4.75 mm SMA Performance and Cost-Effectiveness for Asphalt Thin Overlays

This paper presents the design of stone matrix asphalt (SMA) with 4.75-mm nominal maximum aggregate size (NMAS) and alternative surfacing cross-section for an asphalt wearing course that may improve pavement performances while controlling costs by using locally available aggregates. The 4.75 -mm NMAS dense-graded mix was previously used in several states to reduce layer thickness and cost. Because of its poor friction and limited performance, however, it was generally used as levelling binder and placed on low-volume roads. The 4.75-mm SMA is proposed for thinner asphalt overlays in this study to improve its performance as well as surface texture. The ultimate goal of this study is to develop the 4.75-mm SMA and evaluate its performance and engineering benefits as a wearing course under laboratory and field conditions. Test pavement sections were constructed in Northern Illinois and on-site performance tests were conducted to evaluate its performance under actual traffic loading. The engineering cost-benefit analysis with respect to performances from both laboratory and field studies suggests the proper application of 4.75-mm SMA as an efficient and cost-effective wearing course for asphalt thin overlays.     

Sensitivity analysis of dynamic response and fatigue behaviour of various asphalt concrete mixtures

This paper presents the dynamic response (|E*|) and fatigue behaviour of various asphalt concrete mixtures subjected to sinusoidal compressive loading. Eight different wearing and base mixtures including Superpave, Asphalt Institute, British Standard dense bituminous macadam and Pakistan's National Highway Authority gradations were selected, and gyratory compacted specimens were fabricated. Laboratory investigations of |E*| at various temperatures (4.4 to 54.4 °C) and loading frequencies (0.1 to 25 Hz) were used to construct stress‐dependent master curves separately, for wearing and base course mixtures. The indicators of dynamic response and viscous (or elastic) properties of the mixtures were used to derive fatigue parameter to estimate the resistance to fatigue, and results revealed that Superpave wearing and NHA‐B base course had better resistance to fatigue for evaluated mixtures. Also, the sensitivity of the dynamic modulus to the variation in hot mix asphalt mix properties using different aggregate gradation, diverse loading frequencies and temperature were evaluated.     

Improved method of considering air void and asphalt content changes on long-term performance of asphalt concrete pavements

Mixture properties (aggregate gradation and volumetric quantities), rate of loading and environmental conditions are the most important factors that affect the |E*| values. The main objective of this study was to develop a rational approach to investigate and model the effect of air voids and asphalt content on the |E*| master curves and consequently predict pavement performance. In this study, |E*| tests were conducted on three asphalt concrete mixtures with the same aggregate gradation, but different binder grades. For each of these mixtures, the air void and asphalt contents were varied at three levels. It is found that the developed method provides a more accurate estimate of the effects of volumetric changes in hot mix asphalt. The application of the proposed approach would be most beneficial for quality control/quality assurance purposes, performance-related specifications and for estimating contractors' incentives and penalties, where |E*| is utilised to predict the pavement performance.     

Comparison of response for three different composite pavement sections to environmental loads

Composite pavement structures are constructed mainly either as Portland cement concrete (PCC)-over-PCC or hot mix asphalt (HMA)-over-PCC. Several successful in-service projects have been reported in Europe. The design and construction of these sections in the United States, however, still require effort. The current study includes the analysis of the response of three different composite pavement sections to the environmental loads. These sections were constructed in May of 2010 at the Minnesota Road Research Facility. The sections are constructed in three individual cells, Cell 70, a HMA-over-PCC with recycled concrete aggregate (RCA), Cell 71, exposed aggregate concrete (EAC)-over-RCA and Cell 72, EAC-over-economical concrete. All cells were heavily instrumented with thermocouples, moisture sensors, and static and dynamic strain gauges. This study characterises the structural response of HMA-over-PCC pavements and also PCC-over-PCC to the environmental loads.     

密实型低噪声路面动态模量的超声波法研究

配制了传统的沥青混凝土（AC）、碎石沥青玛蹄脂（SMA）、不同橡胶粉掺量的骨架密实型低噪声路面等3类5个配比的沥青路面，采用超声波法测量了各类沥青路面的动态模量。并且分析了橡胶粉掺量对密实型低噪声路面动态模量的影响，初步得出了以橡胶粉含量为3％的密实型路面的减振降噪效果最好的结论。     

Compact tension test for fracture characterization of thin bonded asphalt overlay systems at low temperature

Asphalt overlays provide an economical means for treating deteriorated pavements. Thin bonded overlay (TBO) systems have become popular options for pavement rehabilitation. In addition to functional improvements, these systems ensure a high degree of waterproofing benefits. Conventional asphalt concrete fracture tests were developed for pavements with homogeneous asphalt concrete mixtures, and typically their thicknesses exceed 50?mm (2?inch). The use of spray paver technology for construction of TBO leads to continuously varying asphalt binder content, up to approximately one-third of the layer thickness. Commonly utilized fracture test geometries for asphalt concrete include the single-edge notched beam, SEN[B], the disk-shaped compact tension, DC[T], and the semi-circular bend, SC[B]. The SEN[B] test geometry is not preferable for use in pavement systems due to difficulties in procuring beam samples from the field. Applications of the other established test geometries, the DC[T] and SC[B] tests, are limited because of the material nonhomogeneity caused by nonuniform distribution of asphalt binder and smaller as-constructed thicknesses of TBO, which are usually less than 25?mm (1?inch) for gap-graded and 50?mm (2?inch) for dense-graded hot mix asphalt (HMA) mixtures. Both the DC[T] and SC[B] tests simulate movement of the crack fronts in transverse or longitudinal directions in the pavement. Use of these tests on field-procured samples of TBO yields a crack front that encounters nonhomogeneous material through the specimen thickness. The crack moves perpendicular to the axis of material nonhomogeneity, which makes data interpretation and fundamental material fracture characterization challenging. In addition, the crack in the specimen is correlated to a crack channeling across the pavement width rather than a bottom-up or top-down direction, which is more desirable from the standpoint of coupling experimental results with currently available simulation models. This paper proposes a test procedure for fracture characterization of graded asphalt pavement systems that have significant material property gradients through their thicknesses. Suitable specimen geometry and testing procedures were developed using ASTM E399 and ASTM D7313-07b as a starting point. Laboratory tests were performed using an optimized compact tension, or C[T], test geometry for field cores as well as laboratory-fabricated composite specimens. Laboratory testing using the proposed procedure clearly showed distinction in the fracture characteristics for specimens prepared with varying material compositions. The capability of distinguishing different materials combined with stable crack growth makes the proposed testing procedure ideal for fracture characterization of thin and graded pavement systems. Statistical analysis of test data revealed that the proposed C[T] test procedure is capable of detecting differences in fracture energy results across a wide range of pavement systems and yields a low test variability. Finite element simulations of the test procedure further indicate the suitability of the test procedure as well as demonstrating a procedure for extraction of fundamental material properties.     

Application of ground-penetrating radar in measuring the density of asphalt pavements and its relationship to mechanical properties

The ground-penetrating radar (GPR) is a proven technology that is used typically to determine the thicknesses of pavement layers. This paper explores the applicability of the GPR to assess the density of the asphalt layer in pavements. The measurements were conducted on three test sections that were constructed using different asphalt mixtures. Each of the test sections was divided into sub-test sections that were compacted using different compaction methods and number of roller passes in order to achieve a range of asphalt mixture densities. The results showed that there was very good correlation between the GPR results and density of extracted field cores. Consequently, the paper examines the correlation between density and mechanical properties of asphalt mixtures. The results of the mechanical tests provided valuable information on the effect of density on performance.     

Analytical approach for the mix design optimisation of bituminous mixtures with crumb rubber

The present paper provides a basis for defining a mix design method specifically tailored to rubberised asphalt that takes into account the behaviour of crumb rubber. An analytical approach to quantifying the recovered deformation of crumb rubber in the post-compaction phase has been developed in order to adjust the number of gyrations proposed by the Superpave method for compacting specimens of hot mix asphalt using a Superpave gyratory compactor. The maximum allowable amount of rubber has been calculated. Finally, a step-by-step protocol has been proposed in order to fabricate and compact crumb rubber modified mixtures with the gyratory compactor.     

Fatigue life and endurance limit prediction of asphalt mixtures using energy-based failure criterion

Fatigue cracking is one of the major types of distress in asphalt mixtures and is caused by the accumulation of damage in pavement sections under repeated load applications. The fatigue endurance limit (EL) concept assumes a specific strain level, below which the damage in hot mix asphalt (HMA) is not cumulative. In other words, if the asphalt layer depth is controlled in a way that keeps the critical HMA flexural strain level below the EL, the fatigue life of the mixture can be extended significantly. This paper uses two common failure criteria, the traditional beam fatigue criterion and the simplified viscoelastic continuum damage model energy-based failure criterion (the so-called G^R method), to evaluate the effect of different parameters, such as reclaimed asphalt pavement (RAP) content, binder content, binder modification and warm mix asphalt (WMA) additives, on the EL value. In addition, both failure criteria are employed to investigate the impacts of these parameters in terms of the fatigue life of the study mixtures. According to the findings, unlike an increase in RAP content, which has a negative effect on the mixtures’ fatigue resistance, a higher binder content and/or binder modification can significantly increase the EL value and extend the fatigue life as was proved before by other researchers, whereas WMA additives do not significantly affect the mixtures’ fatigue behaviour. A comparison of the model simulation results with the field observations indicates that the G^R method predicts the field performance more accurately than the traditional method.     

Influence of different roller compaction modes on asphalt mix performance

This study aims to investigate the relationship between different roller compaction modes and resulting mechanical performance. In order to accomplish these objectives, a trial asphalt pavement section was observed and monitored both during the paving and compaction processes. Asphalt mix was sampled from the paver to be used later in laboratory and evaluate the differences between compaction in-field and laboratory. Asphalt concrete mixes were prepared and compacted in the laboratory using a steel roller compactor, with varying factors that influence compaction in terms of compaction modes (static, vibratory and a combination of both), as well as effort and temperatures in order to attempt to simulate field compaction conditions. The identification of a harmonised compaction procedure for specimen fabrication able to produce mixtures with stiffness properties resembling field compacted mixtures was also investigated based on the performance-based test results.     

Laboratory versus plant production: impact of material properties and performance for RAP and RAS mixtures

Agencies are moving towards performance-based design methodologies for asphalt pavements, and different methods to evaluate the asphalt performance in the laboratory have been developed. The laboratory performance can be evaluated at the mix design and/or production stages. A good understanding of differences in the behaviour of mixtures produced in the laboratory and plant is required to assess anticipated field performance at the mix design stage. The objectives of this paper are to compare the measured properties of plant-produced and laboratory-produced mixtures, to evaluate the effect of mixture variables on the differences observed, and to translate these to anticipated differences in fatigue performance through pavement evaluation using a linear viscoelastic layered analysis. In this study, 11 plant mixed, plant compacted, and their corresponding laboratory-mixed, laboratory-compacted mixtures are evaluated through binder and mixture testing. Mixture variables include aggregate gradation, binder grade and source, and recycled materials’ type and content. Performance grading on extracted and recovered binders, and complex modulus and SVECD fatigue testing on mixtures were conducted, and fatigue life was predicted using layered viscoelastic pavement design for critical distresses software. Most of the results show the laboratory mixtures are generally stiffer than the plant mixtures, but there is no constant shift for all mixtures. Larger differences are observed for the 19 mm and PG 58-28 mixtures and binder source appears to influence the differences as well. Different plants result in different effects on the properties of plant and lab-produced mixtures. This study provides a unique set of data that expands understanding of differences between laboratory and plant production of asphalt mixtures.     

Finite element modelling of field compaction of hot mix asphalt. Part II: Applications

A constitutive model is developed and implemented in the finite element system three-dimensional computer-aided pavement analysis for the simulation of hot mix asphalt field compaction. The details of this model are presented in a companion paper (Masad et al., Finite element modelling of field compaction of hot mix asphalt. Part I: Theory, International Journal of Pavement Engineering, Accepted, 2014). This model is based on nonlinear viscoelasticity theory and can accommodate large deformations that occur during the compaction process. The model was used to study the influence of frequency and amplitude of vibratory compaction rollers on the level of compaction. In addition, it was used to analyse the influence of various methods for compacting longitudinal joints on the percent air voids near these joints. The model was used to simulate the compaction of asphalt pavements with different structures and compacted using various equipment and patterns. The finite element results of the level of compaction and percent air voids were in reasonable agreement with the measurements. The model offers the opportunity to simulate and predict the compaction of asphalt mixtures under various rolling patterns and for different pavement structures.     

Bonded concrete overlay of asphalt mechanical-empirical design procedure

Bonded concrete overlays of asphalt pavements (BCOAs) are becoming a common rehabilitation technique used for distressed hot mix asphalt (HMA) roadways. The original design procedures were based primarily on data from instrumented pavements and finite element modelling. They were governed by the assumption that the failure mechanism was a function of the overlay thickness. However, field observations have indicated that the actual failure modes are dictated by slab size. The newly developed Bonded Concrete Overlay of Asphalt Mechanistic-Empirical design procedure (BCOA-ME) presented here is valid for overlays that are between 2.5 and 6.5 in (64–154 mm), and includes five primary enhancements to the Portland Cement Association and Colorado Department of Transportation procedures that have been traditionally used: 1.) the failure mode is dictated by the joint spacing; 2.) a new structural model for longitudinal cracking for 6-ft × 6-ft (1.8 m × 1.8 m) concrete overlays has been developed to better predict the critical stresses; 3.) the stress adjustment factors have been calibrated with performance data; 4.) the equivalent temperature gradients used as design input are defined based on the pavement structure and geographical location of the project; and 5.) the effect of temperature change on underlying HMA stiffness is considered. Finally, validation studies were completed on the new procedure and comparisons made between the revised procedure and actual performance data for five separate projects showed reasonable results. A sensitivity analysis also revealed that the predicted thickness obtained using the revised procedure was sensitive to HMA thickness, the modulus of rupture of the Portland cement concrete, and the level of traffic, as would be expected.     

Case study: performance effectiveness and cost-benefit analyses of open-graded friction course pavements in Tennessee

The effectiveness and cost-benefit of Open-Graded Friction Course (OGFC) pavements were analysed in this study by investigating the cost, field performance, short- and long-term effectiveness, and accident rate of OGFC projects in Tennessee. Paired sample t-tests were conducted to compare if there was significant difference between OGFC and non-OGFC sections. Investigation on the performance effectiveness showed that OGFC sections provided comparable performance level as traditional dense mix overlays and were effective in improving pavement performance and repairing deterioration except for rutting potential. However, no severe pavement deterioration was observed on the OGFC sections after more than four or five years of service, indicating sufficient durability of the OGFC used in Tennessee where mild freeze-thaw cycles are experienced annually. Although the unit cost ($/m³) of OGFC was about 42% higher than the cost of traditional dense mix overlays, it was observed that the accident rate was significantly reduced especially in rainy days after the OGFC treatment. The cost-benefit analyses based on the ratio of accident rate reduction over cost demonstrated that OGFC was significantly more cost-beneficial in improving driving safety and reducing accident rate in rainy days.     

Influence of selected WMA additives on viscoelastic behaviour of asphalt mixes and pavements

Warm mix asphalt additives are effective in decreasing production, laying and compaction temperatures of asphalt mixes. However, there are still questions concerning influence of warm mix additives on properties of asphalt mixes and pavement performance. This paper presents results of the comprehensive research of viscoelastic behaviour of asphalt mixes and pavement structures with layers made with warm mix asphalt additives at high temperatures. Two additives of significantly different effects on mixes at higher temperatures were selected for analysis, namely aliphatic synthetic wax produced with the use of Fisher–Tropsch method and formulation of surfactant- based molecules (ionic and non-ionic). Viscoelastic properties of mixes with these two additives and, as a reference mix, with neat unmodified asphalt binder were determined in uniaxial compression with sinusoidal loading using Asphalt Mixture Performance Test. The viscoelastic analysis of pavement structures was performed with use of the VEROAD software and data from laboratory testing. Two different pavement structures were analysed, for light and heavy traffic. The temperature distribution in pavement structure during the hottest summer day in northern Poland in 2012 was taken into account. The model of pavement was loaded with moving wheel at different speeds. The analysis has shown that two tested warm mix additives had different effect on viscoelastic transient response at high temperatures. One of them (Fischer–Tropsch wax) evidently caused an increase in resistance of asphalt mix and pavement structure to loading at high temperature. The second additive (formulation of surfactant-based molecules) slightly reduced resistance of asphalt mix and pavement to loading at high temperatures as compared with the reference mix.     

Prediction models of mixtures’ dynamic modulus using gene expression programming

The dynamic modulus (E*) among asphalt mixtures’ mechanical property parameters not only is important for asphalt mixtures’ pavement design but also in determining asphalt mixtures’ pavement performance associated with pavement response. Based on the principle of gene expression programming (GEP) algorithm, this paper explored two different GEP approach models, namely: GEP-I and GEP-II to predict the E* of hot mix asphalt (HMA) and mixtures containing recycled asphalt shingles, respectively. In this paper, The GEP-I was developed from a large database containing 2750 test data points from 205 unaged laboratory-blended HMA mixtures including 34 modified binders, and the GEP-II model was developed using the E* database containing 1701 sets of experimental data from 4 different demonstration projects. Both the GEP-I model and GEP-II model were compared with other E* prediction models. A sensitivity analysis of each model parameter was conducted by correlating these parameters with dynamic modulus. Both the GEP-I model and GEP-II model showed significantly higher prediction accuracy compared with the existing regression models and could easily be established. It is expected that these two GEP models could lead to more accurate characterisation of the asphalt mixtures’ E*, resulting in better performance prediction.     

The effect of aggregate gradation on creep and moisture susceptibility performance of warm mix asphalt

It is clear that the purpose of mixture design is to select optimum asphalt content for a desired aggregate structure to meet the prescribed criteria. Aggregate makes up high proportion of volume and mass of mixtures; hence, it is considered as an important constituent of asphalt concrete. This study postulates that the gradation is an important characteristic of the aggregate in adoption of the optimum mixture. One aggregate source, three gradations and different percentages of Sasobit^® was used to manufacture hot mix asphalt and warm mix asphalt. The test results indicated that the aggregate gradation affects the rutting resistance and especially the moisture susceptibility of the introduced mixtures, differently. Rutting resistance was evaluated using the flow number parameter, and in order to determine the moisture sensitivity mechanism, a mechanical and visual inspection tests were carried out. At the end, it is concluded that the optimum aggregate gradation for these two types of mixtures is different.     

Performance evaluation of asphalt mixtures containing recycled concrete aggregates

Abstract

To evaluate the feasibility of using Recycled Concrete Aggregates (RCA) in asphalt mixtures, the coarse RCA and fine RCA were prepared as a partial replacement of the natural aggregates (NA). Different amounts of replacement of NA with RCA were investigated, and the mechanical properties and pavement performance of asphalt mixtures containing different proportions of RCA were analysed based on laboratory tests. The results indicated that with increasing the RCA percentage, the optimum asphalt content increased and the bulk density of mixtures decreased as well. Mixtures containing 40% coarse RCA or 20% fine RCA both showed satisfactory performance. Besides, the mixture containing 40% fine RCA had the highest asphalt content, but gave much better performance compared to the virgin mix except for its bad resistance to permanent deformation. Finally, the pavement performance of mixtures containing 60% coarse RCA and 50% coarse RCA were unacceptable.     

Interface treatment of longitudinal joints for porous asphalt pavement

In Germany, multiple lanes of porous asphalt (PA) road surfaces should be constructed with a longitudinal hot joint construction over the full pavement width according to the ‘Technical Instruction for Porous Asphalt Surfacing’. In this way, longitudinal cold joints are avoided and the transverse drainage is not impeded. Therefore, the construction of PA always requires the closure of all lanes in one direction of traffic. However, such measures are only possible in exceptional cases with heavily loaded road sections on motorways with 6–8 lanes. In this research, different variants of joint construction methods for PA were realised in practice. The performance of each variant was investigated with respect to the tensile strength, the tensile strain at break, the permeability and the resistance against ravelling of the joint. After comparing the different construction methods for longitudinal joints, three of them proved to be able to ensure both the structural durability and the water permeability in the joint area.     

Mechanistic evaluation of fatigue cracking in asphalt pavements

Over the last several decades, significant research has been conducted to predict the fatigue cracking performance of asphalt pavements. Recently, the simplified viscoelastic continuum damage (S-VECD) model was developed as an efficient method of characterising the fatigue performance of asphalt mixtures under a wide range of loading conditions. Two important material properties that can be determined from the S-VECD model are the damage characteristic curve that defines how damage evolves in a specimen and the energy-based failure criterion that defines when the specimen fails. These two material functions are unique for a given mixture regardless of temperature, mode of loading, stress/strain amplitude and loading history. This study presents the application of the Layered Viscoelastic Crirtical Distresses (LVECD) programme to predict the fatigue performance of 18 pavement sections from different locations in the United States and Canada. The capability of the LVECD programme to capture crack initiation, crack propagation and damage in the pavement sections is investigated by comparing the simulation results with field observations. This study found reasonable agreement in trends between the damage growth throughout the pavement cross sections as predicted by the LVECD programme and the surface crack growth as evidenced by field observations.