Studies of the microstructure of polymer-modified bitumen emulsions using confocal laser scanning microscopy

Laboratory Evaluation of the Residue of Rubber-Modified Emulsified Asphalt

Emulsified asphalt has been widely used in various surface treatment methods such as chip seal for low-volume road preservation. Using modified emulsified asphalt made it possible to use chip seal technology on medium- and even high-volume traffic pavements. The main objective of the study is to quantify the residue characteristics of rubber-modified emulsified asphalt and to assess the effectiveness of using crumb rubber to modify emulsified asphalt binder. The four emulsified asphalt residues used the distillation procedure. Then, the rheology characteristics of emulsified asphalt residue were evaluated. The Fourier transform infrared spectroscopy (FTIR) test analyzed the chemical change of emulsified asphalt during the aging procedure. The results indicate that the evaporation method cannot remove all the water in emulsified asphalt. The mass change during the rolling thin film oven (RTFO) process only represented the component change of emulsified asphalt binder residue. Both the high-temperature and low-temperature performance grade of the two emulsified asphalt binders with rubber were lower. The original asphalt binder adopted to emulsification had a crucial influence on the performance of emulsified asphalt. The rubber modification enhanced the property of the emulsified asphalt binder at low temperatures, and the improvement effect was enhanced as the rubber content in the emulsified asphalt was raised. The C=O band was more effective in quantifying the aging condition of the residue. The findings of this study may further advance the emulsified asphalt technology in pavement construction and maintenance.

Visualization of materials using the confocal laser scanning microscopy technique

The development of materials science always benefits from advanced characterizations. Currently, imaging techniques are of great technological importance in both fundamental and applied research on materials. In comparison to conventional visualization methods, confocal laser scanning microscopy (CLSM) is non-invasive, with macroscale and high-contrast scanning, a simple and fast sample preparation procedure as well as easy operation. In addition, CLSM allows rapid acquisition of longitudinal and cross-sectional images at any position in a material. Therefore, the CLSM-based visualization technique could provide direct and model-independent insight into material characterizations. This review summarizes the recent applications of CLSM in materials science. The current CLSM approaches for the visualization of surface structures, internal structures, spatial structures and reaction processes are discussed in detail. Finally, we provide our thoughts and predictions on the future development of CLSM in materials science. The purpose of this review is to guide researchers to build a suitable CLSM approach for material characterizations, and to open viable opportunities and inspirations for the development of new strategies aiming at the preparation of advanced materials. We hope that this review will be useful for a wide range of research communities of materials science, chemistry, and engineering.

Correlated time-variation of bulk microstructure and rheology in asphalt binders

We use near-infrared dark-field optical microscopy to probe isothermal time variation of the volume fraction of naturally-occurring, subsurface microstructures in PG 64-22 asphalt binders at temperature T=30∘C, following a rapid heating (cooling) increment |ΔT|=20∘C from initial temperature T0=10∘C(50∘C). We compare these microstructure variations with isothermal time variations of the magnitude |G30∗(t)| of the bulk complex shear modulus measured for identical sample conditions with a Dynamic Shear Rheometer. The main findings are: (1) Microstructure volume fraction (inferred from intensity I(t) of near-infrared optical scatter) and |G∗(t)| both continue to change appreciably long after measurable changes of binder temperature cease. Moreover, delayed time variations in I(t) and |G∗(t)| (2) correlate closely with each other; (3) evolve on three distinct time scales - several minutes, ∼1 h, >1 day; (4) depend on binder aging; (5) are more pronounced after a cooling step (ΔT=-20∘C) than after a heating step (ΔT=+20∘C); and (6) account for hysteresis in I(t) and |G∗(t)| curves observed during heating-cooling cycles.

Imaging techniques applied to characterize bitumen and bituminous emulsions

The purpose of this article is to present some important advances in the imaging techniques currently used in the characterization of bitumen and bituminous emulsions. Bitumen exhibits some properties, such as a black colour and a reflecting surface at rest, which permit the use of optical techniques to study the macroscopic behaviour of asphalt mixes in the cold mix technology based on emulsion use. Imaging techniques allow monitoring in situ the bitumen thermal sensitivity as well as the complex phenomenon of emulsion breaking. Evaporation-driven breaking was evaluated from the shape of evaporating emulsion drops deposited onto non-porous and hydrophobic substrates. To describe the breaking kinetics, top-view images of a drying emulsion drop placed on an aggregate sheet were acquired and processed properly. We can conclude that computer-aided image analysis in road pavement engineering can elucidate the mechanism of breaking and curing of bituminous emulsion.