Asphalt Pavement Analyzer Research Articles

Laboratory characterization of recycled crumb-rubber-modified asphalt mixture after extended aging

This paper presents a limited study that characterizes the recycling of artificially aged crumb-rubber modified (CRM) mixtures depending on their recycling percentage and aggregate type. Eight mixtures [six recycled mixtures containing rubberized reclaimed asphalt pavement (RAP) and two control virgin mixtures] were designed and tested. Two types of aggregates were used in this research project. The rubberized RAP used in the study was artificially aged in the laboratory using an accelerated aging processes. The percentages of the RAP, by total weight of the mix, incorporated into the recycled mixtures were 15%, 25%, and 35%. Evaluation of all mixtures included the following testing procedures: tensile strength ratio (TSR), asphalt pavement analyzer (APA), resilient modulus, and indirect tensile strength (ITS) after long-term oven aging. The results from this study showed that (i) the recycled aged CRM mixtures (with 15%, 25%, and 35% rubberized RAP) can satisfy the current Superpave mixture requirements, including moisture susceptibility and rutting resistance, and (ii) in general, there was no significant difference between the control and the recycled CRM mixtures for the properties evaluated in this study.

An Inverse Approach for Evaluating the Properties of Asphalt Concrete Using the APA Test

ABSTRACT Rutting is one of the most serious distresses for asphalt pavement. The occurrence of rutting affects the performance of the pavement. Simulative tests including Asphalt Pavement Analyzer (APA) tests have been widely used to evaluate the rutting potential of Asphalt Concrete (AC). However, they usually cannot give fundamental properties of AC due to the complex stress and strain fields. In this study, a computational simulation method for the A PA test was developed to predict the rutting potential of AC through a viscoplasticity model and three-dimensional (3D) Finite Element Method (FEM). The model material parameters such as the elasticity modulus, yielding stress, and rutting factor (f) were obtained through an inverse method. Sensitivity of the material parameters on the influence of the rutting behavior was also evaluated. The comparison between A PA test results and the model simulation indicates that the model can capture rutting behavior of AC very well. The inverse technique enables characterization of fundamental material properties through simulative tests and saves tremendous efforts for calibration of advanced models. The computational simulative test also makes it possible to simulate rutting tests at different scales.

Mechanistic Characterization of Superpave Asphalt Mixes in Costa Rica

ABSTRACT This paper presents an investigation of the dynamic modulus, fatigue properties, and static creep of ten different Superpave mixes used in Costa Rica. The mechanistic properties were compared with empirical properties and also with equivalent Marshall Mix designs. The effect of the volumetric properties on the mechanistic and empirical properties was investigated. It was found that resilient modulus has a high correlation with Indirect Tensile strength yet it is not a good estimator for dynamic modulus. Effective binder content was found to correlate with the fatigue resistance. Asphalt Pavement Analyser (APA) results are highly influenced by the air voids of the specimens, whereas the benefits of using gap-graded gradations (e.g., SMA) is not reflected by the APA results. The paper shows that the tensile strength ratio (AASHTO T183 test) is highly sensitive to gradation and it fails to quantify moisture effects.

Investigation of Simple Performance Characteristics of Plant-Produced Asphalt Mixtures in Tennessee

With the recent adoption of the dynamic modulus, flow number, and flow time tests as simple performance tests (SPTs) to complement the Super-pave® volumetric mixture design and the selection of dynamic modulus as a basic material property input in the new AASHTO 2002 M-E design guide, SPTs have been receiving more attention and have been more often used in the asphalt community. This paper presents the results from a laboratory study with the asphalt mixtures used in Tennessee obtained by SPTs. Eleven plant-produced mixtures with asphalt cements with different PGs and different aggregates were evaluated by the dynamic modulus and flow number tests. The asphalt pavement analyzer (APA) test was also included in this study to characterize the rutting resistance of asphalt mixtures. The results indicated that generally repeatable data can be obtained from the dynamic modulus test. The flow number test was able to identify the effects of both asphalt cement and aggregate in the rutting resistance of mixtures. The SPTs and APA test produced consistent results in this study.

Laboratory Study of the Effects of Compaction on the Volumetric and Rutting Properties of CRM Asphalt Mixtures

The compaction conditions (e.g., compaction temperature and compaction level) of crumb rubber modified (CRM) asphalt mixtures should be determined carefully because the viscosity and amount of the CRM binder affects the compactability of the mixtures. Furthermore, the properties of CRM mixtures relating to the compaction conditions have not been studied in great detail. In this study, a laboratory investigation was conducted on the volumetric and rutting properties of CRM mixtures as a function of compaction conditions. For this research work, four Superpave mix designs for four different asphalt binders (control, SBS modified, 10% rubber modified, and 15% rubber modified) were carried out to determine the optimum asphalt contents. A total of 260 specimens were fabricated using the Superpave gyratory compactor at four compaction temperatures (116, 135, 154, and 173°C) and five compaction levels (20, 40, 60, 80, and 100 gyrations). The volumetric properties were obtained and analyzed, and the rutting resistance of the mixtures was measured using the asphalt pavement analyzer. The results from this study indicated that: (1) the compaction temperatures used in this study significantly affected the volumetric properties of the CRM mixtures, unlike the control and SBS-modified mixtures; (2) in general, the air void contents of the mixtures were significantly influenced by the compaction levels; and (3) as expected, the higher air void contents of the CRM mixtures seemed to have a detrimental effect on the rutting resistance.

Comparison Between Flat Rubber Wheeled Loaded Wheel Tester and Asphalt Pavement Analyzer

ABSTRACT Rutting has been identified as one of the primary distresses in asphalt pavement. Loaded Wheel Tester (LWT) has been widely used to evaluate the permanent deformation (rutting) of asphalt mixture. In China, a flat solid rubber wheeled LWT (FLWT) has been adopted by the highway design guide for many years. Dynamic Stability (DS), the number of load repetitions to generate 1-mm rutting during the last 15-min of one-hour testing, has been selected to characterize rutting of hot-mix asphalt (HMA). During the recent years, the Asphalt Pavement Analyzer (APA), has been introduced into China, and has gained popularity in pavement industry. APA uses final rut depth to evaluate the rutting performance of HMA, and there is no criterion for the APA rut depth for HMA design in China. In order to compare both data, a correlation between FLWT and APA test will be necessary. The present study selected seven mixtures commonly used in China and correlated the test results between FLWT and APA. The mixtures selected in this study included gyratory (Superpave) designed 25, 19 and 13-mm mixtures, dense-graded mixtures (25, 19 and 13-mm) designed with Marshall mix design method, and a 13mm SMA mixture. The result from this study indicated that a strong correlation existed between the FLWT DS and APA rut depth for the mixtures studied. Recommended design criterion of APA rut depth was derived from the existing DS specification and the correlation developed between the FLWT DS and APA rut depth.

Effects of Rejuvenating Agents on Superpave Mixtures Containing Reclaimed Asphalt Pavement

Rejuvenator is not a commonly used softening agent to be used in recycling of reclaimed asphalt pavement (RAP). In this study, Superpave mixtures containing RAP were designed using rejuvenating agents, including a rejuvenator and a softer binder, and subsequently evaluated in terms of the volumetric results, obtained the indirect tensile strength (ITS) of samples as well as evaluating the mixtures for rutting using the asphalt pavement analyzer (APA). The content of the rejuvenator used for those mixtures containing the rejuvenator was determined from the blending charts of RAP binders containing the rejuvenator. A total of 12 Superpave mixtures including 10 containing RAP and two virgin were designed. The results indicated, for the mixtures tested for this project, that: (1) properties of the recycled mixtures using the rejuvenator, such as ITS and APA, were better than those containing the softer binder; (2) 10% more RAP could be incorporated in the Superpave mixtures by using the rejuvenator than using the softer binder; and (3) the blending charts established under the Superpave binder specifications can be used to determine the content of the rejuvenator for the recycling.

Toward a Mechanistic Approach for Analysis and Design of Asphalt Pavements

Most current analysis and design methodologies of asphalt pavements rely on experience and empirical relationships. These relationships were developed on the basis of results of laboratory tests and by monitoring the performance of actual pavements and sections in accelerated loading experiments. The empirical relationships are limited in accounting for the fundamental properties of the materials, loading configuration, distribution of loads, and variable environmental conditions. In spite of these limitations, fairly good pavements could be constructed until recently, primarily because the lack of appropriate models could be backed up by practical experience. Relying on experience is, however, not acceptable any more because of the rapidly changing conditions of the road network. First, the significant increase in the capital investment in road construction and the need for maintenance-free roads encouraged the design of improved pavement materials modified binders, aggregate treatment, layer stabilization, and new designs of asphalt mixes . In addition, economical and environmental factors have put more emphasis on the use of local and secondary recycled building materials. Advancing the material properties and the use of locally available materials should be accompanied by developing experimental and analytical approaches that can accurately determine the effect of these materials on the design of long-lasting pavements and life-cycle cost. Second, the number and loads of trucks have increased beyond expectation as a consequence of the need to increase road transport efficiency. Furthermore, the expected introduction of aramide-reinforced truck tires in combination with foreseeable changes in wheel configurations will result in extremely high wheel pressures. Recently, a significant change in design philosophy has occurred through the development of the empirical-mechanistic design guide. The mechanistic part refers to the use of layered elastic analysis and viscoelastic material properties in some parts of the guide to determine the pavement response. Empirical relationships are used to link the calculated pavement elastic response at critical points within the structure and damage mechanisms such as permanent deformation and cracking. The empiricalmechanistic design guide includes approaches to account for traffic distribution over time and for the influence of environmental conditions on material properties. Although the empirical-mechanistic approach is considered a major step, the constitutive material models in this approach are still considered to be oversimplified because they are not able to accurately determine all aspects of the inelastic triaxial and

Effects of mineral fillers on hot-mix asphalt laboratory-measured properties

It is well recognized that mineral fillers play an important role in the properties of mastics and hot-mix asphalt (HMA) mixtures. Better understanding of the effects of fillers on the properties of mastics and HMA mixtures is crucial to good mix design and high performance of HMA mixtures. This paper presents a laboratory investigation into the effects of different fillers on some properties of asphalt mastics and HMA mixtures. Three filler types and four filler contents were used to obtain the master curves of mastics and to characterize the stiffening effect of filler in mastics. The effects of filler on the characteristics of HMA mixtures were also investigated. The properties of HMA mixtures evaluated include optimum asphalt cement (AC) content, indirect tensile (IDT) strength, toughness index (TI), tensile strength ratio (TSR) and asphalt pavement analyzer (APA) rut depth. The results suggested that fillers had significant influence on the properties of HMA mixtures. With the increase of filler content, some properties of HMA improved while others decreased. Filler content for mix design should be determined based on the overall performance of HMA mixtures.

Comparison Between Flat Rubber Wheeled Loaded Wheel Tester and Asphalt Pavement Analyzer

ABSTRACT Rutting has been identified as one of the primary distresses in asphalt pavement. Loaded Wheel Tester (LWT) has been widely used to evaluate the permanent deformation (rutting) of asphalt mixture. In China, a flat solid rubber wheeled LWT (FLWT) has been adopted by the highway design guide for many years. Dynamic Stability (DS), the number of load repetitions to generate 1-mm rutting during the last 15-min of one-hour testing, has been selected to characterize rutting of hot-mix asphalt (HMA). During the recent years, the Asphalt Pavement Analyzer (APA), has been introduced into China, and has gained popularity in pavement industry. APA uses final rut depth to evaluate the rutting performance of HMA, and there is no criterion for the APA rut depth for HMA design in China. In order to compare both data, a correlation between FLWT and APA test will be necessary. The present study selected seven mixtures commonly used in China and correlated the test results between FLWT and APA. The mixtures selected in this study included gyratory (Superpave) designed 25, 19 and 13-mm mixtures, dense-graded mixtures (25, 19 and 13-mm) designed with Marshall mix design method, and a 13mm SMA mixture. The result from this study indicated that a strong correlation existed between the FLWT DS and APA rut depth for the mixtures studied. Recommended design criterion of APA rut depth was derived from the existing DS specification and the correlation developed between the FLWT DS and APA rut depth.

MnLayer

Layered elastic theory (LET) has been used successfully for many years in the design and analysis of asphalt pavements. An attractive feature of this approach is its ability to represent the layered-pavement structure with variable interface conditions between consecutive layers. Several computer programs (BISAR, WESLEA, and JULEA) for the analysis of pavement systems were developed on the basis of LET. A new Mechanistic–Empirical Pavement Design Guide (MEPDG) procedure was recently developed by NCHRP under AASHTO sponsorship. It requires that layered elastic analysis be performed more than 1,000 times for a single design simulation of a flexible (asphalt) pavement, which makes the flexible design process extremely time consuming. An important step toward reducing the time needed to use the MEPDG software is improvement in the computational efficiency of the layered elastic analysis. In this paper, a new layered elastic analysis program, MnLayer, is presented. Several improvements in the numerical evaluation of the inverse Hankel transform of the layered elastic solutions were implemented into the program. A comprehensive comparison of MnLayer with two widely used layered elastic analysis programs demonstrated that MnLayer's accuracy matches or exceeds the accuracy of these other programs while its computational time is as little as 1/20 of theirs.

Evaluating Georgia's Compaction Requirements for Stone Matrix Asphalt Mixtures

This study determined a compaction level for stone matrix asphalt (SMA) mixes with the Superpave® gyratory compactor (SGC) that would match a 50-blow Marshall compaction using aggregates and mix designs common in Georgia. SMA mix designs were prepared with five aggregate sources using a 50-blow Marshall compaction and using 50, 75, and 100 gyrations with an SGC. Optimum asphalt contents from the mix designs were compared. Aggregate breakdown from each of the compactions was analyzed. Laboratory rutting tests were conducted on each mix design by using the asphalt pavement analyzer (APA). Results of the laboratory mix designs indicated that generally 35 gyrations in the SGC provided the same density as Marshall compaction. At 50 gyrations, the optimum asphalt contents for the SMA mixtures were 0.1% to 0.5% less than when the Marshall hammer was used; however, four of the five mix designs with 50 gyrations met Georgia Department of Transportation (DOT) specifications. Aggregate breakdown was slightly less with the SGC than with the Marshall hammer. APA tests showed that the mix designs were not sensitive to asphalt content, and all passed Georgia DOT requirements. Testing with plant-produced SMA mixtures confirmed that 34 gyrations in the SGC yielded specimen densities equivalent to the Marshall compaction. For the plant-produced mixtures, compaction in the SGC caused less aggregate breakdown than with the Marshall hammer. The field mixtures also performed well in APA testing. On the basis of results from the laboratory and field mixes, 50 gyrations are recommended with the SGC to replace 50-blow Marshall compaction for SMA mix design in Georgia.

Field Performance of Warm-Mix Asphalt at National Center for Asphalt Technology Test Track

Warm-mix asphalt (WMA) mixes produced by an emulsion process were evaluated under accelerated loading in three total sections of the National Center for Asphalt Technology Test Track and used as the surface mix for two of the sections. Evotherm was incorporated into the same mixes used previously on the track. In-place densities of the WMA surface layers were equal to or better than the hot-mix asphalt (HMA) surface layers, even when compaction temperatures were reduced by 8°C to 42°C (15°F to 75°F). Laboratory rutting-susceptibility tests conducted in the asphalt pavement analyzer indicated similar performance for the WMA and HMA surface mixes with the PG 67-22 base asphalt. However, laboratory tests indicated an increased potential for moisture damage with the WMA mixes. The two WMA sections and the HMA section showed excellent rutting performance in the field after the application of 515,333 equivalent single-axle loads in a 43-day period. One of the WMA sections was also evaluated for quick turnover to traffic and showed good performance.

Investigation of Superpave Fine Aggregate Angularity Criterion for Asphalt Concrete

Fine aggregate angularity (FAA) requirement is one of the aggregate consensus properties recommended by SHRP. Many state highway departments include FAA as part of their Superpave® mixture design specifications. Recent concerns about pavement performance and aggregate shape have caused these agencies to reinvestigate whether standard FAA testing provides information indicative of performance. This paper presents the results from standard FAA tests and digital imaging to investigate the validity of FAA requirements. Testing was performed on four asphalt mixtures representing a range of FAA values. Dynamic modulus testing was performed at three temperatures and five frequencies, and master curves were obtained using nonlinear regression. Asphalt pavement analyzer data obtained at one temperature were analyzed with respect to the rutting curve and rate of rutting. The experimental results for aggregates and mixtures were analyzed together by using statistical methods to develop correlation coefficients and linear trends. It was found that dynamic modulus and rut resistance values were strongly related to aggregate blend FAA. Some additional parameters from digital imaging also predicted modulus and rut resistance very well and should be included in future research.

Noninvasive Measurement of Three-Dimensional Permanent Strains in Asphalt Concrete with X-Ray Tomography Imaging

Because of the stiffness differences between aggregates and mastics, permanent deformation of asphalt concrete is localized mainly in the soft mastics. Therefore, studies on the microresponse of the aggregates and mastics could provide a better understanding of the macrobehavior of asphalt concrete. A method is presented to measure the deformations in the mastics; this was correlated with the permanent deformation resulting from the asphalt pavement analyzer test. An automated procedure with tomography images to reconstruct three-dimensional particles was developed. The translations of the particles can be obtained from the coordinate differences of the mass centers before and after testing. The microstrains in the mastics and macrostrains in the mixture can be calculated on the basis of particle translations. The procedures described have significance for future study on how the aggregated shape, size, and arrangement affect the macroresponse of the mixture in three dimensions and how the relative stiffness of aggregates and mastics affects rutting potential.

Comparative Laboratory Study of Sasobit and Aspha-Min Additives in Warm-Mix Asphalt

Warm-mix asphalt (WMA), which reduces the production temperatures (mixing and compaction) while maintaining the advantages of hot-mix asphalt (HMA), is becoming an attractive paving material. In this study, rheological properties of two commonly used performance grade (PG) binders (PG 64-22 and PG 70-28) were evaluated, with and without Sasobit and Aspha-Min additives. For PG 64-22,2%, 3%, and 4% Sasobit additive reduced the mixing temperature of the pure binder from 163°C to 147°C (i.e., by 16°C). In case of the PG 70-28, the reductions are 10°C, 12°C and 13°C, respectively, for 2%, 3%, and 4% Sasobit additive. No significant decrease in mixing temperature by the Aspha-Min additive was observed in using the rotational viscometer. Evaluation of the binders on the basis of G*/sin(δ) demonstrates no negative effect on high-temperature grading due to high-temperature viscosity reduction. With the addition of 4% Sasobit additive, the high-temperature binder grading of PG 64 (actually PG 65) increases to PG 69, while 4% Sasobit additive improves the PG 70 (actually PG 75) to PG 80. No significant changes in grading were observed with the addition of the Aspha-Min additive. In fact, reduction in binder viscosity and improvement in binder grading without increasing the viscosity indicate two-way reductions (both direct and indirect) in production temperatures by the Sasobit additive. Finally, the Sasobit additive is found to decrease the asphalt pavement analyzer rut depths significantly, and these rut depths correlate well with the rutting factor G*/sin(δ). It was also observed that rutting potential decreases with decreasing mixing and compaction temperatures. Comparatively, a smaller reduction in rut depths was observed by adding the Aspha-Min additive.

Numerical Analysis of Asphalt Pavements under Moving Wheel Loads

ABSTRACT The responses of the pavement in service are the basis for the design of the semi-rigid base course asphalt pavement. Due to the dynamic characteristics of wheel loads and the temperature loads, the dynamic response analysis is very significant. In this article, the dynamic analysis of asphalt pavement under moving wheel loads is carried out using finite element method coupled with non-reflective boundary method. The influences of the base modulus, thickness, the vehicle velocity, the tire pressure, and the contact condition at the interface are studied using parametric analysis. The results of numerical analysis show that it is not appropriate to simply increase the base modulus or thickness in the design. It would be beneficial if the base design is optimized synthetically. The increase of damping is also beneficial to the pavements because of the surface deflection and the stresses declination. Furthermore, the good contact condition at the interface results in good performance because it combines every layer of the pavement to work together. As overload aggravates the working condition of the pavement, it is not allowed.

Cold in-place recycling pavement rutting prediction model using grey modeling method

The rut depth prediction model (RDPM), based on grey modeling method, can be an efficient and accurate model to predict rut depth. The concept of grey modeling method is introduced and the model prediction equation is derived. The RDPM was developed using rut depth data from wet and dry test conditions by asphalt pavement analyzer (APA). All cold in-place recycling (CIR) test samples consisted of reclaimed asphalt pavement (RAP) mixed with asphalt emulsion and additives were fabricated using a Superpave gyratory compactor. The parameters of RDPM are determined from two of the compacted samples and the model is verified by one of the samples of the same asphalt emulsion contents and test condition. The regression analysis shows that the RDPM is useful for making rut depth predictions, regardless of dry or wet test conditions. Thus, the RDPM can be used to estimate anticipated rut depths if the loading cycles are known.

Simulative Performance Test for Hot Mix Asphalt Using Asphalt Pavement Analyzer

Abstract Permanent deformation, or rutting, has been and continues to be a problem in the performance of hot mix asphalt (HMA) pavements. This paper presents a summary of work conducted under National Cooperative Highway Research Program (NCHRP) Project 9-17. This research project was undertaken to evaluate the Asphalt Pavement Analyzer (APA) to determine its suitability as a general method of predicting rut potential. There was a need to identify test conditions within the APA that produced results most related to field rutting performance. Ten HMA mixes of known field rutting performance were tested within a full factorial experiment designed to determine the combination of testing conditions for the APA that best predicts field rutting. The experimental plan consisted of different specimen types (beam and cylinder), air void contents in compacted test specimen (4 and 7 %), hose diameters (25 and 38 mm), and test temperatures (high temperature of standard PG grade based upon climate and 6°C higher temperature). Based upon the test results and analysis, a tentative standard method of test was developed and recommended. A standard practice for establishing maximum specified rut depth for APA by highway agencies has also been recommended.

Recycling of Laboratory-Prepared Reclaimed Asphalt Pavement Mixtures Containing Crumb Rubber-Modified Binders in Hot-Mix Asphalt

The recycling of reclaimed asphalt pavements (RAP) containing crumb rubber—modified binder is an important issue because some of these types of pavements are more than 10 to 15 years old in some areas in the United States. In this study, a laboratory investigation was conducted on the possibility of laboratory-prepared crumb rubber—modified RAP being recycled in Superpave® mixtures according to a normal recycling practice. Six mixtures (three recycled mixtures containing laboratory-prepared crumb rubber—modified RAP and three control virgin mixtures) were designed and tested. Three types of aggregates and two types of crumb rubber—modified binders were used for the mixtures. The crumb rubber-modified RAP used in the study was artificially aged in the laboratory with an accelerated aging process. The percentage of the RAP incorporated into the recycled mixtures was 15%. Evaluation of all mixtures included the following testing procedures: indirect tensile strength, asphalt pavement analyzer, and resilient ...