This project, undertaken in 1992, simulated the situation when a bridge is widened with a new concrete extension and then, after a delay period, traffic continues to use the existing old concrete bridge while the extension is curing. Traffic effects were simulated by repeated vertical displacements of ‘old’ concrete, connected by starter bars to ‘new’ concrete which is not displaced. The effects of these displacements and of a range of delay times on the bond between the ‘old’ and ‘new’ concrete during curing were then quantified.
After 28 days curing, the ‘old’ and ‘new’ concrete specimens were pulled apart and the maximum loads achieved during this process were recorded. The project results give a rough guide to practical delay times that can be used in construction applications before the passage of traffic is allowed. These results apply to cases of pure shear deformation between old and new concrete, and do not allow for variations in temperature.
Keywords: Bond, bridges, concrete, concrete bridges, curing, deck, New Zealand, roads, strength