Decheng Feng

Performance and Thermal Evaluation of Incorporating Waste Ceramic Aggregates in Wearing Layer of Asphalt Pavement

Industry waste materials are commonly used in road engineering. In this study, crushed ceramic waste aggregates (CWAs) were utilized and added into asphalt mixtures to investigate their potential usage. A finite-element method (FEM) was employed first to examine the effect of material thermal conductivity on the temperature gradient of pavement structure. A significant effect of the surface layer’s conductivity in asphalt pavement on the temperatures (at the top and bottom positions of the middle layer) was found in model simulation. Next, the mix design for asphalt mixtures with different percentages of CWAs was developed, and their thermal properties were tested. It is concluded that asphalt mixtures with a reasonable substitution percentage of CWA can satisfy pavement performance requirements. The addition of CWAs can reduce the thermal conductivity of asphalt mixtures, which is proven helpful in reducing the temperature gradient of pavement. Finally, it is recommended that less than 40% CWA be added into asphalt mixtures to replace natural coarse aggregates considering its effect on the performance of mixtures.

Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation

Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.

Characterization of the Bonding Fracture Properties of the Asphalt-aggregate System Using a Thin-film Interface Test

Adhesion between asphalt-aggregate and cohesion within asphalt mastic has a significant effect on the performance of asphalt mixtures. Conventional testing methods and studies normally only focus on one of the damage modes (adhesion or cohesion), although in real asphalt mixtures (asphalt-aggregate system), these two failure modes can happen together depending on the material and loading conditions. The objective of this paper was to characterize the interface bonding characteristics of the asphalt-aggregate system using the thin-film interface test and the fracture property parameter, critical state energy density (CSED), and identify the key factors that could affect the interface bonding characteristics. The thin-film interface test simulated a more realistic bonding condition and monitored the damage between thin-film asphalt and aggregate. Experimental results showed that the effects of temperature and loading rate on the interface bonding characteristics were significant. The time-temperature superposition principle is found to work in both the linear viscoelastic range (dynamic modulus test) and the damage domain (interface bonding fracture test). Binder type, degree of aging, and types of aggregates all played an important role in the bonding performance for an asphalt-aggregate system.

Tire–Pavement Contact Stress with 3D Finite-Element Model—Part 1: Semi-Steel Radial Tires on Light Vehicles

Vehicles pass their loads through tires onto pavements. Traditionally, the vertical contact pressure is assumed to uniformly distribute in a rectangle or circular area, whereas the shear contact pressure is ignored in pavement design. Experiments have demonstrated that the interaction between the tire and the pavement surface is very complicated. The contact area is not a regular shape and the distribution of contact pressure is not uniform. However, experimental approaches to measure contact pressure are usually time and energy consuming, whereas the results are subject to errors introduced by measurement sensors. On the other hand, numerical simulation can describe the interaction between tire and pavement surface under all circumstances, such as various driving conditions, different tread types, and so on. In this paper, a three-dimensional finite-element model for tires was developed. The model was validated by the static test data. Then the interactions of different tires with pavement were analyzed, including the vertical and shear contact-pressure distributions on tires and on pavement surfaces. The influences of pavement friction and load level on the contact-pressure distributions of tires and pavement were investigated as well. It was found that vertical and shear contact pressures on tires and pavement were quite different when the type of tire or the friction changed. The contact-pressure distribution was found not uniform and the shape of contact area changed as the load level varied. The complicated interactions between different tires and pavement indicate that sophisticated tire models are necessary to obtain more accurate pavement responses.

Tire–Pavement Contact Stress With 3D Finite-Element Model—Part 2: All-Steel Tire on Heavy Vehicles

Heavy vehicles increase on highways in China year by year. Heavy loads are among the most important factors causing pavement distresses. The distribution of contact stresses between tires and pavement surface greatly influences the initiation and propagation of pavement distresses, especially for the top-down cracking. Therefore, to accurately and precisely describe pavement responses, the distribution of contact stresses should be first investigated thoroughly. This study focuses on simulating the contact stresses between all-steel tires on heavy vehicles and the pavement surface. A 3D finite-element model was proposed and used to simulate the distribution of contact stresses in different conditions of tires, including standstill, free rolling, accelerating rolling, and decelerating rolling conditions. This model was validated by previous study of the authors. There were three loading levels used in this study, including 20 kN, 40 kN, and 60 kN. In the standstill condition, the maximum pressures on pavement surface were simulated as 1.2 MPa, 1.2 MPa, and 2.4 MPa in 20 kN, 40 kN, and 60 kN loading levels, respectively, which were much higher than 0.7 MPa, the standard contact pressure in pavement design specification in China. An interesting phenomenon was observed that when the load passed a certain value, the width of contact area kept constant, whereas the length of contact area was prolonged. And the length of the contact area prolonged linearly with the increase of load. Based on this phenomenon, the Hertz contact theory was applied to simplify the traditional 3D finite-element model. In the simplified model, the complicated 3D all-steel tire was simplified to an equivalent medium. The 3D finite-element model and the simplified model were compared with the analytic method. This indicates that the simplified model can simulate the contact stress of all-steel tires closely to the analytic results (no more than 10 % difference) and greatly improves the calculation efficiency.

Calibration on MEPDG Low Temperature Cracking Model and Recommendation on Asphalt Pavement Structures in Seasonal Frozen Region of China

In order to implement the Mechanistic-Empirical Pavement Design Guide (MEPDG) to design and maintain asphalt pavements in China, it is necessary to calibrate transfer functions of distresses in MEPDG with local conditions, including traffics, environment, and materials as well as measured pavement distresses data in field. Comprehensive single factor sensitivity analyses of factors that influence thermal cracking of asphalt pavements were conducted utilizing the MEPDG low temperature cracking (LTC) model. Additionally, multiple factor sensitivity analyses were carried out as well, based on which pavement structures with sound thermal cracking resistance were recommended for seasonal frozen regions in China. Finally, the field data of thermal cracks on typical asphalt pavements in China was utilized to calibrate the LTC model in MEPDG. An improvement was proposed on MEPDG LTC model, after which was applied, the predicted thermal cracking from MEPDG LTC model agrees well with measured thermal cracking in China.

Effect of Testing Conditions on Laboratory Moisture Test for Asphalt Mixtures

Moisture damage is one of the major causes of premature failure in asphalt pavements, and it also accelerates the severity of other distresses. To date, no moisture test has been widely accepted that is reliable and practical in predicting the field moisture performance of the asphalt mix during the design stage. One reason is because the sample conditioning methods cannot represent the field conditions, resulting in inconsistent results with the field performance of some mixtures. Taken into account this concern, this paper investigates how different testing conditions, including sample preparation, moisture saturation, and loading methods, can affect the results of laboratory moisture tests. In conclusion, it is found that the degree of vacuum pressure for achieving moisture saturation and air voids distribution has a significant impact on the moisture testing results. Multiple freeze-thaw cycles have a limited effect on the variation of mechanical performance (i.e., compressive dynamic modulus). If one or several freeze-thaw cycles are to be used in a moisture test, the effect of aging should be considered. It is recommended that a sample without coring and cutting should be used for a moisture test as the coring and cutting process is found to change the air voids distribution, i.e., the percent of connected air voids, thus making the sample not representative to the field condition. Finally, the moisture test results are more sensitive under tension mode than under compression mode.

Study on the Influential Factors of Noise Characteristics in Dense-Graded Asphalt Mixtures and Field Asphalt Pavements

Determining the influential factors of noise characteristics in dense-graded asphalt mixtures and field asphalt pavement is important in constructing highways that are both low noise and environmentally friendly. In this study, the effects of nominal maximum aggregate size, asphalt binder type, air void percentage, and the service life of pavement on the noise absorption characteristics of asphalt mixtures were first investigated in laboratory. Thereafter, tire/pavement noise measurements were conducted on different types of dense-graded asphalt pavements. The effects of the service lives of the pavements, the types of the pavements, driving speeds, and test temperatures on the noise levels of the pavements were also studied. The Zwicker method is used to calculate psychoacoustic parameters on the tire/pavement noise spectrum. The laboratory results indicate that reducing the nominal maximum aggregate size, using rubber asphalt, and increasing air void percentage as well as surface texture depth improve the sound absorption performance of asphalt mixtures. The field measurements show that laying down asphalt pavements with a shorter service life or larger texture depth, using rubber asphalt, reducing traffic speed, and increasing air temperature can reduce noise.

Studies on surface energy of asphalt and aggregate at different scales and bonding property of asphalt–aggregate system

Adhesion between asphalt and aggregate is rather essential to the service performance and durability of asphalt pavement. The surface energy of the asphalt binder and aggregate was proved effective to characterise the adhesive behaviour of asphalt–aggregate system, which had been studied with various measuring methods in recent years. However, most of these existing methods focus on the interfacial bonding characteristics at a macro-scale. The physical and mechanical properties of asphalt and aggregate at a micro-scale still needed to be clarified. In this study, Atomic Force Microscopy (AFM) was introduced to measure and calculate the surface energy of the asphalt and aggregate at nano-scale based on the classical Johnson–Kendall–Roberts and Fowkes theory. The surface energy of the asphalt and aggregate were also measured and determined with Sessile Drop method at millimetre scale. These test results were then related to the bonding property of the asphalt–aggregate system with a pull-off test. The aging was found to have a significant effect on the surface energy of the asphalt binder and thus affect the bonding performance between asphalt binder and aggregate. The measured surface energy of asphalt and aggregate by AFM method was found to represent the surface characteristics of materials and be able to characterise the bonding property between asphalt and aggregate.

Experimental Study of Elastic Properties of Saturated Clay Subjected to Freeze-Thaw Cycles

This research aims to investigate shear wave velocity and small-strain shear modulus of saturated thawed clay. Various numbers of no-water supplied freeze-thaw cycling were experienced on the saturated clay firstly, then the wave velocity measurement setup was employed to carried out a series of non-destroyed wave velocity tests on each sample. During which, one pairs of BE were install on the top surface as transmitter and another on bottom surface as receiver, respectively, and another two pairs of BE were installed on horizontal direction. The effects of compaction degree and numbers of freeze-thaw cycles on elastic properties for vertical and horizontal direction were analyzed and discussed. The results indicate that initial density and freeze-thaw cycling exhibits a notable effect on elastic properties. The shear wave velocity and small strain shear modulus in vertical direction are greater than in horizontal direction, and both of them increase with increasing of initial density. However, they decrease after various numbers of freeze-thaw cycles and sharply drop at 1st F-T.