Estimation of moisture damage and permanent deformation in asphalt mixture from aggregate gradation

The present study explains the effect of aggregate gradation on moisture damage in bituminous mixes. Three types of aggregate gradation, two types of binder; VG-30 and Polymer modified bitumen (PMB-40) and two types of mixes Bituminous Concrete (BC) and Dense Bituminous Macadam (DBM) are used. Moisture susceptibility tests like retained stability and tensile strength ratio are conducted on Marshall specimens. The static creep test was also conducted for conditioned and unconditioned specimens to observe the effect of moisture on creep behaviour. The results indicate that Marshall stability and flow values are higher in PMB-40 mixes than in VG-30 mixes. Moisture susceptibility of PMB-40 mixes is low when compared with mix using VG-30. The reduction in retained stability, and Indirect Tensile Strength (ITS) and increase in creep are evaluated for finer, coarser and normal gradation of aggregates to observe the effect of gradation on moisture susceptibility of mixes. The retained stability is least affected when compared with other moisture susceptibility parameters. Also, gradation parameters s1 and Gradation Ratio (GR) are introduced in this paper to establish relation between aggregate gradation and moisture susceptibility and permanent deformation. Models are suggested to estimate rut depth from ITS and stability values.