CONCRETE IN MARINE ENVIRONMENT

CONCRETE

IN

MARINE ENVIRONMENT

CE 599 SEMINAR

PRESENTATION

Osmanuddin Adil Syed

May 30th 2006

Concrete in Marine Environment OSMANUDDIN ADIL 30th May 2006 2

Content:

Introduction

Marine Environment Deterioration of concrete structure Case Studies Conclusions

Ongoing research Work


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.


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.

MARINE ENVIRONMENT:


MARINE ENVI’MENT

DIVISION

SUBMERGED ZONE

TIDAL ZONE

SPLASH ZONE

ABOVE GROUND

ZONE

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.



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.



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.



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.



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.



From long-term studies of Portland cement mortars 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.

DETERIORATION OF CONCRETE


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.

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.


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.



ACTION OF CO2:

a) Ca(OH)2 + CO2 + H2O CaCO3 + 2 H2O Precipitate

aragonite Calcite [COATING]



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]



ACTION OF CHLORIDE: MgCl2

d) Mg2+ Ca22+ 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]



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.

STUDIES


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.


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.


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.


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.


REFRENCESLong 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.


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


Mix No.Additives

kgMix No.

Additiveskg

M1 - M820%FA

M2 - M9 -

M3 - M10Coal tarepoxy

M48%SF

w/c = 0.3M11

SIKA901

M5 - M12SIKA903

M60.2 % PP

FibersM15

10%Super-Pozz

M78%SF

M1730%FA

Property Zone Ranking per property

M4 M7 M15 M17 M8 M1 M10 M5 M3 M2 M11 M9 M6 M12

CompressiveStrength

Tidal5 4 3 6 8 2 9 1 11 12 7 10 14 13

Below2 1 5 7 8 4 14 3 6 9 12 13 11 10

Above1 2 4 8 7 3 14 5 6 9 11 10 13 12

ChloridePermeability

Tidal3 4 1 2 5 6 9 7 11 12 8 13 10 14

Below3 1 4 6 2 5 12 8 7 10 13 11 9 14

Above8 1 2 5 3 7 11 9 4 12 6 10 14 13

ElectricalResistivity

Tidal5 2 7 8 4 3 6 10 1 12 9 11 14 13

Below10 7 4 5 9 6 1 2 14 8 11 3 13 12

Above13 3 6 5 4 2 1 14 10 11 9 8 12 7

Water Absorptoin

Tidal2 8 7 9 3 1 12 5 6 4 11 14 13 10

Below3 6 9 10 4 2 1 5 8 7 13 14 12 11

Above 3 11 13 14 9 2 2 8 5 4 7 12 10 6

Water Per’bility

Tidal4 11 2 3 14 13 1 5 12 7 6 8 10 9

Below3 5 10 8 6 11 1 4 9 7 13 12 14 2

Above5 2 4 3 7 6 1 9 11 12 8 10 13 14

Total68 70 81 86 93 99 100 105 136 145 148 161 168 179

Overall Ranking 1 2 3 4 5 6 7 8 9 10 11 12 13 14


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CONCRETE IN MARINE ENVIRONMENT