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Protection Of Reinforcement Steel From Corrosion Prepared By: Mohamed A. El-Reedy, Ph. D. © Dr. Mohamed A. El-Reedy.

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Presentation on theme: "Protection Of Reinforcement Steel From Corrosion Prepared By: Mohamed A. El-Reedy, Ph. D. © Dr. Mohamed A. El-Reedy."— Presentation transcript:

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2 Protection Of Reinforcement Steel From Corrosion Prepared By: Mohamed A. El-Reedy, Ph. D. © Dr. Mohamed A. El-Reedy

3 Protecting Reinforced Concrete Structure From Corrosion Concrete design and execution quality control External methods © Dr. Mohamed A. El-Reedy

4 Protect Steel Bars From Corrosion By Concrete Quality Maintain concrete cover according to specifications Maintain concrete strength according to design Control compaction procedure Good execution Curing It is found that in case of good quality control no need any protection until 20 yrs. Except marine structures (c) Dr. Mohamed A. El-Reedy

5 Concrete Cover Min. cover thickness for cast-in-place concrete as the ACI Committee 301 Type of structure Min. Cover, mm Concrete deposited against the ground75 Formed surfaces exposed to weather or in contact with ground No. 6 bar or greater No. 5 bar or smaller Formed surfaces not exposed to weather or not in contact with ground Beams, girders and columns Slabs and walls, No. 11 bar or smaller Slabs and walls, No. 14 and 18 bars (c) Dr. Mohamed A. El-Reedy

6 Concrete Cover Concrete Requirements in ENV-206 and BS Exposure condition Max. W/C Min. cement Content (kg/m3) Min. concrete cover (mm) Conc. grade Dry C30/37 Humid a) no frost b) frost C30/37 C35/45 De-icing salts C35/45 Sea water a)no frost b) frost C35/45 Aggressive Chemical - Slightly - Moderately - highly (c) Dr. Mohamed A. El-Reedy

7 Sealers and membranes have been used traditionally for providing resistance to concrete structures exposed to severe chemical attack. Membranes and sealers can provide protection by: (i)Eliminating or slow down the penetration of chlorides and carbonation, to keep the steel passivated (ii)Reducing moisture movement into the concrete to keep it dry and slow the propagation of the corrosion reactions. Sealers and Membrane (c) Dr. Mohamed A. El-Reedy

8 Sketch for different types of coating © Dr. Mohamed A. El-Reedy

9 These consists of continuous film applied on the concrete surface with a thickness in the range of 100 to 300 micro. m. The film is composed of a binder and fillers. It is brushed or sprayed on the concrete surface. The successful coating/sealers depends on the applications. The concrete surface should be clean and sound. Weak and cracked concrete should be removed and holes should be filled. If the membrane applied is of a polymeric composition, the surface should be dry. Coating should usually be applied in two layers to obtain a continuous film without pinholes. The service life of the membranes/sealers ranges between 5 to 20 years. A- Coating and sealers. (c) Dr. Mohamed A. El-Reedy

10 These treatment are based on processes by which the surface of the pores in the concrete are lined with materials which reduce the surface energy, to make the concrete water repellent. Silicone compounds are most frequently used for this purposes. Silicone resin can be dissolved in organic liquid which after evaporation deposits a film of the resin on the pore surface B- Pore lining (c) Dr. Mohamed A. El-Reedy

11 These treatments are based on materials which penetrate into the pores and then react with some of concrete constituents. The resulting products are insoluble and are being deposited in the pores to block them. The most common materials used for this purpose are liquid silicates and liquid silicofluorides. C- Pore Blocking Click movie (c) Dr. Mohamed A. El-Reedy

12 Protect Steel Bars From Corrosion By External Methods Anodic Inhibitor Galvanized steel bars Coating steel bars by epoxy Using stainless steel reinforcement Coated concrete surface Cathodic protection (c) Dr. Mohamed A. El-Reedy

13 Anodic Protection The most common anodic inhibitor is calcium nitrite. It inhabits corrosion by stabilize of the passive film which tend to be disrupted when chloride ions are present at the steel level. What is the required dose? (c) Dr. Mohamed A. El-Reedy

14 Calcium Nitrite Dosage Required for Protection of Chloride –induced corrosion Calcium Nitrate content (Kg/m3, 30% sol.) Chloride ion content at steel level, (kg/m3) Anodic Protection (c) Dr. Mohamed A. El-Reedy

15 Anodic Protection This type of protection don’t have any effect on concrete properties in case of fresh or hardening Sodium nitrate or potassium nitrate has a good efficiency but react with alkaline aggregate and cement and cause problems. If use calcium nitrate will be accelerator so it need to add retarder additives. This materials is react with chloride so it need increase in chloride concentration to cause corrosion (c) Dr. Mohamed A. El-Reedy

16 Galvanized Steel Bars THE FHWA report suggested 15-year life for galvanized rebar in good quality concrete. Galvanized bar is used effectively in structure exposed to carbonation. Accelerated depletion of the galvanizing if galvanized bars are mixed with ungalvanized bars. The galvanized coating must be tested after bending the steel bars. Take care in case of using welding in manufacturer. The maximum zink cover is around 200 Micro. It is follow ASTM A767/A767A M-90 (c) Dr. Mohamed A. El-Reedy

17 Galvanized Steel Bars Based on on ASTM There are two classes: Class I with thickness 85 micrometer and weight 610gm/m2 Class II with thickness 150 micrometer and weight 1070gm/m2 In case of chloride it not prevent corrosion but it decrease the corrosion rate but it increase the chloride content to start corrosion To % to increase the time of corrosion to 4 times. (c) Dr. Mohamed A. El-Reedy

18 Epoxy Coated Steel Bars It is used extensively in USA and CANADA as for 18 years more than 100,000 building used coated bars which is equal to 2 million tons of epoxy coated bars. The coated steel bar must follow ASTM A 775M/77M-93 which required the following: The coating thickness in the range of micro.m Bending of the coated bar around a standard mandrel should not lead to formation of cracks. The number of pinhole defects should not be more than 6/m. The damage area on the bar should not exceed 2%. (c) Dr. Mohamed A. El-Reedy

19 Stainless Steel Reinforcement Stainless steel bars has been applied in certain circumstances. There are duplex steel which is mild steel in the core and stainless steel outer 1-2 mm offered in the market. It is high cost which is around from 8 to 10 times the normal steel. The cost of stainless steel is higher than coated bar by around from 15% to 50%. There are 3 level of yield strength,300, 420 and 520 Mpa. (c) Dr. Mohamed A. El-Reedy

20 Stainless Steel Reinforcement In the market there are steel covered with stainless steel with yield strength 500 Mpa and the max. tensile strength 700 Mpa. The available diameters 16, 19, 22, 25 and 23 mm, in process of manufacturing 40 mm. Not acceptable welding for steel covered with stainless steel (c) Dr. Mohamed A. El-Reedy

21 Reinforcement from GFRP There are some Structures in Canada were established using bars of GFRP such as marine structure at the port of Wharf. This structure is thick wall of pre-cast concrete and the design of the concrete is to have maximum strength 450 kg / cm 2. The mechanical properties it to the maximum strength is about 5975 kg / cm 2 and the maximum bond strength is 118 kg / cm 2, but we find that the modulus of elasticity with the less steel modulus of elasticity for iron five time. (c) Dr. Mohamed A. El-Reedy

22 Cathodic Protection (c) Dr. Mohamed A. El-Reedy

23 Cathodic Protection I-Sacrifical Anodes Explored in 1824 by Sir Humphrey Davey Its an external current supply by connecting the steel to a metal which is higher in the electrochemical series (e.g. zinc). Used effectively in submerged structure where the concrete is wet and the resisitivity is low. II-Impressed Current It is used for building has chloride inside the concrete The continuous current needed The concrete must be conduct electricity Avoid aggregate with alkaline (c) Dr. Mohamed A. El-Reedy

24 - + Rectifier Voltameter Anode pole Steel bar External cover Embeded Electrical circuit to cathodic protection © Dr. Mohamed A. El-Reedy

25 Cathodic Protection II-Impressed Current Most designers take the electric current around 10 to 20 mm Amber for m 2 of steel bars. The voltage is around 12 to 24 volts (c) Dr. Mohamed A. El-Reedy

26 Sketch for conduct asphalt and the anode position at the surface (c) Dr. Mohamed A. El-Reedy

27 Anode Pole cover Source of Direct Current + - Sketch present anode pole embedded in concrete (c) Dr. Mohamed A. El-Reedy

28 Source of direct current Conductive cover layer Preliminary conductive + - Sketch present anode conduct cover layer system 10 cm (c) Dr. Mohamed A. El-Reedy

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30 Thanks Dr. Mohamed A. El-Reedy Mobile: © Dr. Mohamed A. El-Reedy


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