Flexible Asphalt Pavement Research Articles

Effect of low-content crumb rubber modification on the performance of bitumen and asphalt

The performance of flexible pavements is greatly influenced by rutting, fatigue, and durability, leading to premature failures under environmental conditions. The limitations of traditional bitumen in flexible asphalt pavements are due to the significant rise in traffic loads and volumes. The reason for incorporating tire waste into bitumen is its incredible qualities and economical price as a bitumen modifier. The quality of crumb rubber (CR)-modified bitumen mainly depends on the concentration of low-content CR dispersed into the base bitumen. The primary target of this research is to modify the bitumen with low-content CR to improve the thermal properties, rheology, rutting resistance, fatigue resistance, and moisture-damaged performance. The three concentrations, i.e., 5%, 10%, and 15% of CR, were selected based on extensive preliminary trials when dispersed in conventional 60/70 penetration grade bitumen. The consistency and mixture test results concluded that the optimum dosage of CR-10% provides a 20% improvement in thermal performance, a 15% increase in rheological stability, a 25% enhancement in rutting resistance, a 30% boost in fatigue resistance, and a 10% reduction in moisture damage susceptibility. The inclusion of CR makes rubberized asphalt an attractive and effective solution for highway construction, aligning with sustainable construction practices. The findings demonstrate that low-content CR-modified asphalt improved the durability of asphalt mixtures against moisture-induced damage and other benefits, such as reduced cracking and maintenance requirements. The CR technology led to a significant subsidization in the environmental impact of asphalt paving from 5 to 10% compared to standard paving applications.

Use of Waste Phonolite as Filler Material in Flexible Asphalt Pavements

I In the scope of the study, the use of waste phonolite (PW) obtained from phonolite wastewater formed during the processing of phonolite stone blocks as filler in hot-mix asphalt (HMA) was investigated. For this purpose, samples were produced with 4 %, 5 %, and 6 % PW mineral filler and 5 % limestone (LS) mineral filler. Phonolite supplied as waste was sieved through a sieve no 200 and made ready for use as a filler. HMA specimens were prepared with PW and LS at the rates of 3.5 %, 4 %, 4.5 %, 5 %, 5.5 %, and 6 % bitumen. For each filler ratio, a bituminous hot mix design was made by the Marshall method and optimum bitumen ratios (OBR) were determined. Bituminous hot mixture specimens were prepared based on OBR. Retained Marshall stability (RMS) test, indirect tensile strength (ITS), and moisture damage resistance tests and Marshall stability (MS) test after the freeze-thaw (F-T) cycle was applied to the prepared Marshall samples. The results obtained were evaluated according to the Turkish Highway Technical Specification (HTS). As a result, it was determined that the PW could be used as filler in HMA under low-intensity traffic.

Preliminary optimization design of inverted asphalt pavement structure using response surface method

Inverted asphalt pavement (IAP) has the advantage of maintaining good performance under the condition of thin asphalt concrete (AC) layer compared with conventional flexible asphalt pavement. The stress-dependent property of unbound aggregate base (UAB) plays an important role in mechanistic responses of IAP. The focus of this paper is to quantitatively analyze the function of UAB’s stress-dependent property on the structure combinations design of IAP using response surface method (RSM). In this paper, an improved UMAT subroutine was developed to characterize the stress-dependent stiffness of UAB. The three-dimensional FE pavement model was established and validated against KENLAYER calculation and field FWD test deflection data. The critical mechanical response, maximum principal strain and bulk stress, were selected to evaluate the fatigue performance of AC layer and stress-dependent property of UAB. The significance analysis was conducted to describe the relationship between input variables (thickness and stiffness of structural layers) and the critical mechanical response variables. An optimization design method to balance the fatigue performance and stress-dependent property was proposed to obtain the optimal structure combinations of IAP. Research results demonstrate that the thickness and stiffness of the AC and UAB layers present a clearly significant impact on the maximum principal strain at the bottom of AC layer and the bulk stress in UAB, particularly during the summer season, whereas the thickness and stiffness of CTB and stiffness of subgrade have a minor impact. The responses of bulk stress and maximum principal strain can be empirically predicted by 2FI and Quadratic models. Optimal structure combinations (13.6 cm AC layer and 10 cm UAB) were recommended after quantifying the stress-dependent properties of UAB. The recommended structural combination has good fatigue resistance and can also efficiently minimize AC and UAB layer thickness.

Moisture Sensitivity Evaluation of the Asphalt Mortar-Aggregate Filler Interface Using Pull-Out Testing and 3-D Structural Imaging

Moisture damage is one of the undesired distresses occurring in flexible asphalt pavements, mostly through water intrusion that weakens and ultimately degrades the asphalt mortar-aggregate interfacial bond. One method to mitigate this distress is using anti-stripping or anti-spalling filler materials that, however, require a systematic quantification of their interfacial bonding potential and moisture tolerance properties prior to wide-scale field use. With this background, this study was conducted to comparatively evaluate and quantitatively characterize the moisture sensitivity and water damage resistance of the interfacial bonding between the asphalt mortar and aggregate fillers. Using an in-house custom developed water-temperature coupling setup, numerous laboratory pull-out tests were carried out on the asphalt mortar with four different filler materials, namely limestone mineral powder, cement, slaked (hydrated) lime, and waste brake pad powder, respectively. In the study, the effects of moisture wet-curing conditions, temperature, and filler types were comparatively evaluated to quantify the water damage resistance of the asphalt mortar-aggregate filler interface. For interfacial microscopic characterization, the Image-Pro Plus software, 3-D digital imaging, and scanning electron microscope (SEM) were jointly used to measure the spalling rate and the surface micromorphology of the asphalt mortar and aggregate filler before and after water saturation, respectively. In general, the pull-out tensile force exhibited a decreasing response trend with more water damage and interfacial bonding decay as the moisture wet-curing temperature and time were increased. Overall, the results indicated superiority for slaked (hydrated) lime over the other filler materials with respect to enhancing and optimizing the asphalt mortar-aggregate interfacial bonding strength, moisture tolerance, and water damage resistance, respectively—with limestone mineral powder being the poorest performer.

A Comprehensive Review of Biochar Utilization for Low-Carbon Flexible Asphalt Pavements

A large amount of biomass waste is produced globally, and its production and improper management are major environmental issues. Pavement industries consume large amounts of natural resources and adversely impact the environment. Thus, the utilization of waste materials, such as biochar from biomass, has been prioritized as an innovative and sustainable strategy. However, there is currently a paucity of knowledge regarding the utilization and performance of biochar in flexible asphalt pavements. Thus, the purpose of this study was to provide a comprehensive literature review of studies conducted between 2010 and 2022 on the advancement and application of biochar in flexible asphalt pavement production. This review also highlights biochar production materials (feedstocks) and processes. This review further evaluates the viability of biochar as a carbon-neutral material utilized in producing asphalt pavements. Owing to its exceptional and variable physicochemical properties, biochar has demonstrated improved performance for a variety of applications in flexible asphalt pavements. According to the review, for optimum performance, a particle size < 75 µm is recommended as a modifier for asphalt binders and mixtures with a content range of 5–10 wt.% of the binder, while a particle size of 1–5 mm is recommended as a filter layer. In addition, the review concluded that as a carbon-neutral material, biochar has many possibilities that can aid in reducing CO2 emissions. The challenges and future perspectives, underlying study niches, and future research suggestions for biochar application in the flexible asphalt pavement industry are also highlighted. As a result, this review will contribute to the increased sustainability and eco-friendliness of flexible asphalt pavements by encouraging the transition to carbon-negative and emission-reducing pavements. The current review will assist researchers in identifying research gaps that will encourage the high-potential, sustainable, and multifaceted application of biochar in the pavement industry for greater environmental benefits.

Experimental Study of the Effect of Tack Coats on Interlayer Bond Strength of Pavement

The performance and lifetime of the flexible asphalt pavement are mainly dependent on the interfacial bond strength between layer courses. To enhance the bond between layers, adhesive materials, such as tack coats, are used. The tack coat itself is a bituminous material, which is applied on an existing relatively non-absorbent surface to ensure a strong bond between the old and newly paved layer. The primary objective of this study was to evaluate the effects of various types of tack coat materials on interlayer bond strength and to determine the optimal application rate for each type. The tack coat types used in this paper were RC-70, RC-250, and CSS-1h. Both laboratory-prepared and field-constructed hot mix asphalt concrete pavements using the tack coats were tested for the binding strength between the layers. A direct shear test was used for the testing. The results obtained from the study showed that the optimum application rate for RC-70 was 0.1 L/m2, and for RC-250, it was 0.2 L/m2, while the optimum application rate for CSS-1h was 0.1 L/m2. From the field test, the optimum application rate of the RC-250 tack coat was 0.1 L/m2.

Analisis Sistem Pengambilan Keputusan Penentuan Konstruksi Jalan dengan Perkerasan Kaku atau Fleksibel (Studi Kasus Jalan di Propinsi Maluku Utara)

ABSTRACT
 This research discussing about decision support system analysis in determining concrete and composit road construction compared to asphalt construction for the case of roads in North Maluku Province. This study uses the Analytic Hierarchy Process (AHP) method or model as a method to analyze the feasibility of concrete and composit construction compared to asphalt construction. There are at least 7 (seven) factors that are considered as AHP inputs, namely road conditions, technical pavement, ecomonical/cost, duration/method of construction, availability of equipment, environmental conditions, and availability of materials. This study method includes data collection and analysis methods. For data collection, this study uses a questionnaire method that contains questions related to technical and non-technical factors that are used to assess the feasibility of a road for selecting a type of road pavement with flexible or rigid pavement. The construction feasibility of concrete and composite pavements is better than that of flexible asphalt pavements on road constructions, with the following sub-criteria conditions; roads that have bends and inclines, lower road maintenance costs, excellent weather and environmental resistance, less dense traffic, easy work execution and can be done at any time, do not require a lot of AMP and equipment, and asphalt availability can't fast time. The alternative of road pavement type is effective as a weight value of 33.78% with using the composite pavement construction.
 Keywords: Roadworthiness, Composite pavement, AHP, Decision Support System, North Maluku

Mechanical Feasibility of Asphalt Materials for Pavement Solar Collectors: Small-Scale Laboratory Characterization

Rutting (i.e., depressions along the wheel path) is a distress exhibited by flexible asphalt pavements at high in-service temperatures negatively affecting ride comfort and safety. In this regard, the fine asphalt mortar (i.e., bitumen filler and fine sand) plays a key role in the rutting potential of the asphalt mixtures. Given this background, this manuscript presents a small-scale laboratory experimentation aimed at assessing the rutting-related performance of a plain bitumen combined with natural (limestone) or manufactured (steel slag) fine aggregates (size up to 0.18 mm) through advanced experimental and theoretical approaches. Specific rheological tests through dynamic shear were carried out to achieve this goal. The investigated asphalt blends came from a wider research project focused on the implementation of a pavement solar collector (a road system to harvest the solar energy irradiating the pavement). In particular, the present paper aimed at verifying the mechanical suitability of the produced asphalt mixes with respect to permanent deformation resistance. Such a small-scale investigation mainly showed that the previously selected constituent materials did not imply criticisms in terms of rutting response.

On the sustainable use of recycled plastics in flexible asphalt pavements

Reusing plastic waste in asphalt has been an ongoing practice because of potential environmental and economic benefits. However, most research has come to contradictory conclusions about the merits of using plastic in road construction. As part of a pre-engineering study for a major pavement trial utilizing recycled plastics in the Regional Municipality of Durham, Ontario, this report documents and discusses test results on plastic-modified binders and mixtures. Locally sourced high density polyethylene (HDPE), low density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS) waste plastics were used to modify asphalts. It was found that high temperature binder grades improved while low temperature grades were relatively unaffected. Plastics increase strength but reduce strain tolerance in ductile failure . Hence, only binder course layers should be modified to prevent undue risk for premature and excessive surface cracking. Hamburg wheel tracking tests on mixtures showed rather uneventful findings at 50°C. In contrast, modified mixes were significantly less strain tolerant in ductile failure. In order to accommodate significant amounts of plastic and realize overall improved performance, it is proposed that the base asphalt is adjusted to a softer grade. This facilitates high additive contents to produce a rut resistant mix without sacrificing ductile failure properties.

Investigation on the impacts of gradation type and compaction level on the pavement performance of semi-flexible pavement mixture

Semi-flexible pavement (SFP) has been widely used to address rutting distress across China in recent years. The field application shows that SFP has excellent anti-rutting performance but relatively poor anti-cracking ability when compared with flexible asphalt pavement. Formation of cementitious network is closely related to the connected voids within porous asphalt mixture (PAM). Different gradations and compaction levels would contribute to different volumetric contents and distribution of connected voids in asphalt skeleton. Thus, the pavement performance of SFP could be theoretically regulated by using different combination of gradations and compaction levels for PAM fabrication. However, the relationship between aforementioned two factors with pavement performance of SFP is not well established. Therefore , volumetric properties of PAM samples fabricated with three different gradations and three compaction levels are characterized firstly in present paper. The pavement performances of grouted samples are evaluated then. Afterwards, the relationship between volumetric parameters of PAM and pavement performance of SFP are analyzed. In the end, the reusable two-factor analysis of variance is carried out to check the significance of different factors. Results show that the 25℃ IDT strength of SFP ranges from 0.7 to 1.0 MPa while that of PAM is from 0.3 to 0.6 MPa by using different gradation types and compaction levels. TSR of all the SFP samples exceed 80%, which indicating that SFP has excellent anti-freeze–thaw ability. The Cantabro loss of SFP can be approximately decreased from 13% to 9% by using finer gradation. Different SFP samples have similar flexural strengths but significantly different maximum flexural strain and modulus. It is found that gradation type has the more significantly impacts on the pavement performance of SFP than compaction level. Based on the results in present paper, SFP samples fabricated with the VCV of PAM lower than 19% exhibit excellent all-around pavement performances. The findings can provide a guidance for the design and application of SFP in the field.

Evaluation of the elastic modulus of pavement layers using different types of neural networks models

Introduction. This paper studies the capability of different types of artificial neural networks (ANN) to predict the modulus of elasticity of pavement layers for flexible asphalt pavement under operating conditions. The falling weight deflectometer (FWD) was selected to simulate the dynamic traffic loads and measure the flexural bowls on the road surface to obtain the database of ANN models.Materials and Methods. Artificial networks types (the feedforward backpropagation, layer-recurrent, cascade back- propagation, and Elman backpropagation) are developed to define the optimal ANN model using Matlab software. To appreciate the efficiency of every model, we used the constructed ANN models for predicting the elastic modulus values for 25 new pavement sections that were not used in the process of training, validation, or testing to ensure its suitability. The efficiency measures such as mean absolute error (MAE), the coefficient of multiple determinations R2, Root Mean Square Error (RMSE), Mean Absolute Percent Error (MAPE) values were obtained for all models results.Results. Based on the performance parameters, it was concluded that among these algorithms, the feed-forward model has a better performance compared to the other three ANN types. The results of the best four models were compared to each other and to the actual data obtained to determine the best method.Discussion and Conclusions. The differences between the results of the four best models for the four types of algorithms used were very small, as they showed the closeness between them and the actual values. The research results confirm the possibility of ANN-based models to evaluate the elastic modulus of pavement layers speedily and reliably for using it in the structural assessment of (NDT) flexible pavement data at the appropriate time.

Rutting prediction of hot mix asphalt mixtures reinforced by ceramic fibers

One of the most severe problems with flexible asphalt pavements is permanent deformation in the form of rutting. Accordingly, the practice of adding fiber elements to asphalt mix to improve performance under dynamic loading has grown significantly in order to prevent rutting distress and ensure a safe and long-lasting road surface. This paper explores the effects of a combination of ceramic fiber (CF), a low-cost, easily available mineral fiber, and thermal insulator fiber reinforced to enhance the Marshall properties and increase the rutting resistance of asphalt mixes at high temperatures. Asphalt mixtures with 0%, 0.75%, 1.5%, and 2.25% CF content were prepared, and Marshall stability and wheel tracking tests were employed to study the effect of added CF on asphalt mixture performance. Scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) were also used to investigate the morphologies of CF and reinforced asphalt mixtures and to identify the mechanism of improvement .According to the study results, the ideal ceramic fiber content was 1.5%, which yielded an improve in Marshall stability and reduced rut depth by 22.05% and 27.71% at temperatures of 50°C and 60°C, respectively, when compared to asphalt mixtures without CF. Microscopic analyses clearly revealed the surface properties, particle diameter size, and fiber distribution of the reinforced mixture, including the network structure and strength mechanism, which improved the performance of the asphalt mixture by forming a three-dimensional network.

Moisture susceptibility and fatigue performance of asphalt binder modified by bone glue and coal fly ash

The main purpose of incorporating waste into asphalt binder is due to their excellent properties and low cost as binder modifiers, in contrast to the impracticability of typical binder in the current flexible asphalt pavement by the increase of heavy traffic loads and volumes. The focus of this study is to use coal fly ash (CFA) with bone glue modified asphalt to check the effect of coal fly ash (CFA) towards fatigue resistance and moisture sensitivity. This study combined 60/70 penetration grade binder with optimum percentage of bone glue (10%) and 2%, 4%, 6% and 8% of fly ash. After conducting consistency tests and some mixture tests, it is concluded that fly ash gives superior fatigue life to flexible asphalt pavement and the effect towards moisture sensitivity is slightly good.

Assessment of carbon dioxide emissions during production, construction and use stages of asphalt pavements

The carbon dioxide emissions generated during the life of flexible asphalt pavements are an important indicator of the sustainability of these infrastructures. The study aims at tentatively quantifying the CO2 released during production, construction and use stages of a road pavement, the analysis is performed adopting a Life Cycle Assessment approach. Each stage is structured based on data retrieved from an extensive literature review. Special focus is given to the use stage, which is usually only partially addressed. The study is achieved employing the “HERMES CO2” spreadsheet tool developed for the purpose and it is publicly available to maximize openness and the interaction with the user. As an illustrative application, the study then quantifies the generation of carbon dioxide for the three major categories of Norwegian highways referring to 1 km as functional unit with lifespan of 50 years. The analysis documents that the overall CO2 amount is approximately equal to 1 million metric tons, which is significantly related to the albedo and rolling resistance of the use stage. Overall, the research establishes a common methodology and analysis frame which is relevant to early planning of road pavements and can be refined further for specific case-studies.

Effective control of flexible asphalt pavement cracking through quality assurance testing of extracted and recovered binders

A total of 54 asphalt binders were obtained from six different Canadian (four municipalities) and United States (two State Departments of Transportation (DOTs)) user agencies. Regular AASHTO M 320 grades, critical crack tip opening displacements (CTOD), extended bending beam rheometer (EBBR) limiting low temperature grades (LLTG), and limiting phase angles grades T(δ = 30°) and T(δ = 45°), were determined for tank-sampled and extracted and recovered materials.While nearly all binders sampled from storage tanks at asphalt plants pass regular contract quality assurance (QA) requirements with ease, enhanced test methods showed major variability for materials of ostensibly the same AASHTO M 320 grade. The CTOD provides a measure of strain tolerance in the ductile state around the freeze-thaw regime. It ranged from a low of 8.4 mm for a contract in a PG minus 28 zone—likely burdened by too much reclaimed asphalt pavement (RAP) and/or poor virgin binder quality—to a high of 48.4 mm for a contract in a PG minus 34 zone. The CTOD varied by as much as threefold within the same climatic zone. Tank samples graded consistently better according to the CTOD compared to recovered binders, at times in a major way.Grade losses due to cold conditioning in the extended BBR protocol, which provide a measure of durability, ranged from a negligible 0.9 °C to a very significant 9.1 °C after only 72 h of cold conditioning. The EBBR LLTG was found to be highly correlated with the T(δ = 30°) grade (R2 = 0.85), and somewhat less correlated with T(δ = 45°) (R2 = 0.74). The CTOD was found to be highly correlated with the T(δ = 45°) (R2 = 0.90), and somewhat less correlated with the T(δ = 30°) grade (R2 = 0.86). Hence, the two limiting phase angle temperatures may be used, in the future, in a more precise, accurate, and practical specification protocol for the control of cold temperature cracking.

Effects of different fillers on pavement deformation of hot mix asphalt in hot climates

Permanent deformation in the form of rutting is one of the major distresses affecting flexible asphalt pavements. This is a serious issue in hot countries and is closely associated with the viscosity of the bitumen binders used. In hot countries, temperatures can exceed 45 °C. Even in the construction of primary roads, bitumen 60/70 (B60/70), which is a relatively low-grade and soft bitumen, continues to be used for Hot Mix Asphalt (HMA) construction. Libyan asphalt concrete pavement roads therefore develop extreme deformations in the form of rutting. This study tests the effects of filler materials on mechanical and volumetric HMA performance with recourse to cellulose fiber (CF) and Ordinary Portland Cement (OPC). CF and OPC were added to a B60/70 HMA mix according to Superpave design specifications. Three percentages of OPC (2%, 4%, and 6%) and three different percentages of CF (0.25%, 0.5%, and 0.75%) were used as filler; there was also a control mix with no filler (0%). Mix performance was assessed with the rutting analyzer and The Indirect Tensile Stiffness Modulus (ITSM). ITSM test were conducted at −5 °C, 10 °C, 25 °C and the rutting analyzer test was conducted at 60 °C to simulate temperatures in the region. The mixes using cellulose fiber performed better than those with OPC. The results suggest potential budgetary savings because roadworks projects can use inexpensive additives instead of more expensive bitumen binders.

Mechanical feasibility of using red mud as filler in asphalt mixtures to improve permanent deformation

A lama vermelha é um resíduo sólido resultante do processamento do minério de bauxita para obtenção da alumina (óxido de alumínio – Al2O3), que é o principal composto químico para produzir alumínio. O Brasil possui uma grande reserva de bauxita no estado do Pará e o minério é processado em larga escala. No entanto, no país, a lama vermelha tem sido armazenada inadequadamente no meio ambiente. O Pará está situado no norte do Brasil e apresenta alta temperatura durante todo o ano. O elevado volume de tráfego e as altas temperaturas contribuíram para o surgimento precoce de defeitos nos revestimentos asfálticos dos pavimentos flexíveis. Este estudo laboratorial visa à introdução deste resíduo como fíler em misturas asfálticas densas. Para tanto, foram produzidas misturas de asfalto com 3%, 5% e 7% de lama vermelha (tamanho nominal entre 0,02 a 2.800 micrometros). Como referência, foi produzida uma mistura convencional com 7% de fíler de pó de pedra (tamanho nominal inferior a 0,075 mm). A resistência à deformação permanente das misturas foi avaliada através do simulador de tráfego francês. Como resultado, a mistura com 5% de lama vermelha apresentou o melhor desempenho à deformação permanente e obteve, aos 30.000 ciclos, a porcentagem de afundamento de 3,5%. As misturas asfálticas com lama vermelha apresentaram bom desempenho, com redução da deformação permanente de 12,63 a 42,62% em relação à mistura de referência. A lama vermelha como fíler em misturas asfálticas mostrou ser uma opção viável para reutilizar este resíduo, além de ser uma alternativa ecologicamente adequada.

The Impact of Heavy Vehicle Traffic Trends on the Overdesign of Flexible Asphalt Pavements

Given their environmental impact, the careful design of asphalt pavements is crucial. Previous research has highlighted the influence of several parameters on the outputs of different pavement design methods. In this study, the focus is on heavy vehicle trends, considering both the percentage of heavy vehicles in the average traffic flow and its evolution over time, which is usually included as a growth factor in the design inputs. Since these factors are very often assumed to be based on old estimates, the first aim of this study was to update them by exploring a recent series of continuous data collected on the Italian motorway network and showing how to infer estimates from historical traffic data. Subsequently, the variability of these input factors is introduced in standard pavement design methods to assess their influence on the design process and to quantify the risk of overdesign. While the analysis of historical heavy vehicle traffic data may reveal an overall zero-growth traffic tendency, different scenarios should be considered and assessed in cost-benefit analyses given the not negligible influence of growth factors on pavement thicknesses. This influence is shown here in different simulated design conditions, with different initial traffic volumes, share of heavy vehicles, and resilient moduli.

Influence of bonding conditions on flexible base asphalt pavement under non-uniform vertical loads

ABSTRACT In this study, considering the non-uniform action of actual wheel loads, the influence of bonding conditions at the surface layer/base and base/subbase interfaces on the structure of flexible base asphalt pavement was investigated. The mechanical response under two extreme bonding conditions – one with full slip and the other with complete continuity – was calculated by using the three-dimensional finite element software EverStressFE. Moreover, the dynamic evolution of the life of the pavement structure under different bonding conditions was comprehensively explored. The results show that the bonding conditions had different effects on pavement surface deflection, shear strain, flexural-tensile strain, and maximum vertical compressive strain at the top of the subgrade. The life of the pavement structure controlled by fatigue cracking and permanent deformation decreased non-linearly with the gradual deterioration of bonding conditions. The main mode of damages to the pavement structure alternated between permanent deformation and fatigue cracking, thereby increasing the difficulty of design, construction, and maintenance. Compared with the non-uniform action of wheel loads, the bonding conditions had a larger and independent impact on the structure of flexible base asphalt pavements.

Numerical analyses of rigid and flexible pavements responses under heavy vehicles’ loading

In an attempt to better understand the interaction between heavily loaded trucks and the pavement structure; rigid and flexible pavements’ responses (stresses, strains and deflections) were evaluated under simulated loading of 11-axle trucks (MI-20, MI-18, MI-14, MI-13) at gross vehicle weights (GVW) of 164,000 lb with different axle configurations, which are allowed in the state of Michigan. These responses were compared against results of a standard 5-axle semi-trailer at GVW nearing the common 80,000 lb standard in most states. Using these heavy truck types, the combined effects of truck loading, pavement thickness, joint spacing, material properties and thermal conditions on the pavement damages were evaluated. The major fatigue and faulting damages for rigid pavements as well as fatigue damage and subgrade rutting for flexible (asphalt) pavements are analysed. The finite element method (FEM) based program ISLAB2000 and multilayer elastic theory (MLET) based program JULEA were used to compute rigid and flexible pavements responses, respectively. Results show that the standard 5-axle truck yields up to 50% more fatigue damage potential under positive temperature gradient across slab (during daytime) even at a much lower gross vehicle weight than that of Michigan (MI) trucks. However, the 11-axle MI trucks provide up to 45% higher fatigue damage potential under negative temperature gradient (during nighttime). In comparison with the standard truck, the 11-axle MI trucks yield up to 17% less faulting damage for the typical rigid pavement with a thickness of 8 mm and up to 18% more faulting for larger pavement thickness. In flexible pavements, the standard truck exhibits up to 39% higher asphalt concrete fatigue damage than MI trucks. However, up to 80% more subgrade rutting damage for typical flexible pavements is observed for MI trucks with the multi-axles group configuration and larger GVW than the standard truck.