Flexible Pavement Rehabilitation Research Articles

Characterizing the Aging and Performance of Asphalt Binder Blends Containing Recycled Materials

Abstract The aging of asphalt concrete is mainly governed by the aging of the asphalt binder, which is a naturally occurring organic hydrocarbon. Both chemical and rheological properties of asphalt binder are expected to change as aging continues. The pavement industry is increasing the use of different recycled materials in the construction and rehabilitation of flexible pavements to preserve natural resources, save costs, and reduce environmental emissions. The aged binder from recycled materials is expected to alter the binder properties and its aging characteristics in the new mix. In this study, 3 different virgin base binder types (PG 64-16, PG 58-22, and PG 70-10) and 7 different binder blends containing recycled binders (up to 100 % binder replacement) were subjected to different aging conditions. The rheological and chemical properties of these binders were characterized using a dynamic shear rheometer and Fourier transform infrared spectroscopy, respectively. It was found that the Glover-Rowe parameter distinctively captured the change in binder rheological properties with aging for the different binder blends. A good correlation (R2 value of 0.83–1.00) was observed between binder chemical and rheological properties. The source and performance grade of the base binder were found to govern the correlation between the rheological and chemical properties of the blended binder. Hamburg wheel tracking (for rutting and moisture sensitivity) and indirect tensile asphalt cracking test (for fracture) tests were conducted on asphalt mixes maintaining the same blended binder ratios. The laboratory mix performance parameters were found to correlate well with the properties of the blended binders. Therefore, properties of the blended binders can be an important source of information for predicting the performance of asphalt mixes containing recycled materials.

Fatigue behavior of ultrahigh-performance fiber-reinforced concrete as an alternative for flexible pavement rehabilitation

The fatigue behavior of ultrahigh-performance fiber-reinforced concrete for use as an overlay in the typical rehabilitation of a flexible pavement structure was analyzed in this study. Compression and four-point bending tests were carried out to characterize the concrete mechanical properties. Fatigue tests were performed using the four-point method, and test beams were evaluated without precracking. The specimens were subjected to constant-amplitude sinusoidal loading with a loading frequency of 10 Hz. The magnitude of each stress level was calculated as a percentage of the initial crack stress. The following results were obtained for the concrete: a compressive strength of 127.1 MPa, bending yield strength of 6.23 MPa, maximum bending stress of 9.89 MPa, Young's modulus of 38.1 GPa, and dynamic modulus of 28.6 GPa. The stress and strain at one million cycles were 6.0 MPa and 166 μm/m, respectively. The fatigue test results indicated superior properties of the ultrahigh-performance concrete to those of similar materials.

Performance of Asphalt Rubber Mixture Overlays to Mitigate Reflective Cracking.

Adequately predicting overlay behaviour is essential for flexible pavement rehabilitation to reach the predicted lifespan. Reflective cracking is one of the main failure mechanisms affecting overlay performance. This failure may occur due to cracks in the lower layers that propagate to the overlay due to traffic loads, temperature variations, shrinkage cracking of cement-treated layers, and subgrade movements. This work aims to assess the reflective cracking phenomenon of asphalt rubber mixtures as an overlay through laboratory tests and numerical simulation. Four-point bending equipment and the reflective crack device were used to perform the laboratory tests. A numerical simulation through the finite element method was accomplished to estimate the von Mises strain and develop reflective cracking fatigue laws. The results showed that the asphalt rubber mixtures are suitable for extending overlay lifespan considering reflective cracking. The evaluated asphalt rubber mixtures presented reflective cracking resistance almost eight times greater than the conventional ones.

Evaluating the Potential Environmental Benefits of Cold Recycling-Based Methods for Flexible Pavement Rehabilitation in Virginia

This paper describes a study conducted to quantify the potential environmental benefits of recycled asphalt pavement projects completed in Virginia. Three restorative maintenance projects were evaluated: (i) a 5-in. hot-mix asphalt (HMA) over 5-in. cold in-place recycling (CIR) with foamed asphalt stabilization; (ii) a 3.5-in. HMA over 5-in. CIR with emulsion stabilization; and (iii) one non-recycling structural overlay (5-in. HMA over an existing pavement). In addition, the following reconstruction projects—the first three constructed on primary roads and the last two constructed on interstates—were assessed: (i) a 2.5-in. HMA over 9.6-in. full depth reclamation (FDR) with asphalt stabilization; (ii) a 3.5-in. HMA over 9.0-in. cement stabilized FDR; (iii) a non-recycling reconstruction project (7-in. HMA over 12-in. aggregate base and subbase); (iv) a 6-in. HMA over 6-in. asphalt-stabilized cold central plant recycled layer over a 12-in. lime-stabilized FDR base; and (v) a non-recycling reconstruction project (8-in. HMA over 18-in. aggregate base and subbase). When considering exclusively cradle-to-laid system boundaries, the results show that pavement recycling projects used for interstate reconstruction and primary route restorative maintenance yielded lower global warming (GW) than non-recycling approaches. When considering the entire life cycle, the study found that approximately 98% of the total GW came from pavement–vehicle interaction that takes place during the use stage. Finally, to reduce GW, the Virginia Department of Transportation could encourage (or even incentivize) practices that improve the initial pavement smoothness for recycling projects and use structural designs that are expected to have a low annual deterioration rate.

Climate Change Challenges for Flexible Pavement in Canada: An Overview

This paper provides an outlook on the effects of climate change and the severity and frequency of extreme weather events on the performance of flexible pavements across North America. Now more than ever, the climate is changing at a rapid pace, which will alter long-term environmental loading parameters and extreme weather events. Such alterations will pose implications for the design, maintenance, and rehabilitation of flexible pavements, especially in terms of their serviceability, safety, and functionality. In northern Canada, roads are founded on various terrain types, including thaw-sensitive ice-rich permafrost underlying terrains. Such roads have experienced signs of embankment and pavement damage, which are usually induced by the degradation of the underlying permafrost due to climate change. Therefore, the development and implementation of new permafrost thaw mitigation techniques for vulnerable roads are essential and will be discussed in this paper. Resilient flexible roads should be designed to withstand the conditions that are likely to occur during their design life, taking into account the impact of the climate change on pavement performance in response to daily and seasonal changes in heat, precipitation, freeze–thaw cycles, and extreme weather events.

Crack propagation analysis in bituminous mixtures reinforced by different types of geogrids using digital image correlation

In the rehabilitation of flexible pavements, the use of reinforcement by geogrids has substantially increased recently, aiming to extend the service life of pavements. This work evaluated the effect of fiberglass grid reinforcement on crack propagation of bituminous mixtures. To conduct the research, five different configurations of pre-notched beams constituted of two bituminous mixtures layers, with and without geogrid, were tested. Two different fiberglass geogrids, ultimate tensile strength (UTS) of 100 and 50kN/m, and emulsions as tack coat, made of bitumen pure and modify by polymer (SBS), were combined for the fabrication of three reinforced configurations. In addition, two unreinforced configurations were also fabricated. The first one was a single layer slab and the second one was bi-layered slab composed of two bituminous mixtures layers glued by a tack coat. The specimens were subjected to the four-point bending notched fracture (FPBNF) test, designed at the University of Lyon/ENTPE. A 3D Digital Image Correlation (DIC) technique was used to determine the strain field on specimen central length area during crack propagation. The results showed that the effect of geogrids was clearly noticeable when the specimen is subjected to high strain and the crack starts to propagate into the beams. DIC analysis allowed the observation of grid reinforcement effect on retarding the cracking propagation of bituminous mixtures layers.

Performance Evaluation of Dynamic Modulus Predictive Models for Asphalt Mixtures

Dynamic modulus characterizes the viscoelastic behavior of asphalt materials and is the most important input parameter for design and rehabilitation of flexible pavements using Mechanistic–Empirical Pavement Design Guide (MEPDG). Laboratory determination of dynamic modulus is very expensive and time consuming. To overcome this challenge, several predictive models were developed to determine dynamic modulus of asphalt mixtures instead of laboratory testing. Present study utilizes a large database of 1320 dynamic modulus test results developed at the University of Maryland to evaluate the performance and accuracy of different dynamic modulus predictive models. For this purpose, six conventional dynamic modulus predictive models including Witczak, Modified Witczak, Hirsch, Al-Khateeb, Global and Simplified Global models were considered and dynamic moduli of asphalt mixtures were determined. These moduli were then compared with those determined from laboratory test results. Performance evaluation of the models showed high prediction accuracy and low prediction bias with good correlation between predicted moduli and measured values for Witczak and Global models.

Determination of complex modulus gradients of flexible pavements using falling weight deflectometer and artificial intelligence

The modulus gradient of asphalt concrete (AC) layers is an important feature of flexible pavements. The variation of the modulus with depth results from the synthetical effect of material properties, the service time of pavements, loading and environmental conditions. Since the modulus gradient directly affects critical responses and performance of pavements, the determination of the modulus gradient of AC layers is necessary for the evaluation, maintenance and rehabilitation of flexible pavements. This paper aims to propose a method to obtain layer moduli of flexible pavements at different loading frequencies, which include a power function describing the modulus gradient of AC layers. The method utilizes results from a typical nondestructive test in the field applying the falling weight deflectometer and techniques of the fast Fourier transform, finite element model updating, kriging model and artificial intelligence. The method is validated by comparing layer moduli obtained from the proposed method and other backcalculation softwares.

Effect of Bio-Oils on Binder and Mix Properties with High RAP Binder Content

AbstractThe use of reclaimed asphalt pavement (RAP) has significantly increased in construction and rehabilitation of flexible pavements to ensure proper use of limited natural resources. Bio-oils ...

Preliminary Local Calibration of Performance Prediction Models in AASHTOWare Pavement ME Design for Flexible Pavement Rehabilitation in Oregon

AbstractThe Oregon Department of Transportation (ODOT) is in the process of implementing the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG) for new pavement sections. However, the vast ...

Method to determine the dosage of bituminous tack coat in function of the texture of milled asphalt layers to be overlaid

ABSTRACT In the rehabilitation of flexible pavements with asphalt layers, it is necessary to apply a bituminous tack coat with a pre-established dosage, which usually does not take into account the degree of texture generated if a milling operation is previously performed since this increases the surface at the interface. On the other hand, when milling, grooves are obtained that could lead to the runoff of bitumen emulsion with excessive deposition in their valleys due to dosages greater than those needed. This work analyses the above mentioned and achieves a compromise solution, with its corresponding method of application, based on the mechanical behaviour obtained with different degrees of texture and validated for typical materials used in Argentina.

Flexible pavement rehabilitation with continuously reinforced concrete slab with HFRP bars - mechanistic analysis

Asphalt road pavements are subject to damage under the influence of loads from the traffic of vehicles and of the environmental factors. One of the ways to strengthen damaged flexible pavements is to apply a cement concrete overlay with continuous reinforcement. The purpose of this paper is to analyze the road structure with concrete overlay with continuous reinforcement HFRP composite bars, which is laid on the existing cracked asphalt layers of a typical flexible road of KR3 traffic category. In HFRP bars some of the basalt fibers have been replaced with carbon fibers with the addition of resin binders. This do the possibility of making concrete slabs with increased resistance for environmental aggression, with good mechanical properties, which is especially important in the case of road constructions. An analysis of fatigue life of the strengthened asphalt pavement with a concrete slab with continuous reinforcement of HFRP bars was carried out, implementing the mechanistic model of the pavement structure. The stress analysis in the structure under the action of static loading was determined by the Finite Element Method using the Abaqus/Standard program. The maximum value of stress caused by temperature gradient in the concrete slab was calculated from the Westergaard’s formula for infinite slab. It has been shown that strengthening the analyzed road pavement with a continuous reinforcement is a technology that ensures an increase in fatigue life and reinforcement with HFRP bars further increases durability due to the negative impact of environmental factors.

The adjustment of pavement deflections due to temperature variations

ABSTRACT One of the most important steps in the rehabilitation of flexible pavements is the evaluation of their bearing capacity, which is used to assess the moduli of the pavement layers. The evaluation of the bearing capacity is usually carried out by measuring pavement deflections using a Falling Weight Deflectometer (FWD). This evaluation is undertaken in equally spaced points, usually 100 metres apart, with temperature variations throughout the day. Due to the viscoelastic behaviour of the asphalt layers, these FWD measurements are influenced by the pavement temperature, and the moduli can only be compared if they correspond to the same temperature. Thus, this work develops a model to adjust the pavement deflections to a reference temperature based on the characteristics of the pavement; namely: the asphalt layer thickness, subgrade stiffness, the distance between the FWD sensors, the load magnitude, and the pavement temperature.

Aging of asphalt binder in hot pavement rehabilitation

Construction of new asphalt road pavements as well as traditional maintenance requires the use of a great amount of non-renewable resources, having important negative environmental and economic impacts. Thus, extending the service life and promoting the recycling or reuse of pavement materials represent two pillars of a sustainable development model. These strategies include also two approaches which involve heating and softening of the existing hot-mix asphalt (HMA) pavement, such as healing and hot-in place recycling. Modern and more efficient technologies potentially used for the on-site heating of flexible pavements are no longer based on electrical resistance systems but use microwaves or infrared radiant heaters, which can however lead to a further potential aging of asphalt binder and therefore negatively affecting the mechanical properties of recycled HMA.This article aims, through an experimental laboratory approach, to directly compare two heating methods potentially used in flexible pavement rehabilitation, i.e. infrared and microwave radiations, for a preliminary assessment of the heating process characteristics (temperature distribution, energy consumption and duration) and on asphalt binder aging phenomenon. The thermographic and rheological analyses revealed that microwave radiation represents a more energy-efficient solution compared to infrared, producing minor aging effects on asphalt binder.

Prediction of performance and evaluation of flexible pavement rehabilitation strategies

Abstract Five test sections with different additives and strategies were established to rehabilitate a State-maintained highway more effectively in Rhode Island (RI): control, calcium chloride, asphalt emulsion, Portland cement and geogrid. Resilient moduli of subgrade soils and subbase materials before and after full depth rehabilitation were employed as input parameters to predict the performance of pavement structures using AASHTOWare Pavement ME Design (Pavement ME) software in terms of rutting, cracking and roughness. It was attempted to use Level 1 input (which includes traffic full spectrum data, climate data and structural layer properties) for Pavement ME. Traffic data was obtained from a Weigh-in-Motion (WIM) instrument and Providence station was used for collecting climatic data. Volumetric properties, dynamic modulus and creep compliance were used as input parameters for 19 mm (0.75 in.) warm mix asphalt (WMA) base and 12.5 mm (0.5 in.) WMA surface layer. The results indicated that all test sections observed AC top-down (longitudinal) cracking except Portland cement section which passed for all criteria. The order in terms of performance (best to worst) for all test sections by Pavement ME was Portland cement, calcium chloride, control, geogrid, and asphalt emulsion. It was also observed that all test sections passed for both bottom up and top down fatigue cracking by increasing thickness of either of the two top asphalt layers. Test sections with five different base/subbase materials were evaluated in last two years through visual condition survey and measurements of deflection and roughness to confirm the prediction, but there was no serious distress and roughness. Thus these experiments allowed selecting the best rehabilitation/reconstruction techniques for the particular and/or similar highway, and a framework was formulated to select an optimal technique and/or strategy for future rehabilitation/reconstruction projects. Finally, guidelines for long-term evaluation were developed to verify short-term prediction and performance.

Factors Influencing Deformations of Geocell-Reinforced Recycled Asphalt Pavement Bases under Cyclic Loading

AbstractA significant amount of recycled asphalt pavement (RAP) material is produced from flexible pavement rehabilitation projects. RAP can be used as a base course material for sustainable pavement construction. Performance of a pavement largely depends on the strength of its foundation, which consists of the subgrade and base course layers. Geocell was used in this study to increase the strength of RAP bases. Nine large-scale laboratory cyclic plate loading tests were conducted on unreinforced and geocell-reinforced RAP bases with three different thicknesses (150, 230, and 300 mm) over weak and moderate subgrades to investigate the influence of geocell confinement, base course thickness, base course strength, and subgrade strength on permanent and resilient deformations of RAP bases. The subgrade was prepared by mixing Kansas River sand with kaolin and compacted at weak [target California bearing ratio (CBR)=2%] and moderate (target CBR=5%) strengths. The test results showed that geocell confinement im...

Methodology for Determining Performance Life of Hot-Mix Asphalt Mixtures

A critical component of the life-cycle cost analysis for staged design and rehabilitation of flexible pavements is to estimate the service lives of various hot-mix asphalt (HMA) mixtures, which in some cases is carried out subjectively. This paper describes a process for using the existing data to develop an objective and data-driven process for estimating the service lives of common HMA mixtures. Spatial information along with construction records and distress and functional condition logs are merged to assess the “cradle-to-grave” service lives and deterioration patterns, statewide or regionally. One of the most challenging steps was linking separate databases to compile a comprehensive pavement performance database. The end result was an online tool that enabled the extraction of HMA service life data and descriptive statistics of several thousand road sections. The probabilistic performance life of each common mix was then estimated through an integrated approach of survivability analysis that considers the historical longevity of mix types, the age of the HMA surface course, distress history–based life predictions, field case study life predictions, and department of transportation personnel perceived service lives. The results as applied to Texas data showed bimodal longevity distributions of service life. In general, the mean service life of the analyzed dense-graded mix met or exceeded the mean perceived service life expressed by two dozen pavement engineers statewide. However, a fraction of the projects exhibited shorter lives because of a number of technical and institutional factors. Overall, the proposed methodology proved to be a consistent process when assessing HMA service life.

Development of Holding Strategies for Deteriorated Low-Volume Roads

Heavily deteriorated low-volume roads in the United States often face the plight of insufficient maintenance funding. Funding priority is usually given to roads that are part of the National Highway System (NHS). Rural highways that have the geometry and speed limits intended for lower traffic volume are not included in the NHS and may be managed by state highway authorities, counties, or townships. Low-volume roads provide access to areas that are less populated and typically have traffic counts of less than 1,500 average daily traffic. To improve such roadways, highway agencies are interested in holding strategies that are more aggressive than preventive maintenance but not as extensive as rehabilitation. The Iowa Department of Transportation constructed test sections with 10 holding strategy treatments to aid in the development of appropriate guidelines. Holding strategy treatments use various combinations of thin surfacing technologies and base recycling and strengthening treatments for flexible pavement rehabilitation and preservation, including single- and multiple-layer chip seals, thin and ultra-thin asphalt overlays, cold in-place recycling, and full-depth reclamation. This paper summarizes the construction of the test sections and recent observations of the performance and maintenance of the treatments. On the basis of the construction costs and treatment life expectations from the literature, a draft decision table is proposed for the selection of holding strategy treatments. The decision table recommends the most cost-effective holding strategy treatment among the 10 treatments that were constructed for a specified holding period. The decision table will be validated in the future with further performance observations.

A Laboratory Investigation into the Effect of Long-Term Oven Aging on RAP Mixes Using Dynamic Modulus Test

Reclaimed Asphalt Pavement (RAP) has been widely used in the construction and rehabilitation of flexible pavements. A proper understanding of the performance of hot mix asphalt (HMA) prepared with RAP is important to ensure better and longer lasting pavements. The present study was undertaken to evaluate the effect of long-term oven (LTO) aging of HMA mixes containing RAP using the dynamic modulus (|E*|) test. Two different HMA mixes, namely Mix-1 and Mix-2, were collected from asphalt plant. Mix-1 contains performance grade (PG) 64-22 unmodified binder mixed with 25% RAP, while Mix-2 includes PG76-28 styrene-butadiene-styrene (SBS)-modified binder mixed with 15% RAP. Both mixes have the same aggregate type (primarily limestone), aggregate gradation and binder content. Specimens were compacted using a Superpave Gyratory Compactor (SGC) at four target air voids of 6%, 8%, 10% and 12% (i.e., percentage compactions of 94% to 88% of the maximum theoretical density). LTO-aging of compacted specimens was done in accordance with AASHTO R30. |E*| tests were conducted on un-aged and LTO-aged compacted specimens at four different temperatures of 4°C, 21°C, 40°C and 55°C and at six different loading frequencies of 25 Hz, 10 Hz, 5 Hz, 1 Hz, 0.5 Hz and 0.1 Hz. Mix-1, with a softer grade binder (i.e., PG64-22) and a higher amount of RAP (25%), had a higher |E*| compared to Mix-2 with a stiffer grade binder (i.e., PG76-28) and lesser amount of RAP (15%). Furthermore, statistical analyses using the standard ”student t-test” revealed that, irrespective of binder grade, higher amounts of RAP result in stiffer mixes with higher |E*|. LTO-aging increased |E*| of the compacted samples by 42% to 60%, depending on the amount of RAP and air void content in the compacted specimen. It is expected that the present study will be helpful in understanding the behavior of HMA mixes containing RAP.

Factors Affecting Strength of Road Base Stabilized with Cement Slurry or Dry Cement in Conjunction with Full-Depth Reclamation

Full-depth reclamation (FDR) in conjunction with cement stabilization is an established practice for the rehabilitation of flexible pavements. Conventionally, the FDR process involves applying dry cement powder with a pneumatic spreader, but this process can create undesirable fugitive cement dust. To solve this problem, cement slurry has been proposed because it can allow cement stabilization to be used in urban areas. This research sought to (a) identify construction-related factors that influence the strength of road base treated with cement slurry in conjunction with FDR and quantify the effects of those factors and (b) compare the strength of road base treated with cement slurry with that of road base treated with dry cement. Full-factorial laboratory experimentation on a road base sampled from an FDR project was conducted. The 7-day unconfined compressive strength was measured as the dependent variable. The independent variables included cement content; slurry water batching temperature; presence of a set-retarding, water-reducing admixture; cement slurry aging temperature; cement slurry aging time; cement–aggregate mixing time; and form of cement. The results suggested that the slurry water batching temperature, the haul time, the environmental temperature, and the presence of a set-retarding, water-reducing admixture would not significantly affect the strength of a cement-treated base (CTB) within the ranges of the factors investigated in this research. However, cement content and cement–aggregate mixing time were found to be positively correlated with CTB strength, regardless of the cement form. Additionally, the use of cement slurry was found to result in slightly lower strength values than the use of dry cement.