CS254525B1 - Slag-alkali concrete - Google Patents

Abstract

In the case of slag-alkaline concrete mixtures, the economically significant knowledge of the application of waste foundry sand and possible partial replacement of aggregates with slag is applied while maintaining the very good properties of the resulting slag-alkaline concrete products, free of cement. Specific recipes allow for a wide application of the mixture, which can also be produced directly within foundry operations, where there are significant problems with waste foundry sand.

Description

The invention relates to a slag-alkaline concrete mixture based on ground slag, preferably granulated blast furnace slag, a solution or suspension of a basic-reacting compound of an alkali metal or alkaline earth metals, or a mixture thereof, and aggregates.

In addition to concrete mixtures with Portland cement as a binder, so-called slag-alkaline concrete mixtures are known, the production of which uses a mixture of finely ground high-peony slag, an alkaline component, e.g. sodium hydroxide or water glass, and aggregates, i.e. sand and gravel, or crushed stone.

Slag-alkali concretes exhibit some very advantageous utility properties, their stability for a period exceeding 15 years is documented in the professional literature. The mass application of these concretes is currently hindered by, among other things, the lack of ground slag and especially the lack of suitable alkaline compounds, primarily sodium carbonate, hydroxide or silicate.

The increasing shortage of raw materials and energy in the construction industry is reflected in the fact that energy-intensive cement is being saved and at the same time quality aggregates, which are becoming scarce, especially good gravel and sand. The costs of their extraction and transportation are increasing, which has adverse economic consequences. On the other hand, many industrial enterprises produce large amounts of solid waste during their production process, which should not only be deposited or disposed of, but also reused as so-called secondary raw materials.

For example, foundries produce significant amounts of various wastes during the production process, each in the order of tens to hundreds of tons per day. These wastes are often very expensive to store or dispose of, with a negative impact on the environment. This mainly concerns waste foundry sands, foundry slag, or sludge from extracted dust.

For the production of foundry molding mixtures, sands of a certain quality are used, which are becoming scarce. The most common additive to these mixtures is an alkaline component - a solution of water glass, which essentially acts as an air mortar; its content in the mixture must not exceed a certain upper limit. Even if in some foundry plants it is proposed to use the mixtures several times, each time after a certain additional addition of water glass, the result is finally a mixture that is no longer satisfactory due to its high alkali content. Removing alkalis by washing is practically not carried out; it is a difficult and expensive process that creates problems with wastewater.

The alkali or powdered coal content makes these materials unusable as aggregates for the preparation of classic concretes with Portland cement, but the higher alkali content is favorable for the preparation of slag-alkali concretes.

Another method of preparing molding mixtures is based on the use of organic hardeners, which often contain organic substances harmful to health, such as phenols, so their disposal or storage poses technical and hygienic problems and makes environmental care difficult.

In many foundries, used sands are therefore accumulated, which are often provided free of charge, so that new storage facilities, which often take up agricultural land, do not have to be established. There are currently no economically viable options for using used waste foundry sands on a large scale. Another waste is steel or foundry slag, which is now mostly taken to landfills; only a small part is used in agriculture.

These slags in granular form, usually with a grain size of up to 5 mm, have a reactive surface and are very hard, so they can serve as suitable aggregates in concrete mixtures.

Another suitable raw material for mortar mixtures is fly ash produced by burning solid fuels in power plants or heating plants, which is available in many times larger quantities than the construction industry can use and causes serious environmental problems.

In some foundries, sludge from dust particle extraction is produced as technological waste, which is thickened in sedimentation tanks and also transported to landfills.

The invention aims to create such a slag-alkaline concrete mixture that will allow significantly reducing or in some cases even eliminating the use of expensive high-quality aggregates, i.e. gravel sand or crushed stone, by replacing them with the aforementioned waste foundry sand, or alternatively using another type of granular or crystalline slag and fly ash from the combustion of solid fuels.

The essence of the invention lies in the fact that the concrete mixture contains, based on 1 m2 of hardened concrete, from 200 to 700 kg of ground blast furnace slag with a specific surface area of 250 to 700 m2/kg, from 200 to 1,800 kg of waste foundry sand, up to 250 kg of water, up to 1,200 kg of crushed stone or other aggregate, from 52 to 420 kg of a solution of hydroxide, silicate, sodium or potassium carbonate with a density of 1.05 to 1.40 g/cm2, and/or an aqueous suspension of lime hydrate or lime carbide, with the content of oxides _Na2O , potassium _K2O and calcium CaO in the concrete mixture being 2 to 30% of the weight of ground slag. I

Another feature is that the silicate solution is formed by sodium and/or potassium water glass with a silicate modulus of 0.5 to 3.5 and a density of 1.05 to 1.4 g/cm^.

According to the invention, an amount of up to 1,200 kg of crushed stone or other aggregate is replaced by at least granulated untreated blast furnace, foundry or steel slag and/or fly ash from solid fuels, the maximum amount of which, relative to the content of ground slag, is 20% by weight.

The mentioned mixture solves the problem of valorizing the mentioned foundry secondary raw materials by processing them into slag-alkali concretes, so that, for example, within a foundry plant, almost waste-free management is achieved, which is desirable and often necessary for ecological reasons.

The prepared concretes have compressive strengths of 5 to 50 MPa as conventional concretes and up to 120 MPa as special high-strength concretes. The tensile strengths during bending reach approximately 10% of the compressive strength. Slag-alkaline concretes from mixtures produced according to the invention can be used in various fields of construction, especially in prefabrication.

A significant advantage of slag-alkali concretes is the possibility of using waste foundry sands, even with a certain proportion of clay, dust or organic components, which cannot be used for the preparation of conventional concretes based on Portland cement. To prepare a slag-alkali concrete mixture for the production of 1 m of ready-made concrete, the following is used:

- ground blast furnace slag with a specific surface area of 250 to 700 m/kg in quantities of 200 to 700 kg?

- waste foundry sand with grain sizes up to 1 mm in quantities from 200 to 1,800 kg?

- up to 1,200 kg of crushed stone 4 to 22 mm or other aggregate?

- silicate solution, for example sodium or potassium water glass with a silicate modulus of 0.5 to

3.5 and with a density of 1.05 to 1.4 g/cm in an amount of 52 to 420 kg, or a solution of sodium and/or potassium hydroxide with a density of 1.05 to 1.4 g/cm?

Waste sodium hydroxide solutions, e.g. from food industry plants, can be successfully used as an alkaline solution. For mixtures with the most common content of 350 to 550 kg of ground slag per 1 m of solidified concrete, the water or solution content most often ranges from 120 to 180 liters. A larger amount of water slows down the setting, and at the same time causes lower strengths?

- and/or an aqueous suspension of lime hydrate, preferably waste carbide lime, wherein the sum of the content of oxides NaO, potassium K ₂ O and calcium CaO and the concrete mixture is 2 to 30% by weight of the content of ground slag?

- mixing water in an amount of up to 250 kg, whereby when using lime carbide sludge, the calculation also takes into account the water contained in the sludge and the water contained in the aggregate?

- granulated slag with a grain size of up to 20 mm, e.g. as waste from foundry or steel mill operations, in quantities of up to 1,200 kg?

- any granulated gravel, sand or other aggregate up to 1,200 kg;

- fly ash from the combustion of solid fuels, most often from power plants or heating plants, the loss of which upon annealing reaches a maximum of 7%, in an amount of up to 20% by weight of the ground slag used, preferably with a higher CaO content;

- can also be used for up to 50 kg of sludge from extracted dust from foundry work areas.

Examples of the mixture according to the invention are given in the following examples, containing the composition of the mixture per 1 m of finished concrete in kg, with the achieved weights of 1 m of finished concrete ranging from 1,790 to 2,500 kg.

In all the examples given, a sodium water glass solution with a silicate modulus of 1.33 and a density of 1.26 g/cm 3 is used as the alkaline solution.

In examples 1 to 6, warming is used, in examples 7 to 15, normal maturation and moist storage are used.

The stated achieved strengths are understood as compressive strengths i k 1 a d 1 2 ground slag, 280 m /kg 640 kg alkaline solution 227 kg foundry sand 1,584 kg granulated slag 0-16 mm 96 kg water 140 kg strengths achieved in 7 days 25 ί MPa, in 28 days 3C > MPa. : k 1 and d 2 2 ground slag 280 m /kg 640 kg alkaline solution 227 kg foundry sand 560 kg granulated slag 0-16 mm 30 kg embroidery 540 kg crushed 4-16 mm 550 kg water 80 kg strength achieved in 7 days 30 MPa, for 28 days 33 MPa. : k 1 and d 3 2 ground slag 280 m /kg 640 kg alkaline solution 227 kg foundry sand 560 kg granulated slag 7-16 mm 30 kg crushed 4-16 mm 1,090 kg water 80 kg strength achieved in 7 days 36 MPa, for 28 days 36 MPa. [ k 1 and d 4 ground slag 280 m^/kg 640 kg alkaline solution 227 kg foundry sand 560 kg

gravel 4-16 mm 1,120 kg water 80 kg achieved strength in 7 days 35 MPa, in 28 days 36 MPa.

Example 5

2 ground slag 280 m /kg alkaline solution 640 kg 227 kg foundry sand 1,120 kg water 80 kg grit 4-16 mm 560 kg

achieved strength in 7 days 30 MPa, in 28 days 32 MPa.

Example 6

ground slag 280 m' 7kg 640 kg alkaline solution 227 kg foundry sand 1,090 kg granulated slag 0-16mm 30 kg water 80 kg grit 4-16 mm 560 kg

achieved strength in 7 days 35 MPa, in 28 days 38 MPa.

Example 7 ground slag 307 m^/kg 479 kg foundry sand (containing 2% coal) 958 kg carbide lime (slurry containing 51% water) 328 kg

water achieved strength for for volumetric weight 7 28 days 1.5 MPa days 4.9 MPa 183 kg 1 950 kg/yr Example 8 2 ground slag 307 m /kg 270 kg foundry sand 720 kg mined sand 0 to 4 mm 360 kg calcium hydrate 130 kg water 275 kg sodium hydroxide 19 kg strength achieved in 3 days 3.62 MPa for 28 days 6.40 MPa

Density 1,789 kg/m

Example 9

ground slag 307 m /kg foundry sand 279 kg 744 kg mined sand 0 to 4 mm 37 2 kg calcium hydrate 135 kg water 279 kg potassium hydroxide 23 kg

achieved strength in 3 days 1.94 MPa in 28 days 7.60 MPa bulk density 1,832 kg/m ³

Example 10

2 ground slag 307 m /kg 589 kg foundry sand 589 kg grit 8 to 16 mm 589 kg carbide lime (slurry with obsal hem 5 1% in ods) 196 kg potassium hydroxide (10% solution) 216 kg strength achieved in 7 days 5.2 MPa for 28 days 11.2 MPa volumetric weight 2 ! 175 kg/m 3 1 and 11 o ground slag 307 m /kg 365 kg foundry sand 468 kg grit 8 to 16 mm 972 kg power plant fly ash 36 kg sodium hydroxide solution 53 kg carbide lime (slurry containing 5: 2% water) 121 kg water 194 kg strength achieved in 1 day 1.8 MPa for 7 days 9.3 MPa for 28 days 22.3 MPa volumetric weight 2 227 kg/m 3 1 and 12 2 ground slag 307 m /kg 640 kg foundry slag 640 kg foundry sand 640 kg power plant fly ash 57 kg sodium hydroxide solution (10%) 83 kg alkaline solution 217 kg strength achieved in 7 days 24.8 MPa for 28 days 33.7 MPa volumetric weight 2 280 kg/m 3 1 to 1 and d 13 ground slag 280 m ² /kg 440 kg foundry sand 1 320 kg fly-by from ferrosilicon production .and 40 kg potassium hydroxide 48 kg water 208 kg strength achieved in 1 day 20.1 MPa for 60 days 32.2 MPa volumetric weight 2 055 kg/m 3 1 and 14 2 ground slag 280 m /kg 445 kg foundry sand 1 335 kg

Ί fly ash from ferrosilicon production 89 kg potassium hydroxide 29 kg water 200 kg sodium methylsilanolate (plasticizer) 5 kg achieved strength in 1 day 14.5 MPa in 180 days 35.6 MPa bulk density 2,087 kg/m

Example

ground slag 307 m^/kg 600 kg foundry sand (with 2% coal content) 600 kg mined sand 0 to 4mm 300 kg crushed 8 to 16 mm 600 kg power plant fly ash: nsky 30 kg hydroxide solution ; sodium 4 kg alkaline solution 245 kg water 42 kg

achieved fortress for 1 day 2.5 MPa for 7 days 19.2 MPa for 28 days 56.7 MPa volumetric weight 2 421 kg/in

The elastic moduli of samples made from the above mixtures and their deformation profiles under load are practically identical to the values achieved for products made from normal cement concrete.

If necessary, additives can be added to modify some properties of the mixtures, e.g. setting retarders, plasticizers, waterproofing, aerating or defoaming additives, etc. Due to the different nature of slag-alkali concretes, the type and quantity of the respective additive must be tested in advance.

The method according to the invention can be implemented with the machinery of conventional mixing plants on mobile and stationary mixers supplemented with an alkaline solution or lime suspension management system; this is usually part of every foundry.

The mixing time is determined by the type of mixer and is identical to the mixing time of concrete mixtures based on Portland cement. The transportation of mixtures mixed in this way can be ensured by conventional methods - containers, multi-carts, cars, mixers, under-hanging grooves, flatbed trucks, belt conveyors, etc. The use of transporting the mixture in pipe distribution is not suitable. Slag-alkaline concrete mixtures are best processed within 30 minutes of preparation using conventional concrete technologies used on construction sites or in prefabrication. By adding suitable retarders, the beginning of solidification can be practically arbitrarily delayed.

For use directly in foundries, i.e. for local processing of the described foundry waste, processing in the form of simple prefabrication is best suited, i.e. for the production of simple concrete products in the range of concrete goods, such as tiles, curbs, land reclamation elements, gutters, etc., as well as simple building components, such as road panels, cultivation panels, fence components, mast bases, etc. These products can be produced in closed and semi-closed forms, stripping frames, when compacting using attached vibration, submerged, using vibration cores and vibrating tables, pneumatic vibration, pressing, and generally by all known methods of compaction.

Products can be produced on flat surfaces, steel pads, as parts of simple lines using crane transport or other lifting devices for product transport. Solidification and hardening can be left to the process of free maturation or accelerated by heating, which can be used when it is necessary to increase the turnover of molds or pads. Polypropylene oil appears to be the most suitable separator; numerous separators common when using mixtures with Portland cement are not very effective in slag-alkaline concretes due to the higher alkalinity of these mixtures.

Before warming, it is necessary to allow the mixture to age properly at temperatures up to 30 °C for 2 to 24 hours. The optimal warming regime is to achieve a maximum heating of 80 °C in the mass with the regime; 2 hours of temperature rise, 4 to 8 hours of temperature resistance, 2 hours of cooling. Waste heat from foundries can also be used for warming. After the process of accelerating the hardening of concrete is completed, the products can be safely handled when the compressive strength of approximately 25 to 30 MPa is reached. During free maturation, i.e. during the natural process of solidification and hardening, the mentioned strengths are achieved for heavy mixtures after 4 to 21 days. When using carbide lime, steaming is not recommended.

For concretes hardening by normal maturation, the method of treatment is also important; temperatures from 20 to 35 °C and the presence of an optimal amount of water in the mixture have a positive effect on the development of strength, so it is usually desirable to moisten the hardening concrete. Due to the content of the alkaline compound solution, concreting can also be done in frost.

When using local waste raw materials, recipes with ingredient quantities defined according to the invention according to previously conducted tests can be used.

The use of the mixture according to the invention is not limited to its production only within foundry operations, i.e. directly at the source of the said waste, even if it appears to be particularly advantageous from a cost perspective, or only in the production of concrete parts or elements. The mixtures are also applicable for structural concretes, e.g. cheaper ones with carbide lime with compressive strengths of 8 to 20 MPa for the production of floors of industrial halls, sidewalks, parking lots, parking areas, in road construction, etc.

Claims (3)

CLAIMS 1. A slag-alkali concrete mixture based on ground slag, preferably blast-furnace granulated, of a solution or suspension of an alkaline or alkali metal soil or mixtures thereof and aggregates, characterized in that it contains from 200 to 700 kg of ground blast furnace slag with a specific surface area of from 250 to 700 m / kg, from 200 to 1 800 kg of foundry sand, based on 1 m of hard concrete , up to 250 kg of water, up to 1 200 kg of pulp or other aggregates, from 52 to 420 kg of a solution of hydroxide, silicate, sodium or potassium carbonate with a density of 1,05 to 1,4 g / cm, and / or an aqueous suspension of lime hydrate, or % of sodium oxide, potassium and CaO in the concrete mixture is 2 to 30% by weight of the ground slag content. 2. The slag-alkali concrete mixture of claim 1, wherein the silicate solution is a sodium and / or potassium water glass having a silicate modulus of 0.5 to 3.5 and a density of 1.05 to 1.4 g / cm < ^{3 &gt};. 3. The slag-alkali concrete mixture according to claim 1, characterized in that the quantity up to 1200 kg of grit or other aggregate is replaced by at least partially granulated untreated blast furnace, foundry or steel etruscan and / or solid fuel fly ash, the maximum amount of which the slag is 20% by weight.