Junyan Yi

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.

Impact of Gradation Types on Freeze-Thaw Performance of Asphalt Mixtures in Seasonal Frozen Region

Asphalt pavement performance in seasonal frozen region is affected severely by the freeze-thaw cycles. Gradation has important effects on asphalt mixture’s freeze-thaw durability. This paper presented the standard test methods of freeze-thaw cycles and analyzed the freeze-thaw durability of asphalt mixtures with different gradation. The test results showed that the freeze-thaw damage of asphalt mixtures goes through three stages. With the increase of freeze-thaw cycles, the splitting strength of mixtures decreased and the volume expanded gradually. The performance stabilized until the next rapid deterioration caused by the loss of interfacial adhesion between the asphalt and aggregate. The results also indicated that the mixtures with dense gradation had the best freeze-thaw stability than others, and the semi-open graded mixtures performed worst. The study results can be used in technical guideline for freeze-thaw durability of asphalt mixtures in seasonal frozen region.

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.

Modelling and Laboratory Studies on the Adhesion Fatigue Performance for Thin-Film Asphalt and Aggregate System

Adhesion between asphalt and aggregate plays an important role in the performance of asphalt mixtures. A low-frequency adhesion fatigue test was proposed in this paper to study the effect of environment on the asphalt-aggregate adhesion system. The stress-based fatigue model had been utilized to describe the fatigue behavior of thin-film asphalt and aggregate system. The factors influencing the adhesion fatigue performance were also investigated. Experiment results show that asphalt has more important effect on the adhesion performance comparing with aggregate. Basalt, which is regarded as hydrophobic aggregates with low silica content, has better adhesion performance to asphalt binder when compared with granite. The effects of aging on the adhesion fatigue performance are different for PG64-22 and rubber asphalt. Long-term aging is found to reduce the adhesion fatigue lives for rubber asphalt and aggregate system, while the effect of long-term aging for aggregate and PG64-22 binder system is positive. Generally the increased stress amplitude and test temperature could induce greater damage and lead to less fatigue lives for adhesion test system.

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.

Diffusion characteristics of asphalt rejuvenators based on molecular dynamics simulation

ABSTRACT In recent years, the regeneration technology of aged asphalt in construction engineering has received much attention. The diffusion performance of the rejuvenator is a key factor in this kind of regeneration technology. But at present, the relevant research is still not mature. To forward this research, this study established molecular dynamic models of three diffusion systems with the open source large-scale atomic/molecular massively parallel simulator, including new asphalt, short-term aged asphalt and long-term aged asphalt. This study then analysed the diffusion mechanism and influence factors including temperature, ageing and the diffusion laws of different kinds of molecules. It was found that besides thermal motion, molecular force also greatly contributes to the diffusion of asphalt and rejuvenator. It was also found that micro voids in asphalt increase the contact area and promote the fusion of the rejuvenator and asphalt. Diffusion speed increases as temperature rises, and diffusion speed in aged asphalt is higher than that in new asphalt, especially at higher temperatures. The simulation results also suggest that small or catenarian molecules diffuse faster than the network structures.