Experimental studies of the dilution of vehicle exhaust pollutants by environment-protecting pervious pavement.

This study determines whether environment-protecting pervious pavement can dilute pollutants immediately after emissions from vehicle. The turbulence-driven dry-deposition process is too slow to be considered in this aspect. The pavement used is the JW pavement (according to its inventors name), a high-load-bearing water-permeable pavement with patents in over 100 countries, which has already been used for more than 8 years in Taiwan and is well suited to replacing conventional road pavement, making the potential implementation of the study results feasible. The design of this study included two sets of experiments. Variation of the air pollutant concentrations within a fenced area over the JW pavement with one vehicle discharging emissions into was monitored and compared with results over a non-JW pavement. The ambient wind speed was low during the first experiment, and the results obtained were highly credible. It was found that the JW pavement diluted vehicle pollutant emissions near the ground surface by 40%-87% within 5 min of emission; whereas the data at 2 m height suggested that about 58%-97% of pollutants were trapped underneath the pavement 20 min after emission. Those quantitative estimations may be off by +/- 10%, if errors in emissions and measurements were considered. SO2 and CO2 underwent the most significant reduction. Very likely, pollutants were forced to move underneath due to the special design of the pavement. During the second experiment, ambient wind speeds were high and the results obtained had less credibility, but they did not disprove the pollutant dilution capacity of the JW pavement. In order to track the fate of pollutants, parts of the pavement were removed to reveal a micro version of wetland underneath, which could possibly hold the responsibility of absorbing and decomposing pollutants to forms harmless to the environment and human health.

Assessment of clogging of permeable pavements by measuring change in permeability.

Permeable pavements are a common solution for stormwater management. Porous areas in the pavements allow water to percolate into the subsurface layers, reducing surface runoff. However, it is common for substances to clog the voids, decreasing the porous area and permeability of the pavement system. This study examined the change in permeability over time at a site with two permeable pavement systems, the JW Eco-technology (JW) and pervious concrete (PC). Square frames SF-4 and SF-9 were used to perform falling-head and constant-head permeability tests, respectively. Results show that JW had a similar permeability across the test locations, 6.27-7.64 cm/s when using SF-4, and 0.95-1.00 cm/s when using SF-9. While the permeability at the center locations of PC showed no significant loss of permeability, there was a significant reduction of permeability on the corner and edge areas, where permeability ranged 0.28-1.73 cm/s using SF-4 and 0.14-0.36 cm/s using SF-9, suggesting the occurrence of clogging over time at corner locations. Furthermore, the measured values highlighted the measurement variability in permeability between the falling-head based method and the constant-head method, with measurements from SF-4 being approximately 6.2-7.6 and 2.0-5.7 times higher than those from SF-9 on JW and PC, respectively. In addition, as no current literature quantifies the relationship between permeability and extent of clogging for the JW Eco-technology pavement, evaluation of the proportionate change in permeability with respect to voids, or individual aqueducts, of JW pavement were investigated. While not a 1:1 linear relationship, data indicate that the permeability increased with an increase in non-blocked aqueducts. The JW pavement maintained more than 50% of its capacity when half of the aqueducts were fully blocked. Even when only one aqueduct was clear from clogging, the system had 36% (SF-4) and 19% (SF-9) of maximum permeable capacity.