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The pavement mechanistic-empirical design (PMED) is a widely used pavement analysis and design approach. The transfer functions are generally calibrated to implement the PMED for local conditions. The least square (LS) approach has been commonly used to calibrate these transfer functions. Although LS is a simplistic approach, the assumptions may not be valid, especially for non-normally distributed data. This paper uses the maximum likelihood estimation (MLE) approach to calibrate bottom-up cracking, total rutting, and international roughness index (IRI) transfer function for flexible pavements. The results show that overall, MLE outperforms the LS approach for synthetic and measured data. The difference is more evident in the case of bottom-up cracking data, which does not follow a normal distribution. Gamma distribution for bottom-up cracking and total rutting, whereas negative binomial for IRI is the most suitable distribution for the MLE approach. Overall, MLE using resampling methods provides a robust and better estimate than the LS approach. [ABSTRACT FROM AUTHOR]

Global road development accelerates environmental harm, resource depletion, and fossil fuel consumption due to conventional aggregate and hot mix asphalt (HMA) use. To combat this, sustainable pavement construction is vital. cold bitumen emulsion mixtures (CBEMs), a type of cold mix asphalt (CMA), offer a sustainable path forward. Incorporating waste materials as fine aggregates in cold mix asphalt addresses waste issues and flexible pavement development. Our research pioneers using crushed waste glass (WG) as a fine aggregate substitute in CBEM's binder layer, emphasizing unique microstructural analysis to uncover strength improvement mechanisms not explored before in binder layer gradation. This study replaces virgin fine aggregate with WG at varying percentages (0% to 100%, in 20% increments) and evaluated mechanical performance, including Marshall stability/flow, indirect tensile strength (ITS), resilient modulus (ITSM), dynamic modulus, flow number, fatigue life, and durability (retained Marshall stability). CBEM-WG mixes with around 60% WG content exhibited mechanical performance comparable to normal CBEM (NCBEM)/conventional HMA and showed improved performance beyond 60% dosage and maximum at 100% WG content. Moisture damage resistance decreases with increasing WG content but remains comparable to HMA. [ABSTRACT FROM AUTHOR]

Electric vehicles offer higher acceleration than conventional internal combustion engines due to larger engine torque. The design and placement of battery packs in heavy-duty electric vehicles are still being optimized, as they can affect axle load distributions and consequently impact pavement analysis and design. This study presents a finite element model of a dual tire assembly considering varying load and acceleration conditions to investigate the effect of conventional and electric heavy-duty vehicles on tire–pavement contact forces. Three scenarios for battery pack locations were examined, leading to six loading conditions for both internal combustion engines and electric trucks. The resulting 3D contact forces, compared at a specific line of points along the contact patch and throughout the entire distribution via kernel density estimate, determined that the load increase due to battery location had a much greater impact than the change in torque for both internal combustion engine and electric trucks provided they are at the same rolling condition. Higher loads altered the vertical and longitudinal contact forces and led to a broader contact area. On the other hand, transverse contact forces showed the least variation, although this may differ under cornering scenarios. Finally, a higher slip ratio exacerbated the contact forces in the traveling direction, highlighting the importance of considering rolling conditions in future analyses of pavement damage caused by heavy-duty electric vehicles. Practical Applications: Truck loading usually governs pavement design, layer thicknesses, and corresponding materials while considering local environmental conditions. For flexible pavements, in particular, the details of the distribution of the forces at the tire–pavement interface play a significant role in driving failure near the pavement surface. As the electrification of heavy-duty truck platoons becomes a reality, it is paramount for pavement engineers to quantify the effect of the torque and battery location from electric trucks on contact forces and evaluate its impact on flexible pavements—this paper provides such quantification. The study found that battery location, rather than increased torque, is the controlling variable for the electric trucks due to increased load influence on vertical contact forces. [ABSTRACT FROM AUTHOR]

Lateritic soils, particularly abundant in tropical regions, have been successfully used in the construction of unbound layers of flexible pavements in Brazil since the 1970s. Despite their potential, these soils are often discarded or only recommended after stabilization processes, based on traditional parameters such as gradation requirements and Atterberg limits. This study investigates the mechanical characteristics of a lateritic soil from Roraima, focusing on its resilient modulus and permanent deformation properties, assessed through repeated load triaxial tests. Specifically, this research examines the effect of adding 20% sand on the mechanical behavior of the material. The results indicate that sand addition did not significantly improve the mechanical performance. The laterite–sand mixture exhibited an average resilient modulus (RM) of 744 MPa, lower than the 790 MPa of pure lateritic soil, suggesting that pure laterite remains suitable for pavement applications. Furthermore, the permanent deformation analysis revealed that the mixture with sand experienced nearly twice the plastic strain compared to pure laterite, which demonstrated superior accommodation under repeated loading. In the shakedown analysis, pure laterite exhibited a more stable performance, indicating greater durability in pavement applications. These findings highlight the importance of understanding the mechanical behavior of lateritic soils beyond conventional testing methods, emphasizing the potential of pure laterite as a viable alternative to enhance the strength and durability of pavement structures. [ABSTRACT FROM AUTHOR]

In this study, the geopolymerisation method was employed to enhance the properties of highly expansive subgrade soil. Two precursors, namely coconut shell ash (CSA) and metabentonite, were mixed with NaOH alkali solution at various mix ratios generated using the Taguchi orthogonal array. The study aimed to improve geotechnical properties such as compaction, California bearing ratio (CBR) and unconfined compressive strength (UCS). The results from the experimental data revealed significant enhancements in UCS and CBR compared to natural soil, with increases of 425.79% and 691.97% for UCS after 7 and 28 days of curing, and a 132.46% increase in unsoaked CBR. These improvements were attributed to the complete dissolution of silica (Si) and alumina (Al) from the precursors, which encourages significant polymerisation and subsequently results in the formation of geopolymeric gels of N–A–S–H and C–A–S–H. Additionally, the pozzolanic reaction and presence of Ca(OH)2 contributed to the formation of secondary calcium silicate hydrate (C–S–H) gel. The optimal soil–geopolymer mix for CBR and UCS was determined as 10% CSA + 20% metabentonite + 2M NaOH. Using paveXpress software, pavement design analysis under heavy traffic loading conditions revealed a 28.57% reduction in pavement thickness compared to the natural subgrade soil. [ABSTRACT FROM AUTHOR]

The effectiveness of rejuvenation agents in reducing the stiffness of aged binder in Reclaimed Asphalt Pavement (RAP) material during the initial service life is well documented. However, their long-term efficacy remains under evaluation. This is partially due to the wide variety of rejuvenation agents, with varying chemical compositions, which impact the short- and long-term performance of the rejuvenated material. This paper addresses this concern by assessing the effectiveness of five types of vegetable-based rejuvenation agents across the ageing stages of asphalt mixtures during the service life of flexible pavements. The evaluation includes monitoring the rheological, chemical and performance-related properties of the rejuvenated binder blends (i.e., a combination of aged asphalt binder, virgin asphalt binder and rejuvenator) as ageing progresses. The results indicate that the benefit of rejuvenation decreases with time and that this reduction is a function of the type of rejuvenator. These results highlight that an appropriate selection of a rejuvenator should consider not only the improvement of the material during the production of the mixture and a good response and performance in the initial stage of the pavement operation, as is often the case, but also its capability to maintain these positive effects in later stages of its service life. [ABSTRACT FROM AUTHOR]

The Traffic Speed Deflectometer (TSD) is a mobile vehicle that measures deflection slopes. Deflection slopes have been utilised in previous studies to backcalculate pavement layers' moduli. However, the nonlinear stress-dependency and cross-anisotropy of unbound granular materials and fine-grained soils were overlooked in those studies. Utilising the Finite Element Method (FEM) based on static analysis in this study to evaluate a three-layered flexible pavement system with specific material properties and layer thicknesses revealed that neglecting the nonlinear stress-dependency of base and subgrade layers underestimated the permanent deformation life of the backcalculated pavement by more than 45%. Neglecting the cross-anisotropy of the base layer with the design anisotropy ratio of 0.5 increased the backcalculated Asphalt Concrete (AC) modulus by more than 21%, increased the estimated permanent deformation life of the pavement by more than 160%, and decreased the backcalculated base modulus by around 28%. Neglecting the cross-anisotropy of the subgrade with the design anisotropy ratio of 0.5 almost increased the estimated permanent deformation life of the pavement by 15%. The results underscore the necessity to consider the nonlinear stress-dependency and cross-anisotropy of unbound granular materials and fine-grained soils in backcalculating pavement layers' moduli from TSD deflection slopes. [ABSTRACT FROM AUTHOR]

Flooding can cause considerable damage to flexible pavements and negatively affects their performance over time. This study aims to evaluate the flooding effects on the flexible pavement performance and the potential resiliency of the pavement network through a mechanistic-empirical (ME) pavement analysis approach. The Unified Pavement Distress Analysis and Prediction System (UPDAPS) programme, which includes ME analysis models, was used to develop the UPDAPS-Flood programme. A total of 7,655 flexible pavement sections were extracted from the Highway Pavement Management System (HPMS) database in three United States regions. Finally, the resiliency of the pavement network to flood events was quantified using the loss of pavement service life based on the international roughness index (IRI). The results showed that flooding has the highest impact on rutting performance, followed by IRI and fatigue cracking. It has been found that a proper drainage system can reduce the flooding impact by a factor of two. The predicted pavement performance was found to be very sensitive to the coefficients of the rutting model, which brings the need for further studies to re-calibrate the rutting prediction model at higher moisture content levels. [ABSTRACT FROM AUTHOR]

Pavement rutting poses a significant challenge in flexible pavements, necessitating costly asphalt resurfacing. To address this issue comprehensively, we propose an advanced Bayesian hierarchical framework of latent Gaussian models with spatial components. Our model provides a thorough diagnostic analysis, pinpointing areas exhibiting unexpectedly high rutting rates. Incorporating spatial and random components, and important explanatory variables like annual average daily traffic (traffic intensity), asphalt type, rut depth and lane width, our proposed models account for and estimate the influence of these variables on rutting. This approach not only quantifies uncertainties and discerns locations at the highest risk of requiring maintenance, but also uncover spatial dependencies in rutting (millimetre/year). We apply our models to a data set spanning eleven years (2010–2020). Our findings emphasise the systematic unexplained spatial rutting effect, where some of the rutting variability is accounted for by spatial components, asphalt type, in conjunction with traffic intensity, is also found to be the primary driver of rutting. Furthermore, the spatial dependencies uncovered reveal road sections experiencing more than 1 millimeter of rutting beyond annual expectations. This leads to a halving of the expected pavement lifespan in these areas. Our study offers valuable insights, presenting maps indicating expected rutting, and identifying locations with accelerated rutting rates, resulting in a reduction in pavement life expectancy of at least 10 years. [ABSTRACT FROM AUTHOR]

This study explores the use of re-refined engine oil bottom (REOB) as an alternative to bitumen in asphalt mixtures for flexible pavement structures. REOB is considered due to its low cost, availability, large production volume, and eco-friendliness. This paper investigates the effects of adding 5, 9, and 14 wt% of REOB to neat bitumen on the asphalt mixture's characteristics, mechanical behaviour, and ecological implications. The findings reveal significant reductions in indirect tensile strength by up to 51%, moisture resistance by up to 17%, rutting resistance by up to 79%, and cracking resistance at intermediate and low temperatures, especially when 14 wt% of REOB is added. While the heavy metal concentrations in both bitumen and REOB exceed permissible limits, the leached metal concentrations from the asphalt mixture remain within the safe range. Despite the potential environmental benefits of using REOB, the economic evaluations suggest that incorporating REOB into asphalt mixtures slightly increases the construction cost. Therefore, careful economic consideration should be performed for each project. [ABSTRACT FROM AUTHOR]

Bonding strength between asphalt binder and aggregate is one of the major factors considered when developing flexible pavements. This study considered five factors to understand the most influential factor affecting the bonding strength at the asphalt aggregate interface and its impact on distresses in an attempt to limit their propagation. 60/70 penetration grade asphalt binder with different types of aggregate (basalt, granite, limestone, and marble) were investigated using the Binder Bond Strength (BBS) test. Three aging levels (unaged, RTFO, and PAV) with different curing temperatures (25, 40, and 60°C) and curing durations (24, 48, and 72 hr) were examined at two different curing conditions (dry and wet). Three-way analysis of variance (ANOVA) using SPSS software was utilised to quantify the significance of each factor on pull-off tensile strength (POTS) values. The results demonstrated that aging level, aggregate type, and curing temperature had a significant effect on bond strength. In contrast, curing type and curing duration did not show a significant effect as individual factors on the POTS values. It was found that increasing temperature had a detrimental effect on POTS for all combinations. On the other hand, short-term and long-term aging significantly increased the POTS values. Moreover, POTS values strongly depended on the aggregate type, as various aggregate types had different rankings. The POTS values decreased when samples were conditioned in water with a change in failure type. In dry conditions, the failure occurred within the asphalt (cohesive failure). The failure type changed from cohesion to adhesion after conditioning specimens in water. [ABSTRACT FROM AUTHOR]

Rising costs of constructing and maintaining asphaltic concrete pavements present a challenge requiring an alternative solution. Nanomaterials can be cost-effectively integrated with asphalt binder to provide beneficial effects for asphaltic concrete mixture. This paper investigated seven different types of nanomaterials, namely nanoclay, carbon nanotube, nanosilica, nano-titanium dioxide, nano-zinc oxide, graphene oxide, and carbon nanofiber by examining their production methods, benefits, applications, and limitations based on the data available in published literature. Challenges and limitations discussed include economic, production, and blending problems, some of which are due to the lack of research on the topic. This study provides a framework from which the pavement engineering community can conduct experimental research on nanomaterials for applications in asphaltic concrete pavements. The review of previous studies reveals that new asphalt binders and asphaltic concrete mixtures incorporating nanomaterials can be developed for improved performance of flexible pavements. It is expected that further research can be devoted to overcoming the current challenges faced by aging transportation infrastructure through use of nanomaterials in asphalt binder and asphaltic concrete. Above all, research gaps in the present state of knowledge have been identified and certain recommendations are given for future investigations. [ABSTRACT FROM AUTHOR]

The transportation sector is responsible for significant greenhouse gas (GHG) emissions, with medium- and heavy-duty trucks (MHDTs) being major contributors. In response, medium- and heavy-duty electric trucks (MHDETs) are being explored as zero-emission alternatives. However, the weight of high-capacity batteries needed for long-haul trips and heavy loads could increase the axle loads as well as the gross vehicle weight (GVW) of heavy-duty electric trucks (HDETs), leading to extra damage on flexible highway pavements. This study simulated the GVW increment of HDETs and assessed its effects on pavement damage, environmental impacts, and life-cycle costs of four typical highway pavement structures in Illinois (known as thick–weak, thick–strong, thin–weak, and thin–strong). The utilisation of electric trucks resulted in significant reductions in diesel combustion related global warming potential (GWP) emissions and costs (in $2022) by 73% and 11.5%, respectively. However, the results demonstrated that with a 100% penetration of HDETs carrying an additional weight of 8 kips per truck, the pavement deterioration accelerated compared to traffic with conventional trucks. As a consequence, GWP and costs were reduced by 69% and 10.6%, respectively. [ABSTRACT FROM AUTHOR]

This investigation seeks to enhance 'Iowa's Pavement Preservation Guide' with a data-informed decision-making framework. Iowa DOT's databases were used as the data source for evaluating pavement performances under different preservation treatment regimens and determining the effectiveness of those strategies. Five preservation treatment methods for flexible and composite pavements, namely, crack sealing-and-filling, microsurfacing, slurry sealing, patching, and thin hot mix asphalt (HMA) overlays were evaluated using historic data from about 7000 road segments between 1998 and 2020. The data included various attributes describing pavement, road, and traffic characteristics required for analysing condition-based performance and treatment impacts. Two key indicators, service life extension (LE) and index benefit (IB), were defined and used to quantify treatment effectiveness in terms of pavement condition improvement and impact on deterioration rate. The treatment-effectiveness indicators were then factored into the cost analyses to assess the cost-effectiveness of preservation strategies. The results of the treatment effectiveness analysis were used to develop decision matrices that provide insights for selecting preservation treatments based on benefit–cost analysis considering both the overall condition and the dominant distress. This approach to treatment effectiveness highlighted the distinction between an optimum pavement preservation strategy and one that targets maximum service life extension. [ABSTRACT FROM AUTHOR]

Considering that the road network shares traffic flow as a system, this study aimed to predict the network-level flexible pavement performance, using an optimised artificial neural network (ANN) approach to predict the pavement performance of each individual road, and the Ford-Fulkerson algorithm to determine the weight coefficients of roads. ANNs were developed to predict distress conditions, functional conditions and structural performance using the inputs of the pavement age and structural, traffic and climatic conditions. ANNs were trained with Long-Term Pavement Performance (LTPP) program data, and almost all the coefficient of determination values between ANN outputs and measured results are larger than 0.9. This ANN approach was optimised by establishing grey models to provide predictive short-term performance data for training ANNs, and employing Kalman Filter to modify the long-term performance prediction. Applications in typical LTPP sections validated the effectiveness of the optimisation method. This study used the reduction in road network capacity due to the assumed unavailability of a certain road to quantify its role (weight coefficient), which was calculated using the Ford-Fulkerson algorithm. This network-level performance prediction approach was applied in a 25-expressways network in Shanghai, which validated the good generalisation capabilities of ANNs and feasibility of the Ford-Fulkerson algorithm. [ABSTRACT FROM AUTHOR]

Extreme and fluctuating weather has a significant impact on the material properties of flexible pavements. Lightweight cellular concrete (LCC) can effectively mitigate weather effects due to its favourable insulating properties. To date, there has been little research on predicting temperature for different layers of conventional and LCC subbase pavements. This study investigates the application of LCC as a subbase material and its impact on layer temperature. Temperature profiles of two test roads, Erbsville and Notre Dame Drive (NDD), in Canada, have been collected for evaluation. Extreme gradient boosting (XGBoost) and genetic programming (GP) models were employed to forecast layer temperatures of Erbsville control and LCC-subbase sections based on inputs including ambient temperature, day of the year and constant depth. Shapley adaptive explanations (SHAP) were utilised for XGBoost, and parametric analysis was conducted for GP. Results indicated the superior performance of XGBoost (R2> 0.98, MAE < 1.5°C) over GP (R2> 0.97, MAE < 1.87°C), with both models demonstrating better predictive accuracy for LCC-subbase compared to the control section. SHAP, parametric analysis and external validation using NDD sections further validated the models' effectiveness in predicting temperatures for both control and LCC sections at various densities up to a depth of 0.8 m. [ABSTRACT FROM AUTHOR]

An evidence-based estimate of the load-related road deterioration due to heavy vehicles on the road network is needed for underpinning heavy vehicle road user charges on Australia's arterial roads. A network level model for estimating the percentage (%) load-related road deterioration was developed for typical sealed unbound pavements in Australia's sealed road network. This model was based on a network level roughness deterioration model using observational data from long-term pavement performance (LTPP) and long-term pavement performance maintenance (LTPPM) sites and accelerated loading facility (ALF) experimental data. The model estimates that the % load-related road deterioration varied with changes to the traffic load, pavement strength and an environmental coefficient. This outcome also implies that the roughness deterioration model for sealed granular pavements is likely to be more appropriate for predicting Australia's sealed granular pavement deterioration than past internationally based roughness deterioration models which were originally based on the deterioration of asphalt bound pavements. [ABSTRACT FROM AUTHOR]

Flexible airport pavements may require polymer-modified asphalt binder for their asphalt concrete (AC) mixes to withstand heavy gear loading and slow traffic moving in taxiways and aprons. Waste plastics could be repurposed as a possible alternative to Styrene–butadiene-styrene (SBS) modifiers. In this study, the feasibility of using granulated recycled high-density polyethylene (HDPE) waste was evaluated as an asphalt binder modifier for airfield pavements. A base asphalt binder was modified with waste HDPE to obtain a Superpave performance grade (PG) of 70-22. Adding waste HDPE would increase binder's stiffness and bond to aggregate, it slightly improved ductility and elasticity; but less than SBS polymer-modified binders. The AC mixes prepared with waste HDPE-modified binder showed less potential for rutting and cracking compared control AC mixes with PG 64-22. However, the rutting and cracking potential was higher when compared to their SBS-modified PG 70–22 counterparts. On the other hand, AC mixes containing waste HDPE-modified binder were less susceptible to moisture-induced damage. It appears that using waste HDPE-modified binder is feasible where improving adhesion and resistance to moisture-induced damage AC mixes are needed and embrittlement and elastic recovery are not critical, while meeting rutting and cracking potential regional thresholds. [ABSTRACT FROM AUTHOR]

Cement Treated Base (CTB), when used in base course, has shown better performance against rutting than conventional base materials. This study focuses on the use of recycled coarse aggregates (RCA) as partial replacement of natural coarse aggregates (NCA) in CTB and hot mix asphalt (HMA) layers of flexible pavements. 30% NCA were replaced with RCA to study the rutting performance of flexible pavements by using 100 mm thick rutting samples prepared with 50 mm thick layers of CTB and HMA each. Four types of specimens with 100% NCA, 30% RCA and 70% NCA in CTB only, 30% RCA and 70% NCA in HMA only, and 30% RCA and 70% NCA in both CTB and HMA were used. Specimens were tested at 40°C, 50°C, and 60°C at a constant number of 10,000 passes (5,000 load cycles). It was concluded that the CTB has a significant impact on the overall rutting performance of the samples due to its rigidity. Use of 30% RCA as a replacement of NCA was found to be acceptable, except for pavements with RCA in both layers. A statistical model was also developed and predicted responses from the proposed relationship were in close agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The current study aims to determine the impact of lime and Corex slag on the strength, durability, and compaction properties of coastal soil from Gujarat, India. Twelve mixes of soil with Corex slag (0%, 10%, 20%, 30%, 40%, and 50%) and lime (2% and 4%) were added to determine their suitability as admixtures for stabilizing the subgrade layer. The Atterberg limits, free swelling index (FSI), compaction characteristics, California bearing ratio (CBR), durability, and unconfine compressive strength (UCS) of the stabilized soil with different curing days (0, 7, and 28) using standard Indian procedures were determined for the flexible pavement's subgrade layer. The test results show that Corex slag positively affects the maximum dry density (MDD), optimum moisture content (OMC), and soil plasticity. Furthermore, the findings demonstrated that the strength properties and durability were effectively improved after stabilization. The strength of the stabilized coastal soil significantly improved as a result of the binding gel formation, according to examinations using scanning electron microscopy (SEM) and X-ray diffraction (XRD). [ABSTRACT FROM AUTHOR]

Non-destructive testing (NDT) systems are essential tools and are widely used for assessing the condition and structural integrity of pavement structures without causing any damage. They are cost-effective, provide comprehensive data, and are time efficient. The bearing capacity and structural condition of a flexible pavement depends on several interrelated factors, with asphalt layers stiffness being dominant. Since asphalt mix is a viscoelastic material, its performance can be fully captured by the dynamic modulus master curve. However, in terms of evaluating an in-service pavement, although a dynamic load is applied and the time history of deflections is recorded during testing of FWD, only the peak deflection is considered in the analysis. Therefore, the modulus of stiffness estimated by backcalculation is the modulus of elasticity. While several methods have been introduced for the determination of the field dynamic modulus master curve, the MEPDG approach provides significant advantages in terms of transparency and robustness. This study focuses on evaluating the methodology's accuracy through an experimental study. The data analysis and validation process showed that routine measurements with the FWD and GPR, within the framework of a pavement monitoring system, can provide valuable input parameters for the evaluation of in-service pavements. [ABSTRACT FROM AUTHOR]

Lateral restraint is the primary stabilization mechanism associated with the interlocking of aggregate particles in the geogrid apertures. This paper presents findings from a laboratory study which quantifies the local stiffness enhancement of aggregates through micromechanical interlocking provided by two different types of geogrids. These findings are applied to model the resilient response characteristics of geogrid-stabilized base course composite systems. Using three pairs of bender elements as shear wave transducers, horizontal stiffness profiles were determined above mid-heights of aggregate specimens. For two types of geogrids with square- and triangular-shaped apertures, the shear modulus profiles decreased moving away from the geogrid location. Based on a relationship for aggregates, resilient modulus was estimated from the shear modulus. Considering the variations in resilient moduli with distance from the geogrid location, the local stiffness enhancements provided by the two geogrid types were assigned to modulus profiles of a geogrid-stabilized aggregate base course in flexible pavement mechanistic analysis and modeling. The modeling results demonstrate the effect of geogrid base stabilization on the computed pavement resilient responses for both geogrid types. The sublayering approach which properly considers modeling of the geogrid influence zone could be effectively used in mechanistic analysis of a geogrid-stabilized pavement system. [ABSTRACT FROM AUTHOR]

Current endeavors are being made to develop substitute asphalt binders using different biomass sources for upcoming flexible pavement construction, propelled by sustainability and the escalating expenses of traditional petroleum-centered asphalt. The primary objective of this research is to explore the feasibility of employing activated carbon (ATC) produced from biowaste, specifically walnut shells and sawdust, as a modification for petroleum-based virgin asphalt binders through chemical, physical, and rheological assessments. A comprehensive array of evaluations was carried out, encompassing examinations of homogeneity, physical characteristics, Carbon, Hydrogen, Nitrogen, Sulphur, and Oxygen (CHNSO) analysis, proximate analysis, infrared spectroscopy, multiple stress creep and recovery (MSCR), rheological attributes, and temperature sweep. The CHNSO analysis provided the elemental composition and helped develop molecular formulas for ATC. The results show that binders modified with ATC exhibited a heightening carbon content proportionate to the AC ratio, analyzed at 5%, 10%, and 15%. Temperature sweep tests revealed that adding AC significantly increased binder stiffness in accordance with the complex modulus (G*) and phase angle (δ). This increased rigidity from the ATC modification declines the temperature susceptibility of the modified binders. [ABSTRACT FROM AUTHOR]

A new numerical simulation was developed to obtain various structural parameters by employing a nonlinear finite element method using ABAQUS: stress, strain, and the displacement response of five layers on the flexible pavement. The primary purpose of this study was to develop a new simulation that can accurately and effectively characterize stress and strain problems in flexible pavement. New constitutive model equations were developed based on Hooke's law the three-dimensional model for stress and strain. 40 kN wheel load was used to represent a set of dual tires, assuming a uniformly distributed contact area between the tire-pavement surfaced using linear viscoelastic and nonlinear viscoelastic materials. Four tire-inflation pressures were used 380, 490, 630, and 700 kPa. Results indicated that each flexible pavement layer created with a nonlinear viscoelastic material exhibited a 40% vertical plastic strain reduction compared to linear viscoelastic materials after 7000 s and repeated for 30,000 cyclic loadings. The implication of this newly developed constitutive model was verified against published experimental data. Analyses were completed to simplify the results model results considering the effects of stress and strain on flexible pavement layers. The newly developed constitutive model for solving stress and strain characterization problems can predict the effects on flexible pavement layers and various types of observed flexible pavement failure. [ABSTRACT FROM AUTHOR]

A prerequisite for the reliable design of low volume roads (LVRs) is the development of simple and reliable testing techniques to simulate the behavior of unbound granular materials (UGMs) under conditions similar to those that occur when subjected to traffic. Therefore, there is a need for a simple correlation method to characterize the mechanical behavior of UGM under the action of moving traffic loads. This paper discusses the results of the experimental study and statistical analysis on the resilient modulus (MR) characterization of UGMs through laboratory Dynamic Cone Penetration (DCP) test, this correlation is intended to be adopted in the of UGMs used in LVRs. The laboratory study was conducted on twenty-one UGMs samples to obtain index, strength, MR, and laboratory DCP-Dynamic Number (DN) parameters. The correlation has been achieved by correlating MR values compacted at 95% of Maximum Dry Density (MDD) with the laboratory DCP-DN values. The results show that MR values of UGMs significantly correlate with laboratory DCP-DN values and follow the power equation of M R = 700 × DN - 0.7 with coefficient of determination value of 0.99. Furthermore, a cyclic load triaxial test was carried out on UGMs to validate the result of the MR–DN. The MR–DN relationship estimates a reasonably resilient modulus of UGMs which can be used as an input into the mechanistic-empirical (M-E) pavement design analysis of LVRs in the absence of Repeated Load Triaxial (RLT) testing facilities. [ABSTRACT FROM AUTHOR]

This study investigates the effect of using steel slag in different layers of a flexible pavement structure on the permanent deformation performance and life cycle cost (LCC). Materials were obtained from a recent expressway pavement construction project. Physical and chemical properties of steel slag produced in Oman indicated that it can be used in the pavement layers. Results indicated that 100% of slag can be used in the base or subbase layers resulting in a CBR value of 212%. For wearing course (WC) and bituminous base course (BBC) layers, a 30% and 25% replacement of coarse aggregate was recommended based on Marshall mix design method. A finite element program was used to model the pavement sections. Rutting performance was determined based on the dynamic modulus |E*| results and mechanistic empirical pavement design guide (MEPDG) rut models. Rutting was not significantly different from the control section when steel slag was used in the base and/or subbase pavement structure. Rutting increased from 12.5 to 17.9 mm at the end of design life when slag was used in the WC layer. Further increase in rutting resulted when the steel slag was introduced in the BBC layer. LCC analysis based on 75 mm milling and overlay and zero slag cost indicated a reduction of 29.4% in cost when slag is used in both base and subbase layers. Steel slag in WC was recommended for lower volume roads with a higher target rut depth (16.5 mm), in which case LCC increased by 12% compared to the control section. [ABSTRACT FROM AUTHOR]

One of the main priorities of airport authorities is to maintain a high level of serviceability of runway pavements due to the high safety requirements for aircraft at high speeds. Accordingly, the assessment of the functional condition of airfield pavements is crucial for the proper operation of an airport. The most critical functional parameter appears to be pavement roughness. It characterizes the condition of the runway surface and is directly related to the safety of aircraft flights, as it affects the handling characteristics and braking performance of the aircraft, the increase in operating costs, and the wear of the aircraft. Worldwide, there are several indices for assessing the roughness of airfield pavements. This study aims to compare some of these indices to assess their ability to capture the characteristics of airfield pavement roughness. For this purpose, roughness data were collected along a runway with flexible pavement at a regional airport in southeast Europe and corresponding indices were estimated. The analysis of the data leads to the most efficient index for assessing the roughness of airfield surfaces to date. However, the need for a new index that expresses the response of the aircraft remains a critical issue. [ABSTRACT FROM AUTHOR]

This paper provides an evaluation of the numerical method for limiting the effect of spectral leakage on the frequency normalisation results of the pavement load and displacement functions which were induced with a dynamic impulse generated during FWD tests. The main part of the paper is concerned with the presentation of a method, which can be used to effectively reduce the effect of spectral leakage on the frequency normalisation of signals obtained through pavement testing with FWD. The method developed is supported by the observed differences between the results of the backcalculations carried out for the measurement results of the test section pavement deflections, which were subjected to frequency normalisation with and without spectral leakage reduction. The signals, where the proposed spectral leakage mitigation method was applied, were the only ones for which the identified values of the elastic modulus of the asphalt layer package model increase as the frequency increases, which agrees with the generally accepted relationship observed under laboratory conditions. [ABSTRACT FROM AUTHOR]

The depletion of high-quality natural resources such as soils and aggregates emphasize the necessity of incorporating alternative sustainable materials in road construction. Utilizing these waste materials not only addresses the challenge of their safe disposal but also contributes to sustainable road infrastructure development. The present work examined the potential of coal pond ash (Class F) modified with cementitious material like lime (L) and quarry dust (Q) in the subbase layer of flexible pavements. Through a series of tests including compaction, unconfined compression strength, durability assessment, and repeated load triaxial testing, it was determined that a mixture containing lime modified pond ash (70% P + 10% L) along with quarry dust of 20% exhibited the desired strength and durability characteristics required for subbase material in flexible pavement construction. Also, the proposed mixture demonstrated higher resilient modulus (MR) than the traditional subbase layer (GSB). Further, the performance of pavement structure with the proposed mix by using KENLAYER analysis showed service life ratio (SLR) values of 1.175 for fatigue and 1.143 for rutting criteria in compared with GSB. From these findings it is suggested that the proposed mix offers a viable and sustainable solution for the road applications. [ABSTRACT FROM AUTHOR]

This study establishes the state-of-the-art requirements verification process applied to compute the damage of flexible airfield pavement from new French rational method. Flexible pavement structures with platforms A, B, C, and D, recommended by International Civil Aviation Organization (ICAO), were modelled under static loading of bogies from heavy weight aircrafts A340, B777, and A380 using Cast3M 3D finite element modelling. From the results of these computations, it appears that these structures A, B, C, and D recommended by ICAO are not equivalent from the point of view of mechanical behaviour as claimed by the empirical method for the design of aeronautical bituminous pavements with abacus. The representation of the strain shapes was done with 3D and 2D profiles to improve the quality of response and to clearly identify the critical areas when an aircraft bogie is passing. The four- and six-wheels bogies of the aircraft A380 are more destructive to flexible pavements than the bogies of the other aircrafts tested in this study. The calculation of damage according to the new French rational method for aeronautical flexible pavements revealed that the main damage to these pavements is due to the fatigue of the bituminous layers and not the rutting of subgrade and the unbound granular material layers.

The mechanistic-empirical pavement design method (Pavement ME) uses linear-elastic analysis to calculate the strain responses induced by single and multiple axle loadings, and the method relies on the concept of equivalent or predominant loading frequency to determine the representative elastic modulus of the asphalt concrete (AC) layer. An investigation of the characteristics of multiple axle loading frequencies and the accuracy of predicting critical strains under both single and multiple axle loadings using the same frequency (e.g., Pavement ME) is presented. This paper compares the Pavement ME frequency with several other loading frequencies derived from single, tandem, and tridem axle loading scenarios in 12 cases with combinations of different AC layer thicknesses, moduli, and temperatures, as well as different vehicle speeds. The validity of these frequencies was determined by comparing the strain responses simulated by linear-elastic analysis using each of the frequencies with the results obtained from full dynamic viscoelastic analysis. The study showed that a lower loading frequency needs to be used for multiple axle configurations especially for AC layers with low to moderate stiffness if one wants to achieve a high accuracy of vertical stain prediction; the accuracy of maximum horizontal strains predicted by all loading frequencies is acceptable and is independent of axle configurations or frequency methods in general. [ABSTRACT FROM AUTHOR]

Stone-matrix asphalt (SMA) relies on stone-on-stone contact of coarse aggregate (CA) to generate a load carrying structure or an aggregate skeleton that minimizes flexible pavement rutting potential. Local CA may require relatively shorter distance hauling thereby making SMA more sustainable and cost-efficient but may have lesser quality characteristics than igneous aggregate. Hence, possible aggregate breakage must be quantified and addressed in the mix design. In this paper, SMA was designed using limestone, dolomite, and crushed gravel aggregates, which may result in relatively greater aggregate breakage. Fourteen SMAs were designed using different CA sources with various qualities. A methodology was proposed to measure aggregate breakage during compaction and rut testing of SMA by recovering the aggregates through extraction. An index was introduced and calibrated to quantify aggregate breakage. This allows assessing aggregate structure integrity during SMA production and paving. [ABSTRACT FROM AUTHOR]

Wide-base tires (WBTs) have been gradually adopted for trucks to improve fuel economy and driving comfort. This study aims to investigate the impact of WBTs on flexible pavement responses as compared to dual tires (DTs) coupling the effects of multiaxle and dynamic loading. A semi-analytical finite element model (SAFEM) was developed to simulate pavement responses under dynamic moving loads with high efficiency and good accuracy. The model was validated by comparing simulation results with field measurements from the instrumented section in the Long-Term Pavement Performance (LTPP) database. The influence of tire type, axle configuration, and pavement roughness was analyzed in terms of four critical pavement responses: longitudinal tensile strain at the bottom of asphalt layer, transverse tensile strain on pavement surface, near-surface shear strain, and compressive strain at the top of subgrade. The analysis results show that pavement responses induced by dynamic loads conform to normal distribution, and the variation of pavement responses increases linearly with that of dynamic loads. WBTs cause greater pavement damage than DTs in general. Among four pavement distresses, the highest damage ratio is observed for top-down cracking and the least one is for near-surface rutting. The damage ratios vary with axle configuration or speed rather than pavement surface roughness, especially for top-down cracking. The study emphasizes the impact of pavement roughness, tire type, and axle configuration on pavement responses. [ABSTRACT FROM AUTHOR]

The deterioration of the US transportation highway network and the onset of new technologies in the freight industry are expected to cause changes in the axle load magnitude and distribution, further exacerbating the reduction in the service life of flexible pavements. In this study, a reviewed framework to incorporate roughness-induced dynamic wheel loading into tire–pavement contact stress prediction is presented. The response to nonfree-rolling conditions, usually overlooked, was considered. State-of-the-art numerical models were used to account for pavement unevenness, vehicle dynamics, and 3D and nonuniform contact stresses. In this framework, for a given target international roughness index, an artificial multitrack roughness profile was converted into a dynamic loading profile based on the mechanical properties of a Class 9 vehicle. Upon discretization of the dynamic loading profile into a finite number of loads based on percentile distributions, a 3D finite element model of a dual-tire assembly was used to predict the contact stress distribution over a rigid surface. The performed numerical simulations allowed us to analytically quantify the variation of vertical and in-plane contact stress distribution. Hence, changes in the stress/strain field distribution and peak values under various axle loading scenarios were determined. The findings reveal that disregarding the effect of road roughness and vehicle maneuvering could result in considerable underestimation of the net forces and contact stress distribution developed at the tire–pavement interface. These considerations are particularly impactful on in-plane contact stresses, which, in turn, are associated with near-surface distresses. Practical Applications: The distribution of contact stresses at the tire–pavement interface influences the likelihood of failure near the surface and is greatly affected by driving behavior (braking, cornering, and acceleration). Truck electrification is likely to modify driving behavior due to the instant torque availability provided by electric powertrains, and the incorporation of battery packs is likely to alter the distribution of axle loading. The impact of these variables on the applied load to a pavement system could be further exacerbated by road conditions. In that regard, this paper aims to quantify the changes in the contact stress distribution when roughness, driving behavior, and axle loading are compounded. Because these considerations are not taken into account by current pavement analysis procedures, pavement engineers can use the results to assess the importance of each parameter on load characterization, a controlling variable on the prediction of pavement responses. [ABSTRACT FROM AUTHOR]

Freeze-thaw (F-T) cycles are a primary contributor of pavement damages in seasonal frost regions. Geosynthetics stabilization has been a promising solution for enhancing the roadways performance in cold regions. However, in comparison with the practical applications, research on the geosynthetics stabilization in cold-region roads is scarce and its efficacy is yet to be quantified. This study presents the full-scale test on geosynthetics-stabilized sections in a flexible pavement in Sturgeon County, Alberta. It focused on the investigation of three separate test sections with bases stabilized by two types of geocells and one geogrid composite, each fully instrumented with earth pressure cells, thermocouples, and moisture sensors. This experimental program consisted of plate loading tests and trafficking tests on each test section before and after the first F-T season, and monitoring of soil temperatures, moisture contents, and loads transferred to subbases while the sections were open to general traffic. The results showed seasonal F-T cycles resulted in increased pavement settlement, decreased load transfer ratio, and increased stress distribution angle under the plate loading. The traffic-induced stress on the subbases increased during the spring thaw but decreased afterwards. • Fully instrumented full-scale short-term tests on geosynthetics stabilized bases in pavements in cold regions. • Long-term monitoring of the geosynthetics-stabilized bases over the first seasonal freeze-thaw cycle. • The seasonal freeze and thaw resulted in increased settlement of pavement, decreased load transfer ratio under plate loading. • The traffic-induced stress on the subbases increased during the spring thaw but decreased afterwards. • 300-mm Type-C NPA geocell bases performed equivalently as the 350-mm geogrid bases throughout the first freeze-thaw season. • Type-C NPA geocell section gained the post-thaw recovery sooner than the geogrid composite section. [ABSTRACT FROM AUTHOR]

Bonding between asphalt layers is a crucial factor affecting the durability and mechanical response of flexible pavements. The effect of tack coat application on this bonding has been extensively studied, with several factors influencing the degree of bonding achieved. These include the type of tack coat, application rate, temperature, and moisture, among others. This study evaluated the effect of binder type and application rate on the interface shear strength of bituminous layers made of asphalt concrete type MDC-19, using theLaboratorio de Caminos de Barcelona (LCB) shear test. Two types of asphalt emulsions, CRL-1 and CRL-1hm (conventional and modified with polymers, respectively), were used as tack coats at five residual application rates. The results of the study showed that the CRL-1hm tack coat developed a higher shear strength than the CRL-1 tack coat. Additionally, there was a variation in strength with an increase in application rate, leading to the determination of an optimum rate. These findings demonstrate the importance of binder type and application rate in achieving optimal bonding between asphalt layers, with potential benefits for the longevity and performance of pavements. Overall, this research provides valuable insights for pavement engineers seeking to optimize the bonding between asphalt layers. The study highlights the potential of modified emulsions, such as CRL-1hm, and the importance of carefully considering the application rate to achieve the desired bonding performance. [ABSTRACT FROM AUTHOR]

In recent years the increased traffic, axle load, tire pressure, and hot weather have hastened the spread of rutting in flexible pavements. Recent research indicates that nanomaterials and crumb rubber considerably alter asphaltic mixture characteristics. This research aims to examine the impact of Nano Clay (NC) combined with Crumb Rubber (CR) on the Marshall characteristics and the rutting resistance of HMA. It involves determining the optimal asphalt content, by using the method of Marshall design, as well as the rutting depth for asphalt mixes with varying amounts of NC (1%, 3%, and 5%) and CR (10%, 20%, and 30%) as a percentage of the asphalt binder. The optimal content of asphalt was 4.93% for the control mix. The Marshall stability was enhanced by the inclusion of NC and CR, with the combination of 5% NC and 30% CR exhibiting the most significant increase of 20.9%. Marshall flow was decreased by adding NC and CR. The control mix had a Marshall flow of 3.30 mm, but when using 3% of NC and 30% of CR, the flow decreased to 2.88 mm, which was the greatest reduction. The ideal proportion of NC and CR was 5% and 30%, respectively. This resulted in a 40.85% reduction in rut depth compared to the control mixture. [ABSTRACT FROM AUTHOR]

In this study, inexpensive dual precursors namely rice husk ash (RHA) and quarry dust (QD) were mixed with an alkali solution (NaOH solution) in different mix proportions. Next, the effect of the dual precursors-alkali solutions (geopolymers) on the strength parameters of the different soil-geopolymer mixes subjected to various curing days were assessed. The result obtained from the assessment showed that the dual precursors-alkali solutions improved the strength properties of all the different soil-geopolymer mixes. The optimum soil-geopolymer mix proportion that resulted in the best improvement of the expansive subgrade soil properties was observed at a combination of 15%RHA+15%QD+3M NaOH. Furthermore, micro-pore analyses (porosity and pore size distribution), which were implemented with scanning electron micrographs and an image segmentation technique, local adaptive thresholding algorithm, showed progressive reduction in the porosity of the natural expansive subgrade soil and that of the optimal soil-geopolymer mix proportion cured for 7 and 28 days. [ABSTRACT FROM AUTHOR]

Utilizing waste materials in road construction has become a compelling alternative owing to the availability of high-quality natural aggregates and the challenges associated with disposing of industrial waste. This study delves into the potential of class F fly ash from coal combustion, which is not self-cementing, requiring additional activators for stabilization. Activators such as lime, ground granulated blast furnace slag (GGBS), and bottom ash were incorporated in diverse proportions. The experimental analysis included tests like modified Proctor compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), and repeated load triaxial tests. Results revealed that the introduction of 1–3% lime, 3–21% ground granulated blast furnace slag, and 10–30% bottom ash, combined with extended curing durations, augmented both compressive strength and California bearing ratio values. The resilient modulus of these mixtures showed an improvement of roughly 70% compared to traditional Wet Mix Macadam. Advanced microscopic studies using X-Ray diffraction (XRD), field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA) identified the formation of calcium silicate hydrates and ettringite as contributing factors to the increased strength. The optimally formulated mixtures met the requirements outlined by the Indian Roads Congress, suggesting their suitability for inclusion in base, subbase courses of flexible pavements, and the dry lean concrete layer of rigid pavements. [ABSTRACT FROM AUTHOR]

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