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Thus if the location position or elevation of a

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Thus, if the location (position or elevation) ofa concrete member is critical to the project, thenspecifying appropriate tolerances in the projectdocumentation that are more stringent than thoseallowed under AS 3600 is recommended.Table ±Acceptable quality of formed surfaces(after AS 3610)QUALITy OF SURFACE FINIShClass 1Class ±Class 3Class 4Class 51Blowholesrefer photographs in AS 3610 for examplesn/An/A±Form face deflectionlesser oflesser ofGreater ofGreater of2 mm or3 mm or3 mm or3 mm orspan/360span/270span/270span/270n/ATolerance for straight elements with smooth surface, in millimetres% of readings95100901008010070100701003Face stepwithin the element12233558at insitu construction joint23233558**4Surface undulations**l= 300(a – b)12243457**l= 1500(a – b)2436578105Flatness1.25 m grid4567710****at 5 m over 10 m577101015****(not applicable to precast concrete)6Out of plumbheight<3 m354657****3<height<8 m688101012****(not applicable to precast concrete)notes*limited by AS 3600**a and b are respectively the maximum and minimum distances from the straightedge.Figure 4:concrete frame may require tolerancesappropriate for the fitting of components such asprecast units.
Page 5 of 9>tolerances for concrete surfacesNATSPECnATSPec nominates a flatness tolerancefor each of three classes of unformed surfaces, viz:nClass AMaximum deviation from a 3-mstraightedge is 3 mm.nClass BMaximum deviation from a 3-mstraightedge is 6 mm.nClass CMaximum deviation from a 600-mmstraightedge is 6 mm.class A should not automatically be specifiedfor all floor applications. Achieving a maximumdeviation of 3-mm under a 3-m straightedge isdifficult and may require special constructiontechniques at increased cost. referring toTable 1,a reasonable tolerance for a conventional finishwould be a maximum deviation of 12 mm under a3-m straightedge. With careful level control andre-screeding where required, it may be possible toachieve a maximum deviation of 8 mm under a 3-mstraightedge for the majority of a pavement area.More-stringent tolerances should be specified onlyif required for the application, eg a television studiofloor or operating theatre, both of which requiresensitive equipment to be moved across the floor. Inthese cases class A may be the appropriate flatnessto specify, but consideration needs to be givento achieving the specified tolerance on site. Thespecification of a less stringent tolerance and useof a self-levelling topping (after construction) maybe an option to achieve more-stringent tolerances,particularly if suspended and/or post tensionedfloors are involved. Deflections after formworkremoval or stressing can easily exceed the ‘flatness’tolerance specified. note that the waviness of thefloor may be more critical than having a class Afinish. Fewer ‘waves’ will effectively increasethe flatness and allow smoother movement ofequipment over the floor surfaceFigure ±.

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