Use of a concrete alternative saved 62t of CO2 during works to upgrade Chatham station in Kent.
Chatham station in Kent has two platforms and serves about three million people every year.
It’s part of the government’s Access for All (AfA) scheme, which aims to provide obstacle-free, accessible routes to and between platforms across the rail network.
Upgrades are being delivered by BAM Nuttall under Network Rail’s multi-discipline framework.
The works being undertaken at Chatham include replacing the step-only footbridge structure with a new, Disability Discrimination Act-compliant footbridge, and installing two lifts to ensure the routes to and between platforms are accessible for all.
The challenge
During the design development stage, the project team discovered a disused cellar beneath one of the platforms, measuring approximately 20m x 6m and 2.5m deep.
Previously used as both a coal store and a railway workers’ social club, it had become redundant and was a maintenance liability for Network Rail.
The foundations for the new AfA structure needed to be installed at the cellar location, so it was decided that the best option was to infill the cellar.
Before doing so, Network Rail’s carbon-saving targets, the government’s goal of net-zero carbon by 2050, and BAM Nuttall’s own carbon emission reduction targets (according to the Science-Based Targets initiative [SBTi]), needed to be taken into consideration.
The solution
The BAM Nuttall delivery team had been introduced to a cement-free alternative to conventional concrete called Cemfree, produced by DB Group, about a year before the project.
Cemfree falls within the general product category of alkali-activated cementitious materials (AACMs).
It gains strength, and other properties, via a chemical reaction between a source alkali (calcium oxide) and other minor constituents and aluminate-rich material – ground granulated blast-furnace slag (GGBS) fly ash, etc.
DB Group’s 5% patented AACM is currently blended with 95% GGBS either as a whole binder solution or a concentrated 5% AACM to 20% GGBS, using local GGBS for the remaining 75% of the blend.
Replacing 100% of the ordinary Portland cement (OPC) with a Cemfree binder results in embodied CO2 that is up to 80% lower than OPC-based concretes.
Similar to OPC, Cemfree is a powder delivered via road tanker into a silo at a concrete production facility as a direct replacement for Portland cement.
The benefits of this new product led BAM Nuttall to work collaboratively with Network Rail engineering teams, Robert West Consulting, Hanson Concrete and DB Group to develop the design and methodology to use Cemfree.
The standards
One of the issues involved in using the material was compliance with Network Rail standards.
To obtain client approval, Cemfree had to satisfy a list of requirements relating to design strength, pumpability, health and safety, CO2 savings and supply.
BAM Nuttall and DB Group produced a technical proposal for Network Rail suggesting that the designer could specify Cemfree via Network Rail Model Clauses as a designed concrete within the appendix of the specification.
One example is Cemfree’s compliance with PAS 8820:2016 (Alkali-activated cementitious material and concrete) durability testing requirements as an alternative means of demonstrating its longevity.
This instead of the conventional use of BS 8500, which excludes non-Portland cement-based concretes and is usually required by Network Rail standards for concrete.
At the conclusion of this process, Network Rail assurance engineers agreed that the permanent works designer could specify the use of Cemfree as a constituent part of a design concrete mix for the cellar infill works.
The methodology
In advance of the main pour, Hanson Concrete undertook trial mixes, including rheology assessment and slump retention, to check the mix design both for pumpability and ease of placement.
The target 28-day strength was 10 N/mm² and the concrete achieved an average of 14 N/mm² at 28 days.
The cellar fill was undertaken as a continuous pour of 300m3 over a 10-hour period. It was the largest single use of Cemfree to date and the first time the product had been used on a Network Rail infrastructure project.
The material was easily adapted to a pump mix, the required pour method.
The pour was undertaken with the same procedures and control methods as with normal OPC concrete and the material behaved as expected during the pour, with no additional equipment needed.
The material reached its required strength of 10 N/mm2 within seven days of the pour, enabling the project to continue to the next stage of the works as planned.
The benefits
As Cemfree is a blended mix containing pozzolanic by-product materials (GGBS and fly ash), it mitigates raw material depletion and diverts waste from landfill.
It also benefits from decreased water use as the mix contains 40%-60% less water than OPC-based equivalents.
Traditional concrete production contributes about 8% to global carbon emissions – more than three times the output of the global aviation industry.
That carbon footprint is largely caused by the energy-intensive methods that go into the production of cement, a vital component of traditional concrete.
By working with Network Rail to agree the use of this revolutionary product, DB Group has ensured that vital railway improvements can continue to be delivered with less impact on the environment.
This case study underlines DB Group’s commitment to developing innovative sustainable solutions for UK rail.
It has the potential to make a huge contribution towards the reduction of carbon emissions across the construction industry.
The use of Cemfree generated 62t of CO2 savings, equating to 83% compared with OPC concrete.
This is equivalent to planting 308 trees or turning off 2,089 LED lightbulbs for a year.
ICE’s Carbon Champions
ICE’s Carbon Champions initiative aims to celebrate individuals and their teams who are committed to achieving net zero.
Applicants are invited to submit their examples of carbon reduction in practice, giving details of their projects’ carbon savings.
Apply to become an ICE Carbon ChampionName of Project: Chatham Station AfA Scheme
ICE Carbon Champions involved in this project:
- Nick Moss, BAM Nuttall
- Adam Ferguson, BAM Nuttall
- Steve Caucutt, BAM Nuttall
- Aaron Lucid, DB Group (Holdings) Limited
- Andrew Rayner, Network Rail
