While asphalt can occur in nature as a result of crude oil’s exposure to weather, the asphalt used today in modern paving is a by-product of the oil refining process. What is referred to as asphalt in modern construction is actually asphaltic cement concrete, a flexible paving material composed of a mixture of asphalt cement (the binder), aggregates, and fine aggregates such as sand. Asphalt concrete mixes can be prepared off-site as a plant mix, or mixed-in-place at the project site.