A multi-gradient analysis of microscopic void characteristics' influence on the mechanical properties of open-graded friction course bituminous pavement

Abstract

The mechanical properties of the open-graded friction course (OGFC) bituminous pavement are tied to its microscopic void structure, but multiple void parameters influence void formation and distribution. Solely using air voids as an indicator of pavement stability is challenging. Thus, a multi-gradient analysis of void structure factors is vital for advancing OGFC pavement's mechanical property research. This study used computerized tomography (CT) and digital image processing (DIP) to gather data on void structure distribution, size, and complexity in OGFC bituminous mixtures. Mechanical experiments assessed high-temperature deformation, low-temperature cracking, and water damage resistance. Analysis of void parameters' influence led to a predictive model for mechanical property in OGFC mixtures. The study found that as air voids increase within the 18 %–24 % range, both equivalent void diameter and void fractal dimension increase, while void count decreases. Conversely, coarser gradation and a larger nominal maximum aggregate size (NMAS) lead to increased equivalent void diameter but decreased void fractal dimension, reducing void complexity. The mechanical properties of OGFC mixtures decline with rising air voids but improve with coarser gradation and larger NMAS. The predictive model highlights the void fractal dimension and NMAS as critical indicators, with other factors showing weaker influence or multicollinearity issues that are unfit for model fitting. The findings could provide useful references for the structural design, property evaluation, and quality control of OGFC bituminous pavements in actual road construction.