Investigation on the erosion mechanism of simulated salt conditions on bitumen

Abstract

Bitumen, a widely used adhesive material in the construction of asphalt pavement, can be eroded by the aqueous solution present in the service environment. In addition, different solutes are present in the aqueous solution under different service environments, which influences the erosion of bitumen. Hence, the erosion mechanism of bitumen under various salt erosion conditions (de-icing brine solution, sea fog, seawater, saline-alkali solution) was investigated in this paper. Several solutes (NaCl, Na2SO4, Na2CO3, and NaHCO3), which are most commonly presented in various salt erosion conditions, were utilized to prepare the simulated salt conditions. Virgin bitumen was immersed in salt solutions. Furthermore, virgin bitumen without immersion and immersed in deionized (DI) water used as control groups. After the immersion, the residual solution and treated bitumen were analyzed. The residual solution was characterized through pH value and total organic carbon (TOC) tests. The morphology, functional groups, molecular weight, rheological properties, and surface free energy of bitumen treated by various erosion conditions were studied by scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), gel permeation chromatography (GPC), dynamic shear rheometer (DSR), and contact angle tests. The results indicated that erosion of bitumen is accelerated under salt erosion conditions. The characteristics of bitumen after erosion are manifested as: accelerated dissolution of soluble components in bitumen, accelerated aging of bitumen, increased composite modulus and viscosity of bitumen, increased polar components and surface free energy of bitumen. The severity of salt erosion conditions on the characteristics of bitumen decreased as follows: Na2CO3 > NaHCO3 > Na2SO4 > NaCl > H2O. The newly proposed mechanism of salt erosion consists of migration, dissolution, penetration, and reaction.