​​Melting and Boiling Points of Asphalt: Why Does It Soften at High Temperatures? ​​

Asphalt, a complex mixture of hydrocarbons, lacks a sharp melting point due to its heterogeneous composition.  Instead, it exhibits a ​​softening point range​​ (typically 40–60°C for petroleum asphalt), beyond which it transitions from solid to viscous liquid.  This behavior stems from its ​​colloidal structure​​:

​​Molecular Dynamics​​: At high temperatures, the liquid oil fraction (maltenes) within asphalt becomes more fluid, weakening the solid asphaltene matrix.  This reduces intermolecular forces, causing softening.
​​Temperature Sensitivity​​: Asphalt’s viscosity drops exponentially with heat.  For example, at 60°C, standard asphalt may lose 90% of its stiffness, leading to rutting under traffic loads.  Modified asphalts (e.g., SBS or high-modulus types) resist this via polymer networks that stabilize the structure up to 70°C or higher.
​​Boiling and Decomposition​​:
Asphalt decomposes before reaching a true boiling point (below 470°C), releasing toxic gases like benzene.  Thus, boiling point is less relevant than ​​flash point​​ (~204°C), which marks combustion risk during heating.

​​Practical Implications​​:

​​Pavement Failures​​: Summer temperatures exceeding 50°C can soften asphalt, causing permanent deformations like rutting.
​​Solutions​​: Use ​​modified binders​​ (e.g., SBS) or ​​cooling additives​​ to enhance high-temperature stability.
In summary, asphalt softens due to ​​colloidal breakdown​​ and ​​thermal susceptibility​​, necessitating material innovations for durability.