Specialty Cements

Specialty Cements
Dr. Kimberly Kurtis
School of Civil Engineering
Georgia Institute of Technology
Atlanta, Georgia
Specialty Cements
• Portland cements do not always meet every need of the construction
industry.
• Other specialty cements have been developed to meet these needs.
• Generally much smaller production, limited availability, and
increased cost.
modified portland cements – some particular component has been
added to portland cement to provide the desired quality
In these cements, the calcium silicates continue to provide the
strength, but changes are made to the aluminate and ferrite phases
non-portland cements – Do not rely on the calcium silicates for
strength, but on the hydration of other phases
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Today’s Cements
Wide range of portland, blended & other hydraulic cements available
•
Sulfate-resisting cements
•
White or colored cements
•
Low-heat cements
•
Masonry cements
•
Rapid strength gain cements
•
Mortar cements
•
ASR resistant cements
•
Expansive cements
•
Air-entraining cements
•
Rapid setting cements
•
Blended cements
•
Rapid hardening cements
•
Oil well cements
•
Biogenic cements
•
Calcium-aluminate cements
White or Colored Cements
•
•
•
•
•
Fe, Mg give clinker and cement gray color
Can produce white cement if F<0.5% in raw materials
Burn clean fuels
Controlled cooling to retain Fe2+
Use ceramic ball mill
http://www.svdpla.org/Newsletters/Vincen3.gif
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White or Colored Cements
• Fe, Mg give clinker and cement gray color
• Can produce white cement if F<0.5% in raw materials
• Add pigments to white cement to achieve desired color:
- red, yellow, brown, black - iron oxides
- green - chromium oxide
- blue - cobalt blue
White cements are ~3x
cost of ordinary portland
cement
http://www.ahi-supply.com/speccem.html
Masonry & Mortar Cements
Properties of masonry mortars:
• Workability
• Water retentivity
• Consistent rate of hardening
• Durability
• Compressive strength
• Bond
• Volume stability
• Appearance
Composition of masonry mortars:
• Cementitious material
• Masonry sand
• Water
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Masonry & Mortar Cements
Masonry cement consists of:
• Portland cement or blended hydraulic cement
• Hydrated or hydraulic lime
• Other materials like talc, clay, fly ash, slag, air entrainers
ASTM C 91 Standard Specification for Masonry Cement
Mortar cement:
• Similar to masonry cement
• Lower air content
• Bond strength requirement
ASTM C 1329 Standard Specification for Mortar Cement
Masonry & Mortar Cements
Masonry & Mortar Cements:
• Type M
• Type S
• Type N
ASTM C 91 Standard Specification for
Masonry Cement
Mortars:
• Type M
• Type S
• Type N
• Type O
ASTM C 270 Standard Specification for
Mortar for Unit Masonry
ASTM C 1329 Standard Specification for
Mortar Cement
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Masonry & Mortar Cements
ASTM C 270 Property Specifications for Laboratory-Prepared Mortars
Mortar Type
Minimum 28-day
compressive
strength,
MPa (psi)
Minimum
water
retention,
%
Maximum air content, %
Masonry
cement
Mortar cement
Or
Cement-lime
M
17.2 (2500)
75
18
12
S
12.4 (1800)
75
18
12
N
5.2 (750)
75
20*
14*
O
2.4 (350)
75
20*
14*
*2% lower if structural reinforcement is embedded in mortar
Masonry & Mortar Cements
Recommended Guide for Selection of Mortar Type
Building Segment
Exterior, above grade:
Type
Load bearing
Non-load bearing
Parapet wall
Exterior, at or below grade:
Interior:
N or S
N
N or S
S or M
Load bearing
N or S
Non-load bearing
O or N
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Masonry & Mortar Cements
ASTM C 270 Proportion Specifications
Mortar
type
M
S
N
Parts by volume
Portland or
blended
cement
Masonry or mortar cement type
Sand
N
Hydrated
lime or lime
putty
M
S
-
1
-
-
-
-
-
1
-
1
-
-
-
¼
2¼ to 3½
times the
total
volume of
cement
plus lime
1
-
-
1
-
-
½
-
-
1
-
1
-
-
-
¼-½
-
-
-
1
-
1
-
-
-
1
Masonry & Mortar Cements
Requirements for Masonry and Mortar Cements
(ASTM C 91 & C 1329)
• Fineness
• Autoclave expansion
• Time of setting
• Compressive strength
• Air content
• Water retention
• Bond strength
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Masonry & Mortar Cements
Requirements for Mortar Cements (ASTM C 1329)
Property
Type of Mortar Cement
M
S
N
Compressive strength minimum, MPa (psi)
7 days
12.4 (1800)
9.0 (1300)
3.4 (500)
28 days
20.0 (2900)
14.5 (2100)
6.2 (900)
Air content, volume %
Minimum
8
8
8
Maximum
15
15
17
0.7 (100)
0.5 (70)
Bond strength minimum, MPa (psi)
28 days
0.8 (115)
Expansive Cements
• Ordinary portland cements expand slightly during early hydration,
but the effect is far outweighed by the amount of drying shrinkage
that occurs early.
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Expansive Cements
Expansive Cements
Expansive cements expand during the early setting period
Can be used as:
• Shrinkage compensating cements - induce a small (25-100psi)
self-stress in restrained members to offset drying shrinkage and
avoid cracking
• Chemically prestressing or self-stressing cements - induce a
larger self-stress (500-1000psi) for prestressing precast elements
Shrinkage compensating
concrete at Love Airport
taxiways
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Expansive Cements
Expansive cements are generally a blend of portland cement or
calcium aluminate cement and some expansive component
ASTM Type K - Blend of Type II or V portland cement and the
calcium sulfoaluminate Kleinite (C4A3S)
C4A3S + 6C + 8CS + 96H --> 3(C3A·3CS·H32) or 3(C6AS3H32)
• Amount of Kleinite depends on degree of desired expansion (850% by mass)
• Ettringite produced by this reaction is believed to produce the
expansion
- “colloidal ettringite”
- topochemical growth
• Typically good sulfate resistance
Expansive Cements
ASTM Type M - Blend of portland cement, calcium aluminate
cement, and calcium sulfate
CA + 3CS + 2CH+ 30H --> C6AS3H32
• Precast units made with solids in the ratio 66:20:14
ASTM Type S - Portland cements with high C3A content (~20%) and
suitable amounts of gypsum
• Difficult to control setting
• Rapid slump loss
• Sulfate durability problems
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Expansive Cements: Influence of Curing Conditions
Expansive Cements: Influence of Curing Conditions
It is desirable for the
ettringite to form after
setting, rather than in
plastic concrete, to
maximize expansion.
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Rapid Setting and Hardening Cements
Type III cements harden rapidly, but may not set quickly enough
for some applications, such as repair.
Rapid setting and rapid
hardening cements
include:
• Calcium sulfoaluminate
cements
• Calcium fluoroaluminate
cements
fc>1000psi at 1 hour
Rapid Setting and Hardening Cements
Calcium sulfoaluminate (or very high early strength) cements
• Typically contain more C4A3S than Type K cement
• C4A3S is formed during clinkering (rather than used as an addition, added
after grinding)
• CS is added to feedstock or during grinding
• Contain little C3S and much C2S
• Contain little C, which is believed to produce non-expansive ettringite
with better strength
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Rapid Setting and Hardening Cements
Calcium fluoroaluminate or regulated-set cements
• C3A is replaced by C11A7•CaF2 (20-25%)
• C11A7•CaF2 can be produced in kiln or added during grinding
• C11A7•CaF2 reacts even more vigorously than C3A
• Use very soluble additives, such as citric acid and/or sodium sulfate, to
control reaction rate
• Setting can be controlled to occur 2-40 min.
• Initial strength due to C11A7•CaF2 hydration; later strength due to C3S
Other Rapid Setting/Hardening Cements
High iron cements (HIC)
• Use a combination of C4A3S and C4AF to produce ettringite
Finely ground cements
• Type III cements ground to high fineness (700-900 m2/kg)
• May contain chemical accelerators as well
Mixtures of Type I cement and gypsum
Magnesium phosphate cements
Mixtures of calcium aluminate and portland cement
• Use of 20-80% calcium aluminate cement in a blend can produce an
almost instantaneous set
• Early strength will be very high, but late strength will be low
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Oil Well Cements
• Make up 5% of portland cement used in US
• Not used for structural concrete
Oil well cement slurries
are used to:
• protect casing from
damage from surrounding
water
• give strength
• prevent fluid migration
Oil Well Cements
Extreme conditions exist:
• slurry must be flowable for hours and then set rapidly
• slurry may be pumped thousands of meters below the surface
• slurry may be exposed to high temperatures (100-250C) at the
bottom of the well (up to 300C)
• slurry may be exposed exposed to high pressure (>20,000 psi)
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Oil Well Cements
Eight classes:
• Class A - general use, like Type I
• Class B - sulfate resistant, like Type II
• Class C - rapid hardening, like Type III
• Classes D, E, F - sulfate resistant with set modifying admixtures;
Class E can be used in hotter conditions than Class D, and Class F
hotter still
• Classes G and H - sulfate resistant with stringent “thickening” times;
Class H is more coarsely ground
• Class J - withdrawn, was a C2S-based cement with silica flour (finely
ground quartz)
In US, Type H is most common
Outside US, Type G is most common
Oil Well Cements
In addition, there are 3 grades:
• O - ordinary
• MSR - moderate sulfate resistant
• HSR - high sulfate resistant
Class A - only grade O
Class B - only MSR, HSR
Class C - O, MSR, HSR
Class D, E, F - only MSR, HSR
Class G, H - only MSR, HSR
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Oil Well Cements
Oil Well Cements: Temperature Effects
High temperatures during oil well applications can influence slurry
properties and chemistry:
• Many retarders and water reducers decompose at T > 150C
• Cement hydration, particularly of C2S and C4AF phases, is accelerated
at ~70-90C
• Changes in C-S-H structure and strength can result
>100C, C-S-H --> α-C2SH (crystalline, low fc, high permeability)
>200C, α-C2SH --> C6S2H3 (Jaffeite, similar properties)
• Silica flour is added to prevent strength retrogression
initially form C5S6H4 (tobermorite)
>150C C5S6H4 --> C6S6H + C2S3H2 (xonotlite and gyrolite)
> 250C residual tobermorite and gyrolite form truscottite
> 400C truscottite and xonotlite decompose
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Biogenic Cements
• Rice hull ash (RHA) is most common
source of biogenic silica for cement
manufacture
• Rice hulls are an abundant by-product
in many developing countries
• Contain cellulose, lignin, and
hemicellulose, but are also 10-20% silica
by mass
• Rodrigues et al. have produced β-C2S
from biogenic silica at relatively low
temperatures (650-800oC)
• Cements are typically doped with
barium or manganese to increase
reactivity.
1µm
unhydrated
6% Ba2+ β-C2S
Calcium Aluminate Cements
Calcium aluminate cements or high alumina cements (HAC) or
ciment fondu rely on hydration of calcium aluminate phases, rather
than calcium silicates.
Composed of:
• alumina ~40%
• lime ~40%
• ferric or ferrous oxides ~15%
• fused silica ~5%
• small amounts of titanium dioxide,
silica, and magnesia
Common applications are for
refractory brick and where sulfate
resistance is needed
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Calcium Aluminate Cements
• Raw materials are bauxite and limestone
• Composition varies (iron rich vs. iron poor)
• Monocalcium aluminate (CA) is principal phase
Calcium Aluminate Cements: Hydration
CA + H
<10C --> CAH10
10-30C --> C2AH8 + AH3
>30C --> C3AH6 +2AH3
no CH
In addition, xC12A7 + yH --> zC2AH8
• C12A7 sets within a few minutes, but CA sets more slowly; CAC with
higher C:A sets more rapidly
• Generally, setting time is comparable to portland cement
• However, strength gain is RAPID, achieving 80% ultimate fc at 24 hours
• 24 hour strengths for CAC are similar to 7 day strengths for PC
• Total heat evolved is similar to PC, but rate is 3x as fast
• Excellent sulfate resistance
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Calcium Aluminate Cements: Conversion
With these great properties why isn’t CAC more widely used?!?
CONVERSION
Both of the primary hydration products are metastable at both normal
and elevated temperatures. In the presence of moisture,
3CAH10 --> C3AH6 +2AH3 + 18H
3C2AH8 --> 2C3AH6 + AH3 + 9H
• The original hydration products have a lower density than the
conversion products
• Thus, conversion leads to increased porosity and hence reduced
strength and impermeability
Calcium Aluminate Cements: Conversion
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Calcium Aluminate Cements: Conversion
• Higher temperatures, higher concentrations of lime, and greater
alkalinity all promote conversion.
Calcium Aluminate Cements: Conversion
• Some have suggested that post-conversion strength of CAC concrete
with w/c<0.40 may be adequate for some structural applications.
• Current French recommendations require maximum w/c of 0.40 and
minimum cement content of 400kg/m3.
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Calcium Aluminate Cements: Conversion
• Small variations in w/c can significantly affect strength after conversion
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