n alignment with National Grid Electricity Transmission’s (NGET’s) objectives of achieving net-zero construction, we aim to evaluate the suitability of polymer concretes as a sustainable alternative to traditional concrete for NGET’s construction operations, appraise their readiness for construction trials, and support NGET in undertaking some of the required trials to demonstrate these materials’ suitability. Earth Friendly Concrete (EFC) has been utilised on the LPT2 (London Power Tunnels 2) project in several areas, but mainly for bulk fill or in temporary works. To further this concrete technology and use EFC more extensively, HMJV in conjunction with its Supply Chain Partners will conduct trials to establish the potential for use in Precast Segmental Lining Elements for the benefit of future projects as part of the LPT legacy.
Benefits
EFC saves 131.5 kgCO2e/m3 of finished product – this material could be used on future National Grid projects, which will help the company reach its net zero target and generate significant interest. Upcoming National Grid shaft and tunnelling projects which could benefit from these EFC C50/60 trials are: West London: Ealing – Laleham (22km) , Iver – North Hyde (15km) and Ealing – Willesden (7km). It is anticipated that EFC will have 40% less emissions/tonne compared to conventional concrete when used across future aforementioned projects. According to the business case, the carbon savings in next 10 years can be 13,187 tCO2e. Apart from carbon savings and wider adoption opportunity, EFC provides enhanced durability, sustainability, and low heat of hydration which is a key parameter when it comes to tunnel temperature and working conditions
Learnings
Outcomes
The objective of this trial was to assess the performance of Earth Friendly Concrete (EFC) an alkali-activated cementitious material (AACM) as a potential ultra-low-carbon alternative to traditional concrete for future National Grid tunnelling projects. The aspiration was to determine whether this innovative concrete could meet the technical and durability requirements necessary for underground infrastructure, based on its performance across a range of controlled tests
The extensive testing scope was developed collaboratively between HMJV, AECOM and National Grid ahead of the trials, and was conducted out across a variety of testing laboratories and research centres in the UK and Ireland. As with previous EFC trials conducted by HMJV over the past four years, the material continued to demonstrate strong performance under rigorous testing conditions.
Once the current mix design was finalised, fresh concrete flow testing showed consistent results, and batching produced uniform material with stable workability and flow characteristics. Both compressive and tensile strength testing met the original HMJV strength requirements for tunnel segments. In fact, the performance exceeded expectations in several areas, notably impressing senior management at Shay Murtagh with its strength development.
The hot box test further demonstrated the lower heat of reaction and reduced temperature differentials in EFC, compared to traditional Portland cement concrete. These results highlight a key advantage of EFC and AACM concretes in mitigating the risk of early-age thermal cracking. This thermal performance suggests that EFC may be particularly well suited for thick concrete elements, where elevated internal temperatures can otherwise lead to cracking and long-term durability concerns.
The fire testing conducted by BRE in accordance with the ISO 834 standard fire curve can be considered a success for the EFC C50/60 mix. The test panels showed no signs of external spalling and performed identically to the traditional Portland cement specimens, which also contained both steel and polypropylene fibres. This comparative testing reinforces the critical role of fibre-reinforced concrete in precast and tunnelling applications, particularly where fire performance and spalling resistance are key design considerations
Therefore, from a performance testing perspective and aside from the minor delay required to re-run the shrinkage testing the EFC C50/60 mix has successfully met the objectives and scope of the trial.
One of the most compelling arguments for considering EFC as a viable alternative to traditional Portland cement concrete in tunnelling applications is its significantly lower carbon footprint. Using the AMCRETE Carbon Impact Model, the EFC C50/60 trial mix was calculated to have a CO₂e value of 133 kg/m³, representing a substantial reduction compared to the 280 kg CO₂e/m³ for the equivalent C50/60 Portland cement mix.
Hypothetically, had the EFC technology been available, tested, and approved at the start of the LPT2 contract, the manufacture of the 172,000 tunnel segments for the LPT2 project could have achieved a saving of 10,000 tonnes of CO₂e. This is equivalent to the energy to approximately 3,800 UK homes’ annual carbon emissions, or the equivalent of taking over 4,000 petrol cars off the road for a year.
Lessons Learnt
HMJV learned that securing materials early and developing a clear understanding of timelines, supported by regular progress meetings, significantly improved productivity and organisational efficiency.
Frequent engagement with National Grid, designers, and other third parties allowed the team to refine the design, address logistical challenges, and maintain budgetary control.
Conducting pre-trials proved invaluable, as they enabled HMJV to identify and resolve issues in advance, ensuring that full-scale trials were successful and that the concrete mix was optimised before implementation.
