The kinetics of carbonyl formation in asphalt

TLDR

Asphalt oxidation, a major cause of pavement failure, proceeds in two stages at constant temperature and oxygen pressure: an initial rapid‑rate period followed by a long constant‑rate period. The study presents low‑temperature oxidation kinetics for 14 asphalt samples. The 14 asphalts exhibit activation energies of 64–109 kJ mol⁻¹ and oxygen reaction orders of 0.25–0.61, grouping them into high‑ and low‑value sets; the data point to an isokinetic temperature near 100 °C and show that the extent of initial rapid oxidation is inversely related to the constant‑rate reaction order, casting doubt on evaluating road‑condition hardening rates at a single elevated temperature or pressure.

Abstract

Abstract The oxidation of asphalt is a major cause of pavement failure. The low‐temperature oxidation kinetics of 14 asphalts are presented. At constant temperature and oxygen presure, asphalt oxidation occurs in two stages: (1) a relatively rapid‐rate period, followed by (2) a long period of constant rate. Activation energies for the constant‐rate region vary from 64 to 109 kJ/mol, and reaction orders relative to oxygen pressure vary from 0.25 to 0.61. This variation in activation energy and reaction order leads to skepticism regarding the present practices of evaluating road‐condition asphalt‐hardening rates at a single elevated temperature and perhaps at an elevated pressure. The asphalts occur in essentially two groups, one at high values of both activation energy and reaction order and the other at low values of each. The data indicate the existence of an isokinetic temperature near 100°C. The degree of oxidation that occurs during the initial rapid‐rate region varies inversely with the oxygen reaction order of the constant‐rate region.