Farhad Salour Doctoral Thesis

Figure
2
Typical Tjäl2004 frost rod measurements from county road 126 near 
Torpsbruk in southern Sweden (November 2010 to April 2011). 
In Finland the Percostation system is used to optimize the use of load restrictions 
throughout the road network (Vuorimies, 2004). Percostation consists of electrical 
conductivity, dielectric value, and temperature sensors that are collected using eight 
individual channels with minimum measurement intervals of 60 seconds. The measured 
data are then stored in a data collection unit which can be read using a modem 
connection. The collected data are further analysed and the condition of different 
pavement layers and subgrade is assessed. The data are then compared to the critical 
limits and the decisions to impose or lift load restrictions and to determine the 
maximum allowed axle load and/or number of axles are made. 
2.2.
 
Pavement moisture regime 
Moisture condition in pavement structures continuously evolves throughout the year 
(Erlingsson et al., 2002; Doré and Zubeck, 2008; Erlingsson et al., 2009a). The moisture 
content of the unbound material that is usually set close to the optimum during the 
compaction in the construction phase will eventually change towards a natural 
equilibrium state (Zapata et al., 2009). Similar to the temperature condition of the 
pavement, the moisture regime is also governed by the boundary conditions of the 
system. The natural equilibrium moisture content is greatly dependent on the material 
properties and distance to the groundwater table level and its variation. Generally, the 
moisture condition at the bottom of the pavement system is relatively stable. However, 
at the upper sections in pavement systems, moisture condition can vary widely from 
very dry conditions to fully saturated states due to climatic events. The moisture 
condition of the upper section of the pavement greatly depends on the surface 
characteristics as well as its longitudinal and transverse position within the pavement 
system (Doré and Zubeck, 2008). The moisture content of the materials close to the 
pavement edges and in the vicinity of surface cracks usually shows higher variations due 
to climatic events such as rainfall (Hansson et al., 2005). 

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7 
The moisture evolution of the pavement systems throughout the year is the result of a 
complicated interaction of several factors that contribute to moisture intake and 
removal from pavement systems. There are four sources that contribute to moisture 
intake in pavement structures: infiltration of precipitation water, lateral moisture 
transfer, capillary rise and frost-thaw action. The two main factors that contribute to 
moisture extraction from pavement systems are moisture drainage and moisture 
evaporation (Doré and Zubeck, 2008; Erlingsson et al., 2009b). Figure 3 illustrates the 
factors that contribute to moisture regime variations in pavement structures.