DAS P K, Kringos N, Birgisson B
Division of Highway and Railway Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
J Microsc. 2014 May;254(2):95-107. doi: 10.1111/jmi.12122. Epub 2014 Mar 20.
This paper investigates the mechanism of bitumen surface ageing, which was validated utilizing the atomic force microscopy and the differential scanning calorimetry. To validate the surface ageing, three different types of bitumen with different natural wax content were conditioned in four different modes: both ultraviolet and air, only ultraviolet, only air and without any exposure, for 15 and 30 days. From the atomic force microscopy investigation after 15 and 30 days of conditioning period, it was found that regardless the bitumen type, the percentage of microstructure on the surface reduced with the degree of exposure and time. Comparing all the four different exposures, it was observed that ultraviolet radiation caused more surface ageing than the oxidation. It was also found that the combined effect was not simply a summation or multiplication of the individual effects. The differential scanning calorimetry investigation showed that the amount of crystalline fractions in bitumen remain constant even after the systematic conditioning. Interestingly, during the cooling cycle, crystallization of wax molecules started earlier for the exposed specimens than the without exposed one. The analysis of the obtained results indicated that the ageing created a thin film upon the exposed surface, which acts as a barrier and creates difficulty for the wax induced microstructures to float up at the surface. From the differential scanning calorimetry analysis, it can be concluded that the ageing product induced impurities in the bitumen matrix, which acts as a promoter in the crystallization process.
本文研究了沥青表面老化的机理，该机理通过原子力显微镜和差示扫描量热法进行了验证。为了验证表面老化，将三种不同天然蜡含量的沥青以四种不同方式进行处理：紫外线和空气共同作用、仅紫外线作用、仅空气作用以及无任何暴露，处理时间分别为15天和30天。从处理15天和30天后的原子力显微镜研究结果发现，无论沥青类型如何，表面微观结构的百分比都随着暴露程度和时间的增加而降低。比较所有四种不同的暴露情况，发现紫外线辐射比氧化导致更多的表面老化。还发现综合作用并非简单地是各个作用的相加或相乘。差示扫描量热法研究表明，即使经过系统处理后，沥青中结晶部分的量仍保持恒定。有趣的是，在冷却循环过程中，暴露试样中蜡分子的结晶开始时间比未暴露试样更早。对所得结果的分析表明，老化在暴露表面形成了一层薄膜，这层薄膜起到了屏障作用，使得蜡诱导的微观结构难以在表面上浮。从差示扫描量热法分析可以得出结论，老化产物在沥青基质中引入了杂质，这些杂质在结晶过程中起到了促进作用。
