Ggbs readymix

Arivusudar NagarajanArivusudar NagarajanSenior Manager (Operation & Special products Senior Manager (Operation & Special products marketing)marketing)

The blast furnace slag is a by-product of the iron manufacturing industry. Iron ore, coke and limestone are fed into the furnace and the resulting molten slag floats above the molten iron at a temperature of about 1500C to 1600C. The molten slag has a composition of about 30% to 40% SiO2 and about 40% CaO, which is close to the chemical composition of Portland cement.

Use of high grade of cement should not be taken for granted to yield high grade (Strength) concrete, Increase in cement Grade does not increase the quality of concrete

Concrete may possess high strength but may deteriorate sooner than expected, concrete made should satisfactorily in both strength and durability

Beyond a certain period all grades shows same strength, only advantage of use of higher grade cement is faster rate of gain in strength during initial period

Oxides OPC GGBS PFA SiO2 21 32 50CaO 64 37 2

Al2O3 6 19 27MgO 2 8 2Fe2O3 4 1 8Others 4 5 10

C-S-H

OPC –43/53+

WATER

C-S-H + Ca(OH)2

Ca(OH) 2 - Weakest component

Higher C 3S - More Ca (OH) 2

C 3S Produce - 61 % CSH + 39 % CH

C 2S Produce - 82% CSH + 18% CH

High Early Strength - High C 3S

High C 3S - High heat of Hydration

Blended Cement+

WATER

C-S-H + Ca(OH)2

+

composite components

Chemical reactions during hydration

When water is added to cement, the following series of reactions occur:

•The tricalcium aluminate reacts with the gypsum in the presence of water to produce ettringite and heat:Tricalcium aluminate + gypsum + water ® ettringite + heat C3A + 3CSH2 + 26H ® C6AS3H32, D H = 207 cal/gEttringite consists of long crystals that are only stable in a solution with gypsum. The compound does not contribute to the strength of the cement glue. •The tricalcium silicate (alite) is hydrated to produce calcium silicate hydrates, lime and heat:Tricalcium silicate + water ® calcium silicate hydrate + lime + heat 2C3S + 6H ® C3S2H3 + 3CH, D H = 120 cal/gThe CSH has a short-networked fiber structure which contributes greatly to the initial strength of the cement glue.

•Once all the gypsum is used up as per reaction (i), the ettringite becomes unstable and reacts with any remaining tricalcium aluminate to form monosulfate aluminate hydrate crystals:Tricalcium aluminate + ettringite + water ® monosulfate aluminate hydrate 2C3A + 3 C6AS3H32 + 22H ® 3C4ASH18,The monosulfate crystals are only stable in a sulfate deficient solution. In the presence of sulfates, the crystals resort back into ettringite, whose crystals are two-and-a-half times the size of the monosulfate. It is this increase in size that causes cracking when cement is subjected to sulfate attack. •The belite (dicalcium silicate) also hydrates to form calcium silicate hydrates and heat:Dicalcium silicates + water ® calcium silicate hydrate + lime C2S + 4H ® C3S2H3 + CH, D H = 62 cal/gLike in reaction (ii), the calcium silicate hydrates contribute to the strength of the cement paste. This reaction generates less heat and proceeds at a slower rate, meaning that the contribution of C2S to the strength of the cement paste will be slow initially. This compound is however responsible for the long-term strength of portland cement concrete.

•The ferrite undergoes two progressive reactions with the gypsum:

in the first of the reactions, the ettringite reacts with the gypsum and water to form ettringite, lime and alumina hydroxides, i.e.

oFerrite + gypsum + water ® ettringite + ferric aluminum hydroxide + limeoC4AF + 3CSH2 + 3H ® C6(A,F)S3H32 + (A,F)H3 + CH

the ferrite further reacts with the ettringite formed above to produce garnets, i.e.

•Ferrite + ettringite + lime + water ® garnets•C4AF + C6(A,F)S3H32 + 2CH +23H ® 3C4(A,F)SH18 + (A,F)H3

The garnets only take up space and do not in any way contribute to the strength of the cement paste.

Mechanism of Cement Hydration

Heat of Hydration

Cement hydration generatesheat. Heat dissipates from concrete slowly;the thicker the section, the longer it willtake the interior to cool. This can result inlarge temperature differentials between theconcrete surface and its interior. Theconcrete is then subject to high thermalstresses, which can result in cracking andloss of structural integrity.

Benefits of GGBS in concrete

Heat of Hydration

220KJ/Kg 195KJ/Kg

Gradual hydration of GGBS with cement generates lower heat than Portland cement, This reduces thermal gradients in the concrete, GGBS is used to limit the heat of hydration A reduction in the early-age temperature rise can reduce the risk of early-age thermal cracking


Water demandLower W/C Ratio High Compressive Strength Reduced water Cement Ratio will contribute to compressive Strength gain

GGBS is a glassy material and its smoother surface requires less water to adequately cover the particles. Though powder volume increase due to low specific gravity as the percentage of GGBS in the mix increases, any reduction in water may become smaller due to the higher powder volume.

Rheological behavior between GGBS and Portland cement enable a small reduction water demand of 3–5% (i.e., 5 to 10 litres of water per Cubic meter of concrete).

Setting Time Increased setting time may be advantageous in extending the time for which

the concrete remains workable and, may reduce the risk of cold joints. This delay is mainly due to the slower initial rate of reaction of GGBS, compared to that of OPC. The effect is magnified at higher percentages

AppearanceGGBS cement also produces a smoother, more defect free

surface, due to the fineness of the GGBS particles GGBS is effective in preventing efflorescence when used at

replacement levels of 50% to 60%

Bleeding Bleeding is a form of segregation where some of the

water in the concrete tends to rise to the surface of the freshly placed material. Delaminations are more likely to occur when factors that extend the bleeding time

Dusting is developed as a of a fine, powdery material

that easily rubs off the surface of hardened concrete

Fineness of GGBS reduce bleeding than that of Portland cement and therefore reduces risk of delaminations


WorkabilityGGBS particles are less water absorptive than Portland

cement particles and thus GGBS concrete is more workable than Portland cement concrete. For equivalent workability, a reduction in water content of up to 10% is possible

Sulphate Resistance Sulphates react with C3A and Ca(OH)2 present in OPC

concrete, causing the concrete to expand and crack. GGBS is a sulphate-resisting, Specifying GGBS at 50%–70% content gives optimum protection against sulphate attack.

Alkali Aggregate Reaction Alkali–silica reaction (ASR) is a reaction between the hydroxyl ions in the

pore water within a concrete and certain forms of silica which occur as part of some aggregates. The product of the alkali–silica reaction is a gel which imbibes pore fluid and expands; in some instances this expansion induces internal stress in the concrete of such magnitude that extensive macro-cracking of the concrete occurs. GGBS reduce the deleterious effect of AAR due to its low reactive alkali content and its ability to inhibit AAR. The overall lime-to-silica (Ca/Si) ratio of the hydration products (CSH) was reduced by inclusion of GGBS, The hydration products of low Ca/Si ratio can ‘immobilize’ free-alkalis and hence reduce the risk of AAR

Chemical and Minerological Composition Of the Slag

Parameters SiO2Al2O3Fe2O3CaOMgOMnOLOIIRSulphide SulphurGlass Content(%)

JSW Slag

37.73%14.42%1.11%37.34%8.71%0.02%1.41%1.59%0.39%

92 – 95%

IS:12089 Limits

-----------------------17.0% Max.5.50% Max.------5.00 Max.2.00 Max.

85.00% Min.

Microscopic examination reveals the glassy nature of GGBS particles

18

Application GGBS replacement %On the ground concrete structures with higher early age strength requirement

25-35%

Underground concrete structures with average strength requirement

35-50%

Mass Concrete or concrete structures with strict temperature control requirement

50-65%

Speciality concrete structures with higher requirement on durability i.e. Corrosion resistant marine structures, sewerage treatment plants, etc.

50-70%

Replacement levels of OPC with GGBS in Concrete.

Fly Ash is the finely divided mineral residue resulting from the combustion of powdered coal in electric generating plants.

GGBS is obtained by quenching molten iron blast furnace slag in water or stream, to produce a glassy granular product that is then dried and ground into a fine powder.

Slag is the co-product of a controlled process, iron production, which results in a very uniform composition from source to source.

Fly ash is a byproduct of electric power generation that varies from source to source.

Fly Ash usually contains very high SiO2 and Al2O3, but very low in CaO (<2%).

GGBS has very similar chemical compositions to Ordinary Portland Cement (OPC) such as 30-42% of CaO, 35-38% of SiO2, 10-18% of Al2O3, 10-18% of MgO etc.

Depending upon the reactivity of fly- ash, only a limited amount, and not the entire calcium hydroxide is consumed due to pozzolanic reactions. All the Ca(OH)2 in concrete cannot be consumed simply by addition of 20-30 percent fly ash . Stoichiometry indicates that equal weights of lime (Ca(OH)2)and active silica combine in pozzolanic reactions.

The amount of Ca(OH)2 liberated in hydration is about 25 percent by weight of cement. For example, if there is 400 kg of OPC in the mix,100 kg of Ca(OH) 2 will be liberated, which will require 100 kg of active silica for chemical reaction

Indian Fly Ashes contain about 55 percent SiO2, out of which only 20 to 25 percent are in glassy form. Hence, addition of 100 kg of fly ash (that is,25 percent of OPC), will consume only about 14 percent of Ca(OH)2; and 86 percent will remain unconsumed.

This calculation is in line with the fact that all of Ca(OH)2 in concrete was shown to be consumed only when 50 percent of Slag or 30 percent of silica fume was used, which is mostly active silica.

Fly Ash is not a hydraulic material, hydration will not take place on its own, and it will only harden with the use of activators (e.g. OPC).

GGBS, in contrast, is a hydraulic material, which means that it will set and harden due to a chemical reaction with water.

After hardening, it will retain some strength development and remain stable even under water. Concrete containing GGBS cement has a higher ultimate strength than concrete that uses 100% Portland cement.

The permitted replacement ratio of Fly Ash in OPC is 15-35% (IS 1489 Part-1), but it’s usually no more than 30% in concrete.

On the other hand, the permitted replacement ratio of GGBS in OPC or concrete is 25-70%(IS 455).

7 9028

Com

pres

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Stre

ngth

- M

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GGBS MIX

OPC MIX

AGE - (DAYS)

It is wrong perception that PSC/GGBS sets slow.

In fact, the concrete made with PSC /GGBS has a lower early strength (up to 7days) , and after 8-10 days it possess strength higher than that of OPC.

Lateral Strength of GGBS/PSC Mix is 126-140 % of OPC Mix

STRENGTH COMPARISON OF OPC & PSC

60

Days OPC (53) MixOPC with

30% FlyAshOPC with

40% GGBS3 19 13 117 23 18 19

28 31 30 3190 42 39 45

Strength Comparison of M25 Mix in Mpa

OPC=6300/MT: PFA=1100/MT: GGBS= 2850/MT

GRADE M15

Item Qty Amount Item Qty Amount Item Qty AmountCement 220 1386 Cement 180 1134 Cement 120 756

Fly ash 80 88 GGBS 130 3711386 1222 1127

GRADE M20


Fly ash 90 99 GGBS 150 4281890 1485 1373

GRADE M25

Item Qty Amount Item Qty Amount Item Qty AmountCement 320 2016 Cement 265 1669.5 Cement 176 1109

Fly ash 100 110 GGBS 160 4562016 1780 1565

OPC + GGBS MIX

cementecious cost cementecious cost

OPC + FLY ASH MIX

cementecious cost

PURE OPC MIX

OPC + GGBS MIX

cementecious cost cementecious cost cementecious cost

PURE OPC MIX OPC + FLY ASH MIX OPC + GGBS MIX

PURE OPC MIX OPC + FLY ASH MIX


OPC=6300/MT: PFA=1100/MT: GGBS= 2850/MT

GRADE M30

Item Qty Amount Item Qty Amount Item Qty AmountCement 350 2205 Cement 295 1858.5 Cement 210 1323

Fly ash 90 99 GGBS 157 4472205 1957.5 1770

GRADE M35


Fly ash 60 66 GGBS 180 5132394 2334 2057

GRADE M40


Fly ash 80 88 GGBS 200 5702520 2482 2208







M15 M20 M25 M30 M35 M40

OPC 1386 1890 2016 2205 2394 2520

OPC +PFA 1222 1485 1780 1957 2334 2482

OPC+ GGBS 1127 1373 1565 1770 2057 2208

0

500

1000

1500

2000

2500

3000

Cubi

c met

er c

ost

Cementecious cost

M15 1386 1222 1127 300 164M20 1890 1485 1373 578 190M25 2016 1780 1565 509 190M30 2205 1957 1770 491 271M35 2394 2334 2057 392 357M40 2520 2482 2208 368 366

GRADE Savings w.r.t OPC Mix

Savings w.r.t OPC + PFA

OPC+ GGBSOPC +PFAOPC

GGBS is used to make durable concrete structures in combination with ordinary Portland cement and/or other pozzolanic materials.

GGBS has represented high percentage of total production in cement consumption by many countries in recent years, Netherlands around 60%, Belgium – 32%, France – 32% and West Germany – 24%

GGBS has been widely used in Europe, and increasingly in the United States and in Asia

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Ggbs readymix