Within Transport Infrastructure Ireland, TII-Structures is responsible for the management of approximately 3,500 national road structures. Of these, about 800 are masonry arches, 1,000 are reinforced concrete boxes or culverts while the rest are primarily concrete bridges.
“A lot of these structures, if properly maintained, will probably be there in two or three hundred years “ Fergal Cahill, Head of National Road Structures at Transport Infrastructure Ireland says that GGBS has played an integral role in national road infrastructure for more than twenty years. In those early days, it was specified for durability and aesthetic reasons; concrete made with GGBS is lighter and whiter than the trademark grey of high-carbon concrete. Critically however, it was the capacity of GGBS to create durable structures that led to its widespread inclusion in concrete standards for transport infrastructure.
“Our design philosophy is that we build long-life structures,” says Cahill. “You’re talking about a 120 year design life. What does that mean in practice? A lot of these structures, if maintained adequately and with appropriate interventions, will probably be there in two or three hundred years.”
Durability also has a direct impact on cost. Once a bridge has been specified, the design team evaluates lifecycle cost alongside construction cost. The cheapest option at the construction phase isn’t necessarily the cheapest option over the life of the structure.
“You can’t take a bridge out of service without significant impact on road users, and so we’re trying to make sure these structures operate at low cost, with little intervention for as long as possible. And GGBS is one mechanism for giving us those long-life durable structures.”
Today, TII requires that all non-prestressed concrete located within the splash zone (that part of the structure subject to spray from the road surface) must have either a minimum of 50% GGBS content or must use stainless steel reinforcement, though the inclusion of GGBS is the typical choice.
A GGBS content of 50% or above provides high resistance to chloride ingress. The finer pore structure limits de-icing salts from penetrating to the structural steel and corroding it.
While GGBS was originally chosen for technical rather than sustainable reasons, a structure designed to last for hundreds of years is inherently sustainable. Moreover, these days, there’s an open acknowledgment of the need to substitute away from high-carbon cement.
TII have been pioneers in the brave new word of life cycle assessment, and whole life carbon calculation, relying on Ecocem’s support to help them make sense of how to account for the embodied carbon of their main construction material.
Cahill points out that in structural concrete, 58% of the total embodied carbon from life cycle stages A1-A5 — that is, cradle to practical completion — comes from the cement content. This is why TII now encourages designers to boost the GGBS content in their designs. Many of the median barriers on motorways out of Dublin now include GGBS.
As the largest builder of residential homes in Ireland, Cairn Homes is also leading the way in reducing carbon emissions. In 2024, the company announced that it was adopting the passive house standard for all new flagship developments as a way of reducing the energy demand of the homes it builds.
The consortium of Cairn, UCD, Kilsaran, and Ecocem has secured €50,000 in funding from Construct Innovate, Ireland’s national Construction Technology Centre, to validate an innovative low-carbon cement capable of significantly cutting Ireland’s CO2 emissions from the construction sector.
