WO2017167321A1

WO2017167321A1 - Cement-reduced concrete and method for producing cement-reduced concrete

Info

Publication number: WO2017167321A1
Application number: PCT/DE2017/000076
Authority: WO
Inventors: Helmut ROSENLÖCHER; Dagmar TRETBAR
Original assignee: HALSER, Leopold; DATTINGER, Florian
Priority date: 2016-03-29
Filing date: 2017-03-27
Publication date: 2017-10-05
Also published as: DE102016003644B4; DE102016003644A1

Abstract

The invention relates to a method for producing cement-reduced concrete, according to which, in a first step, a proportion of water, a proportion of a mineral material, including cement and at least one cement substitute, and a proportion of plasticizer are suspended in a suspension mixer such that a binding agent suspension is produced, in a second step a proportion of aggregate is provided, the proportion of particles smaller than 0.125 mm being less than 10%, preferably less than 5%, and in a third step the proportion of aggregate is mixed with the proportion of binding agent suspension. The invention further relates to a cement-reduced concrete produced according to said method.

Description

Cement-reduced concrete and process for producing cement-reduced concrete

The invention relates to a method for the production of cement-reduced concrete according to the features of claim 1 and a cement-reduced concrete according to the features of claim 10.

Concrete is one of the most widely used construction materials worldwide. As a result of growing industrialization and increasing urbanization, there has been a steady increase in concrete consumption in the past, especially in emerging markets. However, this has negative consequences for the environment. For example, the production of cement as a constituent of concrete is currently responsible for 7% of global carbon dioxide emissions. It is therefore attempted to reduce the consumption of cement by reducing the cement content in the concrete. This can be achieved by mixing cement with materials such as limestone, dolomite, fly ash, or hides. is used, which cause significantly lower carbon dioxide emissions in their production. In the practical implementation of cement-reduced concrete mixtures, however, it has been shown that with decreasing cement values, the water content must be reduced, whereby the processing ability of the fresh concrete is adversely affected.

The currently known prior art is documented by the published patent application DE 10 2012 105 071 A1, which discloses a ready-mixed concrete with a low cement content. The disadvantage is that the concrete mixtures described therein do not meet the requirements for concretes according to DIN EN 206 with respect to the permissible water / cement values according to this standard or only to a limited extent. It can be seen from the formulation constituents listed in DE 10 2012 105 071 A1 that the qualities of the resulting low-cement concretes generally do not meet the requirements, since the excessively high water / cement values caused by the savings are in part outside of DIN EN 206. It can therefore be assumed that the production of cement-reduced concretes using conventional mixing technology can only be achieved to a limited extent or leads to unsatisfactory results with regard to the resulting concrete qualities.

It is known that the fines in the aggregates - with fines are particles with a size of less than 0.125 mm - have a high water retention capacity. Due to the water retention capacity of the fine fraction of conventional concrete production water is delivered in an insufficient amount of cement, so that the initially still liquid concrete is stiff and poorly workable.

In order to achieve a processing capability corresponding to the requirements, additional water must be supplied to the fresh concrete mixture. In the overall mixture, which usually consists of sand, gravel, cement, water and additives, the water binding capacity of the fines in the aggregates leads to one for the hydraulic Setting process unnecessary surplus of water. Thus, fines are generally disturbing in the aggregates for concrete production, especially because with the conventional mixing technique with very slow-running mixing tools to about 100 U / min direct processing of these shares can not be achieved.

In order to ensure the highest possible concrete quality with maximum cement substitution, the reduction of the cement content in the equivalent to the reduction of the water content while maintaining the processing parameters of the resulting fresh concrete must be made technologically manageable.

It is therefore an object of the present invention to propose a method according to which a cement-reduced concrete can be produced which meets the requirements of the technical regulations and the requirements with regard to processability.

A further object of the invention is to propose a cement-reduced concrete which meets the requirements of the technical regulations and the requirements with regard to processability.

According to the invention the object is achieved with a method having the features of claim 1 and with a cement-reduced concrete having the features of claim 10. Advantageous embodiments and further developments of the invention can be realized with features designated respectively in the subordinate claims.

In the method according to the invention for the production of cement-reduced concrete, the procedure is such that, in a first step, a proportion of water, a mineral content comprising cement and at least one cement substituent, and a proportion of flow agent are suspended in a suspension mixer to provide a binder suspension. The mineral content may preferably contain particles of a size smaller than 0.125 mm. In a second step of the method according to the invention, a share of impactor, in which the proportion of particles having a size smaller than 0.125 mm is less than 10%, preferably less than 5%. In a third step, the proportion of additive is mixed with the proportion of binder suspension.

For better understanding, the proportion of particles having a size smaller than 0.125 mm in the context of the invention may be referred to as fines or fines. Surprisingly, it has been found that by the process according to the invention using additives with less than 10% fines, that is less than 10% particles with a size smaller than 0.125 mm, cement- and water-reduced concretes can be provided. Because the absence of these fines in the aggregate provided separately under defined conditions binder suspension is not contaminated during mixing with the aggregate with other fine particles, so that the function of the binder suspension is not impaired as a glue for bonding the aggregate grains.

Advantageously, cement-reduced fresh concretes can thereby be provided, which have improved flowability and, consequently, a higher settling flow rate and slump without the need to additionally supply water to the mixture.

Preferably, the mineral content, which is formed from a proportion of cement and at least a proportion of cement substituent, exclusively on particles having a size smaller than 0.125 mm. According to an advantageous embodiment of the method according to the invention, a sand and / or gravel fines fraction with particles smaller than 0.125 mm can be used as the cement substituent, the sand used and / or the gravel used being provided as an additive in the second process step.

Due to the separate suspension mixing of the mineral content, which according to one embodiment of the method according to the invention can exclusively comprise particles with a size smaller than 0.125 mm, it is ensured in the first process step that the particles contained in the mixture are completely in contact with water come and thereby can form a water jacket around the particles. Advantageously, clumping and agglomeration of particles can thereby be avoided, so that a particularly homogeneous binder suspension is provided. Due to the absence of the fines fraction in the aggregate, the binder suspension in the third process step comes into direct contact with the surface of the coarser constituents of the aggregate and bonds them together without the properties of the binder suspension being influenced by further fines.

By working up all the fines in the suspension mixer according to the invention, a reduction in the ratio of the water / fines content or the water / flour / grain ratio in the resulting concrete mixes is achieved. It has been found that the cement and water-reduced concretes produced in this way have a higher ultimate strength and are also more sustainable in their properties.

Although compared to conventional concrete production process with the suspension concrete method according to the invention in the resulting total mixture of concrete recipe quantitatively equal proportions of fines may be included with particle sizes of less than 0.125 mm, are achieved by the separate workup of all fines in the suspension mixer much better fresh concrete properties.

With regard to the use of the concretes produced by the process according to the invention, there are basically no restrictions. Thus, the concretes produced by the process according to the invention are suitable as ready-mixed concrete or as concretes for the production of precast concrete parts. Conveniently, a concrete produced by the process according to the invention can be used as ready-mixed concrete. Furthermore, a concrete mixture can be provided which is particularly suitable for the production of precast concrete parts. Advantageously, the process according to the invention can be carried out by a dual concrete mixing technique in which, in the first step, the binder suspension, which can also be referred to as a glue component, is prepared in a separate suspension mixer under defined conditions. In the suspension mixer, the mineral content is absorbed in water and mixed using high shear forces. Preferably, the binder suspension may be provided at a stirring speed of a stirring tool of the slurry mixer of more than 600 rpm. Particularly advantageous is a stirring speed in the range of 600 rev / min to 1600 rev / min prove.

Subsequently, the binder suspension or glue component prepared in this way is combined with the additive (s) in a conventional mixer and mixed to form a homogeneous liquid concrete mixture.

Because of the good availability, ground minerals, preferably limestone flour, can be used as the cement substituent. However, it can also be provided that dolomite, blast furnace slag, fly ash, silica fume and / or fine sand with a particle size smaller than 0.125 mm is / are used as the cement substituent. Furthermore, it is also possible to use a combination of several and various inert and / or reactive additives, such as trass, fly ash or silicate dust in the mineral content.

According to a preferred embodiment of the method according to the invention can be used as aggregate sand and / or gravel with a particle size of 1 mm to 8 mm. However, it can also be provided that sand or gravel is used with a larger grain size. According to the invention, sand or gravel is used as an additive in which the proportion of particles having a size smaller than 0.125 mm is less than 10%, preferably less than 5%.

For the preparation of preferred concrete mixtures water and cement can be used in a proportion of less than 0.6, wherein a proportion of water and mineral content of less than 0.45 is maintained. The numerical value of the proportion of water and cement is the quotient of the water content and the cement content. The numerical value of the proportions of water and mineral content is the quotient of the water content and the mineral content.

Due to the substitution of the cement content in the mineral content, based on the concrete mixture, a reduced cement content of less than 300 kg / m ³ , preferably less than 250 kg / m ³ can be used. In an advantageous embodiment of the invention

Process cement and cement substituent can be used in equal proportions, so be used in the same ratio. In this case, half of the usual cement content is replaced by the cement substituent. In this case, the quotient of the proportion of cement and cement substituent is 1, 0. As a result, concrete mixtures can be provided that meet the legal requirements with regard to emission limit values for carbon dioxide.

Aggregates, such as sand or gravel usually contain fines (fractions with particle sizes smaller than 0, 125 mm) in the

Range of grain spectrum 0 mm to 4 mm. In the conventional production (prior art), these fines together with the cement or in combination with other additives, such as granulated blastfurnace, rock flour or fly ash in the concrete mix the glue component, which in the concrete mixture as solid

Matrix is formed. For this reason, the fines in the aggregate, in particular the proportions with particle sizes less than 0, 125 mm attributable to Bindemittelleim or the Leimkomponente, as these in combination with the cement and other additives in the concrete mix as a carrier or as binder for the larger grain larger serve as 1, 0 mm.

It may therefore be provided that, according to an advantageous embodiment of the method according to the invention, the proportion of aggregate is provided by sieving a bulk material. Here, the sieved fines, the so-called sieve bottom with a particle size smaller than 0.125 mm can be used as a cement substituent in the first step. For sieving the bulk material (sand or gravel), for example, a vibrating screen with a hole size of up to 1 mm can be used. It can also be provided that, to provide an aggregate, a plurality of sieve steps with different hole sizes are carried out in order to obtain fractions having different particle sizes. Advantageously, the provision of the aggregate can be carried out by sieving as a preparation step before the first process step or as an intermediate step.

By providing the sieve plate with a particle size of less than 0.125 mm as a cement substituent in the first method step, a particularly environmentally friendly solution is realized, by which in particular cement substituents can be logistically saved.

The invention further comprises a cement-reduced concrete produced by the method according to the invention. According to the invention, the cement-reduced concrete is a mixture of a proportion of binder suspension consisting of proportions of water, mineral, comprising cement and at least one cement substituent, and flow agent, and a proportion of aggregate, wherein in the aggregate, the proportion of particles having a size less than 0.125 mm is less than 10%, preferably less than 5%.

The cement substituent may be selected from a group consisting of limestone meal, dolomite, blastfurnace slag, fly ash, silica fume and fine sand having a particle size smaller than 0.125 mm. Advantageously, I am at the fine sand to the sifted fines from the aggregate. The use of suitable cement substituents has the advantage that the cement content of the concrete according to the invention can be reduced, with at the same time demanded technological properties or processing properties of the concrete can be met.

In principle, it is possible to use additives having different particle sizes, provided it is ensured that the fine fraction in the additive is less than 10%, preferably less than 5%. According to a variant of the concrete according to the invention, the aggregate can be sand and / or gravel and have a grain size of 1 mm or larger.

Furthermore, different flow agents can be used, wherein a flow agent may have a minimum proportion of 2 kg / m ³ .

By changing the proportions of the mineral content, the technological properties of the concrete mix can be influenced. In a preferred variant of the concrete according to the invention it can therefore be provided that water and cement are maintained in a proportion of less than 0.6, wherein a proportion of water and mineral content of less than 0.45 is complied with. Accordingly, the concrete of the invention may have a water cement value of less than 0.6.

Advantageously, the cement content may be less than 300 kg / m ³ , preferably less than 250 kg / m ³ . Furthermore, it can also be provided that cement and cement substituent are used in the same ratio.

The invention will be explained in more detail by way of example with reference to the following recipe examples, wherein in table A two

Formulation examples 1 and 2 are shown, which correspond to the prior art. Table A below shows two recipe examples 1 and 2 for concrete compositions according to conventional mixing technique for the production of 1 m ^{3 of} concrete.

According to the prior art (Table A) is used as an aggregate sand or gravel with grain sizes from 0 to X mm, where X can assume values of 2 to 8.

Table B below shows two recipe examples 3 and 4 for concrete compositions according to the invention for the production of 1

For the inventive production of 1 m ³ cement-reduced concrete according to Formulation Example 3, in a first step, 140 kg of water and a mineral content which has a content of 250 kg cement CEM I 42.5 R and a content of 200 kg limestone flour, with the addition of 3.6 kg of a superplasticizer, such as Superplaticizer, in a suspension mixer at a speed of rotation of the agitating tool of 600 U / min suspended to 1600 rev / min, wherein a binder suspension is provided. In a second step, 1620 kg of sand or gravel is provided as an aggregate, wherein the aggregate in the present example has a particle size of 1 mm to 8 mm and the proportion of particles having a size smaller than 0.125 mm is less than 10%. Subsequently, the additive thus provided and the binder suspension provided in the first step are mixed together in a third step in a conventional mixer until a desired consistency is achieved.

The inventive method of producing 1 m ³ cement-reduced concrete according to Formulation Example 4 is followed as in the preceding example, with the difference that the shares listed in Table B for Formulation Example 4 are used for water, mineral, superplasticizer and additive.

In one embodiment of the method according to the invention, the aggregate having the desired particle size can be produced directly by sieving. According to a further embodiment variant, however, it is also possible to provide for the use of a mixture of admixtures, wherein in the finished mixture the proportion of particles having a size smaller than 0.125 mm is less than 10%, preferably less than 5%. Ideally, sand or gravel is used as an aggregate that does not have any particles with a size of 0.125 mm.

In comparison with Formulation Examples 1 and 2, with the concretes of Formulation Examples 3 and 4 produced by the process according to the invention, similar water cement values can be achieved with simultaneous reduction of the cement and water content. In contrast to conventional concrete production, sand or gravel with a particle size or grain size of 1.0 to X mm (with X = 2, 3, 4, 5, 6, 8) is primarily used as an additive according to the process of the invention, the proportion of Particles with a size smaller than 0.125 mm less than 10%, preferably less than 5% and is. Ideally, an additive used according to the method of the invention has no particles with a size smaller than 0.125 mm. As a result, the aggregate lacks substantial amounts of fines. A subset of these fines is replaced according to the invention by an increased proportion of concrete additives or binders, according to the present examples by limestone. By this procedure, it is possible that almost all flour grain components - these are proportions with particle sizes smaller than 0.125 mm - can be worked up exclusively in the suspension mixer in the first process step.

Due to the rotational speeds of the agitating tool at 600 rpm to 1600 rpm, the surfaces of the mineral fines of the binder are activated by mechanical friction resulting from the suspension process to provide a reactive and stable water-binder suspension as a result. This surface activation of the mineral fine constituents of the binder ensures that the concentrated binder suspension produced in this way can be used for a quality-optimized concrete mixture, but essentially for the bonding of the aggregates sand and gravel.

Table C below compares another recipe example 6 for a concrete composition according to the invention for producing 1 m ^{3 of} concrete by the process according to the invention and a formulation example 5 for a concrete composition according to a conventional preparation process. Table C shows a recipe comparison C 30/37 XC2, F52, GK 22. Table C Formulation example 5 Formulation example 6 (conventional manufacture (dual concrete mixing technique) nik (suspension concrete))

M _ilffiltt ne _r asoane cement 320 kg CEM 1 52.5 R CEM I 42.5 R 260 kg

Cement sub-0 kg 60 kg

stituent

limestone

Proportion of water 192 kg 140 kg

Proportion flow agent 2.8 kg 2.8 kg

Superplaticizer

Share aggregate 989 kg sand 0/4 mm 989 kg sand 0/4 mm (sand and gravel) 203 kg gravel 4/8 mm 203 kg gravel 4/8 mm

593 kg gravel 8/16 mm 593 kg gravel 8/16 mm 207 kg gravel 16/22 mm 207 kg gravel 16/22 mm

Water cement value 0.600 0.538

Quotient of the .600 .437

share ratio

Water / mineral content

Slump 54cm 55cm

Strength development after 6 h = 2.2 N / mm ² after 6 h = 6.4 N / mm ² (dry chamber after 8 h = 9.1 N / mm ² after 8 h = 14.8 N / mm ² mer 44 ° C ) after 16 h = 18.2 N / mm ² after 16 h = 27.4 N / mm ²

Compensation of the compartments for 1, 0 m ³ for 52 kg water = plus 140 kg surcharge

The following Table D shows another recipe compared SCC 40/50 B2 GK 16 mm, wherein Formulation Example 7 _ff according to the conventional M M _ilt ne _r _r ASOA ethod and Formulation Example 8 after dual concrete mixing technique (suspension concrete) is made.

Table D Recipe example 7 Recipe example 8

(conventional manufacture (dual concrete mixing technique) nik (suspension concrete))

Cement 440 kg CEM I 52.5 R 320 kg CEM I 42.5 R ω

Cementub- 80 kg 200 kg

stituent

limestone

Proportion of water 210 kg 167 kg

Proportion flow agent 5 kg 5 kg

Superplaticizer

Share aggregate 865 kg sand 0/4 mm 865 kg sand 0/4 mm (sand and gravel) 293 kg gravel 4/8 mm 293 kg gravel 4/8 mm

559 kg gravel 8/16 mm 559 kg gravel 8/16 mm

Water cement value 0.477 0.521

Quotient from the 0.403 0.321

share ratio

Water / M i n e ra I Substance i i

Slump 68cm 73cm

Strength development after 8 h = 2.35 N / mm ² after 8 h = 3.6 N / mm ² after 20 h = 28.44 N / mm ² after 20 h = 29.3 N / mm ² after 28 d = 78 , 22 N / mm ² after 28 d = 72.1 N / mm ²

Compensation of the compartments for 1, 0 m ³ for 24 kg water = plus 65 kg surcharge

Table E shows an optimization variant for C30 / 37 GK 8 mm

Advantageously, costs can be saved by the cement substitution in the concrete mixture, since rock flour, such as limestone powder as a substituent is much cheaper. A further advantage of the cement saving is in particular that a correspondingly produced concrete has a better CO ₂ balance compared to concretes produced conventionally. At the same time, it is ensured by the production method according to the invention that cement-reduced concretes meet the technological requirements and have improved processing properties.

Claims

claims

A process for the production of cement-reduced concrete in which, in a first step, a portion of water, a mineral content comprising cement and at least one cement substituent, and one level of flow agent are suspended in a suspension mixer to provide a binder suspension and a portion in a second step Aggregate is provided in which the proportion of particles having a size smaller than 0.125 mm less than 10%, preferably less than 5%, and in a third step, the proportion of aggregate is mixed with the proportion of binder suspension.

A method according to claim 1, characterized in that a mineral content is used, in which the particles contained therein have a size smaller than 0.125 mm.

A method according to claim 1 or 2, characterized in that is used as a cement substituent limestone, dolomite, blastfurnace slag, fly ash, silica fume and / or fine sand with a particle size smaller than 0.125 mm.

Method according to one of claims 1 to 3, characterized in that as an aggregate sand and / or gravel with a grain size of 1 mm to 8 mm is used, wherein the proportion of particles having a size smaller than 0.125 mm less than 10%, preferably less than 5%. Method according to one of claims 1 to 4, characterized in that water and cement is used in a proportion ratio of less than 0.6, wherein a proportion ratio of water and mineral content less than 0.45 is maintained.

Method according to one of claims 1 to 5, characterized in that a cement content of less than 300 kg / m ³ , preferably less than 250 kg / m ³ is used.

Method according to one of claims 1 to 6, characterized in that the binder suspension is provided at a stirring speed of a stirring tool of the suspension mixer of more than 600 U / min, preferably in a range of 600 U / min to 1600 U / min.

Method according to one of claims 1 to 7, characterized in that the mixing of the binder suspension and the additive in the third process step is carried out in a conventional concrete mixer.

Method according to one of claims 1 to 8, characterized in that the proportion of aggregate is provided by sieving a bulk material, wherein the sieved fines fraction having a particle size smaller than 0.125 mm is used as Zementsubsti- tuent in the first step.

Cement-reduced concrete produced by a process according to any one of claims 1 to 9, wherein the cement-reduced concrete is a mixture of

- A proportion of binder suspension, consisting of proportions of water, mineral, comprising cement and at least one cement substituent, and flow agent, and a proportion of aggregate, wherein in the aggregate, the proportion of particles smaller than 0.125 mm in size is less than 10%, preferably less than 5%.

11. Cement-reduced concrete according to claim 10, characterized in that the mineral content has a particle size of less than 0.125 mm.

12. Cement-reduced concrete according to claim 10 or 11, characterized in that the cement substituent is selected from a group consisting of limestone, dolomite, granulated blastfurnace, fly ash, silica fume and fine sand with a particle size smaller than 0.125 mm.

13. Cement-reduced concrete according to one of claims 10 to 12, characterized in that water and cement is maintained in a proportion of less than 0.6, wherein a proportion of water and mineral content of less than 0.45 is complied with.

14. Cement-reduced concrete according to one of claims 10 to 13, characterized in that the cement content is less than 300 kg / m ³ , preferably less than 250 kg / m ³ .

15. Cement-reduced concrete according to one of claims 10 to 14, characterized in that cement and cement substituent are used in the same ratio.