Flexible Pavement Performance Research Articles

Laboratory simulation of the impact of solar radiation and moisture on long-term age conditioning of asphalt mixes

Ageing is a renowned phenomenon for pavement engineers that can substantially affect the durability and long-term performance of flexible pavements. Several factors affect the mechanism of age-related changes, including asphalt cement’s chemical composition, mix properties, and environmental conditions. Most of the laboratory accelerated age hardening procedures are trying to simplify conditioning by considering heat as the main affecting factor and neglecting the others, such as humidity, precipitation, and solar radiation. This research aims to examine the validity of such an assumption and evaluate the effect of photo-oxidation, moisture and precipitation on the chemical and rheological properties of the asphalt cement and mix.In this research, a plant produced asphalt mix was selected and subjected to four different age conditioning procedures including Long-Term Oven Ageing procedure (AASHTO R30), Atlas® Whetherometer™, and using a bespoke chamber by applying dry and wet cycles of solar radiation and water conditioning. After running the Complex Modulus test on unconditioned and conditioned asphalt mix samples, asphalt cement was recovered and subjected to chemical and rheological analysis. The 2S2P1D model was employed to develop Complex Modulus and Phase Angle master curves. Results of this research showed that concerning chemical changes, extended heating at excessively high temperatures would result in different chemical products of oxidation as compared to solar radiation technique in terms of Carbonyl and Sulfoxide Indices. Moreover, it was observed that the extended heating procedure resulted in less stiffening at the low-temperature range in comparison with solar radiation. From the results of this research, it can also be concluded that water plays a vital role in the age conditioning procedure using solar radiation.

Development of 3-D Finite Element Models for Geo-Jute Reinforced Flexible Pavement

In this study, three dimensional (3-D) finite element analysis are performed to evaluate the effect of geo-textile interlayer on the performance of flexible pavement. The main objective of this study is to evaluate the improvement in stress distribution of flexible pavement due to the application of geo-jute at three specific positions i.e., subgrade-base interface, base-asphalt layer interface, and within asphalt layers. Stress, strain and displacement values are investigated and compared for the application of geo-jute interlayer on various positions. Moreover, to better understand the mechanistic behavior of geo-jute on pavement subgrade, a separate 3-D finite element model is developed to simulate the California bearing ratio (CBR) test on geo-jute reinforced soil. Results showed that the inclusion of geo-jute on flexible pavement significantly improves the pavement performance by producing lower stress, strain, and displacement at top of the subgrade. Moreover, the bearing capacity of subgrade soil increased more than 20% due to the inclusion of geo-jute.

Performance of geosynthetic-reinforced flexible pavements in full-scale field trials

The paper presents the results of a series of full-scale trials carried out in Thailand examining the performance of geosynthetics as reinforcement for flexible pavements. The geosynthetics were embedded at different pavement depths and the structural response was monitored across four test sections by means of strain gauges, pressure sensors, deflection points and deflection plates. The results show that all reinforcement configurations helped reduce the vertical static stresses developed at the base of the pavement by up to 66% and by up to 72% for dynamic stresses. The performance enhancement expected to prolong the lifespan of the base layers. The reinforcement layers closer to the base experienced the highest lateral strains of up to 0.13%, providing evidence that geosynthetics can also effectively reduce lateral spreading. All reinforcement configurations helped enhance rut resistance with maximum traffic benefit ratio (TBR) of 13.70, effectiveness ratio (EF) of 12.70 and minimum rutting reduction ratio (RRR) of 0.74. The best configuration included a geotextile within the asphalt concrete layer and a geogrid under the base layer. Non-linear finite element analyses of the test sections predicted very well the strains and stresses in the pavement. The study provides a benchmark for future studies in this field and concludes that geosynthetics can help increase maintenance periods and extend the lifetime of flexible pavements.

The effect of axle load spectra from AASHTO method on flexible pavement performance

Currently, methods used for pavement design are empirical and based on experiments conducted in the 1960s. Due to the number of variables that can influence an empirical analysis, the National Cooperative Highway Research Program (NCHRP) proposed a mechanistic-empirical method. Based on this method, the MEPDG (Mechanistic-Empirical Pavement Design Guide) software was developed and later, its improved version, the AASHTO Ware Pavement ME Design. In both software versions, default values were developed from traffic data of the United States. However, characteristics of the Brazilian traffic are different from characteristics in the United States. Therefore, this study aimed to verify the effect on national pavement performance due to the use of the default axle load spectra that are available on both software versions. Thus, computer simulations were performed using Brazilian axle load spectra, based on data collected at the Imigrantes Highway in Sao Paulo, and using the default load spectra of the software. The results show that the Brazilian axle load spectra studied damages more the national pavement than the default spectra of the software. Therefore, it is not recommended the use of default spectra for designing Brazilian highways similar to the one studied, because this would lead to under-designed structures.

Effects of Recycled Polyethylene Terephthalate (PET) on Stiffness of Hot Asphalt Mixtures

In recent years, Chile’s vehicle fleet has undergone great changes, with 25% growth in motor vehicles. This increase is directly related to improvements in the performance of flexible pavements, which make infrastructure less susceptible to permanent deformations and/or cracking at high and low temperatures, respectively. In 2016, the Ministry of the Environment passed the Law on Recycling and Accountability to promote the search for innovative ideas and materials in different sectors. This research focused on the experimental study of the mechanical behaviour of a mixture of hot asphalt, incorporating thick particles of polyethylene terephthalate (PET) from bottle recycling, using the Marshall stability and flow test and the resilience module (rigidity) test at 5°C and 22°C. Based on previous research, significant PET fibre sizes were used, increasing the optimum amount of polyethylene terephthalate from 6% to 14% in the mixture. The results show that incorporating this polymeric additive provides greater stability, in addition to an increase in resistance to permanent deformations and fatigue, compared to a “traditional” mixture.

Quantifying the Impact of Climate Change on Flexible Pavement Performance and Lifetime in the United States

Flexible pavement design requires considering a variety of factors including the materials used, variations in water tables, traffic levels, and the climatic conditions the road will experience over its lifetime. Most pavement designs are based on historical climate variables such as temperature and precipitation that are already changing across much of the United States, and do not reflect projected trends. As pavements are typically designed to last 20 years or more, designs that do not account for current and future trends can result in reduced performance. However, incorporating climate projections into pavement design is not a trivial exercise. Significant mismatches in both spatial and temporal scale challenge the integration of the latest global climate model simulations into pavement models. This study provides a national-level overview of what the impact of climate change to flexible pavement could look like, and where regional focus should be placed. It also demonstrates a new approach to developing high-resolution spatial and temporal projections that generates hourly information at the scale of individual weather stations, and applies this as input to the AASHTOWare Pavement ME Design™ model. The impact of three different future climates on pavement performance and time to reach failure thresholds in 24 locations across the United States are quantified. Changes to projected pavement performance differ by location, but nearly all result in decreased performance under current design standards. The largest increases in distress are observed for permanent deformation measures, especially toward the end of the century under greater increases in temperature.

Predicting Rutting Performance of Flexible Airfield Pavements Using a Coupled Viscoelastic-Viscoplastic-Cap Constitutive Relationship

AbstractRutting performance of airfield pavements is predicted using mechanistic-based constitutive relationships for both asphalt and granular layers. Pavement analysis using nonlinear damage appr...

Investigative tests on the performance of asphaltic mixtures modified by additive combinations (hydrated lime and polypropylene)

Scientists and engineers are constantly trying to improve the performance of asphalt mixtures, and a wide range of modifiers are utilised to enhance HMA characteristics against damage such as rutting, aggregate stripping, and cracking.The major objective of this research is to evaluate the performance of flexible pavement using asphalt from the Al-Daurah refinery with two locally additive, hydrated lime and polypropylene. Hot mix asphalt specimens were prepared with aggregate, of nominal maximum size 25 mm (base course) and 19 mm (binder course).Cement is usually utilised as an HMA filler, and a percentage of Portland cement was used in this work, at 5% for the base course and 6% for the binder course. Polypropylene was used as additive with percentages of 1, 2, and 3% by weight of asphalt, and hydrated lime was used in a dry state at a percentage of 1% by weight of aggregate as a part replacer of filler.The main mechanical characteristics of asphalt mixtures were evaluated using the Marshall index of retained strength and indirect tensile strength tests. Using hydrated lime and polypropylene caused the results of Marshall tests and indirect tensile tests to increase by 1.3 and 1.5 times, respectively, compared with the control mixture, while the index of retained strength test increased by 1.3 times compared with the control mixture. In particular, the addition of a combination of 1% hydrated lime by weight of aggregate and 2% polypropylene by weight of asphalt-to-asphalt mixtures satisfied the requirements for stability, moisture sensitivity, and indirect tensile strength.

LONG-TERM PERFORMANCE OF FLEXIBLE PAVEMENTS LOCATED ON CEMENT-TREATED SOILS

Long-term performance of flexible pavements located on cement-treated soils and the longevity of soil-cement subgrades are examined at sections of four highway routes. Ages of the soil-cement subgrades range from 6 to 30 years. Field and laboratory studies were conducted at each section. Generally, the soil-cement subgrades were non-plastic and were classified as SM, or sandy silt, according to the Unified Soil Classification System, although the classification of the untreated soil subgrades located below the treated layers ranged from CL (clay) to GC (clayey gravel). Plasticity index of the untreated soils ranged from non-plastic to 44%. Generally, the untreated soils were moderately plastic. In situ bearing ratios of the soil-cement subgrades were generally very large. Based on a percentile test curve, the in situ bearing ratios of the cement-treated subgrades at the 90th and 50th percent test values were about 24 and 90, respectively. Based on overlay histories of the routes, flexible pavements located on the soil-cement subgrades have performed well. In the older sections, overlays had been constructed every 11 to 14 years. Use of cement to construct stabilized subgrades represents a good design alternative when compared with other stabilizing methods and other design alternatives.

Evaluation of Pavement Performance due to Overload Single-Trip Permit Truck Traffic in Wisconsin

This study investigated the impacts of overweight (OW) permit truck traffic on flexible pavement performance in Wisconsin using field investigation and analysis utilizing the AASHTOWare Pavement ME Design software. A database of overweight single-trip permit truck records was analysed to produce a network of Wisconsin corridors heavily travelled by OW trucks. Four Wisconsin highways were selected for investigation due to high levels of OW truck traffic. The research included field work (traffic counts and visual pavement surface distress surveys) and AASHTOWare Pavement ME Design. Comprehensive analyses were conducted to evaluate pavement performance due to normal traffic loads as well as normal traffic loads plus the OW truck traffic loads. The use of mechanistic-empirical (ME) pavement analyses provided a methodology for estimating the proportion of pavement deterioration attributable to OW truck traffic. OW axle load distributions were developed and integrated with baseline truck traffic levels to develop axle load spectra and other traffic input parameters for the ME pavement analysis. The predicted total pavement deterioration levels from the AASHTOWare Pavement ME Design software were generally consistent with the levels of deterioration observed. The proportion of pavement damage and deterioration attributable to OW truck traffic was predicted to constitute a relatively minor proportion of total deterioration, with most distress indices showing relative increases of approximately 0.5% to 4%, with a few outliers. However, due to the small proportion of OW vehicles relative to the overall traffic levels, the OW vehicles were generally predicted to cause up to ten times the per-truck damage as compared with a typical legal-weight truck, depending on the distress mode and the test site.

Differences in asphalt binder variability quantified through traditional and advanced laboratory testing

The variability in the properties of asphalt binders used for road construction could induce uncertainty in the response, performance, and degradation of flexible pavements. Although in the last 25 years some countries have adopted performance-based classification systems and stricter quality control procedures to reduce the variability of the material during its production, the reality is that most countries—including emerging economies that are extensively investing in road infrastructure—continue using classification techniques based on traditional indexes (i.e. penetration and viscosity). The objective of this paper is to assess the variability of traditional indexes and fundamental properties among eighteen asphalt specimens produced in the same refinery and classified as penetration 60–70 1/10 mm. The results show that the variability of the fundamental properties (i.e. rheological, thermodynamic, and chemical) among specimens is substantially higher than that of traditional asphalt-tests indexes (i.e. penetration, softening point, and penetration index). These results support the necessity for enhancing current classification and production practices in those countries that still use these traditional indexes.

Prediction of pavement remaining service life based on repetition of load and permanent deformation

One of the methods which was applied in the assessment of flexible pavement performance was mechanistic method assuming structures of road pavement to become multi-layer structure for flexible pavement, that the vehicle load working on the pavement layer under repetition with power failure worth 1 (one) unit which was assumed as evenly distributed static load, and therefore the pavement material would provide response in the form of stress, strain, and deflection. This is closely related in order to assess the structure of flexible pavement and to predict the remaining service life on the roads of Pulau Indah sta 0 + 000 to sta. 0 + 845 in Kota Kupang, Nusa Tenggara Timur. The performance appraisal indicator which was used was fatigue cracking happening bottom of the asphalt layer and permanent deformation (rutting) on the surface of subgrade. The strain estimate on the flexible pavement layer structure needs carefulness and high accuracy and therefore a software like KENPAVE which produces horizontal tensile strain of 8,802E-05 and vertical compressive strain of 2,642E-04 was used. By applying equation of The Asphalt Instituteit was obtained repetition of permit load when reaching fatigue cracking (Nf) was 16.071.516 ESAL and permanent deformation (rutting) was 14.703.867 ESAL and also it was predicted the remaining service life of pavement applied the equation of AASTHO 1993 by considering Traffic Multiplier factor (TM 1.8, TM 1.9 and TM 2.0) obtained the remaining life service due to fatigue of 5.51% in the year of 13th (TM 1.8), 7.95% in the year of12th (TM 1.9) and 3.11% (TM 2.0) in the year of 12th, also the remaining service life due to rutting of 4.69% in the year of 12th(TM 1.8), 7.79% in the year of 11th (TM 1.9), and 2.94 in the year of 11th (TM 2.0).

Review of modelling crack initiation and propagation in flexible pavements using the finite element method

Cracking is a major failure mechanism that directly affects the functionality and performance of flexible pavements. The objective of this study is to present the state of knowledge on the use of finite element method (FEM) including cohesive zone model (CZM) to simulate cracking failure mechanisms in flexible pavements under field conditions. Based on this review, a knowledge base is established on how FEM can be effectively applied to predict pavement performance against cracking failure mechanisms. Two main approaches are presented in this study. In the first approach, focused finite element (FE) meshes are used to simulate the crack initiation and propagation phases. Focused meshes allow for estimating the J-integral and the stress intensity factor (SIF) through different contour lines. Since the SIF is a measure of the stress and strain environment around the crack tip (a greater SIF indicates a faster rate of propagation), the rate of crack propagation per cycle can be estimated based on empirical equations such as Paris’ Law. In the second approach, the propagation of damage is simulated using FE and CZM. This approach allows one to study the loading mechanisms responsible for progressing cracking damage in the pavement structure. In summary, both approaches have merits in modelling cracking in flexible pavements. While focused meshes may be used to predict the number of cycles for crack propagation, CZM may be used to study the controlling stresses and mechanisms responsible for crack propagation.

Flexible Pavement Interface Bonding: Theoretical Analysis and Shear-Strength Measurement

Abstract It has been proven that the interface bonding between asphalt layers is critical to flexible pavement performance, especially for pavement overlays. However, the requirement on interface bonding strength has not been specified to prevent premature pavement failure, such as slippage cracking or early fatigue cracking. In this paper, pavement structural analysis was conducted to predict the interface shear stress between the surface and intermediate asphalt layers under the combination of vertical and horizontal loading at different temperatures. The effect of interface debonding on pavement life was quantified using the state-of-art mechanistic–empirical pavement-analysis software (AASHTO Pavement-ME) with local parameters. Field cores were taken to measure the interface bonding strength; using the direct shear device theoretical analysis, results show that the minimum-bond-strength requirement should be around 70 psi to prevent premature pavement failure, such as slippage cracking or fatigue cracking. This requirement can be easily achieved in field projects based on the testing results of bond strength from field cores.

The Influence of Bonding between Layers on Pavement Performance, a Case Study of Malaysian Road

This paper summarizes a theoretical study undertaken to provide a better understanding of the consequences of poor bond on flexible pavement performance. The main objective of this paper is to investigate the influence of bond on the performance of Malaysian road. The pavement structure of Malaysian road was analyzed using a layered linear elastic program, BISAR 3.0 taking into account different state of the bond at the interfaces of the pavement layers and a static horizontal load in addition to the standard vertical dual load. The results indicate that the condition of the bond between the wearing and binder course can reduce the life of the pavement by up to 64%. On the other hand, the results also indicate that the condition of the bond between the binder and road base course, which was made up from asphaltic materials can reduce the life of the pavement by up to 68%.

3D-FEM Analysis on Geogrid Reinforced Flexible Pavement Roads

Nowadays, the need to increase pavement service life, guarantee high performance, reduce service and maintenance costs has been turned a greater attention on the use of reinforcements. This paper presents findings of a numerical investigation on geogrid reinforced flexible pavement roads, under wheel traffic loads, using a three-dimensional Finite Element Method (FEM). The results obtained show the effectiveness of glass fibre grids as reinforcement which, with appropriate design and correct installation, by improving interface shear resistance, can be used to expand the performance of flexible pavements in different ways: by increasing the road service life providing a relevant contribution against superficial rutting or by decreasing the construction costs due to the reduction in the reinforced HMA layer thickness and thus of mineral aggregate required for its construction.

A Study of the Structural Performance of Flexible Pavements Using Traffic Speed Deflectometer

Abstract The falling weight deflectometer (FWD) is a non-destructive testing device that has been used by many road agencies worldwide since 1980 for structural evaluation of flexible pavements. In early 2000, the world first Doppler laser-based traffic speed deflectometer (TSD) was developed by Greenwood Engineering, and now eight TSD vehicles are in use worldwide. The two main advantages of the TSD technology are: (a) the ability to carry out continuous bearing capacity measurements instead of discrete points, (b) that testing can be carried out at traffic speeds without the need for lane closures with a stationary device such as FWD. The objective of this paper was to study the structural performance of flexible pavements using TSD deflection data. The study successfully established a correlation between maximum deflections TSD-D0 and FWD-D0 that are derived from the two devices. This study also drew some interesting conclusions in that deflection data collected by TSD could be transformed to FWD equivalent structural numbers with simple models as derived in the study. The outcome of this study was an established methodology for reporting structural performance at network level utilizing TSD deflection data.

Geosynthetics reinforced flexible pavement: review of laboratory model studies

Number of laboratory studies; have shown that geosynthetics reinforcement improves the performance of flexible pavement either by ex-tending the service life or by savings in base course thickness. In spite of the good laboratory evidence for the geosynthetics reinforced flexible pavement, the mechanism that enables and governs the reinforcement function is still unclear [1]. Cyclic laboratory test has been one of the ways, used for assessing/evaluating the soil-geosynthetic interaction mechanisms. In such a tests contribution of geosynthetics prop-erties, interface shear provided by geotextiles and interlocking provided by geogrids when used under or within the base course of flexible pavement are mainly concentrated. This paper reviews literature of laboratory model studies carried out by various researchers over the globe. This review indicates that, appreciable improvement due to geosynthetics reinforcement depends upon various factors viz. location of geosynthetics, geogrid aperture size, geosynthetics properties, mainly stiffness, variation of base course thickness and strength of subgrade soil. The findings of these laboratory studies are also correlated with the same nature of field studies finding.

Evaluating the impact of different types of stabilised bases on the overall performance of flexible pavements

ABSTRACTThis study was initiated with the aim of evaluating the impact of stabilised and untreated base layers on the performance (i.e. fatigue and rutting) of flexible pavements. Four field sections constructed using stabilised base layers (i.e. bituminous (asphalt emulsion), calcium chloride (CaCl2), Portland cement and geogrid stabilised base layers) and a control section constructed using untreated recycled asphalt pavement (RAP) aggregates were analysed in this study. Falling weight deflectometer tests were conducted on all field sections and the collected data was used to back-calculate the elastic moduli for all layers. The influence of the stabilised bases and the untreated (RAP) base on the mechanical responses (stresses and strains) of the overall pavement structure was also evaluated by conducting layered elastic analyses. In addition, pavement ME design simulations were conducted to determine which of the four stabilised base types enhanced the overall predicted performance of flexible pavements the most. A service life of 20 years was used for pavement ME analysis. Based on the results, it was concluded that the Portland cement-treated base seemed to be more effective than the other stabilised bases at improving the resistance of the pavement sections to fatigue cracking followed by the CaCl2 and bituminous stabilised bases. The geogrid stabilised base appeared to have the least impact on improving fatigue cracking resistance. It was also determined that base layer stabilisation appeared to have little effect on the rutting resistance of the pavement sections.

Mechanistic-empirical models for better consideration of subgrade and unbound layers influence on pavement performance

It has been reported that the pavement performance predicted by the current mechanistic-empirical pavement design shows low or no sensitivity to subgrade and unbound layers. This issue has raised wide attention. Targeting this problem, this paper summarizes the process used by the authors to find better models of the influence of subgrade and unbound base course layers on the performance of flexible and rigid pavements. A comprehensive literature review is first conducted and the findings are categorized. It is found that the resilient modulus, permanent deformation, shear strength, and erosion are key factors. In particular, the properties that provide greater sensitivity are 1) the moisture-dependency of the modulus, shear strength, and permanent deformation; 2) stress-dependency of the modulus and permanent deformation; and 3) cross-anisotropy of the modulus. A number of unbound layer/subgrade models have been located and categorized. Three criteria are developed to identify the candidate models in terms of the degree of susceptibility, degree of accuracy, and ease of development. The first two criteria are used to evaluate the collected unbound layer/subgrade models, while associated development and implementation issues are planned as subsequent work. Two models that the authors previously developed are selected as examples to illustrate the improvement of the performance prediction, including the moisture-sensitive, stress-dependent, and cross-anisotropic modulus model for unbound layers and stress-dependent mechanistic-empirical permanent deformation model for unbound base layers. These two models are verified through laboratory tests and numerical simulations. Moreover, they are compared to their counterparts in the AASHTOWare Pavement ME Design. The advantages of accuracy and sensitivity to the operational conditions (e.g. moisture, traffic stress, and load-induced/particle-induced anisotropy) are obvious. In addition to these two models, the development of the shear strength model and erosion model are sketched. The candidate models need further development and implementation, which address issues such as hierarchical inputs, calibration/validation, and implementation. These are the on-going and planned work on this topic to better incorporate the influence of subgrade and unbound layers so as to contribute to the improvement of pavement designs.