Effect of Active Fillers on the Macroscopic and Microscopic Properties of Foamed Asphalt Cold Recycled Mixtures

The effects of different active fillers on dry and wet indirect tensile strength (ITS), triaxial shear strength, triaxial fracture energy and failure strain were analyzed using ITS and triaxial tests to clarify the influence of active filler on the macroscopic and microscopic properties of foamed asphalt cold recycled mixtures (FCRMs). In addition, the difference in the micro void structure of different active fillers was analyzed using computed tomography (CT) scanning tests. The results showed that the type of active filler had a significant effect on the ITS and shear strength of FCRMs, and the addition of active filler had the most significant effect on the moisture resistance of the mixture. In contrast, the flexibility of a cement active filler mixture is lower than that of a lime active filler, making the triaxial fracture energy large and the failure strain small. Compared with mixture without active filler, amounts of air voids with a volume of less than 0.1 mm3 increased, whereas those with a volume of between 0.1 and 1 mm3 decreased with added active filler. The average air void radius was approximately two to three times that of the maximum distribution frequency air void radius, and all decreased after adding active filler. The maximum distribution frequency radius is more representative of the void size of the mixture. Compared with the average air void radius, the maximum distribution frequency radius can better represent the distribution condition of air voids. The distribution difference in the amount/size of the air voids is the fundamental reason for strength differences in FCRMs. Due to cement hydration, lime crystallization, and lime carbonization, the macroscopic and microscopic properties of the mixtures with active fillers undergo significant changes.