Abstract:

Preparation of crumb rubber modified asphalt(CRMA) is an effective way to recycle waste rubber and to reduce environmental pollution. To study the physical and chemical behavior of crumb rubber in asphalt, dibutylphthalate(DBP) is used to simulate the light components of asphalt. The reaction time is 1.5 h at 175 ℃ after crumb rubber is stirred into the DBP. The light components are separated from crumb rubber. The physical and chemical effects of crumb rubber in the light components are investigated by gas chromatography-mass spectrometry(GC-MS) analysis of the separated light component. To study functional group changes and thermodynamic properties of rubber modified asphalt, CRMAs were respectively prepared under conditions of different temperature and treating time. Infrared spectra(IR) and differential scanning calorimetry(DSC) tests were then conducted on asphalt samples after removing crumb rubber by sieving method. The results indicate that 19 kinds of substances are detected in separated light components. In addition to the highest contents of DBP, the others are speculated to be all the materials from crumb rubber or the products from the complex physical and chemical reactions between crumb rubber and the light components. The absorption peaks of typical functional groups —CH₂ and C=C increase significantly, which fully proves that the molecular chains of rubber rupture and release small molecule materials dissolved into asphalt playing a role of asphalt modification. The strong endothermic peaks of DSC curve appear for asphalt samples prepared at 195 ℃, 1.5 h and 175 ℃, 3.0 h. Therefore, the processing conditions such as high temperature and long time may lead to excessive degradation or aggregation of crumb rubber as well as asphalt aging, which change the physical and chemical properties and performances of CRMA. The production conditions of CRMA are recommended that the dosage of crumb rubber is 20% approximately, at a temperature less than 195 ℃ and the treating time less than 1.5 h.

Key words: crumb rubber modified asphalt, physical and chemical behavior, detected substance, functional group, differential scanning calorimetry analysis