Annotated Literature Review for NCHRP Report 640 (2009)

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78 terminal, arrival at the contractor’s plant and prior to use. The results indicated that the materials met all specifications. 1.16.8 Structural Design No information on structural design of porous asphalt mixtures has been provided. 1.16.9 Limitations No information on limitations of porous asphalt mixtures has been provided. 1.17 Rogge, D. and E.A. Hunt. “Development of Maintenance Practices for Oregon F-Mix – Interim Report SPR371.” Oregon Department of Transportation. Salem, OR. August 1999. 1.17.1 General This paper outlines Oregon’s experience with a 19mm open mix known as the F-mix which they began using in the 1970’s. Even at the time of this report in 1997, little experience and knowledge was available on the correct maintenance and rehabilitation procedures for the F-mix. Thus, the research presented in this work was aimed at determining the current state of practice and future direction for the maintenance and rehabilitation of the F-mix. The research approach by Rogge et al involved surveying ODOT maintenance personnel on their thoughts and perceptions regarding F-mix maintenance, conducting a literature review regarding others experience with porous (open) asphalt, and research into new maintenance materials and techniques. The overall response to the survey conducted in this research was low, with only 25 surveys returned. From these results the most common distresses in the F-mix were: clogging, icing problems, fat spots/bleeding, and cracking (alligator). Other distresses noted were deformation rutting, tire stud rutting, and gouging/scarring (snow plow etc.). The respondents were also asked to identify the maintenance techniques they had employed on the F-mix. Blade patching with a dense-graded hot mix was the most widely used technique followed closely by mill, inlay and screed patch with dense-graded hot mix. Only 8 of the 25 respondents said that they had used a fog seal for the F-mix. Most expressed concerns over fog sealing clogging the porous pavement, reducing skid resistance, and disrupting traffic operations. Finally the survey addressed the perceptions that the maintenance personnel had on the F-mix as compared with a conventional dense mix. Rogge et al state “Clearly the perception of maintenance supervisors is that F-mix requires more maintenance than dense-graded asphalt pavements, and that the repairs for F-mix are more expensive than for dense-graded pavements.” Through the literature review conducted by Rogge et al identified the maintenance challenges of the F-mix. Most significant are clogging, permeability, winter maintenance, and physical/mechanical distress.

79 Rogge et al concluded by discussing new techniques in maintenance for the F-mix. Furthermore they state: a clogged porous pavement still drains better than a conventional mix, conventional repair techniques may be used on limited areas of F-mix provided drainage is not impeded, the greatest hindrance to F-mix repair is lack of F-mix material in small quantities, and optimum maintenance procedures for porous pavements have not yet been identified. 1.17.2 Benefits of Permeable Asphalt Mixtures Rogge et al did not discuss benefits of permeable asphalt mixtures. 1.17.3 Materials and Design Rogge et al did not discuss materials and design. 1.17.4 Construction Practices Rogge et al state that the F-mix is placed 50 mm thick. 1.17.5 Maintenance Practices Rogge et al state that use of traditional dense-graded mixes to repair the F-mix “…destroys the free draining characteristics of the F-mix, changes noise and ride characteristics, and increases the possibility of rutting problems.” Many issues have been raised over the correct emergency maintenance procedures as there are only procedures written for conventional dense-graded mixes. To mitigate clogging, Rogge et al discuss efforts undertaken in Europe to use a suction sweeper to clean the porous pavement, although they conclude that these efforts have not been promising. In regards to winter maintenance, Rogge et al state that a de-icing agent is needed that can stay on the surface of the porous pavement rather than slipping into the voids. Future possibilities include mixing calcium magnesium acetate with another material that will stick to the surface. Rogge et al were unable to find any evidence to endorse or condemn the use of fog seals as a preventive maintenance practice for the F-mix. 1.17.6 Rehabilitation Practices Rogge et al state that there are three methods for porous asphalt rehabilitation: mill and inlay, in-place recycling or repaving, and overlays. 1.17.7 Performance Rogge et al state that field performance of the F-mix has been excellent; however they have many concerns over the proper maintenance and rehabilitation of these mixes as they become older. Furthermore Rogge et al state that, “Dissatisfaction with maintenance procedures could jeopardize ODOT’s continued use of a successful paving procedure (F- mix).”