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.
212 1.53 Flintsch, G.W. âAssessment of the Performance of Several Roadway Mixes Under Rain, Snow, and Winter Maintenance Activities.â Final Contract Report. Virginia Transportation Research Council. VTRC-04-CR18. Charlottesville, Virginia. 2004. 1.53.1 General This report documents a research effort to assess the relative functional performance, including skid resistance and splash/spray, of various HMA surfaces during controlled wet and wintry weather events. The research was conducted in the field at the site of the Virginia Smart Road. The Virginia Smart Road research facility provided a unique opportunity to evaluate full scale pavements during wet and wintry conditions in a controlled manner. Either artificial snow or rain could be applied to the various pavement surfaces in order to research splash/spray during wet weather or various deicing/anti-icing techniques during snow events. Six different wearing surface types were investigated: five hot mix asphalt and one Portland cement concrete. Three of the hot mix asphalt wearing surfaces were designed as dense-graded using the Superpave mix design system while the remaining two hot mix asphalt wearing surfaces were a SMA and OGFC. The final wearing surface was a tined Portland cement concrete surface. [No specifics were provided on the method of tining.] Two separate experiments were conducted by Flintsch. First, artificial snow was produced and spread over the pavement surface. Flintsch described an extensive process that creates the snow and spreads the snow in a reasonably uniform manner. The second experiment involved producing artificial rain to provide wet driving conditions. 1.53.2 Benefits of Permeable Asphalt Mixtures Flintsch concluded that OGFC mixes reduced splash and spray during wet weather events. 1.53.3 Materials and Mix Design No specifics on materials and mix design were given. 1.53.4 Construction Practices No specifics on construction practices were given. 1.53.5 Maintenance Practices The effect of various deicing and anti-icing procedures was evaluated during the wintry weather experiment. Table 105 presents a summary of the various deicing/anti-icing techniques utilized by Flintsch. As shown in Table 105, sodium chloride was utilized in each of the tests. Depending upon the test, sodium chloride was used in a granular, pre- wetted or liquid form. Liquid calcium chloride was also used to pre-wet the granular sodium chloride for some of the tests.
213 Table 105: Summary of Deicing/Anti-icing Techniques Test Test Date Applied Chemical Application Rate Pre-wetting Rate I 2-12-2002 Dry solid sodium chloride 200 lb/lane-mile None II 3-04-2002 Solid sodium chloride prewetted with liquid calcium chloride 200 lb/lane-mile 10 gal/ton III 3-06-2002 Solid sodium chloride prewetted with liquid calcium chloride 200 lb/lane-mile 10 gal/ton IV 3-23-2002 Solid sodium chloride prewetted with liquid calcium chloride 300 lb/lane-mile 10 gal/ton V 1-27-2003 Solid sodium chloride prewetted with liquid calcium chloride 300 lb/lane-mile 10 gal/ton VI 2-06-2003 Liquid sodium chloride solution 40 lb/lane-mile None The research team utilized a general working procedure to produce and spread the snow, apply the deicing/anti-icing chemicals and measuring performance. The procedure generally included identifying appropriate weather conditions (temperature) for the production and placement of the artificial snow. The snow was then generated and applied to the pavement. A spreader then applied the deicing chemicals to the roadway, except in the instance where the anti-icing chemical was placed prior to the production of the snow. Traffic was then initiated. When the snow accumulation had reached approximately 50mm (2 in.), snow generation was ceased and the pavement plowed twice. Friction was then measured using an ASTM D274 skid trailer using a smooth tire. Results from the skid trailer were used to calculate a Skid Number (SN). In all cases, the SNs were very low (Table 106). An analysis of variance conducted on the SN values on each of the sections indicated no significant differences between treatment type (deicer or anti-icing materials) or wearing surface type. Flintsch indicated that the lack of significance could have been caused by the make-up of the artificial snow. Naturally occurring snow has an equivalent water coefficient of 1:10 (1 in. of equivalent water for every 10 in. of snow) while the water equivalent for the artificial snow was approximately 1:4. The extra amount of water may have diluted the deicing/anti-icing chemicals and, therefore, reduced their effectiveness. Flintsch also surmised that the amount of traffic (one truck and one car) was not enough to facilitate the spread of the chemicals and the formation of a liquid layer to prevent the bonding between the pavement and snow.
