Effect of material hydraulic properties on temporal moisture variations and performance of unbound pavements with sprayed seals

Abstract

Moisture is widely recognised as a primary factor responsible for road failures. In particular, unbound pavements with sprayed seals, a common type of flexible pavement used in Australia and New Zealand are highly susceptible to moisture-related performance losses. The wearing course of these pavements, i.e. the sprayed seals, is moderately permeable, which allows for moisture exchange between the environment and the pavement structure throughout its service life. As a result, the moisture content of pavement layers varies according to the prevailing climate, which could cause noticeable performance reductions.This study extensively investigates the moisture variations in pavement layers of unbound pavements with sprayed seals during the service life due to the variations of ambient climatic conditions. The moisture variations in 18 different typical sprayed sealed pavements were numerically simulated for 10-year climates of Melbourne and Adelaide. Both the degree of saturation (Sr) and suction (s) variations were simulated for a number of practical scenarios. The results indicated that the pavement layers reach an equilibrium condition within less than 6 months under the climates considered. A series of sensitivity analyses were performed to evaluate the effect of hydraulic properties of seal, unbound granular material (UGM), subgrade and effect of water table depth on the moisture variations of pavement layers. The parametric analysis revealed that relatively permeable seals facilitate significant wetting of the UGM layer and substantial drying due to variations in prevailing climatic conditions. Moreover, this study identified primary influencing factors that determine the equilibrium state and the temporal moisture variations of the pavement layers. The effect of water table depth is evaluated for different subgrade conditions. A pavement performance evaluation conducted following the effective stress concept, the factor Sr.s is presented in this study. Overall, the results highlight the importance of considering temporal moisture variations in the design stage to improve pavement performance.