Polyurethane-precursor-based chemically modified asphalt and its modification mechanism

Abstract

The research and application of the eco-friendly and durable materials are of great significance to realize the sustainable development of road engineering. The preparation of modified asphalt with Polyurethane-precursor-based Reactive Modifier (PRM) with isocyanate as the active functional group shows significant values in environmental protection and performance improvement. The cross-scale (micro-meso-macro) characterization method was used to clarify the modification mechanism of PRM in detail. Compared with SBS modified asphalt, the rheological mechanical properties and thermal-oxidative aging resistance of PRM modified asphalt were characterized, and the road performance of PRM modified asphalt mixture was evaluated. The results show that there are obvious chemical changes in the modification process with PRM. Based on the urethane and urea functional groups formed in the modification process, the covalent crosslinking network structure based on the presence of asphaltene components can be established in asphalt. This process not only promotes the selective aggregation of asphalt fractions and the reconfiguration of asphaltenes, but also increases the surface free energy of asphalt, so as to obtain a more stable internal structure. The temperature sensitivity of PRM modified asphalt is lower than that of base asphalt, showing good resistance to high-temperature permanent deformation, fatigue damage, low-temperature cracking and thermal-oxidative aging. Compared with the SBS modified asphalt, PRM has obvious advantages in improving high-temperature performance, fatigue resistance and thermal-oxidative aging resistance of asphalt. Besides, it is expected to reduce the production temperature of modified asphalt to 140℃-150℃. Combined with the test results of pavement performance of asphalt mixture, PRM modified asphalt mixture with 2.5% concentration shows equivalent low-temperature performance as well as better high-temperature performance and water stability as SBS modified asphalt mixture with 4% concentration. PRM has significant advantages in improving pavement performance of asphalt mixture. 环保耐久材料的研究与应用对实现道路工程可持续发展具有重大的意义，采用以异氰酸酯为活性官能团的聚氨酯前驱体基反应型改性剂（ＰＲＭ）制备改性沥青在环境保护和性能提升方面展现出了显著价值。采用“微观－介观－宏观”的跨尺度表征方法，对ＰＲＭ 改性机制进行了详细分析。通过与ＳＢＳ改性沥青进行对照，评价了ＰＲＭ 改性沥青的流变学性能和抗热氧老化性能，明确了ＰＲＭ 改性沥青混合料的路用性能。研究结果表明：ＰＲＭ 改性过程存在明显化学变化，依托于改性过程中生成的氨基甲酸酯和脲等官能团，能够在沥青内部建立基于沥青质组分的共价交联网络结构。这一过程不仅促使沥青组分发生选择性聚集和沥青质重新构型，同时增大了沥青的表面自由能，从而获得更加稳定的内部结构。ＰＲＭ 改性沥青较基质沥青温度敏感性有所降低，展现出了良好的抵抗高温永久变形、抵抗疲劳破坏、抵抗低温开裂和抵抗热氧老化的能力。与ＳＢＳ改性沥青相比，ＰＲＭ 在提升沥青高温性能、抗疲劳性能和抗热氧老化性能方面具有明显优势，并有望将改性沥青生产温度降低至１４０ ℃～１５０ ℃。结合沥青混合料路用性能测试结果，２．５％改性剂掺量ＰＲＭ 改性沥青混合料展现了与４％改性剂掺量ＳＢＳ改性沥青混合料相当的低温性能、更好的高温性能和水稳定性能，ＰＲＭ 在提升沥青混合料路用性能方面具有显著优势。