Zhong Wu

Bio: Zhong Wu is an academic researcher from Louisiana State University. The author has contributed to research in topics: Subgrade & Falling weight deflectometer. The author has an hindex of 14, co-authored 71 publications receiving 885 citations.

Fracture Resistance Characterization of Superpave Mixtures Using the Semi-Circular Bending Test

Abstract: The fracture resistance of asphalt mixture is an important property directly related to pavement distresses, such as cracking. This paper reports the investigation of a newly-developed semicircular bending (SCB) test as a candidate test for the fracture resistance characterization of asphalt mixtures. Thirteen Superpave mixtures, designed with four different binder types (AC-30, PAC-40, PG70-22M, and PG76-22M) and four different compaction levels (Ndesign = 75, 97, 109, and 125), were considered in this study. The SCB tests were conducted at 25°C using a three-point bending fixture in a MTS testing system. The fracture resistance was analyzed based on an elasto-plastic fracture mechanics concept of critical strain energy release rate, also called the critical value of J-integral (JC). Preliminary results indicate that the JC values were fairly sensitive to changes in binder type and nominal maximum aggregate size (NMAS) used in Superpave mixtures. This study suggests that the SCB test could be a valuable correlative tool in the evaluation of fracture resistance of asphalt mixtures.

Application of Shakedown Theory in Characterizing Traditional and Recycled Pavement Base Materials

Abstract: To facilitate the use of recycled materials in pavement construction, a mechanistic-based approach is required to better characterize pavement base materials. This paper demonstrates the application of the shakedown theory to characterize the behavior of traditional and recycled base materials based on laboratory repeated load triaxial RLT tests and full-scaled accelerated loading tests. A new approach that is based on dissipated energy is proposed to explain different shakedown responses of tested materials under repeated loading. The dissipated energy approach illustrated that there are two responses during RLT tests, namely, stable and unstable responses, which are dependent on the loading levels and type of tested material. It was also observed that the transition from the stable to unstable response represents gradual microstructural adjustments of tested materials to accommodate the applied loading. This gradual transition explains the difficulties in identifying some material responses within the shakedown theory based only on the permanent strain rate criteria. Based on the results of this study, a mechanistic-based design procedure to incorporate various recycled materials into pavement bases is recommended.

Louisiana Experience with Foamed Recycled Asphalt Pavement Base Materials

Abstract: Utilization of existing recyclable materials has always been key to more efficient and economical highway construction. Use of the foamed-asphalt (FA) technique to stabilize recycled asphalt pavement (RAP) is one strategy for an efficient use of salvaged construction materials. The main objective of this study is to investigate the potential use of FA-treated RAP as a base course material in lieu of a crushed-limestone base beneath a concrete pavement layer. Test sections were constructed at US-190 near Baton Rouge, Louisiana, and used for field evaluation of the FA RAP base. The laboratory mixture design of the FA RAP, the construction of the experimental base section, and the field evaluation of the stiffness of the FA RAP base layers using different in situ testing devices are presented. Preliminary results of both laboratory and field tests showed that the FA-treated RAP mixtures are very promising and can be used as an alternative to the traditional limestone base beneath a concrete pavement layer.

Pavement Structures Damage Caused by Hurricane Katrina Flooding

Abstract: In September of 2005, Hurricane Katrina devastated New Orleans and caused sustained flooding. Limited pre- and postflooding tests indicated that the pavement structures tested were adversely impacted by the flood water. Consequently, the Louisiana Dept. of Transportation and Development hired an independent contractor to structurally test approximately 383 km ( 238 mi ) of the region’s federally aided urban highway system both inside and outside of the flooding area. Falling weight deflectometer (FWD) tests were performed every 161 m ( 0.1 mi ) over each selected roadway, along with other field tests. The FWD data were imported into a geographical information system and plotted against a USGS geo-referenced map. Comparative analyses were made possible through the use of extensive flood maps made available through NOAA and FEMA. This arrangement made it possible to classify spatially and graphically all test points on the basis of flooding versus nonflooding, short flooding duration versus longer flooding ...

Permanent deformation analysis of hot-mix asphalt mixtures with simple performance tests and 2002 mechanistic-empirical pavement design software

Abstract: A complex laboratory study in characterization of permanent deformation resistance of hot-mix asphalt (HMA) mixtures is presented. Six plant-produced HMA mixtures were selected for this study. The main objective was to characterize the permanent deformation characteristics of HMA mixtures based on four laboratory tests, namely, the dynamic modulus |E*|, flow number, frequency sweep at constant height (FSCH), and Hamburg-type loaded wheel-tracking tests. The secondary objective was to evaluate the sensitivity of the dynamic modulus |E*|-test results in pavement rutting performance prediction with the 2002 mechanistic-empirical (M-E) pavement design software. Test results indicate that the |E*|-test was sensitive to the nominal maximum aggregate size in an HMA mixture. Larger aggregates combined with aged materials tend to have high |E*|-values at high temperatures. However, both the |E*|- and FSCH tests could not correctly rank the permanent deformation characteristics for the six HMA mixtures considered i...

Nanoclay-modified asphalt materials: Preparation and characterization

Abstract: The objective of this study is to review existing literature in the area of nano-modification of asphalt and proceed to apply nano-materials to asphalt to improve the performance. This study integrates literature review, preparation, and characterization of nano-modified asphalt materials. In the experimental testing montmorillonite, nanoclay at 2% and 4% by weight of asphalt was blended in asphalt binder at a high temperature to exfoliate the nanoclay within the asphalt. The asphalt binder was then characterized using the Superpave™ rotational viscosity, dynamic shear modulus, and direct tension test. The rotational viscosity results indicate that the addition of the two types of nanoclay, Nanoclay A and Nanoclay B, increased the rotational viscosity by an average of 41% and 112%, respectively, across test temperatures 80, 100, 130, 135, 150 and 175 °C. It was found that the dynamic shear complex modulus ( G *) value increases significantly across a range of testing temperatures (from 13 to 70 °C) and loading frequencies (0.01–25 Hz). With 2% Nanoclay A reinforcement in the asphalt binder, the complex shear moduli generally increased by 66% while the 4% Nanoclay A reinforcement in the asphalt binder generally increased the shear complex moduli by 125%. The 2% and 4% Nanoclay B increased the shear complex moduli by 184% and 196%, respectively. In terms of direct tension strength, the use of Nanoclay A and Nanoclay B reduced the strain failure rate of the original binder while the secant or direct tension moduli showed increase with the addition of the nanoclays. In furtherance of this research, nanoclay-modified asphalt is being tested at percentages higher than 4% to underscore the fact that nanoclays may have the potential to reduce rutting and cracking.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

Abstract: This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Using Semi Circular Bending Test to Evaluate Low Temperature Fracture Resistance for Asphalt Concrete

Abstract: This work presents a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixture. The fracture resistance of six asphalt mixtures, which represent a combination of factors such as binder type, binder modifier, aggregate type, and air voids, and two testing conditions of loading rate and initial notch length, was evaluated by performing SCB fracture tests at three low temperatures. Fracture energy was calculated from the experimental data. Experimental results indicated strong dependence of the low temperature fracture resistance on the test temperature. Experimental plots and low coefficient of variation (COV) values from three replicates show a satisfactory repeatability from the test. The results of the analysis showed that fracture resistance of asphalt mixtures is significantly affected by type of aggregate and air void content. Experimental results also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Analysis of result also indicated that both the loading rate and initial notch length had significant effect on the fracture energy at the highest test temperature, whereas the effect was strongly diluted at the two lower temperatures. No clear trend was found with the fracture peak load from either the effect of loading rate or notch length.

Reclaimed Asphalt Pavement – A Literature Review

Abstract: While the state of Illinois has been recycling Reclaimed Asphalt Pavement (RAP) material into hot-mix asphalt (HMA) since 1980, there continues to be questions regarding the correct approach to design HMA with RAP. The Illinois Department of Transportation's current method of RAP HMA design provides 100% contribution for the residual asphalt binder from the RAP based on solvent extractions. This means that the amount of virgin asphalt binder is reduced by the full amount of asphalt binder in the RAP for the percentage specified. This has recently been reported to be inaccurate and could result in an erroneous HMA job mix formula and may cause dry HMA. Hence, the HMA may become vulnerable to durability cracking and premature failure. The objective of this research project is to develop an understanding of the interaction between aged and virgin asphalt binders in RAP. Based on this understanding, this study will determine the appropriate level of contribution that should be given to the residual asphalt binder in RAP. The level of interaction between aged and virgin binders will then be used to investigate the influence on the performance and the durability of the mixtures as compared to virgin HMA. As a first step in this research project, an in-depth review of the literature related to RAP was conducted. This report presents the findings of the literature review and its implication on this research project. Availability of this report will also serve future research projects dealing with RAP materials.