AbstractsBiology & Animal Science

Moisture movement in highway pavement structures coupled with soil-atmospheric fluxes

by Crystal Lacher




Institution: University of Saskatchewan
Department:
Year: 2010
Record ID: 1854358
Full text PDF: http://hdl.handle.net/10388/etd-06042009-085617


Abstract

The overall performance of a standard highway pavement structure depends on moisture characteristics of the underlying soil layers. Increase in the moisture content of the sublayers caused by moisture fluxes across the soil-atmosphere interface, decreases the strength of the pavement structure, which may cause premature failure of the structure. Therefore, the ability to evaluate the surface fluxes may be helpful in understanding mechanisms, which may enhance or degrade highway pavement performance. This research evaluates the application of the soil-atmosphere modelling software VADOSE/W as a tool for predicting the movement of moisture in highway pavement structures. VADOSE/W is a two-dimensional transient finite element program that simulates coupled heat and moisture migration in unsaturated soils with particular focus on fluxes across the soil-atmosphere interface. A typical standard highway pavement structure in Saskatchewan was chosen to evaluate coupled heat and moisture interactions between highway pavement structures and atmosphere, and the impact that design features may have on moisture movement. A laboratory testing program was established to characterize the material properties of hot mix asphalt (HMA), which is used as a surface layer for the driving lane as well as on occasion for the shoulder of highway pavement structures. HMA was characterized by its saturated hydraulic conductivity, soil-water characteristic curve, vapour flux rate and air permeability. The saturated hydraulic conductivity defines the maximum rate at which water can infiltrate HMA in the absence of cracks. Drastic changes to the saturated hydraulic conductivity of HMA can significantly increase or decrease the amount of infiltration during critical storm durations. The volumetric water content of HMA decreases rapidly at relatively low values of suction suggesting that HMA is either relatively hydrophobic or contains cracking of the internal structure such that it demonstrates very low air entry values. The 'pore spaces' of the HMA are likely only partially filled with water following drainage. The vapour flux rate of HMA defines the maximum evaporation rate through HMA in the absence of cracks. HMA produces a negligible amount of evaporation during the summer period compared with the amount of infiltration. The measured and calculated air permeability results for HMA were quite different indicating that problems might have occurred during the testing process. Some of the possible problems include air bubbles in the manometer, air leakage, and not allowing the flow meter to come into equilibrium. A numerical modelling component evaluated the mechanisms of coupled heat and moisture flux into the pavement structure when using six different design features, which have the ability to either enhance or degrade performance. The six design features include: varying the fluxes on the HMA surface; changing the shoulder conditions from unpaved to paved shoulders; changing the steepness of the sideslope; using both good and poor…