查看更多>>摘要：The resilient modulus measured in the indirect tensile mode according to ASTM D 4123 reflects effectively the elastic properties of asphalt mixtures under repeated load. The coarse aggregate morphology quantified by angularity and surface texture properties affects resilient modulus of asphalt mixes; however, the relationship is not yet well understood because of the lack of quantitative measurement of coarse aggregate morphology. This paper presents findings of a laboratory study aimed at investigating the effects of the material properties of the major component on the resilient modulus of asphalt mixes, with the coarse aggregate morphology considered as the principal factor. With modulus tests performed at a temperature of 25℃, using coarse aggregates with more irregular morphologies substantially improved the resilient modulus of asphalt mixtures. An imaging-based angularity index was found to be more closely related to the resilient modulus than an imaging-based surface texture index, as indicated by a higher value of the correlation coefficient The stiffness of the asphalt binder also had a strong influence on modulus. When the resilient modulus data were grouped on the basis of binder stiffnesses, the agreement between the coarse aggregate morphology and the resilient modulus was significantly improved in each group. Although the changes in aggregate gradation did not significantly affect the relationship between the coarse aggregate morphology and the resilient modulus, decreasing the nominal maximum aggregate size from 19 mm to 9.5 mm indicated an increasing positive influence of aggregate morphology on the resilient modulus of asphalt mixes.
查看更多>>摘要：Hydrated lime is often used as a mineral filler or antistripping additive in hot-mix asphalt (HMA). Many agencies across North America require the use of lime in all HMA mixtures being placed on high-volume roadways. Despite this wide use of lime, its effects on the HMA mixture dynamic modulus (E~*) stiffness have rarely been evaluated. The new mechanistic-empirical (M-E) pavement design guide, Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures, developed under NCHRP Project 1-37A uses E~* as the primary material property of asphalt mixtures for the HMA characterization. A comprehensive study was completed at Arizona State University to assess the effect of lime addition on the E~* stiffness of HMA mixtures. The study demonstrated that the standard test and design methodologies of the new M-E pavement design guide could be used effectively for lime-modified HMA mixes. With these methodologies, hydrated lime was found to increase the E~* of HMA mixtures by 17% to 65% across the range of mixtures, lime contents, and temperature, with an overall average of 25% increase found from 17 mixture-lime percentage combinations across six different HMA mixes. This paper also outlines a provisional protocol for evaluating the E~* master curve for lime-modified HMA mixtures using any of the three hierarchical levels found in the new NCHRP Project 1-37A pavement design guide.
Maria Carolina RodeznoKamil E. KaloushGeorge B. Way
p.20-27页
查看更多>>摘要：The purpose of this study is to assess the way distresses are predicted by using the new Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (design guide), developed under NCHRP Project 1-37A. Two pavement sections were used: a conventional hot-mix asphalt reconstruction and an asphalt-rubber overlay on a portland cement concrete (PCC) pavement. The design guide does not include rehabilitation design for asphalt-rubber overlays. However, many large-scale asphalt-rubber overlays on interstate highways in Arizona have been built and monitored for performance, providing an opportunity to determine to what degree the design guide can predict their performance. The input data for both types of pavements were derived from two different projects on the same highway, Interstate 40. The actual data measurements that summarize the pavement performance were compared with calculated values obtained by using the design guide. Three pavement performance parameters were evaluated on the basis of the available data: rutting, cracking, and international roughness index (IRI). Rutting was one of the distresses that the design guide predicted more accurately. The fatigue cracking prediction, evaluated with Level-3 data input, was not accurate; future analysis should consider calibrated fatigue models for the different mixtures. The predicted IRI results differed from the actual measured field performance because of inaccurate distress prediction. The Arizona experience using asphalt-rubber overlays to rehabilitate aged PCC pavements has been successful. For that reason, a calibration process that allows the use of the asphalt-rubber mixtures in the design guide should be considered in the future.
查看更多>>摘要：This research examines how the addition of recycled asphalt pavement (RAP) changes the volumetric and mechanistic properties of asphalt mixtures. A Superpave~® 19-mm mixture containing 0% RAP was the control for evaluating properties of mixes containing 15%, 25%, and 40% RAP. Two types of RAP were evaluated: a processed RAP and an unprocessed RAP (grindings). Testing included dynamic modulus in tension and compression, creep compliance in compression, and creep flow in compression. Dynamic modulus and creep compliance master curves were constructed with the use of the time-temperature superposition principle to describe the behavior of each mix over a range of temperatures. The voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) of the RAP mixtures increased at the 25% and 40% levels, and there was also an influence of preheating time on the volumetric properties. The dynamic modulus of the processed RAP mixtures increased from the control to 15% RAP level, but the 25% and 40% RAP mixtures had dynamic modulus curves similar to that of the control mixture in both tension and compression. The creep compliance curves showed similar trends. A combination of gradation, asphalt content, and volumetric properties is likely the cause of these trends.
查看更多>>摘要：This paper presents a laboratory study in which the blending process of reclaimed asphalt pavement (RAP) with virgin mixture was analyzed through controlled experiments. One type of screened RAP was blended with virgin (new) coarse aggregate at different percentages. A blended mixture containing 20% of screened RAP was subjected to staged extraction and recovery. The result from this experiment indicated that only a small portion of aged asphalt in RAP actually participated in the remixing process; other portions formed a stiff coating around RAP aggregates, and RAP functionally acted as "composite black rock." The resulting composite layered structure was desirable to improve the performance of the hot-mix asphalt mixture.
查看更多>>摘要：A small device available commercially uses litmus paper and a spectro-photometer to analyze vapors from hot liquid asphalt binders and mixtures to determine the percentage of antistripping additive present. Approximately 60 five-point additive content-color index count regressions were performed on binders and mixtures to determine how well the device measured additive content. The regressions basically fit the quadratic format used by the manufacturer in the recommended calibration process. The regressions were best when the litmus color index count was calculated by subtracting the initial count of the blank strip from the final count after exposure from the mixtures. Changes to the instrument software and testing temperature were necessary as the investigation progressed to accommodate different grades of binders. After the planned testing was completed, some retesting of the binders was performed with the use of modified equipment and procedures. The changes appeared to improve the consistency of the results. Test results with mixtures were less accurate than for binders; however, if the vapor trap is modified as described, the accuracy for mixtures should be improved substantially. Because the test can be performed quickly, it would be possible to perform multiple tests on a sample. Multiple tests would increase the confidence of the test results.
查看更多>>摘要：This study was conducted to develop laboratory and field permeability testing procedures for design and quality control of Superpave~® mixtures in Wisconsin. Sixteen mixes including fine-graded and coarse-graded mixes were evaluated. The in-place field permeability was measured by using the National Center for Asphalt Technology (NCAT) device, field cores were taken for measuring permeability in the laboratory by using the ASTM D5084 method, and laboratory compaction was used to prepare and test samples from loose mixtures recovered from the field. Two compaction procedures called Method A and Method B were used in this study to produce Superpave gyratory compacted (SGC) specimens that have thickness, air voids, and aggregate orientation similar to the field cores. Result indicates that Method B, based on the use of Ndesign gyrations for different sample sizes, can be used to produce samples that give permeability values similar to values measured for field cores. Results of this study also indicate a good relationship between field permeability (using the NCAT device) and lab permeability measured on field cores of fine-graded mixes with the amount passing No. 8 sieve (P8) higher than 45%. However, the relationship between field permeability and lab permeability measured on field cores of coarse-graded mix (P8 lower than 40%) is poor. It is concluded that the NCAT permeability device could possibly be used in the field for fine-graded mix (with P8 higher than 45%). However, to measure the field permeability of coarse-graded mix (P8 lower than 40%), there appears to be no current alternative better than taking field cores and testing them in the laboratory. For estimating permeability during mixture design, a simple method for preparing and testing permeability of SGC specimens and interpolating based on expected field density is introduced.
Thomas BennertFrank FeeEileen SheehyAndris Jumikis...
p.59-68页
查看更多>>摘要：The use of thin-lift hot-mix asphalt (HMA) surface course mixes has gained wide acceptance in the United States as a means of improving ride quality and safety. Generally, these materials are classified as having an open-graded and gap-graded aggregate skeleton, nominal aggregate sizes of 12.5 mm or less, and higher than normal asphalt binder contents and are placed in thicknesses of less than 1 in. (25 mm). The use of the thin-lift materials has been found to improve wet-weather driving conditions, reduce traffic noise associated with the tire—pavement interface, and improve ride quality measurements. Typically, thin-lift HMA surface course mixes found in New Jersey consist of open-graded friction courses and Novachip, with a few roadway sections using microsurfacing and stone-mastic asphalt. Each of these material types is evaluated to provide an assessment of their ride quality and safety. These thin-lift materials are compared with in-service dense-graded asphalt mixes and portland cement concrete (PCC). PCC pavements have three different surface conditions: no treatment, transverse tined, and diamond grind. To establish performance comparisons between the different surface courses, noise measurements using the close proximity method, wet-skid resistance, , and ride quality data consisting of the ride quality index and international roughness index were used. The performance information, along with current costs associated with the materials and construction, can provide a means of establishing the cost-effectiveness for the use of these surface treatments under specific situational conditions.
Francesco CanestrariGilda FerrottiManfred N. PartiEzio Santagata...
p.69-78页
查看更多>>摘要：The performance of multilayered pavement systems depends strongly on interlayer bonding. To guarantee good bonding, tack coats (also called bond coats) are usually applied at various interfaces during pavement construction or overlay. The effectiveness of the tack coat can be assessed with the use of several devices arranged by different laboratories to evaluate interlayer shear resistance. This paper shows how interlayer shear resistance may be evaluated through the Ancona shear testing research and analysis (ASTRA) device. ASTRA results, expressed in units of maximum interlayer shear stress (τ_(peak)), highlight the effects of various influence parameters such as type of interface treatment, curing time, procedure of specimen preparation, temperature, and applied normal load. Moreover, this paper compares the τ_(peak) results obtained by two different shear test devices: the ASTRA tester designed and developed in the Polytechnic University of Marche (Italy) and the layer-parallel direct shear tester created by the Swiss Federal Laboratories for Materials Testing and Research. The two test methods provide different but comparable results showing the same ranking of shear resistance for different interface treatments.
查看更多>>摘要：Open-graded asphalt mixes are often used for wearing surfaces of roads exposed to large amounts of rainfall throughout the year. The high permeability of the mix guarantees fast drainage of the water away from the surface and thus increases road safety. However, the large amounts of water that flow through the asphalt have a negative effect on the material characteristics of the mastic and cause debonding of the aggregates from the mastic, called raveling. To understand and quantify the physical processes and the mechanics leading to raveling, an extensive experimental and analytical investigation is being undertaken at Delft University of Technology in the Netherlands. One goal of the investigation is the development of the finite element tool RoAM (raveling of asphalt mixes), which is capable of simulating the gradual development of damage throughout asphalt mixes due to water infiltration. Desorption, diffusion, and dispersion are included as fundamental processes. This paper shows the results of a computational analysis to identify the impact of the different water damage phenomena and presents results of a sensitivity study of the relevant parameters. From the computational analyses it is concluded that simulation of water damage in asphaltic mixes is possible if the desorption characteristics as well as the diffusion and dispersion coefficients can be determined.
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