Client: London Tunnels West
Contractor: Nishimatsu-Cementation Skanska Joint Venture (NCS JV)
Type of works: for the construction of the four London tunnels, CEMEX developed a very dry mix using certified fly ash to make the concrete cohesive. CEMEX also produced a total of 85 miles of concrete, for troughing, lids and accessories used for vital signalling and communications alongside the Channel Tunnel Rail Link tracks.

Constructing the four London tunnels, totalling 35km, for the Channel Tunnel Rail Link presented a number of concreting challenges. Concrete plant machinery had to be customised to accommodate the alignment of the tunnels and the varying cants. A mix design was also needed for the walkways, which measured up to 1.4m high, so that they would stand up immediately without the need for temporary support.

Working with the contractor for London Tunnels West, NCS JV, CEMEX developed a very dry mix using certified fly ash to make the concrete cohesive. The fly ash is a by-product from coal-fired power stations, which would otherwise go to landfill. After processing, it is used in addition to cement, providing improved water reduction and better long-term strength.

The resulting concrete could instantly be moulded to the required walkway shape by the slipform paving machine. The walkways immediately stood erect without subsiding, even when weight was applied. A tight, high-standard, blemish-free surface finish was also achieved due to the rounded shape of ash particles.

CEMEX also produced a total of 85 miles, or 275,000 units, for troughing, lids and accessories used for vital signalling and communications alongside the Channel Tunnel Rail Link tracks. In addition, 400 tonnes worth of bespoke precast wall and roof segments was supplied to Costain/Skanska/Bachy for the Stratford Box. This contract included 25 rectilinear wall panels and 38 profiled roof panels.