Bitumen is a black, sticky substance used as the binding agent in road construction, giving surfaces firmness, durability and water‑resistance.

Chemically, bitumen consists mainly of complex hydrocarbons of carbon and hydrogen, with smaller amounts of sulphur, oxygen, nitrogen and trace metals.

Although often called asphalt, the two terms differ: bitumen is the binder, while asphalt is the mixture of bitumen and aggregates such as crushed stone, gravel and sand that forms the road surface.

In Kenya’s Rironi‑Mau Summit Highway project, bitumen acts like glue, holding aggregates together; once it cools it hardens, creating a surface that can bear vehicle loads and resist water penetration.

The majority of bitumen used in modern road work is derived from the heavy residue left after crude oil refining, where lighter fuels are separated and the remaining material is processed into bitumen.

Kenya does not produce bitumen domestically and imports the entire supply, primarily from the United Arab Emirates, Iran, Oman, China, Kuwait, Iraq and India.

Iran is identified as the world’s largest exporter of bitumen, reflecting its extensive oil reserves and refining capacity.

Recent reports of bitumen shortages have been linked to delays in opening the Rironi‑Naivasha section of the highway, which was slated for completion by the end of October 2026.

The Rironi‑Mau project is part of Kenya’s broader push to expand its road network, with multiple multibillion‑shilling highways under construction simultaneously.