For a given asphalt sample, which factor most strongly affects its volume?

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Volume changes in asphalt are driven mainly by thermal expansion and contraction. When temperature rises, the molecules in the asphalt binder and the aggregate particles gain energy and move apart, causing the overall volume to increase. When temperature falls, they move closer together and the volume decreases. This thermal response is typically much larger than any volume change caused by moisture, since asphalt is relatively hydrophobic and doesn’t absorb much water, so moisture-related swelling is minimal in comparison. The fines and rocks set the mix’s initial packing and porosity, influencing the baseline volume, but they don’t cause the pronounced temperature-driven expansion or contraction that governs how the volume changes with temperature. So, temperature is the factor that most strongly affects the volume of an asphalt sample.