Project outline

It is a priority for Murphy to find the latest technology to minimise our impact on the environment.

As part of its involvement on the Austrey – Barston Gas Pipeline Diversion Murphy Ground Engineering (MGE) saw an opportunity to test, in agreement with the project client, the potential of cement-free concrete on a large scale project.

Cemfree has been used in the UK since 2010. However, so far it has only been used on small scale projects. 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.

The works for the pipeline diversion included:

  • Diverting the existing high pressure gas pipeline at Austrey to Shrewley to provide mitigation from external loading from future HS2 traffic
  • Constructing secant piled shafts to launch and receive the tunnel boring machine (TBM)
  • Achieving the correct balance of structural performance and durability where required without impeding the installation of the secondary/hard piles

In addition to the emissions savings, the trial of Cemfree would allow Murphy Ground Engineering to better understand and develop its characteristics for future use in piled structures.

Project delivery and innovations:

The main works were completed successfully with the selected  binder  mix  achieving  a  consistent  strength  gain  profile  and  between 17N to 20N at 28 day strength.

Through  trialling  Cemfree  on  the  HP11  gas  main  diversion project MGE has seen a number  of  benefits and have generated interest across both the Murphy family and HS2, including:  

  • For each unused Kg of OPC, MGE saved 3Kg of raw materials
  • For each unused Kg of OPC, 1Kg of waste was diverted from landfill 
  • There was a 65-82% reduction in CO2e. As a result, MGE reduced the global warming potential of the concrete used on the project
  • A 40% reduction in water used to produce the concrete for the piles 

Additionally MGE was able to use Cemfree without having to develop different procedures or use alternative equipment. As a result, there were  no added extra costs. 

With the strength gain performance during the trials of the higher binder content has proving positive and MGE aim to progress the use of Cemfree for a full secant piled shaft in the very near future.   

Further more, by demonstrating the sustainable and economic  benefits  of  Cemfree MGE hope to encourage other ground engineering companies to consider using more sustainable materials and practises.

Key challenges

MGE's aim was to trial Cemfree to assess its installation characteristics (slump, flow, and placement), its strength gain  profile and its ultimate strength gain performance, in the process  measuring how much CO2 MGE could save over using a traditional concrete mix.

The main and initial process was to trial the various binder content mix designs to assess which binder content would be most suited to replace a typical C8/10 primary/soft pile concrete and also observe its in-situ behaviour prior to use in the main shaft piling.

In addition MGE also trialled higher strength binder contents to gather data to consider whether higher strength concretes could feasibly be replaced with Cemfree in the future. 

With the temporary works design status of the TBM shafts there are less onerous design life criteria making this setting ideal for the trial as currently AACM’s in general are not appropriately covered by existing concrete standards making their use in permanent structures more complicated.

The scheme engineers COWI were positive in the adoption and use of Cemfree for the primary/soft piles based on the strength gains achieved during the trial process. 

Key facts
  • Trial of binder mix designs on site pre works allowed assessment of strength gain and ultimate strength profiles 
  • The performance of the higher binder content trial mix has been very positive and further consideration is being given to how MGE can use this data to allow use in higher strength requirements and permanent structures 
  • It is planned to explore further opportunities where Cemfree can be used for secondary/hard piles to create fully Cemfree secant piled shafts/walls
  • MGE's work on live sites will help inform and develop the current codes for AACMs as part of the LOCOWAG project
  • Secant Piled Reception Shaft.
    Secant Piled Reception Shaft.
  • TBM breaking through.
    TBM breaking through.

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