Transcript
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High Strength Concrete
CVLE 519
Concrete Technology
Dr. Adel El Kordi
Professor
Civil and Environmental
Engineering Department
Faculty of Engineering
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A concrete that meets special combinations of
performances and uniformity requirements that cannot
always be achieved using conventional and normal
mixing, placing and curing.
High-strength concrete by definition is:
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• High-strength concrete has a compressive
strength greater than 40 MPa. In the UK, BS EN
206-1 defines High strength concrete as concrete
with a compressive strength class higher than
C50/60.
• High-strength concrete is made by lowering the
water-cement (W/C) ratio to 0.35 or lower. Often
silica fume is added to prevent the formation of
free calcium hydroxide crystals in the cement
matrix, which might reduce the strength at the
cement-aggregate bond.
High-strength concrete
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• High-strength concrete is typically used in high-rise
structures. It has been used in components such as,
shear walls, and foundations. High strengths are also
occasionally used in bridge applications as well. A
high-rise structure suitable for high-strength concrete
use is considered to be a structure over 30 stories.
• High –strength concrete is occasionally used in the
construction of highway bridges. High-strength
concrete permits reinforced or prestressed concrete
girders to span greater lengths than normal strength
concrete girders. Also, the greater individual girder
capacities may enable a decrease in the number of
girders required. Thus, an economical advantage is
created for concrete producers in that concrete is
promoted for use in a particular bridge project as
opposed to steel.
Applications of High-Strength Concrete
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Generally 28 days–compressive. Strength
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This ultra high strength concrete specimen suffered
from a shear failure, where one small section
completely separated from the rest
7shear failure
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Time-dependent probability of concrete cover spalling in a typical reinforced
concrete bridge deck. (NC=normal-strength concrete; HPC=typical high
performance concrete; HPC-IC=high performance concrete with internal curing.
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Temperature distribution at various depths during fire exposure
in normal-strength concrete (NSC) and high-strength concrete
(HSC) columns
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Punching Shear Resistance of High-Strength
Concrete Slabs
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Punching Shear Resistance of High-Strength
Concrete Slabs
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types W/C Fc28,MPa notes
HSC with good
mobility0.25~0.40 50.0~70.0
15~20cm slump
large amount of
cement
high-strength
with normal
consistency
0.35~0.45 55.0~80.0
5~10cm slump
large amount of
cement
high-strength
without slump0.30~0.40 55.0~80.0
< 25mm slump
normal amount of
cement
high-strength
with low W/C0.20~0.35 100.0~170.0 admixture
RPC 0.05~0.20 70.0~240.0 70.0Mpa or above
Classifications of High Strength Concrete
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High-Strength Concrete Materials
Cement
• Use cement yielding highest concrete strength at extended ages (91-days)
• Cement should have min. 7-day mortar cube strength of 30 MPa
• Cement contents between 400 and 550 kg/m3
• All types of cement are applicable.
• To maintain a uniform high strength conrete:
1- Tricalcium silicate content varies by< 4%
2- Ignition loss varies by < 0.5%
3- Fineness varies by < 375 cm2/g (Blaine)
4- Sulphate (SO2) level should be maintained at optimum with variations limited to ± 0.20%.
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It would be difficult to produce high-
strength concrete mixtures without
using chemical admixtures. A
common practice is to use a
superplasticizer in combination with a
water-reducing retarder. The
superplasticizer gives the concrete
adequate workability at low water-
cement ratios, leading to concrete
with greater strength. The water-
reducing retarder slows the hydration
of the cement and allows workers
more time to place the concrete.
Chemical admixtures
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Chemical admixtures
• All type of HRWR, Superplasticizers or PolyCarboxylates can be used.
• Air-entraining admixtures are not necessary or desirable in high-strength concrete as it decreases the value of the required compressive strength.
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Aggregates
• Coarse aggregate: 9.5 - 12.5 mm (3/8 -
1/2 in.) nominal maximum size gives
optimum strength
• Combining single sizes for required
grading allows for closer control and
reduced variability in concrete
• For 70 MPa and greater, the FM of the
sand should be 2.8 – 3.2. (Lower may
give lower strengths and sticky mixes)
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Supplementary Cementing Materials
• Finely divided mineral admixtures, consisting mainly of
fly ash, silica fume and slag cement have been widely
used in high-strength concrete.
• Dosage rate varies from 5% to 30% or higher by mass of
cementing material depending on the type of mineral
used .
Fly ash (Class C ) - Metakaolin (calcined clay) - Silica fume -
Fly ash (Class F) – Slag - Calcined shale (from left)
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Pozzolans, such as fly ash and silica fume, are
the most commonly used mineral admixtures in
high-strength concrete. These materials impart
additional strength to the concrete by reacting
with portland cement hydration products to
create additional C-S-H gel, the part of the paste
responsible for concrete strength.
Pozzolans
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Chemical Analysis of Fly Ash, Slag and Silica Fume
Class F
fly ash
Class C
fly ash
Ground
slag Silica fume
SiO2, % 52 35 35 90
Al2O3, % 23 18 12 0.4
Fe2O3, % 11 6 1 0.4
CaO, % 5 21 40 1.6
SO3, % 0.8 4.1 9 0.4
Na2O, % 1.0 5.8 0.3 0.5
K2O, % 2.0 0.7 0.4 2.2
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Properties of Fly Ash, Slag and Silica Fume
Class F
fly ash
Class C
fly ash
Ground
slag
Silica
fume
Loss on
ignition, %2.8 0.5 1.0 3.0
Blaine
fineness,
m2/kg
420 420 400 20,000
Relative
density2.38 2.65 2.94 2.40
ASTM C 150 → L.O.I. ≤ 3% for O.P.C. Typical value = 1.4
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Quantity of
Fly ash, slag and Silica fume in Concrete
by Mass of Cementing Materials
Fly ash
15% to 40%Class C
15% to 20%Class F
30% to 45%Slag
5% to 10%Silica fume
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Silica fume slurry consists of approximately 50 percent silica
fume and 50 percent water, by mass. When first introduced to
the market, slurried silica-fume products often contained water
reducers or high-range water reducers. Today, slurry is available
without any such additions.
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Effects Of Supplementary Cementing Materials On
@Freshly Mixed ConcreteReduced Increased No/Little Effect/Varies
Fly ash SlagSilica
Fume Nat. Pozzolans
Water Requirements
Workability
Bleeding & Segregation
Air Content
Heat Of Hydration
Setting time
Finishing
Pump ability
Plastic Shrinkage
Cracking
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Effects Of Supplementary Cementing Materials On
Hardened ConcreteReduced Increased No/Little Effect/Varies
Fly ash SlagSilica
Fume
Nat.
Pozzolans
Strength Gain
Abrasion Resistance
Drying Shrinkage &
Creep
Permeability
Alkali-Silica Reactivity
Chemical Resistance
Carbonation
Concrete Color
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1- For high strength concrete, the indirect tensile
strength may be about 5 percent of the compressive
strength.
2- At low strengths, the indirect tensile strength may be
as high as 10 percent of the compressive strength.
Tensile splitting strength
3-The tensile splitting strength
was about 8 percent higher
for crushed-rock-aggregate
concrete than for gravel-
aggregate concrete.
4- The indirect tensile strength
was about 70 percent of the
flexural strength at 28 days.
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Mix Design Procedure:
Fig-1 :Relation between compressive strength and reference number
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Fig-4: Relation between compressive strength and reference number
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Fig-5: Relation between water-cement ratio and Reference Number
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Table – 1: Aggregate cement ratio (by weight) required to give four degrees of workability with different water –cement ratios using ordinary Portland cement
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Example 1Design a high strength concrete for use in the production of precast
prestressed concrete to suit the following requirements:
Specified 28-day works cube strength = 50 MPa
Very good degree of control; control factor = 0.80
Degree of workability = very low
Type of cement = ordinary Portland cement
Type of coarse aggregate = crushed granite (angular) of maximum size
10mm.
Type of fine aggregate = natural sand
Specific gravity of sand = 2.60
Specific gravity of cement = 3.15
Specific gravity of coarse aggregates = 2.50
Fine and coarse aggregates contain 5 and 1 percent moisture
respectively and have grading characteristics as detailed as follows:
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IS sieve size Percentage Passing
Coarse aggregate Fine aggregate
20mm 100 100
10mm 96 100
4.75mm 8 98
2.36mm - 80
1.18mm - 65
600 micron - 50
300 micron 10
150 micron - 0
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Fig-6: Combining of Fine aggregates and Coarse aggregates
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DESIGN OF MIX
Mean strength = (50 / 0.80) = 63 MPaReference number (fig.1)= 25Water cement ratio (fig 5) = 0.35For a 10mm maximum size aggregate and very low workability, the aggregate-cement ratio for the desired workability (table-1) =3.2The aggregates are combined by the graphical method as shown in figure 6, so that 30 percent of the material passes through the 4.75 mm IS sieve.Ratio of fine to total aggregate = 25%Required proportions by weight of dry materials:Cement – 1Fine aggregates – [(25/100)x3.2] = 0.8Coarse aggregates – [(75/100)x3.2)] = 2.4Water = 0.35If C = weight of cement required per cubic meter of concrete, then
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F=50MPa
Control factor = 0.8
Workability = very low
N.M.S = 10mm
sand crusted stone
GS 2.6 2.5
Moisture 5% 1%
Mean strength = 50/0.8 =63 MPA
R.N (fig1) = 25
W/c = 0.35
A/C = 3.2 (fine =0.25, coarse =0.75)
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C/3.15x1000 + W/1000 + F/2.6x1000 + Cs /2.5x1000 = 1
C/3.15X1000 + 0.35C/1000 + 0.25X3.2C/2.6X1000 +
0.75X3.2C/2.5X1000 = 1
(3.17 + 3.50 + 3.08 + 9.6) X 10-4C = 1
C = 104/19.35 = 520 KG
W = 0.35 X 520 = 182 L
Fine = 0.25 x 3.2 x 520 = 416 kg
Coarse = 0.75 x 3.2 x 520 = 1250
Unit weight = 2368 kg
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Dry aggregate Moist aggregate
Cement 520 520
Water 182 182-21-13 = 148
Fine 416 416x1.05 = 437
Coarse 1250 1250X1.01 = 1263
2368 2368
Batch Quantities per cubic meter of concrete
A high strength concrete mix proportions for one cubic meter and the
materials properties are as follows:
Assume air entrained = 2%
Calculate:
1. The mix proportion as ratios to cement weight.
2. The unit weight of concrete.
3. The concrete yield.
4. The cement factor.
5. The amount of cement, sand and gravel required to produced
500 m3 of concrete.
Coarse aggregateFine aggregateWaterCement
1085
2.43
1.59
600
2.57
1.65
165
1
--
550
3.15
--
Weight by kg
Specific gravity
Unit weight t/m3
Example 2
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Air = 2%
• Unit weight = 550 + 165 + 600 + 1085 = 2400 kg/m3
•Yield =
• 50 15 54.55 98.64
•Y = 50/1000x3.15 + 15/1000 + 54.55/2.57x1000 + 98.64/2.43x1000
• = 0.0159 + 0.0150 +0.0212 + 0.0406 = 0.0927
•Y = 1.02 x y = 0.0946 m3
•Cement factor = 1/y = 10.57 bag. *c= 529kg
Cement Water Fine Coarse
kg 550 165 600 1085
Ratio 1 0.30 1.09 1.97
Bag of
cement
50 15 54.55 98.64
ɣ kg/m3 1.65 1.59
Gs 3.15 1 2.57 2.43
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•For 500m3 concrete
Mi x proportion
C w fine coarse
529 159 577 1042
V= 529/3.15x1000 + 0.159 +577/2.57x1000 + 1042/2.43x1000 + 0.02
= 0.1679 + 0.1590 + 0.2245 + 0.4288 + 0.02
V= 1.002 m3
For 500 m3 of concrete
C= 500x 529 = 264500 kg
Fine = 500x 577 = 288500 kg/1.65 = 174.9 m3
Coarse = 500 x 1042 = 521000 kg/1.59 = 327.7 m3
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Design a high strength concrete mix using. The 28-day characteristic cylinder
compressive strength is 600kg/cm2. The required slump is 200mm. The water/
cement ratio = 0.30 and the total aggregate /cement ratio = 2.70. The ratio of sand
to all in aggregate = 0.32. The properties of aggregates are given in table below
(N.M.S of coarse aggregate is 20 mm.).
Calculate:
1. The concrete mix proportions.
2. The unit weight of concrete.
3. The concrete yield.
4. The cement factor.
5. Calculate the indirect tensile strength, and the flexure strength of concrete.
6. Adjust mix proportions, if the coarse aggregate can absorb 1.5% of its weight,
and the fine aggregate has moisture of 0.50%.
Coarse aggregateFine aggregate
2.51
1.65
2.55
1.70
Specific gravity
Unit weight t/m3
Example 3
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W/C = 0.3
A/C = 2.7 (Fine =0.32, coarse = 0.68 )
Fine coarse
Gs 2.55 2.51
1.70 1.65
C/3.15 x 1000 + 0.3C /1000 + 2.7x0.32c/1000x2.55 + 2.7x0.68 c/1000x2.51 =1
(3.175 + 3 + 3.388 + 7.315) x 10-4 c = 1
Concrete mix proportion : C = 1000/16.878 = 593 kg
W = 0.30 x 593 = 178 kg
Fine = 0.32 x 2.7 x 593 = 512 kg
Coarse = 0.68 x 2.7 x 593 = 1089 kg
Unit weight of concrete = 2372 kg/ m3
C W fine coarse
593 178 512 1089
50 15 43.17 91.82
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Y = 50/3.15x1000 + 0.15 + 43.17/1000x2.55 + 91.821/1000x2.51
= 0.0159 + 0.015 + 0.0169 + 0.0366 = 0.0844
Cement factor = 1/y = 11.85 bag
Fc = 600 kg/ cm2
Ft = 5/100 x 600 = 30kg/ cm2
Ff = 30/0.7 = 43kg/cm2
Fine = 512 + 0.005 x 512 =512 + 3 = 515 kg (moisture )
Coarse = 1089 - 0.015 x 1089 = 1089 - 16 = 1073 kg
W = 178 – 3 + 16 = 191 kg
C W fine coarse
593 191 515 1073
Unit weight = 593 + 191 + 515 + 1073 = 2372 kg/ m3
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@HIGH-EARLY-STRENGTH CONCRETE• The time period in which a specified strength should be
achieved may range from a few hours to several days.
• High-early-strength can be obtained by using one or a
combination of the following:
1. Type III or HE high-early-strength cement.
2. High cement content 400 to 600 kg/m3.
3. Low water-cementing materials ratio (0.20 to 0.45).
4. Higher freshly mixed concrete temperature.
5. Higher curing temperature.
6. Chemical admixtures.
7. Silica fume (or other supplementary cementing materials).
8. Steam or autoclave curing.
9. Insulation to retain heat of hydration.
10. Special rapid hardening cements.
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46Applications for Fly ash and Slag Cement.
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Synthetic fibers improve toughness and Plastic
Shrinkage of High Strength Concrete.
Synthetic fibers
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Placing, Consolidating and Curing
1. Delays in delivery and placing must be eliminated
2. Consolidation very important to achieve strength
3. Slump generally 180 to 220 mm (7 to 9 in.)
4. Little if any bleeding—fog or curing agent have to be
applied immediately after strike off to minimize plastic
shrinkage and 7 days moist curing.
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Curing
•Curing is the process of maintaining a satisfactory moisture content
and a favorable temperature in concrete during the hydration period so
that desired properties of the concrete can be developed.
•Curing is essential in the production of quality concrete; it is critical to
the production of high-strength concrete.
•The potential strength and durability of concrete will be fully
developed only if it is properly cured .
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Precast concrete
Prestressed concrete
Precast - Prestressed concrete
Advantages of high strength concrete
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Advantages of high strength concrete
2- Reduced initial construction costs
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3- Wider girder spacing and longer spans
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4- Significant savings in concrete quantities
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5- Reduced long-term costs due to fewer repairs
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6- Significant savings in construction depth
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Strength-Weight ratio becomes comparable to steel
0
5
10
15
20
25
30
35
40
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Structural steel Concrete High strength
concrete
Lightweight HSC
Strength-Weight Ratio
7- Cost Saving
%
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Example 3
The photographs given in Figures from 1 to 6 show different things related
to high strength concrete construction. Discuss what you understand from
each photograph.
Figure2
Figure1
Figure3
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Figure 5
Figure 6
Figure 4
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