Grain breakage in granular materials occurs due to the combined effect of individual grain strength, initial sample conditions such as granulometry which under certain conditions may approach a nearly monodisperse distribution and loading conditions. This study investigates the influence of gap-graded distributions in both homogenous and heterogenous samples through a series of oedometer tests, isotropic compression tests and monotonic drained triaxial tests. The central hypothesis is that modifying an initially monodisperse grading by introducing finer particles can reduce grain breakage and enhances granular samples mechanical behavior without notably altering its initial density. Oedometer tests are conducted on samples of a nearly monodisperse particle size distribution (S1) of clay aggregates with a Dmax/Dmin ratio of 1.28, under vertical stresses ranging from 200 kPa to 5000 kPa, resulting in significant particle breakage. To evaluate the effect of gap-grading, a finer fraction of the same material was added to form a bidisperse, homogenous specimen (S2) with a Dmax/Dmin ratio of 2. Later, gravel particles, with a higher individual particle strength, were incorporated into monodisperse specimens (S1), resulting in a bidisperse, heterogeneous material (S3). All samples were subjected to the same vertical stress levels. Grain breakage was quantified using a breakage index derived from the particle size distribution, considering both potential (up to a fractal distribution) and actual breakage. Key findings indicate that the addition of finer particles slightly reduced grain breakage in the bidisperse homogeneous material (S2), with the effect being more pronounced in the bidisperse heterogeneous material (S3). At higher stress levels (e.g., 5000 kPa), the reduction in grain breakage became less significant. Both S2 and S3 demonstrated lower compressibility compared to the initial monodisperse sample (S1), indicating that even a minor adjustment to particle size distribution has an influence on the material's compressive response. Similar to the oedometer tests, samples of a nearly monodisperse particle size distribution (S1) were subjected to isotropic compression tests and monotonic drained triaxial tests resulting in grain breakage. To assess the effect of incorporating a finer fraction, sand particles were added, forming a new heterogenous bidisperse specimen (S4). The results showed that the addition of sand mainly influenced the volumetric respons