Investigation on Using SBS and Active Carbon Filler to Reduce the VOC Emission from Bituminous Materials

A comprehensive review on asphalt fume suppression and energy saving technologies in asphalt pavement industry

Based on the environmental issues of high energy consumption and high emissions of asphalt fumes that are associated with hot mixing asphalt pavement construction, especially with modified asphalt mixtures such as waste rubber modified asphalt (WRMA) mixtures, significant environmentally-friendly new technologies have been successfully applied in the field of asphalt pavement materials. These include fume purification equipment, fume suppression or flame-retarding asphalt mixture, and warm mixing or cold mixing asphalt mixture. This paper provides a comprehensive review of the latest technology in this area regarding both asphalt fume suppression and energy conservation within the last six years. Firstly, asphalt fume suppression technologies in production, laying, and combustion scenarios of an asphalt mixture are identified, and asphalt fume purification equipment utilized in the production process is thoroughly examined. The impacts and mechanisms of various fume suppressants and flame retardants of asphalt fumes regarding their influence on the performance of asphalt pavement are discussed. Secondly, from the perspective of reducing asphalt mixture temperature, different mixing techniques such as cold mixing asphalt (CMA), warm mixing asphalt (WMA), and warm mixing based retarding viscosity asphalt (WM-RVA) are introduced and evaluated utilizing energy consumption and carbon emission evaluation models. These results show that the combination of advanced oxidation and traditional purification methods is critical for promoting the green production of asphalt mixtures. In-depth research on nanomaterials and composite-type asphalt fume suppression materials, WM-RVA, and effective combinations of high-performance modification, recycled materials, fume suppression functional materials, and WMA or CMA hold great promise for future development in this field.

Investigation on DOPO as reactive fumes suppressant to reduce the fumes emission of asphalt

Asphalt fumes released during pavement construction posed a threat to human health and environment. In this study, 9,10-dihydro-9-oxa-10-phosphorophenanthrene-10-oxide (DOPO) was used as a reactive fumes suppressant to reduce the asphalt fumes emission. The volatilization behavior of DOPO modified asphalt (DOPO-Asphalt) was investigated through thermogravimetric analysis, volatility test and thermal destruction gas chromatography mass spectrometry, and effect of DOPO on the chemical structure and composition of asphalt was explored through nuclear magnetic resonance hydrogen spectroscopy, Fourier transform infrared spectroscopy, and asphalt component testing. The results indicated that 1.0 wt% DOPO reduced the fume content of control asphalt by 1.1% from 120 ℃ - 200 ℃ and the H2S and VOC content by 96.9% and 84.2%, respectively, at 180 ℃. Moreover, 1.0 wt% DOPO reduced the content of aliphatic hydrocarbons, hydrocarbon derivatives, aromatics, and sulfides in control asphalt fumes by 86.8%, 89.7%, 90.7%, and 93.5%, respectively, which may be attributed to electrophilic and nucleophilic reactions between DOPO and volatile substances in asphalt. Chemical structure and composition changing of DOPO-Asphalt confirmed that P-H bond in DOPO was chemically reacted with components in asphalt, generating stable aromatic hydrocarbons and resins. The results provided a novel method for inhibiting the volatilization of harmful substances in asphalt.

Rapid and Direct Assessment of Asphalt Volatile Organic Compound Emission Based on Carbon Fiber Ionization Mass Spectrometry

Due to the complicacy of asphalt fumes, the analytical methods for investigating volatile organic compounds (VOCs) are very limited. In this study, a direct and real-time analysis method based on carbon fiber ionization mass spectrometry (CFI-MS), an ambient mass spectrometric technique, was established and successfully applied in the analysis of asphalt VOCs. The asphalt VOCs can be directly detected in the open atmosphere without the collection step of asphalt fumes, and the mass spectra of one asphalt sample can be obtained in a few seconds in both positive and negative ion modes. By investigating the mass spectral changes of asphalt fumes at different heating temperatures ranging from 50 to 200 °C, the temperature factor of asphalt fume emission was demonstrated in this work. The research results demonstrate that the complexity of asphalt fumes is positively related to the applied temperature. Moreover, the VOCs of saturates, aromatics, resins, and asphaltenes fractions were also analyzed by the direct analysis method. The result shows that aromatics contribute most to the emission of VOCs. In addition, the obtained mass spectra combined with the principal component analysis method show the great potential to quickly screen VOC inhibitors of asphalt materials.

Emission of Volatile Organic Compounds in Crumb Rubber Modified Bitumen and Its Inhibition by Using Montmorillonite Nanoclay

Bitumen emits a large amount of volatile organic compounds (VOCs) during the production and construction of asphalt mixture, which can cause both environmental hazards and health risks. In this study, a setup was designed to collect the VOCs released by base and crumb rubber-modified bitumen (CRMB) binders and their composition was characterized by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). Next, organic montmorillonite (Mt) nanoclay was added into CRMB binder and its inhibiting effect on the VOCs emission of the binder was investigated. Finally, the VOCs emission models for the CRMB and Mt-modified CRMB (Mt-CRMB) binders were established according to reasonable assumptions. The results indicated that the VOCs emission of CRMB binder was 3.2 times larger than that of the base binder. Due to its intercalated structure, the nanoclay can reduce the VOCs emission of CRMB binder by 30.6%. Especially, its inhibition effects on alkanes, olefins, and aromatic hydrocarbons were more significant. After finite element verification, the established model based on the Fick's second law can describe the emission behavior of CRMB and Mt-CRMB binders well. Overall, the Mt nanoclay can be used as an effective modifier to inhibit the VOCs emission of CRMB binder.

The Investigation of Volatile Organic Compounds (VOCs) Emissions in Environmentally Friendly Modified Asphalt

Asphalt pavements are increasingly used in road engineering; however, the release of volatile organic compounds (VOCs) from asphalt can harm the environment and humans. In this study, different types of modifiers are added to 70# virgin asphalt to prepare environmentally friendly modified asphalt, and its performance is analyzed. Through the self-designed simple asphalt heating-emission collection and detection device, the inhibition effect of different types of modifier combinations on VOCs in the asphalt emmissions was explored. Then, VOCs emission curves of modified asphalt at different temperatures were studied, and finally the basic physical properties of the environmentally friendly modified asphalt were tested. The test results showed that the optimal modifier combination was 5% activated carbon and 3% surfactant, in which the VOCs and the peak value of asphalt heating emissions were only 1385 min·ppm and 86 ppm, respectively, which represented the best VOCs suppression effect of other groups. At the same time, the modified asphalt with optimal additives improved the high-temperature performance of 70# base asphalt and did not affect the storage stability.

Recycled plastic modified bitumen: Evaluation of VOCs and PAHs from laboratory generated fumes

A key aspect when investigating the use of recycled plastics in bitumen relates considerably to the issues relating to occupational, health and safety for humans and the environment from a fuming and emissions perspective. This research investigates laboratory-generated fumes in the forms of volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs) generated from producing polymer modified bitumen using five different types of recycled plastics. A comparative analysis of recycled plastic modified bitumen fumes was conducted based on a series of optimized parameters, including working temperatures (160 °C, 180 °C and 200 °C) and polymer contents (1%, 2%, 4% and 6% by weight of bitumen) against neat bitumen and polymer-modified bitumen. Forty-eight volatile organic compounds (VOCs) and sixteen polycyclic aromatic hydrocarbons (PAHs) were quantified using gas chromatography-mass spectrometry (GC-MS). The results from the comparative analysis revealed that the incorporation of recycled plastics could reduce overall emissions from both VOCs and PAHs perspectives. The reduction in emissions can be attributed to the enhancement in thermal stability of the bitumen blend when recycled plastics are added. The reduction rate is heavily dependent on the type and source of recycled plastics used in the blending process. Furthermore, a specific compound concentration analysis of the top-four weighted compounds emitted reveals that the total concentration of emissions can be deceiving as specific compounds can spike when adding recycled plastics in bitumen despite a reduction trend for the overall concentration.

Feasibility Evaluation of Preparing Asphalt Mixture with Low-Grade Aggregate, Rubber Asphalt and Desulphurization Gypsum Residues

Road construction consumes great amounts of high-grade natural resources. Using low-grade natural rocks or some solid wastes as substitute materials is a hot topic. Considering this, the feasibility of using low-grade granite aggregate, solid waste-based filler (desulphurization gypsum residues, DGR) and binder (waste tire rubber modified asphalt, RMA) simultaneously in asphalt mixtures has been fully investigated in this research. The commonly used base asphalt and limestone powder (LP) filler were control groups. Material characteristics of raw materials mainly including micro-morphology, functional group, mineral phase, chemical composition and thermal stability were first evaluated in order to recognize them. Four asphalt mixtures (two asphalt binder and two filler) were then designed by standard Superpave method. Finally, a detailed investigation into the pavement performance of asphalt mixtures was carried out. The moisture damage resistance and low-temperature crack resistance were detected by the changing rules of stability, strength and fracture energy, and the high-temperature stability and fatigue performance were determined by wheel tracking test and indirect tensile (IDT) fatigue test, respectively. Results suggested that RMA and DGR both showed positive effects on the low-temperature crack resistance and fatigue property of the granite asphalt mixture. DGR also strengthened moisture stability. The contribution of RMA on high-temperature deformation resistance of the granite asphalt mixture was compelling. It can offset the insufficiency in high-temperature stability made by DGR. A conclusion can be made that asphalt mixture prepared with granite, DGR and RMA possesses satisfactory pavement performances.