ABSTRACT
This study endeavors to employ a balanced design methodology, aiming to equilibrate the resistance to rutting and cracking exhibited by hot in-place recycling asphalt mixtures containing a high dose of reclaimed asphalt pavement (RAP). The primary goal is to ascertain the optimal amount of new binder necessary for practical engineering applications, ensuring a balanced rutting and crack resistance performance of recycled asphalt mixtures. The investigation mainly employed wheel-tracking tests and semi-circular bending tests to assess the rutting and cracking performance of recycled asphalt mixtures with a different dose of RAP (in China, it is common to use RAP with 80% and 90% content as additives for preparing hot in-place recycling asphalt mixtures), and varying quantities of new binders (10%, 20%, and 30% of the binder content in the total RAP added). The results indicated that the addition of new binder reduced the resistance to rutting of the recycling asphalt mixtures but improved their resistance to cracking. Furthermore, for the recycling asphalt mixture with 80% RAP content aged for 5 days, the optimal new binder content is 1.52%, while the mixture with 90% RAP content requires 1.23% of new binder. After 10 days of aging, the optimal new binder content for the recycling asphalt mixture with 80% RAP content is 1.55%, while the mixture with 90% RAP content requires 1.28% of new binder.
ABSTRACT
The purpose of this study is to investigate the macro and micro properties of stabilized recycled aggregate base layers using gypsum slag cement (GSC) and compare them with ordinary Portland cement (OPC). To achieve this, four levels of recycled aggregate content (0%, 50%, 60%, 70%) and three levels of binder materials (3.5%, 4.5%, 5.5%) were designed, where the binding materials included OPC and GSC. When GSC is used as the binding material with 0% recycled content, two scenarios for the ratio of slag to activator are considered: 4:1 and 4:2. For recycled content of 50%, 60%, and 70%, only the 4:1 ratio is considered. The macro-mechanical properties of the composite material were studied through compaction tests, unconfined compressive strength tests, and indirect tensile strength tests. Microscopic properties were investigated through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Macroscopic test results indicate that, at an equal binder content, GSC exhibits a higher moisture content and maximum dry density compared to OPC. Moreover, the unconfined compressive strength and indirect tensile strength of GSC are higher than those of OPC. Microscopic test results reveal that the hydration products of both binding materials are essentially similar; however, under identical curing conditions, the hydration products of GSC are more abundant than those of OPC.
ABSTRACT
This paper investigated, for the first time, the feasibility of using peanut shell powder, a plant waste residue, as a modifier for asphalt, particularly its self-healing ability. Modified asphalt samples were prepared using varying particle size ranges and concentrations of peanut shell powder. Various tests, including fatigue-healing-fatigue tests, high- and low-temperature rheological property tests, penetration tests for conventional performance, and atomic force microscopy scans, were conducted to investigate the effects of peanut shell powder on the self-healing performance and other properties of asphalt. The results showed that the porous structure of peanut shell powder was able to absorb light components within the asphalt and release them under load, thus improving the self-healing and fatigue resistance properties of the modified asphalt. Experimental conditions such as temperature, healing time, and fatigue damage level also influenced the self-healing performance of asphalt. Additionally, peanut shell powder could increase the dynamic viscosity and high-temperature rheological property of modified asphalt while reducing its temperature susceptibility. However, it had a negative impact on the low-temperature ductility and creep rate, which could potentially lead to premature cracking of asphalt pavement in colder regions. Increasing the content of peanut shell powder and reducing its particle size within a certain range had positive effects. When the content of peanut shell powder was 4% and the particle size range was 80-100 mesh, the overall performance of modified asphalt was satisfactory.
ABSTRACT
Styrene-butadiene-styrene block copolymer (SBS) and crumb rubber modifier (CRM) are commonly used modifiers to modify asphalt binders. The aging of modified asphalt binders is an important factor affecting their performance. In this paper, the effects of the two modifiers (i.e., SBS, CRM) on the aging of modified asphalt binders were studied by using low field nuclear magnetic resonance (LF-NMR) technology and dynamic shear rheological (DSR) tests. Test results showed that when T2, a parameter of relaxation time from NMR test, was within 2.2 milliseconds, the relaxation peak of both modified and unmodified asphalt binders tested showed two peaks (i.e., "M" shape), and when it was greater than 2 milliseconds, extra peaks appeared only in the modified asphalts. These extra peaks gradually disappeared with increased aging; the modifiers carried signal intensities of their own. The addition of a modifier changes the law of "the greater the viscosity of asphalt, the shorter the T2 relaxation time". With the aging process, the normalized peak area (NPA) from NMR decreased, and rutting resistance factor from DSR increased. However, the NPA of modified asphalt increased after the PAV test, which may be related to the change of H semaphore. The rheological properties of the asphalt binders before and after aging were well-correlated with the NPA of T2.
ABSTRACT
The viscosity of modified asphalt binders is the most important property to ensure the durability of open-graded friction course (OGFC). Zero shear viscosity (ZSV) is considered to be the optimum result to reflect the rutting characterization of high viscosity modified asphalt binders, compared with conventional vacuum capillary viscosity. However, there are few reports on using ZSV to evaluate the material characteristics of hybrid modified asphalt binders and to establish the relationship between ZSV and other properties. In this paper, a high viscosity hybrid modified asphalt binder was prepared with Sty-rene-butadiene-styrene (SBS) and Crumb rubber modifier (CRM). ZSV, three major indicators, 60 °C dynamic viscosity, 135 °C Brookfield viscosity, and a dynamic rheological test were used to determine the properties of the hybrid modified asphalt binders. The relationship between ZSV and other properties was studied by the gray correlation analysis method. Results indicated that: (1) The viscosity of hybrid modified asphalt binders increases with the decreasing frequency. When the frequency tends to 0, the viscosity of asphalt at this time is zero shear viscosity; (2) The values of the ZSV of hybrid modified asphalt binders have a large increase as the dose of both CRM and SBS modifiers were increased; and (3) The ZSV at 60 °C correlated well with the performance properties of rutting factor (G*/sin(θ)), indicating that the ZSV of hybrid modified asphalt binders could be a good indicator of performance.
ABSTRACT
To examine the pyrolysis and combustion characteristics of epoxy asphalt, the heat and smoke release characteristics were analyzed via TG-MS and cone calorimeter tests, and the surface morphology of residual carbon after pyrolysis and combustion was observed via scanning electron microscopy. The results showed that the smoke produce rate of epoxy asphalt was high in the early stage, and then sharply decreased. Moreover, the total smoke produced was close to that of base asphalt, and the surface of residual carbon presented an irregular network structure, which was rough and loose, and had few holes, however most of them existed in the form of embedded nonpenetration. The heat and smoke release characteristics of epoxy asphalt showed that it is not a simple fusion of base asphalt and epoxy resin. Instead, they promote, interact with, and affect each other, and the influence of epoxy resin was greater than that of base asphalt.
