NHAI debars contractor, consultant
NHAI debars contractor, consultants for under construction bridge accident in WB. September 2020
The materials used in bridge construction have a direct correlation to the span configuration for superstructure and height and exposure conditions for substructure.
Shashikant Limaye, Member Expert Committee, Pune Metro Project, says, “High-performance concrete with grade of M40 and above is now commonly used in the substructure for durability. In pre-stressed concrete superstructures, HPC with M55 grade is common. For reinforcing steel, corrosion-resistant steel (CRS) is gradually being introduced. For spans beyond 50 m, steel is a preferred material for the superstructure.”
According to SV Desai, Executive Vice-President & Head - Heavy Civil Infrastructure IC, L&T Construction, an emerging trend is to use sustainable and environment-friendly materials for concrete production. “Post-concrete protection of the structure, reducing permeability of concrete and use of special finishing materials are recent norms,” he says. “Grounded granulated blast furnace slag (GGBS) and ultrafine fly-ash are used while designing the concrete mix.” These strengthen the structure while reducing the carbon footprint in concrete production. He adds that to protect these structures, special anti-carbonation coatings and corrosion inhibitors are used to improve strength, quality, durability and service life of a bridge, thereby reducing maintenance cost.
“Steel bridges are effective,” says RVR Kishore, Project Director, Hindustan Construction Company. “The Bogibeel bridge required 80,000 tonne of steel and we have used 410 grade steel with copper bearing, which adds to the durability of steel. Similarly, in concrete, today we can go up to M60 grade. Also, given a choice, we would opt for OPC cement or add fly-ash or GGBS, but these are not easily available across the country. For Bogibeel Bridge, we used pure cement as there were no options of using other materials at the location.”
Citing the use of “concrete, steel, fibre-reinforced polymers, stainless steel or a combinations of those materials,” Vivek Gautam, COO - Strategic Business Group – Core Infra, Tata Projects, says, “Reinforced or pre-stressed concrete is used for construction. Reinforcement in RCC provides ductility. Ductility reinforcement is provided mainly in earthquake-resistant construction. Composite materials are used for new bridges and rehabilitation purposes. Fibre-reinforced plastic is one such material; it is a polymer matrix reinforced with fibres, either glass or carbon. These materials are lightweight, durable, high strength and ductile in nature. New solutions to counter deterioration include reactive powder concrete (RPC), a form of high-performance concrete reinforced with steel fibres. This mix will help make slender columns for bridges of a longer span. Composite materials are used in the repair of bridge columns and any other supporting elements to improve ductility and seismic resistance. Epoxy-impregnated fiberglass is used to cover columns that are non-ductile in nature. This is an alternative to the steel jacket technique.”