Quality cement and Quality control

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Cement Quality and Quality control Tips:

1 Cement Quality and Quality control Tips

Quality Cement: What does it mean?:

2 Quality Cement: What does it mean? 1. Cement which meets the requirements of standards is known as quality cement. 2. Cement which meets the requirements of customers also known as quality cement.

Standard Specifications of Cement:

3 Standard Specifications of Cement Cement producing countries have set their own standards for cement. For example:- 1. Malaysia – MS 2. India _ ISI 3. Japan _ JIS 4. UK _ BS 5. Germany _ DIN 6. America _ ASTM

MS standards (Physical):

4 MS standards (Physical) PHYSICAL STANDARDS 1. Fineness - 225 M 2 /Kg (Min) 2. IST - 45 Minutes (Min) 3. FST - 600 Minutes (Max) 4. Expansion - 10 mm (Max) 5. 3 days CST * - 23 N/mm 2 (Min) 6. 28 days CST * - 41 N/mm 2 (Min)

MS Standards (Chemical):

5 MS Standards (Chemical) CHEMICAL SPECIFICATIONS IR - 5.0 % (Max) SO 3 - 3.0 % (Max) Mgo - 5.0 % (Max) LOI - 5.0 % (Max) Chloride - 0.1 % (Max) LSF - 0.66 (Min) – 1.02 (Max)

What are the requirements of customer in cement quality?:

6 What are the requirements of customer in cement quality? General requirements of a customer are 1. Competitive Price* 2. Superior Quality (better than Competitors cement quality) 3. Dark grey Colour of Cement 4. Moderate Setting Time 5. High Fineness of Cement 6. High Early Strength of Cement 7. Low Heat of Hydration 8. Low Expansion 9. Lump Free cement 10. Faster delivery

Colour of Portland Cement:

7 Colour of Portland Cement 1. Cement colour is very important visual quality parameter to the customer. Every customer prefers cement having darker colour. 2. The normal colour of Portland Cement is grayish green. 3. Colour of cement is not directly related to the properties of cement, such as cement strength.

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8 4. In order to maintain the desired colour of cement the percentage of Ferric & Magnesium oxides in cement must be maintained properly. Affecting factors on change of cement’s Colour are a). In case that clinker is burned in reducing condition* or is quenched very quickly, clinker colour turns to yellow and brown. b). Also lightness and darkness of colour is rather different depending on fineness of Cement.

Setting of Cement * :

9 Setting of Cement * When water is mixed with cement, the paste so formed remains pliable and plastic for a short time. As the reaction between water and cement continues the paste loses its plasticity. The early period in the hardening of cement is called setting of cement.

Setting Time:

10 Setting Time 1. Initial Set – When the Cement paste loses its plasticity and stiffens considerably. 2. Final Set – When the cement has hardened to the point at which it can sustain some minor load.

Abnormal setting of cement:

11 Abnormal setting of cement Flash set False set Quick set

Flash Set:

12 Flash Set If the clinker is ground without gypsum and water is added to the powder, it sets immediately (within no time) and It is called flash set. In order to avoid the flash setting of cement, gypsum dosage in clinker grinding must be observed and maintained.

False Set:

13 False Set If the cement temperature exceeds the limit, (generally 120 o C) gypsum in cement loses 1 1/2 molecules of water and due to insufficient water in gypsum, cement paste sets faster. Slightly longer setting time can be obtained by remixing the cement paste, which has already set. In order to avoid the false setting, cement temperature must be maintained below 120 o C.

Quick Set:

14 Quick Set If the gypsum quantity in cement is insufficient, It sets quickly and It is called quick set. In order to avoid “Quick Setting”, sufficient gypsum content in cement must be maintained. The testing of gypsum content in cement can be done by rapid SO 3 test method.

PowerPoint Presentation:

15 Setting Time of cement paste is affected by a number of factors including: a) Cement Fineness Setting Time decreases when cement fineness increases. b) Water Cement Ratio Setting Time increases when water-cement ratio increases

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16 c) Gypsum Content Setting Time increases when Gypsum content increases. Affects of Setting Time There is a drop in early strength when the setting is low.

What is fineness of Cement?:

17 What is fineness of Cement? It means particle size of cement.

Cement Fineness affects:

18 Cement Fineness affects 1.The fineness of the cement affects the “ Rate Of Hydration” and thus the rate of strength gain. 2. Greater fineness increases the surface available for hydration, causing greater early strength and more rapid generation of heat.

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19 3. The effects of greater fineness on strength are generally seen during the first seven days. 4. The coarser cement will result in higher ultimate strength and lower early strength gain of mortar. 5. Cement Fineness can be measured by several methods: a) Turbid meter b) Blain Air Permeability Apparatus. c) Test Sieves (usually 45, 75, 90, 150 micron)

Compressive Strength :

20 Compressive Strength 1. What is Mortar? 2. What is compressive strength of Mortar?

Mortar:

21 Mortar Mortar is a mixture of sand, a binder such as cement or lime and water.

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22 Compressive Strength 1. Compressive strength is the capacity of a material to withstand axially directed pushing forces (usually from a hydraulic machine). 2. When the limit of compressive strength is reached, materials are crushed. 3. The Strength of material is expressed in Mpa or N/mm 2 *

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23 The strength can be affected by a number of factors including: a) Water - Cement ratio* b) Tricalcium Silicate & Dicalcium Silicate* c) Tricalcium Aluminates* d) Manner of Mixing and Molding Specimens* e) Curing Conditions* f) Moisture Content at the time of test * g) Fineness of Cement*

Heat of Hydration:

24 Heat of Hydration 1. Heat of Hydration * – Heat generation when water and Portland cement react. 2. Heat of Hydration is influenced by proportion of C 3 S and C 3 A in the cement, but is also influenced by water-cement ratio, fineness and curing temperature, As each one of these factors is increased, heat of hydration increases. 3. Higher Heat of Hydration causes a considerable loss in strength and regression at later ages.

Hydration:

25 Hydration P Cement + Water Calcium Silicate Hydrate (CSH) Free Lime Ca(OH) 2 Calcium Silicate is a durable binder and Calcium Hydroxide is a non durable binder

Expansion of cement:

26 Expansion of cement The destructive expansion are two types and caused by excessive amount of Free Lime (FCao) or Magnesium Oxide (Mgo). 1. Lechatlier Expansion 2. Autoclave Expansion

Lechatlier Expansion:

27 Lechatlier Expansion The cause of Lechatlier expansion is due to the presence of excess free lime in clinker. F.Cao + H 2 O Ca(OH) 2 Molecular Weight 56.08 74.09

How to control the free lime?:

28 How to control the free lime? Usually free lime generates due to 1. Higher Lime Saturation Factor 2. Inadequate Burning 3. Insufficient flux in the raw mix 4. Raw mix is too coarse 5. Reducing condition in the kiln

Autoclave Expansion:

29 Autoclave Expansion The cause of Autoclave expansion is due to the presence of excess Magnesium oxide and excess free lime in clinker. Mgo + H 2 O Mg(OH) 2 Molecular Weight 40.31 58.32

PowerPoint Presentation:

30 ASTM C 150, Standard Specification for Portland Cement specifies a maximum autoclave expansion of 0.80 percent for all Types of Portland Cement. There is no specification limit for free lime for Portland cement but Lechatlier expansion is restricted to 10 mm maximum. In order to avoid the autoclave expansion, Magnesia free or less magnesia raw meal must be produced by selecting Magnesia free Raw materials .

Loss on Ignition:

31 Loss on Ignition 1. The weight loss of the sample (due to heating) at 900 – 1000 o C is called LOI. 2. A high LOI Indicates prehydration* and carbonation*, which may be caused by improper and prolonged storage or adulteration* during transportation. 3. Higher LOI causes a considerable loss in early strength.

Prehydration and Carbonation:

32 Prehydration and Carbonation P Cement + Water Calcium Silicate Hydrate (CSH) Free Lime - Ca(OH) 2 Ca(OH)2 + CO2 CaCO3 + H2O (Carbonation)

How to minimize the Loss On Ignition of Cement?:

33 How to minimize the Loss On Ignition of Cement? In order to minimize the Loss on ignition of cement 1. Well burnt clinker must be produced. 2 . Water should not be poured on clinker to reduce its temperature. 3. Clinker must be stored in proper silos or covered storage halls.

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34 4. Ensure that Prehydration should not take place. 5. Gypsum/Additives should not be too wet.

Alkalis:

35 Alkalis 1. Higher Alkalis in Portland Cement leads to internal expansion and Cracking in concrete structures due to the reaction between alkalis and reactive siliceous aggregates. 2. The origin of Alkalis in Portland Cement is mainly from Cement raw materials and Fuel.

Free Lime:

36 Free Lime 1. Lime (Calcium oxide), which is not combined with other constituents in clinker is known as free lime. 2. Free lime is a harmful component in cement and the presence of higher free lime causes expansion in cement and drop of strength.

Insoluble Residue:

37 Insoluble Residue 1 . Materials which are not soluble in Acid and Alkali is known as Insoluble Residue. 2. Insoluble Residue is a non-cementing material which is present in Portland cement.

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38 3. It affects the properties of cement, especially its compressive strength. (drop of early strength). 4. The limit of Insoluble Residue given by ASTM Standard is 0.75 percent maximum in cement. 5. The contribution of Insoluble Residue in cement is mainly from the cement additives such as Limestone, Fly Ash, Volcanic Ash and Burnt Clay.

Storage of Cement:

39 Storage of Cement Portland cement is a moisture – sensitive material. If kept dry, it will retain its quality indefinitely. When stored in contact with damp air or moisture, it will set more slowly and has less strength than Portland cement that is kept dry. When storing bagged cement, a shaded area or warehouse is preferred.

How to maintain the standards of cement?:

40 How to maintain the standards of cement? In order to maintain the standards of cement consistently 1. Proper raw mix design is very important*. 2. Adequate burning the raw mix*. 3. Adequate cooling of the Clinker*. 4. Proper storage of Clinker*. 5. Proper grinding of Clinker and gypsum*.

Proper Raw Mix design:

41 Proper Raw Mix design Raw mix can be designed by many methods. 1. Hydraulic Modulus 2. Lime Saturation Factor 3. Silica Modulus 4. Iron Modulus or Alumina-Iron ratio

Hydraulic Modulus:

42 Hydraulic Modulus Cao = 1.7 - 2.2 Sio2 + Al2O3 + Fe2O3

Lime Saturation Factor:

43 Lime Saturation Factor Cao ________________________________________ 2.8 SiO 2 + 1.18 Al 2 O 3 + 0.65 Fe 2 O 3

Silica Modulus:

44 Silica Modulus SiO2 / Al2o2 + Fe2O3 = 1.2 – 4.0 (Average 2.4 -2.7)

Iron Modulus:

45 Iron Modulus Al2O3 / FeO3 = 1 – 4 (Average1.5 – 2.5)

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46 THANK YOU

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