Comparative analysis of the natural convection process between hollow concrete brick layer and crushed rock layer

► A new hollow concrete brick layer is suggested for Qinghai-Tibet freeway. ► The natural convection velocity is got for the first time by the model experiment. ► The “Thermal Diode” Effect of porous medium is proved. ► The natural convection velocity and temperature difference is linear relation. ► The start-up temperature difference of convection occurrence is existent. ► Asymmetric temperature change result from heat transfer process and speed.