CEMENT 070900vieira.ppt

Concrete Durability - Definition and Requirements
Course for Cement Applications
Silvia Vieira
HGRS/PID

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04.09.2022/SVI
© Holcim Group Support Ltd 2008 Concrete Durability/CCA
Learning Objectives
 To understand what concrete durability means
 To understand what are the factors that influence
concrete durability
 To understand how to improve concrete durability
 To know and understand the standards requirements
related to durability

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Concrete Durability
 Concrete durability can be defined as its capability to
resist to weathering, chemical attacks, abrasion or other
deterioration processes (carbonation, alkali aggregate
reaction, attack by chloride, sulphate, acids, etc).
 These processes lead to the decomposition of hydrated
compounds of cement paste and/or cracks

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Concrete Durability in Numbers
 In United Kingdom approximately 40% of the amount
of resources invested in civil construction goes to repair
and maintenance (Neville 1997)
 In Europe the expenses with repair of bridges
increased, approximately, 65% between 1985 and 1990

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Concrete Durability in Numbers
 According to the Federal Highway Administration (USA)
42% of the 575.600 American bridges can be consider
unsafe or structurally deficient because corrosion
 In the USA, from 1981 and 2000, approximately 102 billion
US$ were applied in repair of these bridges. One estimates
that 1 billion US$ could be saved only by improving
concrete quality

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Concrete Durability
Application and curing
Cement, aggregates, water
DURABILITY
Mix design
Structural design and specification

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Choosing the Right Cement
 There are different types of Portland cement in the
market
 Each one is appropriate for a specific application
 Composite cements normally result in more durable
products
 But the quality of cement is not enough to assure
concrete performance!

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Evolution of Cement Performance vs Concrete
Performance
 Improvement on cement quality and performance, has
resulted in decrease of concrete quality. Why?!
 Because now, to obtain a concrete with the same
strength level as 30 years ago, is possible to use higher
w/c and lower cement content
 In England, in the 40’s, a concrete with 30MPa (28 days)
required w/c = 0.47 and cement content = 300kg/m3
 In the 70’s, the same concrete required w/c = 0.72 and
cement content = 250kg/m3
To guarantee the durability of concrete is necessary to work
with adequate cement content and w/c ratio

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Looking Deeply into Concrete
Aggregate Void of entrained air Void of excess of water
Concrete under optical microscope. Magnification 25x

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Concrete under optical microscope. Magnification 25x
aggregate
Void of entrained air

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Concrete under scanning
electron microscope
m
aggregate
paste
m
aggregate
paste
w/c = 0.50
w/c = 0.30

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Influence of W/C Ratio on Concrete Properties
W/C Ratio
Permeability
Strength
Durability

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Chosen the Right w/c Ratio
 Studies show that capillary porous start to be connected
when w/c is higher than 0.40
 When w/c is higher than 0.70,
all capillary porous are connected
 Based on this:
 Standards tend to establish 0.70 as the maximum value for
w/c ratio
 Higher is the aggressiveness of the environment lower
should be the w/c ratio
 For concrete exposed to a very aggressive environment the
w/c should be lower that 0.40

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Relationship Between w/c and Permeability
0
20
40
60
80
100
120
140
0.2 0.3 0.4 0.5 0.6 0.7 0.8
Water/Cement Ratio
Coeficient
of
Permeability
(-10
-14
m/s)
After Neville (1995) Properties of Concrete

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Trends in Standards Regarding Durability
 European standard EN 206-1:2000 Part 1: Specification,
performance, production and conformity(*)
 Defines exposure classes related to environmental
aggressiveness
 Recommends limits for maximum w/c and minimum
cement content for concretes, according to its exposure
conditions
(*) Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany,
Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway,
Portugal, Spain, Sweden, Switzerland and United Kingdom

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EN 206-1:2000 Part 1: Specification, performance,
production and conformity
EXPOSURE CLASSES
Chloride-induced
corrosion
Carbonation-
induced
corrosion Sea water Chloride
other than
from sea
water
Freeze-
thaw
attack
Aggressive
chemical
environment
XC1 XC4 XS1 XS3 XD1 XD3 XF1 XF4 XA1 XA3
Maximum w/c 0.65 0.50 0.50 0.45 0.55 0.45 0.55 0.45 0.55 0.45
Minimum cement
content (kg/m3
)
260 300 300 340 300 320 300 340 300 360
XC1: dry or permanently wet environment: concrete inside buildings with low
air humidity and concrete permanently submerged in water
XC4: cyclic wet and dry environment: concrete surfaces subject to water
contact
XA3: highly aggressive chemical environment. For example, concrete subject
to pH between 4 and 4.5

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EN 206-1:2000 Part 1: Specification, performance,
production and conformity
 Cement consumption:
  260kg/m3 for concretes exposed to environment with low
degree of aggressiveness
  360kg/m3 for concretes exposed to highly aggressive
environments
 Water/cement ratio
  0.45 for concretes exposed to highly aggressive
environments
  0.65 for concretes exposed to environment with low
degree of aggressiveness

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ACI 318-2008 - Building code requirements of reinforced
concrete
Category Class Condition
F
Freezing and
Thawing
F0 Concrete not exposed to freezing-thawing
F1 Concrete exposed to freezing-thawing cycles and occasional exposure to moisture
F2 Concrete exposed to freezing-thawing cycles and in continuous contact with moisture
F3 Concrete exposed to freezing-thawing cycles and in continuous contact with moisture
and exposed to deicing chemicals
S sulfate Water soluble sulfate (SO4) in soil, % per
weight
Dissolved sulfate (SO4) in water, ppm
S0 SO4 < 0.10 SO4 < 150
S1 0.10 ≤ SO4 < 0.20 150 ≤ SO4 < 1500 (sea water)
S2 0.20 ≤ SO4 < 2.00 1500 ≤ SO4 < 10,000
S3 SO4 > 2.00 SO4 > 10,000
P requiring
low
permeability
P0 In contact with water where low permeability is not required
P1 In contact with water where low permeability is required
C corrosion
protection of
reinforcement
C0 Concrete dry or protected from moisture
C1 Concrete exposed to moisture but not to external source of chlorides
C2 Concrete exposed to moisture and an external source of chlorides from deicing
chemicals, salt, brackish water, sea water or spray from these sources

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ACI 318-2008 - Building code requirements of reinforced
concrete
Category Class Max w/cm Min f’c, psi
F
Freezing and
Thawing
F0 n/a 2500
F1 0.45 4500
F2 0.45 4500
F3 0.45 4500
S sulfate S0 n/a 2500
S1 0.50 4000
S2 0.45 4500
S3 0.45 4500
P requiring low
permeability
P0 n/a 2500
P1 0.50 4000
C corrosion
protection of
reinforcement
C0 n/a 2500
C1 n/a 2500
C2 0.40 5000
Minimum cement content is not defined!

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Influence of Cement Type, w/c Ratio and Cement Content
on Concrete Carbonation Depth
0
5
10
15
20
25
Carbonation
Depth
(mm)
0,45/300 0,45/350 0,65/200 0,65/250 0,65/300 0,65/350
w/c ratio
Slag cement
OPC

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Curing
 Curing is important for concrete durability.
 Adequate curing:
 Increases concrete strength:
- Strength at 14 days of a cured concrete is 2.5 times higher than
the strength of the same concrete non-cured
 Reduces fissures due to shrinkage

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Curing
 Adequate curing:
 Reduces carbonation depth:
0
1
2
3
4
5
6
7
8
9
10
35 40 45 50 55 60
Compressive Strength (MPa)
Carbonation
Depth
(mm)
water curing
without curing

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Concrete Protection for Reinforcement
 ACI 318-2002 - Building code requirements of
reinforced concrete define minimum concrete cover for
reinforcement:
 For concrete permanently exposed to earth: 7.5cm
 For concrete not exposed to weather: 1.25cm

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Summary
 Basically, concrete quality depends on:
 Aggregate quality
 Water quality
 Use of the right cement
 Right structural design and specification
 Right mix design  minimum cement content
maximum water/cement ratio
 Correct application
 Adequate cure

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