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OVERVIEW
Cadent Gas require to divert the existing high pressure gas pipeline at Austrey to Shrewley to provide mitigation from external loading from future HS2 traffic. As well as standard trench construction the diversion also compromises tunnelling at certain locations along the route.
To launch and receive the tunnel boring machine (TBM) a secant piled shaft is constructed at the launch and reception sites.
Secant piled shafts are constructed with bored piles and typically compromise overlapping primary/soft and secondary/hard piles. Primary/soft piles are formed without reinforcement from a weak bentonite slurry to low strength concrete typically C8/10 with secondary/hard piles installed with reinforcement and using structural concrete typically at C30/37 or higher and cutting into the primary/soft piles to form an overlap which prevents water and fines entering an excavation. Secant pile shaft structures for TBM works are typically temporary works designs with less onerous full design life/durability criteria. The selection of the soft/primary pile concrete mix is critical to achieve the correct balance of structural performance and durability where required without impeding the installation of the secondary/hard piles. As very stringent installation tolerances are needed the strength gain profile of the primary/soft pile concrete mix is also required to be clearly understood to calculate the timings of the secondary/hard pile installation.
It is a priority for us to find the latest technology to minimise our impact on the environment. As a result, we were keen to approach DB Group to consider how we could use cement-free concrete on one of our projects. This is where Cemfree comes in. It is an ultra-low carbon alternative to standard concrete whereby OPC is replaced with novel alkali activated cementitious material (AACM). As it does not contain any OPC, it can save up to 88% of CO2 emissions on a project.
Cemfree has been used in the UK since 2010. However, so far it has only been used on small scale projects. Therefore, we have partnered with DB Group, Hanson and BRE to trial Cemfree concrete on the primary/soft piles for the secant shaft piling at our HP11 gas main diversion project and better understand and develop its characteristics for future use in piled structures.
Contact PUDLO Waterproof Systems & Cemfree Zero-Cement Concrete, part of the DB Group Ltd by clicking the button below to find out which products were used in this case study.