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Modeling the Impact of Testing Mode on the Viscoelastic Behavior of Asphalt Concrete
No full textThe variations in the viscoelastic behavior of asphalt concrete due to testing mode is assessed and modeled in the present investigation. Asphalt concrete mixture was prepared at its optimum binder requirement and compacted in slab mold with the aid of roller compaction. Beam specimens of 62 mm width, 400 mm length, and 56 mm depth were extracted from the slab samples and tested using controlled stress and strain techniques under dynamic flexural stresses. The viscoelastic properties such as the cumulative dissipated energy, phase angle, flexural stiffness, micro strain, and permanent deformation were monitored and modeled among the two testing techniques. It was observed that higher permanent deformation and micro strain are detected when the test was conducted under constant strain mode. However, higher phase angle, flexural stiffness, and energy dissipation could be observed under constant stress mode of test. 
Assessing the Ageing Impact on Fatigue Life of Asphalt Concrete
No full textThe fatigue life of asphalt concrete is often related to environmental condition, loading condition, ageing, material composition and properties. This work investigates the influence of short and long term ageing of laboratory beam specimens, asphalt content, and testing temperature on fatigue life of asphalt concrete wearing course. Slab samples of (30 x 40x 6) cm have been prepared, beam specimens of (40x 5x 6) cm were cut from the asphalt concrete slab samples. Beam specimens were tested for fatigue life under the influence of three levels of micro strain (250, 400, and [3]750) at (5, 20, and 30) °C before and after practicing long-term aging. It was observed that the fatigue life decreases by (85 and 97) %, (87.5 and 97.4) %, (71.4 and 95.2) % after increasing the applied microstrain from (250 to 400 and 750) μƐ for control mixture and for mixtures subjected to short-and long-term ageing processes respectively. The fatigue life increases by (142.8 and 257.1) %, (34.4 and 57.8) % and (10 and 30) % when the asphalt content increases from (4.4 to 4.9 and 5.4) % for specimens practicing the applied microstrain of (250, 400 and 750) μƐ respectively. It was concluded that the fatigue life increases by a range of (two to fifteen) folds when the testing temperature increases from (5 to 20 and 30)°C respectively
Impact of Compaction Mode on Strength Properties of Sustainable Asphalt Concrete
No full textVarious modes of compacting the asphalt concrete mixture can createmechanically different behaviour of the prepared specimens and can alterits sustainability. An attempt has been made in the present assessment toprepare asphalt concrete specimens by implementation of three modesof compaction, the gyratory, the roller, and the Marshall hammer. Thespecimens were prepared at the target bulk density of Marshall methodat optimum asphalt content. Extra specimens were prepared at 0.5 %asphalt below and above the optimum. Core specimens have been obtainedfrom the roller compacted slab samples. The specimens were tested forthe Marshall stiffness, tensile, and shear strength. It was observed that atoptimum asphalt content, the indirect tensile strength declines by (18.8and 70.5) % for gyratory and roller compacted specimens respectively ascompared with hammer compacted specimens. At optimum asphalt content,the shear strength declines by (70.5 and 82.2) % while Marshall stiffnessdeclines by (10.2 and 44.8) % for hammer and roller compacted specimensas compared with that of gyratory compacted specimen. Specimensprepared by gyratory compaction are less susceptible to the change inthe testing temperature as compared with other modes of compaction. Itis recommended to consider the mode of compaction to suit the requireddesign property of sustainable asphalt concrete mixture
Influence of Iron-Filings on Marshall and Volumetric Properties of Asphalt Concrete
Get PDFThe growth and expansion of road infrastructure had resulted in the continuous use of materials, increased construction costs of flexible pavements and increased environmental impact during the service life of the road. Consequently, many researchers have sought to use methods to maintain these roadways sustain environmental impact and traffic loads. One of these approaches is the use of additives to improve asphalt's volumetric character. In this research, iron filings were used as partial replacement of fine aggregates, and the Marshall and volumetric properties were assessed before and after the implementation of iron filings. Specimens were prepared with iron filings addition of (2, 4, 6 and 8%) by weight of fine aggregates. The Marshall mix design procedure was used to calculate the optimum asphalt content and the volumetric properties, including bulk density, Total voids, voids in mineral aggregates V.M.A., and voids filled with asphalt V.F.A. The Marshall Flow and Stability were calculated. Test results were assessed before and after the inclusion of the iron filings. It was concluded that the addition of iron filings can enhance the Marshall and volumetric properties of asphalt. The stability increased by 15% when replacing fine aggregates by 2%, of iron filings by total weight. Also, the air voids and the VMA decreased by increasing the percentage of iron filings, while VFA was not significantly affected as compared to the conventional specimen. The ideal ratio of iron filings which fulfill the optimal requirements was 5%
Verifying Moisture Damage Impact in Asphalt Concrete with the Aid of Nondestructive Test NDT
Get PDFOne of the major concerns of pavement durability is its susceptibility to moisture damage. In this investigation, non-destructive test NDT has been implemented to detect the moisture damage issue. Asphalt concrete specimens were prepared using the traditional Marshall method for wearing, binder and asphalt stabilized base course. Specimens were traversed by ultrasound pulse velocity before and after practicing the moisture damage procedure. The variation of dynamic and elastic modulus before and after the moisture damage was considered and related to tensile strength ratio TSR. It was noted that the pulse velocity decline by (11, 11.2 and 16.4) % and the dynamic modulus declines by (28, 6.6 and 28.5) % for asphalt concrete wearing, binder and base courses respectively after moisture damage. The elastic modulus exhibits no significant variation after moisture damage for wearing course while it declines by (9 and 11.7) % for binder and base courses respectively after moisture damage. It was concluded that the elastic and dynamic moduli were unable to clearly distinguish the impact of moisture damage, whereas the Seismic modulus calculated from the Ultrasonic Pulse Velocity test was effective in distinguishing such impact. The linear equation obtained with good coefficient of determination can explain 74 % of the variation in the seismic modulus after moisture damage
Impact of Rejuvenators Type on Physical Properties of Aged Asphalt Cement
Get PDFRecycling can be considered as one of the measures of sustainable methods. The physical traits of the asphalt mixture under the influence of accelerated aging (Long and Short–Term) for asphalt concrete were assessed. Asphalt cement (40-50), aggregate with 12.5 mm nominal extreme size and limestone dust as filler of the mineral was used for the preparation of asphalt concrete mixture. At the optimum content of the asphalt and asphalt of 0.5 percent below and above the optimum value, specimens were prepared by using Marshall Method. Two types of polymers as recycling agents were used (Polyethylene of Low Density and Crumb Rubber) with (0.5, 1 and 1.5) % by weight of the binder. The indirect tensile test was used for the mixtures at 25 ºC and double punch test at 60 ºC. It was determined that the use of (asphalt binder mixed with rubber) as the agent of recycling showed improved performance than the other kind of recycling agent. The indirect tensile strength at 40 ËšC of the recycled mixture was higher than that the control mixture. Punching shear strength was decreased by 84 %, temperature susceptibility was decreased by 69.6 % and the resistance to moisture damage increases by3.3 % at optimum asphalt content
Assessment of Rutting Resistance and Healing for Stone Matrix Asphalt Concrete (SMAC)
Get PDFStone Matrix Asphalt Concrete (SMAC) is known as tough, stable, rut-resistant mixture. In this investigation, SMAC was prepared in the laboratory using gap graded aggregates, asphalt cement, mineral filler and coal fly ash as stabilizing agent. Specimens were prepared using static compaction to the target density based on asphalt content for each case. The prepared Specimens were subjected to the 1200 repeated compressive stresses at 25 ºC under various stress levels using the pneumatic repeated load system PRLS. Specimens were subjected to microcrack healing process by external heating for 120 minutes at 60 °C, then it practices another cycle of repeated compressive stresses. The resilient modulus, permanent deformation, and rutting resistance under three levels of stress have been assessed. It was concluded that the resilient modulus Mr increases by (66, 50 and 31) %, (36, 50 and 31) % and (62, 37 and 69) %, while the permanent deformation decreases by (25, 11.4 and 25) %, (19, 31.6 and 14.5) % and (14, 9 and 8.3) % after implementation of fly ash at (OAC-0.5, OAC and OAC+0.5) % binder content under (0.068, 0.138 and 0.206) MPa of repeated compressive stress respectively. The resilient modulus increased by (17.6, 15.3, 10.5) % , (42.8, 51, 37.5) % and (18.7, 25, 23.6) % and the permanent deformation decline by (3.52, 31.66, 6.25) % under repeated compressive stresses of (0.068, 0.138, 0.206) MPa at (25 °C) after healing for mix with (4.6, 5.1, 5.6) % asphalt content respectively when compared with mixtures before healing
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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