CS266129B1 - A method of making cement mix compositions - Google Patents

Abstract

The solution deals with a method of producing an additive for cement mixtures. Its essence is that 1 mole of aluminum sulfate, preferably containing crystal water, is treated with 0.017 to 5 moles of aluminum oxide contained in aluminum oxide and/or hydroxide at a temperature of at least 180 °C until the residual water content drops to at least 20% by weight. As a result of the action of the aluminum oxide and/or hydroxide, it is consumed, so that it is no longer present in the produced additive. The molar ratio of aluminum oxide to sulfur oxide in the additive produced by the method according to the solution is from 1:0.5 to 1:2.95. It is expedient that the additive prepared in this way is ground to such a fineness that at least 50% by weight of the particles are smaller than 90 µm and at least 30% by weight of the particles are smaller than 63 µm, preferably together with the addition of a hydrophobicizing additive, optionally also a dispersant and an inorganic carrier, optionally other expediently selected known additives and/or admixtures. The additive to cement mixtures, produced by the method according to the solution, can be advantageously used wherever acceleration of the increase in initial strength is required.

Description

Construction practice urgently needs additives to accelerate the increase in the strength of cementitious mixes, such as cement slurries and mortars, grout and cementitious concretes. From MS. 257 142, cementitious mixtures with an accelerated increase in strength are known, containing, based on the weight of cement 0.1 to 12% by weight of additives, consisting of a mixture of calcined aluminum sulphate and basic aluminum sulphates, the molar ratio of aluminum oxide Al ₂ O ₃ to oxide sulfur SO ₃ in the mixture is from 1: 0.5 to 1: 2.95. It is expedient for this mixture to contain at most 20% by weight of residual crystalline water.

From MS. It is further known from the author's certificate 257 142 that, compared to incompletely calcined aluminum sulphate (with a residual water content of 10% by weight), a substance prepared by annealing aluminum sulphate at a temperature of 600 ° C has a higher activity. At this temperature, sulfur dioxide SO ₃ is released from aluminum sulphate (H. Remy: Inorganic Chemistry I, SNTL Prague, 1961, p. 372). Due to the leakage of sulfur dioxide SO _{3, the} original molar ratio of 1: 3 alumina Al ₂ O ₃ to sulfur oxide decreases.

Annealing of aluminum sulfate at higher temperatures, such as H. Remym's stated temperature of 600 ° C, is energy intensive. Leaking sulfur dioxide is aggressive, causes intense corrosion of metal equipment and is harmful from a hygienic and ecological point of view. Capturing escaping sulfur dioxide is difficult on the apparatus.

These deficiencies are addressed by the process for the production of the additive according to the invention. Its essence is that 1 mole of aluminum sulphate, preferably containing crystalline water, is treated with 0.017 to 5 moles of alumina contained in aluminum oxide and / or hydroxide at a temperature of at least 180 ° C until the residual water content falls below at least 20%. by weight.

Since the action of aluminum oxide and / or hydroxide on aluminum sulphate takes place at temperatures lower than the temperatures at which sulfur dioxide SO ₃ escapes according to the process described in AO 257 142, the molar ratio of aluminum oxide Al ₂ O ₃ to sulfur oxide SO ₃ it may be the same in the unreacted mixture as after its reaction, in the range from 1: 0.5 to 1: 2.95. As determined by X-ray phase analysis in mixtures of aluminum sulphate and aluminum oxide and / or aluminum hydroxide, formed by conventional mixing, the characteristic diffraction lines of aluminum oxide and / or aluminum hydroxide are good visible. Upon completion of the action of aluminum oxide and / or hydroxide on aluminum sulfate at a temperature of at least 180 ° C according to the invention, aluminum oxide or hydroxide is not present in the newly formed product. Its characteristic diffraction lines are lost. The preparation of the additive for cementitious mixtures according to the process of the invention does not require the high calcination temperatures mentioned by Remy, nor does it require the cleavage of sulfur dioxide during calcination.

It is expedient if the additive produced by the process according to the invention is ground, preferably together with a hydrophobicizing additive, for example a water-insoluble fatty acid salt such as calcium stearate and / or a dispersant and / or inorganic carrier such as silica sand, crushed limestone, ash, granular (pelletized) or untreated silica fume from the production of ferrosilicon and the like, to such a fineness that it contains at least 50% by weight of particles smaller than 90 [mu] m and at least 30% by weight of particles smaller than 63 [mu] m.

The advantages of the additive produced by the process according to the invention are shown in the following application example:

For comparison, the additive was prepared in a manner known from AO 257 142 by the following procedure:

000 g of commercially produced and supplied granular aluminum sulphate containing 15 crystalline lines were calcined at 200 ° C + 2 ° C for 18 hours. The calcination residue was 614.59 g, i.e. it contained 10% by weight of residual water. The dried product was crushed

It is designed to be less than 50% by weight of particles smaller than 90 .mu.m and less than 30% by weight of particles smaller than 63 .mu.m. The molar ratio of alumina Al ₂ O ₃ to sulfur dioxide SO 2 was 1: 3. 250 g of the product thus obtained were mixed with 50 g of aluminum hydroxide A1 (OH) ₃ ; their mixture was designated as additive I / a. An additional 300 g of calcined and ground aluminum sulfate alone, as described above, was annealed at 600 ° C for 5 hours. The residue after annealing was 210 g, because in addition to the loss of residual water (30 g), sulfur dioxide SO ₃ (60 g) was also cleaved. This reduced the molar ratio of alumina A1 ₂ O ₃ to sulfur oxide to 1: 2.367. The additive thus prepared was again crushed to its original fineness and designated as additive I.

According to the process of the invention, the additive was prepared as follows:

000 g of commercially produced and supplied granular aluminum sulphate containing crystalline v6d (ie 44.128% H ₂ O) and 64.35 g of amorphous powdered aluminum hydroxide Al (OH) _{3 of} purity pa containing 30.82% of water (bound in hydroxyl groups) was homogenized and then reacted for 48 hours at 200 ° C + 2 ° C. Thus, one mole of Al ₂ (SO ₄ ) ₃ · .15 H ₂ O was treated with 0.267 4 moles of Al ₂ O ₃ contained in aluminum hydroxide. The molar ratio of alumina Al ₂ O ₃ to sulfur dioxide SO ₃ , which was 1: 2.367 in the original mixture, did not change during the reaction. The reaction residue 628.38 g contained 4% residual moisture.

300 g of the additive produced by the process of the invention were crushed to the same fineness as in the previous case, i.e. so that at least 50% of the particles were smaller than 90 .mu.m and at least 30% of the particles smaller than 63 .mu.m. The additive thus prepared was designated as Additive II.

and

Another 300 g of the above product were ground together with 10 g of calcium stearate, 30 g of dispersant - sodium dinaphthylmethanedisulfonate and 30 g of silica fume from ferrosilicon production. A similar fineness was achieved during grinding as in the previous cases. The additive thus prepared was designated as additive III.

Of these additives, Portland cement grade PC 400 and standard sand according to

ČSN 72 2117, standard mortars were prepared. The composition of the mortars and the strength measured after 24 hours and after 28 days are given in the following table.

Table

Comparison of the effects of ingredients on standard mortars according to ČSN 72 2117 Type and designation Additive doses strength MPa po ^in% b ™ * · 24 h .28 days of cement _______________________________; ____________ Tensile strength Tensile strength • Bending Comparative without additives - 2.5. 11.2 8.1 '42.8 Known additive I 2% 3.9 18.5 8.2 43.5 Known additive I / a 2% 3.3 16.0 8.1 42.8 Ingredients II according to the invention 2 «4.2 19.0 8.3 43.6 Additive III according to the invention 2% 4.5 20.1 8.4 42.8

It follows from the above table that the additive produced by the process according to the invention has a better efficiency than the additive produced by the known process.

CS 266 129 Bl

The additive produced by the process according to the invention can also be combined with other known additives and / or admixtures expediently selected with regard to the intended use, for example using the following methods:

- a suitably selected known additive or premixes are ground together with an additive prepared by the process according to the invention

- the additive prepared by the process according to the invention is used as one of the components of cement dry prefabricated mixtures

- the additive prepared by the process according to the invention is added as one of the components in the outpatient production of cement mixtures directly on site.

The additive produced by the process according to the invention is preferably used in the preparation and production of cement mixtures, in particular where an acceleration of the increase in initial strengths is required.

Claims (1)

Process for the production of an additive for cement mixtures, characterized in that 1 mol of aluminum sulphate, preferably containing crystalline water, is treated with 0.017 to 5 mol of alumina at a temperature of at least 180 DEG C. until the residual water content falls below at least 20% by weight.