For pavements, conduction of heat is the most important factor for heat transfer. During warm and sunny summer days though, the temperature of a pavement base layer under a thin asphalt concrete, may reach high values and natural convection in a fairly permeable base layer should not, then, be neglected.
Mineral content, porosity, degree of water saturation and temperature affect the thermal conductivity of soils. The total conductivity is a function of the conductivity of each soil phase, solid grains, water and gas. Various equations for these mixtures have been proposed by Keey (1992) and Krischer (1963). Thermal conductivity values range between 1 and 4 W/m°C for saturated soils, and from 0.2 to 0.4 W/m°C for dry soils.
Because thermal conductivity of quartz is 3-4 times higher than that of other minerals the quartz content of a soil greatly affects the thermal conductivity. Typically, cohesive soils have a low quartz content while the quartz content of a fine sand is normally high.
