After more than 75 years continuous exposure to the Pacific Ocean waters on the Queensland coast the 879 reinforced concrete driven piles that supported the superstructure of the Hornibrook Highway bridge appeared to be in remarkably good condition when the bridge was demolished during 2011-2. Detailed investigations revealed excellent, very hard concrete with pH values still around 12 and very little evidence of serious corrosion of the steel reinforcement. The concrete chloride content at the reinforcement was considerably more than the usually accepted limits. However, a few isolated occurrences of very severe localized reinforcement corrosion were found during demolition even though there was little visual external evidence. Possible reasons for the various observations are discussed, together with the practical implications.

There have been few reports of structures that could be examined in detail for long-term behaviour and performance. One opportunity arose in 2002 when the Sorell Causeway bridge, a 45-year-old, 457 metres long, 34 span, pre-stressed concrete bridge in Tasmania, Australia, was demolished. This followed concerns about its safety in the light of the increasing size and frequency of occurrence of longitudinal cracks in the webs of the beams, the cracks appearing to follow the trajectory of the post-tensioning tendons. Corrosion was suspected. Pre-demolition testing had not provided sufficient information for estimates to be made of the remaining capacity of the bridge. After demolition, three bridge beams were selected for very detailed evaluation. The load capacity of the most severely damaged beam was only half that of the apparently sound beam. It failed catastrophically. The more seriously damaged beams showed severe loss of ductility. Progressive failure of the strands in the tendons was recorded in each case. The corrosion of the conventional reinforcement was consistent with expectations. However, some of the pre-stressing strands showed severe localised corrosion with cross-section losses between 75% and 100% but with little evidence of conventional oxidation rust products. Green rusts and ferrous chlorides were observed. The apparently sound beam also showed severe localised corrosion of strands.

The design of prestressed concrete bridge beams usually assumes that the full capacity of the tendons can be achieved under ultimate load, based on the assumption of sufficient deformation capacity of the prestressing wires. Whether this is achieved also in older bridges is of increasing interest in remaining-life assessments since, especially in aggressive marine environments, corrosion of steel is known to cause loss of wire ductility. Results are reported herein of load tests to destruction for three full-sized and deteriorated prestressed concrete bridge beams recovered from a 45-year-old bridge exposed to an aggressive marine environment. The two beams with the greatest superficial deterioration showed progressive and premature failure of the prestressing wires. The beam with little superficial deterioration also showed progressive failure and failed to reach the ultimate load capacity based on current design theory and actual material properties. Possible reasons for the observed behaviour and the practical implications are discussed.

Much concern exists about the apparently short durability of reinforced concrete structures in marine environments. However, there are many examples of structures that have survived for long periods of time with little evidence of reinforcement corrosion. Some of these were made with seawater as mixing water. Others had very little concrete cover. Detailed examination has revealed that reinforced concrete structures made with fine or coarse aggregate consisting of calcium carbonates such as limestone or seashells or with non-reactive dolomite have extended times to commencement of corrosion initiation and to active corrosion. The reasons for this are explored herein. In addition it is shown that some structures can have serious localized reinforcement corrosion without obvious exterior signs such as concrete cracking and delamination. This requires urgent research.

Transversely stressed precast concrete deck unit bridges are a common type of small and medium span bridge on the Queensland road network. This type of bridge is unique in design featuring transverse posttensioned stressing bars with a low level of prestressing, stiff upright kerb units and no shear keys. Recent structural assessments of these bridge types has yielded varied and at times inconsistent results, with theoretical structural deficiencies identified at odds with the lack of evidence of structural distress, demonstrating acceptable performance. A test program was developed to address this disparity and improve understanding of the structural performance of these bridge types. This included static and dynamic load testing with various vehicle types, and long-term monitoring of the behaviour of a representative bridge under ambient traffic. The test results have enabled improved understanding of the behaviour and true capacity of this bridge type, as well as providing inputs to enable validation of analytical structural modelling techniques.