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

    an estimated few hundred dollars would protect all 6 pilecap beams of Munna
    Point Bridge.

•   Chlorides = corrosive ions that are part of common salt (from seawater).

•   Corrosion = the gradual destruction of materials, (usually metals), by chemical
    reaction with its environment. Rusting, with the formation of iron oxides, is a well-
    known example of electrochemical corrosion.

    In the past, steel reinforcement in concrete has been believed to be “non-
    corrodible”, because of the high alkalinity of the concrete and the barrier provided
    by concrete cover. Unfortunately, thousands of concrete structures have been
    prematurely damaged by corrosion (of steel reinforcement and high strength steel
    strands). Usually, corroding reinforcement expands in size as the reaction
    proceeds, and this breaks off large areas of the surface concrete (known as
    spalling).

•   Corrosion threshold value = chlorides (salts) have penetrated the concrete and
    built up to a concentration sufficient to cause corrosion of steel reinforcement.

•   Deck Unit – See Precast Deck Unit

•   Drainage scuppers / scuppers = holes in the bridge deck to let rainwater drain off
    the deck

•   Headstock = reinforced concrete beam that directly supports the bridge deck

•   NSC = Noosa Shire Council. NSC was amalgamated into Sunshine Coast
    Council in 2008, and then de-amalgamated from SCC in 2014.

•   Macrocell = corrosion of one area of reinforcement in preference to another within
    the same component, because of anodic (more positively charged) and cathodic
    (more negatively charged) processes within the concrete.

    For example, wetting-drying cycles of chloride-contaminated water against part of
    the concrete can result in an anodic area that promotes local corrosion of
    reinforcement. The anodic reinforcement is sacrificed in preference to electrically
    connected, more passive reinforcement away from that area. Macrocells can
    make corroding reo less expansive, and sometime spalling of the concrete
    doesn’t occur. Thus, there may be no visual warning that reinforcement is
    corroding.

•   Pier = a structure in the water that supports the bridge deck. The components of a
    pier include a headstock, columns, pilecap beam and piles.

•   Piles = long concrete “posts” that extend deep into the creek/canal bed to support
    the bridge. These contain high strength steel strands (cables) that are tensioned
    (pulled tight) during construction, to increase each pile’s overall robustness and
    capacity. Without high strength steel strands, the piles would be unable to carry
    traffic loads.

•   Pilecap beam = reinforced concrete beam poured over the tops of the piles


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