt Binders

A study was initiated to ascertain whether all performance-graded (PG) 70-22 binders would perform the same in an asphalt mixture in Kentucky, regardless of method of manufacture of the binder. Five PG 70-22 binders and one PG 64-22 binder (control) were incorporated into an asphalt mixture through a hot-mix asphalt plant. Test sections were placed for each binder. The mixture was sampled at the plant and returned to the laboratory for mechanical property testing. The mechanical property tests included repeated shear test at constant height, frequency sweep test at constant height, and indirect tensile creep (ITC) test. These tests were chosen to evaluate the high-, intermediate-, and low-temperature properties of the asphalt mixtures. Only low-temperature properties are discussed. Thermal stress analysis techniques permitted the critical mixture temperature for single-event thermal cracking to be compared with critical binder temperatures. Although the critical binder temperature [calculated from bending beam rheometer (BBR) stiffness] matched the critical mixture temperature reasonably well, the critical binder temperature calculated from the BBR m-value did not match as well. The m-value critical temperature is generally higher than indicated by the low-temperature ITC testing. Although not all PG 70-22 binders performed the same in mixture testing, the research did not clarify whether differences in mixture properties for the PG 70-22 binders are related to differences in binder stiffness, differences in method of manufacture, or both.

Effect of Mineral Filler Type and Amount on Design and Performance of Asphalt Concrete Mixtures

Three methods for classifying aggregate particle shape and texture—AASHTO TP33, ASTM D3389, and the flow rate method—were evaluated. These methods were used to rank four natural river sands and a crushed granite from good to poor performance based on the criteria established by each method. Test results indicate that all methods easily distinguished the crushed aggregate from the natural river sands. The AASHTO TP33 and the flow rate method were found to be somewhat less sensitive to slight differences in particle shape and texture than was ASTM D3398. All the test methods were found to be repeatable, each having low coefficients of variation for all the aggregates tested. To evaluate the effect of particle shape and texture and mineral filler content on mix performance in permanent deformation, one natural sand ranked as average performing was selected and blended with the crushed granite in the proportion of 20 percent natural sand and 80 percent crushed granite. Asphalt-aggregate mixtures containing 4, 6, 8, and 12 percent mineral filler were designed by using the Marshall procedure and were tested in repeated shear test at constant height. Within the range of mineral filler type and contents used, results indicate that mixtures containing 100 percent crushed granite show lower accumulation of permanent strain than does an 80/20 blend of crushed granite and natural sand, and an increase in the mineral filler content of a mixture was found to decrease its accumulated permanent strain while increasing the mixture shear resilient modulus.