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Effect of marine water on concrete made from opc,ppc and psc. Ankit patel Sd. 1110. Introduction. Nowadays concrete is increasingly being used in more hostile environmental condition And durability is depend on materials
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Effect of marine water on concrete made from opc,ppc and psc Ankitpatel Sd. 1110
Introduction • 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
Important factor is permeability. • The deterioration is mainly because of sulphate and chloride content of sea water • Dance concrete prevent deterioration and this can be achieved by replacing cement by mineral admixture.
Sea water constitutes • Soluble salt – 3.5%by weight • Sodium and chloride – 11000 &20000 mg/ltr • Magnesium and sulphate – 1400 to 2700 mg/ltr • And ph of sea water = 7. 5 to 8.4 • This all are sufficient to deterioration of concrete
Effect on concrete due to sea water • Wetting and drying • Leaching • Temp. variation • Corrosion of steel • Battering by waves and tides • Sulphate attack • Freezing and thawing
Type of deterioration in various zones • marine atm. Zone 1. corrosion of reinforcement by chloride 2.frost action • Spash zone 1. corrosion of reinforcement by chloride 2.abrasion due to wave action 3.frost actionf
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
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.
Effects due to humidity • 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 temperature • 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.
Chemical reactions on marine structure • 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.
Alkali silica reaction • some 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.
Cracking- corrosion- cracking cycle Concrete contains micro cracks Humidity and temperature. Impact of floating objects. Chemical attack, leaching of cement paste. Freeze attack, overload and other factor increase permeability of concrete. Highly permeable concrete Sea water and air Crack growth Corrosion of embedded steel
Effects on concrete • 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.
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 non expansive soluble product Substitution reaction replacing ca++ Removal of Ca++ions as soluble product Increase in porosity and permeability Increase in internal stress Increase in deterioration process Loss of alkalinity Loss of strength and rigidity Loss of mass Cracking , spalling deformation
Various Codal Provisions for Marine environment • 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.
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.
Experimental work • The deterioration of concrete exposed to marine environment is a result of collective action of physicalchemical 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
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 exposurecondition facilitate the location of concrete in splash zone.
Fine aggregates coarse aggregates
Chemical admixture • Concrete plasticizer Sea water • Sea water for experimental programme has been prepared in the laboratory by dissolving salts in the following proportion • Nacl – 270 gm/10 liters • Mgcl-32 gm/10 liters • Mgso-22 gm/10 liters • cacl – 13 gm/10 liters • Caso - 6 gm/10 liters
Casting of concrete • Preparation of specimen • Mixing 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
Testing of a fresh 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 hardened concrete • Compressive strength for M35
Testing of hardened concrete • Compressive strength for M40
Conclusion • 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.
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.
References • Indian concrete journal march 1973. • Journal of structural engineering vol.32 oct-nov 2005. • Marine structure by p.kumarmehta. • Marine structure engineering by Gregory P. Tsinker. • Concrete technology by m.s.shetty • Corrosion of steel in concrete by John p. broomfield • Google • wikipedia
