CZ36182U1 - Concrete mixture with improved properties of lower quality aggregate - Google Patents

Description

In the registration procedure, the Industrial Property Office does not determine whether the subject of the utility model meets the conditions of eligibility for protection according to § 1 of Act. E. 478/1992 Coll.

CZ 36182 UI

Concrete mix with improved properties from lower quality aggregate

Field of technology

The technical solution concerns a concrete mix with improved properties of recycled aggregate.

Current state of the art

As a standard, natural aggregate is used as a filler for the production of concrete, either quarried aggregate, which is sorted into individual fractions after extraction, or crushed aggregate, which is crushed on crushing lines and sorted into individual fractions after extraction in a quarry.

Concrete is the most widely used building material, but it consumes a large amount of natural resources such as cement and aggregate. However, the resources of natural aggregates are limited and non-renewable, their availability on the market continues to decrease along with a significant increase in prices. This trend is expected to continue even with greater intensity. In order to achieve the sustainability of the construction industry and especially concrete production and to support the circular economy, special emphasis is therefore placed on greater use of secondary raw materials, in this case lower quality aggregates for the production of concrete and other building materials and structures. As such, this lower-quality aggregate does not, by its very nature, meet some of the requirements for concrete production, e.g. absorbency, and its use in concrete is greatly limited or prohibited in technical regulations out of concern that the resulting properties of concrete are not compromised during standard concrete production.

Recycled aggregate is made from building demolition debris resulting from the demolition of building structures, so it consists of concrete, bricks, roof tiles, ceramics and is produced by crushing and sorting into individual fractions. Artificial aggregate is created as a separate product by a specific production process and in most cases does not meet the requirements for dense aggregate for concrete. In some cases, it can be used as a lightweight aggregate for concrete according to specific standards. A lower quality natural aggregate is one that does not meet the valid standards for use in concrete. However, with all these types of aggregates, some of their properties can be improved to the extent that when they are used, the final product - concrete has the required useful properties.

To improve the properties of recycled aggregate, fine-grained fillers, e.g. silica fume, also called "microsilica", are used until now, which fill the pore structure of the recycled aggregate and thus increase the overall quality of the concrete produced. Necessary fillers such as silica fume are currently produced as secondary raw materials in the production of ferroalloys for steel production and are further distributed to individual concrete production plants. Due to the current direction of ecology, however, in the long term, more and more emphasis is placed on the suppression of steel production with the aim of reducing CO2 emissions and other undesirable greenhouse gases. For these reasons, there is currently a shortage of these fine-grained fillers on the market, as they are also used for the production of ordinary concrete, and the material is becoming a scarce commodity rather than a secondary raw material, with a significant impact on its price and problems with the flow of supplies. With the reduction of production, the transport distances also increase, and thus the transport burden and the carbon footprint associated with these products also increase.

To modify the properties of fresh concrete, or the properties of hardened concrete, liquid additives are used as standard, for example, plasticizing additives to improve workability and reduce the amount of mixing water, aerating additives to increase the effective pores in concrete to improve frost resistance, retarding and accelerating additives to change the workability time and hydration rates, and other special additives, e.g. concrete shrinkage limiting.

Currently, however, there are no known cases of the use of liquid additives to improve the properties of aggregates in concrete, especially the reduction of porosity and the associated reduction of absorbency and possible

-1 CZ 36182 UI increasing the strength of the aggregate in order to achieve up to 100% replacement of high-quality natural aggregate with lower-quality aggregate.

The essence of the technical solution

The mentioned shortcomings consisting in some unsatisfactory properties of lower-quality aggregates, which must be met for the production of standard concrete, are largely eliminated by a concrete mixture with improved properties of lower-quality aggregates according to this technical solution, the essence of which consists mainly in the fact that it contains:

- lower quality aggregate 1000 to 1900 kg /m ³

- liquid additive improving the properties of recycled aggregate 1 to 10 kg/m ³

- cement 200 to 400 kg/m ³

- water 150 to 250 kg/m ³

- plasticizing or superplasticizing additive 0 to 10 kg/m ³

It appears advantageous when the lower quality aggregate is selected from the group consisting of lower quality natural aggregate, recycled aggregate and artificial aggregate.

For improving the properties of lower-quality aggregate, it seems advantageous if the liquid improving the properties of lower-quality aggregate is an acrylate dispersion based on polyvinyl acetate or an acrylate dispersion based on polyvinyl alcohol. Thanks to this, it is possible to replace up to 100% of high-quality natural aggregate with lower-quality aggregate. After cross-linking, the acrylate dispersion forms solid hydrocarbon chains that fill the pores in lower-quality aggregate and thus increase its strength. They also reduce the absorbency of lower-quality aggregates and thus also the resulting humidity, which can fluctuate greatly with lower-quality aggregates, thereby significantly changing the water content of lower-quality aggregates. Fluctuations in the humidity of lower-quality aggregates negatively affect the production of fresh concrete, as it has a fundamental effect on the resulting consistency and total water content in the concrete, and also affects the resulting strength of the hardened concrete. By limiting the absorbency of lower-quality aggregates thanks to the liquid additive, these negative properties are significantly reduced.

Furthermore, it seems advantageous if the concrete mixture also contains other admixtures and additives.

Achieving the desired effect is achieved by the method of producing a concrete mixture, in which, after adding low-quality aggregate to the mixer, a liquid additive is added to improve the properties of the low-quality aggregate, after which the mixture is mixed for 20 to 25 seconds, then cement, water and plasticizing or superplasticizing agents are added ingredient and mixture stirred.

Examples of implementing a technical solution

Inferior quality aggregates here are understood as recycled aggregates, artificial aggregates and lower quality natural aggregates, which due to some of their properties cannot be used in concrete according to valid European and national technical standards or their use is significantly limited in volume. A common physical feature is especially the increased absorbency of these types of aggregate. In order to verify the functionality of the essence of the technical solution, recycled aggregate was selected, in which powder admixtures are already used to improve properties, which was used as a reference sample. For other types of lower quality aggregate, the results will be similar.

The verification of the principle of the technical solution and its functionality was first verified by laboratory tests. For verification, recycled aggregate from a mixed recyclate was used, which is composed of best-in-class raw materials (concrete, brick, bags, ceramics, etc.) and, in principle, exhibits the lowest mechanical properties and the highest absorbency. Therefore, the variant of the "worst" input was chosen, which, when functionality is proven, implies functionality even when materials with better properties are used.

-2 CZ 36182 UI

A concrete composition of 100% recycled aggregate from mixed recycled was therefore proposed, and immediately after its addition, a liquid additive, an acrylate dispersion based on polyvinyl alcohol or polyvinyl acetate, was added to the mixer, and the mixture was mixed together. Then followed the standard dosing of the other components of the concrete mix - cement, plasticizing or superplasticizing additive and water. The controlling component is mainly cement, as its dose affects the final strength and also the amount of water, which has a fundamental influence on the consistency of fresh concrete and the final strength. The dose of the plasticizing additive is also related to this, which affects the processing time of the resulting mixture.

After the laboratory verification of the recipes, several operational mixings took place directly on concrete slabs together with the production of bodies to prove the properties of the final product.

In the operational tests of example 1, recycled brick aggregate was used and a concrete area was made under the aggregate dump for the possibility of long-term monitoring in the operating conditions of moisture, frost, driving of machinery, etc. In the operational tests of example 2, recycled mixed aggregate was used and prefabricated wall elements were made for verification of technological properties such as transportation, processability, vibration, etc. For comparison, in both cases, the production of concrete from the same recycled aggregate using a fine-grained filler, in this case silica fume, was also performed as a reference. Fresh concrete tests were always performed after mixing, and test specimens were created for hardened concrete tests.

Example 1

A typical formula of a concrete mixture with a liquid admixture using the realization of a technical solution for an example of a varnish and a reference formula of a concrete mixture with a powdery fine admixture are shown in Table 1.

Table 1 - Comparison of concrete mix formulas of example 1 for concrete class C 25/30 XC1 S4 with liquid admixture and with powder admixture

Component dosage in kg/m ³ with liquid additive according to the technical solution dosing in kg/m ³ with powder admixture Recycled brick aggregate, fraction 0-22 1530 1500 Liquid additive (acrylate dispersion) 5 Powder additive (silica fume) 25 Cement - CEM I 42.5 250 250 Another admixture - finely ground limestone 50 50 Water 180 180 Plasticizing additive 4 4

A comparison of the test results of the fresh and hardened concrete of Example 1 is made in Table 2.

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Table 2 - Comparison of the basic properties of fresh and hardened concrete of class C 25/30 XC1 S4 of example 1 with a liquid admixture according to the technical solution and concrete with a powder fine-grained admixture

Quantity (Unit) 5 with a liquid additive according to the technical solution 5 powder fine-grained admixture Consistency after mixing (mm) 220 230 Consistency after 60 min (mm) 200 180 Volumetric weight after 28 days (kg/m3) 2020 2070 Compressive strength after 28 breaths (MPa) 32.3 37.3 Compressive strength after 90 breaths (MPa) 36.8 40.0 Borehole compressive strength after 1 year of operation (MPa) 33.1 32.4 Pressure water seepage (mm) 12 16 Coefficient of frost resistance in tensile bending after 100 cycles 1.16 0.82

Example 2

A typical formula of a concrete mix with a liquid admixture using the implementation of the technical solution for example 2 and a reference formula of a concrete mix with a powder fine-grained admixture are shown in Table 3.

Table 3 - Comparison of recipes of concrete mixtures var. 1 for concrete class C 25/30 XC1 S4 with liquid admixture and with powder admixture

Component dosage in kg/m ³ with liquid additive according to the technical solution dosing in kg/m ³ with powder admixture Recycled brick aggregate, fraction 0-22 1530 1530 Liquid additive (acrylate dispersion) 3 Powder additive (silica fume) 30 Cement - CEM I 42.5 320 350 Another ingredient - fly ash 85 Water 195 200 Plasticizing additive 5 6.5

In addition to the above-mentioned examples 1 and 2, a number of other alternative recipes were carried out for concretes of various classes from C 12/15 to C 30/37, also with satisfactory results. On the basis of these results and the experience of the originators, the optimal dosage range of the individual components of the concrete recipes is then set, during which the desired effect defined in the essence of the technical solution will be achieved. They are listed in Table 4. In addition to the listed components, it is possible to use other admixtures or additives that modify the desired properties of fresh or hardened concrete.

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Table 4 - Optimum dosing range of individual components of concrete recipes

Component dosage in kg/m ³ with liquid additive according to the technical solution Recycled aggregate 1000 to 1900 Liquid additive (acrylate dispersion) 1 to 10 Cement 200 to 400 Water 150 to 250 Plasticizing additive 0 to 10

For all the listed recipes in tables 1 to 4, other admixtures and additives can also be used to adjust some of the final properties of concrete mixtures. As admixtures, type I and II admixtures according to ČSN ΕΝ 206+A2 can be used, and as additives all types of concrete additives, such as e.g. plasticizing, superplasticizing, aerating, retarding, accelerating, crystallizing, anti-shrinking, expansive, sealing, or other intended for specific purposes and constructions.

Comparison of test results of fresh and hardened concrete var. 2 is done in Table 5.

Table 5 - Comparison of basic properties of fresh and hardened concrete C 25/30 XC1 S4 of example 2 with a liquid admixture according to the technical solution and concrete with a powder fine-grained admixture

Quantity (Unit) 5 with a liquid additive according to the technical solution 5 powder fine-grained admixture Consistency (mm) 220 220 Density (kg/m3) 2080 2080 Compressive strength after 28 breaths (MPa) 35.2 35.3 Seepage (mm) 17 16 Modulus of elasticity (GPa) 16.6 14.8

From the comparison of the results of the basic properties, it is clear that the concrete produced by the new procedure according to the principle of the technical solution achieves similar properties as the reference concrete with powder fine-grained admixture. This is proof of the practicality of the technical solution and the potential for practical use.

The method of producing the concrete mixture is carried out in such a way that after adding recycled aggregate to the mixer, a liquid additive that improves the properties of the recycled aggregate is added, after which the mixture is mixed for 20 to 25 seconds. The liquid additive that improves the properties of the recycled aggregate is an acrylate dispersion based on polyvinyl acetate or an acrylate dispersion based on polyvinyl alcohol, which after cross-linking form solid hydrocarbon chains that fill the pores in the recycled aggregate and thus increase its strength. They also reduce the absorbency of the recycled aggregate and thus the resulting humidity, which fluctuates greatly with the recycled aggregate, which significantly changes the water content in the aggregate. Fluctuations in the moisture content of recycled aggregate negatively affect the production of fresh concrete, as it has a major impact on the resulting consistency and total water content in the concrete, and also affects the resulting strength of the hardened concrete. By limiting the absorbency of the aggregate thanks to the liquid additive, these negative properties are significantly reduced.

In order to achieve the desired effect, the liquid additives are dosed at the beginning of the concrete mixing directly into the batch of recycled aggregate and mixed for a sufficient time. In this way, the dispersion penetrates into the pores in the aggregate. The greater the porosity of the aggregate, i.e. the absorbency, the more the dispersion penetrates inside and the greater its effect. The porosity of the aggregate is related to its strength. The more porous the aggregate, the lower its strength, but the greater the amount of dispersion penetrates inside the grains

-5 CZ 36182 UI of aggregates and thus greater relative strengthening occurs.

Subsequently, cement, water and a plasticizing or superplasticizing additive are dosed and the mixture mixed.

Thanks to the improvement of the properties of lower-quality aggregates, this technical solution makes it possible to fully replace high-quality natural aggregates with lower-quality ones, thereby saving mineral resources for applications where they are irreplaceable. It therefore contributes to the improvement of the environment, the use of secondary raw materials and the support of the circular economy. The liquid additives used are purpose-built for other purposes as well (therefore it is not a special product), but their quantity on the market is determined by demand, not by the production of another medium, and their availability on the market is therefore not in any way threatened. A significant operational advantage of these liquid additives compared to bulk additives is transport, storage and dosing at the concrete batch. Loose admixtures are transported in special large-volume tanks and stored on concrete slabs in silos specially set aside for that purpose, which often requires additional investment. In contrast, liquid admixtures are transported by standard trucks and stored in standard 1000 1 containers in the same way as ordinary liquid admixtures, so no additional investment is required and the production of ordinary concrete is not limited by this.

Prefabricated wall elements were made from the innovative concrete recipe according to the technical solution, which are intended as elements of gravity retaining walls, dividing walls at landfills, etc. Furthermore, to verify the technological properties of transport concrete, a concrete area under the aggregate dump driven by a loader was realized, while this area does not show approx. 1.5 years of operation, no malfunctions.

As mentioned above, the essence of the technical solution can also be advantageously used to improve the properties of artificial aggregate or lower-quality natural aggregate with high absorbency, which otherwise would not meet the conditions for use in concrete. In general, concrete from recycled, artificial or lower quality natural aggregates conserves non-renewable natural aggregate resources for applications where it is irreplaceable. At the same time, it uses secondary or less valuable raw materials in the form of, for example, recycled aggregates made from construction and demolition debris, which otherwise end up in landfills or are eventually used for backfills and backfills, i.e. for constructions with lower added value.

Lower-quality aggregates inherently have worse mechanical-physical properties than natural aggregates, and it is therefore necessary to improve their properties so that the final product achieves similar useful properties. The use of liquid admixtures to improve the properties of lower-quality aggregates instead of loose, fine-grained admixtures has significant operational advantages, namely:

- in simpler transport - transport in 1000 1 returnable containers on a standard truck instead of special tank cars. In addition, the dose of the liquid additive is 8x to 10x lower compared to the dose of the powder additive. The reverse loading of vehicles can be used to advantage, which is very complicated in the case of tankers. This results in significant cost savings, a reduction in the carbon footprint and a general reduction in the adverse effects of transport on the environment and the population;

- in simpler landfilling - it is landfilled directly in 1000 1 containers instead of silos on loose admixture. The silo is thus not blocked and can be used for different types of cement, or other loose admixtures (slag, fly ash, limestone, ...). In many cases, the investment in new forces is thus saved;

- in simpler dosing - it is dosed through a standard liquid ingredient dispenser instead of dosing with an auger from a silo, which is not as accurate, is more expensive, and requires more maintenance.

Industrial applicability

For example, concrete produced according to a technical solution with a liquid additive and using recycled

-6 CZ 36182 UI aggregates can be used for standard concrete and reinforced concrete structures (foundation and foundation concrete, reinforced concrete walls and partitions, ...). As with concrete with powder fine admixture, it is not designed for structures that are exposed to high stress and external environmental influences. Even so, they can represent approx. 10 to 20% of all concrete production, which 5 is the maximum volume when using most construction rubble.

Concrete produced according to the technical solution is an equivalent substitute for structural and non-structural concrete in a number of residential and industrial building applications. The advantage can be a lower volumetric weight, and therefore a lower coefficient of thermal conductivity when using recycled brick, which can lead to savings on insulation systems, possibly savings on heating energy and also savings on transport costs.

Concrete made from artificial and lower-quality natural aggregates has a similar industrial use.

Claims (4)

PROTECTION CLAIMS 1. Concrete mixture with improved properties of lower quality aggregate, characterized by the fact that it contains: 5 - lower quality aggregate 1000 to 1900 kg /m ³ - liquid additive improving the properties of recycled aggregate 1 to 10 kg/m ³ - cement 200 to 400 kg/m ³ - water 150 to 250 kg/m ³ - plasticizing or superplasticizing additive 0 to 10 kg/m ³ . ιο 2. A concrete mixture with improved properties of inferior aggregate according to claim 1, characterized in that the inferior aggregate is selected from the group consisting of inferior natural aggregate, recycled aggregate and artificial aggregate. 3. Concrete mixture with improved properties of inferior aggregate according to claim 1, characterized in that the liquid additive improving the properties of inferior aggregate is an acrylate dispersion based on polyvinyl acetate. 4. Concrete mixture with improved properties of inferior aggregate according to claim 1, characterized in that the liquid additive improving the properties of inferior aggregate is an acrylate dispersion based on polyvinyl alcohol.