FI85581C - FOERFARANDE OCH TILLSATSMEDEL FOER FRAMSTAELLNING AV BETONG, GJUTKERAMIK OCH LIKNANDE. - Google Patents

Description

85581

Method and admixture for the manufacture of concrete, cast ceramics or the like

The invention relates to a process for the preparation of an alkali-activatable binder according to the preamble of claim 1.

The invention also relates to an additive according to the preamble of claim 5, which can be used for the preparation of a binder.

Slag-based binders, or cements, have been familiar to builders for decades. Alkali-activated slag cements have still been known for about 20 years, but they have not yet become more widely used to this day.

The slag binder is prepared by granulating and grinding iron slag or the like slag, after which it is alkali-activated by mixing with a suitable alkali such as alkali or alkaline earth metal hydroxide or carbonate. Alkali cleaves the silicate chains on the surface of the slag particle and causes them to coalesce from particle to particle. This forms chemical bonds between adjacent particles. Sodium hydroxide in an amount of about 1___5% of the amount of slag to be activated and / or soda, i.e. sodium carbonate, is most commonly used for alkali activation.

When the matrix of hardened slag cement is examined with an electron microscope, it is observed that the space between the particles is completely empty; there are visually perceptible direct contacts between very few particles. Despite this, the matrix has measurable high compressive and flexural strengths. This means that the few bonds that exist are very strong.

With alkali-activated slag cements, e.g. the following indisputable advantages: 2 85581 - fast curing, which can be controlled by the application of chemicals, - chemical resistance, and - fire resistance.

Disadvantages, in turn, are considered to be the treatment of a separate activation solution and micro-cracks in the initial stage of curing. In addition to this, the uncertainty is compounded by the fact that attempts are made to study slag cement and concrete made from it by means and criteria typical of Portland cement, which are not relevant.

Hot ceramics have developed strongly recently. Their research has shown how important it is for strength to control the microstructure of a material, i.e., empty spaces do not increase strength.

In hot ceramics, empty spaces are filled with surface tension forces. You see, the molten small particles join together and the spaces are filled, which is why the sintering step of the ceramics is usually carried out under vacuum and hard compression.

The second category of materials are cold ceramics, ie chemically bonded ceramics. These are virtually all cements. The strengths of cold ceramics differ substantially from the strengths of known cements. Mainly these strength properties are obtained by rolling and pressing, whereby the densities increase and the intermediate spaces decrease.

However, these manufacturing methods are not suitable for construction purposes where the material has to be defined as cast ceramic, as simple casting procedures are an economic necessity in the production of building components.

The object of the present invention is to obviate the drawbacks associated with the prior art and to provide a completely new method for alkali activation of a binder.

• M · 3 B5581

The invention is based on the surprising finding that finely divided iron slag, which is in a substantially glassy state, is almost completely soluble in a concentrated, hot NaOH solution. In this dissolution, a syrupy opal solution is formed in which the remaining particles are on the order of £ 0.2 microns, i.e. below the wavelength of visible light. Apparently, it is the case that the completely dissolved part of the silicate material is broken down into clusters (fine particles) which are so small that a corresponding size can never be achieved by mechanical grinding.

In the context of our invention, it has further been found that when said syrupy solution is diluted with water at room temperature or at elevated temperature, a large amount of small crystals precipitates therefrom. X-ray examination of this material has found e.g. the following minerals:

MgAl5FeSi11042 · 40 H2O and 5 MgO · Al2O3 · 3SiO2 * 4 H2O.

In the production of concrete mass or cast ceramic based on an alkali-activated binder, more water is automatically added to the mixture together with the other material in the mixing step. Upon addition to such a mixture of the syrupy substance obtained from the dissolution of slag described above, precipitation occurs due to dilution, whereby said fine crystals are formed, which are essentially the same material as the other binder to be activated. At the same time, upon dilution, an alkali is released into the mixture, which normally acts as an alkali activator.

More specifically, the method according to the invention is mainly characterized by what is set forth in the characterizing part of claim 1.

The additive according to the invention is in turn characterized by what is set forth in the characterizing part of claim 5.

4,85581

According to a preferred embodiment of the invention, as much slag as the amount of activator used in each case is capable of dissolving is used in the finely divided slag used as a binder starting material. This separately made part is used as an activating and filler additive for the whole material.

In this embodiment, the amount of alkali activator required is first calculated based on the amount of slag binder used. The alkali, i.e. usually an aqueous solution (lye) of sodium hydroxide, is then added with vigorous stirring as much slag as it dissolves into it. Preferably, the addition to the boiling concentrated liquor is performed. The concentration of the liquor used is preferably about 20 to 60% by weight. Accordingly, the amount of slag to be dissolved in the lye is preferably about 10 to 40% by weight of the lye. The resulting syrupy, opaque solution of concrete and cast ceramic admixture is cooled. The solution is added to the concrete mass, which, as other components in addition to the rest of the slag, contains e.g. aggregate, fluidizer and other additives.

The invention provides considerable advantages. Thus, small spaces in the concrete mass are filled with precipitating crystal particles and clusters formed in leaching. At the same time, it is possible to promote the formation of crystal embryos and the subsequent crystallization without the need to increase the amount of alkali activator.

As mentioned above, the process according to the invention provides crystals and other cluster particles which are smaller in particle size than can be obtained by any grinding process. It is well known that the smaller the particles in the matrix, the better the strength of the ceramic and hydraulic binders. According to the general theory of strength of materials, the tensile strength of the matrix follows the following general rule:

II

• · I> 5 85581 / E (1 - p3) R Exp (-kp) - PII c where P is the porosity fraction, E is the modulus of elasticity, R and k are the material parameters and C is the pore size.

It is seen that the strength increases rapidly as the small spaces fill and the pores decrease.

When the processability of the material always requires more mixing water than hydration will require in the case of such casting frames, pores will always remain in the matrix. These pores can be reduced and their proportion reduced when, according to the invention, part of the mixing water is replaced by said dissolution solution. In all cases, the individual size of the pores is significantly reduced when the small crystals fill all the spaces.

The invention will now be examined in more detail by means of an exemplary embodiment.

EXAMPLE

Preparation of the additive 450 g of finely ground iron slag with a fineness of 700 m 2 / kg were dissolved in 1.5 kg of a 50% NaOH solution at 137 ° C, at which point the mother liquor began to boil. The mixture was stirred vigorously for about 20 min. The mixture was then allowed to cool to form a reddish-brown syrupy opaque solution, but no visible particles were found under an optical microscope. When treating the solution, it was found that some (about 25-30 g) of the slag used had remained undissolved on the bottom, it was also found that these represented the largest of the original material: particles.

6 85581

Manufacture of concrete

Said material obtained in dissolution was used for test pieces made in a prism mold according to the following recipe: ground slag 450 g standard sand 1350 g lignosulphonate 1.5% solubilizer 47 g (corresponding to 4.8% NaOH equivalent) Results:

Time Temperature Compressive strength / MPa 1 h 80 eC 15.9 1 day 20 eC 46.4 7 days 20eC 50.5

Substantially fewer microcracks were observed in the swabs taken from the prisms than in the corresponding prisms without solubilizer: The ratio of microcracks was 9/10 with solubilizer and 6.5 / 10 with NaOH activation alone, when 10 denotes a completely undistorted matrix.

The shrinkage of the prisms remains at 0.65 mm / m for 56 days when it was the same in slag cement activated in the normal way as in prisms made with Portland cement, i.e. about 1.0 mm / m.

In addition to minor microcracks, rapid development of initial strength was essential, especially in warm weather.

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Claims (5)

7 85581 A process for the production of concrete, cast ceramics or the like, which comprises - using slag which can be activated by an aqueous alkali as a binder, - mixing the necessary fillers and additives to produce a binder mixture containing at least some water, and , that - before curing, a solution obtained by dissolving the fine slag in the alkali activator is added to the binder mixture. A method according to claim 1, wherein blast furnace slag is used as a binder, characterized in that a part is separated from the slag which is dissolved in the alkali activator used, and - at least substantially all of the alkali activator used is added to the binder mixture in the form of a slag-containing solution. Process according to Claim 2, characterized in that as much slag is dissolved from the binder slag into the alkali activator as the amount of activator used can dissolve. Process according to one of the preceding claims, characterized in that the solution is obtained by adding the slag with vigorous stirring to a boiling concentrated sodium hydroxide solution having a concentration of about 20 to 60% by weight, the amount of slag dissolved in the lye being about 10 to 40 % by weight of lye. 5. An admixture for use in the manufacture of concrete, cast-ceramic or the like containing an alkali-activated binder, characterized in that it comprises a solution of sodium hydroxide of 8 85581 in a concentration of about 20 to 60% by weight and in which about 10 to 40 % by weight of slag. li 9 85581