Influence of Air Voids and Aggregates Composition on Moisture Damage Sensitivity of Bituminous Mixes

Durability of bituminous mixes is affected by presence or intrusion of moisture into it. The intrusion and amount of trapped moisture largely depend on the air voids present in the mixes. This study explores the combined influence of air voids and hydrated lime (HL, as anti-stripping agent) on moisture-induced damage of bituminous mixes prepared from two different aggregate sources. The aggregates used in the study are siliceous sandstone and basalt. Tensile Strength Ratio (TSR) test was used to determine the moisture susceptibility of bituminous mixes. A higher value of TSR depicts that the mixes are more moisture resistant. TSR was reaffirmed to be lowest at an air void range of about 5% to 13% which is termed as pessimum air void range. At this air void range, moisture gets trapped within the mix, resulting in moisture-induced damage. TSR results showed that bituminous mixes prepared with siliceous sandstone is more susceptible to moisture-induced damage as compared to mixes prepared with basalt. Boil water test reconfirmed the results. Use of HL in bituminous mixes improved its moisture-induced damage resistance only marginally. Thus, moisture-induced damage control at pessimum air void range using anti-stripping agent is not always sufficient. Observations show that air void plays a critical role in moisture-induced damage and control of air void during construction needs to be ensured.