ABSTRACT
Concrete is recognized as the second most widely consumed commodity on the planet after water. It also contributes approximately 8% of global carbon emissions; the main source of these emissions is the manufacture of Ordinary Portland Cement (CEM I). In a tunneling project, it is generally considered that 60% to 70% of embodied carbon is contained in the concrete linings of the shafts and tunnels. It is paramount, therefore that the tunneling industry does its utmost to significantly reduce or eliminate its use of cement in all applications segmental linings, in-situ linings, sprayed concrete, and annulus grouts. This is the reason why a great challenge for the coming years will be developing solutions for low carbon lining. Recent projects have demonstrated that structural ductility, durability, and sustainability are going hand to hand, this combined approach will be key requirement in all. The use of Fibre Reinforced Concrete (FRC) allows several advantages summarized in the fib bulletin 83 as follows: Cracking control during construction phases; higher impact resistance; durability advantages at final stage; reduction of costs; sustainability advantages (less material usage through minimizing the amount of steel and concrete cover required). The advantages related to the adoption of FRC use should be evaluated according to the project characteristics. The introduction of the Model Code 2010 has promoted the use of FRC segments. This paper underlines the design principle based upon MC2010 and fib bulletin 83. The use of steel to replace all or a part of conventional reinforcement has been demonstrated to lower the embodied CO2 of the segmental lining as well. The return of experience of the Doha Metro as the Grand Paris Linea 16.1 will provide a good recent illustration.
