Targeted suppression of VOCs and particulate matter emissions from desulfurized crumb rubber modified asphalt using kaolin-expanded graphite composite adsorbents

Desulfurized crumb rubber modified asphalt (DCRMA) improves the compatibility and workability of waste-tire rubber in asphalt, but the associated change in fume composition has not been well defined. This study first compared the temperature-dependent emissions of conventional crumb rubber modified asphalt (CRMA) and DCRMA at 120–180 °C and then designed an adsorptive control strategy according to the pollutant profile identified after desulfurization. Desulfurization markedly reduced NO and H2S emissions, while SO2 remained at a very low level, but it did not reduce volatile organic compounds (VOCs) or particulate matter (PM) in a consistent manner. TD-GC-MS further showed a redistribution of the relative VOC profile, with benzothiazole, 2-methylbenzothiazole, naphthalene, and several long-chain hydrocarbons becoming more prominent in DCRMA fumes. Because the TD-GC-MS comparison was based on relative peak areas, these results indicate compositional redistribution rather than absolute increases in individual VOC species. Kaolin and expanded graphite were therefore combined to provide complementary interfacial retention and diffusion/interception functions. In the present screening, neither single adsorbent provided balanced control across VOCs, inorganic gases, and PM. A total composite dosage of 6 wt% (3 wt% kaolin + 3 wt% expanded graphite; kaolin/expanded graphite = 1:1 by mass) provided the best overall response. At 180 °C, it reduced total VOCs by 62.7% and PM1.0, PM2.5, and PM10 by 93.8%, 96.5%, and 95.6%, respectively, without additional NO or H2S release. The composite also increased the binder complex modulus and rutting factor. At the mixture level, the composite partially recovered the dynamic stability lost after desulfurization, increasing it from 2721 to 2916 cycles/mm, although the value remained below that of CRMA (3184 cycles/mm). SBS was therefore introduced as a second-stage performance compensation modifier; 3–5 wt% SBS increased dynamic stability to 4520–5360 cycles/mm while maintaining acceptable low-temperature cracking resistance and moisture stability. The results establish a pollutant-profile-driven, two-stage framework that links emission-target identification, adsorbent selection, and mixture-level performance compensation for low-emission DCRMA.