CA2076868A1 - Process for producing a hydraulic binder (ii) - Google Patents

Abstract

ABSTRACT
An iron complexing, pH neutral to basic compound is utilized as an activator, especially for shortening the setting times and for. increasing the early and long-term strengths, in a hydraulic binder which contains, as the additive, a soluble salt of carbonic acid. The ferrite proportion of the binder should amount to at least 4% by weight. The iron-complexing compound is to be admixed to the binder in the dry state. A hydraulic binder according to this invention contains preferably at least 3 mmol-%
of an iron-complexing compound and a carbonate donor in a molar ratio, based on the iron-complexing com-pound, of between 0.3 and 4.

Description

CERTIFIED TRANSLATION
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PROCESS FOR PRODUCIN~ A HYDRAULIC BINDER (II) ===========================-===a=_===-===_===

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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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.

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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).

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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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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.

- 9 - 2~7~8~8 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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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;

~ - 13 -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.

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.

. ' : ', 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.

- 18 - 2~76~8 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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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 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, .
. '' , ~ .

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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 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-. .

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.

,: :
. .

~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

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 .~ :

:
- - ^-~

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.

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.

Claims (19)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. Process for the production of a hydraulic binder for use in a mortar or concrete mixture, the properties of which, such as workability, setting time, early and/or long-term strength, are to be regulated by additives, wherein the binder contains, as strength-increasing additives, at least soluble salts of carbonic acid, characterized by admixing to a ground clinker having a ferrite propor-tion of at least 4% by weight, at least one iron-complexing compound in the dry state as an activator for shortening the setting times and for raising the early and long-term strengths.

2. Hydraulic binder for producing concrete having a high early and long-term strength, based on a ground clinker with essentially homogeneously distributed calcium sulfate phases and additives for regulating the workability, setting time, early and/or long-term strength, characterized in that the additives contain a proportion, based on the clinker containing a ferrite proportion or at least 4% by weight, of at least 3 mmol-% of at least one iron-complexing compound and a carbonate donor in a molar ratio, based on the iron-complexing compound, of between 0.3 and 4.

3. Binder according to claim 1 or 2, characterized by a calcium-sulfate-containing additive for prolonging the setting time.

4. Binder according to claim 3, characterized in that the calcium-sulfate-containing additive contains gypsum, anhydrite, or a mixture of both.

5. Binder according to claim 3 or 4, characterized in that the amount of the calcium-sulfate-containing additive is dimensioned so that the calcium sulfate content of the binder, calculated as CaSO4, ranges between 0.7% by weight and 8% by weight.

6. Binder according to one of claims 2-5, characterized by a molar ratio of sulfate to iron-complexing compound of more than 1 and less than 20.

7. Binder according to one of claims 2-6, characterized by a molar ratio of sulfate to iron-complexing compound of at least 3 and at most 8.

8. Binder according to one of claims 2-7, characterized in that the carbonate donor is present in a molar ratio, based on the iron-complexing com-pound, of more than 1 and preferably less than 3.

9. Binder according to one of claims 2-8, characterized in that the clinker is a Portland cement clinker.

10. Binder according to claim 9, characterized in that the Portland cement clinker is present in a grinding fineness according to Blaine of at least 4000 cm2/g, preferably of between 4500 cm2/g and 5500 cm2/g.

11. Binder according to one of claims 2-10, characterized in that the additives contain, as the carbonate donor, salts of carbonic acid soluble in water as well as being sparingly soluble to insoluble therein, especially calcium carbonate, magnesium carbonate and/or dolomite, wherein the sparingly soluble to insoluble salts have been activated by grinding and/or thermal treatment, and that the amount of the salts showing sparing solubility or being insoluble in water ranges between 2% by weight and 20% by weight.

12. Binder according to one of claims 2-11, characterized in that the additives comprise, as the carbonate donor, water-soluble salts of carbonic acid, especially alkali carbonates and/or alkali hydrogen carbonates, and, as the iron-complexing compound, at least one water-soluble salt of poly-oxycarboxylic acid or of polycarboxylic acid, or a diketone.

13. Binder according to claim 12, characterized in that the additives contain, as the carbonate donor, potassium carbonate, potassium carbon-ate trihydrate or potassium bicarbonate, and, as the iron-complexing compound, tripotassium citrate mono-hydrate or a mixture of dipotassium oxalate mono-hydrate and tripotassium citrate monohydrate, wherein the proportion of dipotassium oxalate monohydrate amounts to less than 50 mol-%.

14. Binder according to one of claims 2-13, characterized in that the additives contain a propor-tion, based on the clinker, of at least 4.5 mmol-%, preferably at least 7.5 mmol-%, of potassium citrate.

15. Binder according to one of claims 2-14, characterized in that the additives contain a propor-tion, based on the clinker, of at least 11 mmol-% of citric acid.

16. Binder according to one of claims 2-15, characterized in that the additives, for obtaining a high early strength, contain a proportion, based on the clinker, of at least 5 mmol-% and at most 25 mmol-% of carbonate.

17. Binder according to one of claims 2-16, characterized in that the additives, for obtaining a high long-term strength, contain a proportion, based on the clinker, of at least 9 mmol-% and at most 30 mmol-%
of bicarbonate.

18. Binder according to one of claims 2-17, characterized in that the additives also comprise puzzolan earths, clay minerals, fly ashes and/or extremely finely divided reactive silica.

19. Mortar or fresh concrete, characterized by a hydraulic binder according to claim 2 and a water/cement value in the range of 0.25 - 0.40, particularly 0.30 - 0.37.