Lafarge North America’s Lafarge SF and NewCem slag cements are playing a crucial role in constructing the new Tappan Zee Bridge (New NY Bridge) – the largest bridge construction project in New York history – as more than 300,000 cu. yd. of high-performance concrete will be used.
The 3.1-mile twin-span Hudson River crossing replaces the Tappan Zee Bridge built in 1955, and will be one of the widest cable-stayed structures of its kind in the world. The New NY Bridge will include eight traffic lanes, four breakdown lanes, a bicycle and pedestrian lane, and state-of-the-art traffic-monitoring systems, as well as bus rapid transit and commuter-rail trains.
The project required the crossing’s primary structural components to provide a 100-year service life before needing major maintenance. To meet these stringent requirements for the substructure, Lafarge collaborated with engineers from Tappan Zee Constructors, LLC, to conduct sophisticated life cycle analysis and testing of different high-slag content mix recipes with numerous aggregates and admixture combinations.
Primary considerations in selecting the optimum concrete mix formulation for the bridge towers, piles, columns, caps and piers were strength, long-term durability, low heat of hydration, and excellent ASR mitigation and sulfate resistance. To achieve these performance goals, the team decided on a high-performance concrete containing a 64/36 percent mix of NewCem slag cement and Portland Type I/II cement. Engineered for long-term durability, NewCem slag cement helps structures achieve greater strength potential, reduced permeability, and increased resistance to sulfate attack and alkali silica reaction. High replacement levels of slag cement in properly proportioned mixes also help control shrinkage, creep and thermal cracking in mass concrete structures.
The full bridge is supported by 86 piers, most of which bolster the long approaches (encompassing about 2 million sq. ft.) to the bridge’s main span. To meet the challenges of the approach spans over the river, their driving surface comprises nearly 6,000 precast deck segments of high-performance concrete containing Lafarge’s high-performance SF blended cement. This portland-silica fume cement blend produces concrete with a significantly higher compressive strength than normal concrete and is recommended for structures exposed to seawater, chloride ions, deicing salts and chemical attack, noted Lafarge. For the crossing’s main spans, approximately 1,000 precast concrete deck panels containing Lafarge Portland I/II cement will serve as the roadway.