Asphalt Concrete Thickness Research Articles

Temperature Distribution in Asphalt Concrete Layers: Impact of Thickness and Cement-Treated Bases with Different Aggregate Sizes and Crumb Rubber

The temperature estimation within asphalt concrete (AC) overlaid on cement-stabilized bases (CSB) is necessary for pavement analysis and design. However, the impact of different CSB gradations and rubberized CSB on AC temperature has not been thoroughly investigated. This study aims to clarify this effect by examining two types of CSB with nominal particle aggregate sizes of 25 mm and 31.5 mm, as well as the substitution of 5%, 10%, and 20% graded aggregates with rubber aggregates (RA) in CSB Dmax 25 using Ansys-based numerical simulations. The modelling also investigated 11 scenarios with different AC thicknesses (hAC) ranging from 6 to 26 cm. The results indicated that CSB Dmax 31.5 reduced the daily maximum temperature fluctuation at the bottom of the AC (∆TbottomAC) by approximately 8% compared to CSB Dmax 25. The inclusion of 5% RA in CSB Dmax 25 decreased ∆TbottomAC by up to 20%. Additionally, the rubberized CSB increased the maximum temperature gradient between the top and bottom of the AC (ΔTmaxAC) by 9.5% with 5% RA and a 6 cm AC thickness; however, this increase was insignificant when hAC exceeded 12 cm. This study also proposed the use of artificial neural network (ANN) models to predict the AC’s temperature distribution based on depth, the time of day, surface paving temperatures, and hAC. The proposed ANN model demonstrated high accuracy (R2 = 0.996 and MSE = 0.000685),which was confirmed by the numerical simulations, with an acceptable RMSE ranging from 0.28 °C to 0.67 °C.

Investigation of The Effect of Asphalt Layer and Sub-Base Layer Thicknesses on Pavement Surface Deformation by The Finite Element Method

The layer thickness of flexible pavements is one of the important parameters affecting permanent deformations. In this study, the effect of sub-base thickness and asphalt concrete thickness on the deformations under axial loads was investigated using the Plaxis 2D finite element software. In the study, 100, 200, 300, 400, 500, and 600 kPa pressure were applied to the asphalt pavement surface. In the first case, the base layer of 30 cm thickness was kept constant, and the asphalt layer was changed from 9 to 14 cm. In the second case, the asphalt thickness at 9 cm and the base layer thickness of 30 cm were kept constant, and the sub-base layer thickness was selected at 30, 40, and 50 cm. As a result of the completed analysis, it was observed that the deformations on the pavement surface decreased with increasing thickness of the layers; furthermore, the use of a sub-base layer in the pavement considerably increases the deformation resistance.

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.

Reflective crack initiation of asphalt overlays on jointed concrete pavement using finite element model

ABSTRACT In this study, a three-dimensional (3D) finite element model (FEM) consisting of an asphalt concrete (AC) overlay on top of jointed plain Portland cement concrete (PCC) slabs was developed to investigate the mechanism of the crack initiation of traffic-induced reflective cracking. Strain values at the bottom of AC overlay were the primary response obtained from the simulation results to represent the damage induced in the AC layer. Different bonding situations between the two layers, traffic load locations, material properties and thicknesses of the AC layer were taken into consideration. The analysis results show that the dominating strain for damage is dependent on the bonding condition between the AC and PCC layers. When the AC layer is completely bonded with the PCC layer, the damage will initiate firstly at the top of the joint corner between the PCC slabs to deteriorate the bonding, then the AC bottom will be susceptible to bending strain. It was observed that the most critical load location for modeling the case of fully bonded overlays is related to the AC thickness while in the case of partially bonded overlays, the most critical load location is always located on the top of one side of the PCC joint.

Investigation of the Fatigue Life of Bottom-Up Cracking in Asphalt Concrete Pavements

Traditionally, fatigue cracking in asphalt pavement means fatigue failure, which is the basis for controlling the design thickness of asphalt pavements. In fact, the fatigue failure of asphalt pavements includes three stages: fatigue cracking, crack expansion, and structural failure. Therefore, this paper aims to investigate the fatigue life of the bottom-up cracking of asphalt concrete (AC) pavements considering the different stages of fatigue failure. The dynamic modulus of AC of different grades was experimentally determined. The tensile stresses at the bottom of the AC layer were evaluated by embedding the tested dynamic modulus into a numerical simulation, which can be used to calculate the fatigue cracking life. Then, overlay tests (OTs) at different temperatures were conducted to obtain the fracture parameters A and n from the asphalt mixture. The crack propagation life was calculated via the Paris formula based on the fracture parameters A and n. The analysis results showed that an increase in AC thickness could effectively improve the fatigue crack life of the pavement structure, and the proportion of crack propagation life to fatigue crack life at different temperatures varied significantly. Therefore, when analyzing and calculating the fatigue life of pavement structures, besides the fatigue cracking life, the crack propagation life after cracking should also be considered, which is very important for accurately calculating the entire fatigue life of asphalt pavement structures. This will offer guidance for asphalt pavement thickness design.

Determining pavement structural number with traffic speed deflectometer measurements

Traffic Speed Deflectometer (TSD) overcomes the slow operating speed of the conventional Falling Weight Deflectometer (FWD), but it also introduces new difficulties in estimating the effective structural number (SN) of existing pavements. Due to the different loading mechanisms of TSD and FWD, the FWD-based SN calculation procedure proposed in the AASHTO Pavement Design Guide is incompatible with TSD measurements. To match the existing FWD-based SN records, the authors proposed a new approach to determine the SN with TSD measurements by modifying the AASHTO method. Simulation results show that the difference in AASHTO SN between TSD and FWD essentially came from the difference in the equivalent loading frequency. The asphalt concrete (AC) layer exhibited lower stiffness under TSD than under FWD. The TSD-based AASHTO SN was generally smaller than the FWD-based AASHTO SN (error of 0.74), and the deviation increased with increasing AC thickness. Therefore, an enhanced AASHTO method was proposed for calibrating TSD-based SN by the AC thickness, which made great progress in estimating SN from TSD deflections with an error of 0.17. The proposed method was verified by filed TSD and FWD measurements and was recommended for pavements with AC thickness greater than 4 in..

Impact of the Great Flood of 2016 on the Asphaltic Concrete Road Infrastructure in Louisiana

Extreme weather events, including inundation, are the major causes of weather-related disruption to the transportation sector. Considerable research has been conducted in recent years to evaluate the impacts of inundation on pavement functional and structural conditions. Yet, limited studies quantified how inundation may affect the long-term pavement performance and pavement life-cycle costs. As such, the main objective of this study was to quantify the impact of the 2016 inundation event in Louisiana, U.S., on the long-term pavement performance (in relation to reduction in the pavement service life [PSL]) and on pavement life-cycle costs. To achieve this objective, a total of 10 inundated pavement sections were evaluated. Pavement conditions, fatigue, and rutting indices for these sections were analyzed over a monitoring period of up to 15 years (11 years before and 4 years after inundation). Results indicated that the 2016 inundation event reduced the PSL of the inundated sections to an extent that depended on their pre-flooding pavement condition, traffic level, and asphalt concrete thickness. This reduction was attributed to the accelerated fatigue, rutting damage, or both, that resulted from prolonged water submergence and heavy traffic loading during debris hauling that took place after the inundation event. A logistic regression model with adequate accuracy was developed to predict whether an inundated pavement would experience reduction in its PSL based on the project conditions. The study findings were incorporated into a simple tool to assist transportation agencies make effective decisions for the maintenance and rehabilitation of inundated pavements.

ТЕРМОПРУЖНІ ДЕФОРМАЦІЇ АСФАЛЬТОБЕТОННОГО ШАРУ НА МЕТАЛЕВІЙ ПЛИТІ МОСТА ПРИ ЗМІНІ ТОВЩИНИ АСФАЛЬТОБЕТОНУ

Based on the theory of thermoelasticity, the problem of the thermally stressed state of a two-layer fragment of a bridge structure, consisting of a metal base and an asphalt concrete upper layer, is considered under conditions of changing ambient temperature at different values of the asphalt concrete thickness. It is believed that the materials of the layers are characterized by different thermomechanical parameters, which determine the inhomogeneity of the stress and strain fields. It has been established by computer modeling that these factors lead to the concentration of stresses and strains and a change in the stress-strain state of the bridge structure of the driving deck, which is not taken into account in modern practice of designing and operating bridges, and is one of the causes of premature destruction of the asphalt concrete pavement of the road bridge. To eliminate these shortcomings, on the basis of finite element algorithms, a theoretical analysis of the thermally stressed state of a metal orthotropic slab with an asphalt concrete pavement was performed at different ratios of their thicknesses. It is shown that a decrease in the thickness of the upper layer can lead to an increase in the contact and normal tensile stresses initiated in it. Therefore, when designing bridge structures, these features should be taken into account additionally. KEYWORDS: BRIDGE STRUCTURE, ASPHALT-CONCRETE COATING, ORTHOTROPIC PLATE, TRACKED TRACKS, TRANSPORT LOADS, STRESS FIELD, THERMO ELASTIC STATE.

Mechanistic Responses of Asphalt Concrete Overlay Over Jointed Plain Concrete Pavement Using Finite Element Method

This study focused on the development of a three-dimensional Finite Element Model of an asphalt concrete overlaid on a jointed plain concrete pavement to assess the mechanical behaviour of the pavement under traffic load. The objective of this study was to determine the influence of different asphalt concrete thickness, asphalt concrete modulus, the interface bond between the asphalt concrete and the Portland cement concrete layer, Portland cement concrete modulus, and joint width on the tensile strain at the bottom of the asphalt overlay. The results showed that changes in the pavement parameters result in a large range of variations on the magnitude of pavement responses. The magnitude of the longitudinal tensile strain at the bottom of the overlay varied between 25 με and 460 με. Asphalt concrete thickness, interface contact condition, and asphalt concrete modulus parameters had the most influence on the pavement responses. The interface bonding condition was significant, regardless of the thickness of the surface layer.

Full-Scale Evaluation of Relatively Thin Airfield Pavements

A full-scale airfield pavement test section was constructed and trafficked by the U.S. Army Engineer Research and Development Center (ERDC) to evaluate the performance of relatively thin airfield pavement structures. The test section consisted of four test items that included three asphalt pavement thicknesses and two different aggregate base courses. The test items were subjected to simulated aircraft traffic to evaluate their response and performance to realistic aircraft loads. Rutting behavior, instrumentation response, and falling weight deflectometer response were monitored at selected traffic intervals. It was found that the performance of the airfield pavement sections were most sensitive to aggregate base course properties, where a 50% reduction in base course strength resulted in a 99% reduction in allowable passes. The data suggested that when sufficient asphalt thickness is not provided, the failure mechanism shifted from subgrade failure to base course failure, particularly at higher subgrade CBR values. In addition, the number of aircraft passes sustained was less than that predicted by current Department of Defense (DOD) methods that include assumptions of a high-quality aggregate base and a minimum asphalt concrete thickness. The results of this study were used to extend existing DOD pavement design and evaluation techniques to include the evaluation of airfield pavement sections that do not meet the current criteria for aggregate base quality and minimum asphalt concrete surface thickness. These performance data were used to develop a new base failure design curve using existing stress-based design criteria.

Optimal Structure Combination for Inverted Asphalt Pavement Incorporating Cracks in Cement-Treated Subbase

The structure design and mechanistic calculation of inverted asphalt pavements are mainly based on linear layer elastic theory with the assumption that the cement-treated subbase (CTB) is complete without cracks. This study investigates the optimal structure combination for inverted pavements according to calculated critical responses considering cracks in the CTB layer. A three-dimensional finite element (3D FE) model of inverted pavement with a transverse crack through the CTB layer was developed. Four full-scale inverted pavement sections were built, and a crack 0.01 m wide and 0.05 m deep was sawn on top of each CTB layer after construction. The 3D FE model was validated by strain and deformation measured in falling weight deflectometer tests and used for a parametric study of dominating structure combination factors. Variance analysis results show that interactions with thickness or stiffness of the asphalt concrete (AC) layer presented the most significant effect on critical responses, while CTB stiffness (12588~7668 MPa) had the least impact. Structure variation effect analysis results illustrated that 0.1 m aggregate base (AB) thickness is enough to prevent the CTB crack propagating to the surface. Thin AC structures are highly sensitive to variations in AC and AB stiffness. A thin AC and AB combination (0.05 and 0.10 m) can provide low critical strains similar to a thick AC and thin AB (0.15 and 0.10 m) combination if the stiffness of AC and AB can be maintained at 7175 and 358 Mpa, respectively, or higher. AC thickness of 0.1 m and the combination of thin AC and thick AB are two unfavorable conditions for inverted pavements.

Evaluation of top-down crack propagation in asphalt pavement under dual tire loading

Top-down cracking (TDC) has been recognized worldwide and is regarded as a major type of asphalt pavement distress. In this study, fracture mechanisms behind the TDC propagation and fatigue life of pavements were investigated under dual tire loads using finite element (FE) analysis. By considering the most influencing factors on TDC propagation, stress intensity factors (SIF), including KI and KII, were calculated at critical transverse locations. According to Modes I and II SIF, a greater SIF indicates a faster rate of TDC propagation. The SIF results indicated that considering temperature gradient in asphalt concrete (AC) layer is necessary in determination of critical SIF, and KI and KII are not distributed uniformly within the AC depth. In addition, TDC growth rate significantly depends on AC thickness and base layer type. Finally, the number of load repetitions for TDC propagation rate at different transverse locations is predicted based on Paris’ law equation.

Real-Time Density and Thickness Estimation of Thin Asphalt Pavement Overlay During Compaction Using Ground Penetrating Radar Data

Achieving desired density is crucial for thin asphalt concrete (AC) overlay construction quality control and quality assurance purposes. Ground penetrating radar (GPR) can be implemented for AC pavement layer thickness and density prediction during compaction. However, the overlapping of GPR reflections from surface and bottom of the thin AC overlay, as well as the presence of surface moisture, jeopardizes the prediction accuracy. In this study, a pavement model with thin AC overlay was simulated using gprMax, a finite-difference time-domain-based tool. Surface moisture was simulated as a 2-mm film with mixed electrical properties of water and AC. A nonlinear optimization method was used to address the overlapping and surface moisture issues simultaneously. The error of the thin AC overlay dielectric constant and thickness prediction results was less than 7% and 10%, respectively. Field test during thin overlay compaction was also performed to validate the proposed method. The AC overlay thickness and density estimation accuracies were 91% and 99%, respectively.

Continuous real-time monitoring of flexible pavement layer density and thickness using ground penetrating radar

Static or discrete time prediction of flexible pavement asphalt concrete (AC) layer density and thickness utilizing the ground penetrating radar (GPR) has proved to be relatively accurate compared to other in-situ methods. However, the accuracy during continuous monitoring of construction has not been validated by real construction projects. This study investigated the continuous estimation of AC layer density and thickness using GPR at a construction site in Macomb, Illinois. The first test compared AC layer density and thickness for pavement segments built in two consecutive days. The second test evaluated the construction quality of pavement segments built utilizing two types of material transfer vehicles (MTV). The GPRan software and the proposed truncation algorithm were used to calculate AC layer thickness continuously. The AC layer density and thickness estimation results were compared to core data using the ALL model. The GPR estimation values were found to be reliable. Errors of thickness results between continuous GPR data and core data from two tests are approximate 3% and 6%, respectively. The density of the new pavement segments was larger than the old ones while the thickness was almost the same. The average error between continuous density predictions and core density was 3%. The two MTVs performed similarly based on layer thickness and density results.

Adaptation Planning to Mitigate Coastal-Road Pavement Damage from Groundwater Rise Caused by Sea-Level Rise

Sea level in coastal New England is projected to rise 3.9–6.6 ft (1.2–2.0 m) by the year 2100. Many climate-change vulnerability and adaptation studies have investigated surface-water flooding from sea-level rise (SLR) on coastal-road infrastructure, but few have focused on rising groundwater. Groundwater modeling in New Hampshire’s Seacoast Region has shown that SLR-induced groundwater rise will occur three to four times farther inland than surface-water flooding, potentially impacting 23% of the region’s roads. Pavement service-life has been shown to decrease when the unbound layers become saturated. In areas where groundwater is projected to rise with SLR, pavements with groundwater 5.0 ft (1.5 m) deep or less are at risk of premature failure as groundwater moves into the pavement’s underlying unbound layers. In this study, groundwater hydrology and multi-layer elastic pavement analysis were used to identify two case-study sites in coastal New Hampshire that are predicted to experience pavement service-life reduction caused by SLR-induced groundwater rise. Various pavement structures were evaluated to determine adaptation feasibility and costs to maintain the designed service-life in the face of rising groundwater. This investigation shows that relatively simple pavement structural modifications to the base and asphalt concrete (AC) layers of a regional corridor can eliminate the 80% to 90% service-life reduction projected with 1.0 ft SLR (year 2030) and will delay pavement inundation by 20 years. Pavements with adequate base-layer materials and thickness require only AC thickness modification to avoid premature pavement failure from SLR-induced groundwater rise.

Development of a simple asphalt concrete overlay design scheme based on mechanistic–empirical approach

This study proposes a simple regression model for asphalt concrete (AC) overlay thickness design to be used in urban roads of Seoul city. A synthetic database for AC thickness design was generated using the Mechanistic–empirical pavement design guide. Multiple regression analysis was conducted to develop the AC overlay design model, which is a function of the total AC thickness, thickness ratio of AC overlay and existing layer, modulus ratio of old and new AC, subgrade condition, and traffic volume. The regression model was verified by comparing the predicted and measured annual average daily truck traffic (AADTT) and AC overlay thickness. It was found that the regression model has a correlation coefficient of .97 in determining AADTT. It was further validated using actual field performance data in which it has a correlation coefficient of .83 for AADTT prediction. It is observed from the validation study that the regression model is capable of predicting the AC overlay thickness within a reasonable level of accuracy.

Adaptation of NCHRP Project 1-41 Reflection Cracking Models for Semirigid Pavement Design in AASHTOWare Pavement ME Design

Semirigid pavements are composite pavements that comprise a surface asphalt concrete (AC) layer overlying a cement stabilized base, granular subbase, and subgrade foundation. When subjected to traffic and climate loading, semirigid pavements provide good performance through resistance to rutting or deformation of base and subgrade, moisture damage, and AC fatigue. However, semirigid pavements can develop fatigue and transverse shrinkage cracks in the underlying cement stabilized base layer, which ultimately propagates through the surface AC thickness with repeated applications of axle loads and temperature cycles (i.e., reflection cracking). Although new semirigid pavements have been designed and constructed in the United States since the 1960s, a new semirigid pavement design methodology was not included in Version 1.0 of AASHTOWare Pavement ME Design software. This methodology was omitted because developers and researchers at that time concluded that there were no suitable existing mechanistic-based fatigue or transverse reflection cracking models available to be adapted and included in the design procedure. Under NCHRP Project 1-41—Models for Predicting Reflection Cracking of Hot-Mix Asphalt Overlays, mechanistic-based AC fatigue and transverse reflection cracking models were developed. The models were developed to be compatible and thus easily adaptable into the AASHTOWare Pavement ME Design framework. Work done to adapt the NCHRP Project 1-41 reflection cracking models for the design of new semirigid pavement in AASHTOWare Pavement ME Design is presented.

Multi-scale computational model for design of flexible pavement – part I: expanding multi-scaling

A computational multi-scale procedure for designing flexible pavement is developed in this, the first of a three part series. In this paper, computational analyses are performed on sequentially larger length scales, termed expanding multi-scaling. The model is constructed by the finite element method at each length scale, thereby creating a one-way coupled multi-scale algorithm that is capable of accounting for the effects of variations in design parameters at each length scale on the performance of flexible pavements. For example, the algorithm can be utilised to predict the effects of small-scale design variables such as volume fractions of additives, fines and aggregate, as well as the effects of large-scale design variables such as asphalt concrete thickness and degree of base layer compaction on rutting due to cyclic loading. The computational procedure is briefly herein, including the experimental properties required to deploy the computational scheme for the purpose of pavement design. The paper concludes with several demonstrative examples intended to elucidate the power of this predictive technology for the purpose of designing more sustainable pavements.

Multi-scale computational model for design of flexible pavement – part II: contracting multi-scaling

A computational multi-scale procedure for designing flexible pavements is developed in this, the second of a three-part series. In this study, computational analyses are performed on sequentially smaller length scales, termed contracting multi-scaling. The model is constructed by utilising the finite element method on each length scale, thereby creating a one-way coupled multi-scale algorithm that is capable of accounting for the effects of cyclic loading on the initiation and evolution of cracks on multiple length scales within the roadway. For example, the algorithm can be utilised to predict the effects of small-scale design variables such as aggregate volume fraction, as well as the effects of large scale design variables such as asphalt concrete thickness on pavement cracking due to external loading. The model for predicting roadway cracking is briefly described herein, including the experimental properties required to deploy the cracking model within a computational framework. The article concludes with demonstrative examples intended to elucidate the power of this predictive technology for the purpose of designing more sustainable roadways.

Numerical Analysis of Concrete Block Pavements and Comparison of its Settlement with Asphalt Concrete Pavements using Finite Element Method

Regarding time consuming properties and complex intervention of layers and different materials, it is better to replace laboratory based design and analysis of pavements with quick and powerful software including finite element, finite reduction software and etc. Using finite element software ABAQUS, at first, the paper investigated effects of changes of concrete block thickness in vertical stress and it was validated with experimental results. Also, using this software, effect of asphalt concrete thickness change was studied in vertical strain. And finally, results of finite element model were validated, using experimental data. Regarding that finite element analysis is suitable for crust environments and concrete block pavement does not have such environment, this research tends to compare these two types of pavements, using mathematical equations to analyze settlement. To do this, first, two models were analyzed, one for concrete block pavement and the other one for asphalt concrete pavement. Subgrade and base layers' models were the same in geometrical point of view and types of materials, but thickness of asphalt and concrete block pavement layers and bedding sand changed, alternatively and based on the obtained relations and diagrams, there has been a chance to equate indices of these two types of pavements.