Asphalt Overlays Research Articles

Evaluation of the Impact of Existing Condition and Overlay Characteristics on Asphalt Overlay Design and Performance based on a Mechanistic-Empirical Approach

The present study sought to determine how the overlay design and performance of asphalt concrete (AC) were affected by existing pavement condition and overlay material properties. To that end, this study was performed in different scenarios of traffic and structure with the latest AASHTO design software AASHTOWare (version 2.3). The modulus and rut depth of existing layers, the interface condition between AC overlay and existing pavement, and the AC overlay properties of Poisson’s ratio and performance grade were addressed in the current study. Besides the overlay thickness design, the investigation also focused on pavement performance to determine how separate distresses were impacted by existing pavement condition and the properties of the overlay material. The investigation produced three major outcomes, as follows: the current AC layer thickness and design traffic determined the extent to which the existing AC layer condition affected the overlay design thickness; the overlay performance and design were not significantly affected by the existing base and subgrade condition; and fatigue cracking was more strongly influenced by the existing AC layer modulus and interface bonding condition compared with the rutting potential.

Automated visualization of concrete bridge deck condition from GPR data

Ground-penetrating radar (GPR) is one of the most commonly used technologies for condition assessment of concrete bridge decks. However, there have been no fully automated algorithms to visualize the data collected with this technique. In such context, the current paper presents a method for a full automation of GPR data visualization and analysis. Based on the background removal, depth correction, synthetic aperture focusing technique (SAFT), and interpolation algorithms, this automated method produces a plan view map of amplitude of GPR signals. In the obtained map, two types of information are observed at the same time. First, as the strongest reflectors of electromagnetic energy, rebars will appear as the most visible. Second, the areas of corrosive environment and, thus, likely corrosion, will be detected as having low amplitude rebar reflections. As a proof of concept, the proposed method was implemented for two bare concrete bridge decks and two concrete bridge decks with asphalt overlays. In all cases, the results obtained were excellent where the maps pinpointed the areas affected by corrosion. These areas were confirmed by other methods of evaluation, such as electrical resistivity (ER), half-cell potential (HCP), chloride analysis of core samples, or visual inspection. With the demonstrated performance, the proposed method is expected to be an excellent alternative to the available methods of GPR data evaluation and visualization. In the future, it should be improved to provide an indication of corrosion severity/probability at each deck location.

Analysis of the Fatigue Crack Propagation Process of the Stress-Absorption Layer of Composite Pavement Based on Reliability

The stress-absorption layer in cement concrete pavement delays the development of reflection cracks and is good at fatigue resistance. Laboratory investigations of the anti-crack performance of the high viscous asphalt sand stress-absorption layer (HVASAL) and rubber asphalt stress-absorption layer (RASAL) were carried out by force-controlled fatigue crack propagation tests, for which three types of overlay structures with three types of pre-crack (i.e., the middle crack, the side crack, and the 45° inclined crack) were designed. A probability model was established to describe the propagation of the fatigue cracks. The fatigue crack propagation, the fatigue life, the crack propagation rate, and the crack propagation mechanism of the three types of overlay structure were compared and analyzed. The results show that the stress-absorption layers have good anti-crack fatigue performance, and that the RASAL is better than the HVASAL. The crack propagation patterns of the three types of overlay structure were found. In the double logarithmic coordinate, the curves of the three types of cracks are straight lines with different intercepts and slopes. The probability model quantifies the relationship between the crack propagation rate and ∆K. The influences of the three types of crack on the fatigue properties of the asphalt overlays are different.

Comparative assessment of the interlayer shear-bond strength of geogrid reinforcements in hot-mix asphalt

With the increasing use of geogrid reinforcements to mitigate reflective cracking in hot-mix asphalt (HMA) overlays, interlayer (interface) bonding has become an even more critical aspect of HMA placement/construction to mitigate delamination and debonding of the HMA overlay. To comparatively evaluate the interlayer bond strength due to the effects of the geogrid reinforcements, the shear bond strength test was conducted in this laboratory study, using unreinforced control HMA samples as the reference datum. Cylindrical HMA samples (150 mm diameter) gyratory compacted in two 75-mm lift thicknesses, with the geogrid reinforcement in-between the two lifts, were used for testing at room temperature under a monotonically shear loading rate of 5 mm/min. Emulsified asphalt was used as the interlayer tack coat and six different geogrid materials, which are polyester-based (FA) and fiberglass-based (FG), were comparatively evaluated. As theoretically expected, the control (unreinforced) HMA samples exhibited superiority followed closely by samples reinforced with polyester-based geogrids. Although comparable to the values reported in the literature, HMA samples reinforced with fiberglass-based geogrids performed the poorest with the lowest interlayer bond strengths – that is the polyester-based outperformed the fiberglass-based geogrids. Overall, the interlayer bond strength exhibited a general decreasing trend with a decrease in the geogrid mesh size (open area), increase in the geogrid strand thickness, and material grade. Thus, in as much as reflective crack mitigation is structurally desired, due diligence must be cautiously exercised when selecting the geogrid type/grade for use in HMA reinforcement to ensure sufficient interlayer bonding and minimize any potential delamination/debonding problems in service.

Laboratory assessment of nine methods for nondestructive evaluation of concrete bridge decks with overlays

Overlay systems have been extensively used to extend the service life of concrete bridge decks. There is, however, a lack of systematic studies on nondestructive evaluation (NDE) of concrete bridge decks with various overlays. This study assesses nine NDE methods for evaluation of concrete bridge decks with seven different types of overlays through laboratory concrete specimens. The nine NDE methods are sounding, ultrasonic surface waves (USW), impact echo (IE), ultrasonic testing (UT), impulse response (IR), ground-penetrating radar (GPR), electrical resistivity (ER), half-cell potential (HCP), and infrared thermography (IRT). The seven types of overlays are epoxy, latex modified concrete, silica fume modified concrete, polyester polymer, asphalt with a liquid membrane, asphalt with a sheet membrane, and asphalt without a membrane. Eight concrete specimens with various defects were built and nondestructively evaluated to acquire the detailed information of all embedded defects before placing overlays. One concrete specimen was kept bare as a reference, and the other seven specimens were covered with seven different overlays, respectively. Half of each overlay was bonded to the underlying concrete specimens, whereas the other half was debonded. NDE tests were carried out on the top of overlays. Based on the NDE test results, the applicability of each NDE method for concrete bridge decks with overlays is summarized as follows: (1) GPR and HCP are two effective methods for evaluation of the underlying concrete decks through both bonded and debonded overlays; (2) USW, IE, and UT can image the defects in the underlying concrete decks under bonded overlays, with the exception of the three asphalt overlays; (3) sounding, IR, and IRT can identify overlay debonding; and (4) ER is not effective due to electrical insulation of the overlay materials.

Durability of concrete pavement strengthened with asphalt layer with FRP fibres

SummaryPavements made of cement concrete, used for road constructions, are damaged during use. This applies to both the pavements of rural and forest roads with very low traffic loads, as well as road pavements with high traffic loads. One of the most effective ways of repairing damaged concrete cement pavements is through placing an asphalt overlay on a concrete slab. In order to increase the fatigue life of the asphalt overlay, asphalt mixtures are modified with fibres. One technological solution is to use FRP (Fiber Reinforced Polymer), an innovative material with improved properties. The aim of this paper is to assess the impact of asphalt overlays modified with a new type of fibres to strengthen the durability of weakened cement concrete pavement structures. On the basis of the conducted analyses, it was shown that the use of an asphalt layer reinforcement increases fatigue life, for both 15 cm thick prefabricated slabs and a typical road pavement for average traffic made of 25 cm doweled and anchored concrete slabs. There was a significant increase in the fatigue life of the concrete pavement structure as a result of modifying the overlaid asphalt mixture with FRP fibres.

Application of polymer grids for reinforcement of asphalt pavement roads: Case study of corridor X in Macedonia

Asphalt paved roads prematurely exhibit a cracking pattern similar to that in the old underlying pavement. The cracking in the new overlay surface is due to the inability of the overlay to withstand shear and tensile stresses created by movements concentrated around preexisting cracks in the underlying pavement. This movement may be due to traffic loading causing differential deflections at cracks in the underlying pavement layers, expansion or contraction of subgrade soils, expansion or contraction of the pavement itself due to changes in temperature, or combinations of these phenomena. Due to heavy deformation of asphalt paved surface, using European funds, the Government of Macedonia initiated rehabilitation of Corridor X close to the Tetovo section. For the reconstruction of this important section of the motorway, an experimental programme was conducted to determine the effects of geogrid reinforcement on mitigating reflection cracking in asphalt overlays. The objective of this study is to assess the inclusion of geogrid in the pavement cross-section and the accumulation of permanent deformation. The geogrid position, type of existing pavement, temperature, and joint/crack opening were analyzed in three site trial tests. Crack propagation under repeated loading was monitored as well. The results indicate a significant reduction in the rate of crack propagation in reinforced samples compared to unreinforced samples of old asphalt pavement. The presented pavement design procedure could be tailored to the specific needs of the project and implemented in various road rehabilitation projects.

Kinetics-based aging evaluation of in-service recycled asphalt pavement

Reclaimed asphalt pavement (RAP) is a type of material that already suffers long-term aging in the field, so its aging characteristics become prominent since they are closely related to premature distresses and longevity of recycled pavements. While most of investigations of RAP mixtures are carried out in the laboratory, this study focuses on in situ aging of asphalt pavements with RAP overlays. A kinetics-based aging modeling approach is proposed to analyze and quantify long-term field aging of RAP overlays using the Falling Weight Deflectometer (FWD) data and climate data. The kinetics-based approach contains a modulus aging model with kinetic parameters (e.g. aging activation energy) for asphalt mixtures. Eight asphalt overlays are selected with different mixtures (RAP and virgin), thickness (50 mm and 125 mm), and surface preparation (milling and no milling). An asphalt pavement with an overlay has a composite aging process since the aging speeds of different asphalt layers are different. Thus an approach to separate the FWD modulus is developed in order to obtain the actual aging behaviors and properties of the overlay. By applying the kinetics-based modeling to the separated FWD moduli, the aging activation energies of both the overlays and old asphalt layers are determined. It is found that the RAP overlay has the highest aging activation energies and slowest aging rates among the RAP overlay, virgin overlay, and old asphalt layer for the selected pavements. It also reveals through the aging activation energy that the thick overlays age slower than thin ones, and the overlays on milled pavements age slower than those placed without milling. The findings in terms of the aging activation energy can be used to explain the difference in the field performance of overlay pavement sections.

Effects of asphalt overlay on XCC pile-supported embankment vibration from a moving vehicle

Vibration behaviors of the asphalt pavement-embankment-X-shaped cast-in-situ concrete (XCC) piles reinforced ground system under a moving vehicle are simulated through three-dimensional finite element approach. The influences of asphalt overlays on displacement pattern on the top of pavement, the asymmetric movement of surrounding soil around XCC piles, and the concentration coefficient after laying the overlay are investigated. The obtained results show that the dynamic displacement decreases as a consequence of the increasing stiffness of this system after laying asphalt overlays. It is also shown that the vertical displacement of soil around piles decreases as the thickness of overlays increases. Meanwhile, the asymmetric extent, in which there is an obvious differential displacement between the flat and concave area, is presented. In addition, the concentration coefficient for the embankment's top flat is significantly larger than that for the slope surface, and its increasing is caused by asphalt overlays.

Field performance evaluation of asphalt mixtures containing high percentage of RAP using LTPP data

Recycled asphalt pavement (RAP) has been used in production of new mixtures for many decades and has become a common practice in highway agencies. However, concerns about field performance of RAP mixtures have been lingering on since the beginning of RAP usage. In this study, the field performance of RAP was verified through the Long-Term Pavement Performance (LTPP) program. Particularly, pavement overlays constructed with virgin asphalt and those constructed with a significant RAP percentage were examined and compared regarding their field performance. To achieve this goal, data from the Specific Pavement Study experiment 5 (SPS-5) of LTPP were retrieved and statistically analyzed for comparison. A total of eighteen projects comprised of 162 sections were collected. Various performance measures were incorporated, including alligator cracking, longitudinal cracking (wheel path and non-wheel path), transverse cracking, patching, potholes, rutting, roughness, and pavement surface deflections. In addition to the key variables used in the SPS-5 experiment (thickness, materials and pre-overlay treatment), the impacts of other important factors, including climatic conditions, initial surface condition and subgrade soil classification, were also investigated. Exploratory data analyses and logistic regression were used to compare the performance of RAP and virgin asphalt overlays. Results from the analysis results show that RAP had little effects on longitudinal cracking, transverse cracking, and roughness, but slightly increased the risk of fatigue cracking and weakened pavement structure. As expected, use of RAP was beneficial in reducing the rutting potential of thick overlays. For both RAP and virgin asphalt overlays, thicker overlays performed better than thinner ones in all performance measures except for rutting. Pre-overlay treatment methods and subgrade soil types were found to be critical factors affecting fatigue cracking and roughness. The initial surface condition also showed significant effects on pavement structural capacity and fatigue cracking over the long run.

Finite-Element Evaluations of Geogrid-Reinforced Asphalt Overlays over Flexible Pavements

AbstractGeosynthetics have been extensively implemented as a pavement maintenance solution to minimize reflective cracking. However, geosynthetics within asphalt overlays can also be used to improv...

Correlating laboratory and full-scale reflective cracking tests for airfield pavements

Asphalt overlays minimize moisture infiltration and help in restoring the smoothness and structure of existing airfield concrete pavements, but due to reflective cracking, the new asphalt overlay often fails before achieving its design life. In airfields, the potential for reflective cracking presents a major challenge for rigid pavement rehabilitation involving asphalt overlays. To assist airport engineers and others concerned with the temperature-induced reflection cracks, several full-scale test pavements have been constructed, instrumented, and tested at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF). The main objective of this study was to identify and develop correlations between full-scale and laboratory reflective cracking tests. A customized Overlay Tester (COT) and Cyclic Disc-Shaped Compact Tension (CDCT) Test were used evaluate the fracture and fatigue performance of hot mix asphalt (HMA) materials at low temperatures. The COT was conducted at the same conditions as the full-scale tests and test results were analyzed using several parameters. Temperature effect was pronounced in strain parameters (initial strain, failure strain, and strain at Nf(NLC)). Further fatigue parameters (Nf(crack) and Nf(NLC)) indicated a swifter deterioration of HMA mixture at a higher displacement (cooling) rate. Fracture parameter (Gfini) was found to decrease with the increase of displacement rate due to the brittleness of HMA at low temperatures as excepted. A two-term exponential function from the CDCT tests demonstrated the fracture behavior of HMA under cyclic loading. The released energy rate factor (R2) correlated well with the fatigue life. Finally, a set of shift factors were derived between the full-scale, OT, and CDCT tests. Valuable data obtained from this study provides immediate support to the future FAA reflective cracking research.

Use of Natural Geotextiles to Retard Reflection Cracking in Highway Pavements

AbstractReflective cracking is a major phenomenon leading to premature failure of fresh asphalt overlays. Application of a geosynthetic interlayer system to retard reflective crack propagation is a...

Comparison of Asphalt Concrete Inlay and Overlay for Rehabilitation of Aged Cement Concrete Pavement through Accelerated Pavement Testing and Life-Cycle Cost Analysis

Comparison of Asphalt Concrete Inlay and Overlay for Rehabilitation of Aged Cement Concrete Pavement through Accelerated Pavement Testing and Life-Cycle Cost Analysis

Evaluation of cracking resistance potential of geosynthetic reinforced asphalt overlays using direct tensile strength test

The study aims at evaluation of cracking resistance potential of geosynthetic reinforced two-layered asphalt specimens under direct tensile strength test (DTT), conditioned at different temperatures (20 °C, 30 °C and 40 °C). Apart from determining the tensile stiffness of the asphalt specimens, the DTT is also capable of evaluating the cracking resistance potential through estimating the energy dissipated during cracking. The potential to resist reflection cracking may be improved with the inclusion of geosynthetic-interlayer. To understand the crack propagation patterns and to quantify the resulting strain fields, digital image correlation (DIC) technique was employed. The geosynthetic-interlayers used in the current study consist of a glass-grid composite (GGC), a bi-axial polyester grid coated with polymer modified binder (PE), a biaxial polypropylene grid (PP) and a woven geo-jute mat (GJ).Results indicate that all the specimens conditioned at a temperature of 20 °C have shown better resistance to the cracking than the specimens conditioned at 40 °C. The specimens with GGC interlayer were effective in controlling the cracks as they could mobilize high tensile strength at a low strain value. The digital image analysis was instrumental in quantifying the tensile strains developed in the pavement layers. It was noticed that the control specimens have developed a tensile (vertical) strain of 6.85% at 20 °C against 2–4% in the specimens with geosynthetic-interlayers.

Strain distribution along geogrid-reinforced asphalt overlays under traffic loading

While there is significant field evidence of the benefits of geosynthetic-reinforced asphalt overlays, their use has focused on minimizing the development of reflective cracks. Yet, geogrids in asphalt overlays are also expected to develop reinforcement mechanisms that contribute to the pavement structural capacity. Specifically, the use of geosynthetics in asphalt overlays may also improve the mechanical behavior of paved roads by controlling permanent displacements and reducing strains in the pavement layers. While relevant advances have been made towards identifying the mechanisms in geosynthetic stabilization of base courses, such mechanisms may differ from those that develop in geosynthetic-reinforced asphalt overlays. This paper investigates the development and distribution of tensile strains along geogrids used to reinforce asphaltic layers. Experimental data was collected from large-scale paved road models subjected to the repeated loading imparted by wheel traffic. Specifically, the study examines both the elastic and permanent components of displacements induced in geogrids by using mechanical extensometers attached to the geogrids. The testing program includes a number of geosynthetic-reinforced paved road models, as well as a control (unreinforced) section that was also instrumented for comparison purposes. Asphalt strain gauges were used to measure strains within the asphalt concrete layer, providing an additional source of information that proved to be highly consistent with the results obtained from the extensometers. The experimental results showed a progressive mobilization of permanent geogrid strains that reached a final profile beyond which additional traffic loading did not result in additional straining. In comparison, higher strains developed in the unreinforced model, which showed a continuously increasing trend. Elastic tensile strains in the asphalt mixture and rutting under the wheel load were comparatively smaller when using geogrids. Overall, the results generated in this study indicate that the presence of geogrids in asphalt overlays results in a lateral restraining mechanism that influences on the mechanical behavior of flexible pavements.

Cohesive zone fracture modelling of asphalt pavements with applications to design of high-performance asphalt overlays

Mechanism of fracture in a viscoelastic heterogeneous composite with thermo-rheological properties such as, asphalt mixture is quite involved and cannot be correctly simulated with simpler linear elastic fracture mechanics constitutive laws. Over the last decade and half, a number of researchers have adopted use of cohesive zone (CZ) fracture models for simulation of fracture in asphalt mixtures. CZ interface elements are utilised in finite element (FE) models for representation of crack path, these elements follow traction–displacement relationships that allow for gradually degrading traction capabilities along the crack path with increasing level of crack opening. This paper presents a review of CZ modelling approach for simulation of asphalt pavement and overlay cracking performances. Suitability of CZ modelling approach for capturing discrete fracture in asphalt mixtures at low temperatures is presented through simulation of lab scale test. An example is also presented to demonstrate applicability of CZ-based modelling effort in capturing the crack initiation and propagation in asphalt mixtures at low temperatures. Thereafter, an FE-based pavement simulation approach is discussed that can be utilised in design of asphalt overlays to lower the propensity of reflective cracking. A case study of designing asphalt overlay systems for four real-life pavements in Minnesota is presented to demonstrate the applicability of the CZ-based modelling approach in conducting mechanistic design of asphalt overlays.

Evaluación del comportamiento mecánico de capas bituminosas ultra delgadas como una adecuada estrategia para la rehabilitación de pavimentos urbanos

Very Thin Asphalt Overlay (VTAO) has been introduced as an alternative to traditional thick overlays, seal coats, and micro-surfacings. Nonetheless, there are some challenges that still remain regarding the application of VTAOs (such as mixture type, cohesiveness, wear resistance, cracking and durability), particularly in heavy traffic urban areas. Therefore, this paper presents an extensive comparative evaluation of the mechanical performance, durability and safety issues (cohesiveness, adhesiveness, ageing, cracking, plastic deformation, permeability, macrotexture, skid and wear resistance, and fuel resistance) of a VTAO (20 mm thick) and a high performance BBTM 11B (35 mm thick), commonly used as an open-graded mixture for pavement overlays. The results demonstrated that VTAO is an appropriate material for urban pavements as it provides good durability and resistance to the propagation of defects. Nonetheless, further studies are required to improve its behavior under distresses related to plastic deformations and safety properties.

Quasi-Microstructure Analysis of Asphalt Mixtures Containing Reclaimed Asphalt Pavement

AbstractThe nonuniform distribution of reclaimed asphalt pavement (RAP) in asphalt mixtures can affect stiffness values of RAP mixtures and their field performance in asphalt overlays. This study d...

Evaluation of recycled asphalt pavement using economic, environmental, and energy metrics based on long-term pavement performance sections

Recycled materials have been used in roadway construction for years. Recently, with the advancement of material processing equipment and mix design technologies involving Recycled Asphalt Pavement (RAP), RAP’s use in pavement construction is increasing. RAP’s various desirable properties spur its use in sustainable development. These merits include energy conservation in mix production, cost savings in material consumption, and environmental protection. Although asphalt mix is considered to be recyclable – meaning RAP could be a sustainable material – in-depth studies verifying and quantifying its effectiveness are limited in the literature. Based on real-world data from pavements constructed with 35% RAP and virgin mixes, this study comprehensively evaluates the sustainability of RAP from three different aspects including cost, energy, and environment. The life cycle cost analysis based on RealCost and life cycle assessment based on PaLATE is used to compare RAP and virgin alternatives. The results suggest that using RAP is more economically efficient and environmentally viable than virgin pavement if thin asphalt overlay is involved. The findings of this study support RAP’s use in current pavement rehabilitation practice, which usually involves relatively thin asphalt overlays.