Civil Engineering March 2022 | Vol 30 No 2

Civil Engineering March 2022 27 investigations can be summarised as follows: Q Q The concrete cover was very high (up to 70 mm in some cases). This high level of cover caused small cracks to form in the concrete and allowed chlorides to contaminate it. Q Q The reinforcement was not at risk of carbonation since it was outside the carbonation zone. Q Q Areas of the beams were contaminated with chlorides, which contributed to the corrosion of the reinforcement and spalling of the concrete. Q Q The compressive strength determined from the testing ranged from 20 MPa to 39 MPa for the beams and from 25 MPa to 36 MPa for the piers. These ranges suggested that most of the pier concrete was in good condition. However, there was some uncertainty with the deck concrete. CLIENT REQUIREMENTS FOR NEW DECK CROSS SECTION The client required that the bridge be widened to accommodate pedestrian sidewalks on either side of the roadway. To provide safe passage for pedestrians, para- pets were required between the sidewalks and the roadway, and handrails were re- quired on the sides of the bridge. The new bridge was therefore widened from 11.0 m to 14.5 m. Figure 8 illustrates the cross section of the new deck. The wider deck meant that two additional beams, wider pier seating beams and wider abutment seating platforms were required. DESIGN OPTIONS Three options were considered for repairing the bridge. The options included two extremes: (1) repairing the bridge by only doing repair work and adding a sidewalk and (2) replacing the bridge com- pletely. Between these two extremes was a third option, (3) doing some repair work and replacing some elements of the bridge. Option 3 was proposed as it simplified the construction method and eliminated the need to demolish and replace whole elements of the bridge, which would have involved detailed and complicated repair work. It did, however, require that the entire deck and all pier seating beams Figure 5 Parapets in poor condition Figure 6 Spalled concrete at inside face of beam Figure 7 Spalled concrete at faces near joints Figure 8 Cross section of the new deck