Moisture-Induced Pressures in Concrete Airfield Pavements

Abstract

A mathematical model is developed to predict pressures generated by water and air in the pores of airfield concrete being heated by a jet exhaust. The foundation of this model is a constitutive relationship to characterize the flow of high-velocity, compressible, heated gases through a high-resistance porous medium. The key premise is that the resistance to flow can be modeled with friction coefficients analogous to the method used for simpler geometries. Pore pressure predicted using this model suggest that moisture in the pores of the cement paste is a probable cause of material failure when the pavement is being heated by the exhaust of a vertical takeoff aircraft such as the Harrier. With an initial pore saturation of 90% or greater, high pore pressures and pressure gradients result from air being compressed by the expansion of liquid water. Concrete temperatures beneath a Harrier reach 300°C in about 2 min. Even with a low saturation, the water vapor pressure could eventually be sufficient to cause a tensile failure in portland cement concrete.