Hot-mix Asphalt Thickness Research Articles

Climate change adaptation strategies for Canadian asphalt pavements; Part 2: Life cycle assessment and life cycle cost analysis

Presently, there is strong consensus that significant temperature and weather changes are fast approaching as a result of climate change. Pavements will be significantly affected by increased temperatures, precipitation, and flooding, and will require present design methodology to be modified accordingly. Several climate change adaptation strategies are easily available to agencies including upgraded asphalt binder grades, increased Hot Mix Asphalt (HMA) thickness, modified mix gradations, and stabilized base. The objective of this study is to investigate Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) for climate change adaptation strategies across various locations in Canada, from a Global Warming Potential (GWP) perspective. All analysis was completed leveraging the Athena Pavement LCA software and the LTPP database. The investigated scenarios were (i) a baseline asphalt pavement with no climate change, (ii) a baseline asphalt pavement with climate change, and (iii) an asphalt pavement adapted to withstand climate change, appropriate to the level of changes experienced by the specific location. The study revealed that although there are initial increases in both cost and emission to administer these adaptation strategies, they are offset over the life of the pavements. Increasing the HMA thickness and using stabilized bases were the most expensive and the highest emitting among the investigated strategies, but they are only necessary for extreme coastal climate change regions including British Columbia and Newfoundland. British Columbia is expected to observe a near 30% increase in agency costs to effectively adapt their pavements to climate change. However, these initiatives were found to decrease the overall global warming potential by nearly 10% in comparison to not adapting. The other examined locations, although not returning as drastic of changes, followed similar trends. The conclusions find that climate change adaptation strategies are highly beneficial from the standpoint of both an LCA and LCCA for all of the investigated locations.

Performance evaluation of geosynthetic reinforced flexible pavement: a review of full-scale field studies

Many experimental studies have shown that geosynthetic reinforcement of flexible pavement can be beneficial in terms of extending their service life and decreasing the required structural number of the pavement. Although numerous researches have performed experimental and numerical studies to evaluate the benefits of these reinforcements, comprehensive comparisons are lacking among the different investigations. This paper reviews typical field experimental studies on geosynthetic reinforcement of flexible pavement performed by various investigators. Researchers have found that the main appreciable improvement of geosynthetics reinforcement depends on various factors such as subgrade stiffness, base aggregate thickness and quality, hot mix asphalt thickness and quality, geogrid stiffness/location and so on. The granular equivalent (G.E.) factor was determined based on the results of the falling weight deflectometer (FWD) and the results of the unreinforced and reinforced section were compared to obtain the G.E. factors based on mentioned factors of reinforcements. Then, a unique formula is presented in this study, according to the performed comparison of the results. Although more investigations are needed to develop the presented method and general corrections, the results of this study can be used by the designers to evaluate the geosynthetic reinforcement of flexible pavements in their designs as well.

Accelerated Pavement Testing of Perpetual Pavement Test Sections under Heavy Aircraft Loading at FAA’s National Airport Pavement Test Facility

Abstract Six flexible pavements were constructed for construction cycle 7 (CC7) at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility in Atlantic City, New Jersey. Four test sections on the north side measure 200 mm (LFP-4), 250 mm (LFP-3), 300 mm (LFP-2), and 375 mm (LFP-1) that are made of hot mix asphalt (HMA) over an aggregate subbase (thickness varying between 850 and 1,025 mm) resting on a subgrade with a California bearing ratio of 5.5. The fifth test section, LFC-5, is conventional flexible pavement with 125 mm of HMA over aggregate base and subbase, and the LFC-6 structure is the same as LFC-5 except that the crushed stone base layer is replaced with asphalt-stabilized drainable base. The objective of CC7 tests is to develop perpetual pavement design criterion and to validate or refine the fatigue model for HMA in airport pavement thickness design software FAARFIELD. The HMA fatigue model is based on the ratio of dissipated energy change (RDEC). Four fiber optic strain plates were installed to measure transverse and vertical strains at top and transverse strains at bottom within the HMA layer. Full-scale accelerated pavement tests were performed. Traffic test load parameters were six-wheel gear, 245-kN wheel load (gear load 1,470 kN), and 4-kmph speed. Pavement performance was monitored using crack maps, straight edge rut depth, and surface profile measurements. LFC-5 and LFP-4 showed significant fatigue cracks and rutting. LFP-1 and LFP-2 performed well with no signs of cracking. This article presents a discussion on the RDEC fatigue model, pavement thickness design, pavement material characterization test results, pavement instrumentation, accelerated pavement tests under heavy aircraft gear loads, and pavement responses measured using embedded sensors. The test section performance shows that, under loading conditions used in the study, by increasing HMA thickness from 25.4 to 30.5 cm, fatigue cracking was eliminated for the duration of testing (38,000 passes).

A Framework for Introducing Climate-Change Adaptation in Pavement Management

Greenhouse gas emissions have caused global temperatures to rise since the mid-20th century accompanied by sea-level rise (SLR). Temperature increases and SLR-induced groundwater rise have been shown to cause premature pavement failure in many roadway structures. Hybrid bottom-up/top-down (hybrid) adaptation approaches have shown promise by initially investigating an asset’s response to incremental environmental change and then identifying the timing of critical effects for budgetary planning. This improves practitioners’ understanding of the asset’s climate resiliency and informs adaptation-plan development to minimize both cost and risk. In this study, a hybrid approach to pavement adaptation with climate-change-induced temperature and groundwater rise is demonstrated at a case-study site in coastal New Hampshire. The hot-mix-asphalt (HMA) thickness that achieves a minimum of 85% reliability is calculated for 70 combinations of incremental temperature and groundwater rise. Increasing the base-layer thickness improves resiliency against rising temperatures, but rising groundwater diminishes this improvement demonstrating that both HMA and base-layer thickness increases are needed. Thirteen adaptation pathways are evaluated for pavement performance, life-cycle costs, and road-surface inundation over a 60-year pavement management period. A stepwise and flexible adaptation plan is developed that includes HMA overlays with prescribed thickness and application timing, base-layer rehabilitation options, and re-evaluation opportunities.

Effect of Pavement Structure on the Mechanical Response and Performance of Perpetual Pavements at the National Airport Pavement Test Facility

Construction Cycle 7 (CC7) conducted at the FAA National Airport Pavement Test Facility (NAPTF) was aimed to study the effect of hot mix asphalt (HMA) layer thickness and develop perpetual pavement design criterion for airfield flexible pavements. Four fully instrumented perpetual test pavements were designed, constructed, and tested, with all test items trafficked under heavy aircraft loads using a three duals in tandem configuration. Pavement condition was monitored using heavy weight deflectometer tests, distress surveys, and surface profiles. Comprehensive response data analysis revealed that increasing HMA layer thickness significantly reduced the tensile strain at the bottom of the HMA layer, permanent deformation in the unbound layer, and vertical stress at top of the subgrade. Thicker HMA test items exhibited better rutting performance, as evidenced in both multiple depth deflectometer and surface profile data. The interaction between HMA layer temperature and thickness was captured in the pressure cell responses. More tests are planned to determine the threshold HMA strain to prevent fatigue cracking.

Flexural properties of chemically stabilised subgrade in designing semi-rigid pavements

Although flexural fatigue cracking of chemically-stabilised subgrade (CSS) layers is a major distress in semi-rigid pavements, the fatigue model of the CSS layer in the Mechanistic-Empirical Pavement Design Guide (M-EPDG) has not been calibrated. Design of semi-rigid pavements with regard to flexural fatigue life of the CSS layer was conducted using the M-EPDG method. Cylindrical and beam specimens of a lean clay, mixed with different types (cement kiln dust (CKD) and lime) and amounts of additives were prepared in the laboratory. Resilient modulus, modulus of rupture (MoR), flexural modulus and four-point flexural fatigue (FPFF) beam tests were conducted. Also, finite element (FE) models of different pavement sections having different thicknesses of hot mix asphalt (HMA) and different materials and thicknesses of CSS layer under traffic load were developed. The minimum required thickness of the HMA layer to avoid fatigue failure in the CSS layer was determined for different sections using the laboratory test results and the FE analyses. Finally, the effect of considering the flexural properties and fatigue life of the CSS layer on the designed HMA layer thickness was evaluated. The results showed that for the CSS materials with relatively low laboratory fatigue lives, the fatigue cracking of the CSS layer contained the most critical distress to be considered in designing the pavement structure. It was also found that by substituting the CSS resilient modulus with the properly-determined flexural modulus in the mechanistic-empirical design procedure, the designed HMA thickness, and, consequently, the construction cost could decrease significantly.

Building information modeling utilization for optimizing milling quantity and hot mix asphalt pavement overlay quality

An approach to a practice paving technique using building information modeling (BIM) was developed. When planning hot mix asphalt (HMA) overlay on a concrete slab, in-advance paving simulations can help to preemptively evaluate pavement quality, such as HMA thickness, and prevent excessive HMA quantity. The BIM technique has the capabilities of ‘in-advance simulation’, ‘3-D visualization’, ‘interference identification’, and ‘quantification’. Building information modeling could be successfully implemented to optimize milling quantity and improve HMA pavement quality in an actual paving project. Based on the established BIM model, alternative paving levels were derived and paving sequences were simulated. Through 3-D visualized images, locations where HMA thickness was inadequate could be effectively identified. Quantified information for simulation results enabled optimization of milling and paving options. Milling was selectively conducted for the identified undulations. The cost was reduced by approximately 12%. Paving thickness and density had coefficients of variation (CV) of approximately 15% and 0.2%, respectively.

Bonded concrete overlay of asphalt mechanical-empirical design procedure

Bonded concrete overlays of asphalt pavements (BCOAs) are becoming a common rehabilitation technique used for distressed hot mix asphalt (HMA) roadways. The original design procedures were based primarily on data from instrumented pavements and finite element modelling. They were governed by the assumption that the failure mechanism was a function of the overlay thickness. However, field observations have indicated that the actual failure modes are dictated by slab size. The newly developed Bonded Concrete Overlay of Asphalt Mechanistic-Empirical design procedure (BCOA-ME) presented here is valid for overlays that are between 2.5 and 6.5 in (64–154 mm), and includes five primary enhancements to the Portland Cement Association and Colorado Department of Transportation procedures that have been traditionally used: 1.) the failure mode is dictated by the joint spacing; 2.) a new structural model for longitudinal cracking for 6-ft × 6-ft (1.8 m × 1.8 m) concrete overlays has been developed to better predict the critical stresses; 3.) the stress adjustment factors have been calibrated with performance data; 4.) the equivalent temperature gradients used as design input are defined based on the pavement structure and geographical location of the project; and 5.) the effect of temperature change on underlying HMA stiffness is considered. Finally, validation studies were completed on the new procedure and comparisons made between the revised procedure and actual performance data for five separate projects showed reasonable results. A sensitivity analysis also revealed that the predicted thickness obtained using the revised procedure was sensitive to HMA thickness, the modulus of rupture of the Portland cement concrete, and the level of traffic, as would be expected.

Global Sensitivity Analysis of Mechanistic–Empirical Performance Predictions for Flexible Pavements

The new AASHTO Mechanistic–Empirical Pavement Design Guide (MEPDG) provides pavement analysis and performance predictions for various feasible design scenarios. The MEPDG performance predictions for the anticipated climatic and traffic conditions depends on the values of the input parameters that characterize the pavement materials layers, design features, and condition. This paper focuses on comprehensive global sensitivity analyses of flexible pavement performance predictions to MEPDG design inputs under five climatic conditions and three traffic levels. Design inputs evaluated in the analyses include traffic volume, layer thicknesses, material properties, and groundwater depth. Correlations between design inputs were considered as appropriate. The global sensitivity analysis varied all inputs simultaneously across the problem domain for each of the 15 base cases (five climates and three traffic levels). Two response surface modeling approaches—multivariate linear regressions and artificial neural networks—were developed for modeling the analysis results for evaluation of MEPDG input sensitivities across the problem domain. The response surface modeling approaches based on artificial neural networks were particularly effective in providing robust and accurate representations of the complex relationships between MEPDG inputs and distress outputs. The design limit normalized sensitivity index adopted in the study provided a practical interpretation of sensitivity by relating a given percentage change in an MEPDG input to the corresponding percentage change in predicted distress relative to its design limit value. The design inputs most consistently in the highest sensitivity categories across all distresses were the hot-mix asphalt dynamic modulus master curve, hot-mix asphalt thickness, surface shortwave absorptivity, and Poisson's ratio of hot-mix asphalt. Longitudinal and alligator fatigue cracking were also very sensitive to granular base thickness and resilient modulus and subgrade resilient modulus.

Parametric Evaluation of Design Input Parameters on the Mechanistic-Empirical Pavement Design Guide Predicted Performance

The objective of this study was to conduct a sensitivity analysis to identify the input parameters with the greatest effects on the predicted pavement performance from the Mechanistic-Empirical Pavement Design Guide (MEPDG). Three levels of analysis (low, medium, and high) with five input parameters (traffic level, hot-mix asphalt (HMA) thickness, E*, base course thickness, and subgrade type) were evaluated through a full factorial design. The main influence of each individual input parameter and the combinational interaction effects of the input parameters on the predicted distress response were quantified. It was determined that the traffic level input parameter was the main effect on all predicted pavement distresses in the MEPDG. The second main effect for international roughness index (IRI), fatigue cracking, and total pavement rutting was HMA thickness. For asphalt concrete (AC) rutting, the mixture dynamic modulus ranked second for the main effect followed by HMA thickness. For top-down cracking, it was observed that the base course thickness ranked second for the main effect followed by the HMA dynamic modulus. The influence of base thickness on top-down cracking was not expected but it may be due that the MEPDG adopted a traditional fatigue cracking model to describe this failure mechanism.

Evaluation of Surface-Related Pavement Damage due to Tire Braking

ABSTRACT The response of flexible pavement at near-surface is significantly affected by interfacial tire-pavement contact stresses. In addition to highly non-uniform vertical stresses and surface tangential shear stresses at tire-pavement interface, tire braking at an intersection causes additional significant longitudinal contact stresses on the pavement surface. In this paper, the flexible pavement responses to three-dimensional (3-D) tire-pavement contact stresses at various tire rolling conditions were determined using a developed 3-D finite element model. The hot-mix asphalt (HMA) layer was characterized as a viscoelastic material, and the transient dynamic tire loading was simulated using a continuous moving load and implicit dynamic analysis. The analysis matrix includes two typical flexible pavement structures (76 mm and 152 mm HMA thicknesses) and three tire rolling conditions (free rolling at high speed, free rolling at low speed, and braking). The study concluded that the low-speed vehicle loading and tire braking aggravates the pavement deterioration at an intersection in terms of rutting or shoving in the HMA and surface cracking at the pavement surface. During tire braking, the damage ratios for pavement surface cracking may be as high as 8 to 32 depending on HMA thickness, compared to the normal traffic loading conditions. The tire braking increases the HMA rutting or shoving potential by 2.0 to 2.6 times due to the increased shear strains in two directions. Hence, pavements for intersections should be specified, designed, and constructed differently than regular asphalt pavements to withstand the more severe loading conditions.

<strong>A study of the Hot-Mix Asphalt layer thickness reduction when applied over lateritic soils cement base in airfield</strong><br> DOI: 10.5585/exacta.v7i1.798

In tropical region, in upper layers, soils having red or yellow coloration are generally found and are denominated lateritic soils. They are rich in aluminum hydroxides and ferric hydrates that give an elevated mechanic resistance. When the lateritic soils are used as a construction material in the structural pavement, the exceptional mechanical characteristic reduced the cost over 50% when associated with the sub-base and base layers, or over 25% when the lateritic soil is treated with cement. In São Paulo State, it was made more than ten thousands kilometers of roads where the base or sub-base was made using lateritic soils or lateritic soils treated with cement. In this study, it is showed, through Finite Element Method, a critical analysis of the sub-base and base of airfield pavement using lateritic soils cement base course and Hot-Mix Asphalt thickness surface less than recommended for critical area in according to Federal Aviation Administration (1996). Considering the results, it is possible to propose a reduction of thickness Hot-Mix Asphalt layer, resulting in a reduction of the final cost of implantation of hundreds of airfields in South America.

Quality Control–Quality Assurance Sampling Strategies for Hot-Mix Asphalt Construction

The effects of sampling strategies and size on statistically based decision making in hot-mix asphalt (HMA) construction are presented. For sample sizes agreed on by the agency and the contractor, an acceptable level for an HMA mix parameter is determined with risk balanced between the two organizations. With increased emphasis on specific performance requirements, the use of performance tests on HMA specimens prepared from in situ samples is developing. Examples include direct measures of mix stiffness and permanent deformation characteristics. A measure of rutting resistance, the stabilometer S-value, is used by the California Department of Transportation (Caltrans) for quality control–quality assurance (QC/QA) projects. Although the S-value was used for this simulation because extensive tests were available, this approach is applicable to any performance measures already in use, such as HMA thickness or compacted air void content. A sampling scheme and sampling size through statistical simulation of a fixed length of a one-lane-width placement of HMA are discussed. Sample size is based on the combination of the sample size of the contractor and that of the agency to balance the risk to both organizations and results in a mix that will meet the minimum performance requirement. An example is given for the placement of 15,000 tons of HMA according to Caltrans QC/QA requirements. For this total tonnage, the contractor and agency are respectively assumed to perform a specific number of stabilometer tests for QC and QA. Results of the simulation yield the average stabilometer value that the contractor must obtain to ensure that the quality requirement, that is, the minimum S-value, is met.

Influence of Various Material and Traffic Inputs on Flexible Pavement Design Methods for Alabama Roadways

Statistical analyses of over 2,000 pavement designs using the 1993 American Association of State Highway Transportation Officials Design Guide was conducted. Variations in traffic levels, and subgrade, base, and hot mix asphalt (HMA) moduli and thickness showed that the only significant material and traffic design inputs were the subgrade modulus and the initial ESAL loads. A plus or minus 5% change in the design traffic level did not statistically influence the determination of the structural number (SN). A subgrade modulus of 3,000 psi and a linear growth rate of 4% for roadways with annual average daily traffic of more than 10,000 is recommended for determining the SN. The growth rate for lower traffic volume roadways will vary significantly between 0 and 3%. A more limited evaluation of the 2002 Design Guide showed that a mechanistic–empirical method of flexible pavement design is strongly influenced by the HMA thickness and the distribution of truck types within the annual average daily traffic. Sele...

Pilot Study in Sampling-Based Sensitivity Analysis of NCHRP Design Guide for Flexible Pavements

The mechanistic–empirical pavement design guide (MEPDG), developed under the recently completed NCHRP Project 1–37A, is a complex tool. Sensitivity analyses typically vary a single input parameter while holding other parameters constant. A pilot project is outlined to identify the feasibility of a global sensitivity analysis of the design process by using random sampling techniques over the entire input parameter space. This study sampled the following flexible pavement input variables: hot-mix asphalt (HMA) base nominal aggregate size, climate location, HMA thickness, annual average daily truck traffic (AADTT), subgrade strength, truck traffic category, construction season, and binder grade “bump.” A total of 100 design sections were randomly sampled from these input parameters. The resulting predicted performance of longitudinal and alligator cracking, HMA and total rutting, and international roughness index were analyzed by using the Pearson's and Spearman's correlation coefficients. These coefficients indicate that AADTT, HMA thickness, and subgrade strength have a significant impact on performance, whereas the remaining parameters have lesser impacts. The performance predicted with trial designs with default values of the least significant variables was compared with the original performance predictions using the original input factors. This comparison indicated that the default parameters produced similar performance to designs using all the input parameters. These results demonstrated that this type of sensitivity analysis may be used to identify important input parameters across the entire parameter space. The utilization of a “bumped” binder grade did not appear to have a significant influence on the performance predicted by the MEPDG models. These results indicate that further research to refine the MEPDG performance models may be necessary.

Part 2: Flexible Pavements: Pilot Study in Sampling-Based Sensitivity Analysis of NCHRP Design Guide for Flexible Pavements

The mechanistic-empirical pavement design guide (MEPDG), developed under the recently completed NCHRP Project 1-37A, is a complex tool. Sensitivity analyses typically vary a single input parameter while holding other parameters constant. A pilot project is outlined to identify the feasibility of a global sensitivity analysis of the design process by using random sampling techniques over the entire input parameter space. This study sampled the following flexible pavement input variables: hot-mix asphalt (HMA) base nominal aggregate size, climate location, HMA thickness, annual average daily truck traffic (AADTT), subgrade strength, truck traffic category, construction season, and binder grade bump. A total of 100 design sections were randomly sampled from these input parameters. The resulting predicted performance of longitudinal and alligator cracking, HMA and total rutting, and international roughness index were analyzed by using the Pearson's and Spearman's correlation coefficients. These coefficients...