SummaryPolymer-modified bitumen emulsions present a safer and more environmentally friendly binder for enhancing the properties of roads. Cationic bitumen emulsion binders containing polymer latex were investigated using confocal laser scanning microscopy. The latex was incorporated into the bitumen emulsion by using four different addition methods and all emulsions were processed with a conventional colloid mill. The emulsion binder films were studied after evaporation of the emulsion aqueous phase. We show how the microstructure and distribution of the polymer varies within the bitumen binder depending on latex addition method, and that the microstructure of the binder remains intact when exposed to elevated temperature. It was found that a distinctly fine dispersion of polymer results when the polymer is blended into the bitumen before the emulsifying process (a monophase emulsion). In contrast, bi-phase emulsion binders produced by either post-adding the latex to the bitumen emulsion, or by adding the latex into the emulsifier solution phase before processing, or by comilling the latex with the bitumen, water and emulsifier all resulted in a network formation of bitumen particles surrounded by a continuous polymer film. The use of emulsified binders appears to result in a more evenly distributed polymer network compared to the use of hot polymer-modified binders, and they therefore have greater potential for consistent binder cohesion strength, stone retention and therefore improved pavement performance.
In this work, an oxide-based ceramic matrix composite (CMC) consisting of a zirconia toughened alumina (ZTA) matrix and reinforced with mullite whiskers is produced with the purpose of providing more oxidation resistance and cost-effective alternative to covalent discontinuously reinforced ceramics. ZTA has enhanced toughness, strength and creep resistance over single-phase alumina or zirconia. ZTA can further be strengthened by the inclusion of SiC whiskers; however, these whiskers are prone to oxidation at temperatures above 1000℃ leading to loss of properties. In this work, mullite whiskers are used as the reinforcement due to its stability in oxidizing atmospheres are high temperatures. Mullite whiskers are grown through the molten salt method and incorporated into the ZTA matrix using a colloidal processing route. The microstructure and room temperature properties have been reported in an earlier paper. Whisker additions have been shown to improve the flexural strength of ZTA at 1200℃ by 59.31%. There is some concern over the stability of large diameter whiskers at high temperatures, especially in environments with excessive moisture content or residual alkali contamination. Further work will be carried out to address these concerns as well as to develop a statistical analysis of the results presented.
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