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Tn1 Tn1 Presentation Transcript

  • 9 E8 H7 I6C A L 4 N O T 2 1 The Steel Reinforcement Institute of Australia is a national non-profit organisation providing information on the many uses of steel reinforcement and reinforced concrete. Since the information provided is intended for general guidance only, and in no way replaces the services of professional consultants on particular projects, no legal liability can be accepted for its use. January 2008 3 ESURFACE CONDITION OF STEEL REINFORCEMENTThe bond and anchorage NORMAL CONDITIONS POTENTIAL PROBLEMS loose corrosion and salt[4]. Severelyproperties of bars and mesh corroded and pitted steel should Hot-rolled bars, as delivered from the The major potential problem with rust not be used unless the material hasare not detrimentally affected mill, have a layer of tightly adhering on reinforcement is caused by rain been checked for strength and cross-by a light coating of rust which mill-scale on the surface. If stored washing particles onto the formwork sectional area limitations.has formed on the steel surface under cover this mill-scale will help and this can subsequently causeafter normal exposure to the to preserve the steel. However, staining of the concrete surface on AS 3600, CLAUSE 19.2.4atmosphere[1][2]. with handling and storage of the floor soffits and external facades. This SURFACE CONDITION rods and bars, the mill-scale can be problem can be avoided by ensuring loosened and, if stored in the weather, that all loose and extraneous material AS 3600, Clause 19.2.4 states: rusting can occur and the mill-scale is removed from the formwork prior “At the time concrete is placed, the surface condition of reinforcement can become detached and “loose”. to placing concrete. In some critical 5 shall be such as not to impair its bond Research has shown that the sorting situations, galvanised reinforcement to the concrete or its performance in and normal handling and placing of could be used to eliminate potential the member. The presence of millscale bars removes the loose scale and the staining problems. or surface rust shall not be cause for remaining rust and bonded scale is rejection of reinforcement under this Where reinforcing steel is exposed not detrimental to the bar bond. Clause.” to salt water, more significant Under some climatic conditions, problems may occur. Corrosion AS 3600 Commentary on Clause where the atmosphere is hot and of reinforcement in concrete is 19.2.4 states: T C N humid, “black” rust may form on promoted by the presence of chloride “Rust and millscale has little effect on bundled bars. When unbundled ions which are present in salt water[3]. bond [1],[2]. Moderate rusting has been and exposed to dry conditions, the Reinforcing steel which has been shown to improve bond [5].” corrosion products will dry and subjected to salt water exposure convert to red rust which is powdery and has been severely rusted should and will tend to readily fall off the bar. not be placed in concrete without some prior treatment such as high- pressure washing to remove thewww.sria.com.au
  • 9 E8 H7 I6C A L 4 N O T 2 1 The Steel Reinforcement Institute of Australia is a national non-profit organisation providing information on the many uses of steel reinforcement and reinforced concrete. Since the information provided is intended for general guidance only, and in no way replaces the services of professional consultants on particular projects, no legal liability can be accepted for its use. 2 January 2008 3 EREFERENCES[1] Kemp, E. L. et al, “Effect of Rust and The bond and anchorage Scale on the Bond Characteristics properties of bars and mesh of Deformed Reinforcing Bars”, ACI Journal, Proceedings, Vol. 65, No. 9, are not detrimentally affected Sept 1968. by a light coating of rust which has formed on the steel surface[2] Rejab, H. M. et al, “Effect of Rust on Bond of Welded Wire Fabric”, Techni- after normal exposure to the cal Bulletin No. 265, American Road atmosphere[1][2]. Builders Association, 1986.[3] Campbell-Allen, D. and Roper, H., “Selection of Materials to Improve 5 Performance of Materials in Service”, Handbook of Structural Concrete, Kong F. K. et al, 1983.[4] Pollock, D. J. and Kay, E. A., “Concrete Construction in Hot Climates”, Hand- book of Structural Concrete, Kong F. K. et al, 1983.[5] “The Effect of Initial Rusting T C N on the Bond Performance of Reinforcement” CIRIA Report No. 71, ISSN 0305-408X