Xiaodi Hu

Hot-Mix Asphalt Permanent Deformation Evaluated by Hamburg Wheel Tracking, Dynamic Modulus, and Repeated Load Tests

Permanent deformation (or rutting) is a common distress in hot-mix asphalt (HMA) pavements. As part of the HMA mix and structural design processes to optimize field performance, the Hamburg wheel-tracking, dynamic modulus, and uniaxial repeated load permanent deformation tests have been developed to characterize the HMA rutting resistance potential. The primary objective of this study was to compare the three laboratory rutting tests of HMA mixes and to relate their rutting predictive potential to actual field performance. The research methodology incorporated a two-phase approach: laboratory testing and field performance monitoring of selected mixes under both conventional traffic loading and accelerated pavement testing. For the HMA mixes evaluated, a good correlation was observed in the three laboratory tests and in comparison with actual in situ field performance. Overall, the findings indicated that the Hamburg wheel-tracking test was the most feasible test for daily routine HMA mix design and screening, while both the dynamic modulus and repeated load permanent deformation tests exhibited greater potential for comprehensive characterization of HMA material property (e.g., modulus) and applications for pavement structural design as research-level test tools.

Effects of Layer Interfacial Bonding Conditions on the Mechanistic Responses in Asphalt Pavements

The bonding condition between pavement layers plays an important role in the performance of pavement structures. In this paper, a three dimensional finite-element (3D-FE) program was used for modeling the mechanistic responses (stresses and strains) in the asphalt concrete (AC) layers by simulating two layer interfacial bonding conditions, namely fully bonded and debonded (i.e., the layer separated but still considering friction). The 3D-FE modeling incorporated actual measured vertical tire-pavement contact pressure (TPCP) and assumed horizontal TPCP, including investigating the effects of vehicle acceleration and deceleration. The results of these computational modeling are presented in this paper and indicated that the layer interfacial bonding condition has a significant effect on some pavement mechanistic responses such as the tensile, compressive, and shear stresses/strains in AC pavement structures. In general, layer interface debonding (or separation) was analytically found to indirectly exacerbate pavement distresses such as slippage cracking, fatigue cracking, shoving, shear deformation, and rutting, which is undesirable.

Proposed Loading Waveforms and Loading Time Equations for Mechanistic-Empirical Pavement Design and Analysis

Under the same applied traffic loading, time is traditionally assumed to be a function of only the vehicle speed and the depth beneath the pavement surface. Additionally, no definite loading waveform has been established and/or recommended for any one special loading situation. After numerous computations and analyses in this study, it was found that the loading time is not only a function of the vehicle speed and the depth beneath the pavement surface but is also a function of the moduli ratio between the layer of interest and the immediate succeeding layer below. Furthermore, the loading waveform changed with depth beneath the pavement surface and the moduli ratio. Based on the results of this study, new equations for more accurately determining the loading time were proposed. Additionally, the corresponding loading waveform, which is a function of the depth beneath the pavement surface and the moduli ratio, was recommended. Plausible results were also obtained when an iterated method was introduced to calculate the loading time using the equations proposed in this paper.

Effect of Material Composition and Environmental Condition on Thermal Characteristics of Conductive Asphalt Concrete

Conductive asphalt concrete with high thermal conductivity has been proposed to improve the solar energy collection and snow melting efficiencies of asphalt solar collector (ASC). This paper aims to provide some insight into choosing the basic materials for preparation of conductive asphalt concrete, as well as determining the evolution of thermal characteristics affected by environmental factors. The thermal properties of conductive asphalt concrete were studied by the Thermal Constants Analyzer. Experimental results showed that aggregate and conductive filler have a significant effect on the thermal properties of asphalt concrete, while the effect of asphalt binder was not evident due to its low proportion. Utilization of mineral aggregate and conductive filler with higher thermal conductivity is an efficient method to prepare conductive asphalt concrete. Moreover, change in thermal properties of asphalt concrete under different temperature and moisture conditions should be taken into account to determine the actual thermal properties of asphalt concrete. There was no noticeable difference in thermal properties of asphalt concrete before and after aging. Furthermore, freezing–thawing cycles strongly affect the thermal properties of conductive asphalt concrete, due to volume expansion and bonding degradation.

Development, Calibration, and Verification of a New Mechanistic-Empirical Reflective Cracking Model for HMA Overlay Thickness Design and Analysis

The purpose of this paper is to present a new mechanistic-empirical (ME) reflective cracking model developed for hot-mix asphalt (HMA) overlay thickness design and analysis. After reviewing existing models, the reflective cracking model based on Paris’ law of fracture mechanics was considered as the state of the practice and was selected as the basis for the ME model development in this study. The model consists of stress intensity factor and fracture properties ( A and n ) as the fundamental input parameters for modeling reflective crack propagation caused by both traffic loadings (bending and shearing) and thermal effects (temperature variations). For practical application, 32 SIF regression equations were developed for HMA overlays with three levels of load transfer efficiencies (10, 50, and 90%) at joints/cracks under various traffic loading spectrums (bending and shearing) based on more than 1.6 million finite element simulations and computations. For the thermal induced reflective cracking, a “hybri...

Three-dimensional modelling of multilayered asphalt concrete pavement structures: strain responses and permanent deformation

In any given asphalt concrete (AC) pavement structure, the permanent deformation (PD) in each AC layer has an influence and contributes differently to the total pavement rutting. The degree of influence will generally vary as a function of the AC modulus and layer thickness. Presently, most of the AC material/layer PD characterisation and analyses are based on laboratory and/or field testing in combination with stress-strain modelling under assumed circular and uniformly distributed wheel loading. In this paper, a three-dimensional finite element program, ANSYS, incorporating measured vertical tyre–pavement contact pressure (TPCP) was utilised for computing the PD of each AC layer with different variables such as the AC layer modulus, AC layer thickness, TPCP levels, vertical wheel loads, and tyre inflation pressure. A strain energy concept was also proposed for evaluating the PD rate and contribution of each AC layer. The corresponding results indicated the following: (1) the PD contribution of each AC layer varies as a function of the AC modulus as theoretically expected; (2) the intermediate AC layer significantly contributes to lateral deformation; however, both the intermediate and top AC layers significantly contribute to vertical PD; (3) the AC layer thickness and the magnitude of the lateral TPCP hardly influence the PD of the intermediate AC layer; (4) the PD influence of small light trucks can be quite substantial depending on the loading conditions and cannot be neglected in the analysis of this nature; (5) the distribution of the TPCP has a very significant influence on the PD of the top AC layer and is more pronounced as the TPCP gets more non-uniformly distributed.

Design and Performance Evaluation of Fine-Graded Permeable Friction Course

Permeable friction courses (PFCs) are popular in Texas, where the current specification for PFC (Item 342) has a maximum aggregate size of 1/2 in. and is typically placed in layer thicknesses of 1.5 to 2 in. In this study fine-graded PFCs composed of a single aggregate fraction are proposed for placement at a nominal thickness of 1 in. Initial laboratory testing found that the target air void content for volumetric design would be around 26% air voids, substantially higher than the current PFC designs, which are between 18% and 22% air voids. To minimize the likelihood of failure, extensive laboratory testing was performed to arrive at the proposed design. Tests included Hamburg wheel-track testing, overlay tester cracking, and Cantabro, draindown, and water flow tests. The proposed fine PFC mix was first placed on a test track in Pecos, Texas. Two designs were placed and subjected to limited traffic loadings, field water flow, noise, and skid measurements. These test sections performed well. The next section was placed on a Texas Department of Transportation project in May 2011 and subjected to extremely intense traffic loading conditions on an exit ramp on US-59 in Lufkin. This ramp has a high frequency of wet-weather accidents. In addition to extreme traffic loads, the surface experienced extreme heat (air temperatures approaching 105°F) and heavy localized rain (a 6-in. rain event within a 24-h period). After 3 months the fine PFC is holding up well.

A MECHANISTIC-EMPIRICAL IMPACT ANALYSIS OF DIFFERENT TRUCK CONFIGURATIONS ON A JOINTED PLAIN CONCRETE PAVEMENT (JPCP)

Until the last decade, the 1993 American Association of State Highway and Transportation Officials (AASHTO) design guide has been traditionally used for the design of flexible and rigid pavements in the USA and some parts of the world. However, because of its inability to meet the new traffic and material challenges, a Mechanistic Empirical Pavement Design Guide (MEPDG) was introduced based on an NCHRP 1-37 A study conducted in 2004. This study used the MEPDG software and associated models to determine, through comparative truck damage analysis, the effects of nine different truck configurations on a 12 inch-jointed plain concrete pavement (JPCP). The study recorded truck damages at the end of each analysis period (40 years) and comparatively analyzed the relative pavement damage in terms of fatigue cracking, faulting, and surface roughness. The results indicated that the most critical damage to the concrete pavement was caused by truck cases with high and uneven load distribution and relatively smaller size axles group (e.g. tandem). Other key findings included the following; (1) increase in damage when the truckloads were shifted between the same size axles, (2) decrease in truck damage when the truckloads were shifted from tandem axle to quad axles, and (3) no change in truck damage when the axle spacing was increased between wheels of a quad axle.

Search for a Practical Laboratory Cracking Test for Evaluating Bituminous (HMA) Mixes

As an effort toward developing a simple and practical laboratory cracking test method that can be used routinely, on a daily basis, to optimize Hot-Mix Asphalt (HMA) designs, various monotonic loading single shot cracking tests were comparatively evaluated in the laboratory alongside the repeated (dynamic) loading Overlay Tester (OT R ) test. These monotonic crack tests included the Indirect Tension (IDT) test, Semi-Circular Bending (SCB), Overlay Tester in a monotonic loading mode (OT M ), and Disc-Shaped Compact Tension Test (DSCTT). The research methodology entailed characterizing the cracking resistance potential of various commonly used Texas HMA mixes of known field cracking performance, with different mix-design variables. The corresponding findings indicated that while the monotonic loading tests, particularly the OT M and IDT are much simpler, more practical and more repeatable with lower variability in the test results, the dynamic loading OT R test, where both crack initiation and propagation phases are sufficiently accounted for, exhibited superior screening capabilities in terms of the HMA cracking resistance potential and sensitivity to mix-design variables such as the asphalt-binder content and temperature variations. Overall, the results indicated that both the IDT and OT M could potentially serve as routine surrogate and/or supplementary crack tests to the OTR, subject to field validation.