International Commission on Large Dams (ICOLD) - The Physical Properties of Hardened Conventional concrete in Dams
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ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix B (The physical properties of construction joints in concrete dams)
As submitted for ICOLD review, march 2008
Appendix B-
13
The panels were tested to failure of ages of 28 to 90 days, under rapid and slow
loading conditions. While these in situ tests were performed under difficult field
conditions, where the same degree of quality control could not be maintained as in a
laboratory, the data obtained are useful and pertinent for the evaluation of adequacy of
treatment of construction joints. The principal conclusions derived from the Ross dam
tests were:
• The treatment and preparation of the existing concrete must produce a clean, fresh,
sound, moistened surface, and the new concrete must be carefully placed,
consolidated and cured to obtain a satisfactory bond;
• All adequate bond can be achieved between old and new concrete without the use
of mortar or grout on the contact surface;
• Bond or shear strength, on a properly prepared (even vertical) surface, is about 10
per cent of the unconfined compressive strength of the (new) concrete at an age of
28 to 90 days.
Fig. B.7 - Ross dam: in situ bond test arrangements [B.1]
Displacement controlled shear tests on concrete lift joint specimens with different
surface preparations are sometimes carried out to compare dynamic sliding joint
behavior with the static behavior. Experimental results indicate that the coefficient of
friction decreases with the increase in normal load, under both static and dynamic
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix B (The physical properties of construction joints in concrete dams)
As submitted for ICOLD review, march 2008
Appendix B-
14
shear. Empirical lift joint constitutive models have been developed as a function of a
basic friction coefficient and a roughness friction coefficient that is dependent upon the
type of surface preparation [B.13].
B.4.3 Italian Experience
The performance of horizontal construction joints at Nurraghe Arrubiu arch dam in Italy
is discussed in this section.
B.4.3.1 Nurraghe Arrubiu dam
Geophysical methods were used in Italy to investigate the conditions of the horizontal
joints of the Nurraghe Arrubiu arch dam [B.14].
In the upper part of its upstream face, cracks appeared already in the final stage of
construction (1957), due to the dam big overhanging to downstream (Fig. B.8). Then
the phenomenon slowed down progressively and since 1971 no new cracking of the
construction joints was detected. The extension of each crack was investigated by core
drilling almost up to the downstream face and a videocamera was introduced into the
drillholes to detect the cracks as well as the frequent anomalies like honeycombes.
Resin grouting of the construction joints was carried out in a single stage in 1995,
starting with the most inner holes and continuing toward the upstream face as
schematically shown in Fig. B.9.
Vertical lines for geophysical investigations were implemented on each block and the
wave velocities through the horizontal joints, at different elevations, were measured
before and after the grouting treatment. A typical result is reported in Fig. B.10, showing
a clear increase of performances of the horizontal construction joints and a better
bonding between layers.
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix B (The physical properties of construction joints in concrete dams)
As submitted for ICOLD review, march 2008
Appendix B-
15
Fig. B.8 – Cross section of the dam with cracks at horizontal construction joints [B.14]
Fig. B.9 – Schematic lay-out of the boreholes and equipment; 1- crack and joint to be
grouted; 2- grouting equipment; 3- grout holes; 4- Sealing of the upstream face [B.14].
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix B (The physical properties of construction joints in concrete dams)
As submitted for ICOLD review, march 2008
Appendix B-
16
Fig. B.10 – Geophisical investigations in a test block. 1- wave velocity before grouting;
2- wave velocity after grouting; 3- cracks and construction joints [B.14].
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix B (The physical properties of construction joints in concrete dams)
As submitted for ICOLD review, march 2008
Appendix B-
17
B.5 REFERENCES
[B.1] Pacelli, W.A., Andriolo, F.R., Sarkaria, G.S. “Treatment and performances of
construction joints in concrete dams”, Water Power and dam Construction, November
1993.
[B.2] US Army Corps of Engineers, “ Engineering and Design - Gravity Dam Design”,
EM 1110-2-2200, 1995.
[B.3] Juan Buil Sans (Spain), personal Comunication, 2001.
[B.4] American Concrete Institute, “Mass Concrete – ACI 201.1R-87”, ACI Manual of
Concrete Practice, Part 1, Detroit, MI, USA, 1991.
[B.5] ICOLD, “Materials for joints in concrete dams”, ICOLD Bulletin n° 57, 1986.
[B.6] Tuthill, L.H., Sarkaria, G.S. and Cortright, C.J., “Better concrete for dams; - Recent
experiences and trends in California”, Tenth ICOLD Congress on Large Dams, Q.19,
R.11, Montreal , Canada, 1970.
[B.7] Andriolo, F.R., “Constucoes de concreto - Manual de praticas para controle e
execucao”, Editoria Pini, Aso Paulo, Brazil, 1978. (in Portuguese).
[B.8] Raphael, J. M., “Tensile strength of concrete”, ACI Journal, n° 81-71, March-April
1984.
[B.9] American Standard ASTM C496:1996 – Standard test method for splitting tensile
strength of cylindrical concrete specimens.
[B.10] Pacelli, W.A., “Concrete construcrion joints tests at Itumbiara Dam”, Furnas
Centrais Electricas S.A., Rio De Janeiro, Brazil, 1978.
[B.11] Houghton D.L., Hall, D.J., “Elimination of grout on horizontal construction joints at
Dworshak dam”, ACI Journal, pp. 176-178, March 1972.
[B.12] Sundquist, D.C. and Kollgaard, E.B., “Design and construction of Ross dam in
successive stages”, 13th ICOLD Congress on Large Dams, Q.19, R.11, New Delhi,
India, 1978.
[B.13] Fronteddu, L., Léger, P., Tinawi, R., “Static and Dynamic Behavior of Concrete
Lift Joint Interfaces”, J. Struct. Engrg., Vol. 124, Issue 12, pp. 1418-1430, December
1998.
[B.14] R. Silvano, F. Frongia, A. Mondada, A. Piazza – “Repair works at Flumendosa
arch dam” – 19
th
ICOLD Congress, Q. 75, R. 40, Firenze, 1997.
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix C (Physical properties of concrete subjected to expansion phenomena such
as AAR in dams)
As submitted for ICOLD review, march 2008 Appendix C-1
C PHYSICAL PROPERTIES OF CONCRETE SUBJECTED TO
EXPANSION PHENOMENA SUCH AS AAR IN DAMS
C PHYSICAL PROPERTIES OF CONCRETE SUBJECTED TO
EXPANSION PHENOMENA SUCH AS AAR IN DAMS............................. 1
C1 INTRODUCTION...................................................................................................1
C2 THE NATURE OF THE ASR IN CONCRETE .......................................................2
C3 DAMAGE DUE TO ASR IN CONCRETE DAMS...................................................3
C4 THE PHYSICAL PROPERTIES OF ASR AFFECTED CONCRETE IN DAMS.....7
C4.1 Compressive strength....................................................................................7
C4.2 Expansion as compressive stress dependent parameter ............................10
C4.3 Tensile strength ...........................................................................................12
C4.4 Modulus of elasticity ....................................................................................13
C4.5 Creep...........................................................................................................14
C4.6 Specific fracture energy...............................................................................15
C5 REFERENCES....................................................................................................16
C1 INTRODUCTION
Many existing large dams have been found to be subject to chemical reaction induced
concrete expansion phenomena and the number is growing as awareness of the
phenomena and the use of high-resolution instrumentation increases. Such behaviour
can occur due certain chemical reactions leading to the formation of expansive
products and subsequent expansion of the concrete matrix, frequently with associated
changes in physical properties. These expansion phenomena include sulphate attack,
reaction between sulphur compounds in aggregates and paste and alkali-aggregate
reactions (AAR), both in the forms of alkali-silica reaction (ASR) and alkali-carbonate
reaction (ACR).
Given the increasing frequency of Alkali-Silica Reaction (ASR) problems in dams, this
appendix will focus on this particular expansion phenomenon that can cause serious
problems to the dam structural safety and to the operation of installations associated
such as intakes, sluiceways, shaft and gates [C.1]. Suitable prevention measures for
new constructions, diagnosis procedure for the existing expansive dams and effective
remedial measures are naturally of big concern. However these issues have already
been the subject of the ICOLD bulletin n° 79 (Alkali-Aggregate Reaction in concrete
dams -Review and Recommendations) published in 1991 and moreover a new updated
Bulletin on chemical expansion of concrete in dams & hydro-electric projects have also
been planned.
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix C (Physical properties of concrete subjected to expansion phenomena such
as AAR in dams)
As submitted for ICOLD review, march 2008 Appendix C-2
This Appendix just refers to the influence of Alkali-Silica Reaction on some physical
concrete properties that in turn affect the overall structural integrity of the concrete dam.
The testing results from literature and from ASR-affected dams, mainly derived from the
Bureau of Reclamation experience in USA, have been considered with specific
reference to compressive and tensile strength, modulus of elasticity and creep.
C2 THE NATURE OF THE ASR IN CONCRETE
General information on the nature of the ASR in concrete , the required constituents to
cause its occurrence, namely reactive minerals, sufficient alkalis and moisture, the
expansion mechanism of this phenomenon and the type of deterioration due to ASR on
dams are only briefly reviewed. More information can be found in the proceedings of
the International Conferences on AAR in concrete [C.2] and on more specific
references for hydroelectric plants and dams [C.3] [C.4] [C.5] [C.6] [C.7].
Alkali-silica Reaction (ASR) is a chemical reaction between hydroxyl ions associated
with alkalis in sodium and potassium (mainly from Portland cement) with certain mineral
phases in the coarse and fine aggregates. A gel is formed that absorbs waters and
swells causing expansion phenomena.
The main conditions required for ASR to develop are thus as follows:
• a reactive aggregate must be present;
• the concentrations of alkali (hydroxyl ion) in the concrete pore solution must be high;
• a sufficient moisture must be present.
Reactive rock types include igneous, sedimentary and metamorphic types and
therefore petrographic evaluation is almost always required on aggregates. A variety of
reactive minerals are reactive, including silica minerals like amorphous silica or
crystalline quartz such as:
• Cryptocrystalline quartz (chalcedony, chert, etc.);
• Microcrystalline quartz (many types of rocks, including siliceous limestones);
• Quartz overgrowths in some sedimentary rocks (greywackes, quartzitic sandstone,
etc.);
• Larger quartz grains with internal defects, discontinuities or inclusions.
The proportion of reactive particles within an aggregate is important. Typically, there is
a certain proportion of reactive material that causes a maximum expansion and this is
called the pessimum proportion. For example, opal and chert in aggregates may cause
large rates of expansion if they exist in their pessimum proportions.
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix C (Physical properties of concrete subjected to expansion phenomena such
as AAR in dams)
As submitted for ICOLD review, march 2008 Appendix C-3
The cement is the major source of alkalis in the concrete pore solution. The larger the
cement content (in kg/m
3
) or alkali content (in % Na
2
0
eq
) the larger the expansion due
to ASR. In some cases, alkalis can also be supplied by the aggregates, i.e., by micas
and feldspars present in aggregate. This is especially the case of dam concretes whose
service life exceeds that of normal concrete structures and favour slow alkali leaching
from aggregates inside the concrete.
The availability of water is also an essential condition for the AAR chemical reaction. A
typical threshold relative humidity of 80% is required. For mass concrete structures
such as dams, the humidity conditions appear to be always favourable for ASR
expansion [C.8].
The pressures acting in the cement paste can be as high as 5 - 6 MPa or even more
and these pressures can cause tensile stresses and subsequent micro-cracking on the
cement paste. Another very important ASR related effect is that the reaction is stress
dependent. As the compressive stresses increase, the reaction decreases. At a critical
amount of compression, the reaction will cease, and no further build-up of stress will
occur, as discussed later.
C3 DAMAGE DUE TO ASR IN CONCRETE DAMS
Alkali-Silica Reaction is particularly important in concrete dams and in general in
hydraulic structures because of the high humidity environment and high variable
exposure conditions during their operation. Furthermore the massive nature of such
structures and their long service life, often longer than predicted at the design stage,
increase the risk of ASR reaction, making evident the effects of also very slow reaction.
Other effects, including those from wetting and drying, freezing and thawing as well as
moisture and thermal gradients, often worsen the range of damage, increasing the risk
of further ASR expansion development. If the movements and cracking caused by ASR
expansion cannot be tolerated due to the risk of serviceability and structural integrity,
diligent monitoring and suitable management is required to ensure continued safe
operation.
Because of the large variety of parameters having an influence on this phenomenon,
including reactive particle availability, rate of reaction, level of pore alkaline solution,
humidity and temperature conditions, effect of the stress state, degree of restraint
present in a given concrete section and time dependency, the resulted concrete
expansion are considerably in-homogeneous and anisotropic.
ASR in a concrete dam or spillway will usually exhibit the following [C.9]:
• Concrete expansion: deformation, extrusion of joint seals, closing of joints,
differential movement and gate blockage/binding (Fig. C.1);
• Surface cracking (map cracking): typically polygonal cracking (Fig. C.2);
• Structural cracks: for example expansive upstream crest movement, coupled with
foundation restraint, leading to increasing vertical compression on the upstream
face and horizontal fissure opening downstream (Fig. C.3);
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix C (Physical properties of concrete subjected to expansion phenomena such
as AAR in dams)
As submitted for ICOLD review, march 2008 Appendix C-4
• Horizontal compressive stress along the dam;
• Reaction products: ASR generates gels which may exude on the surface of the
concrete, particularly at joints. The presence of this gel does not necessarily imply
ASR if other signs are not present. And in particular calcium carbonate deposit from
leaching are not to be confused with the silico-alkaline gel from ASR.
Fig. C.1 – Disalignment of concrete blocks at a dam top, due to ASR expansion
Fig. C.2 – Surface map cracking [C.10]
ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix C (Physical properties of concrete subjected to expansion phenomena such
as AAR in dams)
As submitted for ICOLD review, march 2008 Appendix C-5
Fig. C.3 – Lay out of the structural crack at Fontana dam (USA)
In Fig. C.4 a lay out of the typical time evolution of ASR concrete expansion process is
reported. It consists of an initiation period, in which the reaction has started but without
expansion, followed by a period of development and a final period of rest. It is possible
that the ASR reaction become exhausted because of depletion of the reaction
constituents (reactive minerals, alkali and moisture) [C.11]. As already discussed, in the
case of supplementary source of alkalis as, for example, from the aggregates, the
completion of the reaction can take more time or even it could not to have a end.