Cathodic V TraditionalTreatment of SteelworkIn the early 20th century construction techniques moved away from traditional load-bearing masonrytowards masonry clad steel framed buildingsforms of electrochemical corrosion prevention: sacrificialcathodic protection or impressed current cathodicprotection (ICCP).Sacrificial cathodic protection is the older method andconsists of connecting a more corrosive metal like zinc ormagnesium to the steel. The zinc or magnesium corrodesin preference to the steel and generates a protectivecurrent that prevents corrosion of the steel in contactwith the sacrificial anode material. It is worth noting thatsacrificial/galvanic protection has been shown to beunsuccessful on stone buildings.This marked the evolution of the modern high-risebuilding. Corrosion problems associated with these earlysteel framed buildings are inherent due to the nature ofthe early design and engineers and architects of the timefailing to appreciate the destructive nature of corrosion.External masonry tightly notched around the steelworkwith crudely in-filled cavities allows moisture to collectand come into contact with the steel, making the onsetof corrosion inevitable. Moisture can penetrate throughporous cladding materials, open or degraded mortar joints,cracked masonry, or faulty or degraded services such ascracked rainwater downpipes and gutters. Often thecondition of cracking and spalling stonework is referredto as Regents Street Disease due to the number ofbuildings along London’s famous street that have sufferedfrom this.ICCP involves the use of an inert non-corrosive anodematerial being placed in the structure or soil and theprotective current being forced onto the steel structurethrough a power supply. It works on the principle ofpreventing corrosion by passing a current from anexternally placed anode material, through a connectingelectrolyte (facing and mortar) to the corroding steelwork. As a result, electrochemical reactions are preventedat the steel surface through the prevention of ferrous ionformation on the steel surface and the removal of reactivenegatively charged ions.TreatmentThere are two practical methods of treatment forcorroded steelwork in buildings: cathodic protection ortraditional treatment of the steelwork.Cathodic ProtectionThis describes a general area of technology covering twoiiConservation & Heritage Journal82
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