Tunnelers told to stop using ordinary cement

Geopolymer 'concrete' is a cheaper, more practical and more environmentally friendly alternative to OPC, claimed Harding. Harding told tunneller attending the World Tunnel Congress in Croatia last month that Geopolymer 'concrete' replaces OPC with a geopolymer binder that is produced from industrial waste products such as fly ash.

The benefit is a 70 percent or more reduction in carbon emission, said Harding. "Around 1,000km of tunnel was constructed last year. If we assume a conservative average diameter of 5m, thickness of 250mm, and CO2 emissions of 100k per tonne of concrete, you are looking at 10Mt of concrete cast for tunnel lining alone. And CO2 emissions of 1Mt."

In the presentation, Harding did not just reply on the environmental spirit of engineers, he added benefits that include a 10 percent or more cost reduction when compared with cementitious products; almost no curing required and no requirement for steam curing; less vulnerability to early thermal cracking; possible savings from removing or reducing microsynthetic fibres for fire performance.

From the audience, Martin Knights, former ITA president and current tunnelling director at Jacobs Engineering, raised the point of cost reductions as an amazing boost to this technology.