Zhanping You

DISCRETE ELEMENT MODELING OF ASPHALT CONCRETE: MICROFABRIC APPROACH

Micromechanical modeling has tremendous potential benefits in the field of asphalt technology for reducing or eliminating costly tests to characterize asphalt-aggregate mixtures for the design and control of flexible pavement structures and materials. In time, these models could provide a crucial missing link for the development of true performance-related specifications for hot-mix asphalt. A microfabric discrete element modeling (MDEM) approach is presented for modeling asphalt concrete microstructure. The technique is a straightforward extension of a traditional discrete element modeling (DEM) analysis, in which various material phases (e.g., aggregates, mastic) are modeled with clusters of very small, discrete elements. The MDEM approach has all the benefits of traditional DEM (e.g., the ability to handle complex, changing contact geometries and the suitability for modeling large displacements and crack propagation). These models also allow for the simulation of specimen assembly (e.g., laboratory compaction of the asphalt mixture). By modeling inclusions such as aggregates with a “mesh” of small, discrete elements, it is also possible for one to model complex aggregate shapes and the propagation of cracks around or through aggregates during a strength test. A commercially available DEM package was used to demonstrate the usefulness of the MDEM approach. A method was also presented to obtain the properties of the matrix material in an asphalt mixture, which is typically difficult to determine experimentally. This study was limited to two-dimensional analysis techniques and involved the simulation of small test specimens. Follow-up studies involving larger specimen models and three-dimensional modeling capabilities are under way.

A Wireless, Passive Embedded Sensor for Real-Time Monitoring of Water Content in Civil Engineering Materials

A wireless, passive embedded sensor was applied for real-time monitoring of water content in civil engineering materials such as sands, subgrade soils, and concrete materials. The sensor, which comprised of a planar inductor-capacitor (LC) circuit, was embedded in test samples so that the internal water content of the samples could be remotely measured with a loop antenna by tracking the changes in the sensors resonant frequency. Since the dielectric constant of water was much higher compared with that of the test samples, the presence of water in the samples increased the capacitance of the LC circuit (capacitance of the capacitor was proportional to the dielectric constant of the medium between its electrodes), thus decreasing the sensors resonant frequency. Using the described sensor, a study was conducted to investigate the drying rate of sand samples of different grain sizes. A study was also conducted to measure the curing rate of a portland cement concrete slab during casting, and its drying rate after it has been soaked in water. The described sensor technology can be applied for long-term monitoring of localized water content inside soils and sands to understand the environmental health in these media. In addition, this sensor will be useful for monitoring water content within concrete supports and road pavements. The measurement of water content is important for civil engineering infrastructure since excess water may hasten their degradation.

Micromechanical Modeling Approach to Predict Compressive Dynamic Moduli of Asphalt Mixtures Using the Distinct Element Method

A clustered distinct element method (DEM) approach is presented as a research tool for modeling asphalt concrete microstructure. The approach involves the processing of high-resolution optical images to create a synthetic, reconstructed mechanical model that appears to capture many important features of the complex morphology of asphalt concrete. Uniaxial compression tests in the laboratory were employed to measure the dynamic modulus of sand mastic (a very fine sand-asphalt mixture) and asphalt mixtures at three temperatures and four loading frequencies. For a coarse mixture considered in this study, it was found that a two-dimensional (2-D) clustered DEM provided good estimates of mixture dynamic modulus across a range of loading temperatures and frequencies without calibration. However, for a fine-grained mixture, the uncalibrated predictions of the 2-D model were found to reside near the lower theoretical bounds and well below experimentally determined moduli, most likely because of current limitation...

Chemical characterization of biobinder from swine manure: Sustainable modifier for asphalt binder

This paper presents the production, modification, and characterization of biobinder from swine manure. A hydrothermal process was used to convert swine manure to a bio-oil. The bio-oil was fractionated to extract water, solid residue, and some of the organic compounds. The sticky residue after fractionation was used as a replacement for asphalt binder. This paper presents production and chemical and rheological characterization of the biobinder as compared with petroleum-asphalt binder. Biobinder from swine manure was found to be a promising candidate for partial replacement for petroleum-asphalt binder. Considering the limitations imposed on growth of swine farms by manure management practices and environmental regulations and the increasing demand for asphalt binder for infrastructure rehabilitation, this sustainable development will result in major improvements in environmental and economical impacts in both the agricultural and construction sectors. Hence, this study offers a unique approach that simu...

Rheological Properties and Chemical Bonding of Asphalt Modified with Nanosilica

AbstractThe objective of this study is to evaluate the rheological properties and chemical bonding of nano-modified asphalt binders blended with nanosilica. In this study, the nanosilica was added to the control asphalt at contents of 4% and 6% based on the weight of asphalt binders. Superpave binder and mixture tests were utilized in this study to estimate the characteristics of the nano-modifed asphalt binder and mixture. The rotational viscosity (RV), dynamic shear rheometer (DSR), bending beam rhometer (BBR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), asphalt pavement analyzer (APA), dynamic modulus (DM) and flow number (FN) tests were used to analyze rheological properties and chemical bonding changes of the nano-modified asphalt binder and the performance of the nano-modified asphalt mixture. In addition, the performance of nano-modified asphalt after rolling thin-film oven (RTFO) short-term and pressure-aging vessel (PAV) long-term aging was assessed as well...

Evaluation of Low-Temperature Binder Properties of Warm-Mix Asphalt, Extracted and Recovered RAP and RAS, and Bioasphalt

This research project evaluates the low-temperature performance of energy-efficient and environmentally friendly hot-mix asphalt (HMA) paving materials. Innovative materials gaining interest in the asphalt pavement industry includes warm mix asphalt (WMA), recycled asphalt shingle (RAS), reclaimed asphalt pavement (RAP), and bioasphalt. The materials are used as modifiers in typical HMA to enhance low-temperature field performances. Sasobit compounds at 0.5, 1.0, and 1.5%, by weight of performance grade (PG) 52-34 asphalt binder, are used to design the WMA. Five and 10% of RAS were also added to a PG 52-34 asphalt binder. 50% of RAP combined with 50% of the base PG 58-28 binder, and 100% RAP extracted from the PG 58-28 HMA, were prepared and tested. Bioasphalt was produced from swine waste and used to modify PG 64-22 asphalt binder. By using the Superpave bending beam rheometer (BBR) and the new asphalt binder cracking device (ABCD) method, the thermal cracking performance of the samples were tested. The ...

Discrete-Element Modeling: Impacts of Aggregate Sphericity, Orientation, and Angularity on Creep Stiffness of Idealized Asphalt Mixtures

Hot-mix asphalt (HMA) contains a significant amount of mineral aggregate, approximately 95% by weight and 85% by volume. The aggregate sphericity, orientation, and angularity are very important in determining HMA mechanical behaviors. The objective of this study is to investigate the isolated effects of the aggregate sphericity index, fractured faces, and orientation angles on the creep stiffness of HMA mixtures. The discrete-element method was employed to simulate creep compliance tests on idealized HMA mixtures. Two user- defined models were used to build 102 idealized asphalt-mix digital specimens. They were the R-model and the A-model, short for a user-defined rounded aggregate model and a user-defined angular aggregate model, respectively. Of the 102 digital specimens, 84 were prepared with the R-model to investigate the effects of aggregate sphericity and orientation, whereas the remaining 18 were built with the A-model to address the effect of aggregate angularity. Aviscoelastic model was used to capture the interactions within the mix specimens. It was observed that (1) as the sphericity increased, the creep stiffness of the HMA mixture increased or decreased, depending on the angles of aggregate orientation; (2) as the angle of aggregate orientation increased, the creep stiffness of the HMA mixture increased, with the rate depending on the sphericity index values; and (3) compared with the sphericity index and orientation angles, the influence of aggregate fractured faces was insignificant. DOI: 10.1061/(ASCE)EM.1943-7889.0000228.

Preliminary Dynamic Modulus Criteria of HMA for Field Rutting of Asphalt Pavements: Michigan’s Experience

This paper presents a comparative study of laboratory results of both dynamic modulus testing and field rutting performances of hot-mix asphalt (HMA) in the state of Michigan. Fourteen field-produced mixtures at various traffic levels and aggregate sizes were evaluated and compared to those of field rutting. These mixtures were collected from job sites and compacted with a Superpave gyratory compactor to imitate the common air void level used in Mich., which is 7%. Dynamic modulus E∗ was measured at temperatures ranging from −5 to 39.2°C and frequencies ranging from 0.1 to 25 Hz. The results show that the dynamic modulus values increased when the designed traffic level for HMA mixtures increased. The field rutting performance was evaluated based on theoretical pavement rutting life index. Two parameters, | E∗ | and | E∗ | /sin (φ) , were compared to the theoretical pavement rutting index. Based upon the preliminary study, it was found that E∗ was a suitable parameter in comparing the field and laboratory ...

Mechanical Properties of Porous Asphalt Pavement Materials with Warm Mix Asphalt and RAP

The objectives of this paper are (1) to characterize the mechanical properties of porous asphalt pavement mixtures containing reclaimed asphalt pavement (RAP) and a WMA additive (Advera® WMA) using Superpave™ gyratory compactor and dynamic modulus testing. Four types of porous asphalt mixtures were evaluated in this study. They are 1) control mixture, a conventional porous asphalt mixture; (2) porous asphalt mixture with WMA additive (Advera® WMA in this case); (3) porous asphalt mixture containing 15% reclaimed asphalt pavement (RAP); and (4) porous asphalt mixture containing 15% RAP and additional WMA additive. This study evaluated com- paction energy index (CEI), permeability, indirect tensile strength, and dynamic modulus (E � ) for all types of porous asphalt mixtures. All of the porous asphalt mixtures meet the typical minimum coefficient of permeability in this study. Compaction energy required for the WMA containing 0.25% Advera® WMAwas found to be lower compared with the control mixture (HMA). The results from the dynamic modulus test show that WMA made with 0.25% Advera® WMA had significantly lower values than the control HMA mixture. In addition, only a slight decrease in Ewas found when WMA additive was added to the porous asphalt mixture containing RAP. For indirect tensile strength testing, WMA containing RAP was found to have the highest tensile strength among all of the mixtures tested. DOI: 10.1061/(ASCE)TE .1943-5436.0000307.

Three-Dimensional Microstructural-Based Discrete Element Viscoelastic Modeling of Creep Compliance Tests for Asphalt Mixtures

Microstructural-based discrete element (DE) models have been used for a better understanding of asphalt pavement concrete since the late 1990s. Most current studies have been done with two-dimensional (2D) models. Moreover, elastic models are primarily employed for simulation of an asphalt matrix’s time-dependent behaviors. A 2D model is too simple to capture the complex microstructure of asphalt concrete, and an elastic model is not sufficient for simulating an asphalt matrix’s viscoelastic behaviors. Therefore, it is necessary to consider a three-dimensional (3D) viscoelastic model for microstructural-based DE simulation of asphalt mixture behaviors. Currently, it is easy to build such a 3D microstructural-based DE viscoelastic model using the existing techniques presented in the previous studies. A major challenge, however, is to reduce the computation time to run the 3D microstructural-based DE viscoelastic modeling process which is extremely time-consuming. The primary objective of this paper is to s...