Accelerated Pavement Testing Facility Research Articles

Use of Distributed Fiber Optic Sensors for the Monitoring of an Accelerated Pavement Test

The need to develop more efficient pavement management systems has driven continuous improvement in structural health monitoring (SHM) systems for road infrastructures. Factors such as low energy consumption, minimal disruption (small-sized and lightweight devices), resistance to environmental conditions, high durability, and sensitivity are some of the possible improvements worthy of exploration. Fiber optics appear to have several of these desired characteristics. In this context, this article presents strain measurements performed using fiber optic cables installed at various levels in pavement structures tested on the accelerated pavement testing facility at the Université Gustave Eiffel (or fatigue carousel). The results reveal that strains measured with this technology closely align with those obtained using traditional strain gauges. However, an advantage of fiber optics is that they enable distributed measurements over long distances with high precision (10 m with a measurement interval of 2.6 mm in this study). These measurements highlight a significant variability in pavement strains, seemingly attributable to the heterogeneity of pavement materials and variations in layer thicknesses. As a result of these findings, laboratory-scale investigations have been initiated to gain a better understanding of these sources of variability.

An exploratory framework for accelerated airport pavement testing using the geotechnical centrifuge

ABSTRACT Full-scale Accelerated Pavement testing (APT) has been regarded as an essential step to bridge the gap between research and practice for pavement design because it can fully mimic a large number of heavy wheel loading on pavements. Despite being able to test pavements in an accelerated manner compared to Long-term Performance Monitoring (LTPM), conducting one full-scale APT experiment is still demanding in terms of monetary cost, space, time, etc., and the accessibility to APT facilities is only available in a few countries nowadays. In this study, an exploratory APT study with a down-scaled pavement model in a high-g environment created by geotechnical centrifuge was performed with up to half a million simulated aircraft load repetitions. Through this test, it was proved that the centrifuge APT can reproduce the full-scale airfield pavement responses, including rutting, cracking, material fatigue, etc. The transient and permanent deflection of the pavement surface, variations in stress and strain states within the pavement structure over its lifespan can be well captured for analysis. This framework of centrifuge APT provides a new methodology for pavement testing and can significantly save the current cost and time of full-scale APT.

Modulus attenuation of semi-rigid asphalt pavement layer in accelerated pavement testing with MLS66

This research aimed to investigate the attenuation mode of the layer modulus of asphalt pavement in accelerated pavement testing (APT). A full-scale experimental section was constructed and tested using the APT facility. Two non-destructive testing (NDT) methods, named falling weight deflectometer (FWD) technique and portable seismic property analyzer (PSPA) test, were used to obtain the layer moduli of asphalt pavement during the APT test. The variation patterns of layer moduli obtained by FWD and PSPA tests were calculated and compared after the temperature was corrected to 20 ℃. It was found that the variation pattern of surface layer modulus based on field FWD measurements was consistent with the one measured from PSPA tests. That is the modulus of the surface layer increases with the APT load repetitions firstly and then decreases with the rise of the repetitions. The modulus values of the surface layer measured from PSPA tests are obviously larger than those backcalculated based on deflection basins. The ratio of the measured surface layer modulus based on the PSPA test to the backcalculated one based on the FWD test ranges between 2.06 and 2.71. The backcalculated base layer modulus always declines with the increasing loading repetitions. The attenuation patterns of the surface layer modulus and the base layer modulus in the damage stage are described as Ea=421100*N-0.6119 and Eb=128000*N-0.1096, respectively.

Accelerated evaluation of membranes for pavement structures on orthotropic steel bridge decks

ABSTRACT Membranes of sufficient bonding characteristics could improve the integrity of the multi-layer structures on orthotropic steel deck bridges (OSBDs), enhancing thus the structural response of these systems and, ultimately, their service life. In this research, full-scale experiments were performed at the LINTRACK accelerated pavement testing facility of the Delft University of Technology to evaluate the performance of two surfacing systems commonly used in the Netherlands, giving emphasis on assessing the interface response of membranes with the surrounding materials. Results indicated that the tensile strains remain almost uniform at the top of porous asphalt, in both transverse and longitudinal directions, as no appreciable loss in stress-carrying capabilities was seen even at the end of the testing program. The sections exhibited similar behaviour in terms of strains, with some differences in strains indicating the impacts of membranes at interfaces. The importance of membranes of the desired bonding characteristics was also reflected by the relative displacement measurements. The relative interlayer slip had been higher in the transverse direction than the longitudinal one, with slightly higher displacements in one of the test sections. Overall, no cracking was observed on either section, and the current findings support the use of membranes between surfacing layers on OSBDs.

Investigating the Influence of Joint Reinforcements of Portland Cement Concrete Slabs Under Asphalt Concrete Overlays on Vertical Deflections Using Accelerated Pavement Testing

Joint gaps between slabs in underlying Portland cement concrete (PCC) pavements are critical factors in the life span of asphalt concrete (AC) overlays. Therefore, being informed about the vertical deflections that may occur around the joints is important. In this study the joints were reinforced with three different materials: ethylene propylene diene monomer (i.e., rubber joint filler [RJF] reinforcement), bitumen-based sealant (i.e., rubber plate [RP] reinforcement), and steel plate (SP) (i.e., SP reinforcement), to limit the vertical movement of the underlying PCC. Tests were conducted at the accelerated pavement testing facility for two different AC overlay thicknesses, 50 mm and 100 mm, during 100,000 passages to investigate the influence of AC overlay thickness variations on slab vertical deflections and to also evaluate types of joint reinforcement on slab vertical deflections. For 50-mm thick AC overlay, the most effective joint reinforcements to prevent deformations caused by loading were RP, RJF, and SP; for a 100-mm thickness, this was determined to be RJF, SP, and RP, respectively.

Exploring lessons learned from partnerships to establish a regional accelerated pavement testing facility in Wyoming

ABSTRACT A foremost accelerated pavement testing (APT) test road facility is proposed along interstate 80 for the dry-freeze climate by the Wyoming Department of Transportation (WYDOT). A survey was undertaken among states and industries in the region as part of the feasibility study to identify research needs and interests in the test road project. This paper summarises the responses of the survey and lessons learned from the experiences of 3 APT test road facilities in the U.S. Respondents perceive the APT to be relevant and critical to the study and state-of-practice of pavement engineering. Respondents’ research needs include local calibration for the mechanistic-empirical (ME) pavement design, pavement preservations alternatives, and recycled materials for pavements. The presented information and the lessons learned will guide future APT programmes at the planning stage on nurturing partnerships and avoiding the mistakes of earlier APTs to minimise the wastage of scarce resources.

Harmonizing Flexible Pavement Rutting Design with Balanced Mix Design

The state-of-the-practice in asphalt concrete mix design and pavement structural design are two divergent concepts. The simulative laboratory performance tests such as Hamburg Wheel Tracking (HWT) and Asphalt Pavement Analyzer (APA) that are used primarily for balanced mix design are pragmatically accelerated surrogate tests developed to ensure the stability or ranking of mixes. Pavement structural design methods, being empirical or mechanistic-empirical, do not consider these laboratory test results in their analyses, in favor of other fundamental mechanical parameters such as dynamic modulus. As such, the selection of the type of mix to be placed on a project is based on the local experience, and a set of consensus limits, rather than the demand of the pavement section. A harmonized strategy that integrates the results from mix tests with the pavement structure, material properties, environmental conditions, and traffic levels can lead to an optimized pavement system. A framework is proposed to incorporate the laboratory HWT and APA device results into the rutting analysis associated with most mechanistic-empirical structural design algorithms. The proposed framework was applied to the results from two accelerated pavement testing facilities and six in-service pavement test sections to demonstrate its feasibility. The proposed strategy can be potentially used to predict the rutting life of the pavement reasonably well. By balancing the rutting demand of an asphalt layer with the rutting capacity of a given mix, the proposed method can potentially lend itself to the use of local materials for a more economical and sustainable pavement structure.

Performance of AC overlays using geogrids on PCC contraction joints

It is widely known that vertical displacements and strains occur on the joints and these cause defects on the asphalt concrete (AC) overlays on existing Portland cement concrete (PCC) pavements. Various approaches were introduced to minimize these defects. In this study, the effect of joint support formed using the geogrid material with grout mortar on the vertical displacement of PCC and the strain at the bottom of the AC layer. Produced layers were exposed to 1,186,000 Equivalent Single Axle Load (ESAL) in an APT (Accelerated Pavement Test) facility and the results were monitored. According to the obtained results, the use of AC overlay reduces vertical displacement in the PCC by 75%. When geogrid reinforced AC overlay was used, an additional reduction in displacement by 41.2% was achieved. Geogrid reinforcement reduced strain values formed at the bottom of the AC layer from 29.5% to 92.5%. The use of geogrid at joints instead of increasing the thickness of the AC layer from 50 to 80 mm resulted a more significant reduction in both strain and displacement. Besides, the usage of a geogrid interlayer instead of increasing the thickness of the AC layer also provided a significant cost reduction of 57.9% in overall cost.

Stiffness and Strength Improvement of Geosynthetic-Reinforced Pavement Foundation Using Large-Scale Wheel Test

Laboratory cyclic plate load tests are commonly used in the assessment of geosynthetic performance in pavement applications due to the repeatability of testing results and the smaller required testing areas than traditional Accelerated Pavement Testing facilities. While the objective of traditional plate load testing procedure is to closely replicate traffic conditions, the reality is that rolling wheel loads produce different stresses in pavement layers than traditional cyclic plate load tests. This two-fold study investigates the differences between the stress response of subgrade soil from a rolling wheel load (replicating rolling traffic conditions) and a unidirectional dynamic load (replicating traditional plate load test procedures) in order to obtain a more realistic stress response of pavement layers from rolling wheel traffic. Ultimately, results show that the testing specimens that experienced rolling wheel loading had an average of 17% higher pressure measurements in the top of the subgrade than vertically loaded (unidirectional dynamic load) specimens. The second segment of this study is used in conjunction with the first to analyze aggregate base material behavior when using a geosynthetic for reinforcement. The study aimed to determine the difference in the post-trafficked strength and stiffness of pavement foundation. A Dynamic Cone Penetrometer and Light Weight Deflectometer were utilized to determine material changes from this trafficking and revealed that all specimens that included a geosynthetic had a higher base stiffness and strength while the specimen with geotextile and geogrid in combination created the highest stiffness and strength after large-scale rolling wheel trafficking.

Instrumented flexible pavement responses under aircraft loading

ABSTRACT The FAA National Airport Pavement Test Facility (NAPTF) is a full-scale accelerated pavement testing facility located in Atlantic City International Airport, New Jersey. Six flexible and three rigid test sections were built, instrumented and trafficked by Boeing 777 and 747 gears as part of construction cycle one. One flexible test section with an asphalt-stabilised base over a low-strength subgrade was considered in this study. All dynamic sensors, including pressure cells, strain gauges and multi-depth deflectometers were evaluated. A multistep procedure for evaluating the dynamic sensors was developed, and it included data reliability, repeatability, changes in the pavement responses under the Boeing 777 and 747 gears, and comparison with a three-dimensional (3D) finite element (FE) mechanistic model. The mechanistic model was found to predict the pavement responses with good reliability, whenever representative layer moduli are used. The study also found that 60% of the sensors produced acceptable or marginal responses and 40% produced unacceptable responses; therefore, it is recommended to consider this sensor survival rate when instrumenting future test sections. The rutting performance and pavement responses over time were evaluated; the test section was shown to have relatively similar performance and pavement responses under the Boeing 777 and 747 gears.

Full-scale validation of bio-recycled asphalt mixtures for road pavements

Recycling of asphalt has become a well-established practice in many countries, however the road pavement industry remains a bulk consumer of extracted raw materials. Novel solutions that find root in circular economy concepts and life-cycle approaches are needed in order to enable optimisation of infrastructure resource efficiency, starting from the design stage and spanning the whole value chain in the construction sector. Itis within this framework that the present study presents a full-scale validation of asphalt mixtures specifically designed to ensure durability of flexible road pavements and at the same time enabling the reuse of reclaimed asphalt pavement (RAP) through the incorporation of bio-materials as recycling agent. These bio-recycled asphalt mixtures have been first designed in laboratory and subsequently validated in a real scale experiment conducted at the accelerated pavement testing facilities at IFSTTAR. Four pavement sections were evaluated: three test sections with innovative bio-materials, and a reference section with a conventional, high modulus asphalt mix (EME2). Two tests were realized: a rutting test and a fatigue test and for each of them the evolution of bio-recycled asphalt mixtures properties as well as the pavement deteriorations were recorded and studied. Evolution of the bio-asphalt mixtures was monitored for a 5 months period after paving by a bespoke nondestructive micro-coring, extracting and recovering methodology developed at the Western Research Institute (WRI). The structural health of the pavement sections was monitored through periodic falling weight deflectometer (FWD) as well as with strain gages and temperature sensors. As a result the three tailored bio-asphalt mixtures performed similarly or better than the control mixture, both in terms of property evolutions and durability.

Development of full-scale laboratory accelerated pavement testing facility: a step toward performance assessment of geosynthetics reinforced pavement

The road network in India is growing at an exponential rate. The biggest challenge in this scenario is an availability of good-quality pavement materials at a reasonable rate. The demands of these pavement materials are increasing at an accelerated rate due to which good-quality material available in nature is getting depleted rapidly. This may create a threat to the environment in the near future. The rate of depletion may be reduced to a certain extent by adopting measures, viz. use of recycled pavement materials, stabilization of locally available poor-quality materials, and use of reinforced pavement. Assessment of such measures in a limited time is the biggest challenge. This challenge may be tackled by using full-scale accelerated pavement testing setup. However, the full-scale accelerated pavement test is not readily available. Over the globe, accelerated pavement testing setups are developed at only a few universities and research institutes. This paper presents the development details of a full-scale laboratory accelerated pavement testing setup. The calibration of the applied axle load is also presented. The developed full-scale laboratory accelerated pavement testing setup will prove opportunity to test new material/technique which will build up the confidence due to gain of knowledge. This paper also aims to investigate the variation of vertical stress and deformation at the base–subgrade interface of geotextile-reinforced and unreinforced pavement using the developed pavement testing facility.

Bio materials with reclaimed asphalt: from lab mixes properties to non-damaged full scale monitoring and mechanical simulation

Three innovative environmentally friendly pavement materials, designed with 50% of Reclaimed Asphalt and three different biomaterials (2 bio-additivated bitumens and 1 bio-binder), were produced in an industrial plant. These mixes were tested in lab and also at full scale using an Accelerated Pavement Test facility. The asphalt mix viscoelastic properties were measured in lab and their intrinsic viscoelastic response were simulated. These rheological models are used to simulate the pavement mechanical response using both elastic and viscoelastic multilayer codes. Hence, full scale measurement performed during the full scale test at an early stage (without damages) can be compared with these simulations. The overall prediction accuracy, when all the signals are considered, is between 4% and 8% for all materials. It can be concluded that material characterisation in lab as well as the selected models are well adapted to simulate actual loading state under a moving load, even for these non-conventional mixes. For temperatures lower than 25°C, elastic modelling appears to be sufficient for pavement structural design with the innovative materials tested here.

Monitoring of pavement deflections using geophones

ABSTRACT The paper presents tests performed on an instrumented motorway section, to monitor traffic and pavement deflections using geophones. Geophones are sensors used to measure displacement velocities, and by integrating their signal, it is possible to monitor vertical displacements. In this study, 4 geophones have been installed in the base layer of the pavement, and their measurements have been recorded under real traffic, during a period of approximately 18 months, using a remote control data acquisition system, transferring the data to a server. Different methods of treatment of the geophone measurements have been proposed: the first application concerns the detection of different heavy vehicle silhouettes, by analysing the number of peaks of the displacement signals; the second application concerns the measurement of vehicle speeds, by determining the time difference between the measurements of two geophones. The third application concerns the measurement of pavement deflections. To measure accurately the deflection, a procedure has been developed, to correct the geophone response, which is attenuated in the low frequency range. This procedure has been validated by measurements under controlled loading conditions, on the IFSTTAR accelerated pavement testing facility, and then applied to in situ measurements. In conclusion, the study shows that geophones, which present the advantage of being relatively inexpensive and robust sensors, offer interesting possibilities for pavement monitoring.

Assessment of cracks detection in pavement by a distributed fiber optic sensing technology

This paper presents the feasibility of damage detection in asphalt pavements by embedded fiber optics as a new non-destructive inspection technique. The distributed fiber optic sensing technology based on the Rayleigh scattering was used in this study. The main advantage of this technique is that it allows to measure strains over a long length of fiber optic with a high spatial resolution, less than 1 cm. By comparing strain profiles measured at different times, an attempt was made to link strain changes with the appearance of damage (cracking) in the pavement. This non-destructive method was evaluated on accelerated pavement testing facility, in a bituminous pavement. In our experimentation, the optical fibers were placed near the bottom of the asphalt layer. The application of 728,000 heavy vehicle loads (65 kN dual wheel loads) was simulated in the experiment. Optical fiber measurements were made at regular intervals and surface cracking of the pavement was surveyed. After some traffic, a significant increase of strains was detected by the optical fibers at different points in the pavement structure, before any damage was visible. Later, cracking developed in the zones where the strain profiles were modified, thus indicating a clear relationship between the increased strains and crack initiation. These first tests demonstrate that distributed fiber optic sensors based on Rayleigh scattering can be used to detect crack initiation and propagation in pavements, by monitoring strain profiles in the bituminous layers.

Effect of groundwater table rising on the performance of a Swedish-designed gravel road

Abstract Sweden has a wide network of gravel roads. When the water table levels rise during the freeze-thaw and wet seasons, the bearing capacity of the roads will decrease and rut depths increase. The road will suffer a small deterioration every time a vehicle travel over it. Therefore, it has been decided to investigate the long-term performance of a Swedish designed gravel road using an accelerated pavement testing facility. A trial gravel road was constructed and exposed to various levels of ground water table which simulate the weather changes in Sweden. The structure of the trial gravel road consisted of 15 cm (base and surface layer), 20 cm sub-base layer and 260 cm subgrade soil. The trial road was tested using the Heavy Vehicle Simulator (HVS) and the vertical surface deformations and the vertical dynamic deformations were measured by means of laser profile measurement and eMU coils respectively. At the end of 85 000 HVS passes, the tested road suffered from serious deformations as discussed in details in this paper. Furthermore, a transverse trench section was excavated at the end of HVS trafficking in order to investigate the possible mechanism contributing to the tested road failure.

Accelerated Pavement Testing in Slovakia: APT Tester 105-03-01

This article presents the APT (Accelerated Pavement Testing) facility constructed and operated by University of Zilina. The machine is designated as APT tester 105–03–01. The article describes tester's technical properties, operational capabilities, sensory equipment embedded in the pavement and data gathering procedures. The device has several unique design solutions that make it stand out from similar facilities in the world:•The principle of fixed linear APT facility with loading unit not positioned in a fixed frame, but instead, moveable along a guiding rail to better simulate traffic loading.•Loading unit consisting of fixed and movable frame held by support connected by joints for better simulation of suspension like those found on truck axles.•The construction of the electric motor, gear box and frequency inverter and its mounting system on the loading unit.•Frequency converter controlled acceleration and deceleration and speed during the movement.•Hydraulic stabilization system stabilizing the movable frame preventing the load to tip the loading unit in the acceleration and deceleration stage.•Autonomous hydraulic system placed on the outer frame able to lift the loading unit and allows for free manipulation without acting on the pavement.

Mechanical response of flexible pavements enhanced with geogrid-reinforced asphalt overlays

The use of geosynthetic reinforcements placed underneath asphalt overlays, which has been typically used to minimise problems associated with reflective cracking, is evaluated in this study as an approach to improve pavement structural capacity. Whereas geosynthetics have been used to increase the pavement structural performance when used to reinforce the base aggregate, as reported in numerous laboratory and evaluations experiments, such improvement has not been evaluated for the case of geosynthetics within asphalt layers. Accordingly, this paper presents the results of large model tests involving both reinforced and unreinforced hot mix asphalt overlays. Cyclic wheel loads were applied using an accelerated pavement test facility that was specifically developed for this research. A number of pavement sections were constructed using a polyvinyl alcohol geogrid as reinforcement inclusions. The results show a considerable increase in pavements structural performance, as quantified by reduction of strains in the asphalt concrete layers, in the vertical stresses within the pavement layers and in the resilient displacements at the wearing surface. The use of geogrid reinforcements was also found to lead to reduce rutting and permanent lateral movements in the surface layer. Overall, the use of geogrids within asphalt overlays was found to act as a reinforcement element that provide enhanced structural capacity to flexible pavements.

Comparison of Uni and Bi-directional Load Induced Rutting in Flexible Pavement with Accelerated Pavement Testing Facility (APTF)

The Indian Road Network is the second largest in the world after U.S. and flexible pavement is the most sought pavement in India. In fact, majority of roads in India (more then 90%) are flexible pavement due to ease of construction and initial cost of construction. The design of flexible pavement in India mainly consider rutting and fatigue life as per Indian Road Congress (IRC:37-2001). There are many factors that affects the rutting of the flexible pavements namely speed, contact pressure, temperature, quality of construction, wandering of the vehicle and layer thickness etc. The present paper focuses on rutting itself which is governed by direction of traffic, while keeping other parameters nearly same. The effect of movement of heavy traffic in a channelized as well non channelized way on pavement resulting in rutting has been studied with the state of art equipment, Accelerated Pavement Testing Facility (APTF), by CSIR-CRRI, with the aim of finding the performance through evaluation for uni and bi-directional rutting characteristic of pavement. Rutting is the longitudinal depression in the wheel path of the pavement. It can either be instability or structural rutting. Rutting can cause hydroplaning, increase in vehicle operating cost and psychological problems while driving. The amount of rutting under unidirectional loading was compared with the bidirectional loading case with almost the same number of passes. The change in air voids were also calculated from the rutted as well as non rutted portion. The magnitude of rutting under unidirectional loading was more as compared to the one under bi-directional loading. The comparative study has clearly demonstrated that the damage to flexible pavement by rutting with unidirectional load is more critical and nearly twice as compared to the damage by bi-directional loading. This aspect stresses the need for accounting the directional movements in our pavement design guidelines and depending on whether testing uni-directional or bi-directional, a different “transfer function” or relationship to real in service loading is required.

Weigh-in-motion for Direct Enforcement of Overloaded Commercial Vehicles

Heavy commercial vehicle overloads contribute to premature deterioration of infrastructure and increase road unsafety and unfair competition between transport modes and operators. Public authorities and road operators must therefore implement an efficient checking system to enforce weights and dimensions at an affordable cost. A large scale project was launched in 2014 by the French Ministry of Ecology, Sustainable Development and Sea, in charge of Transport, carried out by IFSTTAR and CEREMA, to demonstrate the feasibility of using high speed weigh-in-motion (WIM) systems for direct enforcement of overloaded HCVs. This ambitious challenge requires overcoming technological and metrological gaps, and modifying the current legislation. The required tolerances are ±5% for the gross vehicle weight, and ±10% for axle loads. None of the existing WIM system matches this accuracy for 100% of the vehicles. Therefore the objective is to set up some sorting criteria and algorithms, eliminating the weighings outside these tolerances.The project is divided into 5 WPs, to characterize WIM sensor response under controlled environment and loading conditions and to develop fiber optic WIM sensors, to assess the capability of multiple sensor (MS-) and bridge (B-) WIM systems to meet the requirements, to carry long term road tests and to develop type approval procedures for direct enforcement. This paper presents results gathered on the accelerated pavement testing facility of IFSTTAR in 2014 with 10 WIM sensors. Some results of B-WIM systems are also reported. Perspectives are given how to achieve a WIM system type approval procedure for direct enforcement.