LOW CARBON CONCRETE | RULES OF THUMB


tunnels and possibly eliminate the need for HDPE liners and secondary in-situ linings, and significantly reduce a project’s carbon footprint.


of anti-crack reinforcement required to mitigate early-age thermal cracking. In Australia, Wagners recently fire-tested geopolymer


concrete containing steel fibres and polypropylene fibres at the CSIRO laboratories(5)


. Concrete panels were


placed in the furnace and were then subjected to the RABT-ZTV (Eureka) fire curve for hydrocarbon fires in rail tunnels. The results of the tests indicated a spalling resistance that was equal to the CEM I and 25% fly-ash concrete that is currently being used by Wagners in the production of segmental linings for the Cross River Rail project in Brisbane. A few years ago in New Zealand, Watercare, the


water provider responsible for the construction of the Auckland Central Interceptor sewer tunnel, realised that biogenic corrosion from the conversion of hydrogen sulphide into sulphuric acid in sewer tunnels was a huge problem and so decided to run a test program at the AWMC, University of Queensland(6)


. After one


year in the biogenic corrosion chamber, the concrete samples were removed and their respective rates of corrosion were determined. The results showed that the geopolymer concrete had an even lower corrosion rate than calcium aluminate cement concrete – a material frequently specified and used in the repair of corroded sewer tunnels and manholes. The very low rate of corrosion of geopolymer


concrete could enable low corrosion, single-pass linings to be used in the construction of large-diameter sewer


THE CHALLENGE The challenge to reduce carbon emissions arising from construction activities is enormous and will require innovative design and materials solutions – plus a degree of risk acceptance (something for the underwriters to consider, perhaps). But remember …. if we always do what we always did then we will always get what we always got.


REFERENCES 1 BS PAS 8820:2016 - Construction Materials. Alkali-Activated Cementitious Material and Concrete


2 M. Stanley et al - “Design and construction of the Thames Water Lee Tunnel shafts, London.” – 3rd International Conference on Shaft Design and Construction, London 2012


3 “C.Edvardsen et al – “Consultant’s view of durable and sustainable concrete tunnel constructions in the Middle East” –– WTC Congress 2018, Dubai.


4 Kristina Smith - “The future for low carbon concrete?” – Tunnelling Journal April/May 2021.


5 Allen & Day - “EFC® Geopolymer Concrete – A low carbon solution to long term durability” – ICT Conference 2020, United Kingdom.


6 Jiang, G. and Hogan, B.- “Bio-corrosion tests of five concrete products” - Advanced Water Management Centre (private report owned by Watercare New Zealand), 2018, Brisbane


Above left: Slump test on a


geopolymer concrete mix. Above right:


Demoulding of fibre- reinforced geopolymer concrete tunnel segment


Opposite top: Discharging EFC


geopolymer concrete at HS2 Euston approaches project


Opposite bottom left: Slipforming of the pump shaft lining at the Lea Tunnel project, using 50% GGBS replacement and 30 kg/m3


of steel fibres,


saving approximately 500 tonnes of rebar


Opposite bottom right: The casting of an EFC geopolymer concrete tunnel segment at Max Bogl precast yard for durability testing at RWTH, Aachen University, Germany


Agree or disagree..


Let us know what your experience has taught you. Or let us know what topic should be included in future Rules of Thumb columns: editor@tunnelsandtunnelling.com


November 2021 | 33


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