Asphalt paving at temperatures below freezing : A quick scan of available information and expert opinions

This document reports a 'quick scan' of available literature and information and international expert opinions on the (im)possibilities, limiting conditions and points of attention for laying asphalt mixtures at temperatures below freezing. This targeted on wearing courses of Porous Asphalt (PA), especially the current Dutch standard mix for motorways called ZOAB+ (thickness 50 mm, 0/16 grading with 5,2% bitumen 70/100 in the mixture, and 20% air voids). This quick scan is executed by KOAC•NPC, commisioned by the Innovation Test Centre (ITC) of the Dutch Highways Authority (Rijkswaterstaat) . The background for this quick scan is the amount of frost damage (mainly raveling of PA) on motorways during the harsh winter of 2008-2009. The Dutch Highways Authority strives for low-hindrance road maintenance by immediate and sustainable repairs. Therefore ITC wanted to perform a test during the winter of 2009-2010, having ZOAB+ wearing courses laid at temperatures below freezing. These should have the same properties, quality and service life as ZOAB+ laid under normal weather conditions. This quick scan served as preparation for this test, reviewing the available information. This quick scan comprises the following elements: • some Dutch experiences and likely solutions; • perception of experts in the field; • literature review; • points of interest to develop an assessment for cold weather paving. Although the international experience and literature was almost exclusively based on dense graded asphalt mixtures, it is also relevant for PA. It can be summarized as: "Ensure that adequate compaction is achieved while the asphalt mixture is still sufficiently warm to be compactable". Other points of attention are aggregate drying and heating, extra attention to tack coat and joints, temperature and humidity (preheating and drying) of the underlying structure, monitoring mat temperature during compaction and determination of available compaction time. In spite of these precautions, the weather remains an important factor. Not only air temperature, but also wind speed, precipitation and solar influx.