GROWTH DEDICATED CALL 10/01 TOPIC V.12

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GROWTH


DEDICATED CALL


10/01


TOPIC V.12



Resistance of Concrete to Chloride Ingress



1.

CONFORMITY WITH THE
WORK PROGRAMME


The proposed project relates to objective 6.2.1 “Methodologies to support
standardisation and Community policies” of the generic
activity
Measurements and
Testing

in the GROWTH programme.



2.

KEYWORDS


Chloride ingress, concrete, durability, laboratory methods, performance testing,
reinforcement corrosion, standardisation, verification



3.

SUMMARY OF OBJECTIVE
S AND JUSTIFICATION


Chlori
de induced reinforcement corrosion is the most important degradation process for
reinforced concrete structures. It has very important economical and social
consequences due to the need of new investments for repairing the damaged zones and
sometimes the n
eed to close the facility for the repair work. The open market is likely to
increase the use of materials in environments where no history of performance is
available. Presently, no quantitative performance requirements are included in the
European standar
ds. Thus, applicable models for service life prediction and accelerated
performance test methods, including acceptance criteria, are needed. The objective of
the work is to verify laboratory performance test methods for testing the resistance of
concrete t
o chloride ingress. The combined test methods and acceptance criteria,
preferentially as mathematical models to allow for service life design, shall be verified
by data on the in
-
field performance of concrete structures. The outcome of the work will
be rec
ommendations of practical use of the laboratory test methods and interpretation of
the test results, which will serve as a basis for future standardisation.



4.

BACKGROUND


Every year about 50 million m
3

concrete is produced in the EU for the structures
exp
osed to severe environment containing chloride salt. The annual cost for the
production of these chloride exposed concrete structures is estimated to be 6000
-
12000
MEUROs in the EU. The total value of concrete structures subjected to chloride ingress
is ve
ry high. It is of great strategic importance to Europe that these structures are
properly produced and effectively maintained to result in long service life so as to
reduce investment and repair cost. Chloride
-
induced corrosion of reinforcement in
concrete

is a big problem for the safety and durability of reinforced concrete structures.
Topic V.12 Pg.
2



According to a recent estimation, the repair contracts are expected to take up about 40%
of the total construction contracts. This implies that a lot of money is spent each
year on
repair. Chloride penetrates into concrete in different ways, mostly by diffusion through
water saturated pores and convection by capillary suction and permeation. Chloride
ingress is generally accompanied by chemical and physical binding. The mecha
nisms
behind chloride ingress are complicated and not fully understood. Since 1970’s much
research has been carried out on the topic of chloride ingress into concrete. Different
test methods for measuring and evaluating chloride ingress have been proposed.

Most of
these methods make use of the so
-
called chloride diffusion coefficient to describe the
rate of chloride ingress and for the prediction of chloride ingress into concrete structures
exposed to salt environment such as seawater and de
-
icing agent use
d in the winter
seasons.


In recent years, the parameter chloride diffusion coefficient has already been used in
service
-
life design in some EU member states and specified in some large constructions,
such as the Oresund Bridge and Tunnel between Denmark
and Sweden, the Vasco de
Gamma Bridge in Lisbon, Portugal, the Subway in Copenhagen, Denmark. Chloride
diffusion coefficients measured from different test methods or even different test
conditions of the same method are, however, not comparable and they ma
y vary from
one to two orders of magnitude. Without the common accepted test methods and
verified acceptance criteria on a European level, the free movement of goods (e.g.
concrete products) and the equal competition between construction companies from
dif
ferent EU member states will be hindered. Thus, there is a great need for the
establishment of verified acceptance criteria linked to selected test methods.


Today, there is only one method related to chloride ingress at the European level, prEN
-
13396:1998

“Measurement of Chloride Ion Ingress” proposed by CEN TC 104
-

Concrete, SC 8
-

Repair. The method was criticised by some countries during the public
enquiry. According to some criticises, this draft standard was thought
“rather immature
and inapplicable”
. “It is difficult to use the test results for differentiating materials and
the test results may easily provoke confusion or misinterpretation”.
In addition, the
proposed standard is
“a laborious, time
-
consuming and costly test”
which takes more
than half

a year before the test results can be obtained.



The need for the scientific and technical research on chloride ingress into concrete is,
therefore, significant and urgent. A number of world wide technical committees have
been formed in recent years, for

instance, ASTM Committee C09.66
-

“Concrete’s
Resistance to Fluid Penetration” (1996) with the scope “to develop and maintain
standards related to ion and fluid penetration into hardened concrete”, RILEM TC
-
178
-
TMC “Testing and Modelling Chloride Ingress
into Concrete” (1998),
fib

Commission
5 “Service life of Concrete” (1998), and ACI TC 365
-
A “Modelling the Service Life
and Life
-
Cycle Costs of Reinforced Concrete Structures Exposed to Chlorides“ (1998).
At the Workshop “Design for Durability of Concrete
” organised by DuraNet / CEN TC
-
104 in Berlin, June 15
-
16, 1999, the experts from WG
-
1 (Steel corrosion, carbonation
and chlorides) reached a conclusion on the aspect of chloride ingress:
“For marine
structures, the technology concerning test methods and m
odelling is sufficiently mature
to reach consensus for a harmonised approach within the time
-
span of 5 years. Main
elements to be included will be diffusion coefficient, environmental load and threshold
values for supporting corrosion (e.g. chloride concen
tration)”.

The WG
-
1
recommended the actions as shown in Table 1.

Topic V.12 Pg.
3





Table 1. Recommended actions by DuraNet / CEN TC
-
104, WG
-
1

Organisation

Main field of work

Fib

Pre
-
normative work, design philosophy, modelling

RILEM

Pre
-
normative work, test procedur
es

CEN

Implementation of technology in European standards

EU

Funding


At the 4
th

and 5
th

meetings of RILEM TC
-
178
-
TMC held in Bremen last year and
Lisbon this year, respectively, all the committee members attended at the meetings,
most of which come fro
m the EU member states, agreed upon the need of the pre
-
normative research of the test methods for chloride ingress. CEN TC
-
104 will be the
“end user” of the research results for standardisation of the test methods at the European
level.



5.

ECONOMIC AND SOC
IAL BENEFITS


The concrete construction industry makes a major impact on economic welfare and
social and cultural development in each EU member state through the provision of very
expensive civil engineering infrastructures, such as roads, bridges, tunnels
, off
-
shore
structures and so on. As a matter of fact a safe design is a foundational requirement for
these expensive infrastructures whose failure can be tragedies and can have serious
economic, environmental and social consequences. With the help of the
accepted new
knowledge and test methods on a common European level, more economic and safer
constructional concrete structures could be expected and a lot of post
-
repair work could
be avoided. Thus this proposal has promising benefits from both economic as
pect
(reduced costs of restoration thanks for more proper design) and social aspect (increased
structural safety and service continuity due to reduced post
-
repair work).



6.

SCIENTIFIC AND TECHN
OLOGICAL OBJECTIVES


The scientific and technical objectives in

the research programme should the include
following parts:


Part 1

Evaluation and selection of laboratory performance test methods

In this part different laboratory test methods for chloride ingress shall be evaluated in
terms of the theoretical bases, t
echnical feasibility, measurement precision and
applicability in practical construction design and quality assessment. The test methods
to be evaluated may include existing ones and new ones (under consideration or not
standardised yet). Based on the evalu
ation, two reliable methods
-

one reference method
and another rapid method
-

for testing the resistance of concrete to chloride ingress shall
be selected and, if necessary, shall be further modified. Round
-
Robin tests may be
needed to help the evaluation
and selection. The selected or modified test methods
should have acceptable repeatability and reproducibility.


Topic V.12 Pg.
4



Part 2

Collection of in
-
field performance data for the verification of the
laboratory test methods

In order to verify the laboratory test method
s selected or modified in Part 1, the in
-
field
performance data regarding to chloride ingress and reinforcement corrosion shall be
collected. The collection may cover full range of environmental conditions in the EU, in
which chloride can be introduced in
the structures, and all kinds of structures including
marine structures, bridges, parking decks, houses, etc. The data should be adequately
documented for other circumstances taking into account other aspects such as casting
conditions (“in
-
situ”, pre
-
fabr
icated), types of construction elements (tunnels,
diaphragm walls, secant piles, beams, columns, etc.) and curing conditions.


Part 3

Verification of the laboratory test methods

Since the laboratory test results should be applicable in practical structura
l design and
quality assessment, the test methods selected or modified in Part 1 shall, therefore, be
verified by the in
-
field performance data collected in Part 2. This means that one or
several models are needed to interpret the test results obtained fro
m the laboratory test
methods and correlate them to the in
-
field measurements. A review of existing models
is needed. Based on the review, one or several models should be selected and, if
necessary, modified for the verification. The models used in the ver
ification could be
scientific, empirical, or probabilistic. The scientific models are preferable for a better
understanding of chloride ingress in concrete structures.


Part 4

Recommendations of practical use of test methods and interpretation of
the test
results including proposal of acceptance criteria

In this part the selected or modified laboratory test methods shall be prepared for
transfer to standards. The practical use of the laboratory test methods and the
interpretation of the test results includi
ng proposal of acceptance criteria shall be
recommended.


The results of the project would be:


1)

Technical papers describing the laboratory test methods for testing resistance of
concrete to chloride ingress.


2)

Technical papers describing the verific
ations of the laboratory test methods by
using the collected in
-
field performance data.


3)

Models including the state
-
of
-
the
-
art and relevant computer programs for using the
test results to predict the field exposures.


4)

Draft test procedures specifying

the laboratory test methods as a preparation for
transfer to standards.


5)

Recommendations of practical use of the laboratory test methods and interpretation
of the test results including proposal of acceptance criteria.



Topic V.12 Pg.
5



7. RELEVANT NORMATIVE AND PR
E
-
NORMATIVE DOCUMENTS


prEN 13396:1998, “Measurement of Chloride Ion Ingress”


NT (Nordtest) BUILD 443:1994, “Concrete, Hardened: Accelerated Chloride
Penetration”


NT BUILD 355:1997, “Concrete, Mortar and Cement Based Repair Materials: Chloride
Diffusion
Coefficient from Migration Cell Experiments”


NT BUILD
492:1999
,
“Concrete, Mortar and Cement Based Repair Materials: Chloride
Migration Coefficient from Non
-
steady State Migration Experiments”


ASTM C 1202:1994, “Standard test method for electrical indica
tion of concrete’s ability
to resist chloride ion penetration”