Optimization of Asphalt-Mortar-Aging-Resistance-Modifier Dosage Based on Second-Generation Non-Inferior Sorting Genetic Algorithm.

The use of steel slag powder instead of filler to prepare asphalt mortar was beneficial to realize the effective utilization of steel slag and improve the performance of asphalt concrete. Nevertheless, the anti-aging properties of steel-slag powder-asphalt mortar need to be further enhanced. This study used antioxidants and UV absorbers in steel-slag powder-asphalt mortar to simultaneously improve its thermal-oxidation and UV-aging properties. The dosage of modifier was optimized by second-generation non-inferior sorting genetic algorithm. Fourier-Transform Infrared Spectroscopy, a dynamic shear rheometer and the heavy-metal-ion-leaching test were used to evaluate the characteristic functional groups, rheological properties and heavy-metal-toxicity characteristics of the steel-slag-powder-modified asphalt mortar, respectively. The results showed that there was a significant correlation between the amount of modifier and G*, δ, and the softening point. When the first peak appeared for G*, δ, and the softening point, the corresponding dosages of x1 were 2.15%, 1.0%, and 1.1%, respectively, while the corresponding dosage of x2 were 0.25%, 0.76%, and 0.38%, respectively. The optimal value of the modifier dosage x1 was 1.2% and x2 was 0.5% after weighing by the NSGA-II algorithm. The asphalt had a certain physical solid-sealing effect on the release of heavy-metal ions in the steel-slag powder. In addition, the asphalt structure was changed under the synergistic effect of oxygen and ultraviolet rays. Therefore, the risk of leaching heavy-metal ions was increased with the inferior asphalt-coating performance on the steel-slag powder.

Hazardous characteristics and variation in internal structure by hydrodynamic damage of BOF slag-based thin asphalt overlay.

For the sustainable development of society, recycling of solid waste has received considerable attention worldwide. In this research, steel slag was used to replace natural aggregate in the thin asphalt overlay, and the hazardous characteristics and internal microstructure of this overlay were explored. The resistance to hydrodynamic damage of the overlay containing steel slag was also evaluated and compared with that of the traditional overlay. The results indicate that steel slag has potential leaching risk, which can lead to environmental hazards in long-term leaching processes. However, the recycling of steel slag in thin asphalt overlay inhibits the release of toxic heavy metals due to the encapsulation effect, thereby reducing the leaching concerns. Steel slag can significantly reinforce the skeleton structure and enhance the ability of the asphalt overlay to bear the load. The superior skeleton stability and moisture resistance of the steel slag asphalt overlay were observed after hydrodynamic treatment compared with overlays made of natural aggregate. The variations in the volumetric parameters and connectivity in the steel slag asphalt overlay are significantly less than those in conventional overlay after hydrodynamic treatment. This indicates that the volumetric characteristics of steel slag asphalt overlays are less affected by hydrodynamic pressure.

Environmental performance and functional analysis of chip seals with recycled basic oxygen furnace slag as aggregate.

Resource utilization of industrial waste is a significant global challenge. Steel slag, a typical industrial by-product in the steel-making process, pollutes the environment and causes ecological deterioration. In this study, steel slag was recycled in chip seals as the aggregate, and the functional and environmental performance of the chip seal with recycled steel slag was determined. Economic costs were also discussed and compared with conventional surface layers. The results indicated that recycling steel slag as the aggregate in chip seal has a lower pollution risk and higher environmental benefits compared with those used for landfilling and dumping. Steel slag can significantly increase the heating and de-icing efficiencies of chip seal compared with basalt, particularly for microwave heating. The self-bonded function represented by the durability of aggregate retention can be enhanced by steel slag. The cost of the chip seal containing steel slag and steel fiber is only increased by 0.14 USD/m2 than that of ordinary chip seal, indicating a remarkable economic efficiency of chip seal with de-icing and self-bonded functions.

Profile Features of Emulsified Asphalt Mixture Containing Steel Slag Based on Laser Scanning.

Micro-surfacing (MS), made of emulsified asphalt, is the most commonly used preventive maintenance technology in asphalt pavement. However, the studies on profile features of MS based on aggregate morphology are few. This study evaluated the profile features of MS and its effect on skid resistance. The aggregate morphologies were first characterized and modified emulsified asphalt was prepared. The three-dimensional profile features of four kinds of MS samples were captured by laser texture scanner. Results illustrate that steel slag aggregate can be used to enhance the skid resistance of pavement surface and bring about larger profile indexes than basalt and limestone due to its angularity index and flatness values. Further aging of steel slag to eliminate free calcium oxide (f-CaO) is recommended before being used in pavement surface layer.

Silicone Resin Polymer Used in Preventive Maintenance of Asphalt Mixture Based on Fog Seal.

The commonly used materials in fog seal are emulsified asphalt and modified emulsified asphalt. Nevertheless, there are some intractable problems including aging under ultraviolet, poor permeability, and moisture susceptibility. Therefore, silicone resin polymer was used as a kind of innovative fog seal material in this study. Physicochemical properties of solidified silicone resin were characterized. X-ray computed tomography and 3D reconstruction technology were used to evaluate permeability and distribution of silicone resin polymer in an asphalt mixture. Moisture sensitivity and high-temperature performance of the asphalt mixture maintained by silicone resin polymer were also detected. The results show that surface characteristic of silicone resin can effectively isolate moisture, thereby improving moisture resistance of the asphalt mixture. Silicone resin was found to be evenly distributed throughout the pores of a sample when the dosage was 400 or 600 mL/m2. The pore filling rate increased by 16.3% when the dosage was changed from 200 to 400 mL/m2, whereas it only increased by 3.7% when dosage increased from 400 to 600 mL/m2. Moisture damage resistance of asphalt mixtures generally increased as the dosage of silicone was increased. However, as the dosage increased from 400 to 600 mL/m2, the growth rate in residual Marshall stability (RMS) and tensile strength ratio (TSR) slowed significantly since the pore filling effect of silicone has reached the upper limit. Dosage of silicone resin has little effect on the results of the rutting test while it has significant influence on Hamburg wheel tracking test (HWT). Furthermore, it was found that 400 mL/m2 is the optimum silicone dosage for open-graded friction course (OGFC)-13 mixture in consideration of permeability, distribution, performance of mixture, and economic cost.

Residual Fatigue Properties of Asphalt Pavement after Long-Term Field Service.

Asphalt pavement is widely used for expressways due to its advantages of flexibility, low cost, and easy maintenance. However, pavement failures, including cracking, raveling, and potholes, will appear after long-term service. This research evaluated the residual fatigue properties of asphalt pavement after long-term field service. Fatigue behavior of specimens with different pavement failure types, traffic load, service time, and layers were collected and characterized. Results indicate that after long-term field service, surface layer has a longer fatigue life under small stress levels, but shorter fatigue life under large stress levels. Longer service time results in greater sensitivity to loading stress, while heavier traffic results in shorter fatigue life. Surface and underneath layers present very close fatigue trend lines in some areas, indicating that the fatigue behavior of asphalt mixture in surface and underneath layers are aged to the same extent after eight to ten years of field service.

Evaluation of Fine Aggregate Morphology by Image Method and Its Effect on Skid-Resistance of Micro-Surfacing.

Micro-surfacing is a widely used pavement preventive maintenance technology used all over the world, due to its advantages of fast construction, low maintenance cost, good waterproofness, and skid-resistance performance. This study evaluated the fine aggregate morphology and surface texture of micro-surfacing by AIMS (aggregate image measurement system), and explored the effect of aggregate morphology on skid-resistance of single-grade micro-surfacing. Sand patch test and British pendulum test were also used to detect skid-resistance for comparison with the image-based method. Wet abrasion test was used to measure skid-resistance durability for feasibility verification of single-grade micro-surfacing. The results show that the effect of Form2D on the skid-resistance of micro-surfacing is much stronger than that of angularity. Combining the feasibility analysis of durability and skid-resistance, 1.18⁻2.36 grade micro-surfacing meets the requirements of durability and skid-resistance at the same time. This study also determined that, compared with British pendulum test, the texture result obtained by sand patch test fits better with results of image method.