Skid Resistance of Magnesium Chloride Roads

Abstract

Hygroscopy is the main stabilization mechanism that explains the good performance of Hexahydrated Magnesium Chloride (6H2O•MgCl2) roads as it absorbs and retains the air relative humidity (RH), reducing erosion and increasing durability. However, it has been observed by road users that skid resistance of 6H2O•MgCl2 roads decreases with the increase of RH. To study the skid resistance of 6H2O•MgCl2 roads the drag factor or friction coefficient of the road surface was calculated using the braking test, where an accelerometer is installed in a vehicle and deceleration is recorded during braking. The braking test was used to calculate the effect of air relative humidity and surface condition on the skid resistance in 30 road sections located in the northern region of Chile. The testing was designed using an experiment factorial considering: the surface condition (well-graded, sealed, and loose aggregates), if water was artificially added to the surface (‘normal’, ‘wet’), and a wide range of RH (between 10% and 70%). Results showed that when RH is higher than 35-40% the friction of 6H2O•MgCl2 roads decreases with an increase in RH. Nevertheless, in environments where the air humidity is lower than 60% the friction coefficient is higher than 0.55, which provides suitable friction conditions for most low volume road geometric designs. It was also found that for average RH conditions (30%), the ‘sealed’ and ‘well-graded’ surfaces provided the maximum average friction coefficients of 0.707 and 0.745 respectively. However, the ‘sealed’ surface was the most sensitive to extremely humid conditions, with a reduction in the average friction coefficient of 39% compared to 20% and 24% for ‘well-graded’ and ‘loose aggregate’ surfaces respectively.