Mechanistic-empirical Design Method Research Articles

The mechanical performance of reinforced bituminous interfaces with paving fabric under freeze-thaw conditioning

The application of paving fabric at the interface of bituminous layers as a rehabilitation strategy has proved its effectiveness in extending the pavement service life by delaying the manifestation of reflective cracking on the surface. However, this enhanced performance relies on the adhesion bond supplied at the interface, which in the case of debonding, the structural benefits provided by the interlayer can be compromised. Gaining authentic knowledge about the bonding condition at a reinforced interface exposed to different conditioning impacts helps to improve the reliability of the input data, which has not been adequately considered in the mechanistic-based design methods proposed for reinforced bituminous structures. This research was dedicated to understanding the mechanical behavior of double-layer bituminous layers composed of two different hot mixtures and reinforced with paving fabric when subjected to freeze-thaw cycling. To attain this objective, the initial step involved determining the optimal dosage of bitumen for use as a tack coat at the interface of the paving fabric, which was established as 0.0014 m3/m2 through asphalt retention tests. Subsequently, the results from the shear test, conducted using the slant shear device, were utilized to establish three comparative criteria at the interface, aimed at elucidating distinctions when compared to unreinforced cases. These criteria include the energy absorbed by the interface during shearing, shear stiffness, and the coefficient of interface bonding (CIB). This study revealed that by increasing the number of freeze-thaw cycling, the reinforced interface keeps the shear stiffness and the CIB values unchanged. However, in terms of energy absorption capabilities, the unreinforced interfaces showed better performance. This study showed that using the CIB value to quantify the bonding strength at the interface and energy dissipation and initial shear stiffness to quantify the evolution of interface bonding over number of F-T cycles are all proper representatives to include into mechanistic-empirical design methods for reinforced structures in order to present realistic models.

Atık mermer tozu ile zemin stabilizasyonunun mekanistik-amprik tasarım yöntemine göre incelenmesi

Mermer kullanımının artmasına bağlı olarak, ortaya çıkan mermer atıkları dünya çapında önemli bir çevre sorunu haline gelmiştir. Sürdürülebilirliğin önemli olduğu günümüzde bu tür atıklar inşaat işlerinde çeşitli amaçlar için kullanılmaktadır. Sürdürülebilirliğe en büyük katkı, atık maddelerin yeniden kullanımıdır. Yapılan deneysel ve hesaplamalı çalışmada, üç farklı atık mermer tozunun zemin stabilizasyon malzemesi olarak kullanılabilirliği araştırılmıştır. Çalışmanın deneysel kısmında atık mermer tozları % 0-10-20-30 ve 40 oranlarında iki farklı CL sınıfı killi zemine eklenmiş ve zeminlerin mukavemet özelliklerindeki değişiklikler Atterberg limitleri, standart Proctor sıkıştırma, kesme kutusu, ve Kaliforniya taşıma oranı (CBR) testleri ile izlenmiştir. Hesaplamalı kısımda ise CBR ve AASHTO-93yöntemleri kullanılarak yapılan stabilizasyonun üstyapı kalınlığına etkileri belirlenirken, KENPAVE yazılımı ile Mekanistik-Amprik tasarım metoduna uygun olarak mermer tozu iyileştirmesinin üstyapının yorulma ömrüne olan katkısı araştırılmıştır. Elde edilen test sonuçları mermer toz atıklarıyla stabilize edilen düşük plastisiteli killerin dayanım özelliklerinin iyileştiğini göstermiştir. CBR ve AASHTO-93 metotları ile bu iyileştirmenin gereken üstyapı kalınlığını azaltabileceği, SN sayısındaki azalma ile karayolu imalatında yüzlerce metreküp malzeme kazancı sağlanabileceği hesaplanmıştır. Mekanistik-Amprik yöntem ile yapılan hesaplar da atık mermer tozu stabilizasyonu ile üstyapının kritik tekerlek izi oturması ömrünün ortalama %86’ya kadar artabileceğini öngörmektedir.

Analysis of the manufacturing of concrete paving blocks with by-products from thermoelectric power plant

The key factor in constructing urban roads applying interlocking concrete block pavement (ICBP) is to employ an appropriate design method for better effectiveness. Concrete paving blocks (CPB) can also be manufactured using industrial by-products. Then, this paper aims to analyze CPB with coal bottom ash (CBA) from a Thermoelectric Power Plant through mechanical characterization and design methods for ICBP. To this end, tests, such as void index, water absorption, compressive strength, and elasticity modulus, were done on CPB for each mixture. Furthermore, empirical and mechanistic-empirical design methods for ICBP were applied. Then, four dry concrete mixtures (two with CBA and two without CBA) were designed with two water/cement ratios (0.63 and 0.73) to produce rectangular CPB measuring 20 cm × 10 cm × 8 cm (length × width × thickness) by a vibro-press machine. Furthermore, ICBP sections were designed, applying six simulations from empirical and mechanistic-empirical design methods. The results showed that the mixtures A73 and B73 with more water, i.e., water/cement ratio of 0.73, presented higher characteristic compressive strength at 28 days (25.34 MPa and 15.88 MPa, respectively) than the other mixes A63 and B63 with less water, i.e., water/cement ratio of 0.63 (these two mixes showed 15.85 MPa). Furthermore, the CPB application for bike paths or parking areas was allowed according to the Australian specification of 15 MPa for compressive strength test. Also, all ICBP sections from the mechanistic-empirical design required approximately 24.9% fewer materials for the sub-base layer than the empirical process. Finally, the CPB application is possible for areas with light traffic, and the ICBP technology was more feasible with the mechanistic-empirical design method.

Using Repeated Light-Weight Deflectometer Test Data to Predict Flexible Pavement Responses Based on the Mechanistic–Empirical Design Method

This study investigated the potential of lightweight deflectometer (LWD) data in predicting layer moduli and response measurements within the Mechanistic–Empirical Pavement Design Guide. To achieve this goal, field repeated LWD tests and laboratory repeated load triaxial tests were carried out on granular base material compacted at 3% and 6% water content, sandy subgrade soil compacted at 3%, 4% and 9% water content and silty sand subgrade soil compacted at 8% and 10% water content. The results revealed that substituting traditional repeated load triaxial (RLT) data with LWD data for predicting these parameters was notably effective for cohesionless materials, especially for unbound granular materials (UGMs) compacted at optimum water content. The accuracy and reliability of predictions were remarkably high, showcasing the potential of LWD to enhance efficiency and precision in pavement design within this context. Conversely, for cohesive road materials, the study emphasized the importance of considering specific material properties and water content when integrating LWD into the Mechanistic–Empirical Pavement Design Guide. The distinctive characteristics and behaviors of cohesive materials necessitate a nuanced approach. This understanding is critical to ensuring the accuracy and reliability of pavement design and assessment across diverse conditions. In summary, the study presents a promising avenue for utilizing LWD data in cohesionless road materials, offering potential cost and time-saving advantages. Additionally, it underscores the necessity of tailored approaches when considering material properties and moisture content for cohesive materials, thereby advancing the field of pavement engineering by providing insights for improved practices and adaptable frameworks.

Effects of moisture content and soil suction on the permanent deformation of tropical subgrade soils: experimental investigations and modelling

This study presents the effects of moisture variation and the influence of matric suction on the permanent deformation (PD) of three tropical soils with different geological-geotechnical characteristics used in road subgrades in southern Brazil. The experimental programme consisted in determining the soil-water characteristic curves and in dynamic triaxial tests to obtain the PD in different compaction and post-compaction moisture contents. The variation of compaction moisture content caused microstructural changes, influencing the plastic behaviour of soils: the higher the initial moisture content, the greater their accumulated permanent deformations. As expected, the post-compaction moisture variation (wetting process) tended to increase the plastic deformation of materials, evidencing the influence of the suction variation on the performance of the soils studied. In addition, matric suction proved to be the best variable to represent the effects of moisture variation on the plastic behaviour of soils subjected to cyclic loading. Thus, a PD prediction model for tropical soils with the inclusion of this parameter was proposed. The model proved to be highly predictive and may become an important tool to be incorporated into current mechanistic-empirical design methods.

Evaluation of complex modulus and fatigue properties of cold recycled material mixtures using small-scale specimens

The laboratory mechanical characterisation of cold recycled materials mixtures is necessary to develop mechanistic-empirical design methods for cold recycled pavements. The present paper describes a laboratory experiment where small-scale specimens were used to characterise the complex modulus and fatigue properties of cement bitumen treated materials (CBTM) manufactured with bitumen emulsion and cement. In particular, CBTM specimens with diameter of 38 mm were tested and compared with two group of specimens with diameters of 100 and 75 mm. The complex modulus was measured by means of cyclic compression tests and then rheological modelling was applied. Fatigue tests were carried out in direct tension mode of loading. All tests were carried out at long-term curing conditions. Results and statistical analysis showed that the complex modulus values measured on large specimens (diameter of 100 and 75 mm), were not significantly different. On the other hand, the stiffness modulus values measured on small specimens (diameter of 38) were about 15% lower.

Flexural fatigue design of steel fibre reinforced concrete pavements: a comparative study

Though various material models representing the fatigue response are available for steel fibre reinforced concrete (SFRC), the adequacy of these models for relevant applications such as pavements has not been well established. The objective of the present study is to incorporate generalised fatigue models (based on the various test and fibre parameters) in the available design methods for SFRC pavements and compare the design solutions with existing fatigue models. The study focuses on design methods such as Indian Road Congress – IRC SP 46:2013, modified American Concrete Pavement Association (ACPA) and mechanistic-empirical design method developed at IIT Madras (MEFRC). The design efficiency is considerably improved by the incorporation of generalised models. The MEFRC method with generalised fatigue models (GenFRC) seems to be most efficient in capturing the effect of fibres for both elastic and inelastic regimes of the slab behaviour.

Design life of rigid pavements under dynamic wheel loads

The investigation of the pavement performance under dynamically increased wheel loads combines approaches about the modelling of axle assemblies, the simulation of the dynamic wheel loads due to longitudinal unevenness as well as the estimation of the impact on the service life of pavements. The focus in this work is laid on the determination of distress and service life of rigid pavements under dynamic wheel loads using a recently introduced and for the purpose of this study adopted mechanistic-empirical design method for rigid pavements. The results show a good correlation between the assessed Weighted Longitudinal Profile (WLP) (as an indicator for longitudinal unevenness) and the theoretical service life of rigid pavements. Based on that correlation a rating scheme for longitudinal unevenness is introduced. It allows the classification of the unevennes of roads in a five-grade system depending on the WLP and the definition of limiting values for the longitudinal unevenness.

SENSIBILIDADE DE PARÂMETROS DA ESTRUTURA NA ANÁLISE DE DESEMPENHO DE PAVIMENTOS FLEXÍVEIS

The design of asphalt pavement structures is a process that involves the knowledge of variables that are difficult to predict and model.Sensitivity analysis applied to pavement performance prediction is essential to determine the most influential variables, and enable the optimization of design process. This study aimed to analyze the sensitivity of flexible pavements performance to variations in design parameters related to the thicknesses of asphalt layer, base and sub-base and resilient modulus of asphalt layer, base, sub-base and subgrade. For this purpose, a fractional factorial experiment was conducted, which had as output variables the accumulated damage in pavement structure, related to fatigue cracking and rutting in wheel wander. To obtain the accumulated damage, mechanistic-empirical design method was used, through PerRoad software. It was concluded that asphalt layer thickness isthe most sensitive parameter considering the distresses studied, having a higher sensitivity for fatigue cracking and a slightly lower sensitivity for rutting.

Establishing stress boundaries for various loading and pavement configuration

This article is aimed to understand the relationship between stress and pavement components and finding the boundaries of the vertical and lateral stress distribution. It is carried out on four-layer pavement structure to understand the load distribution behavior through different type of materials in each layer with different resilience modulus values and different thickness. This analysis supports us to improve the pavement design accuracy and realistic, which will reduce the road maintenance cost and increase the pavement service life. Several simplifying assumptions regarding tire load applied location has been used. Therefore, 25,000 different vertical stress values in form of 125 different set of data (difference loading and pavement configuration) under five different loading conditions were analyzed using the KENPAVE software (using mechanistic empirical design method). Conclusions from the data and plot analysis show that pavement layer load distribution is affected unevenly as the effect of thickness is greater than the impact of the strength of the layer. Moreover, the results showed that there is a theoretical boundary for load distribution in the lateral direction at the bottom of the surface layer between (8 in - 14.5 in), bottom of base layer (10 in - 19.5 in) and bottom of sub-surface layer (12 in - 22 in). The stress distribution might be used as an indicator for engineers to determine the pavement behavior under an applied load.

Economic and environmental benefits of thin bituminous surface pavements over thick bituminous surface pavements

The design of bituminous pavements, using mechanistic-empirical design method, involves the selection of thicknesses of the bituminous layer and the granular layers to keep the strains at critical locations of the pavement structure within the allowable limits arrived from performance equations. The tensile strain under the bituminous layer defines the fatigue life, and compressive strain on top of the subgrade defines the rutting life of the pavement based on the performance equations adopted. It is generally considered that increasing the thickness of the bituminous layer decreases the strain at the bottom of bituminous (binder) layer. So, most of the pavement designers increase the thickness of the bituminous layer to restrict the strains. However, this is not always true. In fact, the tensile strain at the bottom of the bituminous layer increases with the increase in the thickness of bituminous layer up to a critical thickness and then slowly starts decreasing as the thickness further increases. The critical thickness of bituminous layer ranges between 50 mm and 100 mm. In the majority of the cases, the critical tensile strain under the bituminous layer corresponding to the thicknesses of the bituminous layers of 25 mm and 200 mm are very close. Apart from the economy, the problem of mix rutting is greatly minimized in the case of thin bituminous surfacing (TBS). The issues in rehabilitation and recycling of pavement materials are very less as the granular layer can be reused without much processing requirements.

Use of mechanistic-empirical method of pavement design for performance sensitivity analysis to asphalt pavement fatigue

ABSTRACT In the new Brazilian mechanistic-empirical design method of asphalt pavements, MeDiNa, the characterization of permanent deformation (PD) for the selection of soils and gravel is based on tests performed with at least 150,000 loading cycles for each of the nine specimens indicated in the DNIT standard. Despite providing information about the material behavior under a wide range of testing conditions, the experimental program related to these PD characterizations is time consuming and it is believed that it can be optimized. This paper evaluates the influence of the number of loading cycle applications on the characterization of the materials. For this purpose, seven materials were analyzed at their optimum moisture content (OMC) and one of them was also compacted in a condition above the OMC, in a total of eight data sets. Statistical regression analyzes were performed to identify the parameters of the predictive model for different numbers of cycles and the PD predictions for the different materials were compared. From these results, simulations were performed in the MeDiNa software to predict the performance of the materials. Four different N values were evaluated, considering 150,000 cycles as reference: discarding the 500 first cycles, but considering the PD accumulated in that interval; discarding the 500 first cycles and considering the PD accumulated in that interval; final N of 80,000; and final N of 100,000. For the analyzed materials, no significant differences were observed in the PD prediction, even considering tests with 50,000 or 70,000 cycles less than the 150,000 cycles required in the standard. This indicates that, although characterization is recommended following standardized procedures, the experimental program of the current PD standard can possibly be significantly optimized by reducing the number of cycles applied to materials in laboratory tests. This possibility must be analyzed for each material.

Mechanistic-empirical analysis of geogrid-stabilized layered systems: Part II. Analysis

In recent years, the mechanistic-empirical design method has become popular for pavement design. In the mechanistic-empirical design of geogrid-stabilized roads, elastic solutions for the geogrid-stabilized layered system are necessary but not yet available. In the companion paper, the analytical solutions for the geogrid-stabilized layered system were derived according to the layered elastic theory and the mechanistic-empirical approach. In this study, the elastic responses (i.e. vertical stresses, radial stresses, and elastic strains) due to the effect of the geogrid were investigated based on these solutions. The analytical solutions were then employed to estimate the reduction of vertical stresses underneath the geogrid compared with the measured results, which show reasonable agreement. A parametric study was conducted to investigate the effect of lateral restraint and tensioned membrane on the elastic responses, with the surface deformation at different base thicknesses and base-to-subgrade modulus ratios. The results clearly show that the lateral restraint effect is more significant compared to the tensioned membrane effect when the surface displacement is less than 75 mm, especially in a section with a relatively thick base course. The analytical solutions may be implemented in the mechanistic-empirical design of geogrid-stabilized unpaved roads.

Performance Evaluation of Whitetopping with Improved Design Practices in Texas

Abstract The design method of whitetopping in Texas is a method suggested by the American Concrete Pavement Association (ACPA). However, one of the limitations on this particular design method is that an existing asphalt pavement condition is not considered for slab thickness. Recently, the Texas Department of Transportation developed an improved whitetopping design procedure considering mechanistic-empirical (ME) behavior. In the present study, performance of whitetopping projects constructed by the ACPA design method in Texas were investigated, and improved design details were suggested in order to minimize distresses, such as corner break and slab movement, in transition areas. To evaluate the structural performance of whitetopping, various tests, including the falling weight deflectometer, ground penetration radar, and investigation of concrete coring were conducted on US 90. According to the field survey and tests results, most of the distress was caused by insufficient slab support conditions related to asphalt concrete pavement materials and inadequate slab thickness design. In addition, early-age behavior of whitetopping constructed by the improved ME design method was evaluated and analyzed, and various gage installations, such as vibrating wire strain gage, electric resistance-type strain gages, porous nonstress cylinder, and impervious nonstress cylinder, are discussed.

Predicting Postconstruction Settlements Generated by Moving Traffic on Highways Built on Soft Soil in China Using Mechanistic-Empirical Design Method

AbstractExcessive postconstruction settlement of a highway seriously affects its service performance, a problem that deserves attention urgently. This paper describes an exploratory study on predic...

The Use of Laboratory-Measured and Strain-Gauge Backcalculated Asphalt Stiffness for Rutting Performance Prediction

Laboratory tests are conducted with asphalt concrete materials to determine the expected in-situ performance. In addition, laboratory test results are commonly used in mechanistic-empirical design methods for material characterization to improve the predictive accuracy of the models. However, the effectiveness of laboratory tests in characterizing the long-term performance of asphalt concrete materials needs to be validated to be able to use the results for pavement design and long-term performance prediction. Inaccurate performance characterization and prediction can directly affect the decision-making process for pavement maintenance, rehabilitation, and reconstruction and result in unexpected early failures in the field. The major objective of this study is to determine the impact of using laboratory-measured asphalt stiffness on the prediction accuracy of mechanistic-empirical models. In addition, the effect of using linear-elastic modeling assumptions (layered elastic theory) and neglecting the nonlinearity of pavement response at high load levels (and/or at high strain levels for weaker structures) on the predicted rutting performance was determined. In this study, the effectiveness of the use of laboratory asphalt stiffness tests for in-situ asphalt stiffness characterization was determined by comparing the rutting performance predicted using laboratory-measured stiffness to rutting predicted using strain-gauge backcalculated stiffness. It was determined that laboratory tests are able to characterize the in-situ stiffness characteristics of the asphalt mix used in this study and the stiffness characterization process suggested in this study can provide reliable rutting performance predictions. Results of this study are only applicable to tested rubberized asphalt concrete mixtures.

Viscosity-Based Complex Modulus and Phase-Angle Predictive Models for the Superpave Asphalt Mixtures of New Mexico

AbstractThe recently developed mechanistic-empirical design method of pavement uses the nationally calibrated dynamic modulus predictive model for the design and analysis of asphalt pavements. This...

Integrating the Dynamic Modulus of Asphalt Mixes in the 1993 AASHTO Design Method

The AASHTO Guide for Design of Pavement Structures 1993 (1993 Design Guide) remains the most widely used pavement design manual by highway agencies and design consultants around the world. As defined in the 1993 Design Guide, the structural coefficient of a pavement layer ( ai) is an abstract measure of the relative ability of a unit thickness of a given material to function as a structural component of the pavement. Nevertheless, the assumed ai values of the asphalt layers and a proposed relationship between ai and the resilient modulus do not account for the mechanical and physical properties of asphalt materials, traffic volume and speed, layer thicknesses (thin versus thick pavements), climate, and unbound layer properties. The purpose of this research was to enhance the design methodology incorporated in the 1993 Design Guide by integrating asphalt mixture properties in the design process. The objective was to devise a relationship between the structural coefficient ( ai) of the asphalt layer and the effective dynamic modulus (|E*|eff.) of the corresponding asphalt mix to yield a more realistic estimate of the structural capacity of the asphalt layer. The paper illustrates the development of a multilinear relationship between ai, (|E*|eff.), and the resilient modulus of the aggregate base layer. Pavement structural designs for various asphalt mixes and design inputs using the developed ai–(|E*|eff.) relationship yielded asphalt layer thicknesses that were generally smaller than those obtained using the typical ai value of 0.44 for the asphalt layer and closer to thicknesses obtained with the AASHTO mechanistic–empirical design method using the Pavement ME software.

Stochastic Estimation of the In-Place Dynamic Modulus for Asphalt Concrete Pavements

AbstractThe dynamic modulus of asphalt concrete mixtures is a key property in assessing asphalt pavement performance based on its role in the mechanistic-empirical design method. The dynamic modulus is also considered to be used as one of the major characteristics in performance-related specifications for quality assurance. However, no feasible method to estimate the mean and variance of the in-place dynamic modulus for the as-built asphalt pavement has been suggested. This paper presents a methodology of stochastically evaluating the in-place dynamic modulus of the as-built asphalt pavement using a relationship of in-place air voids and a set of single dynamic modulus values measured in the laboratory. The methodology was validated with asphalt mix collected from a construction site. The comparison plot between the estimated in-place dynamic modulus and as-designed asphalt mix demonstrated a simple way to evaluate the as-built mix quality. This methodology provides several practical advantages to determi...

Using spatial statistics to characterise pavement properties

This paper provides an overview of the statistical models available to characterise spatial variability, and some applications of these models to pavements. It is intended as an introduction for pavement engineers, because these methods are not widely known in the pavements community, and as a guide for conducting simple spatial analysis. Spatial statistics offer a number of insights into the nature of variability in pavement materials and structure, such as the range over which one can expect to see correlation between measurements, and provide a statistically sound procedure for estimating properties between samples. These models have been used recently to gain insights into variability in pavement performance, which could lead to them being incorporated into mechanistic-empirical design methods, although more works still need to be done in this area.