Reconstruction of Asphalt Pavements with Crumb Rubber Modified Asphalt Mixture in Cold Region: Material Characterization, Construction, and Performance

Dry-processed rubberized asphalt mixture has recently attracted a lot of attention as an alternative to conventional asphalt mixtures. Dry-processed rubberized asphalt pavement has improved the overall performance characteristics compared to the conventional asphalt road. The objective of this research is to demonstrate the reconstruction of rubberized asphalt pavement and evaluate the pavement performance of dry-processed rubberized asphalt mixture based on laboratory and field tests. The noise mitigation effect of dry-processed rubberized asphalt pavement was evaluated at the field construction sites. A prediction of pavement distresses and long-term performance was also conducted using mechanistic-empirical pavement design. In terms of experimental evaluation, the dynamic modulus was estimated using materials test system (MTS) equipment, the low-temperature crack resistance was characterized by the fracture energy from the indirect tensile strength test (IDT), and the asphalt aging was assessed with the rolling thin-film oven (RTFO) test and the pressure aging vessel (PAV) test. The rheology properties of asphalt were estimated by a dynamic shear rheometer (DSR). Based on the test results: (1) The dry-processed rubberized asphalt mixture presented better resistance to cracking, as the fracture energy was enhanced by 29–50% compared to that of conventional hot mix asphalt (HMA); and (2) the high-temperature anti-rutting performance of the rubberized pavement increased. The dynamic modulus increased up to 19%. The findings of the noise test showed that at different vehicle speeds, the rubberized asphalt pavement greatly reduced the noise level by 2–3 dB. The pavement M-E (mechanistic-empirical) design-predicted distress illustrated that the rubberized asphalt pavement could reduce the IRI, rutting, and bottom-up fatigue-cracking distress based on a comparison of prediction results. To sum up, the dry-processed rubber-modified asphalt pavement has better pavement performance compared to the conventional asphalt pavement

Leaching evaluation and performance assessments of asphalt mixtures with recycled cathode ray tube glass: A preliminary study

© 2020 Elsevier Ltd This study intends to evaluate the feasibility of the use of recycled cathode ray tube (CRT) glass in water-foamed asphalt mixtures used in low volume roads. In the asphalt mixture samples, 21.5% (wt.) aggregates were replaced by the recycled CRT glass to evaluate the mechanical performance and leaching potential. First, the leaching test was used to characterize the leaching potential of the CRT mixes since there is high lead content in CRT glass, which may be harmful to the groundwater if the hazardous lead leaches from the CRT mixes. Second, the high-temperature rutting and the low-temperature cracking performance of the asphalt mixtures were measured via the Hamburg Wheel Tracking Test (HWTT) and the Disk-Shape Compact Tension (DCT) test, respectively. In addition, the Moisture-Induced Stress Tester (MIST) was used to simulate the pore pressure generated in a wet pavement under moving traffic loading. The experimental results showed that, although the measured lead leaching of the pure CRT glass particles was higher than the regulatory level of 5 mg/L, the coated asphalt could effectively insulate the contact between CRT glass and the external environment, resolving the leaching issues. In summary, from the view of the mechanical performance of the water-foamed asphalt mixtures containing recycled CRT glass, the performance is acceptable in various temperatures when used in low volume roads. Recycling CRT glass in asphalt mixture should be carried out with extreme caution because if not done correctly, the potential leaching may eliminate the benefits of recycling unwanted waste materials

Characteristics of water-foamed asphalt mixture under multiple freeze-thaw cycles: Laboratory evaluation

A major concern with the application of water-foamed asphalt mixtures is the possible performance degradation caused by the presence of inclusion water during production. Inclusion water left in the asphalt mixture after compaction affects the performance of the asphalt mixture. The objectives of this study are to investigate the impact of different foaming conditions on the performance of water-foamed asphalt mixtures prepared using oven-dried aggregates, examine the freeze-thaw resistance of water-foamed asphalt mixtures, and assess the water-foamed asphalt mixture damage level after multiple freeze-thaw cycles through an ultrasonic direct test. The samples for this study were prepared in the laboratory based on the method of Superpave mix design. The control groups were mixed and compacted at 135°C and 148°C, respectively. The water-foamed asphalt binders were prepared at different foaming temperatures, i.e., 120°C and 135°C, and the amount of water agent used in this process was 0.0%–2.0% by mass of asphalt binder. The water-foamed asphalt samples were mixed at various foaming temperatures but compacted at 135°C. Based on the laboratory test results, the foaming temperature and the inclusion water from the foaming process significantly affected the air void and the tensile strength of the asphalt mixture and the void in the mineral aggregate. The freeze-thaw cycle accelerated the destruction of the internal structure of the asphalt mixture and resulted in an increase in porosity and decrease in cohesive strength between the asphalt binder and aggregate. The ultrasonic direct test method was found to be a feasible approach to assessing the potential damage in water-foamed asphalt mixtures

Waste cathode-ray-tube glass powder modified asphalt materials: Preparation and characterization

Cathode-ray-tube (CRT) is the ingredient of glass used in obsolescent televisions or computer monitors. CRT glass contains a considerable amount of heavy metals, and the landfilling of CRT glass is significantly harmful to the environment. In an effort to recycle waste CRT glass instead of landfilling it, recycled CRT glass powders were introduced to asphalt binders as a modifier in this preliminary investigation. The recycled CRT glass was processed to a particle size smaller than 0.075 mm and mixed with asphalt binder (PG 58–28) to produce asphalt mastics with four different concentrations (0, 5, 10, and 15 wt%). The rheological performance was characterized with the rotational viscosity (RV), dynamic shear rheometer (DSR), and multiple stress creep recovery (MSCR) tests. The fatigue performance was evaluated by linear amplitude sweep (LAS) test. Meanwhile, the low-temperature properties were measured by the asphalt binder cracking device (ABCD). The hazard materials leaching test was applied to evaluate the leaching potential of lead content into the external environment due to the high lead content in the modified asphalt. The test results revealed that the increase of CRT glass powder content improved the energy of activation compared with that of virgin binder, as well as the resistance of permanent deformation. Furthermore, the incorporation of CRT glass powder may slightly increase the fatigue life of asphalt because of the improved physicochemical interaction between glass and bitumen. The low-temperature cracking temperature first decreased with the increase of CRT glass powder content and then increased as the CRT content increased further. The leaching test demonstrated that the CRT glass powders incorporated into asphalt binders represented a lower lead leaching content than that of the original CRT glass powder, where the lead leaching amount of CRT glass modified asphalt binder is obviously lower than the specified level of 5 mg/L. Therefore, it is possibly acceptable to recycle CRT glass powders in asphalt binders as an additive as an environmental-friendly recycling method, in which the optimal addition content of CRT glass powders could be up to 10% (wt.)

A critical review of corrosion development and rust removal techniques on the structural/environmental performance of corroded steel bridges

Corrosion is one of the most severe threats to the stability of steel bridges and regular rust removal techniques is needed for the maintenance of steel bridges. Currently the correlation between rust development/removal process and the structural/environmental performance of the steel bridges has not been fully understood. This study intends to fill this knowledge gap through critically reviewing. The characteristic analysis of the rust on the corroded steel bridges was first introduced, which provided information that was needed to understand the corrosion mechanisms and classify the rust type. Then the related rust removal techniques (chemical and physical methods) are analyzed by considering the environmental impact and cleaning efficiency. Based on the discussion, the laser cleaning method is proposed due to its cleaning efficiency and environmentally friendliness. After that, the influence of developed rust (uniform and pitting) on the structural performance (static and dynamic) of steel members were summarized. Through the discussion, the potential environmental impact of the corroded steel bridges was identified, including runoff of heavy metal and bacteria growth caused by iron rust. Besides that, an improved kinetic model was proposed by considering the influence of rust removal on the corrosion rate. Furthermore, the structural impact of laser cleaning was simulated with the finite element analysis. This study will serve as solid base for the future studies of corrosion development and rust removal on steel bridges, and the proposed technical routes can be proceeded during future studies to better understand the environmental and structural performance of the steel bridges

Application of Reeds as Carbon Source for Enhancing Denitrification of Low C/N Micro-Polluted Water in Vertical-Flow Constructed Wetland

Constructed wetlands have been applied to micro-polluted rivers and lakes. However, they often show poor nitrogen removal efficiency due to insufficient carbon sources for complete denitrification in the waters. In this study, a vertical-flow wetland system was built, in which reeds as a carbon source were added in the middle layer of the substrate. Thereby, the effect of the reed carbon source on denitrification of micro-polluted rivers and lakes with a low C/N ratio in the wetland and the denitrification mechanism were studied. The results showed that the concentrations of NH4+-N, NO3−-N and NO2−-N in the effluent of the constructed wetland were reduced to 0.17–0.35, 0.20–0.49 and 0.01–0.02 mg/L after adding the reed carbon source, and the removal efficiencies of the system for NH4+-N and NO3−-N reached 93.84% and 84.69%, respectively. The abundances of nirK, nirS, hzo and nrfA genes in the wetland substrate increased by 95.51%, 54.96%, 52.89% and 731.95%, respectively, which was considered to be related to the enhanced denitrification, anammox and dissimilatory nitrate reduction to ammonium of the wetland system. Reed planting promoted the increased abundances of amoA and nxrB genes, which might play a positive role in enhancing nitrification in wetland systems. The result of this study may provide a theoretical basis for the ecological restoration of low C/N micro-polluted water bodies

Application of Reeds as Carbon Source for Enhancing Denitrification of Low C/N Micro-Polluted Water in Vertical-Flow Constructed Wetland

Constructed wetlands have been applied to micro-polluted rivers and lakes. However, they often show poor nitrogen removal efficiency due to insufficient carbon sources for complete denitrification in the waters. In this study, a vertical-flow wetland system was built, in which reeds as a carbon source were added in the middle layer of the substrate. Thereby, the effect of the reed carbon source on denitrification of micro-polluted rivers and lakes with a low C/N ratio in the wetland and the denitrification mechanism were studied. The results showed that the concentrations of NH4+-N, NO3−-N and NO2−-N in the effluent of the constructed wetland were reduced to 0.17–0.35, 0.20–0.49 and 0.01–0.02 mg/L after adding the reed carbon source, and the removal efficiencies of the system for NH4+-N and NO3−-N reached 93.84% and 84.69%, respectively. The abundances of nirK, nirS, hzo and nrfA genes in the wetland substrate increased by 95.51%, 54.96%, 52.89% and 731.95%, respectively, which was considered to be related to the enhanced denitrification, anammox and dissimilatory nitrate reduction to ammonium of the wetland system. Reed planting promoted the increased abundances of amoA and nxrB genes, which might play a positive role in enhancing nitrification in wetland systems. The result of this study may provide a theoretical basis for the ecological restoration of low C/N micro-polluted water bodies

Microstructure Characteristics and Corrosion Resistance of Friction Stir Welded 2205 Duplex Stainless Steel

In this study, 2205 duplex stainless steel was friction-stir-welded at different welding speeds. The microstructural characteristics such as grain sizes, grain boundary misorientation angles, and phase contents in the stir zones of the joints were detected. The potentiodynamic polarization and electrochemical impedance spectroscopy were also measured to evaluate the corrosion property of the stir zones. The effects of the microstructures on the corrosion property for friction-stir-welded 2205 duplex stainless steel were analyzed. The results indicated that the FSW process refined the grains and increased the ferrite contents in the stir zones. With increasing the welding speed from 30 mm/min to 50 mm/min, the grain size in the stir zone decreased from 1.64 μm to 0.96 μm, the ferrite content decreased from 59% to 54.4%, and the fractions of low angle grain boundaries for austenite and ferrite phases decreased from 63.9% and 92.6% to 18.0% and 41.1%, respectively. In this study, the effect of grain size on the corrosion resistance was the most significant and it was followed by the phase composition and the grain boundary misorientation angle. The stir zone obtained at 50 mm/min has the highest corrosion resistance, and it is followed by the base material and the stir zone obtained at 30 mm/min

Energetics of Nanoparticle Exsolution from Perovskite Oxides

The presence of active metal nanoparticles on the surface significantly increases the electrochemical performance of ABO₃ perovskite oxide materials. While conventional deposition methods can improve the activity, <i>in situ</i> exsolution produces nanoparticles with far greater stability. The migration of transition metal atoms toward the surface is expected to affect the exsolution process. To study the energetics, we use <i>ab initio</i> computations combined with experiments in a SrTiO₃-based model system. Our calculations show that Ni preferentially segregates toward the (100)-oriented and SrTiO-terminated surfaces, note that this orientation is identical to one reported by the Irvine and Gorte groups. Vacancies in the Sr-site and O-site promote the segregation of Ni, while placing La on the Sr-site has an opposite effect. The corresponding experiments are in agreement with the computational predictions. Fast nanoparticle growth and activity enhancement are found in STO system with Sr vacancies and without La. The approach developed in this Letter could be used to study the mechanism of exsolution in other material systems, and possibly lead to the development of new compositions capable of nanoparticle exsolution with higher activity and stability