Removal Effect of Basic Oxygen Furnace Slag Porous Asphalt Concrete on Copper and Zinc in Road Runoff

In order to improve the utilization efficiency of road runoff and the remove effects of heavy metals, porous asphalt pavements have been used as an effective measure to deal with heavy metals in road runoff. However, the removal effect on dissolved heavy metal is weak. In this paper, basic oxygen furnace (BOF) slag was used as aggregate in porous asphalt concrete to improve the removal capacity of heavy metal. Road runoff solution with a copper concentration of 0.533 mg/L and a zinc concentration of 0.865 mg/L was artificially synthesized. The removal effect of BOF slag porous asphalt concrete on cooper and zinc in runoff was evaluated by removal tests. The influence of rainfall intensity and time on the removal effect was discussed. The results obtained indicated that BOF slag porous asphalt concrete has a better removal effect on copper. The removal rate of copper is 57–79% at the rainfall intensity of 5–40 mm/h. The removal rate of zinc is more susceptible to the changes of rainfall intensity than copper. The removal rate of zinc in heavy rain conditions (40 mm/h) is only 25%. But in light rain conditions (5 mm/h), BOF slag porous asphalt concrete maintains favorable removal rates of both copper and zinc, which are more than 60%. The heavy metal content of runoff infiltrating through the BOF slag porous asphalt concrete meets the requirements for irrigation water and wastewater discharge. The results of this study provide evidence for the environmentally friendly reuse of BOF slag as a road material and the improvement of the removal of heavy metal by porous asphalt concrete.

The Prospect of Microwave Heating: Towards a Faster and Deeper Crack Healing in Asphalt Pavement

Microwave heating has been shown to be an effective method of heating asphalt concrete and in turn healing the damage. As such, microwave heating holds great potential in rapid (1–3 min) and effective damage healing, resulting in improvement in the service life, safety, and sustainability of asphalt pavement. This study focused on the microwave healing effect on porous asphalt concrete. Steel wool fibres were incorporated into porous asphalt to improve the microwave heating efficiency, and the optimum microwave heating time was determined. Afterwards, the microwave healing efficiency was evaluated using a semi–circular bending and healing programme. The results show that the microwave healing effect is largely determined by the steel fibre content and the mix design of the porous asphalt concrete.. Besides, the uneven heating effect of microwave contributes to an unstable damage recovery in the asphalt mixture, which makes it less efficient than induction heating. However, microwaves exhibited the ability to penetrate further into the depth of the test specimen and heat beneath the surface, indicating deeper damage recovery prospects.

Assessing the Marshall Properties of Porous Asphalt Concrete

Porous asphalt paving is a modern design method that differs from the usual asphalt pavements' traditional designs. The difference is that the design structure of porous pavements allows the free passage of fluids through their layers, which controls or reduces the amount of runoff or water accumulated in the area by allowing the flow of rain and surface runoff. The cross-structure of this type of paving works as a suitable method for managing rainwater and representing groundwater recharge. The overall benefits of porous asphalt pavements include environmental services and safety features, including controlling the build-up of contaminated metals on the road surface, rainwater management, resistance to slipping accidents, reduced splashing, and spraying pedestrians and drivers. In this study, the porous mixture's volumetric and physical properties were tested, and the use of carbon fibers as a type of mixture improver. The results were compared after performing the following steps: Selecting the best gradient for the porous asphalt mixture by selecting the largest proportion of air voids from three gradations group according to specifications (ASTM 7064), then choosing the optimum asphalt ratio according to the standard specifications, which are the value of drain down % and the Cantabro abrasion loss % value, as well as the ratio of air voids. After obtaining the optimum asphalt ratio, samples of the asphalt mixture were prepared. Carbon fibers were added to it at a rate of (0.3%) by weight of the total mix and a length of (2 cm) and prepared samples without additives. They were tested by a Marshall device to calculate the stability and flow value and show the effects of fibers on porous asphalt concrete properties. An increase in the stability value and a decrease in the flow and reduction in the drain down rate during exposure to high temperature were observed for the samples containing carbon fibers, by 48.8%, 44%, and 72%, respectively