Accelerated Pavement Testing Research Articles

Evaluation of 4.75-mm Nominal Maximum Aggregate Size (NMAS) Mixture Performance Characteristics to Effectively Implement Asphalt Pavement System

【PURPOSES : This study primarily focused on evaluating the performance characteristics of 4.75-mm nominal maximum aggregate size (NMAS) asphalt mixtures for their more effective implementation to a layered flexible pavement system. METHODS : The full-scale pavements in the FDOT's accelerated pavement testing (APT) program, including 4.75-mm mixtures at the top with different thicknesses and asphalt binder types, were considered for the faster and more realistic evaluation of the rutting performance. The results of superpave indirect tensile (IDT) tests and hot-mix asphalt fracture mechanics (HMA-FM) based model predictions were used for cracking performance assessments. RESULTS : The results indicated that the rutting performance of pavement structures with 4.75-mm mixtures may not be as good as to those with the typical 12.5-mm mixtures, and pavement rutting was primarily confined to the top layer of 4.75-mm mixtures. This was likely due to the relatively higher mixture instability and lower shear resistance compared to 12.5-mm mixtures. The energy ratio (ER) and HMA-FM based model performance prediction results showed a potential benefit of 4.75-mm mixtures in enhanced cracking resistance. CONCLUSIONS : In relation to their implementation, the best use of 4.75-mm mixtures seem to be as a surface course for low-traffic-volume applications. These mixtures can also be properly used as a preservation treatment that does not necessarily last as long as 12.5-mm NMAS structural mixes. It is recommended that adequate thicknesses and binder types be considered for the proper application of a 4.75-mm mixture in asphalt pavements to effectively resist both rutting and cracking.】

Development and calibration of shear-based rutting model for asphalt concrete layers

This study improves a shear-based rutting model for asphalt concrete (AC) layers and calibrates the model with field data. With dynamic modulus-based material parameters, the laboratory rutting prediction model was improved and determined by the wheel tracking test and full-scale accelerated pavement test. Through the field survey on several in-service pavements, the rutting model was calibrated to be applied to AC layers. In the improved rutting prediction model, the ratio of maximum shear stress to shear strength was introduced to combine asphalt material design and pavement structural design. The speed correction coefficient and the new temperature processing method improve the accuracy of the rutting model. The calibrated rutting prediction model proves to be reasonable and accurate in predicting the rutting depth of AC layers.

Internally Cured Concrete for Use in Concrete Pavement Using Accelerated Pavement Testing and Finite-Element Analysis

AbstractThree full-size instrumented test slabs were constructed and tested by a heavy vehicle simulator (HVS) to evaluate the structural behaviors of internally cured concrete (ICC) for pavement use in Florida conditions. Three mix designs from a prior laboratory testing program were selected. The selected mixtures were a standard mixture with 0.40 water-cement (w/c) ratio, an ICC mixture with 0.40 w/c ratio, and an ICC mixture with 0.32 w/c ratio. Concrete samples were made and tested for their strength, elastic modulus, coefficient of thermal expansion (CTE), and shrinkage properties in the laboratory. A three-dimensional (3D) finite element (FE) model developed was calibrated by using a falling weight deflectometer (FWD) deflection basin as well as strain data under the HVS loading. From this study, it was found that ICC slabs appear to have better potential performance on the basis of the results of the critical stress analysis and the visual inspection of the test slabs.

Accelerated Pavement Testing in Slovakia

Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. Accelerated pavement testing is one way where researchers can find answers for these problems. Full-scale accelerated pavement testing APT forms a vital link between the laboratory evaluation of materials used in pavement layers and the field behavior of these materials when combined into pavement structures. For many years APT provided pavement engineers with knowledge that improved their understanding of pavement materials and structures, as well as their behavior under typical traffic and environmental loading. It formed the basis for developing various theories about pavement behavior and supports most of the current pavement design methods.

Deformation Modelling of Instrumented Flexible Pavement Structure

A flexible test road structure was built and tested in an Accelerated Pavement Test (APT) using a Heavy Vehicle Simulator (HVS) to monitor its performance behaviour. In the tests more than one million load cycles were applied, but mid-way the water table was raised, allowing the structure to be analysed in “moist” and “wet” state. The raised water level had a significant effect, decreasing the resilient modulus and increasing the rate of accumulation of permanent deformation (PD). The structure was instrumented to measure stress, strain and deflection responses as a function of load repetitions as well as PD manifested on the surface as rutting. The structure has been modelled in an axisymmetric analysis using a 2D multi layer elastic theory (MLET) as well as a 3D finite element method (FEM). The methods generally both agreed well with the measurements. The observed accumulation of PD of the unbound layers was modelled using three different material models, both stress and strain based with responses gained from both MLET and FEM. The modelled deformation, is compared to the measured deformation in both “moist” and “wet” state, with some difference observed between models and methods but generally reasonably agreement was established.

Pavement Working Platforms Constructed with Large-Size Unconventional Aggregates

As a sustainable construction practice, recent research efforts of the Illinois Department of Transportation (DOT) have been focused on an engineered approach for developing construction specifications and performance validation of the use of large-size virgin and recycled unconventional aggregates in soft subgrade remediation. The Illinois DOT Bureau of Design and Environment has issued a special provision that specifies certain gradation bands for improved aggregate subgrade to allow enhanced use of large rocks from both primary crusher type virgin and recycled sources. Nevertheless, laboratory tests are usually inadequate for characterizing the properties and engineering behavior of large-size unconventional aggregates. Therefore, the recent field performance evaluation study using accelerated pavement testing was initiated at the University of Illinois with 12 full-scale pavement working platforms constructed with selected large-size virgin and recycled materials, including reclaimed asphalt pavement, recycled concrete aggregate, and demolition waste. For in-depth performance testing and evaluation, this paper describes test section construction and quality control sequences conducted at different phases of the study, including state-of-the-art field aggregate and pavement layer imaging techniques. The rutting performance trends of test sections were investigated in light of innovative test devices and techniques, including variable energy penetration testing, geoendoscopy, transverse ground-penetrating radar scans, as well as postfailure trenching images. Penetration of large rocks into the soft subgrade was effective in achieving a stable construction platform. Moreover, reclaimed asphalt pavement as a granular pavement layer was prone to large permanent deformations.

Performance of Geotextile-Reinforced Bases for Paved Roads

Geotextiles have been widely promoted for pavement structure, but only a few full-scale experiments have investigated the effects of geotextile reinforcement on pavement design. In this study, full-scale accelerated pavement testing (APT) was conducted on six pavement test sections with granular bases reinforced with various types of woven geotextiles. The control section had a granular base without any reinforcement. All sections were paved with Superpave® hot-mix asphalt (HMA). Base and subgrade materials were the same, but the test sections had varying thicknesses of base and asphalt layers. Each section was instrumented with two pressure cells at the top of the subgrade, six strain gauges on the geotextile, six H-bar strain gauges at the bottom of the asphalt layer, and two thermocouples. The sections were loaded to 250,000 to 400,000 repetitions of an 80-kN single-axle load of the APT machine. Mechanistic responses of the test sections were periodically monitored and analyzed. Rutting profile, pressure on the subgrade, strains in the geotextiles, and strains at the bottom of the HMA layer were measured. Falling weight deflectometer (FWD) tests were performed before and after loading. Reinforced-base sections with similar cross sections outperformed the control section in terms of rutting, and the reinforced-base layer reduced pressure on the subgrade. Backcalculated moduli from FWD tests demonstrated that the base layer in reinforced sections was significantly stronger than the control section base layer after loading. Strain measurements at the bottom of the HMA layer indicated that fatigue life of test sections did not improve with geotextile reinforcement.

Full-scale Evaluation in a Fatigue Track of a Base Course Treated with Geopolymers

Usually, optimal percentages of additives used to improve the characteristics of soils, are determined by laboratory tests of different complexity. Then, these optimal combinations are used directly in the pavement structures, without analysis of time or scale differences between laboratory and field conditions. This paper presents the results of a full-scale accelerated pavement test on a base course that has been improved by using fly ash and an alkali activator. Initially, the main characteristics of the testing equipment are presented. The optimal amount of the different components was previously obtained by laboratory tests. The components were mixed, the material was extended and compacted in layers and a curing time was permitted. After that, a wheel loaded with a vertical hydraulic actuator, simulating a rear half-axis of a truck, passed on the top layer repeated times. During the test, vertical deformations of the surface were measured in several points along the track. Results after around 10000 loading repetitions were compared against simultaneous measurements on a non-treated material subjected to identical loading application, showing the advantages of the alkali activation in reducing deformability of base courses and the effect of variable natural wheatear conditions on both type of pavement structures.

Development and Validation of a Mechanistic–Empirical Design Method for Permeable Interlocking Concrete Pavement

Fully permeable (or porous or pervious) pavements are pavements whose layers are all intended to be permeable. They are used to minimize the adverse effects of stormwater runoff generated from impervious surfaces. They may also be an effective solution for cool pavement strategies for improving outdoor thermal environments and mitigating heat island effects in hot climates. Most current applications of permeable pavements in North America are used for roads with a low traffic volume, basic access streets, parking lots, and recreation and landscaped areas, all of which carry light, slow-moving traffic. Structural design methods have been empirical in nature. Mechanistic–empirical approaches for fully permeable pavement designs have not been developed, but when available, would probably speed up the implementation of fully permeable pavements and potentially extend their use to pavements with a higher volume of traffic where appropriate. This paper summarizes the development of a mechanistic–empirical design method and design tool for permeable interlocking concrete pavements, which uses mechanistic analysis and partial validation with accelerated pavement testing results. A new example design table, based on the number of days with standing water in the subbase (0, 10, 30, 50, 90, and 120), was developed with an Excel spreadsheet-based design tool. The format of the table is similar to that of the current guideline for permeable interlocking concrete pavements of the Interlocking Concrete Pavement Institute. Designs for a specific set of project circumstances can be developed with the same Excel spreadsheet-based design tool used to develop the tables along with the hydrological design procedures provided in the Interlocking Concrete Pavement Institute guide.

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.

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.

Performance Evaluation of Carbon-Reducing Soil Pavement using Inorganic Binder

PURPOSES : This study intends to develop an inorganic soil pavement material using industrial by-products and to evaluate its applicability as a road pavement material. METHODS : In this study, a compressive strength experiment was conducted based on the NaOH solution molarity and water glass content to understand the strength properties of the soil pavement material according to the mixing ratio of alkali activator. In addition, the strength characteristic of the inorganic soil pavement material was analyzed based on the binder content. The performance of the soil pavement was evaluated by conducing an accelerated pavement test and a falling weight deflectometer (FWD) test. RESULTS : As a result of the soil pavement material test based on the mixture ratio of alkali activator, it was identified that the activator that mixed a 10 M NaOH solution to water glass in a 5:5 ratio is appropriate. As a result of the inorganic soil pavement materials test based on the binder content, the strength development increased sharply when the amount of added binder was over 300 kg; this level of binder content satisfied 28 days of 18 MPa of compression strength, which is the standard for existing soil pavement design. According to the measured results of the FWD test, the dynamic k-value did not show a significant difference before or after the accelerated pavement testing. Furthermore, the effective modulus decreased by approximately 50%, compared with the initial effective modulus for pedestrian pavement. CONCLUSIONS : Based on these results, inorganic soil pavement can be applied by changing the mixture proportions according to the use of the pavement, and can be utilized as road pavement from light load roads to access roads.

Optimal design for concrete pavement situated above box culvert: experimental and numerical study

This study examined the pavement distress data obtained from the field as well as the effects of the soil cover depth, joint position and reinforced slab length on the behaviour of concrete pavement using the finite element method. An ultimate strength model with a similarity of 1/2 was designed and constructed. Finite element analysis incorporating an implicit direct numerical integration scheme was conducted to obtain an optimal design for the pavement structure above a box culvert. An accelerated pavement test was conducted for validation, in which a realistic traffic load was imposed on the pavement model constructed in the laboratory. The strain histories were measured at each section and compared with those of numerical analysis. The optimal joint position and reinforced slab length that can minimise the damage to the pavement structure above a box culvert were also determined.

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.

Using accelerated pavement testing to examine traffic opening criteria for concrete pavements

The risk of cracking in a concrete pavement that is opened to traffic at early ages is related to the maximum tensile stress σI, that develops in the pavement and its relationship to the measured, age dependent, flexural strength of a beam, fr. The stress that develops in the pavement is due to several factors including traffic loading and restrained volume change caused by thermal or hygral variations. The stress that develops is also dependent on the time-dependent mechanical properties, pavement thickness, and subgrade stiffness. There is a strong incentive to open many pavements to traffic as early as possible to allow construction traffic or traffic from the traveling public to use the pavement. However, if the pavement is opened to traffic too early, cracking may occur that may compromise the service life of the pavement. The purpose of this paper is two-fold: (1) to examine the current opening strength requirements for concrete pavements (typically a flexural strength from beams, fr) and (2) to propose a criterion based on the time-dependent changes of σI/fr which accounts for pavement thickness and subgrade stiffness without adding unnecessary risk for premature cracking. An accelerated pavement testing (APT) facility was used to test concrete pavements that are opened to traffic at an early age to provide data that can be compared with an analytical model to determine the effective σI/fr based on the relevant features of the concrete pavement, the subgrade, and the traffic load. It is anticipated that this type of opening criteria can help the decision makers in two ways: (1) it can open pavement sections earlier thereby reducing construction time and (2) it may help to minimize the use of materials with overly accelerated strength gain that are suspected to be more susceptible to develop damage at early ages than materials that gain strength more slowly.

Mechanistic-empirical approach to characterizing permanent deformation of reinforced soft soil subgrade

This study focuses on characterizing the permanent deformation of geogrid-reinforced soft soil subgrade by using the mechanistic-empirical (ME) approach based on both experimental measurements and results of numerical modeling. Two sets of small-scale pavement sections were built over two types of soft soil subgrade and subjected to cyclic moving loads by means of a reduced-scale accelerated pavement testing (APT) device. Each set of pavement sections included one control section and three sections reinforced by different geogrids placed at the base–subgrade interface. The pavement sections were instrumented to measure vertical deformation and vertical stresses at the top of the subgrade. Strains developed in the geogrids were also measured by strain gauges throughout the construction and accelerated testing. Simplified finite element (FE) models were created to simulate both the control and geogrid-reinforced pavement sections and to compute the pavement mechanistic responses. With the experimental measurements from the first set of tests and results of FE analysis, the permanent deformation model in NCHRP 1-37A for unbound layers was adapted and calibrated to model the permanent deformation of the geogrid-modified subgrade. The effects of geogrids on the subgrade permanent deformation were integrated into the ME performance model through both the mechanistic response modeling and the empirical calibration. Predictions from the permanent deformation model were then compared with the second set of measurements and found to underestimate the permanent deformation of the geogrid-modified subgrade. However, the model was able to distinguish the difference in performance among the sections, i.e. the predicted rank of the performance was consistent with the measurements.

INNOVATIVE ASPHALT RESEARCH USING ACCELERATED PAVEMENT TESTING

Accelerated pavement testing is one key for innovations in the field of road pavement structures and materials due to its power of assessing mechanical performance in close to reality situations. This paper discusses two types of mobile load simulators for applying unidirectional wheel loads at comparatively high frequencies, the MMLS3, a one third scale device, and the MLS10, a full-scale device. Through examples it is demonstrated that these devices are suitable for testing complex systems, such as mechanical resistance of light reflectors on pavements, traffic resistance of bituminous plug expansion joints for bridges, performance of grid reinforced pavements as well as water resistance of porous asphalt against traffic induced pumping effects. Moreover, an example of MLS10 ultimate bearing capacity tests on a real test section is shown focusing on the discussion of strain gauge, acceleration, rut depth and falling weight deflectometer (FWD) measurement results.

Numerical validation of viscoelastic responses of a pavement structure in a full-scale accelerated pavement test

This paper demonstrates the application of a generalised layered linear viscoelastic (LVE) analysis for estimating the structural response of flexible pavements. A comparison of the direct layered viscoelastic responses with approximate solutions based on the linear elastic (LE) and LVE collocation methods was also carried out. The different approaches were implemented by extending a layered elastic program with an improved computational performance. The LE and LVE collocation methods were further extended for analysis of pavements under moving loads. The methods were illustrated by analysing a pavement structure subjected to moving wheel loads of 30, 50, 60 and 80 kN using a Heavy Vehicle Simulator (HVS). The various responses (stresses and strains) in the pavement, at pavement temperatures of 0, 10 and 20°C, were measured using various types of sensors installed in the structure. It was shown that the approximated LVE solution based on the LE collocation method agreed very well with the measurements and is computationally the least expensive.

Mechanical performance of pavement structures with paving slabs – Part II: Numerical simulation tool validated by means of full-scale accelerated tests

In recent years, pavement structures with paving slabs have gained importance, especially in urban trafficked areas, because they provide more design options and have great potential with regard to durability and low maintenance compared to flexible pavements. In order to exploit this potential, an accurate and reliable performance prediction by means of appropriate design concepts is necessary. Contributing to this topic, a numerical simulation tool was developed and its performance evaluated by means of full-scale accelerated pavement tests (APT).Within this paper (Part II of this work), a numerical simulation tool is proposed which is able to take into account the non-linear and plastic behavior between paving slabs (vertical joints) and between slabs and sandbed. The material parameters required for the paving concrete slabs, the vertical joints and the base courses are obtained by identification experiments. Finally, the main results from the APT could be reproduced very well with the numerical simulation tool without using phenomenological parameters.

Mechanical performance of pavement structures with paving slabs – Part I: Full-scale accelerated tests as validation for a numerical simulation tool

In recent years, pavement structures with paving slabs have gained importance, especially in urban trafficked areas, because they provide more design options and have great potential with regard to durability and low maintenance compared to flexible pavements. In order to exploit this potential, an accurate and reliable performance prediction by means of appropriate design concepts is necessary. Contributing to this topic, a numerical simulation tool was developed and its performance evaluated by means of full-scale accelerated pavement tests (APT).Within this paper (Part I of this work), the APT using the New Mobile Load Simulator (MLS10) is presented. The APT program was carried out by the Swiss Federal Laboratories of Material Science and Technology on four test sections with concrete slabs of different dimensions. Two of them were instrumented with soil pressure cells and horizontal strain gauges in order to assess the primary response under the 65kN wheel load. With a loading speed of 22km/h under a super single tire, up to 38,400 load passes per day could be simulated on the test sections. With a frequency of the measuring sensors of 100Hz, the stress peaks in the concrete slabs as well as at the top of the upper base course and the subgrade were recorded during the whole testing period. Overall, a very successful test execution has led to valuable and reliable data, which will be used to assess and validate the performance of a numerical simulation tool.