Application of High-Performance Concrete in Singapore’s North-East and Changi MRT lines

In early 1996, the Singapore Government announced its decision to expand the country's mass rapid transit system by building the North-East Line from the World Trade Center in the south of the island to the new towns of Hougang, Sengkang and Punggol in northeastern Singapore. The S$5 b Northeast MRT Line will be approximately 20 km long and it will be built primary underground using precast tunnel-lining segments. The specifications for the precast tunnel lining segments include the use of high-performance concrete with a maximum water-cementitious material ratio of 0.45, a minimum 28-day compressive strength of 60 MPa, and a maximum "rapid chloride permeability" value of 1000 coulombs. In addition, the specification included the use of high yield bars with a fused epoxy coating to mitigate corrosion of the reinforcing steel due to chlorides in the groundwater. At the request of the contractor, the specifying agency accepted the use of silica fume and a corrosion inhibitor as an alternate. Thousands of precast, high-performance concrete tunnel-lining segments are currently being produced for the construction of the underground tunnels. In this paper, information on the development of the high-performance concrete mixtures for the tunnel-lining segments, production issues, QA/QC measures that have been implemented to ensure compliance with the specification, and the impact of the high-performance concrete on the construction schedule are presented and discussed. An overview of the northeast MRT Line project is also presented.