Asphalt Concrete Overlays Research Articles

Development of Full-Scale Reflective Cracking Test at the FAA National Airport Pavement Test Facility

Asphalt concrete overlays must be designed and constructed to withstand reflective cracking. However, the current FAA overlay design procedure (Advisory Circular 150/5320-6E) does not address this common form of premature failure. This paper presents a research project that studied one of the accepted causes of reflection cracks: horizontal movements concentrated at joints in the existing portland cement concrete pavement. A prototype, the temperature-effect simulation system, was developed at the FAA National Airport Pavement Test Facility so that joint opening and closing caused by temperature changes could be simulated mechanically. A test pavement representing a typical airport overlay structure was constructed to support full-scale tests. Both theoretical and experimental studies were performed to determine key test parameters, critical pavement temperature, joint opening, loading rate, and the bonding condition at the interface of asphalt concrete and portland cement concrete. Preliminary full-scale tests demonstrated that the simulation system could not only generate forces that create precise and repeatable joint openings but also effectively control the pavement temperature. Instrumentation data revealed that once bottom-up reflection cracks were initiated, crack development could quickly progress. When the crack length reached a certain level, the crack propagation rate slowed considerably. Information and data presented in this paper will be of immediate assistance to general aviation airports that carry small and light aircraft and experience significant temperature variations.

Investigation and Modification of Available Mechanistic–Empirical Procedures for Reflective Cracking in Asphalt Overlays of Concrete Pavements

In recent decades, state, local, and federal use of asphalt concrete overlays to rehabilitate portland cement concrete pavements has increased significantly. This growth has increased the attention given to mechanistic– empirical modeling of reflective cracking. This paper describes recent research that assessed and modified the state of the art in mechanistic– empirical modeling of reflective cracking. The research reviewed the original Mechanistic–Empirical Pavement Design Guide model and the CalME reflective cracking model. The paper also details research in which the CalME model was modified to facilitate its integration into the design guide for pavement projects of composite asphalt concrete over portland cement concrete.

Lab Simulation Study on Anti-Cracking Performance of Asphalt Concrete Overlays for Fatigue

Currently, researches on anti-cracking performance of asphalt concrete overlays on old concrete pavement for fatigue are still in the early stage of explorations and trials. The reflective crack simulation tests of bending and shearing styles with six asphalt overlays were carried out in order to evaluate the anti-cracking effects of different kinds of anti-cracking materials. It is suggested that Sampave modified asphalt mixture with independent development has excellent anti-cracking performance for fatigue, which provides an experimental reason for extending the anti-cracking technique in stress absorbing layers. Although anti-cracking performances of glass fiber grid and tricot geofabric reinforced composites are better, it is not as good as the one of Sampave. And the effect of paving asphalt concrete directly on old cement concrete pavement is worse.

Toward a Better Understanding of Benefits of Geosynthetics Embedded in Asphalt Pavements

Reflective cracking is a serious issue in asphalt pavements. A common technique for preventive maintenance and rehabilitation is a thin asphalt concrete overlay; however, the application of a reinforcement can be a more suitable solution because such reinforcement can prevent or delay crack propagation. This paper presents research undertaken within a study of asphalt concrete overlays that included geosynthetics. A program of laboratory experiments and detailed analyses was conducted to gain insight into the effect of reinforcement in asphalt pavements by evaluating and quantifying the benefits of geosynthetic interlayers. Two test approaches were used. In the first approach, the specimens were analyzed by means of monotonic tests to investigate the bond at the interface and the contribution of the reinforcement to tensile strength. The results of the direct shear test indicated that the geosynthetic was able to guarantee a good bond at the interface, even at the end of the test. In the second approach, a nonconventional fatigue test was adopted to characterize the reinforced systems’ ability to resist fatigue cracking. X-ray tomography was performed to investigate the void structure of the beams tested under cyclic loadings. The research findings underline the benefits of geosynthetic interlayers embedded in asphalt pavements. The geosynthetics reduce the amplitude of the crack for high displacements and keep the pavement structure intact, even after moderate cracking has occurred in the overlay.

A Laboratory Tool Used to Evaluate the Reflective Cracking in Overlay Asphalt Pavement

Abstract The causes of reflective cracking can be either environmental and/or load associated . The simultaneous movements of an overlay caused by wheel loads (vertical movements),temperature changes, temperature gradients (horizontal movements) induce a complexstress state of cyclic bending tension, and shear within the overlay. Different types of tools are used to simulate the mechanism of reflective cracking inthe laboratory , in this research only the tool which simulates the effect of temperaturevariation (horizontal movement) is studied. Overlay Testing Equipment is constructedand tested in Iraq . All the tested samples are beams of dimensions 7.6cm width, 38.1cmlength with different thickness. Three parameters are taken in this study, filler type,thickness of asphalt concrete beams and additives and their effects on the properties ofasphalt concrete mix. From the results, the samples prepared by limestone as a fillergive higher number of cycles than that prepared by cement, the samples of highthickness give higher number of cycles and the control sample gives best results thanmodified samples.Keywords: Reflection Cracking, Asphalt Concrete Overlay, Filler, Overlay Tester

Minnesota Road Research Data for Evaluation and Local Calibration of the Mechanistic–Empirical Pavement Design Guide's Enhanced Integrated Climatic Model

This paper describes research to evaluate modeling of the thermal behavior of concrete and composite pavements by the Enhanced Integrated Climatic Model (EICM), the climate-modeling package used in the Mechanistic–Empirical Pavement Design Guide (MEPDG). First, the study uses temperature data collected at the Minnesota Road Research Project (MnROAD) facility from portland cement concrete (PCC) and asphalt concrete (AC)–PCC pavements to investigate benefits of AC overlays on the thermal characteristics of PCC slabs. Furthermore, the study validates EICM predictions of thermal gradients through the slabs and investigates the effect of MEPDG-user inputs for thermal conductivity of PCC. Overall, the paper examines measured data from MnROAD for AC-PCC pavements and their single-layer PCC counterparts and attempts to explain how similar pavement systems and their thermal characteristics are taken into account in the MEPDG. The paper concludes that evaluation of the material thermal inputs should be part of a process of local calibration and adaptation of the MEPDG.

Thermal reflective cracking of asphalt concrete overlays

Reflective cracking of asphalt concrete (AC) overlays is one of the most extensive pavement distress and damage mechanisms in composite pavement structures. Numerous studies have been performed to evaluate the reflective cracking potential of AC overlays under different loading scenarios. Most of these studies have focused on reflective cracking due to tyre loading. A very limited amount of work has been performed to evaluate non-load-associated thermal reflective cracking of overlays. Thermal reflective cracking mechanisms have been studied and are described in this paper using recently developed hot-mix asphalt mixture tests and fracture models. A series of finite-element-based pavement simulations were performed in an effort to better understand thermal reflective cracking mechanisms as a function of several key material and pavement structure variables. The enhanced integrated climatic model was used to estimate pavement temperature gradients as a function of position and time. A fracture mechanics-based cohesive fracture model was used for the simulation of damage and cracking, which was tailored for use with quasi-brittle materials such as AC. The pavement simulation model utilises creep and fracture properties from American Association of State Highway and Transportation Officials and American Society for Testing and Materials-specified tests and analysis procedures. Three asphalt mixtures manufactured with Superpave low-temperature performance grades of -22, -28 and -34 were studied in pavement structures with three distinct overlay thicknesses. Simulations were conducted with three Portland cement concrete (PCC) slab conditions to study the effects of joint spacing and rubblisation on thermal reflective cracking. The simulation results provide a new insight towards the mechanisms underlying the development of thermal reflective cracking. The curling of PCC slabs due to temperature differential and joint opening caused by pavement cooling was found to be critical in the initiation of thermal reflective cracking. This effect is greatly minimised or eliminated in the case of pavement rubblisation.

Research on the Temperature Stress Field of Interface End between Asphalt Concrete Overlay and Concrete Pavement

For the interface end formed after paving asphalt overlay on cement concrete pavement, the stress field of interface end is very important for both structural analysis and interface design when the temperature drops. The stress field of interface end can be gotten with the crack-tip field theory that consider displacement continuation and stress equality on each side of interface, but it needs further verification to prove whether the initial stress field can satisfy far field boundary condition when temperature dropping. In conditions of different material properties, different plane dimension and different thickness of asphalt overlay the stress field is calculated with the finite element method (FEM), and the results show that the forms of theoretical solution can exactly describe stress field of the interface end when temperature dropping. The stress field of interface end indicates that when the elastic modulus of asphalt overlay becomes lager, the stress singularity’s degree of interface end will reduce. As for the interface end formed after paving asphalt concrete overlay on the concrete pavement, improving the elastic modulus of asphalt overlay is beneficial.

Staged survival models for overlay performance prediction

Asphalt concrete (AC) resurfacing is used by highway agencies to maintain and improve existing pavement conditions. With a large portion of their budgets being spent on road maintenance and rehabilitation, the agencies are interested in identifying the optimal timing of resurfacing and its life expectations. Using Kentucky's pavement management data, the research as presented by this paper investigated the procedures and methods of establishing thresholds and developing performance prediction models for AC overlays. Both transition probability matrix and data plots were used to investigate the performance trend of overlays. Based on the trend, two stage survival models were proposed to predict the resurfacing cycles. The first stage model can be used to predict the useful life of an overlay before a new resurfacing is required, while the second one can be used to predict the time window during which the new overlay must be applied to avoid accelerated pavement deterioration.

Experimental Study for Evaluating Crack Retardation of Asphalt Concrete Overlays

This paper presents the development of Asphalt Concrete Slab Fatigue Testing Equipment and its use in evaluating crack retardation of AC overlay under opening and mixed modes of displacement. The dense bituminous macadam (DBM) and the unreinforced and geotextile reinforced open graded asphalt concrete (OGAC) overlays are investigated under cyclic simulated thermal and traffic loads having 5 mm differential deflection with zero load efficiency factor. Variation of tensile force and deformation in AC overlay with a number of simulated thermal load cycles are observed and cumulative decay of parameters, viz. tensile force, stiffness, and shear modulus, are computed. Overlay life, decay parameters, base isolation, and fabric effectiveness factors (FEF) are also evaluated. It is found that the unreinforced OGAC overlay performed better than that of DBM as a crack relief layer. In purely opening mode of displacement the best performance shown by the geotextile reinforced OGAC overlay becomes worse under mixed mode of displacement.

Accelerated Pavement Testing to Compare Efficiency of Overlay Materials Used in Brazil

In Brazil, asphalt rubber (AR) has been used to delay reflection cracking in overlays since the 1990s. To quantity reflection cracking evolution in AR and asphalt concrete (AC) overlays, an accelerated pavement testing (APT) study was carried out by the Federal University of Rio Grande do Sul and the State Roads Department. Overlays 5.0-cm thick were set on sections with identical structures (severely cracked AC wearing course and granular base), and from March 2003 to February 2005 a traffic simulator applied 100-kN axle loads on the two full-scale pavements. During the tests, cracks were recorded, and deflections and strains were measured. APT raw data suggested that the efficiency of the AR overlay in delaying reflection cracking was 5.55 times greater than that of the AC overlay. Because the overlays were tested in different seasons, a supplementary laboratory study was carried out to quantify temperature effect on AC and AR resilient modulus, later used in a fatigue analysis. With APT and fatigue ana...

Accelerated Pavement Testing to Compare Efficiency of Overlay Materials Used in Brazil

In Brazil, asphalt rubber (AR) has been used to delay reflection cracking in overlays since the 1990s. To quantify reflection cracking evolution in AR and asphalt concrete (AC) overlays, an accelerated pavement testing (APT) study was carried out by the Federal University of Rio Grande do Sul and the State Roads Department. Overlays 5.0-cm thick were set on sections with identical structures (severely cracked AC wearing course and granular base), and from March 2003 to February 2005 a traffic simulator applied 100-kN axle loads on the two full-scale pavements. During the tests, cracks were recorded, and deflections and strains were measured. APT raw data suggested that the efficiency of the AR overlay in delaying reflection cracking was 5.55 times greater than that of the AC overlay. Because the overlays were tested in different seasons, a supplementary laboratory study was carried out to quantify temperature effect on AC and AR resilient modulus, later used in a fatigue analysis. With APT and fatigue analysis data combined, it was possible to ascertain that if both overlays were tested at identical pavement temperatures, the efficiency of the AR overlay delaying reflection cracking would be 4.84 times greater than that of the AC overlay.

Development of a Single-Edge Notched Beam Test for Asphalt Concrete Mixtures

Abstract This paper describes the development of a fracture test for determining the fracture energy of asphalt concrete. The test will be used in combination with numerical analysis and field studies to obtain a better understanding of the mechanisms of reflective cracking in asphalt concrete overlays. A review of the literature revealed that a single-edge notched beam (SE(B)) test specimen was the most promising fracture test for the objectives of the reflective cracking study. Existing servohydraulic testing equipment was modified to perform the SE(B) test along with new loading fixtures, sensors, data collection, and analysis procedures. Preliminary tests were conducted to develop test procedures, to obtain a better understanding of crack-front characteristics, to investigate test repeatability, to examine variations of fracture energy with temperature, and to investigate mixed-mode fracture. The results from the tests follow expected trends and test variability appears to be within a range typical for asphalt concrete fracture testing.

Analysis of Long-Term Effectiveness of Thin Hot-Mix Asphaltic Concrete Overlay Treatments

Thin hot-mix asphalt (HMA) concrete overlays are preventive maintenance treatments used to address minor distresses, increase ride quality, and extend pavement life. This paper determines the long-term effectiveness of such treatments by using three measures of effectiveness: treatment service life, increase in average pavement condition, and area bounded by the performance curve. For each measure of effectiveness, the pavement performance indicators used are the international roughness index (IRI), rutting, and pavement condition rating (PCR). For each measure of effectiveness and performance indicator, treatment benefits were found to lie within a wide range because of the effect of varying levels of weather severity, traffic, and route type. The service life of the treatment ranges from 3 to 13 years (IRI performance indicator), 3 to 14 years (rutting), and 3 to 24 years (PCR). When the increase in average pavement condition is used as the measure of effectiveness, the results show that such treatments offer 18% to 36% decrease in IRI, 5% to 55% reduction in rutting, and 1% to 10% increase in PCR. For the area enclosed by the performance curve, thin HMA overlay effectiveness ranges from 40 to 360 IRI years (where IRI is in inches per mile), 0.13 to 0.76 RUT years (where RUT is in inches), and 7 to 130 PCR years (where PCR is on a 0 to 100 scale). The wide ranges of thin HMA overlay effectiveness for each combination of measure of effectiveness and performance indicator is suggestive of the sensitivity of the treatment effectiveness to levels of traffic loading and weather severity, and route type. The effectiveness of thin HMA overlay treatments is of interest to pavement professionals and is a vital input in the quest for cost-effective long-term pavement preservation practices.

Part 1: Pavement Management: Analysis of Long-Term Effectiveness of Thin Hot-Mix Asphaltic Concrete Overlay Treatments

Thin hot-mix asphalt (HMA) concrete overlays are preventive maintenance treatments used to address minor distresses, increase ride quality, and extend pavement life. This paper determines the long-term effectiveness of such treatments by using three measures of effectiveness: treatment service life, increase in average pavement condition, and area bounded by the performance curve. For each measure of effectiveness, the pavement performance indicators used are the international roughness index (IRI), rutting, and pavement condition rating (PCR). For each measure of effectiveness and performance indicator, treatment benefits were found to lie within a wide range because of the effect of varying levels of weather severity, traffic, and route type. The service life of the treatment ranges from 3 to 13 years (IRI performance indicator), 3 to 14 years (rutting), and 3 to 24 years (PCR). When the increase in average pavement condition is used as the measure of effectiveness, the results show that such treatments...

Long-Term Performance of Broken and Seated Pavements

A study was developed to evaluate the effectiveness of breaking and seating (B/S) as a rehabilitation strategy for retarding reflective cracking in asphalt concrete (AC) overlays on jointed reinforced concrete pavements (JRCP). Several test sections were constructed by milling the original AC layer, breaking and seating the concrete slabs, and constructing new AC overlays. Control sections were constructed adjacent to the B/S sections in the same way, but without breaking the underlying concrete slabs. Two types of pavement breakers were used in this study: guillotine and pile hammer. The majority of the concrete slabs were broken into 0.46-m (18-in.) segments. Performance of the test sections was monitored for a total period of 9 years. Breaking the concrete slabs into smaller pieces resulted in a reduction in the flexural strength, an increase in the surface deflection (50% to 100%), and a decrease in area and spreadability (20% to 30%). Within 2 to 4 years, reflection cracks developed over more than 80% of the joints in all the control sections. The B/S sections were relatively free of cracks after 9 years. This result clearly indicates that breaking and seating has been extremely effective in minimizing and delaying reflection cracking. Based on the results of this study, it was concluded that breaking and seating is an effective technique for the rehabilitation of composite pavements (AC over JRCP). It provides an effective solution for the maintenance and rehabilitation of in-service composite pavements.

Probabilistic Analysis of Highway Pavement Life for Illinois

The Illinois Department of Transportation has periodically conducted pavement longevity studies to assess the longevities and the traffic loadcarrying capacities of these new and rehabilitated pavements so that any needed improvements to design, construction, or rehabilitation could be identified and implemented in a timely manner. The results of the latest round of pavement longevity studies in Illinois provide performance data updated through 2000 for new hot-mix asphalt concrete (HMAC), jointed reinforced concrete pavement (JRCP), and continuously reinforced concrete pavement (CRCP) construction as well as the asphalt concrete (AC) overlays (first, second, and third overlays) of these original pavements. These studies were conducted on more than 2,000 centerline miles of Interstate and other freeways that were constructed beginning in the 1950s in Illinois. Significant findings on the performance of the original pavements and overlays were obtained, and these findings will be of value to designers and managers to improve pavement cost-effectiveness and life. Survival curves have an economic impact on the agency. Key findings show the impact of pavement type (HMAC, JRCP, or CRCP), slab thickness, geographic location (north or south), durability cracking (D-cracking), and AC overlay thickness (coupled with preoverlay condition) on longevity and load-carrying capacity. The results of the probabilistic analysis illustrate the wide variation in pavement life and traffic carried. The study also provides models for predicting the probability of survival for various designs of original pavements and AC overlays in Illinois for use in pavement management.

Solution for Distressed Pavements and Crack Reflection

It is commonly accepted that cracks in aged asphalt pavements will reflect through seal coat and overlay applications. Pavement fabric placed under asphalt concrete overlays will slow this crack reflection, but not stop it. Nineteen years of experience working with the same fabric under a double chip seal has shown that using a modified technique, developed through trial and experimentation, adds substantial pavement life at a reduced cost over typical methods of repair used in the industry. In addition, pavement deterioration due to oxidation and stripping has been eliminated because air and water are unable to penetrate the surface. The subgrade dries out and regains its original strength, minimizing deflection under traffic loadings. This method reduces crack reflection by more than 90% over alternate methods. The reduction is due mainly to a regaining of the subgrade strength along with an increase in the flexibility of the surface through the use of a higher percentage of oil in the total mix. The most surprising aspect of this process is that alligatored pavement can be repaired without having to remove and replace the damaged pavement.

Using Pseudostrain Damage Theory to Characterize Reinforcing Benefits of Geosynthetic Materials in Asphalt Concrete Overlays

Reflective cracking is one of the more serious distresses associated with existing hot-mix asphalt (HMA) or portland concrete cement pavements overlaid with a thin bituminous layer. Preventive maintenance techniques have included incorporating geosynthetic materials (defined here as grids, fabrics, or composites) into the pavement structure. These materials have exhibited varying degrees of success, and their use within a particular agency has been based primarily on local experience or a willingness to try a product that appears to have merit. A methodology is described that was used to compare the relative effectiveness of six commercially available geosynthetic materials in reducing the severity or delaying the appearance of reflective cracking in HMA overlay. Each geosynthetic material was incorporated into compacted HMA specimens and tested to failure. Engineering fracture mechanics and pseudostrain energy concepts based on the elastic-viscoelastic correspondence principle were used and demonstrated to be appropriate and efficient in characterizing the fatigue damage process. By considering the effects of the geosynthetic products on the loading and unloading paths of the HMA specimens, a new concept was developed and termed the reinforcing factor, R. The use of this value allows the industry to characterize the relative reinforcing benefits of geosynthetic materials in reducing reflective cracking in HMA overlays. A crack speed index was then derived to summarize the complex interactions of the material properties. In general, grids and composites performed better than fabrics, which in turn performed better than a thin tacked surface as compared with unreinforced specimens. Design equations were developed between the fracture properties of the geosyntheticmixture system and the relaxation modulus properties of the HMA, which can be used in forward-calculating design methods to predict the rate of crack growth and support the design of an HMA overlay to resist reflective cracking. To calibrate the design equations, comparative field test pavements were constructed in three regions of Texas (Amarillo, Waco, and McAllen) using each geosynthetic material. These pavements will be monitored over the next 4 years.

Development and Performance of Interlayer Stress-Absorbing Composite in Asphalt Concrete Overlays

An interlayer stress-absorbing composite (ISAC) was developed and evaluated for the purpose of effectively alleviating or mitigating the problem of reflection cracking in an asphalt concrete (AC) overlay. ISAC materials and performance properties were carefully selected through comprehensive theoretical studies and laboratory evaluation programs. The ISAC system consists of a low-stiffness geotextile as the bottom layer, a viscoelastic membrane layer as the core, and a very high stiffness geotextile for the upper layer. In order to evaluate the effectiveness of the ISAC layer to control reflective cracking, a laboratory pavement section with an AC overlay placed on a jointed portland cement concrete slab was constructed and tested in an environmental chamber. A mechanical device was used to simulate thermal strain in the slab, and the joint was opened and closed at an extremely slow rate. The testing was conducted at −1.1°C, and strain in the overlay was monitored using a sensitive linear variable differential transducer device. The force required to pull and push the slab was monitored using a load cell placed between the slab and a hydraulic ram. Performance of ISAC was evaluated by comparing the cycles to failure of an ISAC-treated overlay with the performance of a control section without ISAC and of test sections containing two commercially available products. The base isolation properties of the ISAC system were demonstrated in the laboratory evaluation studies, which indicated that the ISAC system vastly outperformed the control section and the sections with the two commercial products tested. Several years of field performance testing have show that the ISAC system is highly effective for mitigating reflective cracking in AC overlays used on both airport and highway pavement systems.