Ankit patel

Sd. 1110

Effect of marine water on concrete made from opc,ppc and psc

Nowadays concrete is increasingly being used in more

hostile environmental condition

And durability is depend on materials

In marine structure the concrete has to withstand the

physical, chemical , mechanical action of sea water

and alternate wetting and drying condition with salted water

Introduction

Important factor is permeability. The deterioration is mainly because of

sulphate and chloride content of sea waterDance concrete prevent deterioration and

this can be achieved by replacing cement by mineral admixture.

Soluble salt – 3.5%by weightSodium and chloride – 11000 &20000 mg/ltrMagnesium and sulphate – 1400 to 2700 mg/ltrAnd ph of sea water = 7. 5 to 8.4This all are sufficient to deterioration of concrete

Sea water constitutes

Wetting and drying LeachingTemp. variationCorrosion of steelBattering by waves and tidesSulphate attackFreezing and thawing

Effect on concrete due to sea water

Constituents of sea water

Exposure zones

marine atm. Zone

1. corrosion of reinforcement by chloride

2.frost actionSpash zone

1. corrosion of reinforcement by chloride

2.abrasion due to wave action

3.frost actionf

Type of deterioration in various zones

Tidal zone

1. corrosion of reinforcement by chloride

2.frost action

3.abrasion due to wave action

4.biological fouling

5.chemical attack Submerged zone and sea bad

1.chemical attack

2. biological fouling

Reinforcement corrosion

• The corrosion products forming on the steel have a larger volume than the original steel, and the expansion of these products exerts a pressure that increase gradually and becomes strong enough to crack the concrete cover.

Changes in relative humidity can lead to dimensional changes in material with deformation & cracking.

Prolonged high humidity promote fungal growth and subsequent decay of organic materials.

And corrosion rate increases due to destruction of protective coatings.

Effects due to humidity

The corrosion velocity is doubled for every 10 degree C increase in temperature.

sea salt dissolve more easily at the higher temperature.

The temperature changes causes alternate expansion & contraction of material. It leads to high stresses and gradual deterioration & rupture.

When surface temperature fall sufficiently, moisture may condense on surface, which become thoroughly wetted. This may cause corrosion of material.

Effects due to temperature

DETERIORATION OF A RCC STUCTURE IN SEA WATER

Acid attack Portland cement is not very resistance to acid attack.In case of sulfuric acid attack it deteriorate concrete and

acid is able to reach to reinforcement.The concrete leading to the loss of cement paste and

aggregate from the matrix and cracking , rust staining, spanning is occurred.

Chemical reactions on marine structure

Alkali silica reactionsome aggregate containing silica that soluble in highly

alkaline solution.expand , disrupting the concrete. Sulfate attack

there are two chemical reaction involved in sulfate attack on concrete.

first the sulfate react with free calcium hydroxide which is liberated during hydration of cement from calcium sulfate.

Next The gypsum combines with hydrate calcium aluminates to form calcium salfoaluminate.

Both this reaction result in an increase in volume of concrete.

This two chemical reaction in which growth of crystals of sulfate salts disrupt the concrete.

Concrete contains micro cracks

1. Humidity and temperature.2. Impact of floating objects.3. Chemical attack, leaching of

cement paste.4. Freeze attack, overload and other

factor increase permeability of concrete.

Sea water and air

Highly permeable concrete

Corrosion of embedded steel

Crack growth

Cracking- corrosion- cracking cycle

Colour of concrete change from deep grey to lime grey expose to sea water.

There is continuous increase in permeability in concrete due to sea water and its attribute to sulphate attack on concrete.

Compressive strength over a year is decrease about 15 to 30% with respect to 28 day compressive strength expose to sea water.

Effects on concrete

Deteriorations of concrete by chemical reaction

Exchange reaction between aggressive fluid and components of hardened cement paste

Reaction involving hydrolysis and leaching of the components of hardened cement paste

Reaction involving formation of expansive product

Removal of Ca++ ions as soluble product

Removal of Ca++ ions as non expansive soluble product

Increase in porosity and permeability

Substitution reaction replacing ca++

Increase in internal stress

Loss of alkalinity

Loss of mass

Increase in deterioration process

Loss of strength and rigidity

Cracking , spalling deformation

• As per IS 456:2000• Min.grade of concrete for RCC is M30.• Min.cement content is 320 Kg/m3.• Max.W/C ratio is 0.40 – 0.45.• Max.chloride content is 0.60 Kg/m3.• Total sulphate content should not exceed 4% .• Use Pozzolana cement or slag as far as possible.• No construction joints within 600mm of the

upper & lower planes of wave action .• Nominal cover is 45mm – 75 mm.

Various Codal Provisions for Marine environment

• As per BS CP 110• Min.grade of concrete for RCC is M40.• As per Australian code • Min.grade of concrete for RCC is M30.• As per IS 456:2000• Min.grade of concrete for RCC is M30.

•w/c kept as low as possible.•Minimum cover should be increased where abrasion may occur.•Proper curing.

The deterioration of concrete exposed to marine environment is a result of collective action of physical chemical and biological factors. So stimulating such environment in the laboratory is very difficult.

To facilitate such environment the following exposure condition was adopted. The cubes and beams casted for all the three mixes of opc,ppc and psc were

Experimental work

exposed to sea water in following ways: Specimens fully submerged in sea water

prepared in laboratory to facilitate the condition of concrete ir submerged zone.

Specimens were half submerged in sea water in order to facilitate the condition in tidal zone

Specimens were alternately wetted and dried and this cycle was completed in 24 hours. This exposure condition facilitate the location of concrete in splash zone.

Test of materialscementOrdinary Portland cement

Portland pozzolana cement

Portland slag cement

Fine aggregates

coarse aggregates

Concrete plasticizer

Chemical admixture

Sea waterSea water for experimental programme has been prepared in

the laboratory by dissolving salts in the following proportion

Nacl – 270 gm/10 litersMgcl -32 gm/10 litersMgso-22 gm/10 literscacl – 13 gm/10 litersCaso - 6 gm/10 liters

Preparation of specimenMixing and compacting

mixer machine of capacity 25 kg is used

C.A -20mm, C.A -10mm,F.A,cement,water,plasticizer Curing

1.after 24 hours the concrete was kept in normal water

curing tank.

2. after 3,7 and 24 days the specimen were kept in sea water

Casting of concrete

For workability the concrete which was taken out from mixer is tasted for slump.

No segregation was observed in any mixes and all mixes were sticky and highly cohesive.

For both M35 and M40 concrete.

Testing of a fresh concrete

SLUMP IN MM

PPC 45

PSC 40

OPC 37

Compressive strength for M35

Testing of hardened concrete

Exposure condition

OP-35 compressive strength in mpa

PP-35 compressive strength in mpa

PS-35 compressive strength in mpa

Curing in days

3 7 28 3 7 28 3 7 28

Fully submerged 51 53.33

57.7 50 50 48.88

49.77

49 50.5

Half submerged 50 53.53

55 48 50 48 48 48.1 50

Alternate wetting and drying

45 46.22

48.5 41 47.11

47.11

42 47.2 49

Compressive strength for M40

Testing of hardened concrete

Exposure condition

OP-40 compressive strength in mpa

PP-40 compressive strength in mpa

PS-40 compressive strength in mpa

Curing in days

3 7 28 3 7 28 3 7 28

Fully submerged 58 60 61 54 53 57.7 54.22

50.1 55.7

Half submerged 58 58 57.5 53 52 57.7 52 51 53.5

Alternate wetting and drying

51 48.88

50.3 48 48.88

53.53

48.88

49 53.33

Chloride penetration

Exposure condition

OP-40(mm) PP-40 (mm) PS-40 (mm)

Curing in days

3 7 28 3 7 28 3 7 28

Fully submerged 20 18 15 17 15 15 14 12 12

Half submerged 20 18 15 17 15 15 15 10 15

Alternate wetting and drying

22 20 19 20 20 20 19 10 18

Exposure condition

OP-35(mm) PP-35(mm) PS-35(mm)

Curing in days

3 7 28 3 7 28 3 7 28

Fully submerged 22 20 20 20 17 18 16 13 10

Half submerged 23 20 20 21 17 19 16 12 11

Alternate wetting and drying

25 22 20 24 20 22 20 18 15

M35

days

0 15 30 45 60 75 90

PP 0.0 0.0020 0.015 0.046 0.070 0.095 0.17

PS 0.0 0.0003 0.014 0.039 0.055 0.080 0.10

OP 0.0 0.0120 0.049 0.084 0.150 0.300 0.40

Sulphate expansion in %

M40

days

0 15 30 45 60 75 90

PP 0.0 0.001 0.014 0.038 0.050 0.062 0.078

PS 0.0 0.0 0.006 0.025 0.040 0.055 0.064

OP 0.0 0.0 0.017 0.055 0.065 0.080 0.120

M35

days

0 15 30 45 60 75 90

PP 4.64 4.66 4.68 4.70 4.70 4.74 4.79

PS 4.67 4.65 4.67 4.68 4.70 4.72 4.75

OP 4.85 4.84 4.83 4.83 4.85 4.85 4.85

Ultrasonic pulse velocity in m/s

M40

days

0 15 30 45 60 75 90

PP 4.71 4.73 4.75 4.77 4.8 4.86 4.9

PS 4.77 4.78 4.79 4.81 4.81 4.83 4.85

OP 4.81 4.84 4.87 4.91 4.9 4.91 4.91

Slag cement has the least expansion, no weight loss and least weight gain due to sulphate attack . as found in literature review it is more resistant to sulphate attack than Ordinary Portland cement and Portland Pozzolana

After 60 days the weight loss is seen in OPC concrete while no weight loss is seen in concrete with PPC and PSC till 90 days. Thus OPC starts showing deterioration due to sulphate attack after 60 days.

Conclusion

Pulse velocity in concrete with mineral admixtures is more at early age but decreases with time and A 90 becomes almost equal to that of OPC concrete. As the grade of concrete increases the Pulse velocity increase in all three concretes. Thus, concrete becomes denser by increasing the grade of concrete.

Alternate welting and drying (Splash zone) condition is the most deteriorating exposure condition. In this condition least damage is found in PSC and most damage is found in OPC concrete.

Ordinary Portland cement has more compressive strength in fully submerged and half submerged condition and Portland Pozzolana cement and Slag cement have almost equal compressive strength. The strength in half submerged condition is little less than fully submerged condition in all cases.

PPC and PSC concrete have more effect of curing than OPC concrete for 3 days. But after 7 days curing the effect of curing becomes equal on all the three concretes. The strength and chloride ion penetration resistance increases as curing period increases from 3 days to 26 days.

Chloride penetration is least in slag cement and most in Ordinary Portland cement.

In alternate wetting and drying condition slag cement has the highest strength and Ordinary Portland cement has the lowest strength.

Thus Slag cement>Portland Pozzolana cement>Ordinary Portland cement is the series of durability of cements as far as sea water exposure is concerned.

Indian concrete journal march 1973. Journal of structural engineering vol.32 oct-nov 2005. Marine structure by p.kumar mehta. Marine structure engineering by Gregory P. Tsinker. Concrete technology by m.s.shetty Corrosion of steel in concrete by John p.

broomfield Google wikipedia

References

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