Effect of Filler and Binder Contents on Air Voids in Hot-Mix Asphalt for Road Pavement Construction

Filler and binder make up a small proportion of bituminous mixtures, hence they are considered as important ingredients of mixtures. Sometimes due to equipment error during production, some mixtures retain extra or a reduced amount of filler or binder as compared to the design mix formula. It is thought that the poor performance of bituminous mixtures is a result of inadequate proportioning of materials and the use of inappropriate compaction tools. This study was intended to appreciate the influence of contents of filler and binder in relation to durability in asphalt mixtures. Filler used was crushed stone passing 0.075 mm sieve, while the binder was 35/50 penetration grade. Several trial mixes were prepared following Ugandan specifications for Road and Bridge Works, and the Asphalt Institute in MS-2. Marshall design method was used, studying volumetric properties with an average stability value of 22.3 kN, average flow value of 3.7 mm, VA of 4.4%, VFB of 69.3%, and VMA of 14.2%. Also, compaction of mixtures to assess its performance at optimum filler and binder contents was done. Compaction was done using an Automatic Impact Hammer, a Vibrating Hammer, and a Superpave Gyratory compactor aimed at simulating secondary compaction by traffic and assessing the retained air voids which was 3.3%, 1.3%, and 0.7% respectively. Generally, in bituminous mixtures when a vibrating hammer or a gyratory compactor is recommended for compaction, coarser mixes would be the best choice.