sab 2112 - introduction to cement v2

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Civil Engineering MaterialsSAB 2112

Introduction to Cement

Dr Mohamad Syazli Fathi

Department of Civil EngineeringRAZAK School of Engineering & Advanced Technology

UTM International Campus

July 25, 2010

Introduction to Cement

CONTENT SCHEDULE – 1st Meeting

1. Introduction, cement manufacturing process, types of cement, chemical composition of OPC

2. Hydration of cement, testing of cement, types of aggregates, physical and mechanical characteristics gg g p yof aggregates

3. Size distribution and testing of aggregates, water in concrete, types of chemical admixtures

Objectives of the lecture

• The main objective of this lecture is to explain to studentsthat:

• How cement is manufactured, its principal constituents, thetypes of cement, cement standards and the application oftypes of cement, cement standards and the application ofdifferent types of cement

Leonard P. Zakim Bunker Hill Bridge in Boston. (Image courtesy of the Federal Highway Administration.)

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• Cement is a mixture of limestone, clay, silica and gypsum.

• It is a fine powder which when mixed with water sets to a hard mass as a result of hydration of the constituent compounds.

• It is the most commonly used construction material

Definition

• In BS EN 197-1, ‘cement’ is defined as:

“ … A hydraulic binder, i.e. a finely ground inorganicmaterial which, when mixed with water, forms a pastewhich sets and hardens by means of hydraulic reactionswhich sets and hardens by means of hydraulic reactionsand processes and which, after hardening, retains itsstrength and stability even under water.”

• Factory produced EN 197 cements are given thedesignation ‘CEM’

• In British Standards, mixer combinations are given thedesignation ‘C’ not CEM

History of Cement

• In 1824, Joseph Aspdin, a British(Leeds) stone mason, obtained apatent for a cement he produced inhi kit hhis kitchen.

• The inventor heated a mixture offinely ground limestone and clay inhis kitchen stove and ground themixture into a powder create ahydraulic cement-one that hardenswith the addition of water.

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History of Cement

• Aspdin named the product Portlandcement because it resembled a stonequarried on the Isle of Portland offth B iti h C tthe British Coast.

• With this invention, Aspdin laid thefoundation for today's Portlandcement industry.

Cement is so fine that one kg of cement contains more than 300billion grains

Basic Composition

TheThe rawraw materialsmaterials requiredrequired toto produceproduce PortlandPortlandcementcement areare foundfound andand exploitedexploited inin nearlynearly allall partsparts ofofthethe world,world, whichwhich isis aa significantsignificant reasonreason forfor itsitsuniversaluniversal importanceimportance asas aa buildingbuilding materialmaterialuniversaluniversal importanceimportance asas aa buildingbuilding materialmaterial..

TableTable 11 indicatesindicates thethe standardstandard mineralogicalmineralogicalcompositioncomposition ofof PortlandPortland cementcement andand TableTable 22 indicatesindicatesitsits standardstandard chemicalchemical compositioncomposition..

Basic Composition

Chemical NameChemical Name Common Common NameName Chemical NotationChemical Notation Abbreviated Abbreviated

NotationNotationMass Contents Mass Contents

(%)(%)

tricalcium silicatetricalcium silicate alitealite 3CaO.SiO3CaO.SiO22 CC33SS 3838--6060

Table 1 Mineralogical Composition of Portland Cements (Brandt, 1995)

dicalcium silicatedicalcium silicate belitebelite 2CaO.SiO2CaO.SiO22 CC22SS 1515--3838

tricalcium tricalcium aluminatealuminate belitebelite 3CaO.Al3CaO.Al22OO33 CC33AA 77--1515

tetracalcium tetracalcium aluminoferitealuminoferite celitecelite 4CaO.Al4CaO.Al22OO33.Fe.Fe22OO33 CC44AFAF 1010--1818

pentacalcium pentacalcium trialuminatetrialuminate celitecelite 5CaO.3Al5CaO.3Al22OO33 CC44AFAF 11--22

calcium sulphate calcium sulphate dihydratedihydrate gypsumgypsum CaSOCaSO44.2H.2H22OO CSHCSH22 22--55

Basic Composition

Tetracalcium Aluminoferrite(8%)

Gypsum(3.5%) Other

(1.5%)

Tricalcium Silicate(50%)

Dicalcium Silicate(25%)

Tricalcium Aluminate(12%)

Basic Composition

Chemical Chemical NameName Common NameCommon Name Chemical Chemical

NotationNotationAbbreviated Abbreviated

NotationNotationMass Mass

Contents(%)Contents(%)

calcium oxidecalcium oxide limelime CaOCaO CC 5858--6666

ili di idili di id iliili SiOSiO SS 1818 2626

Table 2 Chemical Composition of Portland Cements (Brandt, 1995)

silicon dioxidesilicon dioxide silicasilica SiOSiO22 SS 1818--2626

aluminium aluminium oxideoxide aluminaalumina AlAl22OO33 AA 44--1212

ferric oxidesferric oxides ironiron FeFe22OO33 + FeO+ FeO FF 11--66

magnesium magnesium oxideoxide magnesiamagnesia MgOMgO MM 11--33

sulphur sulphur trioxidetrioxide

sulphuric sulphuric anhydriteanhydrite SOSO33 SS 0.50.5--2.52.5

alkaline oxidesalkaline oxides alkalisalkalis KK22O and NaOO and NaO22 K + NK + N <1<1

Manufacturing of Cement

• Producing a cement that meets specific chemical andphysical specifications requires careful control of themanufacturing process.

• The first step in the Portland cement manufacturingprocess is obtaining raw materials.G ll t i l i ti f bi ti f• Generally, raw materials consisting of combinations oflimestone, shells or chalk, and shale, clay, sand, oriron ore are mined from a quarry near the plant. Atthe quarry, the raw materials are reduced by primaryand secondary crushers.

• Stone is first reduced to 5-inch size (125-mm), then to3/4-inch(19 mm). Once the raw materials arrive at thecement plant, the materials are proportioned to createa cement with a specific chemical composition.

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Type of Manufacturing • Wet Process• Dry Process 74% of cement produced• Dry Process - 74% of cement produced• Preheater/Precalciner Process

Manufacturing of Cement – Dry ProcessDry Process• In the dry process, dry raw

materials are proportioned, groundto a powder, blended together andfed to the kiln in a dry state.

• In the wet process, a slurry isformed by adding water to the

l ti dproperly proportioned rawmaterials. The grinding andblending operations are thencompleted with the materials inslurry form. After blending, themixture of raw materials is fedinto the upper end of a tiltedrotating, cylindrical kiln.


Source: http://www.crushersmill.com/production-line/cement-plant.html

In cement plant, to produce cement need seven steps1.Crushing and Preblending• In cement production process, most of the material need to be

broken, such as limestone, clay, iron ore and coal, etc. Limestone is the largest amount of raw material in cement production, after mining the size of limestone is large, with high hardness, so the limestone crushing plays a more important role in cement plant.

2. raw material preparation• In cement production process, producing each 1 ton of Portland

cement need grinding at least 3 tons of materials (including raw materials, fuel, clinker, mixed materials, gypsum). Grindingmaterials, fuel, clinker, mixed materials, gypsum). Grinding operation consumes power about 60% of total power in cement plants, raw material grinding takes more than 30%, while coal mill used in cement palnt consumes 3%, cement grinding about 40%. So choosing the right grinding mills in cement plant is very important.

3. raw materials homogenization• Adopting the technology of homogenization could rationally get the

best homo-effect and afford an eligible production to the demand4. preheating and precalcing• Preheater and calciner is key equipment for precalcing production

technique.

Image from : http://www.adelaidebrighton.com.au/Images/cement%20manufacturing%20process%20low-res.jpg

Manufacturing of Cement – Dry Process

5.burning cement clinker in a rotary kiln.• The calcination of Rotary Kiln is a key step of cement production , it makes directly influence on the quality of cement clinker.6. cement grinding• Cement grinding is used for grinding cement clinker (and gelling agent, performance tuning materials, etc.) to the appropriate size (in fineness, specific surface area, said), optimizing cement grain grading, increasing the hydration area, accelerating the hydration rate to meet the requirements of cement paste setting, hardening.7. cement packing

Source: http://www.tradekorea.com/products/heater.html?nationCd=CN&linkFlag=

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• In the dry process, dry raw materials areproportioned, ground to a powder, blendedtogether and fed to the kiln in a dry state.

• In the wet process, a slurry is formed by addingwater to the properly proportioned raw materials.Th i di d bl di i h• The grinding and blending operations are thencompleted with the materials in slurry form.

• After blending, the mixture of raw materials isfed into the upper end of a tilted rotating,cylindrical kiln.

• The mixture passes through the kiln at a ratecontrolled by the slope and rotational speed ofthe kiln.


• Burning fuel consisting of powdered coal or natural gas is forcedinto the lower end of the kiln.

• Inside the kiln, raw materials reach temperatures of 1430oC to1650oC. At 1480oC, a series of chemical reactions cause thematerials to fuse and create cement clinker-grayish-black pellets,often the size of marbles.

• Clinker is discharged red-hot from the lower end of the kiln andtransferred to various types of coolers to lower the clinker tohandling temperatures.

Summary of Kin Reactions

Source: http://www.aboutcivil.com/engineering-materials/cement-composition-types-and-manufacture.pdf

Clinker

• Cooled clinker is combined withgypsum and ground into a finegray powder. The clinker is


g y pground so fine that nearly all ofit passes through a No. 200 mesh(75 micron) sieve.

• This fine gray powder isPortland cement.

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Manufacturing of Cement – Wet Process

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Cement Standards

• BS EN 197-1:2000 (Inc. Amendment No.1:2004)– Composition, specifications and conformity criteria for common

cements

• BS EN 197-4:2004– Composition, specifications and conformity criteria for low early

strength blast furnace cements

• BS EN 196-series– Methods of testing cement

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Cement Standards

• Cements are factory produced materials primarily conforming toBS EN 197-1 or BS EN 197-4

• Some cements, such as Sulphate-resisting Portland cement(SRPC) are however, still covered by residual British Standards

• There is a wide range of cements ranging from simple Portlandg g g pcement to Composite cements containing up to three majorconstituents

• Cements may be produced by inter-grinding or blending theconstituents at the cement works

• Cements can be CE marked against BS EN 197 standards usingBS EN 197-2 Conformity evaluation

Types of Portland Cement

• Different types of Portland cement are manufactured to meetvarious physical and chemical requirements.

• The American Society for Testing and Materials (ASTM)Specification C-150 provides for eight types of Portland cementSpecification C 150 provides for eight types of Portland cement.

• BS EN 197-1 specified Five main classes of Portland cement• However, Both BS EN and ASTM specified some other types of

cements for special functions.

Types of BS EN 197-1Portland Cement

How are Cements Designated

Portland Cement

Portland cement is CEM I

NOT

Ordinary Portland cement OPC or PCOrdinary Portland cement, OPC or PC

BUT

CEM I

Cement strength Classes (I)

Note: Use of comma rather than decimal

i tpoint

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Cement strength Classes (II)

These classes apply to all CEM cements

Cement strength Classes (II)

Low Heat Cement

Example: CEM III/B 32,5N - LH

Minor Additional Constituents (I)

• BS EN 197-1 allows for the inclusion of up to 5% by mass of a minor additional constituent (or ‘mac’) in all types of cement

• A ‘mac’ is defined as: “specially selected inorganic natural mineral materials, inorganic mineral materials derived from the clinker production process or [specified cement] constituents unless they are [already] included as main constituents in the cement”

• Materials typically used as a ‘mac’ include:– Finely ground limestone– Fly Ash– Cement kiln dust (CKD)

Minor Additional Constituents (II)

A CEM I Portland cement with 5% mac is still a Portland cement and will perform in the same way as

a similar cement without a mac !

Other Cements

These standards will eventually be replaced by new European Standards, but progress on a standard for

‘sulfate-resisting cement’ is slow

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••

CHEMICAL COMPOSITION OF CHEMICAL COMPOSITION OF PORTLAND CEMENTPORTLAND CEMENT

Compound Chemical Formula

Common Formula*

Usual Range,

weight (%)

Tricalcium silicate 3CaO SiO2 C3S 45 – 60

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Dicalcium silicate 2CaO SiO2 C2S 15 – 30

Tricalcium aluminate 3CaO Al2O3 C3A 6 – 12

Tetracalcium aluminoferrite

4CaO Al2O3Fe2O3

C4AF 6 – 8

*The cement industry commonly uses shorthand notation for chemical formulas: C = calcium oxide. S = silicon dioxide, A = aluminium oxide and F = iron oxide.(Michael S. Mamlouk & John P. Zaniewski, 1999)

HYDRATION PROCESS OF CEMENT HYDRATION PROCESS OF CEMENT

Cement + H2O C-S-H gel + Ca(OH)2Chemical reaction between cement particles & water.It is an exothermic process where heat is liberated.

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The silicates, C3S and C2S, are the most important compounds, which are responsible for the strength of hydrated cement paste.C3S provides the early strength and liberated higher heat of hydration.

Hydration Reaction 1 & 2Hydration Reaction 1 & 2

TricalciumTricalcium SilicateSilicate2C2C33S + 6H S + 6H CC33SS22HH33 + 3CH+ 3CH

waterwater CC--SS--H H calcium hydroxidecalcium hydroxide

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cement gelcement gelDicalciumDicalcium SilicateSilicate2C2C22S + 4H S + 4H CC33SS22HH33 + CH+ CH

1/3 to 1/21/3 to 1/2 1/4 1/4 volvol

Hydration Reaction 3 & 4Hydration Reaction 3 & 4

TricalciumTricalcium AluminateAluminate (C(C33A)A)CC33A + 6HA + 6H CC33AHAH66

calcium calcium aluminatealuminate hydratehydrateCC33A + 3CASHA + 3CASH22 +26H+26H CC66ASHASH3232

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ettringiteettringite2C2C33A + CA + C66ASHASH22 + 4H+ 4H 3C3C44ASHASH1212

monosulphaluminatemonosulphaluminate+ new sulphate ions = + new sulphate ions = ettringiteettringite

TetracalciumTetracalcium AluminoferriteAluminoferrite (C(C44AF)AF)Similar to CSimilar to C33AA

Development of structure in the cement paste

Water+ + + + + + + + + +C S3C S

The C-S-H phase is initially formed. C Aforms a gel fastest.

3

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+ + ++

++

C S2C A3

C AF4

(a)

The volume of cement grain decreases asa gel forms at the surface. Cement grains

hydration grows weak interlocking beginsare still able to move independently, but as


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(b)

hydration grows, weak interlocking begins.

vibration can break the weak bonds.Part fo the cement is in a thixotropic state;

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The initial set occurs with the developmentof a weak skeleton in which cement grainsare held in place.


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(c)

and spacing between cement grainsrigid, cement particles are locked in place,Final set occurs as the skeleton becomes


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and spacing between cement grains

(d)

increases due to the volume reduction ofthe grains.

filled with hydration products as cementSpeaces between the cement grains are


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paste develops strength and durability.

(e)

Clinker Microstructure


Grinding Mill


Cement hydration

Cement hydration is affected by:-1. time,2. temperature,2. temperature, 3. water:cement ratio, and 4. cement fineness and composition.

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Typical results for heat evolution at 20°C of different Portland cements:

(A) low heat, (B) ordinary & (C) rapid hardening

400

500

600

on (J

/g)

B

C

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100

200

300

1 day0

3 days 7 days 28 days 90 days 1 yr 5 yrs

Age (log scale)

Hea

t of h

ydra

tio

A

Rates of Hydration of Cement Rates of Hydration of Cement Compounds in OPC PasteCompounds in OPC Paste

100100

8080

6060%%

CC33AA

CC33SS

62

6060

4040

2020

001001008080606040402020

Time (days)Time (days)

CC22SS

CC44AFAF

Compressive Strength Development Compressive Strength Development in OPC Pastein OPC Paste

6060

4040

%% CC33SS5050

7070

63

4040

2020

001001008080606040402020

Time (days)Time (days)

CC33AACC22SS

CC44AFAF1010

3030

Significant of Fineness

HYDRATION PROCESS OF HYDRATION PROCESS OF CEMENT CEMENT

C2S reacts slowly, provide later strength, highly chemical resistance (sulphate & chloride).C3A is undesirable, it contributes little or nothing to the strength of cement except at early ages and

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the strength of cement except at early ages, and when hardened, cement paste is attacked by sulphates, the formation of sulphoaluminate(ettringite) may cause disruption.However, C3A is beneficial in the manufacture of cement in that it facilitates the combination of lime & silica.

HYDRATION PROCESS OF CEMENT HYDRATION PROCESS OF CEMENT

C4AF does not affect the behaviour of cement hydration significantly.However, it reacts with gypsum to form calcium

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sulphoferrite and its presence may accelerate the hydration of silicates.

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Hydration of Cement

• When Portland cement is mixed with water its chemical compoundconstituents undergo a series of chemical reactions that cause it toharden (or set).

• These chemical reactions all involve the addition of water to thebasic chemical compounds This chemical reaction with water isbasic chemical compounds. This chemical reaction with water iscalled "hydration". Each one of these reactions occurs at adifferent time and rate. Together, the results of these reactionsdetermine how Portland cement hardens and gains strength.

• Tricalcium silicate (C3S). Hydrates and hardens rapidly and islargely responsible for initial set and early strength. Portlandcements with higher percentages of C3S will exhibit higher earlystrength.

Hydration of Cement

• Dicalcium silicate (C2S). Hydrates and hardens slowly and islargely responsible for strength increases beyond one week.

• Tricalcium aluminate (C3A). Hydrates and hardensquickest. Liberates a large amount of heat almost immediately andcontributes somewhat to early strength Gypsum is added tocontributes somewhat to early strength. Gypsum is added toPortland cement to retard C3A hydration. Without gypsum, C3Ahydration would cause Portland cement to set almost immediatelyafter adding water.

• Tetracalcium aluminoferrite (C4AF). Hydrates rapidly butcontributes very little to strength. Its use allows lower kilntemperatures in Portland cement manufacturing. Most Portlandcement colour effects are due to C4AF.

Hydration of Cement

• The result of the two silicate hydrations is the formation ofa calcium silicate hydrate (often written C-S-H because ofis variable stoichiometry).

• C S H makes up about 1/2 2/3 the volume of the• C-S-H makes up about 1/2 - 2/3 the volume of thehydrated paste (water + cement) and therefore dominatesits behavior (Mindess and Young, 1981).

TESTING OF CEMENT TESTING OF CEMENT

Why do we have to conduct the tests?•To ensure the quality of cement.•To determine the properties of cement.

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What are the properties of cement?•Chemical properties•Physical properties


Tests should be conducted according to the relevant standard:1. MS 522 Part 1, 2, 3 – OPC2. BS 12: 1978 – OPC and RHPC3. BS 4550: Part 1: 1978 – Methods of testing cement.

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New Standards1. BS EN 197-1:2000 (Inc. Amendment No.1:2004)

– Composition, specifications and conformity criteria for common cements2. BS EN 197-4:2004

– Composition, specifications and conformity criteria for low early strengthblast furnace cements

3. BS EN 196-series– Methods of testing cement


Testing of cement includes:• Chemical composition• Fineness of cement

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• Setting time• Soundness• Strength

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Chemical Composition Chemical Composition

• To determine the amount of C3S, C2S, C3A and C4AF.

T b i d d h f

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• Test being conducted at the cement factory.

• For research, test has to be conducted in the lab.

Physical Properties of Cement

• Portland cements are commonly characterized by theirphysical properties for quality control purposes.

• Their physical properties can be used to classify andcompare Portland cements.

• The challenge in physical property characterization isto develop physical tests that can satisfactorilycharacterize key parameters.


• Keep in mind that these tests are, in general, performed on "neat"cement pastes - that is, they only include Portland cement andwater.

• Neat cement pastes are typically difficult to handle and test andthus they introduce more variability into the resultsthus they introduce more variability into the results.

• Cements may also perform differently when used in a "mortar"(cement + water + sand).

• Over time, mortar tests have been found to provide a betterindication of cement quality and thus, tests on neat cement pastesare typically used only for research purposes (Mindess and Young,1981).

• However, if the sand is not carefully specified in a mortar test, theresults may not be transferable.


Fineness• Fineness, or particle size of Portland cement affects hydration rate and thus the

rate of strength gain. The smaller the particle size, the greater the surface area-to-volume ratio, and thus, the more area available for water-cement interaction perunit volume. The effects of greater fineness on strength are generally seen duringthe first seven days (PCA, 1988).

Fineness can be measured by several methods:Fineness can be measured by several methods:– AASHTO T 98 and ASTM C 115: Fineness of Portland Cement by the

Turbidimeter.– AASHTO T 128 and ASTM C 184: Fineness of Hydraulic Cement by the 150-

mm (No. 100) and 75-mm (No. 200) Sieves– AASHTO T 153 and ASTM C 204: Fineness of Hydraulic Cement by Air

Permeability Apparatus– AASHTO T 192 and ASTM C 430: Fineness of Hydraulic Cement by the 45-mm

(No. 325) Sieve

Fineness Test Fineness Test

• Rate of hydration depends on the fineness of cement.• Fineness is a vital property of cement; both BS and

ASTM require the determination of the specific surface (m2/kg).

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f ( g)

• The specific surface can be determined by the following apparatus:• Air Permeability Lea & Nurse:• Blaine test:

Air Permeability Lea & NurseAir Permeability Lea & Nurse

By the Air Permeability Lea & Nurse:• Measure the pressure drop when dry air flows at a

constant velocity through a bed of cement of known porosity and thickness.

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p y• From this the surface area per unit mass of the bed

can be related to the permeability of the bed.• BS 4550: Part 3: Section 3.3: 1978.

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Blaine testBlaine test

Blaine test:• A modification of the above method.• ASTM C240-84.• The air does not pass through the bed at a constant

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p grate, but a known volume of air passes at a prescribed average pressure.

• The rate of flowing diminishing steadily.• The time of flow to take place is measured• For a given apparatus and standard porosity, the

specific surface can be calculated.

Fineness Test Fineness Test

Fineness Strength ???Fineness Workability ???Fineness Bleeding ???

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Fineness Bleeding ???Fineness Heat of hydration ???Fineness Cost of production ???

Physical Properties of Cement - SoundnessSoundness• When referring to Portland cement, "soundness" refers to the

ability of a hardened cement paste to retain its volume aftersetting without delayed destructive expansion (PCA,1988). This destructive expansion is caused by excessiveamounts of free lime (CaO) or magnesia (MgO). Most Portlandcement specifications limit magnesia content andexpansion. The typical expansion test places a small sample of

t t i t t l ( hi h t l)cement paste into an autoclave (a high pressure steam vessel).• The autoclave is slowly brought to 2.03 MPa (295 psi) then kept

at that pressure for 3 hours. The autoclave is then slowlybrought back to room temperature and atmosphericpressure. The change in specimen length due to its time in theautoclave is measured and reported as a percentage. ASTM C150, Standard Specification for Portland Cement specifies amaximum autoclave expansion of 0.80 percent for all Portlandcement types.– The standard autoclave expansion test is: AASHTO T 107 and ASTM C

151: Autoclave Expansion of Portland Cement

Soundness Soundness

• It is essential that the cement paste after setting does not undergo a large change in volume i.e. expansion.

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• Expansion may occur due to reactions of free lime, magnesia and calcium sulphate.

• Free lime – hydrates very slowly occupying a large volume than the original free lime oxide.

Soundness Soundness

Magnesia – reacts with water in a manner similar to CaO, but only the crystalline form is deleteriously reactive so that unsoundness occurs.

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Calcium sulphate – cause expansion through the formation of calcium sulphoaluminate (ettringgite) from excess gypsum (not used up by C3A during setting).

Soundness Soundness

• Cements exhibiting this type of expansions are classified as unsound.

• Le Chattelier’s accelerated test is prescribed by BS 4550: Part 3: Section 3.7: 1978 for detecting unsoundness due to

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gfree lime only. For OPC, expansion not more than 10 mm.

• In practice, unsoundness due to free lime is very rare.• Autoclave test – ASTM C 151-84 – for testing

unsoundness due to magnesia.• Calcium sulphate – no specific test is available.

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Physical Properties of Cement – Setting time

Setting Time• Cement paste setting time is affected by a number of items

including: cement fineness, water-cement ratio, chemicalcontent (especially gypsum content) and admixtures.

• Setting tests are used to characterize how a particular cementg ppaste sets. For construction purposes, the initial set must notbe too soon and the final set must not be too late.

• Additionally, setting times can give some indication of whetheror not a cement is undergoing normal hydration (PCA, 1988).

• Normally, two setting times are defined (Mindess and Young,1981):– Initial set. Occurs when the paste begins to stiffen considerably.– Final set. Occurs when the cement has hardened to the point at which

it can sustain some load.

Setting Time Setting Time

• Term to described the stiffening of cement paste or the change from fluid to a rigid state.

• Cement paste = Cement + Water

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Cement paste Cement + Water

• Setting mainly caused by a selective hydration of C3A & C3S and is accompanied by the temperature rises in the cement paste.


• Initial set – corresponds to a rapid rise of temperature.

• Final set – corresponds to the peak temperature

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Final set corresponds to the peak temperature.

• False set – different from initial and final set. Sometimes occurs within a few minutes of mixing with water. No heat is evolved in a false set and the concrete can be remixed without adding water.


• Flash set – caused by the rapid reaction between C3A with water and liberate heat. Prevented by the addition of gypsum

• Test can be conducted using Vicat apparatus.O C d C

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• For OPC and RHPC:• Initial set time – not less than 45 minutes.• Final setting time – not more than 600 minutes.• Final time = 90 + (1.2 × Initial time)

• Final time is affected by:• Temperature 20 ± 2°C• Relative humidity 65% − 90%.

Physical Properties of Cement – Vicat & Gillmore

• These particular times are just arbitrary points used tocharacterize cement, they do not have any fundamentalchemical significance.

• Both common setting time tests the Vicat needle and the• Both common setting time tests, the Vicat needle and theGillmore needle, define initial set and final set based on thetime at which a needle of particular size and weight eitherpenetrates a cement paste sample to a given depth or fails topenetrate a cement paste sample.

• The Vicat needle test is more common and tends to give shortertimes than the Gillmore needle test. Table 3.14 shows ASTM C150 specified set times.

Test Method Set Type Time Specification

VicatInitial ≥ 45 minutes

Final ≤ 375 minutes

GillmoreInitial ≥ 60 minutes

Physical Properties of Cement – Vicat& Gillmore

GillmoreFinal ≤ 600 minutes

The standard setting time tests are:AASHTO T 131 and ASTM C 191: Time of Setting ofHydraulic Cement by Vicat NeedleAASHTO T 154: Time of Setting of Hydraulic Cement byGillmore NeedlesASTM C 266: Time of Setting of Hydraulic-Cement Pasteby Gillmore Needles

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Strength• Cement paste strength is typically defined in three ways:

compressive, tensile and flexural.• These strengths can be affected by a number of items including:

water-cement ratio, cement-fine aggregate ratio, type and grading, gg g , yp g gof fine aggregate, manner of mixing and molding specimens,curing conditions, size and shape of specimen, moisture content attime of test, loading conditions and age (Mindess and Young,1981).

• Since cement gains strength over time, the time at which astrength test is to be conducted must be specified. Typically timesare 1 day (for high early strength cement), 3 days, 7 days, 28days and 90 days (for low heat of hydration cement).

Strength Strength

• Strength tests are not made on neat cement paste −difficult to obtain good specimen.

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Two methods:• Mortar test• Concrete test – BS 4550: Part 3

Mortar TestMortar Test

Mortar = Cement + Sand + Water

• Cement : Sand = 1 : 3• Mass of water = 10% of the mass of dry materials

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• Sand – standard sand, one size and spherical shape• Cube size of 71 mm• Materials being mixed and compacted using

vibrating table.

Mortar TestMortar Test

• After 24 hours, demould the mortar cubes and cure in water until they are tested in a wet-surface condition.

• Get the average strength for three cubes.• According to MS 522: Part 1:

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1. OPC –• 23 MPa at 3 days• 41 MPa at 28 days

2. RHPC –• 29 MPa at 3 days• 46 MPa at 28 days

Concrete Cube TestConcrete Cube Test

• Cement : Aggregate = 1 : 6• Water cement ratio: 0.6, 0.55, 0.45• Materials must be mixed uniformly in the mixer• Cube size of 100 mm

P ti d th t t t

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• Preparation procedures are the same as mortar test1. OPC –

• 11.5 MPa at 3 days• 26 MPa at 28 days

2. RHPC –• 18 MPa at 3 days• 33 MPa at 28 days


When considering cement paste strength tests, there are two items toconsider:

1. Cement mortar strength is not directly related to concretestrength. Cement paste strength is typically used as a qualitycontrol measurecontrol measure.

2. Strength tests are done on cement mortars (cement + water +sand) and not on cement pastes.

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Compressive Strength• The most common strength test, compressive strength, is carried out on a 50

mm (2-inch) cement mortar test specimen. The test specimen is subjected to acompressive load (usually from a hydraulic machine) until failure. This loading

t t k l th 20 d d th 80sequence must take no less than 20 seconds and no more than 80seconds. Following Table shows ASTM C 150 compressive strengthspecifications.

The standard cement mortar compressive strength test is:– AASHTO T 106 and ASTM C 109: Compressive Strength of Hydraulic Cement

Mortars (Using 50-mm or 2-in. Cube Specimens)– ASTM C 349: Compressive Strength of Hydraulic Cement Mortars (Using

Portions of Prisms Broken in Flexure)


Portland Cement Type Curing Time I IA II IIA III IIIA IV V

1 day - - - - 12.4

(1800) 10.0

(1450) - -

( ) ( )

3 days 12.4

(1800) 10.0

(1450) 10.3

(1500) 8.3

(1200) 24.1

(3500) 19.3

(2800) -

8.3 (1200)

7 days 19.3

(2800) 15.5

(2250) 17.2

(2500) 13.8

(2000) - --

6.9 (1000)

15.2 (2200)

28 days - - - - - - 17.2

(2500) 20.7

(3000) Note: Type II and IIA requirements can be lowered if either an optional heat of hydration or chemical limit on the sum of C3S and C3A is specified


Tensile Strength• Although still specified by ASTM, the direct tension test does not

provide any useful insight into the concrete-making properties ofcements It persists as a specified test because in the early yearscements. It persists as a specified test because in the early yearsof cement manufacture, it used to be the most common test sinceit was difficult to find machines that could compress a cementsample to failure.


Flexural Strength• Flexural strength (actually a measure of tensile strength in bending) is

carried out on a 40 x 40 x 160 mm (1.57-inch x 1.57-inch x 6.30-inch) cementmortar beam. The beam is then loaded at its center point until failure.

The standard cement mortar flexural strength test is:– ASTM C 348: Flexural Strength of Hydraulic Cement Mortars

Specific Gravity Test• Specific gravity is normally used in mixture proportioning calculations. The

specific gravity of Portland cement is generally around 3.15 while the specificgravity of Portland-blast-furnace-slag and Portland-pozzolan cements mayhave specific gravities near 2.90 (PCA, 1988).

The standard specific gravity test is:– AASHTO T 133 and ASTM C 188: Density of Hydraulic Cement


Heat of Hydration• The heat of hydration is the heat generated when water and Portland cement

react. Heat of hydration is most influenced by the proportion of C3S and C3Ain the cement, but is also influenced by water-cement ratio, fineness andcuring temperature. As each one of these factors is increased, heat ofhydration increases.hydration increases.

• In large mass concrete structures such as gravity dams, hydration heat isproduced significantly faster than it can be dissipated (especially in the centerof large concrete masses), which can create high temperatures in the centerof these large concrete masses that, in turn, may cause undesirable stresses asthe concrete cools to ambient temperature. Conversely, the heat of hydrationcan help maintain favorable curing temperatures during winter (PCA, 1988).

The standard heat of hydration test is:– ASTM C 186: Heat of Hydration of Hydraulic Cement


Loss on Ignition• Loss on ignition is calculated by heating up a cement sample to

900 - 1000°C (1650 - 1830°F) until a constant weight isobtained.

• The weight loss of the sample due to heating is thendetermined. A high loss on ignition can indicate pre-hydrationand carbonation, which may be caused by improper andprolonged storage or adulteration during transport or transfer(PCA, 1988).

The standard loss on ignition test is contained in:– AASHTO T 105 and ASTM C 114: Chemical Analysis of Hydraulic

Cement

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Application of Different Types of Cement

Portland Cement CEM I• CEM I is the cement that has been most

commonly used throughout the world in civilengineering and building works.

• Concretes and mortars made using CEM I areversatile, durable and forgiving of poorconstruction practice.

Applications of Type - CEM I


Sulphate-Resisting Cements• SRPC is normally a low alkali cement which benefits concrete

in resisting the alkali silica reaction (ASR). However, it is notthe only sulphate-resisting cement available. Various factory-made composite cements are also sulphate-resisting includingmade composite cements are also sulphate-resisting includingthe generally available CEM II/B-V type of Portland-fly ashcement containing at least 25% of fly ash. Such CEM II/B-Vcements are permitted for use in the same wide-range ofsulphate exposure conditions as is SRPC and are also low inreactive alkalis. Moreover, SRPC is a type of CEM I cementwith a high clinker content, it is no longer manufactured in theUK and is becoming more difficult to source. Consequently,greener sulphate-resisting composite cements will continue togrow in importance.

Applications of Type - CEM II


• SRPC is used where precaution against moderate sulphateattack is important, as in drainage structures where sulphateconcentrations in groundwater are higher than normal but notunusually severe (Table).y ( )

Sulphate Resistant Porland Cement (SPRC)

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Rapid Hardening Portland Cements• Rapid hardening versions of CEM I cements are

available. The average particle size is smaller in thesecements and they gain strength more quickly than docements and they gain strength more quickly than doordinary CEM I types.

• They generate more heat in the early stages and can beuseful in cold weather concreting.

• However, their principal use is in manufacturing precastconcrete units where the high early strength of theconcrete permits quick re-use of moulds and formwork.

Rapid Hardening Portland Cements


White Cement

• White cement is a Portland cement CEM Imade from specially selected raw materials,

ll h lk d hi l (k li )usually pure chalk and white clay (kaolin)containing very small quantities of iron oxidesand manganese oxides.

• White cement is frequently chosen byarchitects for use in white, off-white orcoloured concretes that will be exposed, insideor outside buildings, to the public's gaze.

White Cement

AdmixturesAdmixtures

Material which is added to concrete during mixing in Material which is added to concrete during mixing in order to modify particular properties of order to modify particular properties of concreteconcrete

113

1.1. Accelerators Accelerators -- ((CaClCaCl) ) NaClNaCl, , formateformate triethenolaminetriethenolamine2.2. RetardersRetarders -- Gypsum, sugars, Gypsum, sugars, lignosulphateslignosulphates3.3. Air Air entrainersentrainers -- Wood resins/soaps, fats and oilsWood resins/soaps, fats and oils4.4. Water reducers (plasticisers) Water reducers (plasticisers) --5.5. OthersOthers -- egeg Corrosion Inhibiting AdmixturesCorrosion Inhibiting Admixtures

Summary

• Portland cement, the major ingredient in concrete, is the mostwidely used building material in the world.

• In the presence of water, the chemical compounds withinPortland cement hydrate causing hardening and strength gain.

• Portland cement can be specified based on its chemicalcomposition and other various physical characteristics thataffect its behavior.

• Tests to characterize Portland cement, such as fineness,soundness, setting time and strength are useful in quality controland specifications but should not be substituted for tests on PCC.

sab 2112 - introduction to cement v2

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