How geopolymer injection was used to reduce the carbon footprint of concrete level crossing maintenance.
Concrete level crossings on railways pose significant maintenance challenges, especially when they experience substantial settlement.
This can impact ride quality and compromise the safety of the railway line.
The conventional solution for addressing this issue involves reconstruction, which is time-consuming, expensive, and has a high carbon footprint.
In recent years, the application of geopolymer injection technology has become more common in the maintenance of railway assets, including concrete level crossings.
Geopolymer injection offers the ability to restore concrete level crossings to their intended geometry, improve the strength of the sub-base layer, and create transition zones.
One of the key advantages of this technology is its in-situ application, which eliminates the need for track removal and uses smaller equipment than alternative methods.
These factors minimise disruptions and the need for prolonged track access, eliminating the necessity for full reconstruction.
The problem site
A concrete level crossing situated in the north east of England (see Figure 1) experienced geometric deterioration due to subgrade settlement.
This led to track geometry faults with deviations of up to 60mm from the vertical design geometry.
The primary reasons for this are believed to be the presence of soft underlying conditions combined with inadequate drainage.
Treatment using geopolymer injections
Geopolymer injections were used to lift the level crossing slabs to the design geometry, with a tolerance of +0mm/-10mm, and strengthen the sub-base layer below the slabs.
The geopolymer was injected into the Type 1 sub-base, 50mm below the slab, via 12mm drill holes (see Figure 2).
The amount of lift achieved during the injection process was monitored on site using laser levels and a dedicated surveying team.
Performance post-treatment
To assess the impact of the geopolymer treatment on the performance of the level crossing, consecutive track geometry evaluations were conducted over a one-and-a-half-year period using the New Measurement Train.
Before the treatment, the level crossing was deteriorating by 0.3mm/day. After the treatment, this rate reduced to 0.004mm/day.
This improvement translates to an extension of the asset's lifespan by approximately 22 years, which is the time required to reach the same level of track geometry observed before the treatment was applied.
Carbon footprint analysis
To evaluate the carbon footprint associated with two different solutions, Geobear, in collaboration with a specialist consultant, conducted a "carbon lifecycle assessment" of the geopolymer injection solution implemented at the site, comparing it with the traditional replacement method.
Geopolymer Carbon Footprint
To quantify the carbon footprint resulting from a geopolymer injection intervention, several elements were considered (see Table 1):
| Item | Emissions | |
|---|---|---|
| kgCO2e | Percentage | |
| Raw materials - embodied | 1999.30 | 61.5% |
| Raw materials transport (excluding materials transported by the site team) | 48.79 | 1.5% |
| Implementation fuels (Diesel) | 521.55 | 16.1% |
| Travel to and from site (including materials transported by the site team) | 677.58 | 20.9% |
| Disposal | 0.65 | 0.0% |
| Total emissions from the project | 3247.88 | 100% |
Table 1. CO2e emissions associated with one geopolymer injection intervention
Traditional Replacement Carbon Footprint
The traditional replacement method involves the excavation/removal of the existing concrete rail level crossing and associated transition zone, with a considerable amount of waste material being removed using skips.
This excavation process requires more fuel compared to a geopolymer intervention due to the additional time and machinery involved.
The level crossing/ transition zone is subsequently replaced.
In comparison to the geopolymer method, the carbon footprint associated with replacing the level crossing was a total of 199,367.90 kgCO2e emissions.
Carbon footprint comparison
The traditional replacement method would result in a brand-new concrete rail level crossing with an anticipated life of 60 years.
Considering the life extension analysis, which suggested a life extension of 22 years, it can be said that three geopolymer injection treatments would be required to equate to a traditional replacement of the asset, at 0 years, 22 years and 44 years from the point repair is needed.
The study found that the geopolymer injection solution would generate 95.11% less CO2e over a 60-year lifespan when compared to the traditional replacement method.
Conclusion
This case study has demonstrated the effective use of geopolymer injections for maintaining concrete level crossings and extending their lifespan.
Furthermore, due to the reduced site logistics and disruption associated with geopolymer treatment, the carbon footprint over the asset's lifespan is substantially reduced.
Carbon Champions involved in this project:
- Liam Bromley, Geobear Infrastructure Ltd
- Karl Sivori O’Neill, Geobear Infrastructure Ltd
- Dr Mohamed Wehbi, Geobear Infrastructure Ltd
- Andy Lee, Geobear Infrastructure Ltd
- Richard Holmes, Geobear Infrastructure Ltd
