SH20 Manukau Harbour Crossing
Project Delivery: NZTA, Fletcher Construction, Higgins and BECA
Alliance Design Engineers: BECA
Project Completion: November 2010
Application: Pile Caps and Bridge Piers
Concrete Type: 50 MPa
Cement Type: EverSure™(Type GP) and EverPlus™ (Class C Fly Ash)
Concrete Supply: Firth Industries
Requirement: Construction of pile caps and bridge piers with a specified life of 100 years exposed to marine conditions as detailed in exposure classification C (tidal, splash, spray zone) in NZS 3101:2006. In addition the bridge pier dimensions required consideration to the risk of early age thermal cracking.
Solution: A low water/binder ratio 50 MPa concrete that contained 40% EverPlus Class C Fly Ash was adopted. This reduced the risk of thermal cracking and provided sufficient durability to the marine conditions. To compensate for the absence of water curing, an increased level of concrete cover to 70mm was proposed. Chloride life prediction modelling confirmed the adopted solution provided adequate durability for a specified life of 100 years.