DE10200416C1 - Porous concrete production comprises grinding latent hydraulic foundry sand with sand and water in a sand mill, drying, mixing the wet components with a binder and propellant, cutting into molded bricks, and hardening in an autoclave - Google Patents

Abstract

Porous concrete production comprises grinding latent hydraulic foundry sand with sand and water in a sand mill in a ratio of (foundry sand + sand)/water of 0.5-2.5 and drying to give a residual moisture of 30-45 wt.%, mixing the wet components with a binder and propellant so that the total mixture contains 1-30 wt.% foundry sand, and cutting the stiffed mass into molded bricks and hardening in an autoclave under hydrothermal conditions and pressure. Preferred Features: The binder mixture comprises 95-50 wt.% cement, calcined lime, hydrated lime and/or gypsum, and 5-50 wt.% latent hydraulic ground foundry sand having a specific surface area according to Blaine of 1500-7000 square cm/g. The propellant is aluminum powder, aluminum paste, organic slurry and/or organic foaming agent.

Description

The invention relates to two processes for the production of autoclave-hardening aerated concrete, where binders, aggregates, propellants and liquids / water are used, which mixed together and during a stiffening period as well as before a hydrothermal process can be foamed under pressure.

The aim of this treatment is a permanent pore structure in the strongly increased by means of propellants Concrete structure to achieve the improved thermal insulation properties of the to be produced Effect of concrete / shaped stone when it is used as a building material. The shaped stones are easier to handle due to their reduced weight and are also hardened Condition can be mechanically processed without any problems.

There are two important reaction phases in the production of aerated concrete. The first phase is characterized by the production of the green aerated concrete up to the achievement of a cuttable green strength. Due to the components lime (CaO) and cement, strongly exothermic reactions take place in the context of CaO hydration. Together with other reactions, this leads to a stiffening of the dispersion. The hardening of the dispersion can last from a few minutes (lime-rich recipe) to 6 hours (cement-rich recipe). The speed of setting also depends, among other things, on the following parameters:

• - Lime content in the recipe
• - total binder content
• - water / solids value
• - temperature and development
• - Alkalinity of the lime, cement and possibly other binding agents
• - target bulk density.

In the second phase, autoclave hardening takes place under hydrothermal pressure conditions (19 ° C, 12 bar, steam atmosphere, 6-12 h holding time under constant conditions). In the process, SiO _{2 is} dissolved, which reacts with the dissolved CaO to form various calcium silicate hydrate phases (CSH) until the CaO is used up. Since more and more SiO ₂ is dissolved, the CSH phases that have already been dissolved give rise to more that are richer in _{SiO 2.}

It is known to use Portland cement, ground quicklime of high purity and quartz sand or powder as a solid mixture for the production of aerated concrete. When using these raw materials, the positive effect of CaSO ₄ additives was recognized (DE-AS 16 46 580, DE-AS 14 71 171 and DE-OS 27 39 181). In order to maintain the required compressive strength, however, this should only be done in low doses in mixtures rich in quartz sand. DE-AS 27 09 858 also includes a process for the production of vapor-hardened aerated concrete. Here, too, the silicate aggregate is used as the dominant solid component in terms of quantity. It is stated that fly ash containing silicate can also be added as a silicate aggregate instead of sand. However, no information is given about the type of dosage and the resulting properties of the aerated concrete.

It is also considered to be known as siliceous materials and additives fine-grain quartz sands and / or quartz sand flour and / or natural or artificial Pozzolans such as B. volcanic tuffs, diatomaceous earth, calcined clay, Use brick dust, ashes rich in silica and / or slag. Also the use von Büttensand is to be regarded as known in this context.

Furthermore, a component and a method for its production are known, which in Form of an autoclave-hardened molded body of high density with a structure of granular Steel mill slag and a graded grain size composition in the grain range of 0 up to 6 mm is produced (DE-OS 197 50 162). The component can be in a Embodiment also mixed with a mineral binder component, pressed and steam-hardened, cement (including fly ash cement) or blast furnace slag with and without stimulators.

The disadvantage of this component and the associated method is that with the compositions used and the starting materials no early special Stiffening of the green aerated concrete takes place, so that the cutting of the shaped stones is only too can be realized at a relatively late point in time. Because of the coarse slag structure and the dense structure is a cutting of the green concrete mass with a wire not possible. A use of binder mixtures of cement components and Slag meal is not described.

The invention is based on the object of a substantial substitution of expensive Cement, which is used as a binder component in aerated concrete, too accomplish without the positive physical properties of the end product affect negatively. In addition, the aerated concrete or the resulting Shaped stones in his / her color without the addition of bleaching agents or the like can be brightened and produced improved in their strength.

According to the invention, this is achieved in that

• a) latent hydraulic blast furnace slag together with to be used as an aggregate Sand and water in a sand mill in the ratio (blast furnace slag + sand) / water of 0.5 to 2.5 wet grinding and with a total water content of the mixture of < 50 mass% is dried to a residual moisture content of 30 to 45 mass% and
• b) the wet component is mixed with binder and then with a propellant in such a way that the total mixture contains 1 to 30 mass% blast furnace slag, the binder mixture being composed of
  • - 95 to 50 mass% cement and / or quicklime and / or hydrated lime and / or gypsum
  • and 5 to 50 mass% of the latent hydraulic, ground blast furnace slag with a Blaine specific surface of 1500 to 7000 cm ² / g originating from a)

exists and

• a) the resulting stiffened mass is cut into shaped stones and placed in the autoclave hydrothermal conditions and pressure is hardened.

Furthermore, according to the invention, it is alternatively

• a) in a first step, part of a sand to be used as an aggregate up to a grind fineness of 1500-3000 cm ² / g according to Blaine is ground separately in a sand mill and in a second step separately, wet blast furnace slag with a blast furnace slag / water ratio of 0, 5 to 2.5 and with a low mill throughput to a specific surface area of more than 3000 cm ² / g according to Blaine and dried with a total water content of the mixture of <70% by mass to a residual moisture content of 45 to 55% by mass is, and the sand together with the slag sand as
• b) wet components are mixed with binders and with a propellant in such a way that the total mixture contains 1 to 30 mass% blast furnace slag, the binder mixture from
  • - 95 to 50 mass% cement and / or quicklime and / or hydrated lime and / or gypsum
  • and 5 to 50 mass% of the latent hydraulic, ground blast furnace slag with a Blaine specific surface of 1500 to 7000 cm ² / g originating from a)

exists and

• a) the resulting stiffened mass is cut into shaped stones and placed in the autoclave Hardened hydrothermal conditions and pressure.

It is advantageous to store the daily requirement for slag sand together with the Sand as sludge in an agitated tank belonging to the mixing plant or separately from Carry out sand also as sludge in a separate stirred tank. the Joint storage and transport by means of pumps through pipelines improves the poor pumpability compared to a pure blast furnace slag / water dispersion in which it to sedimentation with subsequent compaction, which leads to blockages can. Because the proportion of sand in such a mixture is much higher than that of the slag sand these blockages are no longer to be expected.

The propellant used can be aluminum powder and / or aluminum paste and / or mixed in organic sludge and / or an organic foaming agent, which in the Dispersion mixed in and then with compressed air or a turbulence mixer foamed can be used.

In special situations or for special applications, it can be advantageous to dry-grind the blast furnace slag with a specific surface area of over 2,500 cm ² / g according to Blaine.

Surprisingly, the following has been shown according to the invention:
Since slag sand has increased proportions of amorphous SiO ₂ and CaO-rich phases and, due to its special mineralogical composition and active surface, which is increased to a particular extent after grinding according to the invention, together with the other components results in a mixture which at a pH -Value of 13 to 14 forms partly CSH (I, II) gel phases due to the hydration of the other binders under the alkaline environment of the wet mixture, its addition is a main reason for the particularly good formation of the hexagonal platelets, which crystallize out as tobermorite (C. ₅ S ₆ H ₅ ) lead to the formation of increased early and final strengths in relation to blast furnace slag-free aerated concrete of the same bulk density while maintaining its high thermal insulation.

The chemical reactions are:

Phase 1 in green aerated concrete

• 1. Lime
  CaO + H ₂ O → Ca (OH) ₂
• 2. Cement
  3CaO.SiO ₂ + H ₂ O → CSH (II) + Ca (OH) ₂
  2CaO.SiO ₂ + H ₂ O → CSH (II) + Ca (OH) ₂
• 3. Plaster of paris
  2 (CaSO ₄ .1 / 2H ₂ O) + 3H ₂ O → 2 (CaSO ₄ .2H ₂ O)
• 4. Dissociation portlandite
  Ca (OH) ₂ Δ Ca ²⁺ + 2 (OH) ^- alkaline medium
• 5. Slag sand, etc.
  

Phase 2 autoclaving

For example, with this specially prepared mixture, the strengths of DIN 4165 up to PP2-0.35 (bulk density 0.35 g / cm ³ , compressive strength 2.5 MPa) can be achieved without largely using the conventional cement binder.

It is particularly important to add the dry, specially ground slag sand after the wet components, such as sand sludge, back sludge and water and before the Propellants, such as aluminum powder, must be observed in the specified proportion.

This mixing sequence according to the invention is of particular importance because this prevents agglomeration and the propellant is not used up prematurely, which is very detrimental to the foaming process and the formation of an optimal Pore structure would be.

Since slag sand is latent hydraulic, it takes place during its grinding and storage no hardening takes place. The common one is of particular economic advantage Grinding of the slag sand with the sand in a sand mill. You can still do that Buy and use cheaper granulated blast furnace slag.

The disadvantage of the increase in the necessary proportion of binder when the grinding fineness of the entire sand is increased according to claim 2 can be compensated for by increasing the blast furnace slag after grinding a partial stream of sand at a reduced mill throughput and grinding it extra wet. This means that there is less mill wear, less consumption of grinding media and the possibility of separate storage and metering of sand sludge. The possibility of a higher grinding fineness also has the following additional advantages:

• - there are fewer sedimentation phenomena during the driving process
• - Due to the higher alkalinity there is a shorter waiting time until a given sufficient green strength
• - There is a better conversion of the phases in the autoclave, resulting in a Reduction of the autoclaving times leads.

An extra wet grinding of the slag sand / slag granulate is called in this case the addition of 0.76 kg / l, liquid / water to 0.7 kg / l, slag sand / slag granulate into the mill. The particularly high proportions of liquid / water during grinding lead to that when wet grinding all grain surfaces are intensively wetted with water, so that the alkalis and alkaline earths required for excitation are better adsorbed. Also is so that the heat development during fine grinding can be better controlled.

A storage of the ground slag sand sludge in the stirred tank together with the Sand sludge according to claim 4 has the advantage of being used inexpensive night-time electricity and, on the other hand, for more flexible control of the Production process. You can, for example, the grinding in a continuous and let the aerated concrete production run in a discontinuous process. this has special advantages in terms of investment costs, as there is no expansion of the control system as well no new stirred tanks are necessary.

In addition, you can with a grinding according to claim 3 and storage in a separate stirred tank more flexible to recipe changes caused by Fluctuations in the quality and composition of the raw materials, the raw stone densities and strengths, etc. can be caused react. So you have one special good possibility to set an optimal binder ratio in the mixture.

The following advantages are achieved through the use of specially ground slag sand in exchange with cement:

• - decisive reduction in raw material costs
• - Improvement of the mixture properties due to the special mineralogical structure of the ground Slag sand and the formation of CSH (I, II) gel phases, the particularly positive effects on the strength of the have autoclaved aerated concrete
• - When using specially ground blast furnace slag for the production of aerated concrete, hydroxylellestadite [Ca ₁₀ (SiO ₄ ) ₃ (SO ₄ ) ₃ (OH) ₂ ] and hydro garnet are increased
• - the result is lighter colors (without the addition of bleach) Aerated concrete blocks

On the condition that the wet-ground blast furnace slag can only be used for a short time temporarily stored, some of the other binders (quicklime, Portland cement, hydrated lime or gypsum) in the wet milling process. The slag sand then reacts faster due to the combined chemical and mechanical activation as well as more intense. This allows shorter tool life to achieve cutting ability can be achieved and ultimately this leads to a further shortening of the autoclave times. the However, depending on the temperature of the dispersion, intermediate storage should not exceed 2 hours.

The invention will be explained in more detail below on the basis of an exemplary embodiment.

It shows:

Fig. 1 the aerated concrete production in the flow diagram

The aerated concrete production is set up in the manner according to claim 2 in that a sand feed ( 1 ) takes place on a belt scale ( 2 ), after which the weighed sand is fed to a feed (3 ) of the tube mill ( 4 ). The water ( 5 ) is also fed into this feed and, after the sand grinding, the slag removed from a slag feed (6 ) and fed via a belt weigher ( 7 ) is added. All components are then ground up in the tube mill ( 4 ) and, after they are discharged ( 8 ), arrive in an intermediate container ( 9 ), from which the controlled removal to two agitated containers ( 10 ; 11 ) takes place. While one agitated container ( 10 ) is provided for the ground sand sludge, the second agitated container ( 11 ) is used to store the milled slag. The respective contents are fed from both stirred containers ( 10 ; 11 ), with the addition of water ( 12 ), to a wet balance ( 13 ), which is connected upstream of the further process.

By means of the above-mentioned system and using the method according to the invention using the following preferred formulation

lime 90 kg / m ³ cement 45 kg / m ³ Slag sand 45 kg / m ³ plaster 17 kg / m ³ sand 320 kg / m ³ water 360 kg / m ³ Aluminum powder 0.34 kg / m ³

This formulation results in a dry bulk density of 560 kg / m ³ and the compressive strengths that can be achieved are around 7 MPa. The time to achieve green strength is 2.5 hours.

List of the reference symbols used

1

Sand feed

2

Belt scale

3rd

Feed

4th

Tube mill

5

Addition of water

6th

Slag sand feed

7th

Belt scale

8th

Ejection

9

Intermediate container

10

Mixing tank sand sludge

11

Agitated blast furnace slag

12th

Addition of water

13th

Wet scale

Claims (4)

1. Process for the production of aerated concrete, in which

• a) latently hydraulic blast furnace slag together with sand and water to be used as an aggregate in a sand mill in a ratio (blast furnace slag + sand) / water of 0.5 to 2.5 and with a total water content of the mixture of <50 mass% a residual moisture content of 30 to 45 mass% is dried and
• b) the wet component is mixed with binder and then with a propellant in such a way that the total mixture contains 1 to 30 mass% blast furnace slag, the binder mixture being composed of
  95 to 50 mass% cement and / or quicklime and / or hydrated lime and / or gypsum
  and 5 to 50 M .-% of the latent hydraulic, ground blast furnace slag originating from a) with a specific surface area according to Blaine of 1500 to 7000 cm ² / g

exists and

• a) the resulting stiffened mass is cut into shaped stones and hardened in an autoclave under hydrothermal conditions and pressure.

2. Process for the production of aerated concrete, in which

• a) In a first step, part of a sand to be used as an aggregate is ^{ground separately in a sand mill up to a fineness of 1500-3000 cm 2} / g according to Blaine and in a second step, separately, slag sand wet, in a ratio of slag sand / water of 0 , 5 to 2.5 and with a low mill throughput up to a specific surface of more than 3000 cm ² / g according to Blaine and with a total water content of the mixture of <70 mass% to a residual moisture content of 45 to 55 mass% is dried, and the sand together with the slag sand as
• b) wet components are mixed with binders and with a propellant in such a way that the total mixture contains 1 to 30 mass% blast furnace slag, the binder mixture from
  95 to 50 mass% cement and / or quicklime and / or hydrated lime and / or gypsum
  and 5 to 50 M .-% of the latent hydraulic, ground blast furnace slag originating from a) with a specific surface area according to Blaine of 1500 to 7000 cm ² / g

exists and

• a) the resulting stiffened mass is cut into shaped stones and hardened in an autoclave under hydrothermal conditions and pressure.

3. The method according to claim 1 or 2, characterized in that a storage the daily requirement of blast furnace slag together with the sand as sludge in one Mixing system belonging to the agitated tank or separately from the sand also as sludge is carried out in a separate stirred tank. 4. The method according to claim 1 or 2, characterized in that as a propellant Aluminum powder and / or aluminum paste and / or mixed in organic Sludge and / or an organic foaming agent which is included in the dispersion mixed in and then foamed with compressed air or a turbulence mixer will be used.