Portland Cement Concrete
-
Upload
abbasabbasi -
Category
Documents
-
view
36 -
download
5
description
Transcript of Portland Cement Concrete
1
CE 2512 Materials for Civil EngineeringCE 2512 Materials for Civil Engineering
Properties of ConcreteProperties of Concrete
Crushed Stone Crushed Stone or Gravelor Gravel
SandSand WaterWater PortlandPortlandCementCement
Concrete Basics - Materials
2
Concrete Basics - Materials
Supplementary Cementing Materials
• Fly ash• Slag• Silica Fume• Natural Pozzolans
Chemical Admixtures
• Air entrainment• Water reducers• Set modifying• Corrosion inhibitors• Shrinkage reducers• Wide range of others
Concrete Basics - Materials
• Steel• Polypropylene• Nylon• Glass• Carbon
Fibers
Not covered in CE 2512
3
Concrete Basics - Materials
Hydration
Abrams’ LawFor given materials the strength of the concrete (so long as we have a plastic mix) depends solely on the relative quantity of water compared with the cement, regardless of mix or size and grading of aggregate.
Duff A. Abrams, 1918
Concrete Basics - Materials
strength = f (W/C)
where: W = mass of water, C = mass of cement
strength = f (W/CM)
where: W = mass of water, C = mass of cementing materials
4
W/CM = 0.61 by massW/CM = 0.33 by mass
Volume of Water
Volume of Cement= 1 Volume of Water
Volume of Cement= 2
Concrete Basics - Materials
Original water-filled spaces: “Capillary Porosity”
Low W/CM:• Low capillary porosity• Small pores poorly connected• Low permeability• High strength
High W/CM:• High capillary porosity• Large pores - well connected• High permeability• Low strength
5
Concrete Basics - Materials
Reducing the water content and W/CM of concrete leads to:
• Increased strength and stiffness• Reduced creep• Reduced shrinkage• Lower permeability• Increased resistance to weathering• Better bond between concrete and reinforcement
Less Water Better Concrete
Provided the concrete can be consolidated properly!
Concrete Basics – Essentials of Quality Concrete
The performance of concrete depends on:
• Suitable materials
• Mixture proportions
• Mixing and transporting
• Placing and consolidation
• Finishing & jointing
• Curing
• Workmanship
• Environment
6
Properties of Fresh Concrete – Freshly Mixed Concrete
Requirements of fresh concrete:
• Easily mixed and transported• Uniform throughout a given batch (and between
batches)• Flow properties such that it is capable of completely
filling the forms• Ability to be compacted fully without an excessive
amount of energy being applied• Must not segregate during transportation, placing
and consolidation• Capable of being finished properly (either against
the forms of means of trowelling or other surface treatment)
Mindess et al, 2003
7
Properties of Fresh Concrete - Workability
that property of freshly mixed concrete or mortar that determines the ease with which it can be mixed, placed, consolidated, and finished to a homogenous condition.
Workability
the relative mobility or ability of freshly mixed concrete or mortar to flow; the usual measurement is slump for concrete …
Consistency
ACI 116R-00 Cement and Concrete Terminology
Properties of Fresh Concrete - Workability
Factors affecting slump:• Water content• Cement type• SCM’s (especially fly ash or silica fume)• Chemical admixtures (water reducers,
plasticizers and air entrainers)• Temperature• Haul time• Mixing time
8
Properties of Fresh Concrete – Setting & Hardening
Time
Rig
idity
Limits of handling
Beginning ofmechanical strength
InitialSet
FinalSet
Transition(Setting) Rigid
Final setInitial setAddition of water
Dormant Period Setting Hardening
Young et al, 1998
Properties of Fresh Concrete – Setting & Hardening
C-S-H bridging the gap between cement grainsRigid structure develops
Photomicrograph courtesy of Lafarge
9
Properties of Fresh Concrete – Setting & Hardening
The setting time of concrete is influenced by:
• Type and quantity of cement
• Supplementary cementing materials
• Chemical admixtures (retarders & accelerators)
• W/CM
• Temperature
Properties of Fresh Concrete – Testing
• Slump
• Temperature
• Air content
• Unit weight & yield
• Making samples for strength tests
• Uniformity
Tests on fresh concrete
10
Properties of Hardened Concrete – Strength Development
Compressive Strength ofCompressive Strength ofHardened ConcreteHardened Concrete
The compressive strength is the most commonly-used measure of concrete quality and is used in:
• design calculations
• specification
• quality control
the maximum resistance of a (cylindrical) specimen to axial loading
Strength = Max loadArea
0
10
20
30
40
Age (days)
Stre
ngth
(MPa
)
1 3 14 28
Strength Development of Concrete
Concrete will continue to gain strength as long as:
• some unhydrated cement remains
• concrete remains moist (relative humidity > 80%)
• Temperature is above freezing
• The 28-day strength is usually used to characterize a particular concrete mix
35MPa (5000 psi)
Properties of Hardened Concrete – Strength Development
7
6000
4000
2000
0
Strength (psi)
11
0
10
20
30
40
Age (days)
Stre
ngth
(MPa
)
23C40C15C5C
1 3 14 28
Strength Development of Concrete – Effect of Temperature
Properties of Hardened Concrete – Strength Development
7
6000
4000
2000
0
Strength (psi)
Increased Temperature
Increased Rateof Hydration
Increased Strengthat Early Age
But decreasedLong-term strength
0
10
20
30
40
Age (days)
Stre
ngth
(MPa
)
Continuous 7 days 3 days 1 day
1 3 14 28
Strength Development of Concrete – Effect of Curing
Properties of Hardened Concrete – Strength Development
7
6000
4000
2000
0
Strength (psi)
MoistCuringPeriod
10028
897
713
491
28-day strength (% of concrete
cured for 28 days)
Moist curing period
100 x 200 mm (4 x 8 in.) concrete cylinders
12
0
20
40
60
80
100
0
4000
8000
12000
3d 7d 28d 3m 1y 3y 10y20y5y
W/CM = 0.40W/CM = 0.53W/CM = 0.71
Stre
ngth
(MP
a)
Strength (psi)
Age at TestKosmatka et al. 2002
Strength Development of Concrete – Outdoor Exposure
Properties of Hardened Concrete – Strength Development
• 150-mm (6-in.) Cubes
• Type I Cement
• Outdoor exposure in Skokie, Illinois
Exposed concrete will continue to gain strength when the exposure conditions (temperature, moisture availability) are suitable for cement hydration
Strength Development of Concrete – Indoor Exposure
Properties of Hardened Concrete – Strength Development
0
20
40
60
80
850 daysnatural drying
114 daysnatural drying
150-mm (6-in.) Thick Concrete Wall
Rel
ativ
e H
umid
ity o
f Con
cret
e (%
)
Ambient Air= 35% RH
10028 daysnatural drying
13
Properties of Hardened Concrete – Strength Development
Compressive strength of concrete with a given composition is dependent on:
• Age of the concrete at the time of test• Extent of moist-curing• Curing temperature
Standard-cured, 28-day compressive strength of concreteindicates that the strength test was carried out on a specimen which was:
• 28 days old at the time of test• Cured in a fog room (100% RH) or in limewater• Cured at a temperature of 23oC (70oF)
Properties of Hardened Concrete – Strength Development
0
20
40
60
80
0
2000
4000
6000
8000
10000
0.25 0.35 0.45 0.55 0.65 0.75 0.85
Com
pres
sive
Stre
ngth
(MP
a) Com
pressive Strength (psi)
W/CM
• 28-day strength
• Moist-cured cylinders
• Non-air-entrained concrete
• Portland cement only
• Over 100 mixtures (1985 to 1999)
14
Properties of Hardened Concrete – Strength Development
Factors affecting 28-day standard-cured compressive strength:
• W/CM
• Type of portland cement
• Type and amount of SCM
• Air content (~ 5.5% reduction for each 1% air)
• Aggregate strength (in high-strength concrete)
General use concrete: 20 to 40 MPa (3000 to 6000 psi)
Special applications: 70 to 140 MPa (10,000 to 20,000 psi) can be achieved
• Strength usually specified at 28 days and w/cm selected to provide the required strength
• However, strength may be specified at any other age such as at 7 days for loading or 1 day for form removal
• In such cases, relationships between strength and w/cm have to be developed for these ages
15
• When different cementing materials are used the relationships between w/cm, age and strength change
• For example, if 25% fly ash is introduced into a mix – the w/cm will have to be reduced by a small amount to main the same 28-day strength and by a larger amount to maintain the same 3-day strength
• w/cm can be reduced by reducing water content (use of fly ash, water-reducing admixture) or increasing cementitious material content, or both (see example below)
90 days
28 days
3 days25% Fly ash
100% Portlandcement
303028-day strength (MPa)
0.500.60W/CM
160180Water (kg/m3)
800Fly Ash (kg/m3)
240300Portland cement (kg/m3)
Mix BMix A
Tensile Strength of ConcreteTensile Strength of Concrete
Tensile strength of concrete is very difficult to measure directly. It is usually determined indirectly using either:
• Flexural test
• Cylinder splitting
(Indirect tensile test)
16
2P
2P
3L
3L
3L
2bdPLR =
R = flexural strength (MPa)P = maximum load applied (N)L = span length (mm)b = width of specimen (mm)d = depth of specimen (mm)
Flexural StrengthFlexural Strength(Modulus of Rupture)(Modulus of Rupture)
nct fkf ⋅=
A number of empirical formulae for predicting the tensile strength (ft) from the compressive strength (fc) have been developed; many of these are of the type:
The direction of crack propagation in uniaxial tension is perpendicular to the stress direction.
The initiation & growth of each new crack reduces the load carrying area.
c
tf
f = 0.07 to 0.11Typically
17
LdPT
π2
=
T = tensile strength (MPa)P = load at failure (N)L = length of specimen (mm)d = diameter of specimen (mm)
For design purposes, the secant modulus at 40% of the strength of the concrete is usually used
σ = 0.40 fc’
E - secant modulus
1
18
LVD
T
LVD
T
P
PBottom ring firmly fixed(no rotation permitted)
Top ring pivoted(rotation permitted)
The deflection measured by the LVDT is twice the deformation of the sample
150
mm
LVD
T
LVD
T
P
PBottom ring firmly fixed(no rotation permitted)
Top ring pivoted(rotation permitted)
The deflection measured by the LVDT is twice the deformation of the sample
150
mm
CE2512 Concrete Lab 2 - Testing
The load (in Newtons) and the displacement of the LVDT (in mm) will be collected by datalogger and emailed to you in a spreadsheet. You will have to convert load to stress (MPa) and displacement to strain (mm/mm) in order to calculate the modulus
Properties of Hardened Concrete – Strength Development
Other mechanical properties
Flexural strength(Modulus of Rupture)
= 0.7 to 0.8 x √(compressive strength, MPa)
= 7.5 to 10 x √(compressive strength, psi)
Direct tensile strength= 0.4 to 0.7 x √(compressive strength, MPa)
= 5 to 7.5 x √(compressive strength, psi)
Splitting tensile strength = 8% to 14% of compressive strength
Modulus of elasticity= 5000 x √(compressive strength, MPa)
= 57000 x √(compressive strength, psi)
19
Poisson’s ratio, μ, may vary from 0.15 to 0.25 depending on strength, aggregate, moisture content, and concrete age
Properties of Hardened Concrete – Volume Stability & Crack Control
Hardened concrete changes volume due to changes in:
• Temperature
• Moisture
• Stress
Length/volume changes ~ 0.01% to 0.1 % (or 100 to 1000 microstrain)
20
Properties of Hardened Concrete – Volume Stability & Crack Control
CreepStrain
Elastic strain
Elasticrecovery
Creeprecovery
Irreversiblecreep
0
20
400
600
800
1000
0 20 40 60 80 100 120
Mic
rost
rain
Time after loading (days)
After Mindess et al, 2003 Load applied
Load removed
Creep
Properties of Hardened Concrete – Volume Stability & Crack Control
Initial state
Cracking Due to Volume Change
Reduction in temperature and moisture
Unrestrained drying andthermal shrinkage
If unrestrained concrete shrinks due to loss of moisture or cooling
If restrained tensile stresses develop in the concreteTensile stresses
If tensile stresses exceed tensile strength – concrete cracks
21
Properties of Hardened Concrete – Volume Stability & Crack Control
Cracking Due to Volume Change
External restraint
Surface cools (or dries) more rapidly than bulk
Internal restraint
Properties of Hardened Concrete – Volume Stability & Crack Control
Cracking Due to Volume Change
22
Properties of Hardened Concrete – Volume Stability & Crack Control
Measures to reduce thermal cracking
• Minimize temperature rise above ambient• Lower cement content• Use low-heat Type IV cement• Use pozzolans or slag• Lower concrete placing temperature• Use embedded cooling pipes
• Minimize thermal gradient in concrete
Properties of Hardened Concrete – Volume Stability & Crack Control
Measures to reduce drying shrinkage
• Reduce the water content of the mixture
• Minimize paste content
• Increase the aggregate content• Use as large as practical
maximum aggregate size• Optimize grading
• Increase moist curing period
• Shrinkage-reducing admixtures
• Shrinkage-compensating cement
• Steel fibres
0
400
800
1200
150 200 250
250 300 350 400 450Water Content (lb/yd3)
Water Content (kg/m3)
Dry
ing
Shr
inka
ge (m
illio
nths
)
23
Properties of Hardened Concrete – Volume Stability & Crack Control
Crack Control
Reinforcing steel
Isolation joints
Contraction joints
Construction joints
to reduce crack widths
to control the location of cracks
Properties of Hardened Concrete – Volume Stability & Crack Control
Isolation joint • Isolate adjoining parts of a structure• Permit differential movements
24
Properties of Hardened Concrete – Volume Stability & Crack Control
Contraction joints(Control joints)
• Provide for movement within a slab or wall• Cracks induced at predetermined locations
Properties of Hardened Concrete – Volume Stability & Crack Control
Contraction joints(Control joints)
• Provide for movement within a slab or wall• Cracks induced at predetermined locations
25
Properties of Hardened Concrete – Volume Stability & Crack Control
Contraction joints(Control joints)
• Provide for movement within a slab or wall• Cracks induced at predetermined locations
Slab
Wall
Seal outside with joint sealerif leakage is anticipated
26
Properties of Hardened Concrete – Volume Stability & Crack Control
Construction joint
• Stopping place during the construction process (e.g. end of the day’s work)
• A true construction joint should bond new concrete to existing concrete and permit no movement. Deformed tie bars are often used to restrict movement
• However – construction joints are often designed and built to operate as contraction or isolation joints
Spacing of Contraction Joints in Meters
7.56.0250
6.755.5225
6.05.0200
5.254.25175
4.53.75150
3.753.0125
3.02.4100
Maximum-size aggregate ≥ 19 mm
Maximum-size aggregate < 19 mm
Slab thickness, mm
MetricMetric
27
1084
2520102318920168181471512613105
Maximum-size aggregate ≥ ¾ inch
Maximum-size aggregate < ¾ inch
Slab thickness, in.
InchInch--PoundPound
2 feet spacing for each inch of slab thickness
2½ feet spacing for each inch of slab thickness(round up to nearest
whole foot)
Spacing of Contraction Joints in Feet
Properties of Hardened Concrete – Permeability & Watertightness
Watertightness the ability of concrete to hold back or retain water without visible leakage
Permeability amount of water migration through concrete when the water is under pressure or the ability of concrete to resist penetration by water or other substances (liquids, gas, ions, etc
28
Outflow
= Q
Hydrostaticpressure, h l
X-sectionarea = A
hl
AQk ⋅=Coefficient of permeability,
Properties of Hardened Concrete – Permeability & Watertightness
Factors Affecting Permeability of Concrete
Principal Factors
Water/cementitious material
Water Content
Curing
Age
Use of SCM’s• Silica fume• Fly ash• Slag• Natural pozzolans
Secondary Factors
Cement factor
Chemical admixtures
Aggregate type
Air content
29
Permeability does not go to zero – but very small value
Fig 7.28 in M&Z, 2006Fig 7.28 in M&Z, 2006
0.1
1
10
100
1000
0.2 0.3 0.4 0.5 0.6 0.7W/CM
Perm
eabi
lity,
x 1
0-14 m
/s
More appropriate to plot on semi-log scale
W/CM
Fig 7.28 in M&Z, 2006Fig 7.28 in M&Z, 2006
W/CM
Reduce W/CM0.70 → 0.40
Almost double strength
Reduce W/CM0.70 → 0.40
Red
uce
perm
eabi
lity
by 1
00 ti
mes
Compare with Strength
30
Properties of Hardened Concrete – Permeability & Watertightness
Effect of SCM’s
• Fly ash
• Slag
• Silica fume
• Natural pozzolans (e.g. metakaolin)
Permeability reductions of 10 Xor more are possible if concrete is properly proportioned and adequately cured
Properties of Hardened Concrete – Durability
• Cyclic freezing and thawing• Deicer salt scaling• Corrosion of reinforcing steel• Alkali-silica reaction• Sulfate attack• Abrasion• Others
Causes of deterioration:
31
Properties of Hardened Concrete – Durability
• Cyclic freezing and thawing• Deicer salt scaling• Corrosion of reinforcing steel• Alkali-silica reaction• Sulfate attack• Abrasion• Others
Causes of deterioration:
Low Permeability Durability
Involve movement of water(or transport of species in water)
Properties of Hardened Concrete – Durability
Freezing and Thawing of Concrete
32
Properties of Hardened Concrete – Durability
Freezing and Thawing of Concrete
Properties of Hardened Concrete – Durability
Freezing and Thawing of Concrete
Concrete blocks on PCA outdoor test plot after 40 years exposure
(355 kg/m3 cement)
Non-air-entrained concrete Air-entrained concrete
33
Properties of Hardened Concrete – Durability
Freezing and Thawing of Concrete
0
1000
2000
3000
4000
5000
6000
0.3 0.4 0.5 0.6 0.7 0.8 0.9
W/CM
Num
ber o
f Fre
eze-
Thaw
Cyc
les
to 2
5% L
oss
in M
ass Air-entrained
concrete
Non-air-entrainedconcrete
Fog cured 14 daysDried 76 days at 50% RH
Properties of Hardened Concrete – Durability
Freezing and Thawing of Concrete – Deicer Salt Scaling
34
Properties of Hardened Concrete – Durability
Freezing and Thawing of Concrete – ‘D-Cracking’
• The aggregate is frost-resistant
• Sufficient strength is attained prior to first freezing (> 3.5 MPa or 500 psi)
• Sufficient strength is attained prior to cyclic freezing & thawing (> 28 MPa or 4000 psi)
• Adequate Air Void System
Properties of Hardened Concrete – Durability
Freezing and Thawing of Concrete
General criteria for resistance to freezing and thawing
35
Properties of Hardened Concrete – Durability
Corrosion of Reinforcing Steel
Protective (passive) layer
Concrete pore solution: pH > 13
Chloride IonsCarbonation
Breakdown of passive layer
Properties of Hardened Concrete – Durability
Protective (passive) layer
Concrete pore solution: pH > 13
Cl ClChloride ions from:
• Deicing salt• Seawater• Groundwater
Corrosion of Reinforcing Steel – Action of Chlorides
36
Properties of Hardened Concrete – Durability
# 1 cause of concrete deterioration
Corrosion of Reinforcing Steel – Action of Chlorides
Corrosion of Reinforcing Steel – High-Performance Concrete
Low-permeabilityconcrete
NaOHsolution
NaClsolution
60VA
NaOHsolution
NaClsolution
60VA
ASTM C 1202 – “Rapid Chloride Permeability Test”
Apply 60 V across a 100-mm diameter x 50-mm thick concrete sample
Measure total electrical charge passed (in Coulombs) over a 6-hour period
37
Data from Ozyildirim, 1998
0
1000
2000
3000
4000
5000
6000
0 120 240 360Age (Days)
RC
PT (C
oulo
mbs
)
Negligible< 100
Very low100 – 1000
Low1000 – 2000
Moderate2000 – 4000
High> 4000
Chloride Ion Penetrability
Coulombs Passed
Control (no SCM)
20% Fly Ash7% Silica Fume
Fly Ash, slag & most pozzolansLittle effect at early age (e.g. 28 days)Reduction becomes more significant with ageSubstantial reduction at later age
Silica fume, metakaolin (highly reactive pozzolans)
Significant reduction at early age (e.g. 28 days)Smaller decreases with age
SCM Effect on Chloride Permeability
W/CM = 0.38-0.40
SCM & Chloride Permeability
What does the “Rapid Chloride Permeability Test” really measure?
• The RCPT measures electrical conductivity – which is a measures of the ease with which electrical charge can pass through a material.
• Electrical conductivity is the reciprocal of electrical resistivity – concrete with a low electrical conductivity has a high electrical resistivity
• Electrical charge passes through the pore structure of the concrete (the solid phases have a high electrical resistance) – as do chloride ions and water.
• High w/cm concrete with an open and well-connected pore structure will be permeable to water and chloride ions, and have a high electrical conductivity and low electrical resistance
• Low w/cm concrete that contains SCM’s will have a more refined pore structure (small and poorly connected pores) and will have low permeability to water and a high resistance to chloride ion penetration. It will also have a low electrical conductivity and high electrical resistivity
• Thus – electrical conductivity or resistivity – provides an indirect but reasonable indication of the permeability of concrete and its resistance to the ingress of deleterious species such as chlorides
• Care must be taken to ensure that concrete is saturated when its electrical properties are measured as dry concrete (with empty pores) has a very high electrical resistant no matter how open and well connected its pores are.
38
Corrosion of Reinforcing Steel – Carbonation
pH reduced (colourless)Ca(OH)2 + CO2 →CaCO3 + H2OSteel corrodes
Original high pH maintained (purple)Steel in pristine condition
Properties of Hardened Concrete – Durability
Corrosion of Reinforcing Steel – Carbonation
Problems occur when:
• High W/CM
• Poor curing
• Inadequate cover
• High levels of SCM
• Outdoor-sheltered exposure
39
Properties of Hardened Concrete – Durability
Alkali-Silica Reaction (ASR)
• Effects all types of exposed concrete structures
• Has occurred in most, if not all, states of U.S.A. and provinces of Canada
(CSA A864-00)
Occurrences of ASR in CanadaOccurrences of ASR in Canada
Fredericton?
40
Properties of Hardened Concrete – Durability
Alkali-Silica Reaction (ASR)
Cement paste
Reactive chertAlkali-silica gel
Crack
Crack
Microscopic thin section through ASR-affected concrete
Properties of Hardened Concrete – Durability
Alkali-Silica Reaction (ASR)
Preventive Measures for ASR
Use of non-reactive aggregate
41
Use a NonUse a Non--Reactive Aggregate?Reactive Aggregate?
Mactaquac Dam, NB
Aggregate passed criteria for “non-reactivity” that existed at the time of construction
Millions of $$$’s currently being spent trying to deal with ASR problems
Properties of Hardened Concrete – Durability
Alkali-Silica Reaction (ASR)
Preventive Measures for ASR
Use of non-reactive aggregate
Limit alkali content of concrete
1.8 – 3.0 kg/m3 Na2Oe
3.0 – 5.0 lb/yd3 Na2OeTypical values use in specifications
0
0.1
0.2
0.3
0.4
0.5
1.0 2.0 3.0 4.0 5.0 6.0
Alkali Content of Concrete (kg/m3 Na2Oe)
Expa
nsio
n at
2 Y
ears
(%)
CSA Limit
42
Concrete alkali content < 3 kg/mConcrete alkali content < 3 kg/m33 NaNa22OeOe
Concrete alkali content < 2 kg/mConcrete alkali content < 2 kg/m33 NaNa22OeOe Concrete alkali content < 2 kg/mConcrete alkali content < 2 kg/m33 NaNa22OeOe
Examples of ASR in concrete structures with a low alkali content
Properties of Hardened Concrete – Durability
Alkali-Silica Reaction (ASR)
Preventive Measures for ASR
Use of non-reactive aggregate
Limit alkali content of concrete
Use of SCM’s
Concrete without fly ash Concrete with 25% fly ash
43
ASR-Affected Hydraulic Structures, Ontario
A number of dams and associated structures affected by ASR with greywacke/argillite aggregate from Huronian Supergroup
Ontario
Lake Superior
LakeHuron
Lady Evelyn Dam
Diagnosed as ASR in 1965
Demolished and replaced in 1973
ASR-Affected Hydraulic Structures, Ontario
A number of dams and associated structures affected by ASR with greywacke/argillite aggregate from Huronian Supergroup
Ontario
Lake Superior
LakeHuron
Site of Lower Notch Dam
Dam completed in 1969 with known reactive aggregate from the same geological formation
44
0.00
0.02
0.04
0.06
0 1 2 3
Age (Years)
Exp
ansi
on (%
) High-Alkali Cement
High-Alkali Cement+ Fly Ash
Low-Alkali Cement
Lower Notch Dam, Ontario
After testing the aggregate it was decided that the dam would be built using high-alkali cement (1.08% Na2Oe) and a Class F fly ash
– 20% in structural concrete and 30% in mass concrete
Properties of Hardened Concrete – Durability
Alkali-Silica Reaction (ASR)
Preventive Measures for ASR
Use of non-reactive aggregate
Limit alkali content of concrete
Use of SCM’s
Use of chemical admixtures
Concrete without lithium Concrete with LiOH
Long-term effectiveness not yet established
Indications that lithium is not effective with all reactive aggregate types
45
Properties of Hardened Concrete – Durability
Sulfate Attack
The resistance of concrete to sulfate attack can be improved by:
• Use of low-C3A cement with:moderate sulfate resistance (Type II)high sulfate resistance (Type V)
Type I - 14.1% C3A Type V - 1.2% C3A
Courtesy of BRE
Properties of Hardened Concrete – Durability
Sulfate Attack
46
The resistance of concrete to sulfate attack can be improved by:
• Use of low-C3A cement with:moderate sulfate resistance (Type II)high sulfate resistance (Type V)
• Use of low W/CM (to reduce permeability)
Type V Cement: W/C = 0.65 Type V Cement: W/C = 0.38
Properties of Hardened Concrete – Durability
Sulfate Attack
The resistance of concrete to sulfate attack can be improved by:
• Use of portland cement with low-C3A content:moderate sulfate resistance (Type II)high sulfate resistance (Type V)
• Use of low W/CM (to reduce permeability)
• Use of some supplementary cementing materials
Type I - 14.1% C3A Courtesy of BREType I + Fly Ash
Properties of Hardened Concrete – Durability
Sulfate Attack
47
Properties of Hardened Concrete – Durability
Other Forms of Deterioration
• Thaumasite form of sulfate attack (TSA)
• Delayed ettringite formation (DEF)
• Salt crystallization
• Alkali-carbonate reaction (ACR)
• Chemical attack
TheThe EndEnd