RU2767481C1 - Expansion admixture based on iron-containing pulverized waste for expanding cement - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: invention relates to an expanding admixture for tensioning and expanding cements. The expanding additive includes blast-furnace granulated slag, gypsum stone and alumina slag, and additionally contains iron-containing pulverized waste with a particle size of 1-200 microns. To prepare the mixture, components with a moisture content of 1-5% are used.

EFFECT: invention improves the strength characteristics of cements.

2 cl, 3 tbl

Description

The invention relates to the technology of mixed binders and can be used in the manufacture of cements.

Expandable cement is a product obtained by thoroughly mixing cement and expanding additives. A distinctive property of expanding cements is their ability to expand during setting and hardening. The expansion of cement stone is based on the growth of crystals of calcium hydrosulfoaluminate formed during their hardening.

The introduction of an expanding additive during the preparation of a cement mixture regulates the expansion energy of the binder, which makes it possible to obtain concrete for prefabricated and monolithic construction, both with compensated shrinkage and stressing with different self-stress energies.

Expanding additives exclude shrinkage of the cement stone during its hardening, provide linear expansion of the cement stone.

Expanding cement is in demand due to the following operational advantages: increased adhesive properties and uniform expansion, contributing to the tight fit of the mortar to the base and the gradual filling of voids and cracks.

The disadvantage of expanding cements is high water permeability due to the fact that during hardening, air microscopic cavities remain in the surface, which can lead to the destruction of the material.

The claimed invention is aimed at improving water resistance and improving physical and mechanical characteristics.

Known expanding binder containing dihydrate gypsum, blast-furnace granulated slag, cupola slag, iron-containing waste sheet production, water glass, filter-press lime-containing waste sugar production, quicklime, alumina-containing waste from the galvanizing shop of aluminum production and cement clinker [Author's certificate No. 1413072, IPC C04B7/14, 1988].

The disadvantage of this invention is the complex composition of the expanding additive and the instability of its expanding properties, due to the unstable activity of lime, which quickly carbonizes in air and loses its activity, which can adversely affect the expansion process, which can contribute to the deterioration of physical and mechanical characteristics, as well as deterioration of water resistance.

The closest in technical essence to the proposed technical solution is an expanding additive to cement, including, wt.%: alumina slag 4 - 6, gypsum dihydrate 22 - 24, granulated blast furnace slag 60 - 69, waste from the production of wet enrichment of iron ore based on SiO ₂ 5 - 10 [Patent RU No. 2049081, IPC C04B28/04, C04B28/04, C04B22/06, C04B7/00, 1995].

The disadvantage of this invention is that high physical and mechanical properties of density, compressive strength and tensile strength in bending, as well as cement self-stress are achieved only at high temperatures ^of 90 ° C. However, at room temperature 20 ° C ^, these indicators are much lower. There is also no data on water resistance, which is an important characteristic of the cement coating.

The technical result of the claimed invention is the production of an expanding additive used for the production of stressing and expanding cements, which improves the physical and mechanical characteristics of cement containing such an additive, compared with the prototype at room temperature 20 ° C, ^as well as the possibility of recycling unclaimed dusty waste from metallurgical production.

The specified technical result is achieved by the fact that the expanding additive to cement, includes blast-furnace granulated slag, gypsum stone and alumina slag, according to the invention, additionally contains iron-containing pulverized waste, with a particle size of 1-200 microns, and microsilica, in the following ratios, wt. %:

blast furnace granulated slag 55.0 - 75.0 gypsum stone 18.0 - 23.0 aluminous slag 2.5 - 8.0 iron-containing pulverized waste metallurgical production with a particle size of 1-200 microns 3.5 - 11.0 microsilica 1.0 - 3.0

At the same time, components with a moisture content of 1–5% and a specific surface area of 3500 ± 200 cm ² /g are used to prepare an expanding additive.

The essence of the invention.

The essence of obtaining an expanding cement stone is the manifestation and regulation of its own stresses. In order for self-stresses to lead to a significant expansion without destroying the bonds between the elements of the porous structure, the structure must be capable of plastic deformation.

The proposed composition of the expanding additive differs from the known one in that it additionally contains iron-containing pulverized waste from blast-furnace iron production, with a particle size of 1-200 microns.

The use of iron-containing pulverized waste from blast-furnace production of pig iron, with a particle size of 1-200 microns, as part of an expanding additive for cement, helps to increase the density and strength of the mixture with cement, as well as to increase the uniformity of the composition of the mixture.

The sources of pulverized waste from blast-furnace iron production are both blast-furnace iron production and ore and foundry yards.

In the production of iron and steel, a significant amount of untreated waste is generated in the form of dust, the basis of which is iron (III) oxide. Waste is stored at temporary sites and transported to landfills for disposal.

The chemical composition of dusts from metallurgical enterprises differs from each other and can vary widely. The advantage of the dust, which makes it possible to use it in obtaining an expanding additive, is a high content of iron oxide (III), a low moisture content, and a high degree of fragmentation of the particles that make up the waste.

Dust and gaseous emissions from blast furnaces and steelmaking are produced by complex physical and chemical processes. With blast-furnace gas, the dust introduced with the charge and the dust that appeared during the friction of the charge column in the blast furnace itself are removed from the furnace.

The mass of dust introduced by blast-furnace gases is 20-100 kg/t of pig iron. The average dust content of blast-furnace gases is 9-55 g/m3, and in case of malfunctions or small charge it can reach 200 g/m3. The amount of blast-furnace gas produced is 3880 m3/t of wet coke, or 4000 m3/t of dry coke, or 2000-2500 m3. per 1 ton of cast iron.

The chemical composition of dust varies widely. For example, when smelting pig iron, the dust may contain, %: SiO ₂ - 14.6; MgO - 4.35; Al ₂ O ₃ - 4.35; CaO - 11.85; S-0.74; MnO- 3.75, the rest is iron oxides.

The maximum amount of iron is contained in flue dust (up to 40%).

At the ore yard, dust with a high content of iron oxide (III) is released during unloading of wagons, reloading ore, feeding ore to the bunker rack, etc. The specific emission of dust at the ore yard is approximately 50 kg per 1 ton of pig iron, and at the bunker rack - 20 kg per 1 ton of cast iron. The concentration of dust with a high content of iron(III) oxide in the ore yard and the bunker rack ranges from 17 to 1000 mg/m3.

The largest amount of dust with a high content of iron oxide (III) is emitted in the under-bunker room, where raw materials are unloaded into the scale car. The concentration of dust in the air under the bunker premises reaches 500 mg/m3.

In the under-bunker rooms, equipped with conveyors, about 2.5 kg of dust is sucked off by the aspiration system for each ton of pig iron.

In the foundry yard, dust with a high content of iron oxide (III) is emitted from the tapholes of pig iron and slag, troughs of the drain areas and ladles. The specific dust output in this case is 400-700 g of dust per 1 ton of cast iron.

The maximum amount of dust is emitted during the tapping of pig iron and slag.

The average concentration of dust during the release period is 150-1500 mg/m3; the maximum concentration is observed above the main chute and ladle for pig iron.

Thus, the use of iron-containing pulverized waste from blast-furnace iron production is currently very relevant.

The chemical composition of blast-furnace slags is represented mainly by four oxides: CaO (29-30%), MgO (0-18%), Al ₂ 0 ₃ (5-23%) and Si0 ₂ (30-40%). In a small amount they contain oxides of iron (0.2-0.6%) and manganese (0.3-1%), as well as sulfur (0.5-3.1%).

Most blast-furnace slags are characterized by basicity (CaO/SiO ₂ ) in the range of 1.0-1.2 and content of Al ₂ 0 ₃ and MgO 3-20 and 5-15.

Depending on the ratio of CaO / Si0 ₂ and (CaO + MgO) / Si0 ₂ , slags are divided into basic and less basic.

At the Cherepovets Metallurgical Plant, when smelting low-sulfur iron, blast-furnace slag is less basic, containing: MgO is 10-12%, and the ratio of CaO / SiO ₂ and (CaO + MgO) / SiO ₂ is 1 and 1.3.

The chemical composition of blast-furnace slag makes it possible to use it instead of clay and part of the carbonate components in the composition of the raw mixture of expanding additives.

The iron content in untreated converter and open-hearth slags of steelmaking is very high (45-65 wt.%). At the same time, the chemical composition of slags from gas cleaning of electric furnaces is not constant, since it depends on the grade of steel being smelted and is characterized by a lower iron content, as well as the presence of non-ferrous metal impurities.

Usually in the manufacture of cement, slags are used in granular form. Slag granulation is carried out either at the melting unit, or at separate installations, with the molten slag being transported to them in ladles. The main mass of slag melts is processed in out-of-furnace water troughs, pool and drum plants. Crushing of slag in these installations is carried out by water or air jet. The plants consume a lot of water, which after use needs to be cleaned, so the additional use of untreated iron-containing dust-like waste from blast-furnace iron production, not subjected to granulation and other additional processing, can significantly reduce the cost of processing waste.

Gypsum stone is a rock of sedimentary origin with impurities of dolomite, anhydride, iron hydroxide, sulfur, quartzite, consisting mainly of the mineral CaSO ₄ ⋅ 2H ₂ O.

The main purpose of adding gypsum to cement binders is to slow down the hydration process of the cement after it has been mixed with water.

The process associated with cement hydration is as follows. Water is added to the cement, after which the cement begins to harden. The hardening process is very short, so the cement is constantly stirred.

When gypsum and water are added to cement, a reaction occurs with the cations of the particles of the aluminates included in the cement with semi-aqueous gypsum (gypsum stone or calcium hydroxide).

As a result, calcium hydrosulfoaluminate, or ettringite, is formed - a mineral with a whitish or yellowish color, a derivative of aluminum and calcium, sulfate.

Ettringite can initially be formed as very fine grained crystals that form a coating on the surface of the particles. These crystals are too small to bridge the gaps between cement particles. Therefore, the cement mixture remains plastic and suitable.

One of the main reasons for the decrease in the strength of cement is the late formation of ettringite under the influence of various environmental factors.

The primary formation of ettringite crystals in the initial phase of hydration has a constructive effect on the setting control effect, and later the formation of ettringite crystals causes destructive processes.

Introduction to the composition of the expanding additive microsilica - ultrafine material, consisting mainly of silicon dioxide SiO ₂ .

For the primary formation of ettringite crystals in the initial phase of hydration, microsilica is introduced into the composition of the expanding additive, according to the claimed invention - an ultrafine material consisting mainly of silicon dioxide SiO ₂ .

Microsilica is a substance consisting of colorless crystals, which has high strength, hardness and refractoriness, is resistant to acids and does not interact with water.

Amorphous microsilica is capable of reacting with calcium hydroxide at normal temperature to form tobermorite-like calcium hydrosilicates, which ensures the strength and durability of the cement stone.

Metallurgical production slags are materials with potentially binding properties.

The alumina slag used in the claimed composition is a high alumina blast furnace slag containing wt. SiO ₂ 7-12; Al ₂ O ₃ 44-50; CaO 40-43; S 0.7-1.0, MgO 1-3, FeO 0.2-0.5.

The use of aluminous slag in the composition contributes to the achievement of the normative strength of cement within a short time after mixing with water.

In the closest analogue, chosen as a prototype, to obtain good physical and mechanical properties of cement samples, including an expanding additive, the samples are heated to 90 ^o C. This effect is due to the fact that ettringite is unstable at elevated temperatures and at temperatures above 80-90 ^o C turns into the monosulfate form 3CaO⋅Al ₂ O _z ⋅CaSO4⋅12H2O (C ₃ A^H12), which excludes the later formation of ettringite crystals, which contributes to the formation of cracks in the hardened cement and an increase in strength characteristics.

In the claimed invention, the synergy lies in the fact that the addition of steelmaking slag stabilized to prevent silicate decomposition by granulated dust from gas cleaning of electric arc steelmaking furnaces, with an iron oxide content of Fe2O3 of at least 45%, in an amount of 2-5% by weight of the processed slag , and microsilica, without heating the finished samples of cement to 90 ^about C, contributed to the improvement of physical and mechanical properties compared to the prototype.

An example of the implementation of the claimed invention.

Blast-furnace granulated slag, gypsum stone, alumina slag, iron-containing pulverized waste from blast-furnace iron production, with a particle size of 1-200 microns, and microsilica were dried to a residual moisture content of 1-5%, with a dosage in the above ratios, crushed in a ball mill to a specific surface of 3500 ±200 cm2/g.

The composition of the expanding additive is presented in table 1.

Table 2 presents the physical and technical parameters of cement samples after 30 days of hardening, obtained using the claimed composition of the expanding additive.

To obtain samples, an expanding additive in an amount of 20% was mixed with Portland cement M400 and the self-stress of the obtained samples was determined.

To determine the ultimate strength in bending, bending tests of the specimens were carried out on the corresponding test equipment on an MII-100 machine.

The ultimate strength in bending (MPa) was recorded by the counter of the device. The test result was calculated as the arithmetic mean of the two largest test results of the three samples.

The halves of the samples obtained after bending tests were immediately tested for compressive strength. The tests were carried out on a hydraulic press MS-100.

The arithmetic mean of the test results of six halves of the samples was taken as the compressive strength.

As can be seen from table 2, the introduction of the claimed expanding additive allows you to obtain samples of expanding cements, with increased physical and technical parameters at room temperature ^of 20 ° C in relation to the same indicators of the prototype: density, kg / m ² - up to 2650; compressive strength, MPa - up to 50.4; tensile strength in bending, MPa - up to 7.1; self-stress, MPa - up to 5.1.

In terms of water resistance on the 28th day, the cement containing the expanding additive of the claimed composition (20W) exceeded the same indicator for the prototype by more than three times (6W).

From the data of Table 3 it can be seen that in cements containing the claimed composition of the expanding additive, a day after mixing with water, gel-like hydration products are formed on the surface of the cement particles, which are detected already 3 hours after mixing, and crystalline neoplasms of ettringite form appear, which, intertwining, additionally bind cement particles together, increasing its strength. To identify the content of ettringite, X-ray phase analysis was carried out on a diffractometer.

As a result of experimental data, it was found that the content of ettringite in the composition of cement already on day 1, which creates the necessary conditions for obtaining a strong and dense cement structure, the maximum increase in the content of ettringite was found by day 28.

Table 1

Expandable Additive Compositions

Composition The content of components, wt.% one 2 3 4 Blast furnace granulated slag 55.0 62.0 65.0 75.0 gypsum stone 23.0 21.0 19.0 18.0 aluminous slag 8.0 7.0 5.0 2.5 Pulverized waste from blast-furnace iron production, with a particle size of 1-200 microns 11.0 8.0 7.0 3.5 microsilica 3.0 2.0 3.0 1.0

table 2

Comparison of physical and technical strength indicators

Physical and technical indicators at a temperature ^of 20 ° C Lineups one 2 3 4 Prototype Density kg / m ² 2450 2600 2650 2520 2400 Compressive strength, MPa 49.70 46.10 50.40 47.60 41.25 Tensile strength in bending, MPa 7.0 6.85 6.90 7.10 6.75 Self-stress, MPa 4.5 3.7 4.9 5.1 2.3 Water resistance for 28 days, W twenty twenty twenty twenty 6

Table 3

Kinetics of water binding and ettringite crystallization

Claims (3)

1. Expansion additive to tension and expanding cements, including blast-furnace granulated slag, gypsum stone and alumina slag, characterized in that it additionally contains iron-containing pulverized waste with a particle size of 1-200 microns and silica fume in the following ratios, wt. %: blast-furnace granulated slag 55.0-75.0 gypsum stone 18.0-23.0 aluminous slag 2.5-8.0 iron-containing pulverized waste metallurgical production with a particle size of 1-200 microns 3.5-11.0 microsilica 1.0-3.0 2. Expanding cement additive according to claim 1, characterized in that all components have a moisture content of 1-5%.