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Concrete Technology
VCB 2023
Cement
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Learning Outcome
To evaluate the properties of concreteconstituent materials.
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Definition
In BS EN 197-1, cement is defined as:
A hyd raul ic bind er, i .e. a f inely ground inorganicmater ial which , when m ixed w ith water, forms apaste which sets and hardens by means ofhydraul ic react ions and processes and which,after hardening, retains i ts s trength and s tabi l i tyeven under water.
Factory produced EN 197 cements are given thedesignation CEM
In British Standards, mixer combinations are giventhe designationCnot CEM
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History of Cement
In 1824, Joseph Aspdin, a British
(Leeds) stone mason, obtained a
patent for a cement he produced in his
kitchen.
The inventor heated a mixture of finely
ground limestone and clay in his
kitchen stove and ground the mixtureinto a powder create a hydraulic
cement-one that hardens with the
addition of water.
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History of Cement
Aspdin named the product Portland
cement because it resembled a stone
quarried on the Isle of Portland off the
British Coast.
With this invention, Aspdin laid the
foundation for today's Portland cement
industry.
Cement is so fine that one kg of cement contains more
than 300 billion grains
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Basic Composition
The raw materials required to produce Portland cement
are found and exploited in nearly all parts of the world,which is a significant reason for its universal importance
as a building material.
Table 1 indicates the standard mineralogical composition
of Portland cement and Table 2 indicates its standard
chemical composition.
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Basic Composition
Chemical NameCommon
NameChemical Notation
Abbreviated
Notation
Mass Contents
(%)
tricalcium silicate alite 3CaO.SiO2 C3S 38-60
dicalcium silicate belite 2CaO.SiO2 C2S 15-38
tricalcium
aluminatebelite 3CaO.Al2O3 C3A 7-15
tetracalcium
aluminoferite celite 4CaO.Al2O3.Fe2O3 C4AF 10-18
pentacalcium
trialuminatecelite 5CaO.3Al2O3 C4AF 1-2
calcium sulphate
dihydrategypsum CaSO4.2H2O CSH2 2-5
Table 1 Mineralogical Composition of Portland Cements (Brandt, 1995)
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Basic Composition
Tricalcium Silicate
(50%)
Dicalcium Silicate
(25%)
Tricalcium Aluminate
(12%)
Tetracalcium Aluminoferrite
(8%)
Gypsum
(3.5%) Other
(1.5%)
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Basic Composition
Chemical
NameCommon Name
Chemical
Notation
Abbreviated
Notation
Mass
Contents(%)
calcium oxide lime CaO C 58-66
silicon dioxide silica SiO2 S 18-26
aluminium
oxidealumina Al2O3 A 4-12
ferric oxides iron Fe2O3 + FeO F 1-6
magnesium
oxidemagnesia MgO M 1-3
sulphur
trioxide
sulphuric
anhydriteSO3 S 0.5-2.5
alkaline oxides alkalis K2O and NaO2 K + N
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Manufacturing of Cement
Producing a cement that meets specific chemicaland physical specifications requires carefulcontrol of the manufacturing process.
The first step in the Portland cement
manufacturing process is obtaining rawmaterials. Generally, raw materials consisting ofcombinations of limestone, shells or chalk, andshale, clay, sand, or iron ore are mined from aquarry near the plant. At the quarry, the rawmaterials are reduced by primary and secondarycrushers.
Stone is first reduced to 5-inch size (125-mm),then to 3/4-inch(19 mm). Once the raw materialsarrive at the cement plant, the materials areproportioned to create a cement with a specificchemical composition.
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Manufacturing of Cement
Type of Manufacturing
Wet Process
Dry Process - 74% of cement produced
Preheater/Precalciner Process
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Manufacturing of Cement
Dry Process
In the dry process, dry raw materials are
proportioned, 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.
The grinding and blending operations are thencompleted with the materials in slurry form. Afterblending, the mixture of raw materials is fed intothe upper end of a tilted rotating, cylindrical kiln.
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Manufacturing of Cement
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Manufacturing of Cement
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 byadding water to the properly proportionedraw materials. The grinding and blendingoperations are then completed with thematerials in slurry form.
After blending, the mixture of raw materialsis fed into the upper end of a tilted rotating,cylindrical kiln. The mixture passes throughthe kiln at a rate controlled by the slope androtational speed of the kiln.
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Manufacturing of Cement
Burning fuel consisting of powdered coal ornatural gas is forced into the lower end of thekiln.
Inside the kiln, raw materials reachtemperatures of 1430oC to 1650oC. At1480oC, a series of chemical reactions causethe materials to fuse and create cementclinker-grayish-black pellets, often the size ofmarbles.
Clinker is discharged red-hot from the lowerend of the kiln and transferred to varioustypes of coolers to lower the clinker tohandling temperatures.
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Manufacturing of Cement
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The Cement is Ready for Market
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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 primarilyconforming to BS EN 197-1 or BS EN 197-4
Some cements, such as Sulphate-resisting Portlandcement (SRPC) are however, still covered by residualBritish Standards
There is a wide range of cements ranging from simplePortland cement to Composite cements containing upto three major constituents
Cements may be produced by inter-grinding or blendingthe constituents at the cement works
Cements can be CE marked against BS EN 197standards using BS EN 197-2 Conformity evaluation
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Types of Portland Cement
Different types of Portland cement are manufactured to
meet various physical and chemical requirements.
The American Society for Testing and Materials (ASTM)
Specification 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.
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Types of BS EN 197-1Portland
Cement
Composite cementsCEM V
Pozzolanic cements (CEM IV/A, CEM IV/B)CEM IV
Blastfurnace cements (CEM III/A, CEM III/B)CEM III
Portland-composite cements including:
-Portland-fly ash cement (CEM II/A-V, CEM II/B-V)
-Portland-slag cement (CEM II/A-S, CEM II/B-S)
-Portland-limestone cement (CEM II/A-L (LL),CEM II/B-L (LL)
CEM II
Portland cementCEM I
DescriptionDesignation
Composite cementsCEM V
Pozzolanic cements (CEM IV/A, CEM IV/B)CEM IV
Blastfurnace cements (CEM III/A, CEM III/B)CEM III
Portland-composite cements including:
-Portland-fly ash cement (CEM II/A-V, CEM II/B-V)
-Portland-slag cement (CEM II/A-S, CEM II/B-S)
-Portland-limestone cement (CEM II/A-L (LL),CEM II/B-L (LL)
CEM II
Portland cementCEM I
DescriptionDesignation
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How are Cements Designated
Example: CEM II/A-LL 42,5 NExample: CEM II/A-LL 42,5 N
CEM II: Portland composite cement
A-LL: A signifies low proportion ofsecond constituent (6-20% in this case)
L orLL signifies limestone as the
second main constituent (LL signifies
high purity limestone)42,5 N: Cement strength class 42,5
Normal strength development
Portland-limestone cementPortland-limestone cement
Example: CEM II/A-LL 42,5 NExample: CEM II/A-LL 42,5 N
CEM II: Portland composite cement
A-LL: A signifies low proportion ofsecond constituent (6-20% in this case)
L orLL signifies limestone as the
second main constituent (LL signifies
high purity limestone)42,5 N: Cement strength class 42,5
Normal strength development
Portland-limestone cementPortland-limestone cement
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Portland Cement
Portland cement is CEM I
NOT
Ordinary Portland cement, OPC or
PC
BUT
CEM I
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Cement strength Classes (I)
There are three cement strength classes,based on the minimum 28 day mortar prismstrength
32,5
42,552,5
Each class can be subdivided based on earlystrength development
L: Low early strength
N: Normal strength development
R: High early strength
Note: Use of
comma ratherthan decimal point
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Cement strength Classes (II)
-52,5-2052,5 N
-52,5-3052,5 R
62,542,5-2042,5 R
62,542,5-1042,5 N
52,532,5-1032,5 R52,532,516-32,5 N
Max.
28Day
Min.
28Day
Min.
7 Day
Min.
2 Day
StrengthClass
-52,5-2052,5 N
-52,5-3052,5 R
62,542,5-2042,5 R
62,542,5-1042,5 N
52,532,5-1032,5 R52,532,516-32,5 N
Max.
28Day
Min.
28Day
Min.
7 Day
Min.
2 Day
StrengthClass
These classes apply to all CEM
cements
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Cement strength Classes (II)
-52,5-1052,5 L
62,542,516-42,5 L
52,532,512-32,5 L
Max.
28Day
Min.
28Day
Min.
7 Day
Min.
2 Day
StrengthClass
-52,5-1052,5 L
62,542,516-42,5 L
52,532,512-32,5 L
Max.
28Day
Min.
28Day
Min.
7 Day
Min.
2 Day
StrengthClass
These low early strength classes apply
only to BS EN 197- 4 CEM III cements
These low early strength classes apply
only to BS EN 197- 4 CEM III cements
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Low Heat Cement
BS EN 197-1: 2000 (inc. Amendment 1:2004)now covers some low heat cements
Low Heat is defined as a characteristic heatof hydration not exceeding 270 J/g(measured at 7 days (EN 196-8) or 41 hrs (EN196-9))
Low heat cements carry an LH suffix ie:
Example: CEM III/B 32,5N - LH
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Minor Additional Constituents (I)
BS EN 197-1 allows for the inclusion of up to 5% bymass of a minor additional constituent (or mac) in alltypes of cement
A mac is defined as: special ly selected ino rganicnatural m ineral mater ials, inorganic m ineral mater ials
derived from the cl inker product ion process o r
[speci f ied cement] cons t i tuents unless they are
[al ready] included as m ain const i tuents in the cement
Materials typically used as a mac include: Finely ground limestone
Fly Ash
Cement kiln dust (CKD)
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Minor Additional Constituents (II)
Cement containing a mac has to meet the sameperformance criteria as the same cement type andclass without a mac
Setting timeStrength
Soundness/Chemical requirements
In specification terms a CEM cement with a macis considered to be identical to the same CEM
cement without a mac
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 !
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Other Cements
Sulfate-resisting Portland cement: still coveredby residual British Standard BS 4027
Low early strength blastfurnace cements:
covered by British Standard BS 146:2002 (tobe withdrawn Jan 2006)
High-alumina cement: still covered by residualBritish Standard BS 915
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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Hydration of Cement
When Portland cement is mixed with water its chemicalcompound constituents undergo a series of chemicalreactions that cause it to harden (or set).
These chemical reactions all involve the addition of water tothe basic chemical compounds. This chemical reaction withwater is called "hydration". Each one of these reactionsoccurs at a different time and rate. Together, the results ofthese reactions determine how Portland cement hardensand gains strength.
Tricalcium silicate (C3S). Hydrates and hardens rapidly andis largely responsible for initial set and earlystrength. Portland cements with higher percentages of C3Swill exhibit higher early strength.
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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 almostimmediately and contributes somewhat to earlystrength. Gypsum is added to Portland cement to retard C3Ahydration. Without gypsum, C3A hydration would causePortland cement to set almost immediately after adding water.
Tetracalcium aluminoferrite (C4AF). Hydrates rapidly butcontributes very little to strength. Its use allows lower kilntemperatures in Portland cement manufacturing. MostPortland cement colour effects are due to C4AF.
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Hydration of Cement
The result of the two silicate hydrations is the
formation of a calcium silicate hydrate (often written
C-S-H because of is variable stoichiometry). C-S-H
makes up about 1/2 - 2/3 the volume of the hydratedpaste (water + cement) and therefore dominates its
behavior (Mindess and Young, 1981).
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Physical Properties of Cement
Portland cements are commonly characterized by
their physical properties for quality control
purposes. Their physical properties can be usedto classify and compare Portland cements.
The challenge in physical property
characterization is to develop physical tests that
can satisfactorily characterize key parameters.
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Physical Properties of Cement
Keep in mind that these tests are, in general, performed on"neat" cement pastes - that is, they only include Portlandcement and water.
Neat cement pastes are typically difficult to handle and testand thus 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 cementpastes are typically used only for research purposes(Mindess and Young, 1981).
However, if the sand is not carefully specified in a mortartest, the results may not be transferable.
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Physical Properties of Cement
Fineness
Fineness, or particle size of Portland cement affects hydration rate andthus the rate of strength gain. The smaller the particle size, the greaterthe surface area-to-volume ratio, and thus, the more area available for
water-cement interaction per unit volume. The effects of greater finenesson strength are generally seen during the first seven days (PCA, 1988).
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 the150-mm (No. 100) and 75-mm (No. 200) Sieves
AASHTO T 153 and ASTM C 204: Fineness of Hydraulic Cement by AirPermeability Apparatus
AASHTO T 192 and ASTM C 430: Fineness of Hydraulic Cement by the45-mm (No. 325) Sieve
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Physical Properties of Cement
Soundness
When referring to Portland cement, "soundness" refers to the ability of ahardened cement paste to retain its volume after setting without delayeddestructive expansion (PCA, 1988). This destructive expansion is causedby excessive amounts of free lime (CaO) or magnesia (MgO). Most
Portland cement specifications limit magnesia content and expansion. Thetypical expansion test places a small sample of cement paste into anautoclave (a high pressure steam vessel).
The autoclave is slowly brought to 2.03 MPa (295 psi) then kept at thatpressure for 3 hours. The autoclave is then slowly brought back to roomtemperature and atmospheric pressure. The change in specimen lengthdue to its time in the autoclave is measured and reported as a
percentage. ASTM C 150, Standard Specif icat ion for Port land Cementspecifies a maximum 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
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Physical Properties of Cement
Setting Time
Cement paste setting time is affected by a number of itemsincluding: cement fineness, water-cement ratio, chemical content(especially gypsum content) and admixtures. Setting tests are used
to characterize how a particular cement paste sets. Forconstruction purposes, the initial set must not be too soon and thefinal set must not be too late. Additionally, setting times can givesome indication of whether or not a cement is undergoing normalhydration (PCA, 1988). Normally, two setting times are defined(Mindess and Young, 1981):
Init ial set. Occurs when the paste begins to stiffen considerably.
Final set. Occurs when the cement has hardened to the point atwhich it can sustain some load.
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Physical Properties of Cement
These particular times are just arbitrary points used to
characterize cement, they do not have any fundamental
chemical significance. Both common setting time tests,
the Vicat needle and the Gillmore needle, define initialset and final set based on the time at which a needle of
particular size and weight either penetrates a cement
paste sample to a given depth or fails to penetrate a
cement paste sample. The Vicat needle test is morecommon and tends to give shorter times than the
Gillmore needle test. Table 3.14 shows ASTM C 150
specified set times.
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Physical Properties of Cement
Test Method Set Type Time Specification
VicatInitial 45 minutes
Final 375 minutes
Gillmore Initial 60 minutesFinal 600 minutes
The standard setting time tests are:
AASHTO T 131 and ASTM C 191: Time of Setting of Hydraulic Cement
by Vicat Needle
AASHTO T 154: Time of Setting of Hydraulic Cement by GillmoreNeedles
ASTM C 266: Time of Setting of Hydraulic-Cement Paste by Gillmore
Needles
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Physical Properties of Cement
StrengthCement 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 of fine
aggregate, manner of mixing and molding specimens,
curing conditions, size and shape of specimen, moisture
content at time of test, loading conditions and age (Mindess
and Young, 1981). Since cement gains strength over time,
the time at which a strength test is to be conducted must bespecified. Typically times are 1 day (for high early strength
cement), 3 days, 7 days, 28 days and 90 days (for low heat
of hydration cement). When considering cement paste
strength tests, there are two items to consider:
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Physical Properties of Cement
Cement mortar strength is not directly related to concrete
strength. Cement paste strength is typically used as a
quality control measure.
Strength tests are done on cement mortars (cement + water +sand) and not on cement pastes.
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Physical Properties of Cement
Comp ressive 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 a compressive load (usually from a hydraulic machine) until
failure. This loading sequence must take no less than 20 seconds and
no more than 80 seconds. Following Table shows ASTM C 150
compressive strength specifications.
The standard cement mortar compressive strength test is:
AASHTO T 106 and ASTM C 109: Compressive Strength of HydraulicCement 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)
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Physical Properties of Cement
Portland Cement TypeCuring
Time I IA II IIA III IIIA IV V
1 day - - - -12.4
(1800)
10.0
(1450)- -
3 days12.4
(1800)
10.0
(1450)
10.3
(1500)
8.3
(1200)
24.1
(3500)
19.3
(2800)-
8.3
(1200)
7 days19.3
(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
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Physical Properties of Cement
Tens i le Streng th
Altho ugh st i l l speci f ied by ASTM, the direct tension test
does no t prov ide any useful insight into the conc rete-
making propert ies of cements. It persis ts as a specif ied
test because in the early years o f cement manufactu re,
i t used to be the mos t common test since it was di f f icul t
to f ind machines that could compress a cement sample
to failure.
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Physical Properties of Cement
Flexural Streng th
Flexural strength (actual ly a measure of tensi le strength inbend ing ) is carr ied ou t on a 40 x 40 x 160 mm (1.57-inch x 1.57-inc hx 6.30-inch) cement mo rtar beam. The beam is then loaded at itscenter point unt i l fa i lure.
The standard cement mortar f lexu ral strength test is: ASTM C 348: Flexu ral Streng th o f Hydraul ic Cement Mor tars
Specif ic Gravi ty Test
Speci f ic gravi ty is normal ly used in mixture propor t ion ingcalculat ions. The specif ic gravi ty of Port land cement is general ly
around 3.15 whi le the specif ic gravi ty of Port land -blast-furnace-slag and Po rt land -pozzolan c ements m ay have specif ic g ravi t iesnear 2.90 (PCA, 1988).
The standard specif ic gravi ty test is:
AASHTO T 133 and ASTM C 188: Dens ity o f Hydraul ic Cement
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Physical Properties of Cement
Heat of Hydrat ion
The heat of hydrat ion is the heat generated when water and
Port land cement react. Heat of hydrat ion is mos t inf luenced by the
propo r t ion of C3S and C3A in th e cement, but is also inf luenced by
water-cement rat io, f ineness and cu r ing temperature. As each one
of th ese factors is inc reased, heat of h ydrat ion in creases.
In large mass con crete struc tures such as gravi ty dams , hyd rat ion
heat is produced signi f icant ly faster than it can be dissipated
(especial ly in the center of large con crete masses), which can
create high temperatures in the center of these large con crete
masses that, in turn, may cause undesirable stresses as theconc rete coo ls to ambient temperature. Conversely, the heat of
hydrat ion can help maintain favorable cur ing temperatures dur ing
w in ter (PCA, 1988).
The standard heat of hy drat ion test is:
ASTM C 186: Heat of Hyd rat ion o f Hydrau l ic Cement
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Physical Properties of Cement
Loss on Igni t ion
Loss on igni t ion is calculated by heat ing up a cement
sample to 900 - 1000C (1650 - 1830F) un ti l a cons tan t
weight is obtained. The weight loss of the samp le due to heat ing is th en
determ ined. A high loss on igni t ion can indicate pre-
hydrat ion and carbonation, wh ich may be caused by
imp roper and p rolonged storage or adul terat ion du r ing
transpo rt o r trans fer (PCA, 1988).
The standard loss on igni t ion test is con tained in:
AASHTO T 105 and ASTM C 114: Chemical Analysis of
Hydraul ic 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 incivil engineering and building works.
Concretes and mortars made using CEM
I are versatile, durable and forgiving of
poor construction practice.
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Application of Different Types
of Cement
Sulphate-Resisting Cements
SRPC is normally a low alkali cement which benefitsconcrete in resisting the alkali silica reaction (ASR).However, it is not the only sulphate-resisting cementavailable. Various factory-made composite cements arealso sulphate-resisting including the generally availableCEM II/B-V type of Portland-fly ash cement containing atleast 25% of fly ash. Such CEM II/B-V cements arepermitted for use in the same wide-range of sulphate
exposure conditions as is SRPC and are also low inreactive alkalis. Moreover, SRPC is a type of CEM Icement with a high clinker content, it is no longermanufactured in the UK and is becoming more difficult tosource. Consequently, greener sulphate-resistingcomposite cements will continue to grow in importance.
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Application of Different Types
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SRPC is used where precaution against moderate
sulphate attack is important, as in drainage structures
where sulphate concentrations in groundwater are
higher than normal but not unusually severe (Table).
Relative Degreeof Sulfate Attack
Percentage Water-SolubleSulfate (as SO4) in Soil
Samples
Sulfate (as SO4) inWater Samples,
ppm
CementType
Negligible 0.00 to 0.10 0 to 150 CEM IPositive 0.10 to 0.20 150 to 1500 SRPC
Severe 0.20 to 2.00 1500 to 10,000 CEM II/B-V
Very Severe 2.00 or more 10,000 or more CEM II/B-V
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Application of Different Types
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Rapid Hardening Portland Cements
Rapid hardening versions of CEM I cements are
available. The average particle size is smaller in these
cements and they gain strength more quickly than doordinary CEM I types. They generate more heat in the
early stages and can be useful in cold weather
concreting. However, their principal use is in
manufacturing precast concrete units where the highearly strength of the concrete permits quick re-use of
moulds and formwork.
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Application of Different Types
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White Cement
White cement is a Portland cement CEM I made
from specially selected raw materials, usuallypure chalk and white clay (kaolin) containing
very small quantities of iron oxides and
manganese oxides. White cement is frequently
chosen by architects for use in white, off-whiteor coloured concretes that will be exposed,
inside or outside buildings, to the public's gaze.
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White Cement
White cement is a Portland cement CEM I made
from specially selected raw materials, usuallypure chalk and white clay (kaolin) containing
very small quantities of iron oxides and
manganese oxides. White cement is frequently
chosen by architects for use in white, off-whiteor coloured concretes that will be exposed,
inside or outside buildings, to the public's gaze.
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Summary
Port land cement, the chief ingredient in cement paste,
is the most w idely used bui ld ing mater ial in the wo r ld.
In the presence of water , the chemical compounds
with in Port land cement hydrate causing hardening and
strength gain.
Port land cement can be speci f ied based on i ts chem ical
compos i t ion and other var ious physical character ist ics
that affect i ts behavior.
Tests to character ize Port land cement, such as
f ineness, soundness, sett ing t ime and strength are
useful in quali ty contro l and speci f ications but should
no t be subs t i tuted for tests on PCC.
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Thank You
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