Which of the following is a disadvantage of asphalt?

The identified disadvantage of asphalt referring to its degradation at edges without support is indeed a notable concern. When asphalt is used in applications such as pavements or surfaces without proper edging or support structures, the edges can wear away or break down more quickly than the central areas. This is mainly due to factors like water pooling, vehicular traffic, or freeze-thaw cycles that can exacerbate the deterioration of unsupported edges. This degradation can lead to costly repairs or the need for more frequent maintenance, making it a significant downside when considering the long-term durability of asphalt surfaces.

In contrast, the other options do not accurately represent the primary disadvantages of asphalt as they relate to its performance and adaptability. High heat/light reflectivity does not significantly hinder the usability of asphalt; rather, it's noted for absorbing heat, making it warmer than some alternatives. The assertion that it cannot be adapted to various shapes is inaccurate, as asphalt is quite flexible and can be molded into a variety of shapes and forms for different applications. Finally, while maintenance costs can be an aspect of asphalt’s lifecycle, they are often considered manageable thanks to the material's durability when properly installed and maintained. Thus, the degradation of edges without support stands out as a critical disadvantage.