During winter time, road services use deicers to keep or restore a good adhesion level. Deicers are either applied as dry salt or pre-wetted with brine, before or once the sliding phenomenon has appeared. A study was undertaken so as to get a better knowledge of the effect of deicers, which could reach 55 millions of euros, to determine its residual amount on the road, and to evaluate its impact on road safety and environment. A deicer is usually hygroscopic, causing the roads to be damp once applied on their surface. Hydration develops according to ambient relative humidity of the air, or on the ground in a liquid form. The study has consisted in evaluating the effect of the air temperature (from 6 to 10degreesC) and of relativehumidity (from U=75 to 98%) on brines at different concentrations as a function of time. Brine concentration was conducted measuring out chloride, the electrical conductivity, and determining the refractive index of the solution. In these conditions of work, an increase in brine concentration (U < 90%), or a steady one (U > 90%) was observed. Precipitations did not ease the deicer action because of the dilution, the drainage caused by the road slopes, and the spraying-splashing from the traffic. An evaluation has been done based on experimental data. The amount of deicer was decreasedby two to three orders of magnitude in case of rain. The first 2000 vehicles caused the most significant loss of deicer. The spreading appeared forthe first thousand of vehicles before any loss is registered. Traffic caused a heterogeneity between wheels tracks and the rest of the road. An analysis has shown that the loss could account for 25%, a figure close to those given in the literature. A model was developed and quite properly reproduced the effect of traffic (spreading, preferential reduction in wheel tracks). For the covering abstract see ITRD E143097.
Abstract