Grinding Aids For Cement

Prepared by:Shyam R. Anandjiwala

(Construction Management)

INDIAN INSTITUTE OF TECHNOLOGY DELHI

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What are Grinding Aids?

• Grinding mill grinds the hard clinker into fine cement powder.

• Additives used to improve the grinding efficiency of grinding mill.

• Improvement in grinding efficiency leads to reduction in electricity consumption.

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History of Grinding Aids

• The history of cement additives goes back to the 1930s.

• Attempt was made to disperse carbon black in concrete with the help of triethanolamine to solve mottling issue and to improve the strength of concrete. This chemical is given name “Tucker’s Dispersion Aid”.

• By 1960, TDA from Dewey and Almy, 109-B from Master Builders and Polyfon T from West Virginia Pulp and Paper (now Westvaco) were the only approved grinding aids under ASTM.

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Why Grinding Aids should be used?

• Grinding of clinker is affected by cleavage, microcracks or the defects present in its crystal structure.

• Applied shear stress on clinker breaks the ionic bonds and highly reactive positive & negative charges are produced.

• High surface energy on clinker surface

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• Formation of electrostatic charges on surface cause agglomeration of cement particles.

• Decrease in surface area and increase in electricity consumption.

• High surface energy causing “Pack set” • Grinding aids neutralize the electrostatic

charges and inhibits the pack set of cement.

Why Grinding Aids should be used?(contd.)

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• Allows the cement transport in delivery trucks and storage in silos without lump formation.

• Better material handling due to improved fluidity. • Elimination of ‘’coating’’ effect of the clinker on

grinding media and grinding mill walls.• To either increase the surface area of cement at

the given production rate or it can increase the production rate of cement keeping the surface area constant.

Why Grinding Aids should be used?(contd.)

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Fig1. The milling media(balls) coated themselves with cement if no grinding aid is used

Fig2. Grinding aids keep the milling media (balls) clean and increase the productivity

Sika Tech

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Commonly Used Grinding Aids

Amine based GAs Monoethanolamine(MEA) Diethanolamine(DEA) Triethanolamine(TEA) Triisopropanolamine(TIPA)

Alchohol based GAs Ethylene glycol(EG) Diethylene glycol(DEG)

Ether based GAs Poly Carboxylate Ether(PCE)

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Grinding Aid Mechanisms

1. Dispersion Mechanism• 2 basic mechanisms through which dispersion

can take place between the organic molecules1. Gas Transfer2. Surface Contact Transfer

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Gas Transfer

• The temperature in grinding mill is generally in the range of 80-120 °C.

• Alcohols with boiling points below grinding temperature (eg.ethanol-see table 1) get adsorbed weakly due to their high volatility.

• They can be smelt even on cold cement. Therefore it can be assumed that they are dispersed via gas transfer.

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Chemical Boiling Point(°C)

Ethanol 78

Propylene glycol(PG) 188

Diethylene glycol(DEG) 245

Triethanolamine(TEA) 335

Table 1 :Different Grinding Aids with their Boiling Temperatures(°C)

Sika Tech

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Surface Contact Transfer

• Polymers such as PCEs are assumed to be dispersed via surface contact transfer.

• During grinding they retain their action as a plasticizer.

• Therefore evaporation mechanism is assumed to be excluded.

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2. Surface Energy Reduction• Mixture with water• Grinding aids reduce surface energy of clinker in 3 parts:(1)clinker tries to lower its surface energy(E1)

(2) surface energy of the grinding aids(E2) increase due to the gain through the surface energy of clinker

(3) clinker-grinding aid interfacial energy(E3) value should be negative or very small positive.

• The surface energy of the clinker covered with grinding aid(E) is the algebraic summation of E1,E2 and E3.

E= E3 + E2 + E3

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• If E = -ve that means the energy is released and the grinding aid spreads out on clinker’s surface.

• That means Grinding aids not only have to reduce the surface energy of clinker(E1) but also to get strongly adsorbed on the surface of clinker particles and reduce interfacial energy(E3).

• Nonpolar liquids can not be used as the grinding aids even though they have low surface energy.

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Effect of GA on Cement Composition

• Effect on C3S, C2S, C3A & C3A+gypsum

• C3A hydrates to hydrogarnet(C3AH6) before it transforms to ettringite in absence of TEA.

• TEA accelerate the hydration of C3A .• TEA accelerates the formation of ettringite

and as it increase, conversion from ettringite to monosulphate is at faster rate.

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• Extends the induction period of C3S may be due to formation of surface complex on the hydrating C3S .

• TEA also increase the induction period of C2S like C3S but the difference is the slow rate of reaction with C2S.

• Peak due to the C3S formation is extended with the addition of TEA which indicates the hydration of C3S is retarded by TEA.

• So TEA accelerates the aluminate phase hydration and retards the hydration of silicate phase.

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Fig.3 Conduction calorimetric curves of cement hydrated in the presence of TEA

Fig.4 Conduction calorimetric curves of cement hydrated in the presence of CaCl2

T I M E. H O U R S

V.S.Ramachandran

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Effect of GA on Mechanical Properties

GA affects the following mechanical properties of cement:

setting timesurface area compressive strength mortar workability

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Setting Time

• It is not found out whether TEA is a retarder or an accelerator .

• TEA acts as retarder at low dosage (up to 0.5 %) but accelerates the hydration at higher dosage .

• High dosage TEA can be used as an accelerator in place of CaCl2 to eliminate chloride attack.

• MEA and low dosage DEA does not cause much alteration in setting time.

• TIPA increases both initial and final setting time of cement due to its diffusion into pores and cracks of clinker particles.

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Surface Area• All the grinding aids increase the surface area

of cement . Table 2.values of Blaine for different specific energy

consumption

20J.Assad

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0 10 20 30 40 50 60 700

5

10

15

20

25

30

35

40

45

50

0.08% amine GA

0.08% glycol GA

specific energy consumption(kWh/ton)

% in

crea

se to

refe

renc

e m

ix

Fig 5. Comparison of % increase in surface area (cm2/g) due to amine & glycol grinding aids

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• Grinding energy of the mill affects the performance of grinding aids.

• At higher grinding energy the effectiveness of grinding aids to increase surface area of cement increase.

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Compressive Strength

• TIPA increase 7 days and 28 days compressive strength of cement.

• Optimum dosage is 0.01-0.02% for the enhancement of strength by TIPA.

• If dosage>optimum dosage it can increase the strength further very little but it is not economical.

• Higher dosage of TIPA can cause air entrainment in cement. This air entrainment can be as high as 2% compared to the cement without any additives.

• Therefore TIPA is used with air detraining agent at higher dosage.

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• Effectiveness of enhancement of strength by TIPA also depends upon the tetra calcium aluminoferrite (C4AF) content in clinker.

• C4AF content must be > 4% for the improvement in strength using TIPA.

• At higher C4AF content effectiveness of TIPA increases in increasing strength.

• The increase in 1 day strength of cement due to addition of TEA as grinding aid is debatable.

• TEA decreases later age strength of cement.

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Explanations for the decrease in later age strength due to TEA:

• Rapid early hydration may create a dense zone of hydration product around the grains and retard subsequent hydration.

• Formation of hydration product with higher density may promote a more porous structure.

• Cement that has set in a few minutes has obviously not been thoroughly mixed, and consequently there will be a non-uniform distribution of hydration products within the structure that will prevent the development of full strength.

• Rapid formation of ettringite may alter the initial matrix and disturb subsequent bonding characteristics.

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• Combinations of grinding aids can be used to improve grinding aids of cement at all ages.

• When TIPA is added individually it does not make significant difference in strength at 28 days.

• 1 day strength of mixture of TEA and TIPA fall between neat TIPA and neat TEA.

• Combination of TIPA and TEA used in the proportion 3:1 or 1:3 respectively significantly increase the compressive strength at all ages.

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1 day 7 day 28 day0

10

20

30

40

50

60

No GA addition

TIPA

TEA

TIPA:TEA=1:1

TIPA:TEA=1:3

TIPA:TEA=3:1

Age(days)

Com

pres

sive

str

engt

h(M

Pa)

Fig 6.Comparison of compressive strength (MPa) by adding different GAs and their combinations

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Effect of GA on Grinding Mill Output

• Grinding mill can be loaded with higher mass using grinding aids and it can minimize power consumption.

• Table 3. Blaine values at different grinding masses and grinding energies

United states patent: 4,990,190

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Fig 7. . % increase in bline(cm2/g)due to increase in grinding-energy(kWh/ton)[

United states patent: 4,990,190

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Conclusion

• Grinding aids are used to improve grinding efficiency of the clinker particles and to minimize the power consumption.

• Grinding aid also improve some physical and mechanical properties of cement.

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References[1] M. Katsioti,P.E. Tsakiridi,,P. Giannatos, Z. Tsibouki J.

Marinos(2008):”CHARACTERIZATION OF VARIOUS CEMENT GRINDING AIDS AND THEIR IMPACT ON GRINDABILITY AND CEMENT PERFORMANCE” Elsevir Publication Construction and Building Materials

[2] Bravo Anna, Cerulli Tiziano, Giarnetti Mariagrazia, Magistri Matteo:”GRINDING AIDS:A STUDY ON THEIR MECHANISM OF ACTION”Mapei Publication

[3] Dr. Martin Weibel, Dr. Ratan K. Mishra(2014)“GRINDING AIDS INCREASE THE PRODUCTIVITY AND COST-EFFECTIVENESS OF CEMENT PRODUCTION” Sika Technology Center Zürich

[4] Davide Padovani, Matteo Magistri “IMPROVEMENT OF MECHANICAL STRENGTHS BY THE USE OF GRINDING AIDS:OPTIMISATION OF SULPHATE CONTENT IN CEMENT” Mapei SpA, Italy

[5] Howard II. Moorer ,Charleston; Charles M. Anderegg(1971):UNITED STATES PATENT 13,615,785

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[6] David F. Myers, Columbia; Ellis M. Gartner(1991): UNITED STATES PATENT 4,990,190

[7] Preston L. Veltman(1967):” MINERAL GRINDING AIDS AND PROCESS OF GRINDING”UNITED STATES PATENT 33125305

[8] D.W.Fuestenau(1995):”GRINDING AIDS” Kona Powder and Particle Journal[9] Joseph J. Assaad, Salim E. Asseily,Jacques Harb(2008): EFFECT OF SPECIfiC

ENERGY CONSUMPTION ON fiNENESS OF PORTLAND CEMENT INCORPORATING AMINE OR GLYCOL-BASED GRINDING AIDS” RILEM Publication

[10]V.S. Ramachandran(1976):”HYDRATION OF CEMENT-ROLE OFTRIETHANOLAMINE” Cement and Concrete Research.Vol.6, 1976

[11] Z. Heren and H.Olmez(1996): ”THE INFLUENCE OF ETHANOLAMINES ON THE HYDRATION AND

MECHANICAL PROPERTIES OF PORTLAND CEMENT” Cement and Concrete Research.Vol.26,1996

[12] Alejandro Pérez-Velázquez:’’ LOW COST GRINDING AIDS FOR CEMENT’’worldcements.com