BTS/CONCRETE | TECHNICAL


Table 2: Comparative test results of EFC versus production concrete samples, cast in May 2020 Test


Unit VBee


PP fibre content Steel fibre content Comp Str – 7 days Comp Str – 28 days Comp Str – 57 days


Beam test – LOP – 145 days Beam test – LOP – 28 days


seconds Kg/m3 Kg/m3 MPa MPa MPa MPa MPa


EFC 10


1.5 35


39.0 47.0 55.0 6.4 -


Production concrete 11


1.5 35


52.5 69.0 74.5 -


7.2


The table assumes that the embodied CO2


(ECO2


)


footprint of EFC in the UK is the same as in Australia. This is not considered unreasonable when assessing the supply chains and shipping distance of the binder and activator components. It is shown in Table 3. A typical C50/60 concrete mix for tunnel lining


segments in the UK would have a 420kg/m3 cementitious content containing 30% GGBS – i.e. a CEM IIB-S. From the table, it can be seen that the ECO2


binder content of 1m3 263kg/m3


.


EFC with a similar binder content of 420kg/m3 would have a ECO2 value of 49kg/m3


. This represents


a reduction of approximately 214kg of embodied carbon in each cubic metre of concrete – a reduction of 81% compared with a concrete containing 30% GGBS replacement (a mix that some might claim is low carbon itself).


of the of this type of concrete would be


A typical railway tunnel of 7.50m i.d. and segmental


lining of 350mm thickness would contain approximately 8.6m3


of concrete per linear metre of tunnel. By using


EFC in the segments, a carbon footprint saving of 1.84 tonnes per linear metre, or 1,840 tonnes/km of tunnel, could be realised. Since EFC requires a lower curing temperature than


OPC-based concrete for early strength and demoulding, there are possible further savings to be made in both energy costs and carbon footprint. This can only be quantified by working with the segment manufacturer and discussing their heating regime in the curing chambers. In conclusion, geopolymer concrete can be produced


to meets all the hardened concrete design requirements of tunnel segments, has excellent spalling resistance, improved long term durability, and a lower carbon footprint.


Above, table 3: Embodied CO2


NOTES: 1. CO2 2. CO2 3. CO2


contents for CEMI, GGBS blends and EFC


e contents are based on raw material values for cementitious blend and content only e value for EFC is based on Australian values provided by Wagner


e contributions from aggregates, production and transport are not included they are the same for all types of concrete 4. GGBS proportions are those normally used by suppliers


July 2023 | 19


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