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69 7.1 Overview Permeable pavements are different from conventional, impervious pavements in many respects. Therefore, operations on and maintenance of permeable pavements are different from those for other types of airport pavements. The primary concerns with these pavements is maintaining their permeability and preventing infiltration of hazardous or environmentally unsound products into subsurface layers. 7.2 Operations When an airportâs facilities include permeable pavements, it must make sure that employees and contractors using and maintaining the pavements know about them. There needs to be awareness of what permeable pavement is and how it should and should not be used. Signs can be placed in areas with permeable pavements to create this awareness. Additionally, lease agree- ments with tenants should include language that makes the tenants aware of the differences between permeable pavement and conventional pavement. Tasks performed by tenants, such as aircraft maintenance, should be performed inside of hangars and not on permeable pavement. The permeable pavement will need to be inspected routinely to make sure it is free of debris and sediments. Additionally, the pavement should be inspected after rain events to ensure that it is draining properly. Permeability testing once or twice per year is an effective way of monitoring that the pavement is functioning properly. Such tests include ASTM C1701, Standard Test Method for Infiltration Rate of In Place Pervious Concrete, and ASTM C1781, Standard Test Method for Surface Infiltration Rate of Permeable Unit Pavement Systems. Vacuum sweeping should be conducted on a regular basis to maintain surface permeability. While this may be considered a maintenance item, it should become part of normal airport operations. However, the frequency of this maintenance does not appear to be well established. Practices identified in the case studies ranged from weekly to biannually to no scheduled cleanings. The generally recommended frequency is twice per year. However, the required frequency likely varies by site based on the amount of traffic and the potential of fine materials/sediments to be tracked onto the surface (or contained in surface run-on). The use of permeability testing of the surface can help with determining the required frequency. Maintenance may also be required at a certain frequency based on local stormwater requirements to meet water quality objectives. Flushing or power washing has been shown to re-establish permeability (Werner 2016), but there is concern that power washing can drive fine material into the pavement structure. Winter operations on permeable pavements are different from similar operations on impervious pavements. Snow removal with plows should be performed with non-metal blades; references differ on whether the plow blade should be slightly elevated above the pavement. A metal plow C h a p t e r 7 Operations and Maintenance
70 Guidance for Usage of permeable pavement at airports blade on the surface of permeable pavement can abrade the surface and potentially create FOD. Snow should not be piled on the permeable pavement. Sand should not be used on permeable pavements to improve friction during winter opera- tions. Occasional application of sand is acceptable on pervious concrete as long as it is not a fine sand. Permeable pavements usually do not need deicers, or they may require less deicer. Porous asphalt and PICP (for the most part) are not greatly influenced by deicers. The NRMCAâs Pervious Concrete Pavement Maintenance and Operations Guide (NRMCA 2015) further indicates for pervious concrete that: â¢ Anti-icing pretreatments should not be used. â¢ Deicers containing magnesium chloride, calcium magnesium acetate, or potassium acetate, or containing fertilizers such as ammonium sulfate or ammonium nitrate, should never be used. NRMCA indicates that, for pervious concrete, agents containing calcium chloride should not be used until after the first year of service, and it is recommended that these agents not be used even after the first year of service (NRMCA 2015). Tracking of these materials from adjacent areas also needs to be minimized, which may require sweeping adjacent areas and monitoring application in adjacent areas. Permeable pavement surfaces should not be used to stockpile materials such as mulch, topsoil, or aggregate that are being used elsewhere. If it is absolutely necessary to use the area for temporary stockpiling, the area should be covered in tarps, boards, or other material to prevent clogging of the surface. 7.3 Maintenance Permeable pavement will require maintenance activities over time. However, these will be dif- ferent from maintenance performed on conventional pavement. Surface seals that may be placed elsewhere on an airport cannot be placed on permeable pavement. Nor should the permeable pavement receive conventional HMA overlays. Crack sealing is also not performed on permeable pavement. NAPA suggests that conventional, nonporous patching materials can be used for repairs as long as the total area is less than 10% of the paved area (Hansen 2008). This recommendation is acceptable for pervious concrete as well. Approved permeable patching material should be used if the total area of patching exceeds 10%. PICP repairs are typically replacing cracked pavers, replacing joint filler aggregate, or addressing settlement by removing the pavers, repairing the bedding layer, and replacing the pavers and joint aggregate (Smith 2015). At the end of its life, permeable pavement is typically milled off, down to the choker layer. If surface distresses (such as raveling) are prevalent, grinding the surface and overlaying with new permeable material may be possible. This may be appropriate especially for permeable pavements with a stabilized base layer. However, ensuring that fine material does not enter the underlying permeable material to remain may be difficult. The permeability of the remaining material would need to be verified. Adjacent areas need to be maintainedâparticularly vegetated areas that may allow soil to wash over the permeable pavement. These areas should be designed to drain away from the permeable pavement or at least have sufficient vegetation to avoid erosion. Maintenance work includes mowing grasses and seeding bare areas. Drainage structures need to be inspected occasionally to ensure proper functioning. Inspec- tion after major rain events will show if the systems are flowing properly. Underdrain systems should have cleanouts to facilitate inspection and cleaning. Cleaning needs to be performed when water flow is impeded.