Skid resistance of magnesium chloride roads

Abstract

Hygroscopy is the main stabilization mechanism that explains the good performance of magnesium
chloride hexahydrate (6H(2)O.MgCl2 or simply MgCl) roads, as it absorbs and retains relative
humidity (RH), reducing erosion and increasing durability. However, road users have observed that
the skid resistance of MgCl roads decreases with increased RH. To study the skid resistance of
MgCl roads, the study calculated the drag factor or friction coefficient of the road surface with a
braking test, in which an accelerometer was installed in a vehicle and deceleration was recorded
during braking. The braking test was used to calculate the effect of RH and surface condition on
skid resistance in 30 road sections located in the northern region of Chile. The testing was designed
with a factorial experiment that took the following into consideration: surface condition (well-graded,
sealed, and loose aggregate), whether water was artificially added to the surface (normal or wet),
and a wide range of RH (between 10% and 70%). The results showed that when RH was greater
than 35% to 40%, the friction of MgCl roads decreased as RH increased. In environments in which
the air humidity was lower than 60%, the friction coefficient was higher than 0.55, a value that
provides suitable friction conditions for most geometric designs for low-volume roads. The study
showed that a braking test is a simple and consistent tool for assessing braking performance on
MgCl roads. In addition, the study concluded that special attention should be given to surface
characteristics and geometric design where MgCl road sections are exposed to RH greater than
60%.