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CONCRETE IN MARINE ENVIRONMENT

CE 599 SEMINAR PRESENTATION. CONCRETE IN MARINE ENVIRONMENT. Osmanuddin Adil Syed May 30 th 2006. Content: Introduction Marine Environment Deterioration of concrete structure Case Studies Conclusions Ongoing research Work. INTRODUCTION:

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CONCRETE IN MARINE ENVIRONMENT

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  1. CE 599 SEMINAR PRESENTATION CONCRETE IN MARINE ENVIRONMENT Osmanuddin Adil Syed May 30th 2006

  2. Content: • Introduction • Marine Environment • Deterioration of concrete structure • Case Studies • Conclusions • Ongoing research Work

  3. INTRODUCTION: It is estimated that approx. 50% of the expenditure in the construction industry are spent on repair, maintenance and remediation of the existing structures. coastal and offshore sea structures are exposed to the simultaneous action of a number of physical and chemical deterioration processes, which provide an excellent opportunity to understand the complexity of concrete durability problems in practice. oceans make up 80 percent of the surface of the earth; therefore, a large number of structures are exposed to seawater either directly or indirectly.

  4. MARINE ENVIRONMENT: The prevailing environment in and in the vicinity of an ocean or sea. Coastal areas, which can be characterized to have a marine climate, reach normally some 10km from the coastline, due to wind-blown salt mist. However, at special occasions, e.g. during severe storms, the area influenced by the marine climate can be over 100 Km from the coastline.

  5. MARINE ENVIRONMENT (Cont’d.)

  6. MARINE ENVIRONMENT (Cont’d.) Submerged Zone. The submerged zone is below the surface of the water. The surface of a concrete structure in this zone is constantly exposed to water. Tidal zone. The Tidal zone is limited by the extend of the tidal actions. The surface of the concrete structure in this zone is cyclical exposed to seawater.

  7. MARINE ENVIRONMENT (Cont’d.) Splash zone. The splash zone is limited by the extent of splash from breaking waves, above the tidal zone. The surface of a concrete structure in this zone is randomly exposed to seawater. Atmospheric zone. The atmospheric zone is limited by the extent of spray from breaking waves, above the splash zone. The surface of a concrete structure in this zone is randomly exposed to spray from breaking waves.

  8. MARINE ENVIRONMENT (Cont’d.) SUBMERGED ZONE: Reinforced concrete structures that are partially or fully submerged in seawater are especially prone to reinforcing steel corrosion due to a variety of reasons. These include high chloride concentration levels from the seawater; wet/dry cycling of the concrete, high moisture content and oxygen availability. TIDAL ZONE: The tidal zone is characterized by periodical wetting and drying, and possible freeze/thaw-actions. The surfaces in the tidal zones, are mostly wet; with a limited access of oxygen. The extension of tidal zone varies between 0 m up to 15 m.

  9. MARINE ENVIRONMENT (Cont’d.) SPLASH ZONE: The splash zone is characterized by a randomly wetting and drying, depending on the wave-actions. The extension of the splash zone depends on the wave-heights and how well protected the structure in question is. It is also dependent on the variations in tidal water.

  10. MARINE ENVIRONMENT (Cont’d.) The corrosion rate below water level is limited by low oxygen availability, and conversely lower chloride and moisture content limit the corrosion rate above high tide. Corrosion is most severe within the splash and tidal zones where alternate wetting and drying result in high chloride and oxygen content.

  11. DETERIORATION OF CONCRETE From long-term studies of Portland cementmortars and concretes exposed to seawater, the evidence of magnesium ion attack is well established by the presence of white deposits of Mg(OH)2, also called brucite , and magnesium silicate hydrate. In seawater, well-cured concretes containing large amounts of slag or pozzolan in cement usually outperform reference concrete containing only Portland cement partly because the former contain less uncombined calcium hydroxide after curing.

  12. DETERIORATION OF CONCRETE (Cont’d.) Since seawater analyses seldom include the dissolved CO2 content, the potential for loss of concrete mass by leaching away of calcium from hydrated cement paste due to carbonic acid attack is often overlooked. According to Feld in 1955, after 21 years of use, the concrete piles and pile caps of the James River Bridge at Newport News, Virginia, required a $ 1.4 million repair and replacement job which involved 70 percent of the 2500 piles.

  13. DETERIORATION OF CONCRETE (Cont’d.) Similarly, 750 precast concrete piles driven in 1932 near Ocean City, New Jersey had to be repaired in 1957 after 25 years of service; some of the piles had been reduced from the original 550 mm diameter to 300 mm. In both cases, the loss of material was associated with higher than normal concentrations of dissolved CO2 present in the seawater.

  14. DETERIORATION OF CONCRETE (Cont’d.) The presence of thaumasite (calcium silicocarbonate), hydrocalumite (calcium carboaluminate hydrate), and aragonite (calcium carbonate) have been reported in cement pastes derived from deteriorated concretes exposed to seawater for long periods.

  15. DETERIORATION OF CONCRETE (Cont’d.) ACTION OF CO2: a) Ca(OH)2 + CO2 + H2O  CaCO3 + 2 H2O Precipitate  aragonite Calcite [COATING]

  16. DETERIORATION OF CONCRETE (Cont’d.) ACTION OF SULFATE: MgSO4 b) Mg2+ Ca2+ substitution MgSO4+Ca(OH)2 CaSO4 + Mg(OH)2  soluble Solid secondary Precipitate [LEACHING] gypsum [COATING] [EXPANSION] c) Action of secondary gypsum CaSO4 + C3A + 32 H2O  C3A.3CaSO4.32 H2O ettringite [EXPANSION]

  17. DETERIORATION OF CONCRETE (Cont’d.) ACTION OF CHLORIDE: MgCl2 d) Mg2+  Ca2+ substitution MgCl2 + Ca(OH)2 CaCl2 + Mg(OH)2 Soluble precipitate [LEACHING] [COATING] e) Action of CaCl2 CaCl2 + C3A + 10H2O C3A.CaCl2.10H2O Chloro aluminate [EXPANSION]  SO3 C3A.3CaSO4.32H2O ettringite [EXPANSION] CO2 + SiO2 CaCO3.CaSO4.CaSiO3.15H2O thaumasite [EXPANSION]

  18. STUDIES A case study by Di Malo, on the chloride profiles indicates a greater damage due to corrosion was detected in the surface facing the sea and in lower sections of the structure, particularly ground floor columns.

  19. STUDIES (Cont’d.) Use of Admixtures: According to Fookes.P.G. Sulfate resisting cements suffer less chemical decomposition in sea water than OPC, but it is not fully understood which type of cement is most effective in controlling the migration of chloride ions. Calculated addition of the pozzolan can improve the durability of concrete by removing a part of free lime, reducing permeability and at the same time protecting the reinforcement. Many authors have shown that Blast furnace slag cement, especially when well cured, resists the action of seawater fairly well. However, this BFS cannot be always the governing cement.

  20. STUDIES (Cont’d.) Al- amoudi, KFUPM,conducted a study to investigate the durability of two concrete (type 1 & type 5) and three blended cements prepared by Fly ash, Silica Fume and Blast furnace slag, in marine environment. The specimens were exposed to seawater for a period of 2 years. The data on reinforcement corrosion confirmed the superior performance of silica fume cements in sea water, followed by BFS and fly ash Cements.The corrosion resistance of Type 1 cement was marginally better than that of Type 5 cement.

  21. CONCLUSIONS: The marine environments can be distinguished as: 1) The submerged zone 2) The tidal zone 3) The Splash Zone, and 4) The atmospheric zone Investigations of reinforced concrete structure have shown that, generally, concrete fully immersed in seawater suffered only a little or no deterioration; concrete exposed to salts in air or water spray suffered some deterioration, especially when permeable; and concrete subject to tidal action suffered the most.

  22. CONCLUSIONS (Cont’d.) The presence of thaumasite, hydrocalumite and aragonite have been reported in cement pastes derived from deteriorated concretes exposed to seawater for long periods. Major deterioration was observed in the samples having greater thaumisite.

  23. REFRENCES Long A.E., H., G.D. & Montgomery, F.R. (2001). "Why assess the properties of near-surface concrete?" Construction and Building materials, v.15: pp.65-79. Mehta.P.K., Monteiro.P.J.M (October 20, 2001). A textbook on Concrete-Microstructure, Properties and Materials, Prentice-Hall, New Jersey. Fookes, P. G., Barr, J.M., Simm, J.D. (1986). Marine Concrete performance in different climatic environments. International conference on concrete society, London, Concrete in Marine Environment. Gjorv. O.E., J. (1971). "Concrete in Marine environment." ACI, v.68: pp.67-70. Al-Amoudi.O.S.B. (2002). "Durability of Plain and blended cements in marine environments“. Advances in cement Research, v.14.03: pp.89-100. Landau. A (1987). A system of inhibiting steel corrosion in concrete. 23rd Technical conference, New Zealand, New Zealand concrete society. Virmani, Y. P., Jones,W.R., & Jones,D.H. (1984). Public Roads, v.84.03, pp.96. Di Malo. A.A., L. J. L. L. P. T. "Chloride profiles and diffusion coefficients in structures located in marine environments." Structural concrete, v.5.01: pp.23-26.

  24. Jubail Research Center A field exposure station has been established at Khaleej Mardomah in Al-Jubail Industrial City.

  25. THANK YOU

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