Farhad Salour Doctoral Thesis

2.
 
Pavement Environmental Factors 
Pavement structures and their surrounding environment are in continuous interaction. 
Similar to their surrounding environment, pavement structures can also be characterized 
by temperature, moisture content and acting pressure regimes which are governed by 
the physical laws of the pavement porous mineral system (Doré and Zubeck, 2008). 
These parameters undergo daily and seasonal variations as well as a spatial distribution 
as they are interconnected to the constantly evolving environment that surrounds the 
pavement system. The two main environmental factors in pavement engineering are 
temperature and moisture content. 
2.1.
 
Pavement temperature regime 
Pavement temperature is mainly governed by the pavement system boundary conditions 
and the system’s available energy. The temperature of the materials of the pavement 
layers and its variation highly depends on the surrounding environmental conditions, 
the location within the pavement system and the thermodynamic properties of each 
material. While the temperature at the lower depths in the pavement system is almost 
constant throughout the year, being nearly equal to the mean annual atmospheric 
temperature, the temperature in the top part of the system usually shows considerable 
daily and seasonal variations due to a more direct pavement-atmosphere interaction as 
well as exposure to surface solar radiation (Dysli et al., 1997; Hermansson, 2004; Doré 
and Zubeck, 2008). The pavement temperature regime therefore varies between a nearly 
stable bottom temperature and a constantly fluctuating surface temperature (pavement 
thermal regime trumpet). Figure 1 shows a 2 m deep temperature profile in a pavement 
structure in southern Sweden during a three month period. 
 
Figure
1.
Trumpet pavement temperature profile and its variation from February to 
May, 2010. Measurements are from the test site along county road 126 in southern 
Sweden. (Geographical coordinates: +57 3' 1.66", +14 34' 8.26") 

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There are two main factors that contribute to pavement heat intake: solar radiation of 
the asphalt concrete surface layer and geothermal heat flux; and two factors that 
contribute to heat extraction: surface convection and radiation emissions (Hermansson, 
2000; Doré and Zubeck, 2008). Heat may also be induced into or extracted from the 
pavement system due to condensation/evaporation, latent heat of fusion if pavement 
material pores contain moisture or ice lenses and heat exchange due to precipitation. 
Pavement temperature monitoring 
In many countries in the northern hemisphere where pavements experience 
considerable seasonal frost conditions, load restrictions are commonly imposed during 
the spring-thaw period to prevent severe pavement deterioration. During this period, 
the pavement structures are usually exposed to excess moisture content which results in 
reduced bearing capacity in unbound layers and therefore high resilient and permanent 
deformations. Monitoring a pavement’s environmental conditions such as frost zone 
(temperature) and moisture content can help road authorities to decide where and when 
to apply and enforce or to remove load restriction. 
In Sweden, monitoring pavement temperature profiles is carried out. The pavement 
temperature monitoring program consists of continuous pavement temperature 
measurements from sites that are spread over the country’s road network using the 
Tjäl2004 equipment. The Tjäl2004 is a frost rod that was developed at the Swedish 
National Road and Transport Research Institute, VTI (Wilhelmson et al., 2004). It 
consists of a series of temperature sensors mounted along a metal rod which are placed 
in a casing. The temperature sensors are located at 50 mm intervals throughout the 
pavement profile and down to a depth of 2 m. These temperature sensors register data 
at determined time intervals (usually every 30 minutes) using a data logger that is 
supplied with a battery. The temperature sensors are calibrated at 0º C to have the 
highest accuracy in detecting the frost zone. The data are then distributed online via the 
internet (http://www3.vv.se/tjaldjup). This database assists the local road authorities to 
give permission or forbid heavy axle load passages during certain periods by controlling 
the frost zone condition in the pavement structure. Figure 2 shows typical registrations 
from November 2010 to April 2011 from the station along county road 126 near 
Torpsbruk in southern Sweden. The overall formation of the frost zone, repeated 
frost-thaw cycles in the upper part of the pavement, and the thaw penetration can be 
seen in Figure 2. 

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