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82 1.18.5 Maintenance Practices The article states that more salt is needed for winter maintenance because of the porous nature of the layer. The open nature of the layer also causes the layer to cool quicker than typical dense-graded layers and, therefore, it is necessary to initiate winter maintenance earlier. 1.18.6 Rehabilitation Practices No specific rehabilitation practices were given. 1.18.7 Performance No specific performance measures were given. 1.18.8 Structural Design No specifics on inclusion within structural design were given. 1.18.9 Limitations No specific limitations were given. 1.19 Backstrom, M. âGround Temperature in Porous Pavement During Freezing and Thawing.â Journal of Transportation Engineering. American Society of Civil Engineers. Reston, VA. Volume 126, Issue 5, September 2000, pp.375- 381. 1.19.1 General This paper addresses a full scale study of porous pavements during periods of freezing and snowmelt. The objective behind the study was to determine if porous pavements were suitable for storm water management in cold regions. A field site was setup in northern Sweden. The specific existing pavement area had frost damage and was noted to accumulate water (puddle) after snowmelts. The exiting pavement was removed and 45mm thick porous asphalt (5% asphalt content) was placed on one section. On another section a 45mm thick impermeable base was placed (6% asphalt content). These two sections were used for comparative purposes. During the study the following items were monitored for each pavement section: climatic conditions (ambient temperature and precipitation); depth of ground water table below pavement surface; ground temperature; temperature response in each pavement; frost penetration depth; and frost heave. Some highlights of Backstromâs findings were: two major factors that influence freezing in porous pavements (variations in air temperature and ground heat flux from the soil below), frost penetration in the soil below the subgrade was related to the number of negative degree days, tests showed that even a clogged porous pavement retained sufficient drainage capacity to handle snowmelt, and thawing of porous pavement is a function of air temperature, ground heat flux, increased net radiation and energy content of the infiltrating meltwater.
