Mechanistic-empirical Pavement Design Methods Research Articles

The Relationship Between Loading Frequency and Truck Speed on Asphalt Pavements

The mechanistic-empirical road pavement design methods necessitate knowledge of the dynamic modulus master curve of asphalt mixtures. This requires the designer to accurately define both the load frequency and the temperature of the pavement structure. The parameter of load frequency is of great importance in laboratory fatigue tests. However, it presents a challenge since road structures are loaded in the time domain, not the frequency domain. This complexity has prompted researchers to develop time-frequency conversion methods to estimate the corresponding frequency from the duration of traffic-induced stress or deformation pulses. Recent findings indicate that the time-frequency equivalence factor is considerably lower than previously assumed. In this study, we introduce a new four-parameter empirical RAMBO material model, derived from the Ramberg–Osgood equation, which offers parameters to determine the time-frequency equivalence factor for asphalt mixtures. The relationship between the moving wheel load velocity and the load impulse time is analysed, primarily based on experimental data and computational methods from existing literature. A method for determining the wavelength of the load impulse is proposed. The theoretical correlation indicates that a wheel load travelling at 100 km/h results in a dynamic deformation frequency of 10 Hz. However, for a strain impulse, the same speed corresponds to a much lower frequency of 3–4 Hz. This study offers a refined understanding of the time-frequency equivalence factor, which is of crucial importance for more accurate road pavement design and fatigue testing.

Comparative Study of Mechanistic-empirical Structural Design Methods Applied to Sustainable Asphalt Mixtures

Introduction/ Background Nowadays, there is a growing interest in achieving sustainable alternatives to conventional flexible pavements. The incorporation of recycled materials into asphalt mixtures has become a departure point. This study focuses on developing sustainable asphalt mixtures incorporating different residues to find a material that performs well on both technical and environmental grounds. Materials and Methods Mixtures with recycled materials and others are compared on a pavement structure. A mechanistic-empirical pavement design method is used to carry out analyses in different conditions. A Life Cycle Assessment is conducted to consider the balance of positive and negative environmental aspects of each mixture and pavement structure. Results The results indicate that all mixtures with sustainable features have a longer life span and an enhanced performance. They also incur higher impacts per tonne produced. However, the “avoided impact” is considered in their favour. Discussion Mixtures with enhanced mechanical properties are key to achieving long-term environmental benefits. The usage of local materials is also essential. Conclusion Proving that unconventional mixtures have a satisfactory performance requires innovative, properly calibrated models and a thorough material characterization. Accurately reflecting on their in-service behaviour is key to evaluating the environmental benefits.

Evaluation of Subgrade Resilient Modulus using CBR Test Data to Facilitate Mechanistic-Empirical Pavement Design (MEPD)

Sri Lankan road pavement design has relied on empirical design guidelines, and it is now transforming to a more modern approach known as the Mechanistic-Empirical Pavement Design (MEPD) method, aligning with global best practices. One crucial input parameter in this new methodology is the Resilient Modulus (RM) of unbound materials. Determination of RM and establishment of typical values is essential to implement the MEPD. This study has devoted significant attention to the RM evaluation process and developing predictive models for determiningRM from CBR values. Furthermore, typical RMvalues for locally available soil types have been established. In addition to that, ageospatial database has been established with information on soil properties and RMvalues throughout Sri Lanka. This database is a valuable resource for M-E road pavement design, providing quick reference data to conceptual designs and Level 3-MEPD.

Critical fatigue strain calculations of flexible pavements in the mechanistic-empirical pavement design method, shortcomings, and improved methodologies

Fatigue Performance is considered one of the most effective measures for designing and maintaining flexible pavements. AASHTO proposed a Pavement Mechanistic-Empirical (PME) design framework in which the fatigue strains are calculated by the mechanistic part and then turned to fatigue cracking by the empirical part. However, it fails to compute actual fatigue strains since it utilizes multilayered linear elastic analysis and predefined calculation points. This paper aims to discuss the PME approach's deficiency in calculating fatigue strains and to develop simplified methodologies for addressing this issue. This study presents three solutions by comparing the fatigue life estimated from the multilayered linear elastic and viscoelastic analysis. The first solution modifies Asphalt Institute's model by suggesting adjusting factors for each axle load configuration. The second one proposes new response locations instead of predefined ones. The last solution involves developing an Artificial Neural Network (ANN) model to predict pavement fatigue life more accurately.

Development and validation of a pavement temperature profile prediction model in a mechanistic-empirical design framework

An accurate temperature prediction tool is an important part of any mechanistic-empirical (M-E) pavement design and performance prediction method. In this paper, a one-dimensional finite control volume (FCV) model is introduced that predicts the temperature within a pavement structure as a function of time and depth. The main input data required for the model are continuous time series of air temperature for conductive heat transfer, solar radiation for radiative heat transfer, and wind speed for convective heat transfer. The heat balance equation for each control volume of the FCV model is solved using an implicit scheme. To validate the numerical model, comparisons were made to measured temperature data from four test sections in Sweden located in regions with different climatic conditions. A good agreement was obtained between the calculated and measured temperature values within the asphalt layer, and temperature in the granular layers with the values of the coefficient of determination R2 ranging from 0.866 to 0.979. The model is therefore suitable to be implemented as a pavement temperature prediction tool in M-E design.

Analysis of performance of asphalt pavements in Qatar using mechanistic-empirical approaches

Qatar roads are experiencing heavy traffic loads due to the rapid increase in the country’s population and construction projects over the past two decades. Considering the demand for high-performing, sustainable, and cost-efficient pavements, emphasis has been placed on using different asphalt modifiers and recycled materials in pavement layers. These modifiers/recycled materials change asphalt mixture properties, and consequently, influence pavement performance. The main objective of this study is to evaluate the performance of pavement sections that incorporate various types of asphalt mixtures and are subjected to traffic levels that range from 5 to 200 million equivalent single axle loads (ESALs). The analysis of pavement performance was conducted via three methods: Australian pavement design method implemented in Circly software, perpetual pavement design using PerRoad software, and a simplified mechanistic-empirical pavement design method (MEPD) that utilizes performance models used in AASHTOWare. The outcome of these analyses was the selection of suitable combinations of asphalt mixtures as well as the optimization of pavement layer thicknesses for different traffic loads. The results highlighted that the use of a high-stiffness mixture incorporating modified asphalt (PG 82E-10) in the wearing course should be used with caution in high traffic load sections (≥100 million ESALs). These stiff layers could be susceptible to cracking when the underneath asphalt layers have much less stiffness (50–70% less stiffness). However, in the medium traffic level (10–50 million ESALs) sections, pavement performance improved by using a stiff mix incorporating a PG 82E-10 binder in the wearing course layer. In addition, the use of crumb rubber (CR) modified asphalt reduced the material cost of a pavement section relative to the use of polymer-modified binder. The results show that it is desirable to use French EME (Enrobés à Module Elevé) mix in the base course layer for heavy traffic roads as this mix help to reduce pavement layer thicknesses and overall material cost. The outcomes of the analysis showed that the rutting thresholds commonly used in MEPD method are too restrictive (low thresholds) for heavy-duty pavements in Qatar hot climate. It is recommended to increase the rutting thresholds for such pavements.

Calibration of a Mechanistic-Empirical Cracking Model Using Network-Level Field Data

At the core of a mechanistic-empirical (M-E) pavement design method is a collection of performance models that each predicts the development of a specific pavement distress, such as fatigue cracking and surface rutting. Each model has both mechanistic and empirical parts. The empirical parts need to be calibrated to remove bias and increase prediction accuracy. This process has traditionally been conducted with small numbers of field sections for which materials may or may not have been sampled and tested. This paper presents a new calibration approach that uses network-level field data and statewide distributions of material properties, without having to sample and test every individual calibration section. The calibration of the fatigue and reflection cracking models for CalME, the M-E design software developed for the California Department of Transportation, is used as an example to illustrate the new approach. The new approach works by correlating the statistical distributions of M-E design inputs with the statistical distribution of pavement performance, both at the network level. The uncertainties affecting pavement performance are divided into those specific to a given project (within-project variability) and those that vary between projects (between-project variability). This distinction allows a clear definition of design reliability. The results showed that the new approach can overcome some of the network-level data limitations and provides a reasonable calibration ready for routine pavement design.

Implementation of NCHRP 9-44A Fatigue Endurance Limit Prediction Model in Mechanistic-Empirical Asphalt Pavement Analysis Web Application

One of the essential components of various design methods for perpetual (or long-life) flexible pavements is elimination (or minimization) of bottom-up fatigue cracking. For this purpose, the concept of the fatigue endurance limit (FEL) is used. The FEL is defined as a strain threshold below which fatigue damage does not accumulate for any number of load repetitions. Different ranges of FEL values have been reported in the literature. Recent studies have showed that FEL is not a single value and depends on several factors. The NCHRP 9-44A project resulted in an FEL prediction model based on the micro-crack healing concept and stiffness, both of which can fluctuate throughout the service life of a pavement. In this study, NCHRP 9-44A FEL prediction model was implemented in the Mechanistic-Empirical Asphalt Pavement Analysis (MEAPA) web application to investigate the effect of fluctuating FEL on bottom-up fatigue cracking prediction in three typical road sections (low, medium, and high traffic) in Michigan. The critical bottom-up fatigue strains, predicted FEL, and predicted fatigue cracking for each road section have been compared. The results revealed that implementation of FEL is critical for accuracy in the prediction of fatigue cracking in relatively thick pavements that are subjected to high traffic loading. The effect of FEL, however, was minimal in thin pavements with low traffic levels. Therefore, given that the mechanistic-empirical pavement design methods are typically used while designing highly trafficked pavements (e.g., highways, arterials, etc.), proper implementation of the FEL concept in pavement design is very important.

Pavement Optimisation With Aggregate Base Or Asphalt Layers Stabilised With Hexagonal Geogrids

The use of hexagonal geogrids in pavement structures results in the increase of the life of designed structure.This offers the possibility to reduce the thickness of layers without reduction of pavement life, or to increase the traffic capacity of a pavement without the need to increase its thickness. This way of using geogrids in pavements design was introduced to the pavement industry by one producer of hexagonal geogrids as a Pavement Optimisation (PO) concept.It can be transformed into both economic and environmental benefits, and obviously results in savings of natural resources and reduction of carbon footprint of a project. PO with geogrids can be used both in the newly designed pavement structures, and in the asphalt overlays of the existing old pavements. Asphalt overlays enhancement with a geogrid either increases the fatigue life of overlays or allows the reduction of overlays thickness to achieve the same pavement life. In new pavements, stabilisation of aggregate base with geogrids increases the stiffness of aggregate, which increases the performance of a whole pavement. This paper presents several tests results, which confirm beneficial effects of using hexagonal geogrids in asphalt overlays and aggregate base layers, from laboratory to full scale accelerated pavement tests. Also, modifications of Mechanistic-Empirical pavement design method, which allow to implement the geogrid benefits into the design process, are discussed. Finally, case studies of pavements – newly designed and reconstructed – optimised with hexagonal geogrids are presented.

A Simplified Mechanistic-Empirical Flexible Pavement Design Method for Moderate to Hot Climate Regions

Flexible pavement structure design is a complex task because of the variability of design input parameters and complex failure mechanisms. Therefore, the aim of this study is to develop and implement a simplified Mechanistic-Empirical (M-E) pavement design method based on the 1993 American Association of State Highway and Transportation Officials (AASHTO), the National Cooperative Highway Research Program (NCHRP) 9-22, and NCHRP 1-37A and 1-40D projects. This simplified methodology is implemented into a computer code and a user-friendly software called “ME-PAVE”. In this methodology, only two equivalent temperatures, as per the NCHRP 9-22 project, are estimated to adjust the dynamic modulus of the asphalt layer(s) for Asphalt Concrete (AC) rutting and AC fatigue cracking prediction instead of using the hourly climatic data, as in the AASHTOWare Pavement ME. In ME-PAVE, the structural responses at critical locations in the pavement structure are determined by a Finite Element Module (FEM), which is verified by a Multi-layer Elastic Analysis (MLEA) program. To ensure that the simplified methodology is practical and accurate, the incorporated transfer functions in the proposed simplified methodology are calibrated based on the Long-Term Pavement Performance (LTPP) data. Based on statistical analyses, the built-in FEM results exhibit very similar trends to those yielded by MLEA, with a coefficient of determination, R2 of 1.0. For all practical purposes, the proposed methodology, despite all simplifications, yields acceptable prediction accuracy with R2 of 0.317 for the rut depth compared to the current practices, NCHRP 1-37A and 1-40D (R2 = 0.399 and 0.577, respectively); while the prediction accuracy for fatigue cracking with R2 of 0.382 is comparable to the NCHRP 1-40D with R2 of 0.275. Nonetheless, the standard error for both distresses is in good agreement based on the investigated data and the developed methodology. Finally, the conducted sensitivity analysis demonstrate that the proposed methodology produces rational pavement performance.

Comparison of dynamic elastisty modulus with different prediction approaches for Karaman – Konya highway pavement

In pavement design and analysis processes among mechanistic-empirical pavement design method, defining the Dynamic Elasticity Modulus(E*) of asphalt layers are very important. In analysis processes, predicting the deteriorations and E* requires some special devices and a lot of time. To simplify this process different prediction models and different approaches have been developed to predict E*. These prediction approaches prepared with huge amount of input data gathered both from construction site and laboratory tests to predict the binder and the volumetric properties of the HMA. In this paper four prediction equations have been applied to predict E* and compared the results with each other. The infrastructure model has chosen as an existing highway section with known HMA material properties. The analyses have done for five different temperatures (10⁰F, 40⁰F, 70⁰F, 100⁰F and 130⁰F) by using two different frequency values (4Hz and 10 Hz). The aim of this research study is doing a comparative assessment of four widely used E* prediction models. Results have shown a large bias between compared E*prediction results due to temperature, frequency, and material properties. Higher Frequency and newest models have shown higher E* values.

Characterisation of the climatic temperature variations in the design of rigid pavements

ABSTRACT The design of rigid pavements in Austria is currently based on a catalogue of standard structures, which can be chosen depending on traffic-related parameters. This approach does not allow the consideration of real material characteristics, detailed traffic load information, local climate conditions, and other boundary conditions. To overcome these limitations, a new mechanistic-empirical pavement design method for rigid pavements (MEPDR) has been developed. The focus of this paper is laid on the proper characterisation of climatic boundary conditions and their impact on the design results. To simulate the actual temperature distribution within a concrete slab, a temperature prediction model was proposed and validated with measured weather data. Furthermore, representative temperature gradients were established using the proposed model and surface temperature data from measuring stations distributed over the Austrian highway pavement network. Additionally, the effect of these temperature gradients on the design life of a typical pavement structure was demonstrated using the MEPDR.

Frequency adjustment method for in-situ seismic modulus of asphalt concrete

ABSTRACT In a mechanistic-empirical (ME) pavement design method, the modulus of asphalt concrete (AC) is essential. The in-situ AC modulus can be obtained by the surface wave method (SWM). However, the measured modulus needs to be adjusted to the design frequency values. This study aimed to propose a frequency adjustment method for the in-situ AC seismic modulus. For this purpose, coring and dynamic modulus tests, FWD (Falling Weight Deflectometer) tests, and PSPA (Portable Seismic Pavement Analyzer) tests were carried out in the accelerated pavement test (APT). The master curves generated by the dynamic modulus results correlated well with the moduli determined from the other tests. Based on this relationship, a frequency adjustment factor was developed for the seismic modulus of the undamaged AC layer. For the damaged AC layer, the proposed factor was modified by incorporating the effect of the damage. Finally, to validate the frequency adjustment factor, the measured maximum tensile strains in the APT were compared with the values determined from the adjusted seismic moduli. The results prove that the frequency adjustment factor is appropriate to obtain the design modulus from the surface wave test. The PSPA test is also recommended to obtain the in-situ AC seismic modulus.

Flexible pavement overlay design of UFJF ring road based on the new Brazilian mechanistic-empirical pavement design method

Abstract The procedures for design and reinforcement projects regarding flexible pavements available in Brazil are mostly based on empirical models developed from studies carried out in specific localities, and therefore, should only be used in cases where equivalent climatic and traffic conditions are observed. The national highway agencies in partnership with universities and research centers have been working to change this scenario through the development of a mechanistic-empirical method that is more compatible with the Brazilian geographic and technical-scientific realities. The first outcome of this task force is the computer program MeDiNa, which is still under assessment. In this present study, the new flexible pavement software in Brazil (MeDiNa) was used by the Federal University of Juiz de Fora to calculate the overlay asphalt of its the ring road, aiming to recover its functional proprieties. This pavement was evaluated functionally by Computerized Continuous Visual Survey (CCVS) and tests of longitudinal cracks, and structurally by survey deflection measurements (FWD) and shaft sinking. With the data collected from the structural evaluation, the homogeneous segmentation of the stretch and the back-calculation of the data was carried out, aimed at the acquisition of needed parameters for the calculation. After the appropriate design, it was concluded that the best solution for the overlay is resurfacing along its entire length, with the use of the project’s asphalt mixture with single thickness of 5.0 cm, observing the application of the anti-reflective cracking layer in some stretches.

Simple Approach for the Determination of Temperature Susceptibility Characteristics of Pure and Modified Asphalt Binders

Asphalt is considered as a valuable construction material because of its strong, adhesive, and durable characteristics. Asphalt cement (AC) binder is a viscoelastic material with different behaviors under different climate conditions, traffic loadings, and speed. Dynamic modulus of asphalt mixtures E* is an important factor in pavement design. The determination of E* is either by direct testing, which is difficult and expensive, or by using correlations with simple tests. Most correlations depend on viscosity’s determination under different temperatures and loading rates (speed), which can be calculated using temperature susceptibility parameters A–VTS values. This study aims to determine a simple and appropriate method to calculate A–VTS parameters using simple tests. An experimental program has been conducted for testing different typical virgin and modified asphalt binders in Turkey. The results have been analyzed using mechanistic–empirical pavement design method (MEPDM) with an available analysis tool. A simple method for the determination of A–VTS has been recommended using penetration tests at temperatures of 4, 25, and 35 °C, and other significant findings were recorded.

Comparison of Mechanistic-Empirical and Traditional Rigid Pavement Design Methods: Afyon-Emirdağ Trial Section

Türkiye’nin Karayolları Genel Müdürlüğü bünyesindeki ilk beton yol uygulaması olan Afyon-Emirdağ kesimi derzli donatısız beton kaplama olarak Belçika Katalog yöntemine göre tasarlanmıştır. Bu tasarım, hem geleneksel Amerikan Devlet Karayolu ve Taşımacılık İdareleri Birliği ampirik tasarım yöntemi (AASHTO 93); hem de mekanistik-ampirik (M-E) üstyapı tasarım yöntemi ile yeniden analiz edilerek, mevcut yol üzerinden aralıklarla ölçülen düzgünsüzlük (IRI) değerleri ile karşılaştırılmıştır. Saha ölçümleri ile M-E analizleri sonucu tahmin edilen IRI değerlerinin birbirine oldukça yakın olduğu tespit edilmiştir. M-E analizleri sonucunda mevcut yolun servis sürecinde düzgünsüzlük ve faylanma performans kriterlerine göre sınır değerleri aşacağı, ancak enine çatlak yönünden sınır değerler içinde kalacağı öngörülmüştür.

Mechanistic-Empirical Compatible Traffic Data Generation: Portable Weigh-in-Motion versus Cluster Analysis

Abstract Axle load distribution factors (ALDFs) are used as one of the primary traffic data inputs for mechanistic-empirical (ME) pavement design methods for predicting the impact of varying traffic loads on pavement performance with a higher degree of accuracy than empirical methods that are solely based on equivalent single axle load (ESAL) concept. Ideally, to ensure optimal pavement structural design, site-specific traffic load spectra data—generated from weigh-in-motion (WIM) systems—should be used during the pavement design process. However, because of the limited number of available permanent WIM stations (in Texas, for example), it is not feasible to generate a statewide ALDFs database for each highway or project from permanent WIM data. In this study, two possible alternative methods, namely, the direct measurement using a portable WIM system and the cluster analysis technique, were explored for generating site-specific ME-compatible traffic data for a highway test section, namely, state highway (SH) 7 in Bryan District (Texas). The traffic data were then used for estimating pavement performance using a ME pavement design software, namely, the Texas Mechanistic-Empirical Thickness Design System (TxME). The TxME-predicted pavement performance (e.g., rutting) using the portable WIM-generated traffic input parameters closely matched with the actual field performance. Overall, the study findings indicated that the portable WIM (with proper installation and calibration) constitutes an effective means for rapidly collecting reliable site-specific ME-compatible traffic data.

Neural network-based model for prediction of permanent deformation of unbound granular materials

Abstract Several available mechanistic-empirical pavement design methods fail to include predictive model for permanent deformation (PD) of unbound granular materials (UGMs), which make these methods more conservative. In addition, there are limited regression models capable of predicting the PD under multi-stress levels, and these models have regression limitations and generally fail to cover the complexity of UGM behaviour. Recent researches are focused on using new methods of computational intelligence systems to address the problems, such as artificial neural network (ANN). In this context, we aim to develop an artificial neural model to predict the PD of UGMs exposed to repeated loads. Extensive repeated load triaxial tests (RLTTs) were conducted on base and subbase materials locally available in Victoria, Australia to investigate the PD properties of the tested materials and to prepare the database of the neural networks. Specimens were prepared over different moisture contents and gradations to cover a wide testing matrix. The ANN model consists of one input layer with five neurons, one hidden layer with twelve neurons, and one output layer with one neuron. The five inputs were the number of load cycles, deviatoric stress, moisture content, coefficient of uniformity, and coefficient of curvature. The sensitivity analysis showed that the most important indicator that impacts PD is the number of load cycles with influence factor of 41%. It shows that the ANN method is rapid and efficient to predict the PD, which could be implemented in the Austroads pavement design method.

A Comparison between the Empirical and Mechanistic-Empirical Pavement Design Methods

In this paper a comparative study has been carried out between the Mechanistic-Empirical Pavement Design Methods and the Empirical Pavement Design Methods. For the purpose of this paper, nine pavement design sections have been prepared using the Mechanistic-Empirical Methods represented by the Asphalt Institute Design Method (SW-1 software of the Asphalt Institute) and the Empirical Design represented by AASHTO 1993 and TRL Road Note No.31, using the same traffic loading and subgrade strength. Three traffic loading scenarios have been considered for this study.
 (Key words: Mechanistic-Empirical, Empirical, axle loads, Subgrade Strength, pavement design)

Fast falling weight deflectometer as new tool to perform accelerated pavement testing

The development of the falling weight deflectometer (FWD) in the late 1970s made it possible to determine quickly the in situ modulus and critical stresses/strains in pavement structures, which are generally considered the most important input for the ‘mechanistic’ part of the mechanistic–empirical pavement design method. In 2015, the newly designed FastFWD was released and provided the opportunity to speed up the testing procedure and overall productivity significantly. The increased rate of loading prompted the current study into the possibility of performing in situ accelerated pavement testing to predict pavement deterioration, and to fill the gap between the heavy vehicle simulator and small-scale laboratory test methods. Numerous experimental sequences and test sites have been initiated since the start of the research; in the last of these, 1·6 million load applications were applied and the dynamic modulus master curve was back-calculated and used to filter out the viscoelastic response of the asphalt layer caused by temperature changes within the material from the repeated loading. Based on the findings of this research, an incremental-recursive fatigue model has been used to predict accurately the reduction in asphalt modulus as a function of any combination of loads and temperatures for a known material.