Model Mobile Load Simulator Research Articles

Moisture susceptibility evaluation of Hot Mix Asphalt: combined effect of traffic and moisture

To date, most of the studies to evaluate moisture susceptibility of hot mix asphalt have been carried out by quantifying the degradation of the mix properties due to conditioning that simulates the action of moisture in the field. There is a need for research on the identification of moisture susceptible mixes which show the material loss in the wheel-path under the combined action of traffic and moisture. The objective of this study was to simulate and analyze the moisture induced material loss, and also to identify a mix with the potential of moisture induced material loss that has shown damage in the field but not under regular testing in the laboratory. The Moisture Induced Stress Tester (MIST), Ultrasonic Pulse Velocity (UPV), Dynamic Modulus in Indirect tensile mode, Indirect Tensile Strength (ITS), and Model Mobile Load Simulator (MMLS3) tests were utilized in the study. The effluent from the MIST was checked for the gradation of dislodged aggregates and the Dissolved Organic Carbon content. The results from the effluent analysis showed the loss of material and aggregate breakage from a moisture susceptible mix. A similar type of losses from the mix was also evident from MMLS3 loading under wet-hot conditions. The results of the mix mechanical properties showed that the use of MIST in combination with UPV or ITS is ab le to identify moisture susceptible mixes, in particular for mixes with the potential of aggregate breakage.

Analytical study on quantifying the magnitude and rate of subgrade fines migration into subbase under flexible pavement

Abstract Particle transport and subsequent deposition in porous media play a significant role in the performance of civil infrastructure. For example, in pavement systems, the migration (also known as pumping) of fine-grained soil from saturated subgrades into subbase layers can compromise the pavement serviceability and performance. In this paper, an analytical framework is formulated to understand the mechanisms of particle transport in pavements and to provide a reasonable prediction of the amount of fines migration from a saturated pavement subgrade to subbase. The model is verified using results from a set of experimental investigations previously conducted to quantify the magnitude and rate of subgrade fines migration. The tests were performed on two classes of flexible pavement roadways, using one-third scale model mobile load simulator (MMSL3), an accelerated pavement testing (APT) device. Non-plastic saturated silt and partially saturated aggregate were used as subgrade and subbase, respectively. The study suggests that the migration of the subgrade soil into subbase is governed by hydraulic condition, grain size of subgrade, grain size and pore size of subbase, permeability of subbase, and viscosity of pore fluid in the subbase. Moreover, magnitude and duration of applied loads play key roles in the amount of pumping in pavement.

Experimental Simulation and Quantification of Migration of Subgrade Soil into Subbase under Rigid Pavement Using Model Mobile Load Simulator

AbstractRigid pavement structure typically consists of a surface layer (concrete), underlying granular layers (subbase and/or base), and a compacted subgrade soil layer. Because the subgrade is sat...

Reduction of subgrade fines migration into subbase of flexible pavement using geotextile

Pumping in pavement is defined as traffic-induced migration of saturated subgrade fines into overlying granular layers or onto the surface of the pavement, negatively impacting the performance and service life of the pavement. The objective of this study was to assess the capability of geotextile as a separation and filtration layer in reducing subgrade fines migration. A one-third scale Model Mobile Load Simulator, an accelerated pavement testing device, was used to simulate the cyclic traffic loading on a scaled model of a flexible pavement. The results from three scaled pavement tests were compared to evaluate the effectiveness of geotextile separation and filtration in reducing subgrade fines migration. The three tests had identical configurations, except that a geotextile layer was placed at the interface of subgrade and subbase in one of the tests. The lab testing revealed that, under cyclic traffic conditions, the migration of subgrade fines into subbase was significant. However, using a geotextile at the subgrade-subbase interface significantly reduced the subgrade pumping. At the end of the test, the fines that migrated to the subbase, based on % mass of subbase, were 6.39% in the tests without geotextile and 1.81% in the test with geotextile. An approximately 30% reduction was observed in the amount of pavement rutting when using geotextile at the top of the subgrade. The subgrade soil migration in mass percentage increased with the traffic loading cycles, and more migration occurred in the bottom half than in the top half of the subbase. The study concludes that geotextile can be used as an effective means to reduce pumping of subgrade fines in pavement by providing both separation and filtration.

Effect of fine aggregate angularity on skid-resistance of asphalt pavement using accelerated pavement testing

The effect of fine aggregate angularity (FAA) on the skid-resistance of asphalt pavement was investigated in the paper. To achieve the objective, four fine aggregates with various FAA values were used in stone matrix asphalt (SMA) and conventional asphalt concrete (AC), separately. The Model Mobile Load Simulator (MMLS3) was used to simulate the effect of traffic load on the skid-resistance of compacted mixes. After specific loading cycles, the skid-resistance of asphalt mix slabs was measured using the Sand Patch Test and the British Pendulum Number (BPN) Test. Sand Patch testing mainly explores the macro-texture of the pavement, while BPN test mostly investigates the micro-texture of the pavement. The test results show FAA has a significant impact on skid-resistance on the macro-texture level but an only marginal influence was observed on the micro-texture level. The correlation between FAA and skid-resistance is validated using a Forward Selection method. Outcomes of this experimental study can potentially be adopted by both practitioners and researchers.

Dynamic responses of asphalt concrete slab under cyclic wheel loading using acceleration spectrum analysis

The dynamic response of pavement, especially in term of vibration, provides information on pavement damage prediction, noise control and so forth. The vibration of pavement is also a potential energy which can be collected by energy harvester and utilized by sensing technology to obtain information of traffic and pavement conditions. In this research, both laboratory Model Mobile Load Simulator (MMLS) tests and Finite Element (FE) simulation were performed to assess the effects of several factors influencing the dynamic response of Hot Mix Asphalt (HMA) slabs that include material properties, wheel loading speed, top-down cracking and thickness of the slab. The parametric analysis was performed using the validated finite element model based on laboratory MMLS test results to investigate the effects of each parameter. Frequency spectrums of vertical acceleration for the HMA slabs under different loading scenarios were obtained through Fast Fourier Transform (FFT), and analyzed to help formulate recommendations for an actual pavement structure from dynamic responses in the field.

Evaluation of pavement response and performance under different scales of APT facilities

This paper focuses on comparative evaluation of pavement responses and performance under accelerated loading facility (ALF), Model Mobile Load Simulator 3(MMLS 3) and Asphalt Pavement Analyzer (APA) tests, in terms of rut depth, strain response, seismic stiffness and contact stress. Test slabs extracted from the ALF test lanes were trafficked with the MMLS3 under comparable environmental conditions at a laboratory in Virginia Tech. Some small specimens were cut from the slab for APA tests at VTRC. It is found that the monitored parameters yielded by the MMLS 3 test were comparable to the related full-scale ALF test results in terms of intrinsic material characteristics and pavement performance. It is concluded that MMLS 3 is an effective, economic and reliable trafficking tool to characterise rutting and fatigue performance of pavement materials with due regard to the relative structures. The APA test is not suitable to assess the fatigue resistance of pavement material, but is an efficient and effective method to rank rutting resistance of asphalt mixtures. The MMLS 3 test can be employed as the screen testing for establishing full-scale testing protocols as desired or required, which will significantly enhance economics of APT testing.

Performance Evaluation of Chip Seals for Higher Volume Roads Using Polymer-Modified Emulsions: Laboratory and Field Study in North Carolina

Abstract This paper presented a study to evaluate the performance of chip seals for higher traffic volume roads. The evaporation test, bitumen bond strength (BBS) test, and Vialit test were used to investigate curing and adhesive behavior. For the laboratory performance, the third-scale model mobile load simulator (MMLS3) was employed to test for aggregate retention, bleeding, and rutting performance. In field, a total of ten test sections were constructed on three different traffic volume roads using different materials and seal types. Some of the field samples were extracted and moved to the laboratory for performance testing. Also, the field sections were monitored to compare the field performance with the laboratory performance. The main findings presented in this paper were as follows: (1) the laboratory test results indicated that the use of polymer modified emulsions (PMEs) improved the chip seal performance in all areas, i.e., curing and adhesive behavior, aggregate retention, bleeding, and rutting; and (2) the field observations indicated that PME-A (styrene butadiene styrene (SBS) polymer-modified emulsion) performs the best of all the emulsions, regardless of seal type and traffic volume.

Permanent deformation behaviour of reinforced flexible pavements built on soft soil subgrade

This study focuses on evaluating the effectiveness of using various geogrid products to improve permanent deformation resistance in soft subgrade soils commonly encountered during roadway construction in Pennsylvania. Permanent deformation behaviours of the soft soils both with and without the inclusion of geogrids were investigated. Cyclic moving wheel loads were applied through a reduced-scale accelerated pavement testing (APT) device, a one-third-scale model mobile load simulator (MMLS3). Tests were conducted on two soil types, each modified with three different biaxial geogrids placed at the base–subgrade interface. The total permanent deformation/surface rutting of the pavement and the permanent deformation of the subgrade were measured at selected intervals of the wheel loading applications. The pavement sections were trenched upon completion of the accelerated testing to measure the deformed profiles of the cross sections from which the permanent deformations in the asphalt layer and the base layer were determined. Sections modified with geogrids were found to have similar performance with the control section in terms of the total permanent deformation. While the geogrids did not show significant effects on the asphalt layer permanent deformation, sections with geogrids consistently showed a significantly higher base layer permanent deformation as compared to the control sections. Measurements of the subgrade permanent deformation showed that two of the geogrids consistently reduced the permanent deformation of subgrade built with the two types of soft soil. The relative layer contribution to the total permanent deformation suggested a base layer failure in both sets of the accelerated tests, most likely due to the inadequate compaction of the base layer during construction. Sections modified with geogrids exhibited a significantly higher base layer contribution, along with a significantly lower subgrade contribution, to the total permanent deformation, whereas the control section showed the opposite of the layer contributions.

아스팔트 도로포장 유지보수용 표면처리공법의 공용성 평가

PURPOSES : The objective of this study is to evaluate the performance properties of chip seals and fog seals with polymer-modified emulsions. METHODS : The performance of chip seals and fog seals was evaluated on the basis of common issues in surface treatments. Granite aggregate and four types of asphalt emulsions (one of the unmodified and three of the modified emulsions) were used considering the usage in field. A Vialit test was performed to determine the aggregate retention, and the MMLS3 (Third Scale Model Mobile Load Simulator) test was conducted to determine the aggregate retention, bleeding, and rutting. In addition, the fog seal specimens were tested by the BPT (British Pendulum Test) to evaluate skid resistance. RESULTS AND CONCLUSIONS : Overall, the polymer-modified emulsions (PMEs) showed better aggregate retention and bleeding resistance for both chip seals and fog seals. When comparing the performance of the PMEs, the difference was not considerable. In addition, PMEs present significantly better rutting resistance than unmodified emulsions. For skid resistance, if the recommended mix design is applied, the specimens do not cause issues with skid resistance. Although all of the fog seal specimens were over the criteria for skid resistance, the specimen fabricated by the high emulsion application rate (EAR) of the unmodified emulsion was nearly equivalent to the skid value criteria. Therefore, the use of an unmodified emulsion with a high EAR should be carefully applied in the field.

Rutting performance evaluation of asphalt mix with different types of geosynthetics using MMLS3

This paper presents an evaluation of the rutting performance of geosynthetics in asphalt pavements. The rutting performance of both a fibreglass geogrid and a sheet reinforcement material were evaluated using the third-scale model mobile loading simulator (MMLS3). The surface profile of each type of reinforced slab (and a control slab) was monitored and compared. To investigate movement of the mixtures caused by MMLS3 loading as well as the interfaces of the reinforcements in the asphalt slabs, trench cuts were made once the MMLS3 rutting tests were complete. The results demonstrated that reinforcement can reduce downward ruts and that different types of reinforcement exhibited different shear flow behaviour. The geogrid-reinforced slabs showed the shallowest ruts and the most shear flow resistance due to the tension resistance of the geogrid. They exhibited confinement and increased friction due to the aggregate particles that were locked in the geogrid openings. The sheet-reinforced slabs exhibited the highest shear flow humps due to the lack of interlocking and bonding strength at the rutting test temperature. In addition, the geogrid openings, which were supposed to provide interlocking and anchoring, in fact generated a relatively high volume of voids at the interface between lifts. Further research is needed to evaluate the effects of high air voids at the lift interface on pavement performance.

Methodology for relating accelerated trafficking to field trafficking for pavement evaluation

Over the years, numerous Accelerated Pavement Testing (APT) devices have been developed to facilitate quick evaluation of the performance and service life of pavements, materials, and related products under various loading and environmental climatic conditions. However, it is often challenging to translate or extrapolate the onset of distress, severity, and evolution caused by accelerated trafficking to that experienced in the field under different loading and environmental conditions. This is especially true if testing is conducted on specimens or reduced-scale slabs. The objective of this study is to present a methodology for establishing a relationship between accelerated and actual trafficking applied in the field. For this purpose, a Finite Element Method (FEM) analysis was conducted for specimens trafficked by the Model Mobile Load Simulator at 1/3rd scale (MMLS3) at conditions that favor rutting. As expected, it was observed that the rutting models developed and calibrated for field traffic do not accurately predict the rutting progression that was measured in these specimens. A methodology to more accurately predict rutting under accelerated trafficking is suggested, by which the loading effect of the MMLS3 is related to an equivalent 18-kip single axle load. New coefficients for the rutting model are devised to be used in conjunction with the MMLS3 testing.

Mean profile depth analysis of field and laboratory traffic-loaded chip seal surface treatments

This paper presents a laboratory and field study to evaluate the mean profile depth (MPD) parameter that represents the surface texture of chip seal pavements. A three-dimensional laser profiler is used to determine the MPD values from both field pavement sections and field samples that have been tested in the laboratory using the third-scale model mobile loading simulator (MMLS3). Data obtained from five different field-constructed chip seal sections are used to evaluate the effects of different factors on the MPD of chip seal pavements. These factors include aggregate type, emulsion application rate, field versus MMLS3 traffic loading and traffic volume. The results presented in this paper suggest that: (1) chip seal pavements constructed using lightweight aggregate have larger initial MPD values and faster reduction in MPD as a function of the number of wheel passes than those constructed using granite 78M aggregate; (2) MPD values obtained from a drier section (with drier indicating a lower emulsion-to-aggregate ratio than that of the sections it is being compared against) initially drop quickly and significantly, resulting in a much smaller ultimate MPD value; (3) in general, the MPD values obtained under MMLS3 loading are similar to those obtained from field traffic loading, thus allowing the translation of the laboratory MMLS3 data to the field response data; (4) a short rest period in a high-traffic volume road retards the recovery of the binder and, therefore, leads to more permanent changes in the MPD and (5) the initial measured MPD value can help predict aggregate loss performance.

Methods for Fog Seal Field Test with Polymer-Modified Emulsions

Findings from a laboratory evaluation of fog seal emulsions are presented. Curing time and adhesive behavior of polymer-modified emulsions (PMEs) were compared with those of unmodified emulsions as fog seal materials. The study showed that polymer modification could improve certain properties of emulsions, such as an increase in adhesion. The evaporation test and the pneumatic adhesion tension testing instrument were used to investigate emulsion curing and adhesive behavior. Also, the rolling ball test and the damping test were developed as in situ test methods to determine an appropriate traffic opening time for roadways treated with fog seals. Finally, the third-scale Model Mobile Load Simulator was employed to compare the performance properties of the fog seal emulsions. The following main findings are presented: use of PMEs improved the emulsion bond strength and lessened the time a road was closed to traffic; PMEs showed more effective emulsion curing rates than did unmodified emulsions; strong relationships existed between the bond strength and both the measured rolling distance (from the rolling ball test) and the measured percentage of stained area (from the damping test); field test methods could be used to help determine whether emulsions were fully cured; and PMEs exhibited better aggregate retention and bleeding performance properties than did unmodified emulsions as a fog seal.

The use of a multi-set-up, reduced-scale accelerated trafficking simulator for evaluating roadway systems and products

This paper describes the use of an accelerated trafficking device, the one-third scale model mobile load simulator (MMLS3), for evaluating roadway systems and products. While the majority of accelerated load testers have focused on investigating rutting behaviours and moisture damage susceptibility of bituminous materials, this paper sheds light on broader applications using the MMLS3, including accelerated tests on field sections, scaled pavement structures, roadway reflective markings, roadway slip-resistant plates, in addition to performance evaluation tests on hot-mix asphalt mixtures. Results of experiments for the various applications indicate that the MMLS3, when equipped with ancillary instrumentation and devices, is a valuable tool for investigating the structural responses of a roadway system and for evaluating the effectiveness and durability of roadway pavement products. This study shows that the results of accelerated trafficking tests using the MMLS3 are comparable with field full-scale accelerated tests due to the nature of similitude in the MMLS3 design. Using the MMLS3 for accelerated traffic testing for practical and research purposes in the area of pavement engineering is a reliable and economical alternative to full-scale accelerated testing, given the savings in the required time and resources.

Application of MMLS3 in laboratory conditions for moisture damage classification of bitumen stabilised materials

The Model Mobile Load Simulator (MMLS3) is a one-third scale accelerated pavement testing (APT) device. It is well engineered and widely used for simulating long-term pavement performance under in-service conditions. However, the current laboratory-testing protocol using MMLS3 is not defined for testing bitumen stabilised materials (BSMs), such as foamed bitumen and emulsion stabilised materials. The process associated with moisture ingress and damage in the BSMs layer is complex and can occur over a long time, under in-service conditions. It is believed that APT research into moisture damage of BSMs can provide invaluable insights into distress mechanisms in spite of accelerated damage compressed into a shorter time frame. This paper presents the results of an experiment using wet MMLS3 trafficking, aimed at providing measurable damage that can distinguish between resistance of different BSMs. The mix compositions investigated comprised aggregates blends with and without reclaimed asphalt pavement (RAP) and different binder types (bitumen emulsion and foamed bitumen) and addition of active filler (cement and lime). The findings show that the revised MMLS3 testing protocol, as developed for the BSMs investigation, can be used to distinguish between the mixtures of high resistance and high susceptibility to moisture damage.

Effect of temperature on fatigue performance of hot mix asphalt tested under model mobile load simulator

In this study, the effect of temperature on the fatigue performance of hot mix asphalt (HMA) has been investigated with the use of the scaled accelerated loading equipment Model Mobile Load Simulator. Several HMA test slabs instrumented with strain gauges and thermocouples were subjected to running wheel load under controlled environmental condition. Transverse and longitudinal strain and temperature data were acquired with the data acquisition system. The analysis of strain data indicated that the longitudinal strain was dependent on the temperature and the rate of change of temperature with time. A model has been developed to predict the resilient strain under moving load at different temperatures. Models relating fatigue life of HMA with temperature have been presented. It has been concluded that the accurate prediction of fatigue performance of HMA under wheel load should include the effect of temperature and loading. Testing pavement slabs compacted with roller compactor provides results which can identify the effects of different factors encountered in the actual field conditions.

Evaluation of polymer-modified chip seals at low temperatures

This paper compares the performance of chip seals constructed with polymer-modified emulsion (PME; CRS-2L) versus those constructed with unmodified emulsion (CRS-2). The overall performance evaluation is based on aggregate retention performance. The adhesion of the emulsions is examined using the Vialit test with various curing times and temperature conditions. To evaluate the aggregate retention performance of the chip seals, we used the Vialit test, the flip-over test and the third-scale Model Mobile Loading Simulator (MMLS3). The results from these tests indicate that the PME (CRS-2L) enhances aggregate retention performance, and does so more significantly in the early stages and at low temperatures.

소형 포장 가속시험기를 이용한 중온 아스팔트 혼합물의 소성변형저항성 및 수분민감도 평가

Warm-mix asphalt(WMA) technology has been developed to allow asphalt mixtures to be produced and compacted at a significantly lower temperature. The WMA technology was identified as one of means to lower emissions for and has been spread so quickly in the world. Recently, two innovative WMA additives has been developed to reduce mixing and paving temperatures applied in asphalt paving process in Korea. Since the first public demonstration project in 2008, many WMA projects have successfully been constructed in national highways. In 2010, the WMA field trial was conducted on new national highway construction under Dae-Jeon Regional Construction Management Administration. The two different WMA loose mixtures(WMA and WMA-P) and a HMA mixture were collected at the asphalt plant to evaluate their mechanical performance in the laboratory. The Third-scale Model Mobile Loading Simulator(MMLS3) was adopted to evaluate rutting resistance and moisture damage under different traffic and environmental conditions. In this study, plant-produced WMA mixtures using two WMA additives along with the conventional hot mix asphalt(HMA) mixtures were evaluated with respect to their rutting resistance and moisture susceptibility using MMLS3. Based on the limited laboratory test results, plant-produced WMA mixtures are superior to HMA mixtures in rutting resistance and the moisture susceptibility. The WMA additive was effective for producing and compacting the mixture at lower than the temperature for the HMA mixture.

Evaluation of healing effect by rest periods on asphalt concrete slab using MMLS3 and NDE techniques

Fatigue life of asphalt concrete pavement is one of the most important factors in pavement management systems, which can be increased by healing effect. The healing effect by rest periods was evaluated by the third scale Model Mobile Loading Simulator (MMLS3) and Nondestructive Evaluation (NDE) techniques. Impact method of stress wave was optimized to accurately analyze the phase velocity and obtain effective sampling depth. In general, the phase velocities decrease as the pavement structure is degraded by the increase of wheel applications or load levels along both of the stress wave and ultra sonic measurement, while the recovery of phase velocities during rest periods is successfully evaluated by both techniques. Finally, based on the observation of phase velocities of waves, it was possible to confirm the healing effect of Asphalt Concrete (AC) by rest periods.