2015-03-31 I&S Committee - Item 5 - Attachment 1 - Munna Pt Bridge Repairs Level 3 Bridge Report

    •   Deck units in good condition typically have a large factor of safety for structural
        capacity, so that the good units will compensate for the lost strength in the ones
        suffering from ASR.
    •   The good deck units are likely to suffer ASR cracking and reinforcement corrosion
        sometime between now and 2016. The repair bill for the deck units will grow
        exponentially, unless action is taken soon.

o   Headstocks
    • The headstocks have not cracked
    • Headstock reinforcement is likely to be 100% intact

o   Columns
    • Column reinforcement is likely to be 100% intact. A few more tests will be
       required to confirm this.

o   Pilecap Beams
    • The top and side reinforcement cover exceeds the 75mm shown on the original
        drawings, and adopted in the TMR and Opus reports. Tod Consulting measured
        top cover was 100mm, and measured side cover was 89 to 93mm.
    • Reinforcement near the top centre of the pilecap beams has not corroded.
    • Reinforcement near the sides of pilecap beams has significantly corroded, to the
        point of being ineffective.
    • Reinforcement near the bottom of pilecap beams is probably starting to corrode
        now.
    • On this basis, 75-85% of the top reinforcement is likely to still be intact; 50-80% of
        the bottom reinforcement is likely to still be intact, and 66% of the shear
        ligatures/stirrups are likely to still be intact.
    • It is likely that the corroding reinforcement on the sides (and potentially bottom) of
        the pilecap beams has protected the rest of the reinforcement due to Macrocells
        (wetting-drying cycles of saltwater against part of the concrete can result in an
        anodic area that promotes local corrosion of reinforcement. The anodic
        reinforcement is sacrificed to temporarily protect the electrically connected, more
        passive reinforcement away from that area).
    • ASR cracking will continue, and we anticipate that reinforcement will corrode
        heavily, making the bridge dangerous by 2015.

o   Piles
    • The majority of the reinforcement in the piles is likely to be intact, based on the
        two piles where we removed concrete and observed the reinforcement condition.
        This is because most of each pile is underwater; with reduced oxygen making the
        rate of corrosion slower. However, at the pile tops (in the tidal zone), it’s probable
        that the reinforcement has corroded, but it hadn’t spalled (broken) off the concrete
        faces at the time of the February 2014 inspections. We expect that significant
        corrosion of all piles could start in the next 1-3 years (2015-2017), making the
        bridge dangerous and increasingly costly to repair by 2017.



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