Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Lecture-02
Materials By: Prof Dr. Qaisar Ali Civil Engineering Department UET Peshawar drqaisarali@nwfpuet.edu.pk mumarbsc@yahoo.com
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Topics Addressed Concrete
Components
Admixtures
Properties
Factors Affecting Strength of Concrete
High Strength Concrete
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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1
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Topics Addressed
Durability of Concrete
Concrete Subjected to High Temperatures
Reinforcing Steel
Types
Properties
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Topics Addressed ACI Code Provisions for Concrete and Steel
Chapter 3 : Materials
Chapter 4 : Durability of Concrete
Chapter 5 : Concrete Quality, Mixing and Placing
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Concrete A composite material composed of:
Paste (Portland Cement + water)
Aggregates (generally sand and gravel)
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Concrete Components Paste
Cementitious materials
Portland cement
Pozzolans (fly ash, silica fume, ground granulated blast furnace slag)
Water
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Concrete Components Aggregates
Coarse
Gravel
Crushed stone
Fine
Sand
Coarse Aggregates Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Concrete Components Percentage Composition
Paste: 25% - 40%
Cement: 7% - 15%
Water: 14% - 21%
Air: 4% - 8%
Aggregates: 60% - 75%
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Admixtures Definition
A material other than cement, water and aggregates, that is used as an ingredient of concrete and is added to the batch immediately before or during mixing.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Admixtures Uses Admixtures are used to:
reduce the cost of concrete construction.
achieve certain properties in concrete more effectively than by other means.
maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in adverse weather conditions.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Admixtures Types
As per ACI Committee 212, admixtures have been classified into following groups:
Air-entraining Admixtures: causes the development of a system of microscopic air bubbles in concrete, mortar, or cement paste during mixing. Air-entrained concrete should be used wherever water saturated concrete may be exposed to freezing and thawing. Air entrainment also improves the workability of concrete.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
11
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Admixtures Types
Accelerating Admixtures: causes an increase in the rate of hydration of the hydraulic cement and thus shortens the time of setting, increases the rate of strength development, or both.
Water Reducing and Set-Controlling Admixtures: Reduce the water requirements of a concrete mixture for a given slump, modify the time of setting, or both.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Admixtures Types
Admixtures for Flowing Concrete: Flowing Concrete is concrete that is characterized as having a slump greater than 190 mm (7-1/2 in.) while maintaining a cohesive nature.
Miscellaneous
Freeze Resistant, Pigments, Bonding, Grouting etc. (Refer ACI 212 for details and more types of miscellaneous admixtures)
Brief Visit of ACI 212
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Compressive Strength
The uniaxial compressive strength is measured by a compression test of a standard test cylinder. This test is used to monitor the concrete strength for quality control or acceptance purposes.
The specified compressive strength is measured by compression tests on 6 by 12 inches cylinders, tested after 28 days of moist curing (testing methods: ASTM Standards C31 and C39).
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Compressive Strength
Load
Stress Strain Curve
Stress
Typical concrete stress strain curves in compression
Strain Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Tensile Strength
Varies between 8% and 15% of the compressive strength.
The type of test that is used to determine the tensile strength has a strong effect on the value that is obtained.
Two types of tests are widely used:
Modulus of Rupture (Flexural Test)
Split Cylinder Test
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
16
8
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Tensile Strength
Modulus of Rupture (Flexural Test)
b h
fr = Prof. Dr. Qaisar Ali
6M bh2
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Tensile Strength
Modulus of Rupture (Flexural Test)
ASTM C 78 – Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)
ASTM C 293 – Standard Test Method for Flexural Strength of Concrete (Using Simple Beam With Center-Point Loading)
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
18
9
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Tensile Strength
Split Cylinder Test
P
d
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
19
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Tensile Strength
Split Cylinder Test Tension
Prof. Dr. Qaisar Ali
Compression
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Tensile Strength
Split Cylinder Test
P
d
fct = Prof. Dr. Qaisar Ali
2P d
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Tensile Strength
Split Cylinder Test
ASTM C 496 – Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
22
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Relationship Between Compressive and Tensile Strengths
Tensile strength increases with an increase in compressive strength
Ratio of tensile strength to compressive strength decreases as the compression strength increases
Tensile strength fc
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
23
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Relationship Between Compressive and Tensile Strengths
Mean f ct = 6.4fc
For deflections (Eq. 9-10):
fr = 7.5fc
For strength (ACI 11.4.3.1):
Prof. Dr. Qaisar Ali
fr = 6fc
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Time Dependent Volume Changes
Shrinkage
Creep
Thermal expansion
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
25
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Shrinkage
Shortening of concrete during hardening and drying under constant temperature
Moisture diffuses out of the concrete
Exterior shrinks more than the interior
Tensile stresses in the outer layer of concrete
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
26
13
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Shrinkage
Shrinkage Strain
Time Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Shrinkage
When not adequately controlled, can cause:
Unsightly or harmful cracks
Large and harmful stresses
Partial loss of initial prestress
Reinforcement restrains the development of shrinkage.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
28
14
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Creep Load removed
Strain
Load applied Elastic recovery Creep strain
Elastic strain
Creep recovery
Permanent Deformation
Time Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
29
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Creep: Creep strains can lead to:
Increase in deflections with time
Redistribution of stresses
Decrease in prestressing forces
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
30
15
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Thermal Expansion or Contraction
Expansion or contraction due to change in temperature
Coefficient of Thermal Expansion or Contraction
Prof. Dr. Qaisar Ali
Affected by:
Composition of the concrete
Moisture content of the concrete
Age of the concrete
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Thermal Expansion
Coefficient of Thermal Expansion or Contraction
Normal weight concrete
Siliceous aggregate: 5 to 7 x 10-6 strain/F
Limestone/calcareous aggregate: 3.5 to 7 x 10-6 strain/F
Lightweight concrete
Prof. Dr. Qaisar Ali
3.6 to 6.2 x 10-6 strain/F
For calculation purposes, a value of 5.5 x 10-6 strain/F is satisfactory
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
32
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Factors Affecting Concrete Strength
In addition to mixing, conveying, placing and compaction, the strength of concrete primarily depends on:
Water Cement Ratio:
Decrease in water cement ratio increases the
strength.
Aggregate Cement Ratio:
Decrease in aggregate cement ratio
increases the strength up to a value of around 2.0. Further decrease may cause decrease in strength.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
33
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Factors Affecting Concrete Strength
Aggregate:
The concrete strength is affected by the aggregate strength,
its surface texture, its grading and to lesser extent, by the maximum size of the aggregate.
Curing: Prolonged
Prof. Dr. Qaisar Ali
moist curing leads to the highest concrete strength
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Rate of Strength Gain
ACI Committee 209 [3-21] has proposed the following equation to represent the rate of strength gain for concrete made from Type 1 cement and moist-cured at 70°F.
f ’c(t) = f ’c(28) {t/(4 + 0.85t)}
Prof. Dr. Qaisar Ali
Where f ’c(t) = is the compressive strength at age t in days.
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
35
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Properties of Concrete Rate of Strength Gain and Cement Types
Figure shows the effect of type of cement on strength gain of concrete (moist cured; w/c = 0.49).
I = Normal II = Modified III = High early strength IV = Low heat V = Sulfate resisting
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
36
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Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
High Strength Concrete Introduction
Concretes with strengths in excess of 6000 psi are referred to as high strength concrete.
The resulting concrete has a low void ratio.
Only the amount of water needed to hydrate the cement in the mix is provided.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
37
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
High Strength Concrete Shrinkage and Creep
Shrinkage of concrete is approximately proportional to the percentage of water by volume in the concrete. Highstrength concrete has a higher paste content, but the paste has a lower water cement ratio. As a result, the shrinkage of high-strength concrete is about the same as that of normal concrete.
Test data suggest that the creep coefficient for high strength concrete is considerably less than that for normal concrete.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
38
19
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
High Strength Concrete UET Lab Results for Producing High Strength Concrete
Mix design results for 6000 and 8000 psi concrete. Table-A
Trial Test
Proportion
No. of cylinders
Date of preparation
Date of Testing
Slump (in)
Avg. Strength (psi)
6000 psi
(1:1:2) w/c (0.36)
6
25/6/2010
22/7/2010
2.5
6100
8000 psi
(1:0.8:1.5) w/c (0.31)
6
28/6/2010
25/7/2010
2
8000
Admixture used: Sikament 520BA
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
39
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Durability of Concrete Three most common durability problems in concrete are:
Corrosion of steel in concrete.
Breakdown of the structure of concrete due to freezing and thawing.
Breakdown of the structure of concrete due to chemical action.
Prof. Dr. Qaisar Ali
CE 5115 Advance Design of Reinforced Concrete Structures
Fall 2011
40
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