Field-Simulating Laboratory Aging Procedure for Bituminous Mixtures in Tropical Regions

Abstract

This study emphasized binder aging of bituminous mixtures in the field and compared it with newly developed field-simulating laboratory aging procedures. Monthly field cores from a pavement section were collected for this investigation over 2 years. After measuring the field core samples’ bulk density, the air voids were calculated to assess the densification with time due to traffic. Binder was extracted from the field core samples, and further tests were carried out to assess the rate of aging with time. Also, the bituminous specimens prepared in the laboratory at the optimal binder content were subjected to field-simulating oven-aging methods. The bituminous mixture aging process in AASHTO R30 does not match field conditions in tropical countries. Therefore, new techniques have been developed in this study to calculate the number of days required for laboratory aging to simulate field-aging conditions. The oven was modified by introducing ultraviolet bulbs and oxygen supply, termed Laboratory Oven Aging-lll (LOA-III). Test results showed that 10 days of LOA-III corresponded to 47 months in the field. The Fraass breaking point indicated that LOA-III also simulates low-temperature conditions. Experiments conducted in the laboratory revealed that LOA-III accelerates aging and can simulate field conditions in tropical countries more accurately than AASHTO R30. The field study showed that higher initial air voids in the surface layer accelerate binder aging, causing raveling and surface cracking. Therefore, it is recommended to limit the initial air voids to 8% or less immediately after construction. Bitumen aging significantly influences pavement performance, leading to raveling and cracking when coupled with heavy traffic loads. Higher initial air voids, primarily due to insufficient compaction, accelerate binder aging. Binder aging can be minimized by restricting the initial air voids to 8% or less. If the initial air voids are decreased by 1%, pavement service life is increased by 10%. The procedure given in AASHTO R30 does not simulate field aging for tropical regions. Therefore, a field-simulating laboratory method was necessary. This study indicated that aging the mixture for 10 days by introducing UV rays and oxygen in the laboratory oven-aging (LOA-III) method simulates the pressure-aging vessel (PAV) and field aging accurately for tropical regions. The developed field-replicated laboratory aging procedure can be directly adopted to study binder aging on pavement sections in tropical climatic regions with similar pavement crust thickness and traffic. The duration of aging and other factors, like oxygen supply rate and UV light intensity, may need to be modified for pavements with varying thicknesses, traffic volumes, and climatic zones.