Note: Descriptions are shown in the official language in which they were submitted.
CA 02736772 2011-03-10
HYDRAULIC BINDER AND BINDER MATRICES MADE THEREOF
The invention relates to a hydraulic binder, especially for protecting steel
against
corrosion, as well as binder matrices, mortars, concrete adhesives and anodes
produced by use thereof.
BACKGROUND OF THE INVENTION
Hydraulically setting inorganic binders based on calcium and aluminum
silicates have
been known for a long time and are used in various compositions and with
various
properties; see, for example, main class 004 of the International Patent
Classifica-
tion.
Conventional hydraulic binders, e.g. Portland cement, hydraulic limes and
calcium
aluminate cements, harden to become brittle materials such as mortar and
concrete,
having high elastic moduli compared to their strengths. Furthermore,
conventional
hydraulic binders are characterized by a high content of calcium and a high
ratio of
calcium/silicon, and their strengths are determined by sufficient quantities
of dissolv-
ed calcium in the pore solution. If the dissolved calcium is washed out of the
binder
matrix or is immobilized by carbonatization, this may lead to a disintegration
of the
strength-forming mineral phases, i.e. calcium silicate hydrates. Consequently,
the
durability of binders based on calcium silicates is limited.
Furthermore, galvanic corrosion protection (GCP) has been used for many years
for
protecting steel in concrete and steel constructions, tubings etc. against
corrosion, as
described in AT A 1344/2004, EP 1,135,538, EP 668,373, and US-A-4,506,485. The
effect of GCP is based on the formation of a galvanic element between a
sacrificial
anode and the steel. If galvanic protection is used for protecting steel
reinforcements
in concrete, the concrete acts as an electrolyte. For protecting steel
constructions,
usually a gel-like flexible electrolyte is applied between steel and galvanic
anode.
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'
For the most part, the gel-like flexible electrolyte is present as an adhesive
layer an a
metal anode. As the anode material, usually zinc and its alloys, more rarely
alumin-
um and its alloys are used. The anode is usually mounted on the surface of the
con-
struction element to be protected, in some cases it is introduced as "discrete
galvanic
anode" into concrete.
Disadvantages of the known sacrificial anodes in the protection of steel,
especially
reinforced concrete, against corrosion are that zinc passivates in contact
with
calcium ions, especially calcium hydroxide, and is inactivated after a short
period,
Known sacrificial anodes such as zinc applied to a concrete surface by means
of a
plasma spray method according to the Grillo KKS method (WO 2005/03061) are
thus
only effective at high humidity and high chloride contents. Once the system
has dried
out, the zinc passivates irreversibly. In order to avoid these disadvantages,
so-called
discrete anodes, as described in US-A-6,572,760 (B2), have been developed. The
problem of zinc passivation was solved by adding alkalis, usually alkali
hydroxide, to
the binder in which the zinc is embedded. Practice has shown that a pH of
approx-
imately 14 is required for sufficient activation of the zinc anodes. Thus,
these discrete
anodes may only be used on construction sites with substantial safety
measures, as
they are commonly used for highly alkaline corrosive construction materials.
In
addition, it has been shown that, in the medium term, alkalinity is reduced by
galvan-
ic reactions and that zinc passivates, especially in construction elements
being
exposed to dry-wet cycles. Furthermore, alkalis in concrete may have negative
effects on the concrete's strength due to the alkali-silica reaction.
26 Against this background, it was the object of the invention to provide a
hydraulic
binder as well as a sacrificial anode made thereof with which the above dis-
advantages can be largely or entirely overcome.
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SUMMARY OF THE INVENTION
In a first aspect, the present invention achieves this object by providing a
hydraulic
binder, comprising K, Ca, aluminosilicates, as well as optionally Li, Na, and
Mg,
characterized in that it comprises the following components:
a) a latently hydraulic aluminosilicate glass having a ratio of
(Ca0+Mg0i-A1203)/Si02 > 1
and
b) an alkali activator of the empirical formula (I)
a(M20) *x(Si02)* Y(H20) (I)
wherein M = Li, Na, K, a -7- 0-4, and x = 0-5 and y 3-20,
wherein the molar ratio of Ca/Si is <1, the molar ratio of Al/Si is <1, and
the molar
ratio of M/Si is >0.1.
This simplest embodiment already shows the following advantages compared to
the
prior art: The inventive binder is predominantly characterized by a very high
elasticity
and a high strength. Conventional mortars and concretes of hydraulic binders
have
compressive strengths of 18 to 24 GPa at elastic moduli of 15 to 25 MPa, which
may
be calculated using the well-known formula (I) according to the American
Concrete
Institute ACI 318-95 and AC! 318-89:
Ec = 4.73(f) 5 (I)
wherein: Ec = elastic modulus in GPa
= compressive strength in MPa.
For concretes of the strength class 16/20 MPa, according to ONORM 4700 an
elastic
modulus of 27 GPa is characteristic.
In contrast to the tectoaluminosilicate cement described in AT 177,072 T, DE
59109105 0 and US 5,372,640, the inventive binder does not use microsilica.
The
inventive binder is hard and elastic and deformable under pressure - and that
with
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,
high strengths. It is thus especially suitable for the manufacture of thin
sheets and
tiles and for the manufacture of coatings on concrete and metal. For both
application
purposes, high elasticity and increased creep have great advantages.
An inventive binder matrix also has the special characteristic that it is made
of two
components that are both alkaline (e.g. component A: pH 10.35, component B: pH
13.94, mixture of A+B: pH 13.21). Directly after mixing and before hardening,
the pH
value is 13.21, after hardening the pH value is 10.48. The hardened binder
matrix is
thus clearly different from hardened binders according to prior art, such as
Portland
cement: pH 13.6; Roman cement! pH 13.1; hydraulic lime: pH 12.6,
The latently hydraulic aluminosilicate glass (LHASG) in the inventive
hydraulic binder
is a material that ¨ especially in grounded state or powder state ¨ is able to
react
with calcium hydroxide and to harden, i.e. become "hydraulically active", once
it has
been activated by an activator. Preferably, blast-furnace slag is used for
this pur-
pose, but other slags from other processes, e.g. from other smelting
processes,
melting processes in which a slag-like material is formed, such as steel
slags, melt-
ing-chamber fly ashes or fly ashes from coal power plants with high glass
contents,
or any amorphous, glass-like material that is hydraulically active and
corresponds to
the above empirical formula may also be used.
Generally, the alkali activator is substantially an alkali water glass, e.g.
sodium or
potassium silicate. By means of the alkali activator of component b), the
latently
hydraulic component a) is activated. In preferred embodiments, the alkali
activator
contains at least one alkali hydroxide, which increases its effect, i.e.
higher reaction
rate in setting and higher strengths of the hardened products. Especially good
results
were achieved with a potash water glass that contained 10-12 % by weight of
K20
and 20-25 % by weight of SiO2, and to which 10-15 % by weight of potassium
hydroxide were added.
Preferably, the inventive binder additionally contains, as a component c), a
latently
hydraulic additive, e.g, a pozzolan, even more preferably a low-calcium,
especially a
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calcium-free, latently hydraulic aluminosilicate, in order to improve
properties such as
strength and density, since it optionally binds dissolved calcium in the pore
solution
of a binder matrix, thus causes 3-dimensional cross-linking of the matrix, and
reduces the content of soluble calcium hydroxide. Especially preferred, the
latently
hydraulic aluminosilicate consists of either a natural pozzolan, e.g. volcanic
ash or
pulverized volcanic tuff, or an artificial pozzolan, e.g. a therrnically
activated clay
mineral, e.g. calcined between 500 C and 900 C, since these materials are
readily
available and inexpensive. Furthermore, artificial pozzolans are very active,
latently
hydraulic aluminosilicates, and calcined clay minerals have the advantage that
they
have, in contrast to natural pozzolans, a defined composition and thus
controllable
reactivity. Suitable latently hydraulic aluminosilicates also comprise
latently hydraulic
fly ashes from coal power plants with a Ca0 content of <12 % by weight,
preferably
<8 % by weight. Vitrified hard-coal fly ashes have also proven to be
especially suit-
able. Generally, "low-calcium latently hydraulic aluminosilicate" herein means
a CaO
content of <15 % by weight, especially <10 % by weight.
Metakaolin, prepared from kaolin by calcination at approximately 600 C, has
proven
to be especially latently hydraulically active. A test for its latent
hydraulicity resulted
in a solubility of 20 % by weight in 1 N NaOH. The addition of latently
hydraulic
aluminosilicates has also proven advantageous for the mechanical properties of
the
binder matrix: Their addition results in an increase in elasticity, creep and
long-time
strength (>28 days).
Aluminosilicate and aluminosilicate glass are said to be latently hydraulic
when of
2 g, dispersed in 100 ml of 60 C warm 1 N caustic soda solution, at least 2 %
by
weight are dissolved within 1 hour. This test serves for determining latent
hydrauli-
city.
The quantitative ratios of components a), b) and optionally c) are preferably
as fol-
lows:
a) 100-300 parts by weight of latently hydraulic aluminosilicate glass;
b) 20-150 parts by weight of an alkali activator; and
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c) optionally 50-200 parts by weight of a latently hydraulic additive;
wherein the molar ratio of Al/Si is <0.8, and the molar ratio of Ca/Si is
<0.9.
Laboratory and practical tests gave the best results within these ratios, as
will also be
seen in the exemplary embodiments below. The ratio of alkali activator to
hydraulic
aluminosilicate glass is preferably such that at least 95 %, preferably 99 %,
of the alkali
activator are used up during the hardening reaction. It has been shown that
optimal results
may be achieved with the quantitative ratios described above, wherein the
addition of the
latently hydraulic additive requires an increase of the amount of the alkali
activator in
order to achieve optimal results. The ratio M20/(S102 + Al2O3) should be at
least >0.01,
preferable >0.05. Properties such as durability, elasticity and strength
increase with a
decrease of the Ca/Si ratio, wherein the Ca/Si ratio should preferably be
<0.9.
Furthermore, it has been shown that binders in which the molar ratio Al/Si is
<1, especially
<0.8, result in especially good properties.
The inventive binder may in certain embodiments additionally contain at least
one organic
polymer, which, when it is used as a concrete coating, reduces the cracking
tendency,
decreases the elastic modulus, and improves its workability. Preferably, the
organic
polymer is selected from polyacrylates, latex, polyacryl copolymers,
polystyrene
copolymers and polystyrene butadiene.
Furthermore, the hydraulic binder of the invention preferably contains a
soluble zinc salt,
even more preferably a zinc sulfate hydrate, since zinc salts, especially zinc
sulfate, serve
as setting regulators by means of which the setting times may be regulated. in
addition,
zinc is effective against algae and fungal attack. For example, the addition
of 0.5 % by
weight of zinc sulfate heptahydrate already increased the setting time by
approximately
0.5-1 hour to 12 to 24 hours, without negatively affecting the mechanical
properties.
In preferred embodiments, the hydraulic binder additionally contains a lithium
salt,
preferably a lithium chloride, since these salts also increase the galvanic
activity of zinc
anodes produced by use of the binder, support the formation of especially
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durable and cross-linked aluminosilicates during the binder's hardening, and
prevent
or at least reduce alkali-silica reactions with reactive aggregates, such as
opal or
greywacke sands. For increasing the performance of zinc anodes, the addition
of
lithium chloride, e.g. the addition of 0.1 to 2.0 % by weight of LiGI, has
proven
especially advantageous with regard to the stability of the galvanic current.
For the
ionic conductivity of the inventive binder matrix, on the other hand, the
addition of
approximately 0.2 to 6.0 % by weight, preferably approximately 0.4 to 1.0 % by
weight, of lithium salts led to good results.
Also with regard to anodes produced by use of the inventive binder, the binder
preferably additionally comprises a zinc complexing agent, more preferably a
poly-
ethylene imine or polyamide. Zinc complexing agents prevent the passivation of
zinc
anodes in weakly to moderately alkaline environments. Especially polyethylene
imine
durably increased the galvanic performance of a zinc anode. Without the
addition of
polyethylene imine, the zinc anode's current delivery decreased by 90 % after
one
year. The addition of 1-3 % by weight, preferably 2 % by weight, of
polyethylene
imine resulted in a decrease of the galvanic current by only 45 %, which
remained
stable in the further course. By using plastics as complexing agents, the
advantage-
ous effects of the above organic polymers can be achieved at the same time,
and
cationic, basic polymers such as polyethylene imine furthermore increase the
reac-
tivity of the slag, have a positive effect on the development of strength, and
prevent
or reduce crack formation in mortars made of the inventive binder.
Furthermore, in preferred embodiments, the inventive hydraulic binder may
comprise
a thickening agent and/or and thixotroping agent, preferably a cellulose alkyl
ether
and/or a starch alkyl ether. These increase the workability of mortars made of
the
binder: The mortar can be applied more easily because it is "smearier" or
thixotropic,
i.e. it is less viscous or even liquid when applied, however, thickens and
gelates in
the state of rest. In addition, cellulose alkyl ether and starch alkyl ether
act as water
retention agents and thus increase ion conductivity.
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. =
In further embodiments, the latently hydraulic aluminosilicate glass as the
component
b) is mixed with hydrogen peroxide in order to oxidize sulfides in the
aluminosilicate
glass powder and thus convert them into sulfates. The sulfides contained in
some
aluminosilicate glasses, especially in blast-furnace slag, have proven very
detrimen-
tal for the zinc anode's effectiveness. Surprisingly, it has been shown that
the sulfid-
es could be oxidized easily by merely mixing the ground aluminosilicate glass
with a
3 % hydrogen peroxide solution.
The components a) and b) ¨ and optionally also c) ¨ of the inventive hydraulic
binder
can preferably also be provided separately, so that the binder is a two-
component
system, wherein the alkali activator is preferably dissolved in water and the
alumino-
silicate glass (optionally together with the additive) is provided as a powder
or also
already in water, i.e. in liquid form, and the content of the alkali activator
and alkali
hydroxides optionally contained therein is between 10 and 50 % by weight.
The advantage of this embodiment is that the two components of the two-
component
system can be mixed and converted into a binder matrix more easily and
quickly, e.g.
directly at a construction site, than when both components are provided in dry
forms.
In a dry, powdery one-component system, the alkali activator must be provided
in a
dry, but soluble form and then be dissolved by the addition of water before it
may
become active.
In a further aspect, the invention is related to a binder matrix produced by
use of a
hydraulic binder according to the first aspect, which binder matrix is
obtained by mix-
ing and reacting the hydraulic binder ¨ in this case a dry one-component
system ¨
with water. Preferably, in such a binder matrix, the hydraulic binder is mixed
with
water in a ratio of 1:0.5 to 1:4, based on the dry substance of the binder.
Preferably,
the binder matrix has a ratio of Ca0/(5i02+A1203) of <0.9, preferably <0.5, a
ratio of
CaO/SiO2 of <0.9, preferably <0.5, and a ratio of M20/(5102140203) of >0.01,
prefer-
ably >0.05. Alternatively, the binder matrix preferably has a ratio of
Ca0/(SI02+
A1203) of <0,5, preferably <0.3, a ratio of CaO/SiO2 of <0.8, preferably <0.5,
and a
ratio of M20/(Si02+A1203) of >0.02, preferably >0.07.
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A binder matrix with the first ratios has high durability, high adhesion (>1.5
MPa) to
the support, as well as compressive strengths in the range of 10 to 35 MPa; a
binder
matrix with the ratios as in the second case is especially suited for
applications that
require very high durability, high strengths (25 to 75 MPa), and high adhesive
tensile
strengths (>2.5 MPa after 28 days) with comparably low elastic moduli.
Basically, it may be stated that thin slabs of brittle material, e.g. of
Portland cement
concrete, have a cracking tendency already during the concrete's hardening in
the
slabs' manufacture due to their inner tensile stresses that are caused by the
concrete's natural vibrations. If such slabs are mechanically fixed to the
support, the
cracking tendency is further increased by a low creep value. In a smaller
extent, the
same is true for coatings on concrete and steel. The coating material must be
able to
adapt to deformations of the concrete or steel support, e g. due to
temperature
changes or temperature gradients, without cracking. Slabs, tiles and coatings
on
concrete and steel produced of mortar containing an inventive binder matrix
do, even
with high loads, show no cracking, detachment from the support or pop-outs.
In a third aspect, the invention thus provides a mortar obtained by use of i)
a
hydraulic binder according to the first aspect, ii) water and iii) aggregates,
by means
of which mortar the above advantages of the invention can be effective in
practical
use. Mortar made of the inventive binder is especially suitable for the
production of
concrete coatings arid for coatings on steel, for the production of very
stable and
durable slabs and tiles, as well as for the production of galvanic zinc
anodes.
Suitable aggregates are basically all common standard aggregates. Especially
good
results, however, were achieved with calcitic aggregates and with aggregates
of
quartz sand. However, the aggregates must be alkali-resistant, particularly
they must
not be alkali-silica reactive. The grain-size distribution should preferably
correspond
to the Fuller curve, i.e. the maximum density sphere packing. For a plaster
mortar,
very good results were achieved with an aggregate of grounded marble with a
mini-
mum grain size of 0.2 mm and a maximum grain size of 0.5 mm.
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Mortars made of the inventive binder have very low elastic moduli: At
compressive
strengths of 15-25 MPa, elastic moduli of approximately 12 to 15 GPa are
measured.
With a mortar made of the inventive binder consisting of 100-300 parts by
weight of a
latently hydraulic aluminosilicate glass, b) 20-150 parts by weight of an
alkali activat-
or, and c) 50-200 parts by weight Of a latent hydraulic additive, wherein the
molar
ratio of Al/Si is <8 and the molar ratio of Ca/Si is <9, an elastic modulus of
7 GPa
was measured at a compressive strength of 20 MPa. With a mortar made of the
inventive binder with additional alkali hydroxide in the alkali activator, an
elastic
modulus of 5 GPa was measured. Low elastic moduli means high elasticity.
Furthermore, mortars made of the inventive binder show a good creep behavior.
This
means that the hardened mortar is deformable under pressure. With mortar
prisms
made of the inventive binder, a creep value of approximately 0.45 mm/m was
meas-
ured; with mortar prisms made of an inventive binder with the above weight
ratios, a
creep value of 0.54 mm/m was measured; and with mortar prisms made of an inven-
tive binder with zinc salt, a creep value of 0.35 was measured. For
conventional mor-
tars and concretes, however, creep values of only <0.2 mm/m are
characteristic.
Preferred is, for example, a mortar with a ratio of aggregates/binder of
1:0.25 to 1:4
and a ratio of binder/water of 0.25:1 to 2:1. The inventor has found that such
a
mortar:
- sets after 5 minutes to 24 hours;
- has, 4
hours after setting, stored at 20 C, an adhesive tensile strength on
concrete of approximately 0.5 to 3 MPa;
- has, 24 hours after
setting, stored at 20 C, an adhesive tensile strength on
concrete of approximately 1.0 to 4 MPa;
- has, 28
hours after setting, stored at 20 C, an adhesive tensile strength on
concrete of approximately 1.6 to 5 MPa;
- has, 4
hours after setting, stored at 20 C, a compressive strength of
approximately 1 to 3 MPa;
- has, 24
hours after setting, stored at 20 C, a compressive strength of
approximately 2 to 12 MPa;
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- has, 28 hours after setting, stored at 20 C, a compressive
strength of
approximately 10 to 30 MPa.
Partly, these results are considerable improvements compared to the state of
the art.
For example, adhesive tensile strengths of conventional mortars are
approximately
0.5 to 1 MPa after 24 hand 1,5 to 2.5 MPa after 28 days.
In a further preferred embodiment, an inventive mortar has a ratio
aggregates/bin-
ders of 1:0_5 to 1:2 and a ratio binder/water of 0.25:1 to 2:1, which results
in a dyn-
amic elastic modulus of hardened mortars of <15 GPa, sometimes even <10 GPa,
and thus obviously increased elasticity.
Another preferred mortar of the present invention has a ratio of
aggregates/binder of
1:0.2 to 1:5 and a ratio of binder/water of 0.3:1 to 2.5:1 and is thus
especially suit-
able for the production of a metal anode, e.g. a zinc anode, i.e. for
embedding a zinc
grid, zinc net, zinc punched plate or zinc wires_ Such a preferred mortar is
especially
suitable for the production of active and, above all, permanently active zinc
anodes
because the zinc anode also remains active with relatively low prevalent pH
values
(i.e. pH <12, preferably pH <11). Usually, a zinc anode only remains active at
pH
values of >13, preferably >14. A great advantage of the binder and the mortar
made
thereof is that, after an inactive phase due to desiccation, the zinc anode
becomes
active again immediately after remoisturing. The zinc anode's life is thus
increased,
since during dry phases (RH <60 %) the steel to be protected does not corrode
and
thus the zinc anode is not required. When moisture re-enters, the zinc anode
becomes active again, i.e. it is only active when it is really required.
In a further aspect, the invention provides a concrete adhesive that was
produced by
use of an inventive hydraulic binder, an inventive binder matrix or an
inventive
mortar. Due to its high ion conductivity, the inventive concrete adhesive is
especially
suitable for bonding slabs, tiles, metal pads, concrete and mortar precast
units to
concrete surfaces, e.g. of plate-like metal anodes to concrete.
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In a further aspect, the invention comprises the use of an inventive hydraulic
binder,
an inventive binder matrix or an inventive mortar for producing metal anodes,
i.e.
sacrificial anodes, for galvanic corrosion protection of steel, preferably of
steel in
reinforced concrete,
For this purpose, a metal having a more negative standard potential than iron
in the
electrochemical series, or an alloy substantially consisting of one or more
elements
that has/have (a) more negative standard potential(s) that iron, is preferably
embed-
ded into the hydraulic binder, the binder matrix or the mortar. Especially
preferred,
the metal or element is zinc, and the metal or alloy is preferably embedded in
the
form of a grid, net, punched plate or wires. The anode itself may have plate,
cube,
cylinder or grid form, preferably plate form, and it may be applied,
preferably adher-
ed, to a concrete surface or embedded in the concrete.
The inventive metal anode, especially zinc anode, clearly differs from zinc
anodes
according to the state of the art in the above properties of the inventive
binder,
especially in the high strength (approximately 15-25 IVIPa of compressive
strength),
high elasticity (elastic modulus <15 GPa, preferably <10 GPa), high creep
value
(>0.25 mm/m) and high ion conductivity. An inventive anode is further
characterized
in that it can be produced in tile or plate form and be adhered to the
construction
element to be protected by means of a suitable adhesive, preferably the
inventive
concrete adhesive, or be inserted as "discrete zinc anode" into the concrete
con-
struction element to be protected. An inventive zinc anode may also be
produced "in
situ" on the construction element to be protected by embedding the metallic
zinc on
the construction element to be protected into the inventive binder and
hardening it to
= obtain the inventive binder matrix or mortar.
Furthermore, for preventing passivation a zinc anode according to the state of
the art
requires a binder with high alkalinity, such as described in US-A-6,572,760
(82),
where a pH of more that 12, preferably more than 14, is described.
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Surprisingly, the inventive binder is suitable, especially if it contains a
suitable zinc-
complexing agent such as a polyethylene imine, for activating zinc anodes,
even
though the pH value of the inventive binder is only approximately 10.5, as
mentioned
above. The anodes remain active even after longer use (several years) and are
reac-
tivated after dry periods. The activity can be increased considerably by
adding LiCI.
Experiments have shown that zinc anodes in Portland cement concrete or mortar,
even in highly alkaline Portland cement or in Portland cement spiked with
alkalis,
lose considerable activity after a dry-wet change. The inventive binder is
thus also
especially suited for the production of "single anodes, also called "discrete
anodes",
as is e.g. also described in US-A-6,572,760 (82).
In order to guarantee long-lasting functioning of the zinc anode, the addition
of
latently hydraulic aluminosilicates has proven especially effective and
advantageous.
The zinc anode is sensible to dissolved calcium ions that can be released by
the
latently hydraulic aluminosilicate glass during hydration. Dissolved calcium
ions
cause a passivation of the zinc and thus prevent the galvanic corrosion
protection of
being effective, In the long term, this may lead to an almost complete
inefficiency of
a galvanic zinc anode. By means of latently hydraulic aluminosilicate
additions, the
dissolved calcium can be permanently bound in the binder matrix, so that the
zinc
anode's functioning can be permanently guaranteed.
A precondition for the permanent effectiveness of galvanic zinc anodes is an
embed-
ding matrix that is substantially free of dissolved calcium Or contains only
traces of
dissolved calcium. In the inventive binder matrix, optionally dissolved
calcium can be
bound by adding latently hydraulic aluminosilicates. In contrast to calcium-
free
hydraulic binders, high strengths, high adhesive tensile strength, and high
elasticity
can be reached with the inventive calcium-containing binders_ This is another
substantial precondition for the production of the inventive zinc anodes. The
high
strengths are due to the integration of calcium into the binder matrix.
A preferred variant of preparing a galvanic zinc anode according to the
present
invention consists in filling an inventive mortar into a pre-fabricated
formwork, e.g. 50
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x 100 cm and 1 cm deep, up to a height of 0.5 cm; a zinc grid, provided with
elec-
trical connections, is inserted into this mortar layer, covered with mortar,
and thus
embedded in the mortar. The plate-like zinc anode thus produced is then bonded
to
the surface of the construction element to be protected from steel corrosion
by aid of
a suitable concrete adhesive, preferably an inventive concrete adhesive. After
hardening of the adhesive, the individual zinc anode plates are connected to
each
other and preferably twice within each construction element with the steel
reinforce-
ment via the electrical connections.
However, the galvanic zinc anode can also be produced directly on the concrete
construction element to be protected by applying a thin inventive mortar layer
to the
concrete surface. On this mortar layer, e.g, a zinc grid is attached and
embedded in
a second layer of the inventive mortar.
Depositing the zinc grid and embedding it in an inventive mortar layer on the
concrete has, of course, been shown to require high efforts, especially fixing
the zinc
grid by means of plastic dowels inserted into drill holes and soldering the
grids to
each other as well as creating the connection to the steel reinforcement. In
comparison, bonding plate-like galvanic zinc anodes onto concrete can be done
much more easily and quickly. The big advantage of plate-like zinc anodes is
that
they can be pre-fabricated in a workshop according to their intended use and
then be
quickly mounted at the construction site, e.g, by analogy with pre-cast
concrete parts.
In concrete surfaces with complicated structures, e.g. having projections, the
in-situ
production of the galvanic zinc anode can be easier and cheaper.
One embodiment of the inventive galvanic zinc anode is an anode that is suited
for
embedment in the concrete construction element For example, this embodiment
may be embedded in consisting concrete construction elements within the
framework
of concrete repair measures, in order to continuously prevent further
corrosion of the
steel reinforcement in the border area close to reconstructed concrete. For
this
application, prism-shaped and cylinder-shaped galvanic zinc anodes have proven
especially suitable. The galvanic zinc anode may, however, also be fixed as
discrete
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CA 02736772 2011-03-10
" =
anode in drill holes in the concrete construction element in a suitable anchor
mortar,
especially with an inventive concrete adhesive. For this application, again
cylinder-
shaped galvanic zinc anodes have proven especially suitable.
Experiments with a zinc anode embedded in the inventive hydraulic binder and
mounted on a concrete surface showed that, on condition that no fresh water is
able
to enter (e.g. by sealing the surface with a suitable material, e.g. epoxy
resin, PU, PE
foil etc.), chloride is galvanically extracted from the concrete cover during
the gal-
vanic anode's operation and is chemically bound in the solid electrolyte and
entirely
immobilized. Scanning electron microscopic studies showed that the chloride is
bound as zinc hydroxochloride to the zinc hydroxide produced during galvanic
operation and thus entirely immobilized. With 1 kg zinc/m2, 0.56 kg chloride
or an
equivalent of 5.65 % by weight/cement weight can be bound in 3 cm concrete
cover.
This means that over a longer period, e.g. of approximately 2 to 5 years,
chloride can
be entirely extracted from the concrete. If renewed entry of chloride is
prevented,
such a galvanic protection system can be switched off after approximately 5
years or
does not need to be renewed after expiration of its active period, which is
usually
approximately 10 to 15 years.
The galvanic metal anode, especially zinc anode produced according to the
present
invention is thus especially suited for preventive protection of steel in
concrete
against corrosion, for which purpose it is preferably embedded in fresh
concrete
during the manufacture of concrete construction elements. Preferably, the
galvanic
anode is fixed on the steel reinforcement, electrically connected therewith,
and
embedded in the fresh concrete together with the steel reinforcement. In a
last
aspect, the present invention thus comprises the use of such a sacrificial
anode for
protecting steel, especially steel in reinforced concrete, against corrosion.
In the following, the invention will be described in detail by means of non-
limiting
examples.
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CA 02736772 2011-03-10
EXAMPLES
Example 1
Component A
14 parts by weight of water
17 parts by weight of blast-furnace slag
parts by weight of metakaohn
0.1 parts by weight of cellulose ether
10 0.1 parts by weight of defoaming agent
60 parts by weight of limestone flour 0.1-1.0 mm
Component B
30 parts by weight of potash water glass
2 parts by weight of potassium hydroxide
Components A and B were each prepared my mixing the ingredients as an aqueous
suspension (component A) and a clear solution (component B), respectively. The
binder was produced by adding component B to component A. A standard concrete
slab (40 x 40 x 4 cm) was coated therewith. The mass hardened after 30
minutes.
After 24 hours, an adhesive tensile strength of 2 MPa, after 14 days of 2.8
MPa, was
measured. The compressive strength after 28 days was 16 MPa, and the static
elastic modulus was 10 GPa. The creep value, determined after 90 days, was
0.54
mm/m.
The blast-furnace slag had the following composition:
39 parts by weight of SiO2
6.9 parts by weight of A1203
41 parts by weight of CaO
0.4 parts by weight of K20
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CA 02736772 2011-03-10
Example 2
Component A
7 parts by weight of water
15 parts by weight of blast-furnace slag
12 parts by weight of metakaolin
8 parts by weight of a copolymer of butyl acrylate and styrene
50 % aqueous dispersion
0.2 parts by weight of zinc sulfate heptahydrate
0.1 parts by weight of cellulose ether
0.1 parts by weight of defoaming agent
56 parts by weight of limestone flour 0.2-1.0 mm
Component B
25 parts by weight of potash water glass
3 parts by weight of potassium hydroxide
Components A and B were each prepared my mixing the ingredients as an aqueous
suspension (component A) and a clear solution (component B), respectively. The
binder was produced by adding component B to component A, A standard concrete
slab (40 x 40 x 4 cm) was coated therewith. The mass hardened after 2 hours.
After
24 hours, an adhesive tensile strength of 21.7 MPa, after 14 days of 2.6 MPa,
was
measured. The compressive strength after 28 days was 18 MPa, and the elastic
modulus was 5 GPa. The creep value, determined after 90 days, was 0.35 mm/m.
Example 3
Component A
8 parts by weight of water
18 parts by weight of blast-furnace slag
10 parts by weight of metakaolin
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CA 02736772 2011-03-10
12 parts by weight of a copolymer of butyl acrylate and styrene
50 % aqueous dispersion
0.1 parts by weight of cellulose ether
0.1 parts by weight of defoaming agent
55 parts by weight of limestone flour 0.1-0.3 mm
Component B
28 parts by weight of potash water glass
2 parts by weight of potassium hydroxide
Components A and B were each prepared my mixing the ingredients as an aqueous
suspension (component A) and a clear solution (component B), respectively. The
binder was produced by adding component B to component A, The binding agent
thus produced was especially suited as concrete adhesive and tile adhesive.
Applied
onto concrete, the adhesive tensile strength after 24 hours was 2 MPa and
after 28
days 3 MPa.
Example 4
Component A
8 parts by weight of water
12 parts by weight of blast-furnace slag
16 parts by weight of metakaolin
12 parts by weight of a copolymer of butyl acrylate and styrene
50 % aqueous dispersion
0,5 parts by weight of zinc sulfate heptahydrate
0.1 parts by weight of cellulose ether
0.1 parts by weight of defoaming agent
2 parts by weight of lithium chloride
4 parts by weight of polyethylene imine
65 parts by weight of limestone flour 0.2-1.0 mm
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CA 02736772 2011-03-10
Component B
25 parts by weight of potash water glass
3 parts by weight of potassium hydroxide
Components A and B were each prepared my mixing the ingredients as an aqueous
suspension (component A) and a clear solution (component B), respectively. The
binder was produced by adding component B to component A. Into a formwork of
wood (30 x 30 x 2 cm), the mortar was filled up to a height of 0.75 cm, a zinc
grid
(mesh width of 3 cm, wire gage of 1.1 mm) was introduced, and the form was
then
filled up with the mortar.
Then the zinc anode was bonded to a steel-reinforced concrete slab (40 x 40 x
4 cm,
6 mm steel, E 10) with the concrete adhesive and stored in an air-conditioned
roam
at 20 C and 75 % RH. After hardening of the adhesive, the zinc anode was
connect-
ed with the reinforcing steel. A galvanic initial current of 50 mAim2 was
measured,
which decreased over approximately 8 weeks to approximately 8 mA/m2 and remain-
ed stable for at least 6 months (5 to 8 mA/m2).
Example 5
Component A
12 parts by weight of water
34 parts by weight of melting-chamber fly ash (vitrified)
15 parts by weight of pozzolan
8.6 parts by weight of polyethyl acetate
50 % aqueous dispersion
0.86 parts by weight of zinc sulfate heptahydrate
0.19 parts by weight of cellulose methyl ether
0.2 parts by weight of defoaming agent
0.9 parts by weight of lithium chloride
1.7 parts by weight of polyethylene imine
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CA 02736772 2011-03-10
Component B
50 parts by weight of potash water glass
parts by weight of potassium hydroxide
5 Component C
80 parts by weight of quartz sand 0.2-0.5 mm
The melting-chamber fly ash had the following composition:
52 parts by weight of SiO2
12 parts by weight of A1203
16 parts by weight of Ca0
0.6 parts by weight of 1<20
The pozzolan had the following composition:
65 parts by weight of SiO2
30 parts by weight of A1203
5 parts by weight of CaO
Components A and B were each prepared my mixing the ingredients as an aqueous
suspension (component A) and a clear solution (component B), respectively. The
binder was produced by adding component B to component A, and then adding
component C. In a cylindrical formwork of plastic (diameter 9.4 cm, height 12
cm), a
helical zinc grid (total weight of 170 g) was fixed in the center of the
cylinder. Onto
the zinc grid, an isolated copper wire (diameter 2.5 mm2) was soldered. The
mortar
was introduced into the form on a vibrating table, and the form was filled
full to the
brim. The form was stored at 25 C, stripped after 46 hours, and the form was
stored
at 99 % RH for further 5 days.
The zinc discrete anode thus produced was then introduced into a 10 cm wide
and
20 cm deep drill hole, filled with the concrete adhesive of Example 3, in a
steel-
reinforced concrete slab (30 x 30 x 20 cm, 6 mm steel, E 10). After hardening
of the
adhesive, the copper wire was connected to the reinforcing steel via a
measuring
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CA 02736772 2011-03-10
=
device by means of which the current can be measured without resistance. A
galvanic initial current of 8 mA was measured, which decreased over
approximately
8 weeks to approximately 1.2 mA and remained stable for at least 6 months (5
to 8
mA). Even after several dry/wet cycles, a galvanic current of 0.6 to 0.9 mA
was
measured after renewed storing in humid atmosphere.
Example 6
Component A
18 parts by weight of water
2 parts by weight of hydrogen peroxide 35 %
42 parts by weight of blast-furnace slag of Example 1
10 parts by weight of vitrified hard-coal fly ash
5 parts by weight of polyhexyl acrylate
50 % aqueous dispersion
2 parts by weight of zinc sulfate heptahydrate
0.01 parts by weight of starch ether
0.15 parts by weight of defoaming agent
0.5 parts by weight of lithium chloride
2.1 parts by weight of polyethylene imine
Component B
47 parts by weight of potash water glass
1 parts by weight of potassium hydroxide
Component C
65 parts by weight of quartz sand 0,2-0.5 mm
The vitrified hard-coal fly ash had the following composition:
55 parts by weight of SiO2
23 parts by weight of A1203
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CA 02736772 2011-03-10
=
8 parts by weight of CaO
0.6 parts by weight of K20
Components A and B were each prepared my mixing the ingredients as an aqueous
suspension (component A) and a clear solution (component B), respectively. The
binder was produced by adding component B to component A, and then adding
component C. Into a cylindrical formwork of plastic (diameter 9.4 cm, height
12 cm),
a helical perforated sheet of a zinc alloy (70 % Zn, 30 % Al) (total weight of
140 g)
was fixed in the center of the cylinder. Onto the zinc grid, an isolated
copper wire
(diameter of 2.5 mm2) was soldered. The mortar was introduced into the form on
a
vibrating table, and the form was filled full to the brim. The form was stored
at 25"C,
stripped after 48 hours, and the form was stored at 99 % RH for further 5
days.
The zinc discrete anode thus produced was then introduced into a 10 cm wide
and
20 cm deep drill hole, filled with the concrete adhesive of Example 3, in a
steel-
reinforced concrete slab (30 x 30 x 20 cm, 6 mm steel, E 10). After hardening
of the
adhesive, the copper wire was connected to the reinforcing steel via a
measuring
device by means of which the current can be measured without resistance. A
galvanic initial current of 9 mA was measured, which decreased over
approximately
8 weeks to approximately 1 mA and remained stable for at least 6 months (0.5
to 1.0
mA). Even after several dry/wet cycles, a galvanic current of 0.8 to 1.5 mA
was
measured after renewed storing in humid atmosphere.
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