Which of the following has the biggest impact on the overall "strength" of the HMA mixture?

The overall strength of Hot Mix Asphalt (HMA) is significantly affected by the angularity and distribution of particles present in the aggregate mix. Angular aggregates interlock more effectively compared to rounded aggregates, leading to increased stability and strength within the mix. This interlocking capability means that when subjected to load, the angular particles can resist movement and deformation better than smoother particles, thereby providing greater structural integrity.

Furthermore, the distribution of particle sizes also plays a crucial role. An optimal gradation of aggregates ensures that the voids are filled efficiently, enhancing the structural properties of the HMA. This balance between different sizes of particles maximizes contact area and minimizes air gaps, leading to a denser and stronger mixture.

While the asphalt binder grade, surface texture, and specific gravity of aggregates also influence HMA properties, they do not have as direct an impact on the physical interlocking and distribution that contribute to the mixture's strength. Hence, the combination of angularity and the proper distribution of particle sizes is critical for achieving the desired strength in HMA mixtures.