1、英翻中English Literature1 MAINTENANCEMaintenance is a fundamental aspect to consider in any project involving OGFC or PA,since these activities cannot be performed in the same way as for conventional DGHMA. The first part of this section reviews the main issues associated with winter maintenance in bot
2、hOGFC and European PA materials. Next, surface maintenance is discussed, followed by a summary of current rehabilitation practices for OGFC and PA.1 .1 Winter MaintenanceIn general, open-graded mixtures exhibit lower thermal conductivity and reduced heat capacity compared with DGHMA (18). Elevated a
3、ir voids contents in OGFC reduce the flow rate of heat through the material. In fact, the thermal conductivity of OGFC can be 40 to 70 percent the magnitude of that for DGHMA, making OGFC operate as an “insulating course” at the surface (16).As a result of these thermal properties, the surface of OG
4、FC can exhibit temperatures 1 to 2C (1.8 to 3.6F) lower than the surface temperature of adjacent DGHMA, producing earlier and more frequent frost and ice formation (6, 16). Longer periods under such conditions,compared with DGHMA, are thus expected. The occurrence of this phenomenon in PA has been i
5、dentified in Europe (3, 16), in the United States12, and specifically in Texas13. Thus, the time to reach adequate pavement friction values after ice formation has occurred is longer in porous pavement (16). In fact, formation of black ice and extended frozen periods are currently considered the mai
6、n problems associated with OGFC maintenance in the United States12.Consequently, OGFC requires specific winter maintenance practices. For example, in addition to conventional practices for winter maintenance, the use of pavement condition sensors, meteorological instrumentation, and connecting hardw
7、are and software is suggested to monitor the road system and support the decision process involving when and how to treat an OGFC surface (5).More salt (or deicing agents) and more frequent applications than on DGHMA are required to perform winter maintenance on OGFC and PA (15, 16, 18, 32). In Texa
8、s13, deicing agents are currently considered the most effective winter treatment, followed by liquid deicer agents and sand. However, FHWA recommends developing snow and ice control using chemical deicers and plowing and avoiding the use of abrasive materials to improve traction (20).Spreading of sa
9、nd to enhance friction and hasten deicing contributes to the clogging of voids,causing a decrease in drainage and noise reduction capabilities, which are considered two of the main OGFC advantages (5).Since the deicer can flow into an OGFC instead of remaining at the surface, Oregon DOT has suggeste
10、d research on organic deicers with higher viscosity and electrostatic charge technology (similar to that employed in emulsified asphalt) to improve bonding of deicers on the surface (15).Intensive application of liquid deicing salts has allowed Belgium to obtain similar conditions between dense and
11、porous mixtures subjected to snowy weather. Further, higher frequency of application and 25 percent more liquid salting are reported in The Netherlands to address winter maintenance difficulties in PA (3, 6). Furthermore, the use of liquid chloride solutions was reported in the cold Alpine regions o
12、f Italy, Austria, and Switzerland as more effective than the use of solid salt (5). On the contrary, a Japanese study concluded that fundamental modifications are not required to practice winter maintenance in PA surfaces, since considerable differences between these mixtures and DGHMA were not foun
13、d (33).Britain practices preventive salting just before snowfall and more frequent application of salt in comparison with DGHMA (18). They recommend increasing the amount of salt applied on DGHMA sections that are adjacent to PA segments. This recommendation is due to the reduction in the transfer o
14、f salt from the PA to the DGHMA and the differences in response of each material. Additionally, they propose prompt plowing of snow using plows fitted with rubber edges on the blades (to prevent surface damage). Finally, greater control in the homogeneous application of deicing chemical is required
15、in OGFC, as the traffic has minimal contribution in its distribution over the OGFC surface (5).1.2 Surface MaintenanceAccording to a survey conducted as part of the National Cooperative Highway Research Program (NCHRP) Synthesis 284, there are no reports in the United States on the application of ma
16、jor maintenance for OGFC. From 17 states that reported the use of OGFC, only New Mexico,Wyoming, South Carolina, and Oregon employ fog seals to perform preventive maintenance.Although quantitative information about the significance of these treatments when applied to PA is not available, it is expec
17、ted that fog seals extend the life of porous mixtures since they provide a small film of unaged asphalt at the surface (15). FHWA recommends fog seal application in two passes (at a rate of 0.05 gal/yd2 for each pass) using a 50 percent dilution of asphalt emulsion without any rejuvenating agents (2
18、0).Research in Oregon regarding permeability reduction and changes in pavement friction on certain OGFC pavements generated by fog seals concluded that the mixtures still retain porosity and keep the rough texture related to its capability to reduce the potential for hydroplaning (15). However, quan
19、titative conclusions regarding the changes in these parameters are not included. A decrease in pavement friction was noticed immediately after fog seal application, but during the first month, it increased considerably by traffic action.Snow plow blade abrasion has considerable effects on the durabi
20、lity of traffic markings on OGFC. Thermoplastic markings or even some fragments of mixture impregnated with thermoplastic can be displaced when steel snow plow blades are used for winter maintenance.Field trials in Rhode Island showed the lack of durability of the permanent inlaid traffic marking ta
21、pe on modified OGFC under such conditions. Therefore, they recommended suspension of the use of permanent inlaid traffic marking tape until corrections can be implemented to improve durability (34).Rhode Island further reported that recessed thermoplastic traffic markings proved cost effective in co
22、mparison with non-recessed thermoplastic markings. Although recessed thermoplastic traffic markings showed lower snowplow blade damage, fully and semi-recessed markings installed in a tangent highway test section failed to maintain the recommended minimum retroreflectivity in wet night conditions. T
23、his result was associated with the effect of the water film present in the tangent section but was irrelevant in the super-elevated curved test section included in the research (34).Highway agencies in British Columbia, South Carolina, and Maryland reported that thermoplastic marking material was th
24、e most appropriate for OGFC applications (16). The British limit the use of pavement markings with thermoplastic materials to certain directional signs and arrows, considering that on PA the marking material has more opportunity to flow downward into the mixture (18). Although higher demand of marki
25、ng material in OGFC (due to higher porosity) was reported by some agencies in the United States (e.g., Ohio, New York, and Oregon), there were no specific recommendations regarding materials for traffic marking (16).Cleaning of OGFC in the United States is not common practice. This approach indicate
26、s that local agencies accept that OGFC functionality can be maintained due to its auto-cleaning capacity created in highways with relatively high speed and high volumes of traffic by the suction generated by tires rolling on the OGFC (5). High-pressure washing is currently quite expensive and of que
27、stionable value. Current maintenance activities in Denmark include cleaning of the voids by high-pressure water and air suction twice a year as a strategy that combines the construction of two-layer drainage asphalt and cleaning in order to maintain porosity during the pavement lifetime (11). In gen
28、eral, European practice limits placing of PA on highways with speeds higher than 50 km/h (31 mph) to help in keeping the surface clean (10).On the other hand, Japan is applying the “function maintenance” concept that comprises more frequent cleaning operations with only partial debris removal during
29、 each cleaning (31).1.3 Corrective Surface MaintenanceMill and inlay using OGFC was recommended in Oregon to repair OGFC when the quantities of material were enough to justify these activities. If only a small quantity is needed,DGHMA is suggested for patching (15). FHWA advises one to consider the
30、area and the drainage continuity (20). Thus, when the area to be repaired is small and the flow around the patch can be ensured, DGHMA is recommended for patching. Otherwise, the zone should be repaired by using OGFC mixture. Nonetheless, in 2000, the use of DGHMA to repair delaminated areas and pot
31、holes was indicated by all states in the United States that reported the utilization of OGFC. Crack filling was reported only by Wyoming DOT, and according to their experience, drainage problems can result from crack sealing, since water flow inside the materialis diminished (16).In Britain, the use
32、 of PA or open-graded macadam is recommended to repair both small and large potholes. The use of dense bitumen macadam is permitted, if necessary, but its replacement by permeable mixture is recommended. Finally, the application of hot-rolled asphalt(HRA) is limited for repairing small areas (i.e.,
33、on the order of 0.50 m 0.50 m 1.64 feet 1.64feet maximum) (18).To diminish the wheel impact on the patch joint and facilitate the flow of water around a DGHMA patch, rotation of the patch to 45 degrees to provide a diamond shape is recommended.Alternatively, the execution of machine patch, blade patch, or screed patch may be used
