Improved sustainability for sewage and stormwater tunnels

Tunnels Solutions

Stormwater and sewage infrastructure is essential in any urban environment and must be designed to last for as long as possible – 100 years or more. The choice of materials plays an important role in how durable and sustainable the infrastructure will be.

Concrete supplier IBF provides stormwater and sewage tunnel pipes to HOFOR (Greater Copenhagen Utility). In the past, IBF used a mixture of cement and fly ash, a waste product from coal fired plants, to produce durable concrete. However, as fewer and fewer coal fired plants continue to operate, fly ash has become a scarce resource. In 2018, IBF requested COWI to identify alternatives to fly ash that would still produce concrete of equal durability.

The proposed solution was to use a slag concrete consisting mainly of ground granulated blast furnace slag (GGBFS), a waste product of the steel industry with a much lower carbon footprint than fly ash concrete. This solution meets HOFOR’s concrete durability requirements, and also comes with a prolonged service life, high sulfuric acid resistance, less risk for early-age cracking, and up to 50% fewer CO₂ emissions compared to standard portland cement or fly ash concrete.

Slag concrete represents an important step towards sustainability for concrete producers and users and will be an important material in increasing the sustainability of urban sewage and stormwater tunnels.


Copenhagen, Denmark




  • Concrete durability and sustainability related consultancy services

Get in contact

Carola Edvardsen

Carola Edvardsen
Technical Director / Lead Durability Specialist
Tunnels and Underground Infrastructure, Denmark

Tel: +45 56402813