ITMI20070771A1 - ALUMINUM STABILIZERS FOR ALCALER-FREE THICKENERS - Google Patents

Description

Description of the patent for industrial invention entitled:

"ALUMINUM STABILIZERS FOR ALKALI-FREE ACCELERANTS"

The present invention relates to liquid accelerators for Portland cement that favor a high development of mechanical strengths and characterized by a high ability to reduce the setting times of the cement systems to which they are added. The stability of these additives is achieved by using hydrolysable, condensed or synthetic tannins.

State of the art

Modern tunnel excavation technologies require the use of large quantities of cementitious materials (mortars or concretes) necessary for the construction of the temporary or permanent lining. The need to proceed swiftly with the works requires that the cementitious material be placed in place together with the excavation operations and harden quickly, also in order to safeguard the safety of the operators. A technology has therefore been developed that allows the projection of the fresh mixture directly onto the rock, without the use of containment formwork. In order for the material to adhere adequately to the rock walls, avoiding falling back to the ground due to its own weight or rebound due to the intensity of the spray, it must grip and develop mechanical strength quickly, as soon as it comes into contact with the support. Only in these conditions is it possible to create a structural support for the vault capable of allowing the excavation to continue. To obtain these results, accelerating additives are used, capable of producing a rapid setting and an equally rapid hardening of the hydraulic binder. These additives must ensure excellent adhesion of the projected cementitious material to the support, preventing sagging or detachment and favoring a high development of mechanical strength. The first parameter is evaluated on the basis of the additive's ability to reduce the setting times of a cement paste, the second by measuring the development of mechanical strength during the first hours of hydration.

The first accelerators developed for this purpose were alkaline additives such as soda, potash, silicates or aluminates of alkali metals. These accelerators, while allowing a satisfactory initial setting and hardening, inhibit, over time, an adequate development of the mechanical strength of the cementitious material placed in place, compromising the durability of the product. Furthermore, they are highly irritating to the skin and their use makes the working environment highly unhealthy. Their handling requires the adoption of special protection measures for workers. Finally, the release of alkali in the aquifers adjacent to the work site can cause irreparable damage to the aquatic environment as these substances alter the natural pH values of the ecosystem.

To overcome the drawbacks arising from the use of these substances, a new category of additives defined as "alkali-free" or alkali-free has been developed. In accordance with some European standards (for example Òsterreichischer Betonverein Guideline Sprayed Concrete, Richtlinie Spritzbeton "Anwendung und Prüfung", Wien, October 1998 and pr EN 934-5 "Admixtures for Sprayed Concrete-Definitions, Requirements and Conformity"), an accelerating additive it can be classified as “alkali-free” when the concentration of sodium and potassium, expressed in equivalent of Na2O, is less than 1%.

Among these new alkali-free or "alkali-free" additives, patent EP 1167317 B1 describes an alkali-free accelerator, basically composed of fluorine aluminates and aluminum sulphate. This type of additives allows a rapid setting of the concrete, thus allowing considerable speed of installation. However, it has been observed that their use delays, especially during the first hours of hydration, an adequate development of the mechanical strength of the concrete or mortar, with a consequent slowdown in excavation work.

US 6302954 B1 and EP 1114004 B1 describe "alkali-free" accelerating additives based on aluminum carboxylates and aluminum sulphate. These accelerators, although they allow an adequate development of mechanical strengths with respect to those claimed in patent application EP 1167317 B1, are nevertheless not sufficiently effective in the initial setting phase. This delay in setting can have a negative impact on the stability of the material.

WO 2005040059 A1 describes accelerating additives based on fluorocarboxylates of aluminum, sodium aluminate and manganese sulfate which allow an effective reduction of setting times and an adequate development of mechanical strengths.

WO 03/029163 A2 describes accelerating additives based on amorphous aluminum hydroxide, formic acid, phosphoric acid and aluminum sulfate.

WO 2004/106258 A2 describes setting accelerators containing amorphous aluminum hydroxide, dicarboxylic acid anhydrides, aluminum sulfate, magnesium sulfate, possibly stabilized with phosphoric acid.

In order to stabilize the mentioned accelerators, high dosages of stabilizers such as, for example, fluorides, carboxylates or phosphates must be used which can, however, negatively affect the effectiveness of the accelerator. They also heavily affect the production costs of the additive.

Description of the invention

The invention of accelerating additives that determine a good development of mechanical strength associated with an excellent reduction in setting times, with a low stabilizer content, becomes extremely useful and represents a significant technological development.

The present invention relates to an "alkali-free" accelerating product, superior to those developed up to now, characterized by a remarkable ability to reduce setting times and, at the same time, capable of inducing an excellent development of mechanical strengths without the need to resort to high dosages of traditional stabilizers such as for example formic acid, hydrofluoric acid or phosphoric acid. It has in fact been surprisingly found that the reaction product between aluminum hydroxide and / or alumina and / or sodium aluminate and aluminum sulphate stabilized with tannins (hydrolysable and / or condensed and / or synthetic) allows to obtain "alkali- free ”far superior to those developed so far. The characteristics of the additive are further improved due to the addition of amines or alkanolamines, in particular diethanolamine, and / or urea and / or pyrogallol or hydroxy-phenols.

The hydrolyzable tannins of the present invention may comprise one or more of the following substances:

1) Gallotannins from glucose and / or glucitol and / or melose and / or quercitol (for example β- 1,2, 3, 4, 6 - Pentagalloyl-O-D Glucopyranose; 2,6-di-O-Galloyl-1,5 -Anhydro-D-Glucitol; Cisalpina Spinosa Extract) ',

2) Elagitannins (for example the monomers Corilagina ', Geranina', Davidina ', and / or macrocyclic dimers such as Eugeniflorina', Cufina ', and / or macrocyclic trimers such as Nobotannins);

3) Teragallotannins;

4) Caffetannini;

5) Complex hydrolysable tannins comprising mixtures of the chemical species described above and in particular deriving from the esterification of carbohydrates with gallic acid and / or quinic acid and / or caffeic acid and / or ellagic acid (for example Gallo-Elagitannins such as the extract of Castanea Sativa - Domestic chestnut).

The condensed tannins or proanthocyanidins of the present invention comprise one or more of the following substances:

1) Flavan-3-oil derivative polymers (-) epicatechin and / or catechin and / or epigallocatechin and / or gallocatechin;

2) Monomers or polymers of Flavan-4-oils or Flavan-3,4-oils (leukoanthocyanidins).

The synthetic tannins of the present invention comprise one or more of the following compounds:

1) Derivatives of 4,4 'di-hydroxy-di-phenyl-sulfone;

2) Phenol-urea condensation product;

3) Phenol-naphthalene-sulphonic condensation product;

4) Condensation product of naphthalene-sulphonic acids;

5) Condensation product of phenol.

The tannin content can vary from 0.01 to 15% by weight in the final formulation.

The additive object of the invention can be in the form of a suspension or solution and, if the water is evaporated, the resulting powder also retains all the typical properties of the solution in relation to hydraulic systems.

The additive object of the invention can be easily prepared by reacting in water (at a temperature above 40 ° C) a mixture of crystalline and / or amorphous aluminum hydroxide and / or alumina and / or sodium aluminate with aluminum sulphate up to obtain a clear or opalescent solution. The tannin is then added and the mixture is left to stir until a clear or slightly opalescent solution is obtained. Optionally, to improve its effectiveness, an alkanolamine (preferably diethanolamine) and / or urea and / or thiourea or their organic or inorganic derivatives and / or pyrogallol or hydroxyphenols can be added to the mixture.

The additives of the invention may also contain from 0.1% to 10% by weight in the final formulation of one or more carboxylic acids, hydrofluoric acid or phosphoric acid.

The characteristics and advantages of the additive object of the invention are better described in the following examples. The percentages of the components are always expressed by weight.

Example 1

Using a cement II / A-S 42, 5R, two cement pastes containing a commercial accelerator rich in formic acid and an accelerating additive object of the present invention were prepared (Formulation 1; Table 1). The cementitious compositions were prepared using the same quantity of mixing water, expressed by the water / cement ratio (A / C = 0.28) and a dry dosage of accelerator equal to 4.5% by weight on the cement. In addition, a third generation acrylic superplasticizer was added to the samples at a rate of 1% of the weight of cement. The setting times were measured on all cementitious pastes with a Vicat manual pressure gauge in accordance with the EN 196/3 standard. The additive was prepared according to the following procedure: 2 g of a sodium aluminate solution, 0.5 g of diethanolamine and 1.5 g of ground urea were added to 37.75 g of conditioned water at 70 ° C. . The mixture was stirred for about 10 minutes until a clear or slightly opalescent solution was obtained; then 37 g of aluminum sulphate were added which were mixed for 20 minutes in order to obtain a clear or slightly opalescent solution; 16 g of amorphous aluminum hydroxide were added and left under stirring for 40 minutes (70 ° C); a solution of tannin in water was added to the resulting solution, cooled to 30 ° C, which was left under stirring for at least 30 minutes. The results of the end-of-setting times for the various cementitious compositions are shown in Table 2.

Table 1. Composition

Table 2. Setting times on Cem.II / A-S 42.5 R

End of setting time

Accelerating

(EN 196/3)

Formulation 1 1 '15 "

Product

3 '00 "

Commercial

As can be seen from the end-of-setting times reported in Table 2, Formulation 1 determines a considerable reduction in setting times with respect to the commercial product.

Example 2

In this example, the results of the mechanical strength tests of cement mortars containing a commercially available accelerating additive rich in formic acid, and an accelerator produced according to the present invention are compared. The tests were performed on specimens having the following composition:

450 g Cement II / A-S 42, 5R;

1350 g Normalized sand;

0.4 g Antifoam agent;

4.5 g Superplasticizer;

202.5 g Water;

20.25 g of active content of Accelerator.

The mortar was mixed in accordance with the EN 196/1 standard. The accelerating additive was added at the end of the standard cycle, followed by a further mixing of 10 ". The mixture was transferred into the formwork and was compacted using only 60 strokes (compared to 120 required by the EN standard). Since the mortar loses workability very quickly, a metal trowel was used to compact the mixture more effectively. Initially the mechanical strengths were measured with a digital penetrometer (standard Òsterreichischer Betonverein Guideline Sprayed Concrete, Richtlinie Spritzbeton "Anwendung und Prüfung", Wien, October 1998) expressing the data in Newton (effort necessary to be able to pierce a specimen with a needle having length 15 mm and diameter 3mm). When the penetration stress exceeds 300 N, the mechanical performances have been evaluated with Controls model 50 press and have been indicated in MPa. For this test, formulation 2 was used which was prepared in a similar way to formulation 1 with the difference that a tannin extracted from the pods of Cesalpinia spinosa was used to replace the tannin solution extracted from the common chestnut.

The following table (Table 3) compares the mechanical strengths of mortars containing the commercial product with those obtained according to the present invention.

Table 3. Development of mechanical strengths on Cemento II / A-S 42, 5R

Penetration stress (N) and mechanical strength (MPa) Accelerator

30 min 1 hour 2 hours 4 hours 5 hours Formulation 2 51 N 83 N 123 N 214 N 1 MPa Product

12 N 26 N 56 N 153 N 0.7 MPa Commercial

The data show that the additive object of the invention significantly improves the development of mechanical strength (in particular during the first hours of hydration) compared to traditional "alkali-free" accelerating additives rich in formic acid.

Example 3

In this example, the results of the mechanical strength tests of cement mixtures containing a commercially available accelerating additive rich in hydrofluoric acid, and an accelerator produced according to the present invention are compared. The tests were carried out on mortar samples having the following composition:

450 g Cement II / A-LL 42, 5R;

1350 g Normalized sand;

0.4 g Antifoam agent;

4.5 g Superplasticizer;

202.5 g Water;

20.25 g of active content of Accelerator.

The mortar was mixed in accordance with the EN 196/1 standard. The accelerating additive was added at the end of the standard cycle, followed by a further mixing of 10 ". The mixture was transferred into the formwork and was compacted using only 60 strokes (compared to 120 required by the EN standard). Since the mortar loses workability very quickly, a metal trowel was used to compact the mixture more effectively. The mechanical strengths were determined on 4x4x16 cm specimens in accordance with the 196/1 standard. For this test, formulation 3 (Table 1) was used which was prepared in a similar way to formulation 1 with the difference that in addition to the tannin solution extracted from the common chestnut, a synthetic tannin solution (phenol condensation product) was used. urea). The results of the end-of-setting times for the various cementitious compositions are shown in the following table.

Table 4. Development of mechanical strengths on Cemento II / A-S 42, 5R

Mechanical resistance (MPa) Accelerator

8 hours 24 hours Formulation 3 2 13.7

Product

Commercial 1.4 5.1

The data show that the additive object of the invention significantly improves the development of mechanical strength (in particular during the first hours of hydration) compared to traditional "alkali-free" accelerating additives rich in hydrofluoric acid.

Example 4

To verify the stabilizing efficacy of the tannin contained in

accelerator solutions, 100 g of each of the formulations 1, 2, 3 and one

formulation type 1 but without tannin were placed in containers in

100 ml plastic and any sediment formation was monitored.

The results are better described in the following table.

Table 5. Stability tests.

% in volume of sediment

Formula

3 days 7 days 21 days 28 days

Formulation 1

36 50 66 80 Tannin free

Precipitate Precipitate Formulation 1 0 0 barely perceptible perceptible

Precipitate Precipitate Formulation 2 0 0 barely perceptible perceptible

Precipitate Precipitate Formulation 3 0 0 barely perceptible perceptible

The data shown demonstrate the stabilizing effect of tannins compared to

a solution that does not contain them.

Claims (16)

CLAIMS 1. An alkali-free accelerator containing the product obtained from the reaction in water of one or more of the following components crystalline and / or amorphous aluminum hydroxide and / or alumina and / or sodium aluminate with aluminum sulphate stabilized with one or more tannins. 2. An accelerator according to claim 1 wherein hydrolyzable tannins are used. 3. An accelerator according to one or more of claims 1 to 2 in which condensed tannins are used. 4. An accelerator according to one or more of claims 1 to 3 in which synthetic tannins are used. 5. An accelerator according to one or more of claims 1 to 4 in which 0.01% to 15% by weight is used in the final formulation of one or more gallotannins and / or elagitannins and / or teragallotannins and / or caffetannins as tannins hydrolyzable. 6. An accelerator according to one or more of claims 1 to 5 in which 0.01% to 15% by weight is used in the final formulation of complex hydrolysable tannins deriving from the esterification of carbohydrates with gallic acid and / or quinic acid and / or caffeic acid and / or ellagic acid. 7. An accelerator according to one or more of claims 1 to 6 in which 0.01% to 15% by weight is used in the final formulation of condensed tannins derived from Flavan-3-oils and / or Flavan-4-oils and / or Flavan-3,4-oils. 8. An accelerator according to one or more of claims 1 to 7 in which 0.01% to 15% by weight is used in the final formulation of synthetic tannins derived from 4,4 'di-hydroxy-di-phenyl-sulfone and / or phenol-urea condensation products and / or phenol-naphthalenesulphonic condensation products and / or naphthalene-sulphonic acid condensation products and / or phenol condensation products. 9. An accelerator according to one or more of claims 1 to 8 added with 0.1% to 10% by weight in the final formulation of one or more carboxylic acids. 10. An accelerator according to one or more of claims 1 to 9, added with 0.1% to 10% by weight in the final formulation of hydrofluoric acid. 11. An accelerator according to one or more of claims 1 to 10, added with 0.1% to 10% by weight in the final phosphoric acid formulation. 12. An accelerator according to one or more of claims 1 to 11 added with diethanolamine. 13. An accelerator according to one or more of claims 1 to 12 added with urea, thiourea or an organic or inorganic derivative of these substances. 14. An accelerator according to one or more of claims 1 to 13 added with a hydroxyphenol. 15. An accelerator according to one or more of claims 1 to 14 added with pyrogallol. 16. Cementitious compositions containing the additives of claims 1-15.