Rheological Properties and Micromechanism of Warm-Mix Flame-Retardant Asphalt

Abstract

In this study, the influence of flame-retardant materials on the rheological properties of warm-mix asphalt was investigated. The rheological properties of base asphalt and styrene–butadiene–styrene-modified (SBS) asphalt modified with 2% Sasobit and flame-retardant materials, such as alumina trihydrate and organic montmorillonite (OMMT) in a proportion of 3:1 (AM), were systematically explored. The investigation was carried out under three dosages of AM; i.e., 4%, 8%, and 12%. Experiments including dynamic shear rheological tests, multiple stress creep recovery tests, bending beam rheometer tests, Fourier transform infrared (FTIR) spectroscopy tests, gel permeation chromatography (GPC) tests, and fluorescence microscopy (FM) tests were conducted to evaluate the rheological properties and micromechanism of warm-mix flame-retardant asphalt under different AM dosages. The results showed that the rheological properties of warm-mix flame-retardant SBS asphalt (SOA) at high and low temperatures were better than those of warm-mix flame-retardant asphalt (POA) at the same AM dosage. The increase in AM dosage improved the high-temperature rheological properties and decreased the low-temperature rheological properties. Based on the combined analysis of FTIR spectroscopy, GPC results, and FM results, the reason for this phenomenon was speculated to be the occurrence of wax-crystal structure and filler–asphalt interaction between asphalt and AM. Furthermore, organic cations in OMMT adsorbed the lightweight components present in asphalt, which reduced their proportion and improved the high-temperature and rheological properties. Moreover, the increase in AM led to the increase in physical volume filling, which increased the mechanical properties and brittleness of asphalt. The stress concentration led to the worsening of the stress-diffusion capacity of POA and SOA and eventually led to the decrease in the low-temperature rheological properties of POA and SOA.