UK: Tarmac has demonstrated a new concrete product using a high proportion of slag with Align, the joint venture building part of HS2, a new high-speed railway line. It demonstrated the potential to use very high ground granulated blast furnace slag (GGBS) content in excess of 90%, as an alkali activated cementitious material conforming to BS EN197, the standard for cementitious materials allowed to be used in ready mixed concrete, to significantly reduce carbon emissions, whilst still producing a quality finish and allowing normal construction and demoulding times.
Demonstration and testing at full scale used one of three Tarmac concrete batch plants at a Chalfont Lane construction site in Hertfordshire. A structural slab forming part of the new viaduct pre-cast factory and a vertical wall were poured. Tarmac says that the mixes, designed to Align concrete specification, exceeded expectations in both fresh and hardened properties, and showed that the new concrete can be produced in normal concrete plants and placed via mixer truck and by skip with a tremie pipe. The new low carbon concrete has a carbon footprint following industry BSI PAS2050 calculation rules that gives a 62% reduction in CO2e per cubic metre of concrete, compared to a standard CEM I concrete, meeting the same specification in the same raw materials. The footprint covers all aspects of the concrete production and supply with no carbon off-setting applied, delivering an actual footprint of 133kg/m3 CO2e. This represents a saving of 220t CO2e for every 1000m3 produced.
“Together we’ve shown this new concrete is fit for purpose in slabs and walls, with good repeatability and works with standard production and construction methods. This product is a great step along the industry zero carbon routemap, and the demonstration will help accelerate adoption of this new concrete,” said Robert Gossling, head of commercial engineering solutions at Tarmac.
Tarmac is supplying concrete for the construction of the Central 1 section of HS2 Phase One that is being built by Align. This includes a 22km section of high-speed rail infrastructure incorporating a 3km viaduct across the Colne Valley, a 16km twin-bored tunnel, and five vent shafts handling both intervention and tunnel ventilation facilities.
