Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
71 Van Der Zwan et al. (17) state that minor rehabilitation strategies are similar to conventional dense-graded layers; however, they also state that the inherent drainage characteris- tics of the porous asphalt should be maintained and that the preferred method of rehabilitating porous asphalt layers is to mill the existing layer and replace with a new wearing layer. Lefebvre (21) indicates that a distinction needs to be made between minor and major rehabilitation of PFC layers. According to Lefebvre (21) minor rehabilitation entails small local repairs necessary because of small damage or distress while the rest of the pavement layer is in good condition. These circumstances were covered in Chapter 8, Corrective Sur- face Maintenance. Major rehabilitation is conducted when the entire layer is in need of repair. Major rehabilitation techniques include replacement of the entire layer or refurbishment of the entire layer. Replacement of the PFC would include completely removing the layer and replacing with a new layer. Refurbish- ment of the layer would include in-situ recycling. Though largely unsuccessful, it was noted that the Netherlands have been using hot in-place recycling to rehabilitate PFC (21). Pucher et al. (68) state that as of 1997, very little, if any, recy- cling of porous asphalt had occurred in Europe. However, they indicate that both cold-mix and hot-mix recycling are options for PFC layers. Cold-mix recycling would be a process where the reclaimed PFC would be combined with new asphalt and/or recycling agents to produce cold base mixtures. In contrast, hot-mix recycling would be the process of taking reclaimed PFC and combining with new materials through a hot-mix production facility. According to a European point of view, hot-mix recycling would be the highest level of value. Due to expected large amounts of PFC planned by the Dutch, they are placing an emphasis on recycling PFC, both in-plant and in-place. The web-based survey conducted as a part of this research project indicated that the average service of life of PFC pave- ments was between 8 and 10 years. Regardless of the life expectancy, at some point the PFCs will have to be rehabilitated (24). Rogge (66) states that there are three methods for PFC rehabilitation: mill and inlay, in-place recycling or repaving, and overlays. In the same light, Brousseaud et al. (28) mentioned three rehabilitation techniques used in France: replacement with a new PFC, overlaying (with or without seal coat), and recycling in-place or in a plant. According to Rogge (66), mill and inlay only occurs when Oregonâs F-mix is placed on the shoulders. From the survey, when a PFC has reached the end of its functional life or when problems arose that called for rehabilitation, without exception, states milled and replaced the pavement with a new surface. Most agencies will remove the PFC by milling it off and replacing it with another PFC layer. Kandhal (4) states that it is generally recommended to mill off the existing OGFC and replace with a new OGFC or other type HMA. The Georgia DOT did express concern in the survey with placing PFC on milled surfaces. Through no explanation was given, it is assumed that the concern is about the grooves left in the underlying layer. These grooves may hold water. Within the responses to the survey, Georgia DOT indicated that they were investigating micro-milling. Winsatt and Scullion (67) reported major distresses on pavements which had overlays over the top of open-graded mixes. Moore and Hicks (47) indicate two types of rehabilitation practices and Hicks for open-graded asphalt mixes: overlays and mill and fill. They mention that overlays are performed using open-graded or dense-graded mixes, and that mill and fill operation consists of milling off the open-graded mix and replacing with another open-graded mix. They mention that adequate care should be taken to ensure the new material placed as part of the mill and fill operation is able to drain completely. The authors mention that there are several considerations that need to be made for rehabilitation of pavements with open- graded asphalt mixes, and that the appropriate method of rehabilitation of such pavements is being researched. They indicate that a small number of such projects have been reha- bilitated or have been marked for rehabilitation and that important considerations include inlay repairs prior to over- C H A P T E R 9 Rehabilitation of Permeable Friction Courses
laying, changing the wearing surface mix type, and drainage issues with a middle layer of open graded asphalt. Moore and Hicks (47) mention that the European experience indicates a preference for mill and inlay with recycling and that this approach eliminates the challenges associated with overlays and PFC pavements. Overlaying the in-place layer with a dense-graded or open-graded mix or mill and inlay are further emphasized by Moore and Hicks (47). From a state perspective, Massachusetts Highway Department offers the following rehabilitation techniques: the most desired practice is to mill out the OGFC to a depth of 2-1â2 in. and replace it with 1-3â4 in. of dense binder and 3â4 in. of OGFC; the second option is to mill the OGFC to the top of the dense binder and replace it with 3â8 in. or less of surface treatment; and, the final option is to micro-mill the OGFC to the top of the dense binder (36). Bishop and Oliver (53) cite references and experiences to contend that life expectancies for OGFC pavements in British Columbia are about 12 years, compared to 14 to 15 years for conventional pavements. They mention that while riding sur- faces will not be obtained by using methods such as hot in-place recycling on existing OGFC mixes, it is possible to use another OGFC layer as a rehabilitation method, provided the existing OGFC is sealed properly. They also mention that it is impor- tant to rehabilitate the entire pavement, including the shoulders to make sure that adequate drainage is maintained (53). 72
