Demolition of Old Oak Bridge B4113: Condition of a 54-year old prestressed concrete bridge

Abstract

The extension of the 3rd lane on Trunk Road 9 Section 1 (N1) at Bellville in the Western Cape necessitated the demolition and replacement of the Old Oak Road Underpass Bridge B4113. This bridge had insufficient vertical clearance as well as insufficient horizontal clearance for the widening of the road. Furthermore, the existing precast beam and slab deck has suffered from repeated vehicular impact damage over the years, resulting in continued costly repairs. This paper describes the condition of this bridge after a 54-year service life. The primary objective is to report and comment on the condition of this bridge in order for other engineers who have to rehabilitate, raise or widen similar bridges built at the same time, to have an indication of the quality of materials, workmanship, condition and behaviour. During and after the demolition operation, a visual inspection of the rubble was undertaken to evaluate the condition of this bridge which was constructed in 1963. Concrete cores taken before the demolition revealed higher concrete strengths of 50% and more. Carbonation and durability tests done on concrete fragments indicated a robust and durable structure which would easily reach its intended 100-year design life. However, overlays under the bridge reduced the vertical clearance while the expansion joint details led to reduced durability.