WO2006091062A1 - Method for modifying gypsum cements - Google Patents

Abstract

The invention relates to mineral binding agents and can be used for modifying all types of gypsum cements. The inventive method consists in grinding processable gypsum stone and in adding an alkali builder in the form of alkali metal (potassium and/or sodium) oxides or hydroxides in a quantity ranging from 0.1 to 0.4 % of a moisture-free calcium sulphate contained in the gypsum cement. Said additive can be introduced also into hardening water while preparing gypsum solutions. Said invention makes it possible to reduce a water-gypsum ratio of a solution and to increase strength of articles.

Description

 METHOD FOR MODIFICATION OF GYPSUM BINDERS

The invention relates to the technology of binders and can be used in the production and use of semi-aqueous and anhydrite gypsum gypsum binders of both β-form and α-form.

Known methods of modification are changing the properties of gypsum binders, for example, reducing water demand, by introducing additives after grinding the processed (dehydrated) gypsum stone [1, 2].

According to the method of [1], an aqueous solution of hydrochloric acid or sodium chloride in an amount of 0.1-0.3% by weight of gypsum stone is first introduced, and then an aqueous solution of hexafluorosiliceous acid or sodium hexafluorosilica in an amount of 0.05 - 0.1% of mass of gypsum stone. According to the method [2], an aqueous solution of sodium chloride and / or calcium chloride and / or the sodium salt of naphthalenesulfonic acid is introduced in two stages in an amount of 0.2 to 0.4% by weight of the binder, the method comprising administering the additive a second time in powder form.

The disadvantage of these methods is that a decrease in the water-gypsum ratio (water demand) of binders is achieved by the introduction of acid and salt additives that increase the acidity of water-gypsum solutions, which leads to a decrease in the thinning effect when using plasticizing additives based on the joint condensation of formaldehyde with melamine or other organic substances (esters, amines, derivatives) and other plasticizers from the group of superplasticizers used to dilute cement mortars, as well as to the rate of corrosion of reinforcement in gypsum products. The introduction of additives in the form of aqueous solutions in the process of dehydration of gypsum stone leads to an increase in energy consumption for drying the finished product - binder.

Both methods [1, 2] are applicable only in the production of semi-aquatic gypsum binder β-form in gypsum boilers. Another common drawback of the methods [1, 2] is that the introduction of calcium chloride and sodium chloride into the gypsum binder in an amount of more than 0.1% by weight of the binder leads to efflorescence on the surface of the gypsum products. The prototype of the present invention is the invention [2], because after this method, after grinding the processed gypsum stone into the binder, it is assumed that these additives are also added in powder form, which eliminates the need for additional removal of water, which is associated with the introduction of additives in the form of aqueous solutions.

The problem solved by the proposed technical solution is to reduce the water demand of gypsum binders and increase the strength characteristics of products from these binders. In the method of modifying gypsum binders by introducing additives after grinding the treated gypsum stone, according to the invention, a compound (or mixture of compounds) is introduced as an additive, which creates the basic medium during mixing gypsum binders with water. As the compound creating the basic medium during mixing gypsum binders with water, you can enter an oxide and / or hydroxide of an alkali metal, for example, potassium and / or sodium, or a mixture thereof, in an amount of from 0.1 to 0.4% by weight of anhydrous sulfate calcium contained in the binder. A compound or mixture of compounds that creates the basic medium during mixing gypsum binders with water can also be introduced into mixing water in the preparation of gypsum solutions. It has been experimentally proved that the proposed technical solution reduces the water demand of gypsum binders and increases the strength characteristics of products from these binders. Modification of gypsum binders brings their properties closer to cement binders, which are characterized by the alkaline environment of the liquid phase of water-binders, while maintaining the short setting and hardening time characteristic of gypsum binders.

The proposed method is implemented as follows. In the initial two-water gypsum stone, the content of _two -water calcium sulfate CaSO ₄ - 2H ₂ O is 70.8%. The content of crystallization water H ₂ O is 14.8%. The content of anhydrous calcium sulfate CaSO ₄ in the powdered post-hydration dry product - semi-aqueous gypsum binder - 66%. In all examples, take 10 kg of binder G-4 (β-CaSO ₄ - H ₂ O). It contains 6.6 kg. anhydrous calcium sulfate.

Example 1

0.1% K ₂ O by weight of CaSO ₄ (6.6 kg) was added to the binder. The weight of the K ₂ O additive is 0.0066 kg. Example 2

0.2% K ₂ O by weight of CaSO ₄ (6.6 kg) is added to the binder. The weight of the K ₂ O additive is 0.0132 kg.

Example 3. To the binder add 0.3% K ₂ O of the mass of CaSO ₄ (6.6 kg).

The weight of the K ₂ O additive is 0.0198 kg.

The indicated amounts of additives are introduced into the binder in the form of a powder and thoroughly homogenized. From the obtained modified binders, water-gypsum mixtures (solutions) are prepared with a standard 18cm spread (using a Suttard viscometer). From the obtained solutions, prisms are prepared for mechanical tests (40x40x160 mm.) The attached table shows the test results of the obtained modified binders, the original binder (without additives) and the binder of the prototype [2].

The table shows a slight increase in the strength of the modified potassium oxide gypsum binder at two hours of age (compared with the prototype), while changing the pH of the medium from acidic to alkaline. This change in the basicity of the medium affected the effect of dilution of the solutions with the use of C-3 superplasticizer (with an experimentally established optimal addition of 0.7% by weight of the binder) and a corresponding increase in the strength of the molded sample at two hours of age. The achieved effect is explained by the fact that in an alkaline medium, when the plasticizing additive C-3 is added, the number of water molecules in the polymolecular chains around the dispersed particles of the binder with a completely continuous liquid phase of the solution - dispersion medium decreases, which leads to the possibility of reducing the volume of the dispersion medium. This leads to the formation of more solid spatial frames during hydrate and structure formation of gypsum binders.

The alkaline medium of the liquid phase of gypsum solutions prepared on the basis of gypsum binders modified according to the proposed method makes it possible to use superplasticizers used for plasticizing these solutions for plasticizing cement mortars, for example, products of joint condensation of formaldehyde with melamine resins, or aromatic ethers, amines, derivatives, cycloalkanes, or naphthalenesulfonic acids (C-3 also belongs to them) and other organic substances.

Modification of gypsum binders, if they are not modified in the production process in the factory, can also be carried out in the process of preparing gypsum solutions by adding to the mixing water the same amount of alkali metal oxides or hydroxides as indicated in the described technical solution.

Table

Information sources

1. USSR author's certificate N2 998411, cl. From 04 to 11/02, 1982.

2. USSR author's certificate N ° 1511231, cl. C 04 B 11/00, 1989 (prototype).

Claims

Claim 1. A method of modifying gypsum binders by introducing additives after grinding the treated gypsum stone, characterized in that as an additive, a compound or mixture of compounds is introduced, which creates the main medium for mixing gypsum binders with water. 2. The method according to claim 1, characterized in that as the compound creating the main medium when mixing gypsum binders with water, an alkali metal oxide and / or hydroxide, for example, potassium and / or sodium, or a mixture thereof, in an amount of from 0 is introduced , 1 to 0.4% by weight of anhydrous calcium sulfate contained in the binder. 3. The method according to claim 1 or 2, characterized in that the compound or mixture of compounds that creates the main environment when mixing gypsum binders with water, is introduced into the mixing water in the preparation of gypsum solutions.