TECHNICAL | MECHANISED TUNNELLING


6m diameter


Right, figure 2: CO2


equivalent for


segmental concrete and annulus grout per linear tunnel meter of tunnel1


9000 8000 7000 6000 5000 4000 3000 2000 1000 -


6m Tunnel CO2/m/m2 inner space


Annulus grout rest Annulus grout silicate Annulus grout cement Segment rest Segment reinforcement Segment curing Segment cement


149 51 242 676 174


1,021 381


1,671


12m diameter


20%-22%


20%-22%


6m Tunnel


117 96 -


46 204


1,021 272


1,671


12m Tunnel


76 96 458 1,277 392


1,788 861 3,773


The Global Warming Potential (GWP) – this


parameter is defined as the impact of carbon footprint emissions (CO2


eq.) per cubic meter of


grout, considering how long it remains active in the atmosphere – is still rarely calculated. In an average 300 GWP/m3


- 340 GWP/m3 eq./m3 . , cement as


binder of Component A and sodium silicate as activator of Component B are the major contributors of approx. 90% of the total CO2


This article illustrates a new Component A solution


applicable for two-components backfill grouts with reduced carbon footprint emissions, that hopefully will be accepted by the industry.


CONVENTIONAL GROUTING CHALLENGES The major undisputable limitation in annulus grout injection methods is that, after placement, they are located behind the concrete segmental tunnel lining and are therefore not visible for quality inspection. Under these circumstances, with the inability by stakeholders to review the final product, material quality has not been the focus of operations over the last decade. Figure 1 shows an example of backfill grout’s quality


after some time after injection. For more sustainable results, annulus grouts should focus on quality, be more durable for longer lasting structures and reduce cement consumption to reduce CO2


carbon footprint emissions.


Right, figure 3: The new Sika® Stabilizer-7100 TBM Component A


48 | Summer 2024


GWP [kg CO2


eq/m]


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