Showing papers on "Asphalt published in 1997"

The Science and Technology of Civil Engineering Materials

Abstract: I. THE FUNDAMENTALS OF MATERIALS. 1. Atomic Bonding. 2. The Architecture of Solids. 3. Development of Microstructure. 4. Surface Properties. II. BEHAVIOR OF MATERIALS UNDER STRESS. 5. Response of Materials to Stress. 6. Failure and Fracture. 7. Rheology of Fluids and Solids. 8. Fatigue. III. PARTICULATE COMPOSITES: PORTLAND CEMENT AND ASPHALT CONCRETES. 9. Particulate Composites. 10. Aggregates. 11. Portland Cement Concrete. 12. Asphalt Cements and Asphalt Concrete. IV. STEEL, WOOD, POLYMERS, AND COMPOSITES. 13. Steel. 14. Wood and Timber. 15. Polymers and Plastics. 16. Fiber Reinforced Composites. Solutions to Numerical Problems. Index.

Micromechanical Simulation of Hot Mix Asphalt

Abstract: A model based on the discrete element method (DEM), ASBAL, was developed by modifying the TRUBAL program to simulate hot mix asphalt (HMA) To represent asphalt cement, several viscoelastic elements (ie, Maxwell, Kelvin-Voigt, and Burger's elements) were considered The research results from the Strategic Highway Research Program (SHRP) were used for the selection of proper element From these viscoelastic elements the Burger linear viscoelastic element is shown to be the most promising element for modeling asphalt binder behavior, based on mechanical responses and comparisons with physical experimental results Therefore, Burger's elements were added in normal and tangential directions to each aggregate-asphalt-aggregate contact to simulate the asphalt binder in HMA assemblies This new model is called ASBAL (TRUBAL for Asphalt) Several monotonic and cyclic tests were simulated to observe and fine-tune the model ASBAL A carefully conducted physical experiment with X-ray tomographs was simulated and c

Evaluation of crack propagation properties of asphalt mixtures

Abstract: Current failure criteria of asphalt pavements are either empirical or assume linear elastic material response and use a single load level to relate the number of load repetitions to fatigue failure. To better understand the crack propagation properties of asphalt pavements, laboratory tests and nonlinear analysis were performed to evaluate the low-temperature fracture parameters of conventional asphalt concrete and asphalt-rubber mixture. Two approaches based on nonlinear fracture mechanics, the compliance approach and the R-Curve approach, were used. Beam specimens were prepared with different binder contents and tested under three-point bending flexural conditions at two test temperatures. A closed-loop servohydraulic test system was used with the crack mouth opening as the control parameter. Nonlinear fracture parameters were obtained at different stages of crack propagation. Results show that the asphalt-rubber mixture has higher fracture toughness and consequently larger resistance to cracking than asphalt concrete. Also, the asphalt-rubber mixture is less sensitive to temperature than asphalt concrete. Increasing the binder content increased the toughness values for both asphalt concrete and asphalt-rubber mixture in most cases. The R-Curve approach provides a good measure of characterizing the fracture behavior of asphalt mixtures.

Digital image processing for aggregate orientation in asphalt concrete mixtures

Abstract: Asphalt concrete is a composite material which consists of asphalt cement, voids, fine particles, sand, and coarse aggregates. Previous investigations of asphalt concrete mixtures have mainly concentrated on the macroscopic properties of the composite materials based on the assumption that the mixtures are homogeneous and isotropic. This paper applies an innovative digital image processing technique to quantify the orientations of coarse aggregate particles (≥ 2 mm) in asphalt concrete mixtures such as hot mix asphalt, stone matrix asphalt, and large stone asphalt compacted in the laboratory or field. The results indicate quantitatively that asphalt concrete specimens compacted in the field or in the laboratory with gyratory compactor have an oriented structure of aggregate particle distribution where the major cross sections of aggregate particles have the tendency to lie horizontally, and that aggregate particles are more randomly oriented in the asphalt concrete specimens compacted in the laboratory wi...

Sources of Fine Organic Aerosol. 7. Hot Asphalt Roofing Tar Pot Fumes

Abstract: The organic compounds present in fine particulate roofing asphalt tar fumes are characterized using GC/MS techniques. Most of the compound mass identified consists of n-alkanes (73%). Polycyclic aromatic hydrocarbons (PAH) and thia-arenes (S-PAH) contribute nearly 8% of the identified compound mass and account for 0.57% of the total mass emissions. When compared to the PAH mass fraction determined in fine particulate exhaust emitted from catalyst-equipped automobiles (∼0.5%) and heavy-duty diesel trucks (∼0.1%), roofing tar pot aerosols show a PAH content similar to that of vehicular exhaust.

Effect of tack coat on bonding characteristics at interface between asphalt concrete layers

Abstract: タックコートがアスファルト舗装の表層と基層の間の付着力に及ぼす効果について室内試験により検討した. まず, 航空機荷重が舗装表面に鉛直および水平方向に加わった場合に表・基層間に生ずる応力について解析した. 次に, 表・基層間の付着力について施工方法の異なる舗装箇所から採取した試料により調べ, 表・基層間の施工時間間隔がその境界面における付着力に及ぼす影響を調べた, そして, 付着をよくするために使用されるタックコートの効果について境界面に付着する砂などの汚れ, タックコートの養生時間, 材料の違いといった点に注目して検討を加えた. 最後に, 実際の舗装の建設・補修工事の状況を勘案して, 空港舗装に適したタックコート材料の開発を試みた.

Designing recycled hot mix asphalt mixtures using superpave technology

Abstract: Mix design procedures for recycled asphalt pavements require the selection of virgin asphalt binder or recycling agent. This research project was undertaken to develop a procedure for selecting the performance grade (PG) of virgin asphalt binder based on the Superpave PG grading system. Blending charts, similar to the viscosity blending charts, were constructed and evaluated based on test parameters obtained from the dynamic shear rheometer (DSR). The criteria for selection was based on Superpave performance grading (PG) specification. The criteria based on the fatigue parameter was determined to be too liberal and, therefore, was not recommended. An alternative criteria based on the high temperature stiffness was recommended.

Development of a mixture design procedure for stone matrix asphalt (sma)

Abstract: Stone Matrix Asphalt (SMA) has been used successfully in Europe for over 20 years to provide better rutting resistance and to resist studded tire wear. Since 1991, the use of SMA has increased steadily in the United States. At present, some states routinely use SMA even though a standard mixture design procedure is not available. A mixture design procedure that provides guidance on material properties, aggregate gradation, determination of optimum asphalt content, and mixture properties is needed. This paper presents a mixture design procedure for SMA mixtures developed by the National Center for Asphalt Technology. Data for the development of the procedure were collected from a laboratory study conducted with various samples of aggregates, fillers, asphalt binders, and stabilizing additives. Compacted mixtures were tested to evaluate the effects of aggregate structure, asphalt binder, and binder-fine aggregate mortar. Specific conclusions from this study were: (1) The Los Angeles abrasion loss showed good correlation with aggregate breakdown. (2) It appeared that the 3:1 or 2:1 flat and elongated particles provided much better classification for the various aggregates than a 5:1 ratio. (3) The flat and elongated particle ratio showed excellent correlation with aggregate breakdown. (4) In a SMA mix, the percent passing the 4.75 mm sieve must be below 30% to ensure proper stone-on-stone contact. (5) The percent passing the 0.02 mm sieve did not show a correlation with mortar stiffness. However, the dry compacted volume, as obtained from the Penn State test method, did show a good correlation with mortar stiffness and can be utilized to characterize the shape of fillers. Generally, a more angular filler tends to produce a higher air voids result in this test. (6) In-place results from about 86 projects showed that very little rutting has occurred in SMA pavements constructed in the U.S. since 1991. However, for the pavements with air voids falling below the 3% range, some rutting was observed. (7) A voids in mineral aggregate (VMA) significantly lower than specified VMA can be obtained due to aggregate breakdown. Hence, the mix designer must consider aggregate type, compactor type and compactive effort along with the gradation in meeting the required VMA criteria. Specifying a minimum asphalt content can result in different requirements for aggregates with different specific gravity. (8) Fifty blows of Marshall hammer were found to be approximately equal to 100 revolutions of the Superpave gyratory compactor in terms of resultant density. The Superpave gyratory compactor was found to produce less aggregate breakdown than the Marshall hammer. (9) Fiber stabilizers were found to be more effective in reducing draindown than polymer stabilizers. However, mixes modified with polymer showed better resistance to rutting in laboratory wheel tracking tests.

Review of UK Porous Asphalt Trials

Abstract: Porous asphalt as a road surfacing material has been under investigation by TRL since 1967 and is now included in the Specification for Highway Works and the Design Manual for Roads and Bridges published by the Department of Transport and the other Overseeing Departments for UK trunks roads The experience gained from extensive road trials is reviewed and recommendations are derived to assist those involved in the design, manufacture and application of porous asphalt, particularly with a 20 mm nominal aggregate grading The road trials are interpreted in terms of the design and construction of porous asphalt layers; the properties that can be achieved from the material; and the maintenance implications of its use The road trials have shown that porous asphalt can be durable if it is properly designed and constructed and it is laid on suitable sites For such situations, the standard properties required of surface course materials (such as skid-resistance, texture depth and profile) can be provided by porous asphalt, together with the additional benefits through reduction of noise and spray Aspects of maintenance for porous asphalt that are different from that of traditional, impervious surfacings are discussed (A)

Physical properties of asphalt-rubber binder

Abstract: This study was performed to determine how the rheological properties of asphalt-rubber binders are affected by various parameters. Properties studied were asphalt composition, rubber dissolution, and the low-, intermediate-, and high-temperature rheological properties, measured with the bending beam rheometer. dynamic shear rheometer, and rotational viscometer, respectively. The rheological properties of the asphalt-rubber binder were determined to be dependent on the rubber content (weight percent), rubber particle size, and base asphalt composition. By controlling these variables, an asphalt-rubber binder with improved low-temperature cracking resistance, improved mid-temperature rutting resistance and temperature susceptibility, and a non-detrimental high-temperature compaction viscosity, all relative to the base asphalt, can be produced.

Fracture Morphology and Fracture Toughness Measurement of Polymer-Modified Asphalt Concrete

Abstract: Pavement distress occurs through a variety of mechanisms, but it is always controlled by the adhesive and cohesive performance of the asphalt binder. Although the causes of pavement failures are known, the precise mechanisms by which they occur remain to be understood. Observation of the fracture morphology of asphalt concrete can provide some information in this respect. The fracture morphology of asphalt concrete is dependent on the morphology of the binder. A network structure was observed in thin asphalt binder films and the fracture morphology and engineering properties of asphalt concrete were found to be dependent on the network morphology of the asphalt binder. Addition of polymers to asphalt binders causes changes in the nature of the network structure, and its effect can be qualitatively determined by characterizing the fracture morphology. Styrene butadiene styrene (SBS), styrene ethylene butylene styrene (SEBS), styrene butadiene rubber (SBR) latex and an epoxy-terminated reacting polyolefin (...

Fatigue analysis of asphalt pavements with thick asphalt mixture layer

Abstract: In the prevailing structural design of asphalt pavements, fatigue cracking at the bottom of the asphalt mixture layer is considered to be a major failure mode of the pavement structure. In Japan, however, such failure has rarely been observed in the asphalt pavements with a thick asphalt mixture layer, including asphalt stabilized base course which has been in service for more than 20 years. Failure modes of the asphalt pavements are rutting and surface cracking. The asphalt stabilized base courses in such pavements have been alive without major repairing. Therefore, the concept of the structural design should be reconsidered in terms of the fatigue cracking. We conducted fatigue analysis for various asphalt pavements with thick asphalt mixture layer in Japan. Radial strains at the bottom of the asphalt mixture layer and vertical strains at the top of the subgrade were calculated. Then, fatigue damages were estimated by applying the calculated strains to fatigue curves presented in the manual. In the analysis, wheel load distributions were taken into account by employing Miner's law. The results of the fatigue analysis showed that the fatigue crack at the bottom would occur in the asphalt pavements with thick asphalt mixture layer in less than 10 years. The results do not agree with our field experiences mentioned above. We made an assumption that, at the strain level of less than 200 micro, the asphalt mixture would not experience fatigue because of the healing effect. Based on this assumption, we conducted the fatigue analysis again. The results of the analysis seemed to be quite reasonable and agree with our experiences in Japan.

Development of temperature-effect model for predicting rutting of asphalt mixtures using georgia loaded wheel tester

Abstract: Use of the Georgia loaded wheel tester (LWT) to evaluate rutting susceptibility of asphalt mixtures has gained acceptance by the asphalt paving industry. The test is typically conducted at 40°C for 8,000 cycles and the rut-depth value measured at the end of the test is compared with a maximum criteria of 5.0 mm or 7.5 mm to assess rutting susceptibility of the mixture. A temperature effect model (TEM) was developed using the LWT test data from seven asphalt mixtures. The TEM developed can be used to predict the rut-depth values of an asphalt mixture at different temperatures and number of loading cycles from the LWT performed on the asphalt mixture at one testing condition. The predicted rut-depth values from the TEM compared very closely with the measured values. For the five dense-graded hot-mix asphalt mixtures (HMA), only 7 out of 170 predicted rut-depth values deviated from the measured values by more than 0.8 mm. For the two stone-matrix asphalt mixtures (SMA), only 2 out of 64 predicted values devi...

Solvent-free method and apparatus for removing bituminous oil from oil sands

Abstract: A sand/liquid separator provides for the conditioning of oil sands. Clean sand is separated from the ore and discharged for use as backfill. The sand/liquid separator machine includes horizontal shafts with paddles that act on a fluidized bed. The overall height of the machine is increased over prior art devices so the water volume is expanded. For a given residence time, more sand can be separated out than is otherwise possible. The water-to-sand ratio is an independent variable, water is recycled independent of the sand. The rate of water recycle depends only on the heat input needed and the clay content of the feed. The rate of water input is limited by the rise velocity needed to separate sand larger than forty-four micron from the water/liquid phase. This, in turn, determines the maximum oil sand feed rate based on the total clay in the feed at up to six percent, by weight, of clay in the middlings in the machine. This optimizes the performance of the process to cope with all the variables of heat input, ratio of oil sand feed to water, and clay content of the feed.

Long-Term Oven-Aging Effects on Fatigue and Initial Stiffness of Asphalt Concrete

Abstract: An investigation of the effects of long-term oven aging (LTOA) on initial stiffness and fatigue of asphalt concrete was made using two typical California asphalts, known to have different aging characteristics, in mixes with one aggregate. Asphalt content, air-voids content, and days of LTOA were varied independently. Stiffness and fatigue were evaluated using the controlled-strain flexural beam test developed by the Strategic Highway Research Program Project A-003A. The results indicated that both mixes exhibited an increase in initial stiffness with LTOA periods of up to six days. The sensitivity of beam fatigue life to LTOA depended on the asphalt. Beams containing Valley asphalt had virtually no change in fatigue life due to LTOA, whereas beams with Coastal asphalt showed some sensitivity to LTOA. For both asphalts, the average reduction in fatigue life from 6 days of LTOA was less than that caused by a 3 percent increase in air-void content or a 1 percent decrease in asphalt content. Simulations of t...

Polymer enhanced asphalt emulsion

Abstract: The present invention relates to an asphalt composition prepared from bitumen (asphalt), linear and non-linear copolymers of styrene and butadiene, cross-linking agents, and emulsifiers. The present invention compositions are useful for industrial applications, such as hot-mix and emulsified asphalts used with aggregates for road paving, and repair.

Superpave support and performance models management: evaluation of the shrp performance models system

Abstract: A principal result of the Strategic Highway Research Program (SHRP) was a set of pavement performance models for predicting low temperature thermal cracking, fatigue cracking, and permanent deformation in asphalt pavements under environmental and traffic loadings. The Federal Highway Administration, as part of its Superpave implementation plan, awarded a contract to the University of Maryland and a team of subcontractors to provide a comprehensive and unbiased evaluation of the original SHRP pavement performance models. The principal conclusions from this evaluation are: (a) the SHRP Superpave system provides an excellent framework for future modifications and enhancements to the models; (b) the existing non-load related thermal fracture model predicts field behavior reasonably well, although some minor modifications and enhancements to the model are necessary; (c) the performance prediction models for load related fatigue fracture and permanent deformation perform poorly, and substantial corrections and enhancements to these models are imperative if they are to be sufficiently reliable for acceptance and use by industry; (d) although some of the problems in the load related distress models are the consequence of technical and other constraints during the original SHRP research effort, many are the direct result of problems in the asphalt material characterization models and associated test procedures; and (e) the necessary corrections, modifications, and enhancements to the models will mandate new field calibration and validation. Detailed evaluation findings supporting these conclusions are presented in the paper. Future plans for the enhancement and implementation of the Superpave performance models are also briefly described.

In Situ Evaluation of Fatigue Damage Growth and Healing of Asphalt Concrete Pavements Using Stress Wave Method

Abstract: Accurate in situ evaluation of the changes in material properties of an asphalt surface layer due to fatigue loading and rest periods is important for a better understanding of fatigue mechanisms of asphalt concrete in the field and therefore more realistic prediction of the fatigue life of asphalt pavements. A nondestructive technique based on the stress wave propagation method is presented as a means of measuring the changes in the "apparent" modulus of an asphalt surface layer due to fatigue damage growth and healing during rest periods. The method was applied to four asphalt pavements in the FHWA Turner Fairbank Highway Research Center that were loaded by the Accelerated Loading Facility to induce fatigue damage. The dispersion analysis is performed using the Short Kernel Method on the wave transients measured at different loading cycles and after rest periods. The results indicate that (a) the test and analysis technique used provides a sensitive means of evaluating the changes in asphalt surface lay...

Asphalt modifier composition and asphalt composition

Abstract: Preparation of an asphalt composition using an asphalt modifier composition comprising at least one member selected from the group consisting of rubber-base modifiers and resin-base modifiers and a phosphorus compound permits the modifier to be satisfactorily dissolved in asphalt. Further, when paving is conducted by using a composition for paving prepared with such the asphalt composition, the adhesion of asphalt to an aggregate is high, and the resultant pavement has markedly improved in rutting resistance and wearing resistance. Therefore, such the pavement has a prolonged service life.

Process to refine petroleum residues and sludges into asphalt and/or other petroleum products

Abstract: A process for significantly decreasing processing time, reducing capital costs, increasing yield, improving quality, and improving the safety of refining petroleum residues and sludges generated by the oil producers, refineries and re-refiners comprising the steps of heating under vacuum the petroleum residues and sludges with steam or inert gas injection or both until a temperature ranging from between 680° F. to 1000° F. is attained and holding the mixture at this temperature for a short residence time of from less than an hour to abut 6 hours while vacuum and sparging are being carried out to generate asphalt. Volatile products are condensed to produce fuel, waxy oil and can be further processed to produce refined fuel, wax and dewaxed oil.

Method for recycling and rejuvenating asphalt pavement

Abstract: A method for rejuvenating asphalt pavement includes milling and collecting a select thickness of asphalt pavement of a portion of an existing roadbed. A shale oil modified asphalt comprising between 5-25% shale oil modifier and 75-95% asphalt cement is provided. An aggregate comprising about 60-70% virgin aggregate and about 30-40% of the milled and collected asphalt is combined with the shale oil modified asphalt and then applied to a roadbed.

Performance modeling of Arabian asphalt using HP-GPC

Abstract: In this study, Arabian neat asphalt samples were collected from different asphalt producing refineries in the Gulf countries. Another set of polymer modified samples was also included in this study. In the polymer modification process, 5,10, and 15% crumb rubber (CRT) and 3,6, and 9% styrene-butadiene-styrene (SBS) were used. All asphalt samples were subjected to two aging processes to simulate heating, mixing, compaction, and in-service aging. The asphalt samples at the different aging stages were subjected to performance-based tests that were adapted and/or modified by the Strategic Highway Research Program (SHRP) team. High pressure gel permeation chromatography (HP-GPC) was used to chemically analyze the test samples by generating profiles of their molecular size distribution. Models were built to predict the performance-based properties from the produced HP-GPC profiles.

Use of Superpave technology for design and construction of rubberized asphalt mixtures

Abstract: The effect of different mixing times and mixing temperatures on the performance of asphalt-rubber binder was evaluated. Four different types of asphalt-rubber binders and neat asphalt were characterized using the Strategic Highway Research Program (SHRP) binder method tests. Subsequently, mix designs were carried out using both the SHRP Levels I and II mix design procedures, as well as the traditional Marshall mix design scheme. Additionally, performance testing was carried out on the mixtures using the Superpave repetitive simple shear test at constant height (RSST-CH) to evaluate the resistance to permanent deformation (rutting) of the rubberized asphalt mixtures. Also, six rectangular beams were subjected to repeated bending in the fatigue tester at different microstrain levels to establish rubberized asphalt mixtures' resistance to fatigue cracking under repeated loadings. The results indicate that the Superpave mix design produced asphalt-rubber contents that are significantly higher than values used successfully in the field. Marshall-used gyratory compaction could not produce the same densification trends. Superpave mixture analysis testing (Level II) was used successfully for rubberized asphalt mixtures. Results clearly indicated that the mixture selected exhibited acceptable rutting and fatigue behavior for typical new construction and for overlay design. Few problems were encountered in running the Superpave models. The results of the RSST-CH indicate that rubber-modified asphalt concrete meets the criteria for a maximum rut depth of 0.5 in.; and more consistent results were measured for fatigue performance analysis using the repeated four-point bending beam testing (Superpave optional torture testing). The cycles to failure were approximately 26,000 at 600 microstrain.

How good are some rheological models of dynamic material functions of asphalt

Abstract: The main objective of this paper is to show the advantages and disadvantages of several rheological models applied to regular and polymer modified asphalts. The choice of any model is dictated by the purpose of the modelling, however, a "good" model should be able to describe as completely as possible the linear viscoelastic functions of the studied materials.

Method for asphalt compaction and compaction apparatus

Abstract: A method of compacting a mat of hot mix asphalt comprising advancing an asphalt compactor over laid asphalt substantially at the rate of advancement of an asphalt paver and within about 50 M behind the asphalt paver, or at a rate of advancement of no more than about 0.7 m/s, the asphalt compactor having a compaction surface which engages the mat over a length of at least about 1 m wherein the compaction surface is formed by a lower run of at least one belt, and wherein the compaction surface applies a maximum average load stress to the mat of less than about 50 kPa. Compaction may be achieved using a compactor (60) comprising two longitudinally spaced rotatable support assemblies (62), wherein at least one of the support assemblies (62) is adjustable to permit steering of the compactor, and wherein at least one of the support assemblies (62) comprises a modular compaction unit comprising a compaction belt (74).

Performance study of portland cement concrete pavement joint sealants

Abstract: The objective of this research project is to determine the service lives of three different types of joint sealants—polyvinylchloride (PVC)-coal tar, rubberized asphalt, and silicone—and to recommend maintenance strategies to improve the performance of concrete pavements in Utah. The silicone material has been performing well for over 10 years. The PVC-coal tar material had failed in the test sections that are an average of 15 years old, and the rubberized asphalt material has aged beyond its expected service life in the test sections over 20 years old. Survival curves of the three sealants were developed with respect to their ages, and their performance correlated well with their ages. The conical spalling at the bottom of the joints increased after 10 years of service. Based on the limited field data, it is recommended that Utah Department of Transportation (UDOT) should consider the use of a narrower joint width of 6 mm instead of the current 9-mm design, use silicone or rubberized asphalt material, and implement a maintenance plan with a 10-year cycle for recutting and resealing of the joints to 9 x 9 mm.

Homogeneous crumb rubber modified asphalt

Abstract: An improved asphalt composition for pavement and a method for producing the same is characterized by mixing peroxide with crumb rubber to modify the crumb rubber so that mixes more evenly with the asphalt when added thereto. A compatibilizer/polymer is also added to the asphalt. The resulting composition is homogeneous and demonstrates improved settling and rheological properties at high and low temperatures.