Cement for making concrete article having reduced capillary water absorption and method for its production

0001The present invention relates to cements with reduced efflorescence and a method for their preparation.

0002White efflorescence on concrete products provide a frequently observed impairment quality. They go from whitish haze to thick white Scabs that cover the surface. They are better the more visible each darker the background. In colored products, which in recent years increasingly gaining importance, the white veil causes the colors not brilliant, but rather milky hue.

0003Efflorescence be attributed to that water in the component or Building penetration, constituents of the cement washes and drying on the surface leaves. To reduce the efflorescence, therefore, the Water absorption of concrete products can be reduced. A measure of the efflorescence thus the capillary water absorption of a test with a Cement manufactured concrete products that are tested on the basis of sample twilling can.

0004In the prior art are various possibilities for reducing the efflorescence known in components and structures made of cement. These based on a hydrophobic treatment of the concrete surface. This allows water not even penetrate and efflorescence can be prevented.

0005Hydrophobicization one hand by waterproofing admixture carried out and on the other hand by means of a surface treatment of the finished Product can be achieved on its own, see. Concrete u. Precast technology, Heft 11/2000, pages 44-50.

0006A subsequent hydrophobic by surface treatment brings different Problems. Thus, a uniform and adequate treatment difficult to ensure, especially with components of complicated Forms, the application can be for example at very high buildings, bridges, etc., or be problematic in at least partially located in the ground parts.

0007In such cases, an internal water repellency of the component or building preferable.

0008DE 1646502 discloses a hydrophobic cement for soil stabilization is determined. This cement is by co-grinding of cement clinker, Additives and water repellents, which branched out strongly, predominantly tertiary, saturated, aliphatic monocarboxylic acids consists, or alternatively prepared by subsequent application of the hydrophobizing agent, in particular by spraying, on the ground cement. Thereby, the cement particles are hydrophobic as such. The wettability the cement particles is reduced. This is detrimental to the setting behavior from, in general, the setting time is prolonged and the early strength reduced. Nor does such a cement in terms of transport and processing special requirements, because it has an extremely good flowability.

0009A similar binders for shotcrete, DE 298 24 278 U1. According to this document, the binder grains are at least in partial areas a coating of a hydrophobizing agent and a non-alkaline comprise accelerators, so that the curing reaction only begins when This envelope is destroyed upon impact of shotcrete on the wall. The otherwise adverse retardation is for this application so just he wishes. As hydrophobizing agents are stearic acid, oleic acid, waxes, Fatty acid salts, resins, mineral oil emulsions, silanes, siloxanes and silicone oils proposed.

0010Both of the aforementioned documents describe the waterproofing of a Binder. The further material to be processed "binder" is thus water-repellent and not necessary also made of the binder Concrete products.

0011The use of swellable clays, such as bentonite, is also known, however, with respect to the frost resistance of the concrete questionable.

0012Furthermore, an addition of water repellents applied during the preparation of Cement with water known directly before processing. suitable Hydrophobizing agents are, for example, in WO 00/23393 alkali metal salts of fatty acids with 8-16 C atoms or described in EP 1160219 an additive composition of a water demand reducing additive and a compound the formula RO (AO)_n-H, Or wherein R is H or alkyl, A is ethylene Propylene and n is a number of 1 or more.

0013Also cement additives with more hydrophobic components are known. EP 846 668 describes water-repellent compositions Organosilicon compounds and polybutylene having functional groups as an additive.

0014In EP 1149808, a cement additive for improving the flowability and proposed reduction of cracking, which one is a mixture of Polyalkylene glycol and a polyalkylene glycol on (meth) acrylate and unsaturated carboxylic acids based copolymer. contains Scripture also an extensive list of possible other components of the additive. As Hydrophobizing agents are fatty acids or salts thereof, silicone, paraffin, Asphalt and wax called. These can be used as defoamers (a) kerosene, liquid Paraffins, (b) vegetable and animal fats, sesame oil, castor oil and Oxyalkylenadditionsprodukte thereof, (c) oleic acid, stearic acid and their alkylene oxide addition products, (D) Glycerolmonoricinsäureester, alkenylsuccinic and their Derivatives Sorbitolmonolaurinsäureester, Sorbitoltrioleinsäureester or natural Waxes, (e) Oxyalkylenbasierende defoamers, (f) alcohol-based Defoamers, (g) Amidbasierende defoamers, (h) phosphoric acid-based Defoamers, (i) metal soap-based antifoaming agents, or (j) silicone-based Defoamers be included. According to embodiments, the additive is in Mixing water are dissolved.

0015The DE 100 49 072 discloses hydrophobic powder containing at least one carboxylic acid ester and in particular a carboxylic acid-containing polymer powders redispersible and coated with at least one carboxylic acid ester silicic acid contain.

0016From US 6,537,366 is a concrete admixture with improved resistance and Ausblühverminderung known, which contains a dye. The mixture comprises a hydrophobic agent to Ausblühverminderung, which is chosen among Calcium stearate, zinc stearate, sodium stearate, butyl stearate, stearic acid derivatives, Stearic acid salts and mixtures thereof, and a particulate polymer, which is selected from polymers and copolymers of styrene-based, Acrylic-based polymers and copolymers, polyvinyl acetates, polyepoxides, Polyurethanes, butadiene and mixtures thereof, and a dye.

0017A disadvantage of all of these additives, they are mixed at the construction site and therefore dosing there. Additives are therefore predominantly as liquid preparation offered because liquids are easier measured can. In order to offer the additives in liquid form are additions needed. However, such preparations have the disadvantage that the added for the preparation of Additives such as triethanolamine, and negatively on the processability can affect the development of compressive strength (greater stiffening) and Circumstances, favor the production of brown discolorations.

0018The invention is therefore based on the object, a cement with reduced provide efflorescence, which the production of efflorescence Concrete Products simplified and buildings and the aforementioned disadvantages do not have.

0019Surprisingly, it was found that a mixture of cement, a alkali metal or Alkaline earth metal or aluminum salt of a fatty acid and an alkali salt of an unsaturated Fatty acid solves the problem.

0020According to the invention, this cement is produced with reduced efflorescence, by first the cement clinker, in particular Portland cement clinker, grinding with gypsum and optionally other additives such as slag and hydrophobicizing additives then admixing dry. In the mixture are the particles in one area so that neither the flow behavior nor the Ligation is adversely affected.

0021The addition takes place after Ermahlen, where appropriate, preferably But after sifting and before storage in silos or directly in front of the Filling / loading. Surprisingly, it was found that when the above-mentioned Additive in the cement plant between mill and loading are metered, this in smaller doses with less (no) side effects reduce efflorescence and beyond the compressibility of Concrete improvements.

0022The term cement comprises in the present invention both Portland cement as well as cement grinding additives such as slag, fly ash, Silikastäuben, Metakaolin, perlite and mixtures of two or more of these Substances. Typical compositions move in the following limits, the proportions must of course add up to 100%:<tables><table><tgroup cols="2"><tbody><row><entry align="left">5-100%</entry><entry align="left">clinker</entry></row><row><entry align="left">0-65%</entry><entry align="left">Blast furnace slag, a maximum of 95%</entry></row><row><entry align="left">0 - 35%</entry><entry align="left">Fly ash, a maximum of 55%</entry></row><row><entry align="left">0 - 10%</entry><entry align="left">Silica fume, a maximum of 55%</entry></row><row><entry align="left">0 - 35%</entry><entry align="left">natural or tempered pozzolan, a maximum of 55%</entry></row><row><entry align="left">0-20%</entry><entry align="left">Limestone, a maximum of 35%</entry></row><row><entry align="left">0 - 5%</entry><entry align="left">Minor constituents</entry></row></tbody></tgroup></table></tables>

0023The alkali or alkaline earth metal contained in the mixture according to the invention or Aluminium salt of fatty acid is preferably a salt of a saturated unbranched Fatty acid having 12 to 18 carbon atoms. Particularly preferred are the calcium, Aluminum or magnesium salt of stearic, lauric and / or palmitic acid, especially calcium. Also salts of fatty acid mixtures, such as for example be obtained from natural oils or fats, are inventively well suited.

0024The alkali metal salt contained in the mixture according to the invention an unsaturated Fatty acid is preferably the sodium or potassium salt of oleic, linoleic and / or Linolenic acid. Sodium oleate is particularly preferred. Here too, mixtures, such as are obtained from natural oils or fats, as well as suitable.

0025Instead of alkali metal salts and ammonium salts may be used provided that released during processing and curing ammonia does not interfere.

0026In the mixture are preferably from 0.01 to 0.2 wt .-% alkali or alkaline earth metal or Aluminium salt of fatty acid, in particular 0.05 to 0.15 wt .-%, and 0.01 to 0.2 wt .-% of alkali salt of an unsaturated fatty acid, in particular 0.05 to 0.15 Wt .-%, relative to the cement. It is also possible amounts of more than 0.2% for example 0.5% will be used, but this is for reasons of cost not preferred.

0027In a particularly preferred embodiment, the mixture contains cement, 0.05% calcium and 0.05% sodium.

0028In a further preferred embodiment, the invention comprises Mix an additional air-entraining agent, in particular a surfactant and very more preferably sodium lauryl sulfate. The air-entraining agent is preferably added in amounts of 0.001 to 0.1 wt .-%. Such mixtures are especially when it comes to good frost resistance.

0029In a further preferred embodiment, a plasticizing Concrete admixtures, preferably based on polycarboxylates, be added. The Amount is preferably 0.01 to 0.5 wt .-%. By plasticizing Concrete admixtures improve the processability of earth-moist concrete.

0030Furthermore, one or more other customary additives may, in particular Flow agents, Erhärtungsverzögerer, hardening, water retention agents be included and other additives.

0031With the inventive mixtures can without complex dosage or hydrophobic surface treatment components and structures are created. In particular, concrete products can be produced which due to their low capillary water absorption decreased efflorescence compared to Concrete Articles of cement without the erfindungegemäßen hydrophobicizers show.

0032The newly developed cement has - compared to the previously used Cements - improved processability. The durability is not degraded. It is suitable both for the preparation of gray and colored concrete products suitable.

0033The following examples are intended to illustrate the invention without, however, on to limit the described embodiments. All share information, eg Percentages are by weight, unless otherwise is specified.

example 1

0034Specimens with the dimension d = 50mm and h = 60mm were in accordance with the following recipe:<sl><li>1 part cement Portland cement CEM I 42.5 R</li><li>3.5 parts sand</li></sl>

0035The water / cement ratio was 0.36. In each case, with a specimen 30 compacting impacts and prepared with 60 compression strokes.

0036Analog specimens were from a cement according to the invention with the following Recipe and a water / cement ratio of 0.38 prepared ::<sl><li>1 part Hochofenzement CEM III / A 52.5 N</li><li>3.5 parts sand</li><li>0.03 parts of calcium stearate</li><li>0.03 parts sodium</li><li>0.03 parts of sodium lauryl sulfate</li></sl>

0037The specimens from inventive cement was 60 compacting impacts produced.

0038Subsequently, both specimens for 24 hours at 20 ° C were / 65% RH stored. To test the specimens for four weeks camped in a 1 cm high water.

0039Figure 1 shows the two specimens with conventional cement, left with 30, on the right with 60 compression strokes. One can clearly see the efflorescence.

0040In Figure 2, the specimens from inventive cement is shown, he has no visible efflorescence on.

example 2

0041The capillary water absorption was for cements with various amounts Admixtures determined. For this purpose, a cement of the variety CEM III / A 52.5 N with the quantities of hydrophobing additive indicated in the table dry-mixed with water in a water / cement ratio of 0.40 dressed and molded into test specimens. As hydrophobing additive Sodium and calcium were in the ratio 1: 1. The Specimens were after a cure time of one day 1 cm in water provided and determines the suction head after 60 minutes. The capillary water absorption was the formula ω = Dm / (A.√t) calculated, said:<dl tsize="4" compact="compact"><dt>Dm =</dt><dd>Dimensions _moist - Dimensions _dry</dd><dt>A =</dt><dd>Contact surface for water</dd><dt>t =</dt><dd>Test time</dd></dl>

0042The results are summarized in Table 1 below. <tables><table><tgroup cols="4"><tbody><row><entry align="center">Water-repellent additive Wt .-% related. cement</entry><entry align="center">density [G / cm³]</entry><entry align="center">Suction height h H₂O [cm]</entry><entry align="center">capillary water absorption ω [Kg / m²H^0.5]</entry></row><row><entry align="center">0.60</entry><entry align="center">2.09</entry><entry align="center">1.0</entry><entry align="center">0.1</entry></row><row><entry align="center">0.50</entry><entry align="center">2.09</entry><entry align="center">1.0</entry><entry align="center">0.1</entry></row><row><entry align="center">0.40</entry><entry align="center">2.09</entry><entry align="center">1.0</entry><entry align="center">0.1</entry></row><row><entry align="center">0.30</entry><entry align="center">2.08</entry><entry align="center">1.0</entry><entry align="center">0.1</entry></row><row><entry align="center">0.20</entry><entry align="center">2.08</entry><entry align="center">1.0</entry><entry align="center">0.3</entry></row><row><entry align="center">0.10</entry><entry align="center">2.08</entry><entry align="center">1.0</entry><entry align="center">0.4</entry></row><row><entry align="center">0.08</entry><entry align="center">2.08</entry><entry align="center">1.5</entry><entry align="center">1.0</entry></row><row><entry align="center">0.05</entry><entry align="center">2.09</entry><entry align="center">1.5</entry><entry align="center">1.5</entry></row><row><entry align="center">0.03</entry><entry align="center">2.09</entry><entry align="center">2.5</entry><entry align="center">2.7</entry></row><row><entry align="center">0.00</entry><entry align="center">2.08</entry><entry align="center">> 5</entry><entry align="center">7.1</entry></row></tbody></tgroup></table></tables>

0043Already with 0.1% water repellency additive is an excellent where repellency of mortar.

example 3

0044Analogously to Example 2 was used for a variety of cement CEM I 42.5 R the Density and the capillary water absorption in the addition of various amounts hydrophobizing admixtures and air-entraining agents determined. Mortar recipe: Cement: sand = 1: 3.5; w / z value = 0.40. The results are in Table 2 below.<tables><table><tgroup cols="5"><tbody><row><entry align="center">Hydrophobiere ndes admixtures Wt .-% related. cement</entry><entry align="center">air-entraining agent Wt .-% related. cement</entry><entry align="center">density [G / cm³]</entry><entry align="center">Suction height h H₂O [cm]</entry><entry align="center">capillary water absorption ω [Kg / m²H^0.5]</entry></row><row><entry align="center">-</entry><entry align="center">-</entry><entry align="center">2.07</entry><entry align="center">> 5</entry><entry align="center">5.7</entry></row><row><entry align="center">0.04%</entry><entry align="center">-</entry><entry align="center">2.06</entry><entry align="center">2.0</entry><entry align="center">1.4</entry></row><row><entry align="center">0.04%</entry><entry align="center">0.03</entry><entry align="center">2.08</entry><entry align="center">1.0</entry><entry align="center">0.8</entry></row><row><entry align="center">0.04%</entry><entry align="center">0.05</entry><entry align="center">2.09</entry><entry align="center"><1.0</entry><entry align="center">0.6</entry></row><row><entry align="center">0.06%</entry><entry align="center">-</entry><entry align="center">2.07</entry><entry align="center">1.5</entry><entry align="center">0.9</entry></row><row><entry align="center">0.06%</entry><entry align="center">0.03</entry><entry align="center">2.08</entry><entry align="center">1.0</entry><entry align="center">0.6</entry></row><row><entry align="center">0.06%</entry><entry align="center">0.05</entry><entry align="center">2.09</entry><entry align="center"><1.0</entry><entry align="center">0.5</entry></row><row><entry align="center">0.10%</entry><entry align="center">-</entry><entry align="center">2.07</entry><entry align="center">1.0</entry><entry align="center">0.6</entry></row></tbody></tgroup></table></tables>

0045It is evident that a by the inventively preferred additive Air-entraining agent, a further reduction in the amount of additives reached is, without deteriorating the water absorption values.

0046For comparison, the effect of equal amounts of a commercial was waterproofing concrete admixture with sodium determined as an active ingredient. The results are in Table 3 below. <tables><table><tgroup cols="4"><tbody><row><entry align="center">Commercially available hydrophobizing admixtures Wt .-% related. cement</entry><entry align="center">density [G / cm³]</entry><entry align="center">Suction height h H₂O [cm]</entry><entry align="center">capillary water absorption ω [Kg / m²H^0.5]</entry></row><row><entry align="center">-</entry><entry align="center">2.07</entry><entry align="center">> 5</entry><entry align="center">5.7</entry></row><row><entry align="center">0.10%</entry><entry align="center">2.08</entry><entry align="center">3.5</entry><entry align="center">2.2</entry></row><row><entry align="center">0.25%</entry><entry align="center">2.09</entry><entry align="center">2.5</entry><entry align="center">1.2</entry></row><row><entry align="center">0.50%</entry><entry align="center">2.09</entry><entry align="center">1.5</entry><entry align="center">0.9</entry></row></tbody></tgroup></table></tables>

0047To comparable with commercial additives to water absorption values obtained as for the cements of the invention are significantly higher Quantities required, namely 0.5%.

0048In Table 4 the data for a cement are listed, wherein the cement clinker milled and stearic acid as a hydrophobing additive together were.<tables><table><tgroup cols="4"><tbody><row><entry align="center">stearic Wt .-% related. cement</entry><entry align="center">density [G / cm³]</entry><entry align="center">Suction height h H₂O [cm]</entry><entry align="center">capillary water absorption ω [Kg / m²H^0.5]</entry></row><row><entry align="center">-</entry><entry align="center">2.07</entry><entry align="center">> 5</entry><entry align="center">5.7</entry></row><row><entry align="center">0.04%</entry><entry align="center">2.09</entry><entry align="center">3.0</entry><entry align="center">2.7</entry></row><row><entry align="center">0.06%</entry><entry align="center">2.08</entry><entry align="center">3.0</entry><entry align="center">2.3</entry></row><row><entry align="center">0.10%</entry><entry align="center">2.08</entry><entry align="center">3.0</entry><entry align="center">2.2</entry></row><row><entry align="center">0.15%</entry><entry align="center">2.09</entry><entry align="center">2.0</entry><entry align="center">1.6</entry></row><row><entry align="center">0.20%</entry><entry align="center">2.10</entry><entry align="center">1.0</entry><entry align="center">0.5</entry></row></tbody></tgroup></table></tables>

0049The required amount of hydrophobing agent is indeed similar to the the invention, however, such cement is hydrophobic per se, what Setting behavior and processing adversely affected. This can also be the see Figure 3, in which a cement according to the invention with dry added water repellents and a cement with hydrophobic Cement particles shown isothermal Gesamthydratationswärmeentwicklung is. Both cements were set on the basis of a CEM I 42.5 R so that prepared according to Example 2 Specimens a capillary water absorption of 0.5 to 0.6 kg / m²H^0.5 exhibited. The values ​​of the cement according to the invention are as a solid line, those of hydrophobic cement dotted Line shown.

0050One can clearly see that the hydration and consequently the Setting reaction low at the cement with hydrophobic cement particles is. The cement according to the invention is the result of a more rapid Bonding with the same protection against efflorescence and a better protection possible against efflorescence at the same rapid setting.