2022-10-21 Chloride ion migration in capillar-porous system of marine concrete 100

Chloride ion transport in capillarporous system of marine concrete
Lev V. Kim
assoc. professor, PhD,
Polytechnic Inst., Dept Marine Arctic Technologies
Advisor Russian Academy of Architecture and Constr. Sc. (RAACS),
Member of RAACS Scientific Council of destruction concrete and other
building materials
Vladivostok 2022
INTRODUCTION
2
ARCTIC CHALLENGIES
(source: Guidance for offshore operation in the Barents Sea – JIP “Barents-2020”)
• Low temperatures
• Working Environment
• Cold Flow
• Selection of materials
• Ice
• Sea ice and ice loads
• Icebergs and Ice management
• Icing
• Darkness
• Working environment
• Rescue
• Remoteness
• Emergency preparedness
• Transportation of personnel and equipment
• Vulnerable Environment
3
The Sea of Okhotsk
4
Far Eastern Federal district of Russia
Deterioration types:
Chloride deterioration - 66 %,
Carbonation – 5 %,
Frost attack – 5 %,
Other – 24 %.
Sakhalin island climate conditions
• on the boundary of matrix
Cracks
with aggregate.
Pores in cement stone with cracks.
Table 1. Average amount of days with raining and time of humidity
Offshore zone along
eastern coast of
Sakhalin island
North-East
East
Southern-East
Days with rainfalls
hNd≥2.5 mm/year
167
147
99
Humid
period
ToW, years
0.464
0.408
0.275
Offshore and
port objects
7
Durability of concrete means ability of concrete to resist weathering
action, chemical attack, abrasion, settlement/deflection/deformation
within specified limit or any process of deterioration.
Permeability is the property that governs the rate of flow of a fluid
into a porous solid. One of the major causes is high content of
void/porosity (in cement past, aggregates, and concrete) which may lead
to earlier failure of concrete structures.
Air content in concrete shall not exceed more than 2.5 % and in
reinforced concrete, any crack of width more than 0.3 mm under loaded
conditions needs more attentions to protect from, water/acid rains
causing chemical and physical processes of degradation.
For deterioration by surface wear, abrasion by dry attrition (wear on
pavements and industrial floors by traffic) special attention shall be given
to the quality of concrete surface.
8
Testing of concrete of structures in ports
Kholmsk and Korsakov, Sakhalin, 2018
9
Reinforced concrete is widely used in the marine environment (docks
and harbours, quays, jetties, wharves, seawalls, pipelines, tunnels etc.).
External causes of deterioration:
1) physical: moisture content, temperature, freezing/thawing;
2) chemical: aggressive gases and liquids;
3) mechanical: load, friction and vibration.
It is known that the degradation process is strongly influenced by the
environmental conditions.
The rates of most deterioration processes are controlled by the
transport of particular aggressive species through the concrete cover.
Goal of work - to study the various transport
mechanisms that may take place in the
deterioration of a concrete structure.
10
1. Permeability,
capillary and pore system,
chloride ion migration,
reinforcement damage
11
Pile structure
12
Gravity structure
Concrete durability problems arise from
the aggressiveness of the environment
to which the structure is exposed.
The main reasons for such durability
problems are the interconnected porous
nature of the hydrated cement paste.
Exposure conditions in the marine environment
(BS 6349-1 Maritime Structures Part 1: Code of
Practice for General Criteria. British Standards,
London, UK, 2000)
The is no simple relationship between
strength and any of the durability
parameters.
13
14
There are 3 basic visual symptoms of distress:
•
cracking;
•
spalling;
•
disintegration.
Although each of the basic symptoms is readily differentiated from
the others, each occurs in several forms, each having a different
significance.
A great number of models describing the continuum behavior,
phase transitions in them, criteria of ice body destruction and
fragmentation under the load as well as the continual destruction
models are known.
Marine effects: aggression chloride, the transport of salt solutions,
chemical degradation, cyclic freezing-thawing, low temperature, etc.
reduce the durability.
15
The sea water have typical salt content 30-35 g/liter and the
ions present Na+, Mg+2,Cl-, and (So4)2- and also gases. They
plays an important part in the chemical and electrochemical
phenomena influencing concrete durability.
Oxygen (O2) in the air and in water, varying concentrations of
dissolved carbon dioxide (CO2) and hydrogen sulfide (H2S) may
cause lowering of the pH from its normal value 8.2-8.4 to 7 or even
less.
Acidic waters reduce the alkalinity and strength of concrete, and
enhance the electrochemical corrosion of the embedded steel.
Marine growth involving barnacles and mollusks are frequently
found on the surface of porous concrete whose alkalinity has been
greatly reduced by leaching.
16
17
Concrete fracture failure
Physical
Chemical
Impacts
Carbonation
Ice action
chlorides
Wave action
sulfates
Wave + Ice
action
Design
External causes of deterioration influencing on durability of concrete:
1) main physical factors: moisture content, temperature, freezing and
thawing;
2) main chemical factors: aggressive gases and liquids;
3) main mechanical factors: load, friction and vibration.
The phenomenon which induces such distress may be associated with
one of the phases (e.g. design, construction, operation).
There are 3 basic visual symptoms of distress:
- cracking;
- spalling;
- disintegration.
Although each of the basic symptoms is readily differentiated from the
others, each occurs in several forms, each having a different significance.
A great number of models describing the continuum behavior, phase
transitions in them, criteria of ice body destruction and fragmentation under
the load as well as the continual destruction models are known.
19
Internal factors affecting corrosion
•
Cement composition: The cement provides protection to the
reinforcing steel by maintaining a high pH.
• Impurities in aggregates: Aggregates containing chloride salts cause
serious corrosion problems, particularly those associated with seawater.
• Impurities in mixing and curing water: Mixing and curing water, either
contaminated with sufficient quantity of chloride or being highly
acidified due to any undesirable substance present in water, may
cause corrosion.
• Admixtures: Addition of calcium chloride in concrete, as a common
admixture for accelerating the hydration of cement is perhaps the most
significant reason for the presence of chloride.
• w/c ratio: Low w/c ratio decreases the concrete permeability, which in
turn reduces the chloride penetration, carbonation and oxygen
diffusion.
20
Internal factors affecting corrosion
•
Cement content have a significant effect on durability due to formation
of honeycombs and other surface defects. Its help in the penetration
and diffusion of gas.
• Aggregate size and grading: for a given w/c ratio, the coefficient of
permeability of concrete increases considerably with increasing size of
aggregates.
• Proportion of coarse and fine aggregates is important for the production of a
durable concrete.
• Construction practices: 1) aggregate washing for deleterious materials, if any;
2) control of chloride:water, cement, aggregate, and admixtures; 3) strict
enforcement of designed and recommended levels of w/c ratio, cement
content, cover thickness, etc.; 4) proper consolidation of freshly placed
concrete; 5) proper curing of concrete.
21
Internal factors affecting corrosion
• Cover over reinforcing steel: Cover depth has a significant effect in
case of corrosion due to penetration of either chloride or carbonation.
• Chemical composition and structure of the reinforcing steel: The
differences in the composition and structure create different
potentials at different locations on the surface of reinforcement,
causing the formation of differential corrosion cells.
• pH of the concrete porewater: the high alkalinity of the concrete
porewater results in a passive film on steel. The gases form a
carbonated zone, which gradually penetrates into exposed concrete,
reducing the pH.
• Carbonation is characterised by a pH up to 4 describing the real
corrosiveness of the concrete pore solution.
22
Internal factors affecting corrosion
• Cover over reinforcing steel: Cover depth has a significant effect due to
penetration of either chloride or carbonation. This effect of cover is
limited within the time of casting to the time at which the reinforcement is
depassivated and corrosion is initiated.
• Chemical composition and structure of the reinforcing steel: The
differences in the chemical composition and structure of reinforcing
steel and presence of stress in the reinforcement, either static or
cyclic, create different potentials at different locations on the
surface of reinforcement, causing the formation of differential corrosion
cells, which leads to its corrosion.
• pH of the concrete porewater: In reinforced concrete structures steel is
protected against corrosion by the high alkalinity of the concrete
porewater resulting in a passive film on steel. The agressive gases
reacts with the alkaline constituents of the cement paste to form a
carbonated zone, reducing the pH of the affected region to a value where
23
corrosion will occur.
24
2. CHLORIDE INGRESSION
25
The influence of chloride aggression on the durability of concrete
In the study of the penetration of chlorine in concrete two main steps can
be identified:
-
3 principal chloride transport models can be distinguished:
a) diffusion - movement of ions under the influence of a concentration
gradient;
b) convection - the movement of ions and fluid flow;
c) movement of ions under the influence of an external electric field.
- securing the chlorine ions in the cement stone.
Steel reinforcement in concrete is protected from corrosion passivation
thin film consisting of oxides of iron, which is formed on the surface of the
valve due to the strongly alkaline environment of concrete pore water.
Depassivation of the steel reinforcement occurs in the presence of a
particular chlorides, the so-called threshold or critical content. The negative
impact of chlorides in concrete contrasted self-healing passivation film.
The influence of chloride aggression
on the durability
The traditional assumption has been that chloride ingress into concrete obeys
Fick's 2nd law of diffusion for a semi-finite medium with constant exposure, and
that there is a critical value of the chloride content in the concrete. The aim is to
develop prediction method taking into account climatic conditions of Sakhalin.
The effect of the environment is represented in the parameter Cs in Fick’s law
which identifies the representative chloride concentration at the concrete surface
during the time of exposure. It depends on the water salinity, possibly porosity of
the surface layer (amount of saline pore water) and the length of wetting versus
drying in the splash zone.
DuraCrete model is considered only diffusion, excluding convection. The
magnitude of the convection zone is 2-10 mm, at a greater depth the main
transport mechanism is diffusion. Therefore, to assess the content of chlorides in
the reinforcement of occurrence depth (40 mm or more) can be applied DuraCrete
model.
Chloride forms in concrete
Chlorides from the environment can diffuse into concrete as a result of:
- the sea spray and seawater wetting;
- the deicing salts;
- the use of chemicals (berth, storage, brine tanks etc.)
In concrete chloride may be present in any of the following forms:
• Acid soluble chloride which is equal to the total amount of chloride present
in the concrete or that is soluble in nitric acid;
• Bound chloride which is the sum of chemically bound chloride with
hydration products of the cement, such as the C3A (tricalcium aluminate)
or C4AF (tetracalcium aluminoferrite) phases, and loosely bound chloride
with C-S-H gel;
• Free or water-soluble chloride which is the concentration of free chloride
ions Cl- within the pore solution.
28
Chloride concentration
The following equation shows the relationship between the chloride
concentrations present (HETEK-53, 1996):
cTOTAL = cFREE + cBOUND
where c is the concentration in [kg/m3], [moles/volume] or [kg/kg]. The free
chlorides are usually given per volume of solute, i.e. [kg/m3 solution]. The
bound, and total amount of chlorides, however, are often given per weight of
binder or concrete.
The chloride critical level, required for corrosion, can be defined as:
• total chloride content by weight of concrete;
• total chloride content by weight of binder;
• free (water soluble) chloride concentration in the pore solution;
• ratio between the free chloride and the free hydroxide concentration.
A value of 0.4 % by weight of cement is critical (Bamforth, 1999).
29
Chloride concentration
For given structure it depends on:
• w/c ratio; cement type;
pH of the pore solution;
• capacity of the cement paste to bind the chloride ions;
• the exposure conditions - are “cast-in” or ingressing from an external source ;
• measurement difficulties (e.g. free chloride and hydroxide);
• local variations in chloride concentration at the reinforcement.
30
Chloride concentration
determination
• Concrete pH varies with the type of cement and concrete mix. A tiny
pH change represents a massive change in hydroxyl ion (OH-)
concentration.
• Chlorides can be bound chemically (by aluminates in the concrete)
and physically (by adsorption on the pore walls).
Sulphate resisting cements have low aluminate (C3A) content which
leads to more rapid diffusion and lower chloride thresholds.
• In very dry concrete corrosion may not occur even at very high Clconcentration as the water is missing.
• In sealed or polymer impregnated concrete, corrosion may not occur
even at a very high Cl- concentration if no oxygen or moisture is present to
fuel the corrosion reaction.
• Corrosion can be suppressed when there is total water saturation due
to oxygen starvation, but if some oxygen gets in, then the pitting corrosion
can occur.
31
Chloride induced reinforcement corrosion
The damage process and service life is normally modelled as an
initiation and a propagation period (Tuutti, 1982) according to the two
main processes.
First there is a transport period until critical chloride content or
sufficiently carbonated material is reached at the steel surface. The
subsequent probability of deterioration is determined mainly by
corrosion parameters which in turn rely on transport parameters
(moisture, oxygen, chlorides, etc.) and fracture parameters.
For this particular case the Tuutti’s general service life model is
extended into three phases; initiation, degradation of zinc coating and
finally corrosion of the steel bar.
32
33
Four factors
Deterioration process includes:
• Abrasion
• Diffusion
• Chemical reactions
• Transition etc.
Main factors:
1 - type of concrete,
2 - cover depth to reinforcement,
3 - site practice,
4 - severity of exposure.
Interaction between many forms of deterioration is to accelerate
degradation accounting for its superposition. We input the interaction
coefficients and coupled degree of degradation equations.
Use of calibrated computer simulations and service life models is
proposed.
34
Cl- ingress
Chloride penetration into concrete determines the time to
depassivation initiation of localized corrosion and is thus one of the most
decisive processes for durability and service life of reinforced concrete
structures.
Water and chlorides are transported rapidly into concrete by capillary
suction.
Besides the dominating influence of concrete porosity and pore size
distribution the rate and amount of chloride ingress are related to the
humidity gradients present in the concrete matrix as well as to the
chemical properties of the hardened cement.
Usage of cements with high C3A (3CaO·Al2O3) content is considered
to be conducive to good resistance to corrosion because of its ability to
bind chlorides chemically by forming calcium chloro-aluminate,
3CaO·Al2O3·CaCl2·10H2O, sometimes referred to as Friedel's salt.
35
However, sulphate attack from seawater results in a decomposition of
calcium chloro-aluminate, thus setting chlorides free by formation of
calcium sulpho-aluminate (Neville 1995).
Chlorides become therefore again available for the corrosion process.
Carbonation of hardened cement paste in which bound chlorides are
present has a similar effect on setting free the bound chlorides and thus
increasing the risk of corrosion. It has been found that the presence of
even a small amount of chloride ions in carbonated concrete enhances
the rate of corrosion induced by low alkalinity of carbonated concrete
(Glass et al., 1991).
Whereas active corrosion of the reinforcing steel bars can be detected
in the laboratory and onsite by non-destructive electrochemical
techniques as potential measurements, no such possibility exists for the
detection and quantification of chloride ions in concrete.
Only qualitative information on chloride distribution can be obtained
from potential mapping.
36
LIST OF ION TRANSPORT PROCESSES
Pressure-induced water flow due to the application of a hydrostatic
head. A water permeability coefficient has been learned more detailed than
any other.
Water absorption is the uptake of water resulting from capillary forces,
characterized by a sorptivity coefficient. In environments where significant
concrete drying is possible, water absorption may lead to very rapid
penetration of species dissolved in the water. E.g. concrete in the splash
zone of marine structure or bridge elements under deicing salts attacks have
rapid chloride ion ingress due to water absorption.
Water vapour diffusion is the diffusion of water as a vapour,
characterized by a water vapour diffusivity coefficient. This is the process by
which concrete dries and it controls the moisture distribution in a concrete
element after a period of drying.
37
LIST OF ION TRANSPORT PROCESSES
Wick action is a combination of water absorption and water vapour
diffusion, characterized by sorptivity and water vapour diffusivity coefficients
respectively. Wick action is the transport of water from the wetted face of a
concrete element to a drying face. Species dissolved in the water are
transported to the zone of the element where drying occurs and may result
in salt crystallization.
Ion diffusion is the movement of ions as a result of a concentration
gradient, characterized by an ion diffusion coefficient. Ion diffusion is only
significant where the concrete is nearly or completely water saturated. The
ions that are usually of most interest are chlorides and sulphates.
Compared with most other transport processes, ion diffusion is very slow,
but is often rapid enough to cause deterioration well within the design life of
a concrete structure.
38
LIST OF ION TRANSPORT PROCESSES
Gas diffusion is the movement of gas molecules as a result of a
concentration gradient, characterized by a gas diffusion coefficient.
Diffusion of carbon dioxide into concrete results in carbonation.
In some situations, diffusion of oxygen controls the rate of corrosion of
steel in concrete.
Pressure-induced gas flow is the flow of gas due to a pressure
gradient, characterized by a gas permeability coefficient.
Gas permeability is relatively easy to measure, but is not relevant to the
behaviour of the vast majority of concrete structures.
39
Chloride ion penetration
The transport and distribution of chlorides in a concrete structure is
very much a function of the environmental conditions, mainly the
concentration and duration of the solutions in contact with the concrete
surface.
The conditions are quite different in different exposure situations.
Below the level of sea water, the concentration of chlorides is more
or less constant with time.
The penetration is a pure diffusion process at constant boundary
conditions. At early ages, however, a negative pressure (suction) is
produced as the hydration of cement takes place in the interior parts of
the concrete (Gonzalez, Jalali 2004).
Most other cases of exposure situations have boundary conditions
that change according to a more or less rapid and complicated
relationship with time.
40
Chloride ion penetration
In the splash zone above sea water level, salt water is sucked into
the concrete surface.
Rain water washes the surface free from chlorides and may remove
some of them. Evaporation increases the concentration.
Chlorides move inwards and outwards due to moisture flow and ion
diffusion.
The distribution of chlorides, i.e. concentrations at different depths, is
a time-dependent function of the environmental conditions, the design of
the structure and the material properties.
The mechanisms of chloride transport and binding involved are
complex and usually combined in a complex way. Chloride binding in
concrete is important since the binding process removes chloride ions
from the concrete pore solution into the solid hydrated binder phase.
The processes are not always understood and still not easy to
quantify.
41
Chloride ion penetration
• The environmental data are atmospheric temperature, humidity, air-borne
chloride content and wind speed.
• The evaluation of chloride/carbonation profiles must be incorporated. This
investigation helps to statistically characterise the diffusive property of concrete
and evaluate the distribution of surface chloride concentration.
• The every project is unique and precise characteristic of the design are
quantified by testing the material used at site.
• The measurements of concrete cover thickness may done using ground
penetrating radar, electromagnetic test, ultrasonic and radiography.
• The chloride diffusion coefficients are measured on structural concretes
under standard conditions by rapid migration method. The concrete surface
chlorides and airbourne chlorides are obtained.
• The critical threshold chloride concentration is evaluated by the accelerated
chloride threshold testing. Additions of admixtures such as ground granulated
blast furnace slag, fly ash, silica fume and metakaolin alter the properties of
ordinary portland cement concrete.
42
Type of concrete
Predictions of durability are difficult to make given the complexity of
deleterious physical and chemical interactions depending on seawater,
concrete and structure parameters.
The physical properties of concrete control it transport properties
but ignoring chemical effects.
Chloride ingress into concrete is not only determined by the
permeability of the pore system but also by interactions between the
concrete and the diffusant that depletes the concentration and
constricts the pore structure.
Concrete containing fly ash and slag have good chloride binding
characteristics with high chloride resistance.
43
Result of chloride ingression –
CORROSION OF REINFORCEMENT
External factors affecting corrosion :
• oxygen and moisture at reinforcement level;
• relative humidity;
• temperature;
• carbonation and penetration of acidic gaseous pollutants to the reinforcement
level;
• aggressive anions reaching the reinforcement level;
• biocorrosion;
• Concrete quality:
- w/c ratio;
- cement composition;
- impurities in aggregates;
- impurities in mixing and curing water;
- admixtures (calcium chloride etc);
44
CHLORIDE ION MIGRATION
Chloride ions act as catalysts in the disruption of the passive ferric oxide
layer and are recycled for use elsewhere along the steel surface.
A minimum concentration of chlorides at the steel, known as the
corrosion threshold level, is required to depassivate reinforcement under
normal alkaline conditions.
45
Corrosion due to Cl- ions
Chloride ions present in the cement paste surrounding the reinforcement react
at anodic sites to form hydrochloric acid which destroys the passive film.
The surface of the steel form the anode, and the passive surface – cathode. It
is the corrosion in the form of localized pitting.
46
- cement content;
- aggregate size and grading;
- construction practices;
- cover over reinforcing steel;
- chemical composition and structure of the reinforcing steel;
- pH of the concrete porewater.
The corrosion rate is dependent on if the reinforcement corrosion has
been initiated by chloride ingress or carbonation.
In extreme cases the corrosion rate can be up to 5 mm/year for
corrosion initiated by chloride ingress and 0.05 mm/year for carbonationinitiated corrosion.
Corrosion have two primary forms: cracking and spalling of cover
concrete due to the formation of expansive corrosion products at the
reinforcement.
Corrosion of steel in concrete depends on pH of the pore solution,
temperature, internal stresses, stray currents and electrolytic potentials.
47
Result of carbonation –
CONCRETE INTEGRITY DESTRUCTION
Carbon dioxide and the chloride ion penetrate the concrete without
significantly damaging it.
The aggressive chemical species pass through the pores in the concrete and
attack the steel.
Other acids and aggressive ions such as sulphate destroy the integrity of the
concrete before the steel is affected. The chemical elements attack the
concrete.
48
3. LAWS FOR CHLORIDE
INGRESSION
49
• The simulation of transfer phenomena in porous cement composites to
assess long-term safety and reliability of mechanical characteristics of
concrete in extreme conditions.
• Approach 1 focuses on the development of a generalized model of the
"Hydration-Transport" (GT), which explicitly takes into account the impact
of the porous microstructure, nano, interfacial transition zones (MPZ) and
micro / MacroTrap-women on the moisture diffusion and transport
phenomena.
• Approach 2 focuses on mechanical degradation model (GTM) of
concrete, which is exposed in chloride concentration from the sea or other
sources and, in particular, on the impact of these processes on long-term
service life.
Multiscale modeling of fracture process of concrete to simulate the mass
transport of ions and / chlorides is necessary data on natural conditions
(metocean), the results of the surveys. Analysis is based on hydration
model of cement, microporous model, the equation of equilibrium of the
moisture transport model.
50
Mathematical implementation
Due to the stochastic nature of the parameters that govern the
performance of concrete structures, a probabilistic approach is
needed to generate reliable service life predictions.
IImprovements to the basic of Fick`s 2nd Law include the time
dependency of the model, and the temperature effect on the
diffusion coefficient.
Some of the models advantages are the ability to use different
diffusion coefficients obtained either from the Rapid Chloride
Migration and the Chloride Profile Method, the evaluation of the
chloride profiles and the determination of the surface concentration
of chlorides as well as the diffusion coefficient based on the best fit
curve of the profile by Fick’s 2nd law and the prediction of future
chloride profiles based on present profiles.
From a probabilistic point of view, the use of several distribution
types and the incorporation of a variable to account for model
variability are also advantages.
51
Fick’s law assumes that the ions move independently of each
other (uncharged particles) and that the interaction with the matrix
system is very weakly or non exist. However, ions move in strong
electrostatic fields created by all the charged particles in the matrix.
Many of the ions interact very strongly with the negative charged
hydration products. Therefore, the diffusivity of the chloride ions in
concrete does not follow Fick’s law adequately, particularly in high
density concrete with a fine pore structure
52
Laws of diffusion of Cl- ions
The traditional assumption has been that chloride ingress into concrete obeys
Fick's 2nd law of diffusion for a semi-finite medium with constant exposure, and
that there is a critical value of the chloride content in the concrete. The aim is to
develop prediction method taking into account climatic conditions of Sakhalin.
The effect of the environment is represented in the parameter Cs in Fick’s law
which identifies the representative chloride concentration at the concrete surface
during the time of exposure. It depends on the water salinity, possibly porosity of
the surface layer (amount of saline pore water) and the length of wetting versus
drying in the splash zone.

x
Cx  Csn 1  erf
2 Da  t  t


,

Corrosion deterioration model
The design model for chloride-induced corrosion is adapted from the
analytical model of diffusion.
With the DLS specified as the corrosion initiation state (a), the design
equation
G = Cth − C(Cs, xd, Dc, TSL)
(1)
The objective being to obtain cover thickness (xd) and specifications of
the concrete such as the chloride diffusion coefficient of concrete (Dc) for the
specified design life (e.g.TSL=80 years)
C is the chloride concentration function in concrete. The governing
parameters:
•
Threshold chloride concentration (Cth)
•
Concrete surface chloride concentration (Cs)
•
Chloride diffusion coefficient of concrete (Dc)
•
Concrete cover thickness (xd)
54
Chloride penetration models
Model
Dura Crete
Mejlbro-Poulsen
ClinConc
MsDif
Chloride concentration
Service life design
56
Service life - model Tuutti (1982)
57
Tuuttii model
Once the steel is effectively depassivated, the corrosion rate and
subsequent damage will depend on micro-effects such as availability of
oxygen and moisture and macro-effects such as structural geometry,
anode/cathode ratios and general ambient conditions.
Chloride ions act as catalysts in the disruption of the passive ferric oxide
layer and are recycled for use elsewhere along the steel surface.
Once the steel is effectively depassivated, the corrosion rate and
subsequent damage will depend on micro-effects such as availability of
oxygen and moisture and macro-effects such as structural geometry,
anode/cathode ratios and general ambient conditions.
Tuutti model ( 1982) describes the two processes.
1 - transport of ions until critical chloride concentration or sufficiently
carbonated material is reached at the steel surface. The subsequent
probability of deterioration is determined mainly by corrosion parameters
58
Tuuttii model
Equation yields for chloride induced reinforcement
corrosion of hot dipped galvanised reinforcing steel
in concrete (Sistonen et al., 2006).
59
Fick’s Second Law
A durability model for the reinforcement corrosion, based on the second
Law of Fick, is developed that takes into account the time dependent
parameter for diffusion coefficient and the influence of temperature.
The existing models are either difficult to use due to the complexity of
calculations, and the fact that they require sophisticated tests for collecting
the necessary data, or are too simplistic to provide reliable results.
The proposed model requires few basic data, either available or easily
obtainable, without compromising its scientific robustness and validity.
60
Fick’s law - diffusion model for transport mechanism
In the 1970’s Fick’s laws were introduced by Collepardi (1970) for
describing the ingress of chlorides into concrete. The diffusion of chloride
in concrete can be expressed by means of the ionic flow J, which is by
definition positive, if the chlorides move in positive x-direction.
If the concentration decreases in x-direction the flow is negative
where J - ionic flow, kg/m²s; D - diffusion coefficient, m²/s; c - chloride
concentration in solution, kg/m³; x - distance, m.
61
Fick’s law - diffusion model for transport mechanism
Fick’s first law of diffusion. However, time dependency was not taken
into account. To describe the diffusion process, the particle density must
be function of space and time. Starting with Fick’s 1st law and considering
the law of mass conservation, Fick’s second law is obtained.
The application of Fick’s laws of diffusion to describe the transport
processes in concrete is based on the simplified assumption that concrete 62
is homogeneous, isotropic and inert (Tang 1996).
The main problem with using Fick´s second law is that the chloride
ions interact with the concrete and that diffusion is not the only transport
mechanism working. The movement of negatively charged ions induces
the movement of positively charged ions. The sodium and chloride move
at different velocity (Tang 1996).
Fick’s law - diffusion model for transport mechanism
But model gave unrealistic rapid transport of chloride ions because
of constant diffusion coefficient (Cairns et al 2003).
Fick’s law assumes that the ions move independently of each other
(uncharged particles) and that the interaction with the matrix system is
very weakly or non existent.
However, ions move in strong electrostatic fields created by all the
charged particles in the matrix.
Many of the ions interact very strongly with the negative charged
hydration products. Therefore, the diffusivity of the chloride ions in
concrete does not follow Fick’s law adequately, particularly in high
density concrete with a fine pore structure.
63
Fick’s law - diffusion model for transport mechanism
Takewaka et al. (1988) proposed to describe diffusion coefficient as a power function
of time.
64
The α exponent reflects the decrease of the diffusion coefficient with age
due to the combined effect of hydration and all other mechanisms as ion
exchange with seawater.
Thus α=β+γ, where β - effect of hydration of the cement, γ - effect on the
concrete skin by being in contact with the seawater. They are obtained from
laboratory or field tests.
Predicted chloride profiles (3 variants) in concrete cover
Cl- change near steel bars and reliability index during service life accounting for repairs
DuraCrete model
In DuraCrete (1997) three different types of service lives are
defined:
• Technical service life: The technical service life is the time in service
until a defined unacceptable state of deterioration is reached;
• Functional service life: The functional service life is the time in
service until the functional performance of the structure becomes
obsolete, due to changed requirements from e.g. authorities or the
owner;
• Economic service life: The economic service life is the time in
service until it is economically interesting to replace the structure
than to maintain it.
67
DuraCrete model is considered only diffusion, excluding convection. The
magnitude of the convection zone is 2-10 mm, at a greater depth the main
transport mechanism is diffusion. Therefore, to assess the content of chlorides in
the reinforcement of occurrence depth (40 mm or more) can be applied DuraCrete
model.
The model is based largely on observations of penetration of chlorides in actual
construction, which reduces the need for verification.
DuraCrete model also takes into account the decreasing diffusivity of concrete
with age. The task - to measure the potential properties of the materials in the
laboratory, to adapt them to the actual conditions and use them in the calculation
of chloride penetration in natural conditions.
DURACRETE MODEL
As can be seen from the equations DuraCrete model uses three
factors, taking into account the environmental effects (Table 1).
Table 1: The parameters of DuraCrete model
Parameter
Description
kC,T
factor that accounts for the influence of temperature on the chloride content of the
surface
kD,RH
factor which takes into account external conditions, in particular, the influence on
the PH chlorides diffusion coefficient
kD,T
factor which takes into account external conditions, in particular, the influence of T
on the diffusion coefficient of chlorides
4. CAPILLARY-POROUS
MICROSTRUCTURE
70
Three parameters are important in modeling chlorine penetration in concrete:
1) concrete permeability; 2) concentration of chlorine; 3) chlorine threshold value
as a function of time.
The water transport is possible only in keeping with the mechanism of
molecular diffusion. Micro-capillaries cause capillary condensation.
Three main types of pores are built up in the cement stone:
1) the pores of cement gel; 2) capillary pores; 3) conventionally closed
pores.
The water in the pores of gel does not freeze when the concrete and
reinforced concrete frames are in operation, and it can be explained by their
size and the presence of electrolytes in the pore fluid.
Capillary pores can be presented as the part of water volume of the
cement-water paste which is not filled with cement hydration products. 71
FORCES IN CAPILLARY PORES
(study of prof. Leonovich and Kim)
The liquid in a capillary tube is kept by forces of surface tension, which
magnitude is determined under the formula
Pc   ac cos 
where  is surface tension of a liquid;  is angle of wetting or boundary angle on
the boundary "a liquid is wall of a capillary tube"; ac is diameter of a capillary
tube.
CAPILLARY PORES
5. FEFU modeling of solution
transport in concrete cover zone
and chloride profiles
78
79
Destruction under water tensile stress
These water movements locally generate internal pressures,
which may, eventually, exceed the tensile strength of concrete
(Helmuth, 1961).
Investigations on the subject show how degradation is linked to
the degree of saturation of the material (Bager, et al., 1986;
Fagerlund, 1971; Marchand, et al., 1995).
Frost damage typically occurs in the form of cracking and/or
surface scaling.
The basic facts of frost durability remain that air-voids work as
protection, that the damage is linked to the material degree of
saturation and access to water during freeze/thaw due to the
freeze/thaw pumping effect and that concrete with sufficiently low
water/binder ratio and high strength can be made frost durable even
without air entrainment.
80
Destruction
The influence could well be on the capillary pore system (effect on
freezable water, ice formation in pores and water movements) or on the
microstructure of the surface layer (resistance as a function of type and
quantity of hydrates and of air voids).
The composition of the concrete mixture can also have a combined
effect by modifying the sensitivity of concrete to other parameters.
Several mechanisms have been proposed to explain salt scaling
degradation. Most
of them rely on pressures developed related to the ice formation in
the pore
system (Marchand, et al., 1994; Pigeon, et al., 1996a).
According to these theories, damage does result from pressures
exerted by the ice on pore walls or by hydraulic and osmotic pressures
developed by the expulsion of water during the growth of ice in the pore
system.
Others suggest that pressures could be due to the crystallization of
salts or expansive products in the pore system. Valenza and
Scherer proposed a new mechanism that accounts for several
experimental observations (Valenza and Scherer, 2005).
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Ice abrasion
The “glue-spall” mechanism explains the “pessimum” salt concentration
of around 3% and why the scaled material consists of thin flakes.
The ice layer that would penetrate the concrete surface and bifurcate in
such a way as to remove small flakes of mortar.
During cooling, salt in the outer solution would create brine pockets in
the ice that would act as flaws.
The “pessimum” concentration of salt in the outer solution is explained
by the fact that pure water ice is too strong to crack and at higher
concentrations, the ice/brine mixture is not rigid enough to develop
stresses.
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Mathematical implementation
Due to the stochastic nature of the parameters that govern the
performance of concrete structures, a probabilistic approach is
needed to generate reliable service life predictions.
IImprovements to the basic of Fick`s 2nd Law include the time
dependency of the model, and the temperature effect on the
diffusion coefficient.
Some of the models advantages are the ability to use different
diffusion coefficients obtained either from the Rapid Chloride
Migration and the Chloride Profile Method, the evaluation of the
chloride profiles and the determination of the surface concentration
of chlorides as well as the diffusion coefficient based on the best fit
curve of the profile by Fick’s 2nd law and the prediction of future
chloride profiles based on present profiles.
From a probabilistic point of view, the use of several distribution
types and the incorporation of a variable to account for model
variability are also advantages.
83
• The simulation of transfer phenomena in porous cement composites to
assess long-term safety and reliability of mechanical characteristics of
concrete in extreme conditions.
• Approach 1 focuses on the development of a generalized model of the
"Hydration-Transport" (GT), which explicitly takes into account the impact
of the porous microstructure, nano, interfacial transition zones (MPZ) and
micro / MacroTrap-women on the moisture diffusion and transport
phenomena.
• Approach 2 focuses on mechanical degradation model (GTM) of
concrete, which is exposed in chloride concentration from the sea or other
sources and, in particular, on the impact of these processes on long-term
service life.
Multiscale modeling of fracture process of concrete to simulate the mass
transport of ions and / chlorides is necessary data on natural conditions
(metocean), the results of the surveys. Analysis is based on hydration
model of cement, microporous model, the equation of equilibrium of the
moisture transport model.
84
Capillar-porous concrete model
Concrete is a quasi-brittle porous material
(Bazant, et al., 1998). Under usual exposure
conditions, its pore structure is partially (or even
fully) saturated with an aqueous solution.
If the ambient temperature is reduced below
the freezing point of the aqueous solution, ice
will progressively form in the saturated pores.
The ice formation process is directly affected
by the pore size distribution of the material
(Helmuth, 1960; Zuber and Marchand, 2000).
This partial solidification of the pore solution will often force the remaining
unfrozen water to move.
Depending on the temperature history, unfrozen water can either be
expelled from the freezing sites or attracted to the ice crystals formed within
85
the material’s pore structure (Powers, 1949; Powers, et al., 1953).
Hydrodynamic model of ion transport
Object is concrete cover. The concrete is considered as complex of solid
round particles with porous cement paste. The reinforcement bar is round solid
body too. The problem is plane 2D.
The contact and surface problems of chloride distribution are complex and
inherently non-linear due to the moving boundary and the different properties
along the contact surfaces. The size of the contact areas and the contact
pressure depend on geometry of the ice feature and the structure and changes
during the interaction process.
The aim is the development of theory and numerical techniques for the
determination of kinematic field on the base of consistency between constitutive
equations and solution trajectories (or flow lines). These lines are considered as
“conditional” capillaries. The nearest analogous method is the Strain Path
Method of M. Baligh (J of Geotechnical Engg ASCE, V. 111, GT9, 1985. 11081136).
The fixed velocity field of ice features is calculated using theorem of velocity
summation.
86
Capillary diffusion flow lines of solution transport
Absolute system
Relative system
Concrete surface
Chloride profile
Capillary lines
Bar
87
Chloride profile simulation
at convection process
88
Test chloride profiles
89
3 years
existing
5 years
Chloride reaches threshold at
cover of 60mm in 13 years
Cl- profile during construction
For construction work in marine environment, recent
experience has also shown that a high chloride
penetration may take place already during the
construction period before the concrete has reached
sufficient maturity and density.
91
Cl- profile for
harbour concrete
vs exposure
period
92
Cl- profile for marine high-performance
concrete
93
Cl- profile vs underwater levels
94
Cl- profile vs coating
95
Chloride profiles for marine and road concretes
(Nilsson et al, 2000, Tang, 2003
96
FEFU tests in port Kholmsk
(different marine structures), 2018
2 – pile of bridge; 3 – berth 50 years; 4 - Japaneese
berth 70 years; 6 – superstructure of berth
97
1 - Convection zone
2 – Diffusion zone
98
Convection and diffusion zones
Sandberg (1998)
Nilsson et al (2000)
99
Predicted chloride
profiles from different
models
100
101
Chloride profile equation
102
Models are divided into three groups: 1) kinematic (Lighthill-Whitman); 2) models
of 2nd order; 3) models on the base of kinetic equations. Kinematic (hydrodynamic)
models are based on mean terms such as concentration, velocity, flow etc. Kinetic
(gas dynamic) models consider density in phase space.
The surface of shaft is divided on several areas : compression, stick-slip, sliding and
back.
The main assumptions are: 1) fixed velocity field is calculated using theorem of
velocity summation; 2) contact normal and tangential stresses are calculated using
the resultant velocity field.
103
104
105
106
107
108
109
110
CONCLUSIONS
The interaction between forms of damage is to accelerate degradation.
Degree of degradation is based on superposition of degree of degradation
with interaction coefficients and coupled degree of degradation equations.
Material data and observations of rate of degradation under several
types of deterioration in field and/or in accelerated laboratory tests can be
used to determine the coupling coefficients.
The deterioration has a significant impact on the strength of the
structure but only in the splash zone, where under the influence of sea level
variations.
More important to assess the quality of concrete during fdurability tests.
It is clear that, in order to improve the accuracy of the predictions of the
service life of reinforced concrete structures, a performance based
methodology should be adopted associated with probabilistic methods.
By using probabilistic methods, it is possible to take into consideration
the variations of material properties, the environmental loading and the
effect of the quality of execution during construction.
Future directions of research
1. To define the joint diffusion mechanical model for road
concrete on the base of microporous model for water diffuse
transport (“transport model”), depending on the capillar way
net, porosity of the cement stone and matrix of pore bond
properties.
3. To develop the model of concrete damage based on
the criteria of specific destruction energy obtaining from
tests.
4. To represent the deteriorations of concrete on the base
of FEM for multiscale analysis of the diffusion process in the
concrete.
5. To study nanodimensional and microporous structures
on hydration of concrete using the Delft Hymostruc software.
6. To develop the analysis method of concrete service
lifetime prediction for specific operation conditions.
Main publications of author
Kim L.V., Shaly E.E. Capillary-Porous Effects in Concrete during Ice Abrasion // Solid State
Phenomena, September 2017, London. Trans Tech Publications.
Kim L.V., Leonovich S.N. Offshore concrete structures in cold region // Proc Int Symposium
on Okhotsk Sea & Sea Ice, February 21-23 2016, Mombetsu, Japan. 6 p.
Kim, L.V. et al. Increase of concrete strength using nanosilica extracted from the
hydrothermal solutions. Proc Int Offshore and Polar Engineering Conference (ISOPE), 2013. P.
148-152.
Kolomiets, V. I., Kim, L. V. Frost resistance and abrasion resistance of concrete gravity bases
of oil and gas platforms. J Building materials, 7, Moscow, 2007. in Russian.
Bekker, A. T., Jacobsen, S., Uvarova, T. E., Pomnikov, E. E, Kim, L. V. (2011). Evaluation of
danger from ice abrasion of offshore platforms in Far Eastern seas. Proc RAO/CIS Offshore
conference, St-Petersburg, 262-265.
Leonovich S.N., Shalyi E.E., Falaleeva N.A., Kim L.V. The influence of carbon dioxide on the
durability of offshore concrete structures // Proc Int Ocean and Polar Engineering Conference,
Rhodos, Greece, 26.06-02.07.2016.
Leonovich S.N., Shalyi E.E., Kim L.V. et al. Chloride ingression of concrete embankments //
Proc IACGE Int Symposium on Geotechnical and Earthquake Engineering, 11-15.10.2016, Beijin.
Leonovich S.N., Kim L.V. Frost resistance of marine concrete structures // Proc 11th Int
Symposium in Cold Region Development (ISCORD), May 18-20 2016, Incheon, Korea.
Leonovich S.N., Shalyi E.E., Kim L.V., Dzhogolyuk A.G. Degradation of Marine Reinforced
Concrete Berth Structures on Sakhalin Island // Proc 27th Int Ocean and Polar Engineering
Conference, San Francisco, USA, June 25-30 2017. 124-127.
113
Main publications of author
Jacobsen, S., Kim, L.V., Pomnikov, E.E. Concrete destructure due to ice-indentation pore
pressure. Proc Int Offshore and Polar Engineering Conference (ISOPE), 2013. P. 1258-1263.
Bekker, A.T., Kovalenko, R.G., Luybimov, V.S., Kim, L.V. Steel constructions corrosion
wear processes modeling of sea hydraulic engineering structures. Proc Int Offshore and Polar
Engineering Conference (ISOPE), 2011. P. 319-326.
Kovalenko, R.G., Kim, L.V. Durability evaluation of marine and offshore structures. Proc Int
Offshore and Polar Engineering Conference (ISOPE), 2009. P. 233-239.
Tsuprik V.G., Zanegin V.G., Kim L.V. Mathematical Modelling of Ice-Structure Interaction //
IOP Conference Series: Earth and Environmental Science, 2019. 272. 022063. DOI
10.1088/1755-1315/272/2/022063.
Falaleeva, N.A., Tyitrin, R.S., Kim, L.V., Seliverstov, V.I. Corrosive resistant of slag
concrete with volcanic rock for offshore conditions. Proc Int Offshore and Polar Engineering
Conference, 2015. P. 105-106.
Falaleeva, N.A., Tyitrin, R.S., Kim, L.V. Marine concrete from granulated phosphorite slag
cement. Proc 11th Pacific/Asia Offshore Mechanics Symposium (PACOMS), 2014. P. 96-99.
Kim L.V. Cognitive maps for structural reliability control. Proc Int Offshore and Polar
Engineering Conference (ISOPE), 2008. P. 434-441.
Leonovich S.N., Chernyakevich O.Y., Kim L.V. Carbonation of reinforced concrete
sytructures : monography. Vladivostok, FEFU, 2018. 61 p.
Leonovich S.N., Stepanova A.V., Tsuprik V.G., Kim L.V., Gurinovich V.Y. Durability of
concrete under chloride ingression : monography. Vladivostok, FEFU, 2020. 100 p.
11 patents of Russia, 13 handbooks for students.
114
REFERENCES to presentation
Arup H. The Study of Transportation Mechanisms Using Migration Experiments. Some
Caveats and Ideas for Future Research. Nordic Miniseminar: Chloride Penetration into
Concrete Structures. January 1993, Goteborg.
DuraCrete. Modelling of Degradation. Probabilistic Performance-based Durability Design
of Concrete Structures. EU-Project Brite EuRam III No BE95-1347, Rept 4-5, 1998.
Jacobsen, S., Sellevold, E. J. Sæther, D. H. Frost testing high strength concrete: frost/salt
scaling at different cooling rates. RILEM/Materiaux et Constructions, V. 30, 195, 1997. P. 33–
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Maage, M., Poulsen, E., Vennesland, O. & Carlsen, J.E. Service Life Model for Concrete
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REFERENCES to presentation
Kruschwitz, J., Bluhm, J. Modeling of ice formation in porous solids with regard to the
description of frost damage. Computational Materials science, V. 32, 2, 2005. P. 407-417.
Puatatsananon, W., Saouma, V. E., Nonlinear Coupling of Carbonation and Chloride
Diffusion in Concrete. J Materials in Civil Engineering (ASCE)/May/June 2005. P. 264-275.
Scherer, G. W. Freezing gels, J of Non-Crystalline Solids, V. 155, 1993. P. 1-25.
Scherer, G. W. Crystallization in pores, Cement and Concrete Research, V. 29, 8, 1999. P.
1347-1358.
Zuber, B., Marchand, J. (2000), Modeling the deterioration of hydrated cement systems
exposed to frost action, Cement and Concrete Research, Vol. 30, p. 1929-1941.
Zuber, B., Marchand, J. (2004), Predicting the volume instability of hydrated cement
systems upon freezing using poro-mechanics and local phase equilibria, Materials and
Structures/Concrete Science & Engineering, V. 37, 268. P. 257-270.
Ferreira, R.M. Probality-based durability analysis of concrete structures in marine
environment. Rui Miguel Ferreira. Guimaraes, Portugal, 2004.
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Thank you for attention!
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