Abstract: Using a rejuvenator to improve the performance of asphalt pavement is an effective and economic way of hot asphalt recycling. This research analyzes the rejuvenating effect on aged asphalt by means of a Mortar Transfer Ratio (MTR) test, which concerns the ratio of asphalt mortar that moves from recycled aggregates (RAP aggregates) to fresh added aggregates when aged asphalt is treated with a regenerating agent and comes into contact with fresh aggregates. The proposed MTR test analyzes the regeneration in terms of the softening degree on aged asphalt when the rejuvenator is applied. The covered area ratio is studied with an image analyzing tool to understand the possibility of mortar transferring from RAP aggregates to fresh aggregates. Additionally, a micro-crack closure test is conducted and observed through a microscope. The repairing ability and diffusion characteristics of micro-cracks can therefore be analyzed. The test results demonstrate that the proposed mortar transfer ratio is a feasible way to evaluate rejuvenator diffusion during hot recycling. The mortar transfer ratio and uncovered area ratio on fresh aggregates are compatible, and can be used to quantify the contribution of the rejuvenator. Within a certain temperature range, the diffusing effect of the rejuvenator is better when the diffusing temperature is higher. The diffusion time of the rejuvenator is optimum when diffusion occurs for 4–8 h. When the rejuvenator is properly applied, the rough and cracking surface can be repaired, resulting in better covered aggregates. The micro-closure analysis visually indicates that rejuvenators can be used to repair the RAP aggregates during hot recycling.
Keywords: rejuvenator; mortar transfer ratio; micro-cracks; preventive maintenance
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Abstract: Aged asphalt mixture is heavily involved in pavement maintenance and renewed construction because of the development of recycling techniques. The aged bitumen binder has partially lost its viscous behavior. Rejuvenators are therefore designed and used in this recycling procedure to enhance the behavior of such aged reclaimed bitumen. However, tests have not yet been clearly specified to understand the diffusion characteristics of rejuvenators in aged bitumen. In this research, molecular dynamic simulation is proposed and conducted with Materials Studio software to study the diffusion behavior of rejuvenators in aged bitumen at the molecular level. Two rejuvenators, named R-1 and R-2, were included. The difference between these two rejuvenators is their chemical composition of C=O. The diffusion coefficient is determined by studying the molecular movement. Results illustrate that the proposed models can be used to study the diffusion of rejuvenators in aged bitumen sufficiently. In the meantime, a dynamic shear rheometer (DSR) is used to evaluate the recovery influence on aged bitumen resulting from rejuvenators. The experimental results strengthen the model simulations and indicate that the aging index of bitumen has a significant influence on the rejuvenating effect. Research results indicate that rejuvenators have a sufficient rejuvenating effect on the long-term aged bitumen and a limited effect on short-term aged bitumen.
Keywords: bitumen binder; molecular simulation; diffusion of rejuvenator; aged bitumen; rheological properties
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Abstract: The primary objective of this article was to investigate the feasibility of steel slag as fillers, particularly the fillers milled from raw steel slag with different particle size, also the steel slag fillers’ effects on rheological properties of asphalt mastics. Four types of fillers were analyzed, including limestone filler (LF) and three steel slag fillers obtained by milling different raw Basic Oxygen Furnace (BOF) steel slags whose original particle sizes were 0–9.5 mm (ASSF, type A Steel Slag Filler), 9.5–13.2 mm (BSSF, type B Steel Slag Filler) and 13.2–26.5 mm (CSSF, type C Steel Slag Filler) separately. Surface characteristics, chemical compositions, phase distributions, thermal properties of fillers were first studied. By applying Bending Beam Rheometer (BBR) at lower temperature and Dynamic Shear Rheometer (DSR) at higher temperature, the rheological properties of asphalt mastics were also investigated. Results show that along with the increase of raw steel slag’s particle size, the Fe content in steel slag filler presented a growing trend obviously. Besides that, compared with LF, steel slag fillers have different surface characteristics, chemical compositions, phase distributions and thermal properties. Furthermore, all steel slag fillers presented outstanding rheological properties, which indicated that they can be used as potential materials to replace LF. Moreover, ASSF corresponding mastic owned the best high-temperature rheological properties while BSSF corresponding mastic revealed the most balanced low-temperature rheological properties.
Keywords: Filler; Steel slag; Particle size; Rheological properties
Highlights: • Steel slag fillers can be utilized in asphalt pavements. • With the increase of raw steel slag’s particle size, the Fe content in it presents a growing trend. • Compared to limestone fillers, steel slag fillers present outstanding rheological properties.
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One of our research papers, Effect of hydration and silicone resin on Basic Oxygen Furnace slag and its asphalt mixture, has been selected as the ESI Highly Cited Papers (HCP).
Here is the Abstract of this paper:
The primary purpose of this research was to evaluate the effect of hydration and silicone resin on material characteristics of Basic Oxygen Furnace (BOF) slag and performances of BOF slag asphalt mixture. BOF slags modified by different methods were prepared. Surface textures, elements distributions, pore characteristics and volume stability of various BOF slags were first studied. Then the performances of asphalt mixtures containing various BOF slags including volume stability, thermal property and moisture resistance were well evaluated. Results showed that the combined modification of hydration and silicone resin can lower the asphalt absorption of BOF slag, and improve the asphalt mixture’s volume stability and thermal efficiency, which meant the applicability and economy of BOF slag asphalt mixture got enhanced when proper combined modification was applied on BOF slag.
Z.W. Chen, S.P. Wu, Y. Xiao* (Corresponding Author), W.B. Zeng, M.W. Yi, J.M. Wan. Effect of hydration and silicone resin on Basic Oxygen Furnace slag and its asphalt mixture, Journal of Cleaner Production, Volume 112, Part 1, (Jan. 2016), P: 392-400.