Hao Wang | Rutgers, The State University of New Jersey (original) (raw)

Papers by Hao Wang

South Dakota statutes limit the weight of nonsteering axles to 500 lb/in. of tire width. The load... more South Dakota statutes limit the weight of nonsteering axles to 500 lb/in. of tire width. The load allowance for single axles or spread tandem axles with wide-base tires is less than the axle load limit for dual tires. The objective of this research is to assess the potential impact of policy change if the load limit on wide-base tires is increased to be the same as the load limit on dual tires. First, a comprehensive literature review was conducted. Results indicated that the impact of wide-base tires on pavement damage varied, depending on pavement structure and damage mechanism. Pavement response and performance data were obtained from previous studies to calculate damage ratios between wide-base tires and dual tires with the same load. Different pavement failure mechanisms (fatigue cracking, top-down cracking, primary rutting, and subgrade rutting) were applied. Cost functions were then developed by relating the life-cycle cost of four typical asphalt pavement structures used in South Dakota to design traffic levels. The impact of the policy change on the cost of pavement damage was estimated by using detailed traffic data for each road segment in the state highway network. It was found that the cost of pavement damage increased because of wide-base tires on thin asphalt pavements commonly used in secondary roads. However, the impact of wide-base tires on Interstate highways was minimal. In addition, the environmental benefits brought about by the use of wide-base tires were equally significant, especially when the reduction in fuel consumption and air pollution was considered.

$Research paper thumbnail of Micromechanical analysis of asphalt mixture fracture with adhesive and cohesive failure$

This paper investigated the fracture behavior of asphalt mixture using randomly generated two-dim... more This paper investigated the fracture behavior of asphalt mixture using randomly generated two-dimensional (2-D) microstructure models. Asphalt mixture was modeled as a multi-phase heterogeneous material with both adhesive and cohesive failure potential. Viscoelastic properties were assigned to asphalt binder. Two different fracture models, cohesive zone model (CZM) and extended finite element model (XFEM), were adopted to simulate the fracture damage within the Fine Aggregate Matrix (FAM) (cohesive failure) and at the FAM-aggregate interface (adhesive failure), respectively. The numerical simulation offers both qualitative and quantitative results to understand the fracture behavior of asphalt mixture considering the interaction between cohesive and adhesive failure. Parametric studies were conducted to evaluate the effect of loading rate, FAM modulus, and fracture parameters on fracture potential of asphalt mixture. This study provides an effective method to study the fracture mechanism of heterogeneous material by considering different fracture mechanisms for matrix material and bi-material interface.

This paper intends to develop and validate an innovative method to determine the effective therma... more This paper intends to develop and validate an innovative method to determine the effective thermal conductivity of asphalt concrete considering thermal properties of individual components and volumetric compositions. Three-phase microstructure models (asphalt binder, aggregate, and air void) of asphalt concrete were randomly generated based on aggregate sizes and gradations. A finite-element (FE) model was developed to calculate the effective thermal conductivity of asphalt concrete by applying a steady heat transfer process. A multiscale simulation approach was used to consider the effect of different-sized aggregates at various length scales using a hierarchical framework that reduces computational cost. The prediction results were validated with experiment data and showed better accuracy than the results predicted from other analytical models. The influences of air void content and distribution, coarse aggregate content, aspect ratio of aggregate, asphalt binder with conductive and insulation additives, and lightweight aggregate on the effective thermal conductivity of asphalt concrete were analyzed. In general, the effective thermal conductivity decreases with the increase of air voids or the decrease of coarse aggregate content. However, when the distribution of air voids is nonuniform in asphalt concrete, the effective thermal conductivity may deviate from the normal range. On the other hand, the effective thermal properties of asphalt concrete could be equally affected by thermal modification of asphalt binder or replacement of lightweight aggregate. individual papers. This paper is part of the Journal of Materials in Civil Engineering, © ASCE, ISSN 0899-1561/04015045 /$25.00. © ASCE 04015045-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015045-2 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015045-3 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015045-4 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015045-5 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015045-6 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015045-7 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015045-9 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by RUTGERS UNIVERSITY on 04/16/15.

The objective of this study is to develop performance-related pay adjustment (PA) for in-place ai... more The objective of this study is to develop performance-related pay adjustment (PA) for in-place air void of asphalt pavements using pavement management data and life-cycle cost analysis (LCCA). In-place air void data were collected from quality assurance (QA) records for a large number of projects constructed in New Jersey from 1995 to 2005. Pavement condition index data were extracted from pavement management database for the pavement sections where air void data were available. Empirical pavement performance models were developed with sigmoidal functions and used to predict pavement service life. An exponential model form was used to relate the expected pavement service life to the quality measures of in-place air voids. After the rationality of the model was checked, LCCA was performed to derive the PA using different analysis periods and maintenance strategies. Monte Carlo simulations were conducted to capture the variation of PA due to the uncertainty of overlay service life. The PA could be significantly affected by the maintenance strategy if it is estimated using the short analysis period with single overlay, while the PA calculated using the infinite analysis period provides a conservative boundary that is not sensitive to the maintenance strategy. The developed LCCA framework provides the flexibility of determining the PA based on state agencies' practice on QA and pavement maintenance.

Generate three-dimensional microstructure of asphalt concrete with three-phases. Simulate steady ... more Generate three-dimensional microstructure of asphalt concrete with three-phases. Simulate steady heat transfer to predict thermal conductivity of asphalt concrete. Validate finite-element simulation results with experimental data. Evaluate effects of aggregate characteristics, conductive filler, and specimen sizes. a b s t r a c t Thermal conductivity of asphalt concrete determines the temperature distribution in asphalt pavements and thus affects viscoelastic modulus of asphalt concrete and the microclimate environment near pavement surface. This paper developed an innovative model to evaluate thermal conductivity of asphalt concrete with heterogeneous microstructure. The three-dimensional (3-D) microstructures of asphalt concrete was simulated with different-sized aggregates and air voids randomly distributed in asphalt binder. A hierarchical multi-scale finite element (FE) modeling approach was used to simulate the steady heat transfer process for predicting the effective thermal conductivity of asphalt concrete. The results were validated with experiment data reported in the literature. With the developed model, the effects of aspect ratios and orientation angles of aggregate, conductive filler, and specimen size on thermal conductivity of asphalt concrete were analyzed. Results show that the orientation angle and aspect ratio of aggregate have combined effects on thermal conductivity of asphalt concrete, depending on the orientation of the longest diagonal of aggregate with respect to the direction of heat conduction. The thermal conductivity of asphalt concrete is affected by the content and shape of graphite filler for thermal modification. On the other hand, it is recommended that the specimen size should be at least five times the maximum aggregate size for measuring thermal conductivity. The larger ratio of specimen size to maximum aggregate size is needed when the maximum aggregate size increases. In general, the developed model can be used as an analysis tool to guide the mix design of asphalt concrete for thermal optimization.

A laboratory investigation was carried out to study the effects of various compaction technologie... more A laboratory investigation was carried out to study the effects of various compaction technologies on moisture susceptibility, rutting resistance, and fatigue characteristics of various asphalt mixtures. The methodologies used in this study included three technologies such as common hot mix asphalt (HMA), warm mix (WMA), and half-warm mix asphalt (HWMA) technologies. In addition, in terms of WMA and HWMA mixtures, a foaming technology was used to produce the samples. The experimental design for WMA and HWMA included one aggregate moisture contents ($0.5 % by weight of the dry mass of the aggregate), three lime contents (0 %, 1 % and 2 % lime by weight of dry aggregate), and 2 % foaming water content. For HMA, 1 % lime content and completely dried aggregate were used. Three aggregate sources (designated as A, B, and C) and one PG 64-22 binder were used in this study. A total of 9 Superpave mix designs and 21 mixtures were completed. A total of 84 indirect tensile strength (ITS) samples, 126 asphalt pavement analyzer (APA) samples, and 30 fatigue beams were tested in this research. The major properties such as gyration number, ITS, tensile strength ratio (TSR), rut depth, deformation, toughness, as well as fatigue life were measured and computed for all mixtures. The test results indicated that various compaction technologies would slightly affect the Superpave mix design and obviously have an influence on gyration number, ITS values, rut depth, flow, toughness, and fatigue life of various mixtures regardless of aggregate source and lime content. In addition, the aggregate source significantly affected the ITS and rutting resistance in this study.

─────────────────────────────────────────────────────── Abstract: The purpose of this study is to... more ─────────────────────────────────────────────────────── Abstract: The purpose of this study is to evaluate the residual strength of reclaimed asphalt pavement (RAP) to understand the strength forming mechanism of RAP in cold recycled asphalt mixture. The mechanical properties of the RAP were investigated as compared to the properties of pure aggregates. Triaxial shear tests were conducted to analyze the residual cohesion of asphalt binder in the RAP. The gradation and specific surface area of RAP were analyzed to understand the agglomeration structure of coarse RAP particles. Splitting strength of cement-RAP mixtures was tested as compared to cement-aggregate mixtures. It can be concluded that the RAP in the cold recycled asphalt mixture does not act exactly like -black color‖ aggregates. The aged asphalt in the RAP has active cohesion although its cohesion strength is much lower than the binder in the hot-mix asphalt mixture. The coarse RAP particles formed by agglomeration of fine particles and the aged binder have important influences on the strength of cold recycled asphalt mixtures. The cement-RAP mixture has much lower splitting strength than the cement-aggregate mixture with the same gradation and cement content. It is important to add new aggregate into the recycled mixture to increase the effective aggregate surface area that can be coated with the new binder.

Asphalt binder is a kind of natural polymeric material. The pyrolysis behavior is the first step ... more Asphalt binder is a kind of natural polymeric material. The pyrolysis behavior is the first step of asphalt binder conversion process, such as combustion, carbonization, etc. To better understand the asphalt conversion when exposed to fire, the pyrolysis characteristics of asphalt binder and the dynamic evolution of gaseous products were investigated in this study.

Heavy-weight truck loading is one of the main causes of rapid flexible pavement deterioration. At... more Heavy-weight truck loading is one of the main causes of rapid flexible pavement deterioration. At the tire-pavement contact area, truck tires produce highly nonuniform vertical contact stresses as well as surface transverse and longitudinal tangential stresses (1). It has recently been shown that surface tangential contact stresses highly affect pavement responses near the surface, and these responses diminish as the depth increases. The three-dimensional (3-D) contact stresses result in a complex stress state near the pavement surface. This increases pavement damage potential, including top-down cracking, near-surface cracking, and hot-mix asphalt (HMA) rutting (2, 3).

This study, part of the NCHRP 9-45 Project, analyzed the effect of mineral filler properties on a... more This study, part of the NCHRP 9-45 Project, analyzed the effect of mineral filler properties on asphalt mastic and the rutting potential of asphaltic mixture. The mineral filler properties were characterized by four tests: Rigden voids (RV), fineness modulus (FM), calcium oxide (CaO) content, and methylene blue value. The rheological properties of asphalt binder and mastic were characterized with the use of apparent viscosity and multiple stress creep recovery tests. Dynamic modulus and flow number tests were conducted to examine the asphaltic mixture rutting potential. The tested mixtures included several variables: four asphalt binder types, including virgin and polymer modified; two aggregate gradations; and a selected group of fillers. The study concluded that asphalt mastic performance was significantly affected by the fractional voids in the filler and possibly by the CaO content and FM. This effect, however, depended on binder type. On the one hand, the styrene-butadiene-styrene modified binder showed the strongest effect as a result of the mineral filler inclusion when tested as mastic. On the other hand, RV and CaO content showed relatively greater correlation with the mixture rutting potential, as compared with other filler properties. Addition of RV improved the prediction models for dynamic modulus and flow number. The effect of RV on the mixture rutting potential was more pronounced for the coarse mixture than for the fine mixture.

ABSTRCT: A three-dimensional finite element model was developed to investigate the fracture behav... more ABSTRCT: A three-dimensional finite element model was developed to investigate the fracture behavior of a hot-mix asphalt (HMA) overlay on a jointed concrete pavement (JCP). Moving vehicular loads were applied to the HMA overlay on top of a joint to develop reflective cracking. A bilinear cohesive zone model (CZM) was inserted in the HMA overlay right over the joint. An interface constitutive model was implemented to specify interfacial behaviors between HMA-concrete layers. This study primarily examined the effects of interface bonding conditions on reflective cracking. The local and global behaviors of reflective cracking were investigated under various interface conditions regarding interfacial stiffness and bonding strength. Reflective cracking potential is quantified with representative fracture area (RFA) which represents a fractured area in the cross section of the HMA overlay. As a result, the fractured area increases significantly as the interface bonding strength becomes lower. On the contrary, the fractured area decreases slightly as the interface stiffness becomes lower.

of the bending stiffness within the tire structure. The restricted inward movement of the tire ri... more of the bending stiffness within the tire structure. The restricted inward movement of the tire ribs causes transverse stresses to develop, and the longitudinal stresses are primarily controlled by the tire-pavement friction forces (2). The three-dimensional (3-D) tire contact stresses result in a complex stress state near the pavement surface, which increases the potential for pavement damage, including top-down cracking, near-surface cracking, and hot-mix asphalt (HMA) rutting. In addition, stress rotations and loading rates induced by moving loads accelerate pavement deterioration.

There is a need to evaluate the damage caused by the new generation of wide-base tires on low-vol... more There is a need to evaluate the damage caused by the new generation of wide-base tires on low-volume secondary roads because of their increased use on trucks. In this study, a three-dimensional (3D) finite-element (FE) model was built to simulate the realistic tire loading on secondary road pavements. The model allows for predicting pavement responses to loading applied by various tire configurations. In addition, the model incorporates the measured 3D tire-pavement contact stresses, models hot-mix asphalt (HMA) as linear viscoelastic material, simulates continuous moving load, and utilizes implicit dynamic analysis. The analyzed pavement structures comprised a 76-mm HMA layer and an aggregate base layer with various thicknesses (203, 305, and 457 mm). The impact of a wide-base tire on secondary road pavement damage was analyzed using available damage models and was compared to that resulting from conventional dual-tire assemblies. It was found that the new wide-base tire (455/55R22.5) caused greater fatigue damage, subgrade rutting, and HMA rutting (densification) but less HMA rutting (shear) and base shear failure compared to the conventional dual-tire assembly when carrying the same load. The findings indicate that wide-base tires' impact on secondary road pavements depends on the roads' predominant failure mechanisms. Hence, calculated combined damage ratios can be used for road usage pricing and pavement design practice when wide-base tires are used.

In this paper, the mechanism of near-surface cracking under critical loading conditions was inves... more In this paper, the mechanism of near-surface cracking under critical loading conditions was investigated using mechanistic modeling approaches. These loading conditions were represented by a combination of nonuniform tire contact stresses in three directions generated during vehicle maneuvers (free rolling, acceleration/braking, and cornering) that were predicted from a tire-pavement interaction model. Three-dimensional finite element models of uncracked and cracked pavements were developed to evaluate the critical factors that are responsible for crack initiation and propagation at the near-surface of a typical full-depth pavement structure. It was found that the near-surface cracks in the proximity of tire edges showed strong mixed-mode (tension and shear) fracture potential. The pavement responses from both uncracked and cracked pavement models indicated that shear mode of fracture in the presence of compression appeared to be the dominant mode of damage for near-surface cracking. Compared to the free rolling condition, tire braking/acceleration and cornering induced high tangential contact stresses on the pavement surface, which could significantly accelerate the development of cracks at the pavement near-surface. The near-surface cracking potential was dependent on the variations of localized tire contact stress distributions. The findings presented in this study shed light on the experimental characterization of the near-surface cracking phenomenon, which appears to be driven by different stress conditions than the classical bottom-up fatigue cracking. This study also highlights the impact of vehicle maneuvering on premature pavement damage that is often neglected in the current pavement design process.

There is an urgent need for accurate measurement of pavement surface profile and smoothness index... more There is an urgent need for accurate measurement of pavement surface profile and smoothness index. This investigation compared the precision (repeatability) of the measured international roughness index (IRI) at the Virginia Smart Road for 19 profilers and their accuracy (bias) with respect to the rod-and-level reference measurement. Two existing accuracy criteria (ASTM Standard E950 and cross correlation) were compared for evaluating the relationship between the accuracy of profile elevation and IRI bias. It was found that there were profilers available that could produce the level of IRI accuracy and precision required for construction quality control and assurance. However, the accuracy and precision degraded when measuring hot-mix asphalt pavements with coarse texture and using the rod-and-level measurement as the reference. The crosscorrelation method appeared to have some advantages with respect to the conventional elevation tolerance method for providing better consistency between profile accuracy and IRI bias. On the sites investigated, good cross correlation among the measured and reference profiles assured acceptable IRI accuracy.

The effects of curing time and reheating on the short-term performance of stone-matrix asphalt (S... more The effects of curing time and reheating on the short-term performance of stone-matrix asphalt (SMA) mixtures with various warm-mix additives (i.e., Evotherm, Sasobit, and foamed asphalt) was evaluated in laboratory performance tests. The laboratory tests included complex modulus, loaded wheel track, indirect tensile (IDT) strength, and semicircular beam (SCB) fracture. In the tests, plantproduced mixes that were sampled from a field overlay project were compacted in the laboratory with and without reheating, and performance tests were conducted at various curing times after compaction. The effect of curing time on mixture characteristics was dependent on the mixture type and performance test considered. The mixtures containing warm-mix additives showed similar variations in mixture properties due to curing time compared to the control mixture. The reheating process caused asphalt mixtures to have greater modulus, tensile strength, and rutting resistance but smaller fracture resistance. Among the mixtures containing various warm-mix additives, the mixture containing Sasobit showed the relatively smallest changes in mixture properties attributable to reheating. Finally, it was discovered that the warm SMA mixtures showed variations in different performance characteristics, depending on the type of warm-mix additives and recycled materials, than the control mixture.

$Research paper thumbnail of Micromechanical analysis of asphalt mixture fracture with adhesive and cohesive failure$