Note: Descriptions are shown in the official language in which they were submitted.
CERTIFIED TRANSLATION
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2076868
PROCESS FOR PRODUCIN~ A HYDRAULIC BINDER (II)
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Fleld of Art
The invention relates to a process for the
production of a hydraulic binder for use in a mortar
or concrete mixture, the properties o~ which, such as
workability, setting ~ime, shor~-term and/or long~term
strength, are to be regulated by additives, wherein the
binder contains, as strength-i~creasiny additives, at
least soluble salts of carbonic acid.
The invention ~urthermore concerns a hydraulic
binder for the production of concrete having a high
short- and long-term strength, based on a ground
clinker with substantially homogPneously distributed
calcium phases and additives for regulating the work-
ability, setting time, and short- and long-term strength.
..
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:.... . .
2~7~8~
State of the Art
The hydraulic binders encompass diverse
standardized cements, Por~land cement being the main
representative. The lat~er consists essentially of
highly basic compounds of lime with silicic acid
(SiO2), aluminum oxide (A12O3) and iron(III) oxide
tFe2O3). This cemen~ contains, as the secondary
ingredients, oxide forms of magnesium, alkalis,
titanium and manganese. The mineral structure of
Portland cement consis~s of C3S ttricalcium silicate),
C2S (dicalcium silicate), C3A (tricalcium aluminate)
and C4AF (tetracalcium aluminoferrate).
In accordance with the standard (ASTM
C150, DIN 1164), Portland cement is produced by fine
grinding of Portland cement clinker with calcium
sulfate tgypsum). The approximate chemical composi-
tion of Portland cements is as follows:
SiO218 - 33 % by weight
A12O33 - 7 % by weight
Fe2O32 - 4.5 % by weight
CaO60 - 65 % by weight
SO3 2 - 4 % by weight
Generally known properties of commercially
available ordinary Portland cements are, inter alia,
the relatively ow short-term s~rengths as well as the
~ 3
~7~8
low durability and resis~ance with respect to environ-
mental influences, such as, for example, frost, salt of
condensation, and sulfate-containiilg waters. The
unsatisfactory durability is essenlially due to the
porosity of the mortar and concrete mixtures prepared
with the binder, this porosity being high on account of
the rather high water/cement values (about 16-18 vol-~).
Another disadvantage in the ordinary Portland cements
is the considerable volume contraction ~shrinkage)
after setting.
In the construction indus~ry and in the building
trade, there has been for a long time and for a wide
Eield of special applications a need for a hydraulic
cement having high short-~erm strengths and a low
porosity.
Increased s~rengths can be obtained to a
limited extent in Portland cements even without additives.
This is possible, on the one hand, by increasing the
fineness of grain ~Blaine 4000-5500 cm2/g), on the
other hand, by increasing the C3A content. However,
problems reside in that the water requirement of the
cements rises undesirably wlth the grinding fineness
and the sulfate stability fades with an increasing
C3A content.
2~7~
It is known that the durability and, in
particular, the attainable streng~hs increase wlth a
decreasing porosi~y of the mortar or the concrete mix-
ture. For this reason, enormous strength increases can
be obtained by reducing the water/cement ratio. In
order to yet maintain the flowability of the fresh
concrete at a level requirPd for working, so-called
liquefiers (sulfonated formaldehyde resins or ligno-
sulfates~ are utilized. The water requirement of Port-
land cements can thus be lowered to 30% lusually about50%) and, when furthermore using additives, such as
microsilica, down to 20~. Compressive strengths of
up to 24 MPa could thereby be obtained 8-12 hours
after production of the concrete mixture.
High short-term strengths (15-20 MPa earlier
than 6 hours after preparation of the fresh concrete)
are obtained with extremely finely ground Portland
cements only with the addition of chemical activators,
such as calcium chloride, or alkali activators, such
as alkali hydroxides, carbonates, aluminates, silicates.
Frequently, the activators are utilized in conjunction
with liquefiers and set-retarding agents. The cited
additives can also be used with the desired effect in
hydraulic binders markedly different from Portland
cement in their composition (for example, in calcium
fluoroaluminate and calcium sulfoaluminate cements).
~ ~) 7 ~
Such binder formulations with hi~h short-
term strength are utilized, above all, as spray con-
crete or dry mortars for concrete work wherein a saving
in time is accompanied by an enormous saving in cost,
such as, for example, when repairing roadway, garage,
and landing strip surfaces, or molds for metal casting
operations.
A hydraulic binder is known from US 4,842,649
which hardens reliably at high as well as low tempera-
tures, especially below ~he freezing point of water.This binder, known under the trada name of "Pyrament",
consists of 50-80% by weight of Portland cement and
diverse additives, such as, for example, fly ash from
coal-burning power plants, blast ~urnace slag, meta-
kaolin, microsilica, as well as activating additives,such as alkali hydroxides or carbonates and, if neces-
sary, citric acids and cltrates as setting retarders.
The high shor~- and long-term final strengths of cor-
responding concrete formulations are apparently due
to the activation and acceleration of the puzzolanic
reaction between hydroxides and silicate or alumino-
silicate materials.
The conventional binders have the drawback of
a large number and quantity of, in part, expensive ad- -
ditives (microsilicate, metakaolin) to the Por~land
cement, requiring an expensive mixing procedure.
- 6 - 2~76~8
Furthermore, practical experimen~s showed that the
setting times can only be controlled with great
difficulties.
JP 59-064 551 discloses a spray concrete
formulation wherein a carboxylic acid, especially
citric acid or citrate is added as a retardiny agent
to a mixture of Portland cement, calcium aluminate
cement and alkali carbonate. In this way, high early
as well as final strengths are to be obtained with
good workability.
For many applications, adequate workability
time is absolutely necessary. Therefore, the re-
producible adjustability of the setting time of concrete
mixtures of high early strength is of cen~ral impor~ance.
Practlcal experiments have shown that all
binders known thus far for obtaining high-early-strength
concrete have the disadvantage that the regulation of the
setting times can be only insufficiently reproduced.
Furthermore, many of the known special cements are
sensitive, with regard to their properties ~workability,
setting time, strength development), to changes in the
water/binder ratio and the temperature during fresh
concrete production.
On account of the aforementioned drawbacks,
the use o the conventional high-early-stren~th hydraulic
binders has remained limited to a few applications
insignificant in volume.
2076~G8
Descriptian of the Invention
It is, then, an object of the invention to
indicate a process for the production of a hydraulic
binder avoiding ~he disadvantages inherent in the
state of the art and, in particular, making it possible
to regulate, in reproducible fashion, the workability,
setting time, early and/or long-term strength by the
controlled admixture of additives.
This object has been attained according to
the invention by admixing to a ground clinker with
substantially homogeneously distributed calcium sulfate
phases and a ferrite proportion of at least 4~ by weight
an iron-complexing compound in the dry state, as the
activator for shortening the setting times and for
increasing the early and long-term strength.
The basic aspect of the invention resides in
the realization that the clinker phase, ~errite
(4CaO A12O3 Fe2O3), heretofore considered to be of
low reactivity up to being entirely nonreactive, can be
activated in an unexpectedly advantageous way for
accelerating the setting time and increasing the
short-term and long-term strengths.
The use of iron-complexing compounds leads
to shortened setting times and increased strengths,
especially raised early strengths. The activation
of the ferrite phase according to this invention
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2~8~
can be utilized predominantly in case of clinkers with
a ferrite proportion of at least 4~ by weight, preferab-
ly 6% by weight.
A preferred binder is distinguished in that
S the additives contain a proportion~ based on the
clinker, of at least 3 mmol-~ of an iron-complexing
compound, and a carbonate donor in a molar ratio, based
on the iron-complexing compound, oE between 0.3 and 4.
A mortar or concrete mixture produced with such a
binder is distinguished by low sensitivity of the
properties with respect to changes in the water/cement
ratio.
With a suitable choice of the concentration
ratio of the activators (carbonate donor/iron-
complexing compound~, the ferrite clinker phase,
generally considered to be nonreactive, is hydrated
the fastest (after 24 hours to an extent of 100%) and
thus contributes essentially toward a development of
the high early and long-term strengths.
A suitable additive for prolonging the
setting time is a ca}cium-sulfate-con~aining additive.
This has preferably the form of gypsum, anhydrite,
or a mixture of both.
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Preferably, the amount of the calcium-sulfate-
containing additive is dimensioned so that the calcium
content of the binder, calculated as CaSO4, ranges
between 0.7~ by weight and 8% by weight. Without any
significant effect on the strength evolution, the
setting times can thereby be regulated between 0 and
maximally 300 minutes by the quantity of CaSO4 that
is added.
Typically, in a binder according to this
invention, the molar ratio of sulfate to the iron-
complexing compound is within a range of between 1
and 20, A molar ratio of between 3 and 8 is partic-
ularly preferred.
The low sensitivity of the properties with
lS respect to changes in the water/cement ratio, as
set forth above, is present, in particular, if the
ratio of carbonate/iron-complexing compound is
within a range of between 1 and 3.
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2~7~
In contrast to the conventional binder formula-
tions, the need for water decreases in thls invention
with rising grain fineness. For this reason, use is
advantageously made of Portland cement clinkers and,
respectively, Portland cements in a grinding fineness
according to Blaine of at least 4000 cm2/g. Good
results can be achieved in the rar,ge from 4500 cm2/g to
5500 cm~/g. ~t is thus unnecessary to utilize the
Portland cement clinkers and, respectively, Portland
cements tha~ are ground with great ~ineness (8000 cm~/g
and more) and are thus expensive.
The additives preferably contain as the
carbonate donor salts o carbonic acid which are
soluble in water as well as those which show low or
no solubility therein. Calcium carbonate, magnesium
carbonate and/or dolomite are particularly well suit-
able. The salts showing low up to no solubility, mainly,
have been preactivated by grinding and/or thermal trea~
ment. The amount of the salts of low to no solubility
in water is preferably between 2 and 20% by weight.
Water-soluble salts of carbonic acid, in
particular alkali carbonates and/or alkali hydrogen
carbonates are preferably used as the carbonate donor,
and water-soluble salts of polyoxycarboxylic acid or of
polycarboxylic acid, or a diketone, are used as the
iron-complexing compounds. Suitable as the carbonate
donor is potassium carbonate, potassium carbonate
. .
- 11- 2~76~6~
trlhydrate and potassium bicarbonate. Such carbonate
donors are preferably combined with iron-complexing
compounds, such as tripotassium citrate monohydrate
or a mixture of dipotassium oxaLate monohydrate and
tripotassium citrate monohydrate, the proportion of
dipotassium oxalate monohydrate amounting to less than
50 mmol %.
The iron complexes according to this invention
of polyoxycarboxylic acids, polycarboxylic acids and
diketones have the advantage that they are relatively
strong, especially in comparison with iron-amine com-
plexes.
Citric acid, a polyoxycarboxylic acid, is an
especially ef~ective complexing agent for iron. The
advantage of the citrate resides in that the activating
effect is multiplied by the alkali activators, especial-
ly by potassium carbona~e and potassium bicarbonate.
The activalion of ferrite can lead, in the
drying of mortar and concrete, to the formation of
undesirable brown spots on the surface. This spot for-
mation can be prevented according to this invention by
adding 0.1 - l~ by weight of oxalic acid or, respect-
ively, its alkali salts.
The additives contain a proportion, based on
the clinker, of at least 4.5 mmol-%, preferably at
least 7.5 mmol-% of potassium citra~e (K3C6H5O7 H2O)-
~7~
The additi.ves can contain, based on the clinker,a proportion of a~ leas~ 11 mmol-~ of citric acid.
The carbonate proportion according to this in-
vention ranges between at least 5 mrnol-~ and at most
25 mmol-%. This makes it possible to attain high early
strengths. In order to obtain long-term strength, the
additives contain a proportion, based on the clinker, of
at least 9 mmol-~ and at most 30 mmol-~ of potassium
bicarbonate.
In order for a mortar or concrete mixture pro-
duced with the binder according to this invention to set
extensively independently of the ambient temperature,
in particular also at temperatures below the freezing
point, it is possible to admix as the additives also
puzzolan earths, clay minerals, ~ly ashes and/or most
finely divided reactive silica.
A mortar or fresh concrete according to this
invention is distinguished by a hydraulic binder of the
above-mentioned type and a water/cement value in a
range of 0.25 - 0.4, especially 0.3 - 0.37.
The invention provides the following
advantages important under practical conditions:
(a) high early strengths accompanied by
high long term strengths ( ~ 28 d);
(b) low sensitivity of the strength develop-
ment, especially the early strengths, with respect to
the Por~land cement clinker composition;
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2~7~68
(c) insensitivity of strength evolution with
respect to the composi~ion of ~he customary concrete
aggregates;
(d~ low sensitivity of the strength evolution,
the setting times, and the consistency (workability) with
respect to changes in the water/cement ratio (comparable
to ordinary Portland cements);
(e) low sensitivity of ~he strength evolution,
especially the early strengths and the setting times,
with respect to the processing temperature;
(f) low porosity and high durability.
The following can be noted in detail with
regard to the advantages:
As for ~a): The evolution of the stren~th of
a mortar or unset concrete mixture according to this in-
vention is characterized in that it is possible, with
the usual workability (extent of flow 45-50 cm,
slump 15-20 cm), to obtain about 30 minutes af~er the
end of the setting process strengths of typically
19 MPa, but at least 15 MPa; this corresponds to
about 80% of the 6-hour strength values. Af~er 28 days,
the strengths are typically around 75 MPa. On the
other hand, analogous early strength values can be
obtained 90 minutes after termination of setting, but
a lower generation of heat occurs during hardening, and
- 14 ~0~686~
comparatively higher long-term strengths of about
90 MPa are attained after 28 days.
Thus, according to the invention, the evolu-
tion of the early strength and the heat generation
during the early hardenlng phase are requlated by way of
a simple change of the initial pH value of the binder
mixture.
In contrast to the invention, in known
activated high-early-strength binders (as described,
for example, in US 4,842,649), comparable strengths
could only be attained with far stiffer concrete mix-
tures. ~t the same time, the high production of heat
(especially when using calcium sulfoaluminate and
calcium fluoroaluminate cement~ could be affected to
an only minor extent, or not at all.
As for (b): Basically, adequate early
strengths can be attained with all Portland cement
clinkers of the norm by using a minimum C4AF content
of 4% by weight, preferably 6~ by weight. Optimum
early strengths result with clinkers having at least
9.5~ C4AF, wherein the clinker reactivity affects the
set~ing times, but no~ the strengths.
Differently from ~he invention, in the
binders known from the state of the art, the binder
composition has a substantial influence on the strength
evolution, especially on the early strengths.
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2~76~8
As for (cl: The grading curve and the compo
sition of the concrete aggregates does affect the need
for water, as in the ordinary concrete mixtures, but,
at the same consistency, the strength evolution is in-
dependent of the type of aggregate!3. This is in contrast to thP experiences with the heretofore known,
activated, high-early-strength Portland cements,
especially when using organic liquefying agents.
As for (d): In the invention, the eaxly
strengths (2~4 hours) react to changes in the water/ce-
ment value approximately with the same sensitivity as
the 24 48 hour strengths of ordinary Portland cements.
The same holds true analogously for the consistency and
the setting times of ~resh concrete. This affords the
great advantage in comparison with conventional high-
early-strength binders that it is possible to process
very liquid ~extent of flow ~ 50 cm) and, respectively,
liquid (extent of flow 45-50 cm) concrete ~ixtures in
the same way as concrete of ordinary Portland cement
without having to forego the high early strengths ac-
cording to this invention. The aforementioned proper-
ties can be realized with the invention using water/ce-
ment ratios of 0.33 - 0.36, without any problems.
. ' : ',
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2~7~68
In contrast to the invention, the strengths,
setting times and consistency of the known high-early-
strength binders which are based on Portland cement,
liquefiers and activators as well as optionally addi-
tives such as fly ash, metakaolin and microsilicareact in a very sensitive way to changes in the
water/cement ratio. The low water/cement ratio of
0.20 - 0.26 necessary for attaining the known char-
acteristic early strengths results in a strongly
thixotropic behavior of the fresh concrete and thus
greatly restricts its workability and range of usage.
As for (e~: In the temperature range (tempera-
ture of cement, aggregates and water) of 5 C to 30 C,
the early strengths of a concrete mixture according to
this invention change merely by about 20%, and the
setting times by about 50%. The 24-hour strengths ex-
hibit the same temperature sensitivity as ar. ordinary
Portland cement of the P50 type.
In contrast thereto, ~he conventional
ordinary Portland cements are far more sensitive with
respect to temperature variations, namely as regards
setting times as well as evolution of strength.
Normally, a lowering of the temperature from 20 C to
7 C brings about a slowing down of the strength
evolution and set~ing by a ~actor of 3. Under the same
conditions, in a binder of this lnvention, the setting
times increase by a factor of about 1.3.
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As for_(f): Due to the low water/cement
values (preferably 0.33 - 0.36), the porosity values in
the concrete, as measured after 7 days, lie, in this
invention, markedly ~elow those attainable with Port-
land cement without additives after 28 days (accordingto the invention, 6 vol-%/g as contrasted to 8-18 vol-
%/g in Portland cements without additives). Thereby
the durability (shrinkage, creep, frost/dew, frost/salt
resistance, sulfate resistance) of the hardened con-
crete is clearly better than that of previous concretes
with similar water/cement values.
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Brief Description of t_e Drawi~
The invention shall be described in greater
detail below with reference to embodiments and in
conjunction with the drawings wherein:
Figure 1 illustrates the sensitivity o:E the
properties of the binder in dependence on the
carbonate/citxate ratio;
Figure 2 shows the influence of water,
carbonate donor and potassium citrate on the compres-
sive strength in dependence on the type of clinker and
on the carbonate donor;
. Figure 3 illustrates the dependency of the
6-hour compressive strength on the C4AF content when
using potassium bicarbonate as the carbonate donor;
lS Figure 4 ~hows the dependency of the 6-hour
compressive strength on the C4AF content when using
potassium carbonate as the carbonate donor;
Figure 5 illustrates the dependency of the
4-hour strength of a binder according to this invention
on the water/cement ratio in comparison with the 24-
hour strength of a conventional Portland cement free
of additive;
Flgure 6 illustrates the dependency of the
4 hour and 24-hour strength on the water/cement value,
as compared with a conventional high-early-strength
binder, in case of a binder of this invention;
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207~6~
Figure 7 shows the temperature dependency of
the early strength of a binder according to this inven-
tion as compared with the 48-hour strength of a known
high-early-strength cement;
Figure 8 illustrates the dependency of the
flowability ~FLOW) on the water/cement value with a
binder according to the invention in comparison with a
conventional high-early-strength binder.
Tables 1.1 - 1.3 show a compilation of the
clinkers and Portland cements utilized in the examples;
Table 2 shows the effect of potassium citrate
on the hardening characteristic of Portland cement in
ISO mortar;
Table 3 shows the effect of potassium bi-
carbonate and po~assium citrate on the cement hardeningprocess;
Table 4 shows the effect of alkali carbonate
and potassium citrate on cement hardening;
Table 5 shows an example with ~he additives
citric acid and potassium carbonate;
Table 6 shows hydration of the clinker
phases in dependence on the time;
Tables 7 and 8 show the effect of the hemi-
hydrate in the presence of dihydrate on the properties
o the binder at various formulations of the activating
additive;
- 20 - 2~76~8
Table 9 shows properties of formulations with
various proportions of citrate and, respectively,
citric acid;
Table 10 shows a comparison of potassium
carbonate and potassium bicarbonate at various
water/cement ratios;
Table 11 shows clinker ground without gypsum
with varying amounts of dihydrate and hemihydrate
wherein the additives containl on the one hand,
citrate and, on the other hand, citric acid, each in
combination with potassium carbonate;
Table 12 shows several especially preferred
embodiments;
Table 13 shows examples having particularly
high early strengths;
Table 14 shows the influence of the addition
of dipotassium oxalate, on the one hand, in conjunction
with potassium carbonate and, on the other hand, with
potassium bicarbonate.
- 21 ~ 8
The following expressions and abbreviations
are utilized, inter alia, in the f:igures and tables:
DF compressiva strength
W/C water/cement ratio
CSTR compressive strength (in English)
SET setting time
FLOW flowability
DH dihydrate
HE hemihydrate content
A anhydrite
A nat. natural anhydrite
A sol. soluble anhydrite
CITR.AC citric acid
K3C tripotassium citrate monohydrate
PZ Por~land cement
PK Portland cement cli~ker
- 22 - 2~76~
Ways o~ EXecutinq the Invent.lon
The basis for a binder according to this in-
vention is constituted by a ground clinker having a
ferrite propor~ion of at least 4~ by weight, prefer-
ably a ground Portland cement clinker, and a calcium-
sulfate-containing additive that has been ground
either together with the clinker ox separately. The
cement or the gypsum mixed with the clinker ground
without gypsum constitutes 80 95% by weight of the
binder. The remaining weight proportions are provided
by the activators according to the invention.
It is advantageous in accordance with this
inv~ntion not to exceed 120 C, preferably 70 C,
when intermixing the activators. Depending on the
lS binder composition, excessive temperatures can lead
to undesirable secondary effects (such as, for example,
uncontrolled variation of the setting times~
In accordance with an especially prefexred
embodimen~ of the invention, additives are utilized as
the activators which contain, on the one hand, soluble
salts of carbonic acid and, on the other hand, iron-
complexing, preferably pH neutral to basic compounds.
These agents are used to regulate, on the one hand,
the strengths, particularly the early strengths, and,
on the other hand, the setting times. The iron-
complexing compound (~ox example, potassium citrate
monohydrate or citric acid) here acts surprisingly
- 23 - 2~
as an activator rather than as a retarding agent,
i.e. it accelerates the setting process and
increases the strength.
Advantageously, the iron-complexing compound
. .
is added in an amount of at least 3 mmol-% ~based on
the clinker). The soluble salts of carbonic acid ~e.g.
potassium carbonate) acting as the carbonate donor
are added in a molar ratio, based on the iron-
complexing compound, of between 0.3 and 4. Advanta-
geous properties result from the selection of themolar ratio according to this invention; these will be
explained hereinbelow with reference to an example.
- 2~ -
2~76~3~3
Figure 1 depicts the sensitivity of various
parameters with respect to changes in the water/cement
value (by 9%) in dependence on ~he ratio of carbonate
to citrate. While the flowability (FLOW), the 6-hour
and the 24-hour strengths are only slightly sensitive
in the range between 1.5 and 4.5 (molar ratio), the
sensitivity of the 4-hour strength and the setting time
(SET) greatly increases with the molar ratio, with
carbonate/citrate values of larger than 3 to 3.5.
In other words: if, in the example on which the il-
lustration is based, the carbonate/citrate ratio is
selected to be smaller than 3, then the aforedescribed
properties are extensively insensitive to changes in
the water/cement ratio.
The qualitative information provided by
Figure 1, namely the existence of a molar ratio range
wherein the properties are insensitive to parameter
changes, holds true for all activators according to
this invention. In a quantitative respect, i.e. as to
exact locations of the limits, there may be differences
among the various activator combinations. Thus, it
can be that, for certain activator combinations, the
desired effect will occur already at molar ratios of
smaller than 4 whereas this will be ~he case for
others only below 3.
,.,t
-~ - 25 -
2~76~8
The most advantageous results as regards
strength development, workability and sensitivity are
achieved with a binder according to this invention by
mixing 80-95 parts of Portland cement clinker with a
calcium-sulfate-containing addi~ive and an effectively
strength-raising additive in the dry condition. In
this connection, the Portland cement clinker is ground,
without addition of gypsum, to a fineness of
4000-6000 cm~/g, preferably to about 5000 cm2/g ac-
cording to Blaine.
The calcium-sulfate-containing additive
contains gypsum (CaSO4 2H2O) and/or anhydrite
(CaSO4). It is produced by grinding gypsum and/or
anhydrite, optionally with limestone and/or other
inert additives to grain siæes of smaller than 120 ~m,
preferably smaller than 60 ~m and 90% larqer than 2 um.
Grinding of the calcium-sulfate-containing additive
can be performed in a customary open ball mill, in a
dish-type roll mill, in a micro turbulence mill, or in
some other way. The grinding temperatures and the
storage temperature should lie below the formation
temperature of hemihydrate (lower than 70-80 C).
It is also possible to use, as the calcium-
sulfate-containing additives, for example, residual
materials from the chemcal industry ~citro-gypsum,
phosphogypsum, gypsum from titanium dioxide processing,
etc.) or residual substances from the flue gas
- 26 -
2~7~
desulfurization. I these additives are available in
the required fineness, they can be added directly.
O~herwise they are to be ground up as described above.
The calcium-sulfate~containing additive is
admixed in an amount 50 that the binder contains
0.7 - 8% by weight of gypsum and/or anhydrite (cal-
culated as CaSO4). With this additive, the setting
time is set to a certain basic value of between 0 and
300 minutes. The development of the strength is not
significantly affected thereby.
The effectively strength-increasing additive
contains at least one iron-complexing compound and at
least one carbonate donor or, respectively, carbonate
generator.
As the iron-complexing compound, any compound
can be employed which enters, in an aqueous solution
in an alkaline medium (pH ~ 10) with iron(III) into
stable, soluble complex compounds. Among the latter are
the representatives of the polyoxycarboxylic acids,
such as citric acid, tartaric acid, lactic acid,
gluconic acid, malic acid, etc., and their salts;
also representatives of the polycarboxylic acids, such
as oxalic acid, maleic acid, malonic acid, succinic acid,
etc., and their salts. Finally, also suitahle are
representatives of diketones, such as pyruvic acid,
acetylacetoacetate, dimethylethylsuccinate, etc., and
their saltsO In principle, it is also possible to use
.
d,
.
. '' , ~ .
- 27 -
2~7~8~
hydroquinoline, ami~e, pyridine, glyoxime and similar
compounds. The latter are less preferred because of
certain drawbacks, such as toxicity, odor, or cost.
Especially preferred properties are attained,
for example, with the salts of citric acid, particularly
wlth tripotassium citrate monohydrate (K3C) wherein the
latter can be partially substituted by a polycarboxylic
acid, such as, for example, oxalic acid and/or potas~
sium oxalate.
As the carbonate donor or generator, compounds
can be utilized which release, in an alkaline aqueous
medium, carbonate ions or which react, with reactive
calcium compounds, such as Portlandite Ca~OH)2, C3A,
C3S, etc., to calcium carbonate and/or compunds con-
taining calcium carbonate, such as, for example, carbo-
aluminates 4CaO CaC03 llH20, carboalumoferrites,
taumasite, carboaluminosilica~es, etc.
Soluble salts of carbonic acid, such as
alkali carbonates MC03 and/or alkali hydrogen carbonates
MHC03 (M = Li, Na, K), but also tetraalkylammonium
carbonates act as the carbonate donor. Gompounds which
release, in aqueous media, carbon dioxide and/or
carbonate, such as, for example, compounds of carbamic
acid, act as carbonate generators.
In order to increase shelf life, it is also
possible to use potassium carbonate trihydrate
2X2C3 3 2 -
- 28 -
8 ~ 8
The effective strength-raising additive is
produced by mixing its components, preferably in powder
form, optionally with fillers and/or other strength-
increasing additives (such as, for example, micro-
silica, alkali silicates, etc.). Tha components ofthe strength-raising additive can, however, also be
added to the binder individually.
The strength-increasing additive is dimen-
sioned in its amount so that the binder mixture con-
tains 3-12 mmol-% of iron-complexing compounds (e.g.
0.1 - 4~ by weight of potassium citrate monohydrate)
and 1 - 40 mmol-~ of carbonate donors (e.g. 0.1 - 4%
by weight of potassium bicarbonate).
Advantageous results are also obtained by
adding 0-10~ by weight of sparingly soluble to insol-
uble carbonates, such as, for example, calcium
carbonate. The aforementioned carbonates can be used
separately or jointly with the respective additives as
their component or by combined grinding with the
Portland cement clinker.
The hydraulic binder of this invention is
preferably produced by mixing its componentsin a
conventional dry mixer. As mentioned above, the tem-
peratureduring mixing should not exceed 120 C or,
preferably, 70 C.
:, , ,
. .
'
- 29 ~ 2~76~8
The advantageous properties of the invention are
to be demonstrated by the following individual examples
and comparative tests.
Tables 1.1, 1.2, 1.3 list the elementary
S compositions of the clinkers and cements utilized in the
examples (calculated as oxides~ and the corresponding
clinker phase compositions, calculated according to
Bogue (ASTM C150, modified).
Figure Z shows the factorial effect of water
~coefficient A) ~oward potassium carbonate cr
potassium bicarbonate (coefficient B) and of potassium
citrate ~coefficient C) on the 6-hour strength of a
mortar with various basic binders. The coefficients
were determined statistically (following the known
method of factorial experimental planning) with the
aid of the e~uation set forth below-
. .
- 30 -
8 $ ~
Y' = 1 ~ 2(a~A] + b[B] + c[C] + ab[A][B] ~ ac[A][C] +
bc~B][C~ + abc[A]~B][C]l
Y' = measured variable (6 hour compressive strength),
standardized to Y0 (measured value at central
point)
a ... c coefficientsstandardized to Y0
A ... C concentrations (-1 to + 1) standardized to
clinkers of A = water, B = potassium (bi)-
carbonate, C = potassium citrate
It can be seen from Figure 2 that, in the
binders according to this invention as tested, based
on Portland cement clinkers of a greatly differing com-
position, potassium citrate (especially in the presence
of potassium carbonate) is the component determining
for the 6-hour strength development.
It can also be seen from Figure 2 that the
effect of potassium citrate as well as that of potas-
sium carbonate and, respectively, bicarbonate becomes
stronger with increasing ferrite content.
Figures 3 and 4 show the correla~ion of the
6-hour strengths with the C4AF content (determined
according to Bogue) of a series of clinkers activated
according to this invention. As the activating
additive, a mixture of citrate and bicarbonate was
used in the examples of Figure 3, and a mixture of
citrate and carbonate was used in those of Figure 4.
,: :
. .
- 31 -
~7~8
In the presence of bicarbonate (Figure 3), a
positive correlation can be found of the 6-hour strength
with the ferrite content of the clinker. In other words,
with a rise of the C4AF content from 6% by weight to
about 10% by weight, the compressive strength (DF;
English CS~r = compressive strength) increases from
16 MPa to just about 20 MPa. The relationship can be
considered to be proportional in the first approx-
imation.
When using potassium carbonate (Figure 4),
the rise in strength proceeds in a markedly steeper
fashion that in case of the potassium bicarbonate
(Figure 3).
According to the invention, citric acid and
alkali salts of citric acid exert, due to the activa-
tion of the ferrite phase of the clinker according to
this invention, an accelerating and strength-raising
effect. This is to be explained with reference to
Tables 2-5. Table 2 shows the effect of potassium
citrate on the hardening characteristic of Portland
cement,(~laine 5000 cm~/g, 6~ dihydrate) in ISO mortar,
Table 3 shows the effect of pota~sium bicarbonate and
potassium citrate on the cement hardening process.
Table 4 shows the effect of alkali carbonate and
potassium citra~e on cement hardening. Table 5
finally shows an example with citric acid and potassium
carbonate as additives for increasing the streng~hO
- 32 -
207~868
The values set out in Table 2 clearly show
the accelerating and early-strength-raising effect of
potassium citrate. The setting time is reduced from
240 minutes (without potassium citra~e3 to 20, respect-
S ively 30 minutes with 2~ by weight of citrate. Thisis contradictory ~o the exis~ing teaching according to
which citric acid as well as citrate exert a retarding
effect.
It can be derived from Tables 3 and 4 that
markedly higher strengths(factor 2) are attained with
potassium citrate in combination with alkali carbonates
and, respectively, alkali bicarbonates. At the same
time, the plasticizing effect is enhanced. The addi-
tion of alkali carbonate, especially alkali bicarbonate,
lS brings about a prolongation of the se~ting times as
compared with the carbonate-free binders (Table 2).
In the examples of Table 3, the setting
time is reduced from 240 minutes (0~ by weight of
potassium citrate) to 120 minutes (2.7~ by weight of
potassium citrate). When using potassium carbonate
(Table 4), the setting time is reduced from 220 min-
utes (1.7~ by weight of potassium citrate) to 70 min-
utes (with 3~ by weight of potassium citrate).
The citrate is also the component essential
to obtaining high early strengths in the presence of
carbonates or, respectively, bicarbonates. The effect
of the citrate (high early strengths, reduction of
.~ :
:
- - ^-~
33 -
2 ~
water requirement) is enhanced by the carbonates. The
effect of carbonate, particularly of potassium bi-
carbonate, which delays setting in the presence of
citrate permits a regulation of the setting time which
S is practical for commarcial applications.
The activating action o potassium citrate,
especially in conjunction with bicarbonates, on the
fexrite phase, considered to be nonreactive in the
state of the art, in the Portland cement clinker is
confirmed by determinatlons of hydrated binder paste
carried out by X-ray diffractometry.
Table 5 shows the extent o~ hydration of the
clinker phases, determined by X-ray diffractometry
lclinker 1, 6% by weight gypsum).
A 30% hydration of the C3S phase is also
definitely customary in nonactivated Portland cements,
but here ~he alkali carbonate or bicarbonate present in
the binder of this invention as the carbonate donor
leads to the formation of unusually dense, quasi-
amorphous silicate hydrates, as they cannot be ob-
served in ordinary hydrated Portland cements. These
very dense, partially sulfate-, potassium-, iron- and
carbona~e-containing silicate phases contribute with
certainty toward an increased early and particularly
long-term strength. An alkali activation of the
silicate phases in the early stage of the hydration (up
to 24 hours) cannot be detected, however, in the
presence of citrate.
_ 34 -
2 ~
It is to be noted that the above-described
effects can also be observed with a low po~assium
citrate dosage. Consequently, it appears probable
that the salient feature here is not the ac~ivation of
the C3A phase already observed in the state of the art
with high doses of citric acid. This supposition is
also supported by the ~act that the highest early
strengths have been reached in this invention with a
sulfate-resistant, C3A-free clinker (clinker No. 7).
Tables 2-6 show that in the binder of the in-
vention, potassium citrate, as a representative of a
polyoxy- or polycarboxylic acid, is the important
component for reaching the high early strengths. The
hydration of the ferrite phase, activated by potassium
lS citrate, yields the largest contribution toward the
strengths within the first 24 hours after onset of
hydration (compare Figure 2).
Potassium carbonate or bicarbonate as the
carbonate donor enhances activation of the ferrite and
increases the plasticizing effect of the citrate. The
aforementioned carbonate donors, on the other hand,
retard set~ing. The prolongation of the resting phase
(duration of workability) of the cement paste or of
the mortar is due with great probability to the forma-
tion of a calcium carbonate protective layer on thesurface of the CaO-containing clinker phase
("carbonate effect ~
, . ,
' ,.
2~68~8
Ordinary ~ortland cement usually contains
4-7% by weight of gypsum as the sett:ing retarding agent.
This is added in the form of natural gypsum and/or
chemical gypsum to the Portland cement clinker before qrinding.
In the Portland cement, the gypsum is present as a mix-
ture of dihydrate, hemihydrate and anhydrite. The
quantitative ratios of the calcium sulfate phases
depend to a very great extent on the grinding conditions.
In the binder of this invention, the amount
of the calcium sulfate phases and the manner of ad-
mixing ~he calcium-sulfate-containing additives exert
an effect on the strength evolution and the setting
behavior. Advantageously, dihydrate tCaSO4 2H2O) i5
used advantageously for the calcium-sulfate-containing
additive wherein the latter can also be mixed with
fillers, such as limestone. Alternatively, it is also
possible to utilize anhydrite (CaSO4). The early
strengths attainable in this case range, however,
10-30~ lower than with dihydrate.
If the binder of this invention contains
hemihydrate (CaSO4 0.5H2O, respectively CaSO4 -
0.8H2O), the strength development and the setting
characteristic depend on the type of printer.
Tables 7 and 8 illustrate the influence
of th~ hemihydrate in the presence of dihydrate on the
properties of the binder in dependence on the
- 36 - 2~76~8
formulation of the activating additive. Comm~rcial
Portland cements are compared with the corresponding
clinkers, ground devoid of gypsum according to this
invention, with added dihydrate. The iron-complexing
compound employed is, on the one hand, potassium
citrate and, on the other hand, citric acid, and the
carbonate donor is, on the one hand, potassium carbonate
and, on the other hand, potassium bicarbonate.
The examples in Table 7 have the following
chemical and physical parameters:
Commercial Portland cement (PZll) Blaine 550Q cm2/g
Dihydrate . 1.4% by weight
Hemihydrate 3 % by weight
Anhydrite, insoluble 2.2~ by weight
The above basic mixture was combined with
two different activators:
Al: Total 4.6~ by weight, containing
40% of K2CO3 and 60~ of potassium citrate
monohydrate
A2: Total 3.5% by weight, containing
71% of K2CO3 and 29% of citric acid
. ..
. ~
.,''~
,
~ 37 -
207~68
The chemical and physical properties o~ the
examples in Table 8 are as follows:
Commercial Portland cement (Kleinkems) Blaine 5000 cm2/g
Dihydrate 1.5% by weight
Hemihydrate 1.2~ by weight
This basic mixture was combined with three
different activator formulations:
Al: 4.6% by weight, 40% K2CO3, 60% potassium citrate
monohydrate
A2: 4.7% by weight, 43% K2CO3, 57% potassium citrate
monohydrate
A3: 3.5% by weight, 71~ K2CO3, 29% citric acid
The examples of Table 9 are based on clinker
(PK1/4), ground free of gypsum, having a fineness o~
5300 cm2/g Blaine, and 6% by weight of dihydrate. As
the activating additives, 18.09 mmol-% of K2CO3 was
utilized, combined with varying amounts of citric
acid or citrate (in equivalent molar quantities).
The examples of Table 10 are based on clinker
(PKl/4), ground free of gypsum, having a finenes.s of
5300 cm2/g according to Blaine and 5% by weight of
added dihydrate. As the activating additives, 8.32 mmol-
~of potassium citra~e monohydrate was utili~ed in con-
junction with varying amoun~s of potassium carbonate or
potassium bicarbonate.
38 -
2~7~8~8
The binder mixtures of Table ll are based on
clinker (PKl/5), ground devoid of gypsum, and 0-6~ by
weight of gypsum and 6-0% by weight of hemihydrate.
In eac~l case, the following activating additives were
employed:
Al: 4.6% by weight, 40% K2CO3, 60~ potassium
citrate monohydrate
A2: 3.5% by weight, 71% K2CO3, 29% citric acid
It can be seen from the results of Tables 7
to ll that there exists a marked and significant dif-
ference with respec~ to the influence of the composition
of the activating additive on the properties of the
binder according to this invention between the
clinkers containing Portland cement and clinkers ground
free of gypsum (or hemihydrate-free formulations).
In the presence of potassium carbonate as the
carbonate donor, citric acid acts, in formulations
containing Portland cement, as an efficien~ retarding
agent, whereas it acts, in formulations free of hemi-
hydrate, as an activator with respect to the settingtimes and the strength development. In contrast there-
to, potassium citrate acts in both formulations as an
activator. The water requirement and the sensitivity
with respect to changes in the water/cement ratio is,
in citric-acid-containing formulations, clearly and
significantly higher than in K3C-containing formula-
tions (especially in binder mixtures containing Portland
cement~
. .. ; ~ ~ . , ''~
- 39 - 2~7 ~ ~8
Binder formulations containing potassium
carbonate/citric acid and commercia:L Poxtland cement
~e.g. as described in US 4,842,649 cited in the beginning)
are distinguished, as contrasted to formulations con-
taining potassium carbona~e/potassium citrate, ingeneral by high sensitivity of the setting times and of
the strength development with respect to changes in the
water/cement ratio, and by significantly lower strengthsO
The delaying action of citric acid, described in US
4,842,649, could only be confirmed in formulations
containing Portland cement, rather than in ~ormulations
having a low hemihydrate content. Espeeially when
using clinkers ground without gypsum, the citric acid
acts like an activator with regard to the setting times
as well as the strength development. The retarding ef-
fect of potassium citrate, equated to citric acid in
US 4,842/649, could not be confirmed in mixtures con-
taining Portland cement or in formulations having a low
hemihydrate content (especially, this could not be con-
fixmed in formulations containing clinkers ground freeof gypsum).
40 2~7~ 8
Table 12 shows a compilation of preferred
embodiments. The following activators were used
as thè additives:
CaSO4: S.0 - 5.8% by weight dihydrate, anhydrite~
hemihydrate (calculated as the
dihydrate)
Al: 3.85 - 5.0% by weight, 40-56% K2CO3, 40-60%
potassium citrate monohydrate
A2: 4.7 - 5.7% by weight, 43-53% KHCO3, 47-57
potassium citrate monohydrate
A3: 2.3% by weight, 87% K2CO3, 13% by weight citric
acid
, ':
- 41 - 207~68
Four especially preferred embodiments of the
invention are compiled in Table 13. The binder of
this invention was used in standarcl concrete (400 kg
of cement per m3, standard aggregat:e) at varying
water/cement ratios and, respectively, differing work-
ability of the fresh concrete. The grading curve of
the standard aggregates corresponds to the Fuller
curve.
The binder utilized has the following
formulation:
Clinker PKl/5 ground devoid of gypsum
Dihydrate 6% by weight
Activator 4.55% by weight, containing
40~ K2C03 and 60% potassium citrate
The table shows clearly that, with water/cement
values of between 0.32 and 0.37 and good workability
(extent of flow 35-63 cmt, very high early strengths
(4 hours) can be obtained of markedly above 20 MPa.
After 28 days, the strength was between 80 and 90 MPa.
Table 14 shows the influence of adding
dipotassium oxalate on the binder properties in ISO
mortar mixtures. All binders are based on the clinker
type P~1/5 mixed with 6% by weight of dihydrate.
The results show that K3C (potassium citrate)
can be extensively replaced by oxalate without any
substantial effect on the strength development. The
us of oxalate entails, however, a slight increase in
_ 42 - ~ ~7~8~8
the water requirement and a prolongation of the setting
periods. The reduction in heat of hydration is of
advantage.
Figure 5 shows the dependency of the 4 hour
strength on the water/cement ratio" Activated Portland
cements (PKl/5, 400 kg/m3) are compared with known
high-early-strength Portland cemen1ts (HPC Untervaz and
PC55 Xleinkrems).
It can be seen from Figure 5 that the
dependency of the compressive strength evolution on
the water/cement ratio (W/C) is approximately of the
same magnitude as in case of ordinary Portland cements,
i.e. those without additives. This is a great
advantage.
Figure 6 illustrates that the invention is
clearly distinguished over conventional high-early-
strength binders with respect to the sensitivity to
changes in the water/cement value. The binder
"Pyrament" (according to US 4,842,649) used for com-
parison, called T505 in the figure, is markedly more
sensitiveO With a change of the water/cemen~ ratio
by 10% from 0.33 to 0.30, the 4-hour strength
changes by a factor of 2. In contrast thereto, a cor-
responding change in the water/cement ratio from
0.37 to 0.34 in a binder of this invention leads to
a compressive strength increase of merely about 15%o
Similar remarks apply with regard to the 24-hour
strength.
_ 43 - ~7~8
Figure 7 shows the temperature dependency of
the early strength evolution in case of ISO mortar
mixtures. The temperature in degre,es C is plotted on
the abscissa, and the compressive strength in MPa is
plotted on the ordinate. The binder of this invention
(PKl/5, ground fxee of gypsum to Blaine 5300 cm2/g) was
compared with a known early-strength cement of the type
P50. As can be derived from the figure, the 4-hour
strength and, in particular, the 6-hour strength ob-
tained with the binder according to this invention ismarkedly less dependent on the temperature than the
48-hour strength relevant to P50.
Figure 8 shows the advantageously high flow-
ability (FLOW) of a binder according to the invention
in dependence on the water/cement value (W/C). With
a water/cement value of W/C = 0.34, the FLOW of a
binder based on the clinker PKl/5 amoun~s to about
125~. In case of W/C = 0.37, the FLOW is even at
about 150~.
In case of the "Pyrament" (T505) mentioned
repeatedly above, the FLOW is barely somewhat more
than 110% (standard) with a water/cement ratio of W/C =
0.33. With a W/C value of 0.30, the FLOW is even below
100%. Therefore, the lnvention shows a clearly improved
behavior over the conventional high-early strength
binder.
~ 44 ~ ~76~6~
The following can be noted, in summation:
The subject of the invention is a hydraulic
binder containing Portland cement clinker, a calcium-
sulfate-containing additive, strength-raising additives,
and optionally fillers or aggregate~s as usually found in
mixed cements, and making it possible, as compared with
previous binders, to obtain increased early and final
strengths (> 28 days) in concrete and mortar mixtures.
The invention overcomes, in particular, the following
disadvantages of conventional binders:
- uncommon workability in mortar mixtures and
concrete mixtures,
- high sensitivity of the relevant usage
parameters with respect to changes in
the binder composition,
- sensitivity with respect to the water/cement
ratio,
- great dependency of the early strength on
the working temperature.
The binder of this invention is preferably
distinguished by a hemihydrate content of less than
50%, especially less than 20%, calculated as the
dihydrate. At least one iron-complexing compound
and at least one carbonate donor are pref~rably used
as the strength-increasing additives.
.
_ 45 - ~07~$~
The inven~ion also indicates advantageous
processes for the production of Portland cements
having a defined maximum hemihydrat:e content.
