SK9659Y1 - Active admixture to concrete with low carbon content made from secondary raw material and the concrete made with the secondary raw material - Google Patents

Abstract

There is disclosed a low carbon active admixture to concrete from secondary raw material. The admixture forms fine-grained powder made of wastes from group of: wastes from bricks demolition, wastes from concrete demolition, cinder from power-plant or heat station plant, or wastes from dumping places having pozzolana or latent hydraulic character, individually or in mixture from the mentioned sources. The admixtures from the mentioned sources have defined granulometry in the range from 1 to 150 micrometres with the specific surface by Blaine in the range from 250 to 700 kg/m2 and with efficiency index according EN 450-1 in the range from 60 to 95 %.

Description

The field of technology

The technical solution concerns the use of low-carbon active admixtures in concrete obtained by mechanical activation of secondary raw materials that contain pozzolanic or latent hydraulic substances as partial substitutes for ordinary cements for the production of concrete.

Current state of the art

Currently, in the production of concrete, power plant high-temperature fly ash, finely ground blast furnace granulated slag, silica fumes, metakaolin or micro-ground limestone are used as active admixtures. These are used to replace a part of common cements of class CEM I, CEM II or CEM III or to modify some properties of concrete, e.g. achieving very high strengths, resistance to the action of pressurized water or chemically aggressive environments. The function of admixtures in concrete is both active - together with the cement it creates a binding matrix, and passive - it fills the pores and thereby increases the density of the cement stone. The use of active admixtures also contributes to the reduction of the carbon footprint, which for pure Portland cement is very high between 0.65 - 0.75 tons of CO2 per 1 ton of Portland cement.

Due to the gradual decline of thermal power plants on fossil fuels, the reduction in the production of pig iron or the production of sintered carbides in the Slovak Republic causes a total shortage on the market, which leads to an increase in the prices of the mentioned admixtures.

The goal of the technical solution is to partially replace cements of the CEM I, CEM II, CEM III type with industrially produced active admixtures from secondary raw materials, which partially have a pozzolanic or latent hydraulic character in the production of concrete.

The essence of the technical solution

The mentioned shortcomings are eliminated by a low-carbon active admixture for concrete from secondary raw materials, the essence of which is that it has the form of a fine-grained powder from waste from the group of brick demolition waste, concrete demolition waste, slag generated in power plant or heating plant operations, or previously stored in storage raw materials having a pozzolanic or latently hydraulic character, individually or in a mixture, while admixtures from the mentioned crushed and then ground raw materials have a defined range of grain granulometry in the range from 1 to 150 micrometers with a specific surface area according to Blain in the range of 250 to 70 and an efficiency index according to STN EN 450-1 in the range from 60 to 95%.

Another subject of the technical solution is concrete, which contains the mentioned low-carbon active admixture, in the range from 10% to 90% by weight of the used mass dose of cement (in kg/m ³ ) for each partial recipe of concrete, while the range of the dose of the active admixture is dependent especially from:

a) strength class of the given concrete,

b) type of cement used (CEM I, II, III or V),

c) the activity and quality of the input secondary raw material containing pozzolanic or latent hydraulic substances, from which the active admixture according to claim 1 is created.

Ultimately, a different dose of CEM I, II, III or V cement and a different dose of active admixtures will be used for each partial concrete recipe. Doses of active admixtures in a specific concrete recipe can also change due to changes in the quality of the input secondary raw material.

Implementation examples

Brick or concrete crumb from the recycling of construction waste based on bricks or concrete, slag from coal combustion in energy or heating boilers, or previously landfilled materials of a pozzolanic or latently hydraulic nature, mechanically adjusted to a particle size of 1 to 150 micrometers, is used as an input raw material.

These active admixtures based on fine brick, concrete, cinder or other dust must have a maximum grain size of 150 micrometers or less. The surface area of Blaine particles is 250 to 700 kg/m ² with a grain size of 1 to 150 micrometers. The efficiency index determined by the procedure defined in the EN 450-1 standard must be in the range of 60 to 95%, while the loss by annealing must not be greater than 10% of the weight.

The chemical composition must ensure pozzolanic or latent hydraulic properties.

The mentioned products can be obtained by mechanical grinding of brick or concrete crumb, cinders produced during the burning of thermal coal in power plants or heating plants, or previously stored raw materials having a pozzolanic or latently hydraulic character in landfills.

The products obtained in this way will be able to fully replace the currently used type II active admixtures in concrete. The range of their use for concrete production will be optimized according to their hydraulic activity and activity index so that the requirements of the standards for concrete production according to STN EN 206+A2 and STN P 73 2404 and their subsequent valid versions are met.

The essence of the technical solution is the use of fine-grained admixtures resulting from the mechanical grinding of secondary raw materials, such as brick and concrete rubble, waste slag resulting from the combustion of coal in power plants or heating plants, or raw materials with a pozzolanic or latently hydraulic character that were previously deposited in landfills as partial replacements for CEM cements I, II, III and V for the formation of the binder component forming the matrix of cement composites. Mixtures created in this way can contain 10 to 90% of industrially produced admixtures based on ground bricks or concrete rubble, ground waste slag from coal combustion in power plants or heating plants with a grain size of 5 to 150 micrometers and 10 to 90% of CEM I, II, III, IN.

In the following examples, the complete composition of the concrete formula is given for completeness, but the dosage of the cement and the ratio of the active admixture to it are key to the protection requirements. The stated composition of the recipes is intended to illustrate the applicability in practice, it is not a dogmatic specification.

Reference concrete:

The following reference formula of concrete C25/30, XC2, S3, Dmax 16 mm in kg/m ³ was mixed per 1 m ³ :

CEM I 42.5 R 295 kg Aggregate fraction 0/4 mm 905 kg Aggregate fraction 8/16 mm 955 kg Water 178 kg Superplasticizer 2.4 kg

Example 1

The following formula of concrete C25/30, XC2, S3, Dmax 16 mm in kg/m ³ was mixed for 1 m ³ :

CEM I 42.5 R Admixture from brick demolition waste Aggregate fraction 0/4 mm Aggregate fraction 8/16 mm Water Superplasticizer 235 kg 75 kg (weight ratio 32% to CEM I) 893 kg 942 kg 180 kg 2.4 kg

Example 2

The following formula of concrete C25/30, XC2, S3, Dmax16 mm in kg/m ³ was mixed for 1 m ³ :

CEM I 42.5 R Admixture from concrete demolition waste Aggregate fraction 0/4 mm Aggregate fraction 8/16 mm Superplasticizer 245 kg 70 kg (weight ratio 29% to CEM I) 883 kg 181 kg 2.4 kg

Example 3

The following formula of concrete C25/30, XC2, S3, Dmax 16 mm in kg/m ³ was mixed for 1 m ³ :

CEM I 42.5 R Admixture from concrete demolition waste Admixture from brick demolition waste Aggregate fraction 0/4 mm Aggregate fraction 8/16 mm Water Superplasticizer 240 kg 45 kg (weight ratio 19% to CEM I) 35 kg (weight ratio 15% to CEM I) 879 kg 927 kg 183 kg 2.4 kg

Example 4

The following formula of concrete C25/30, XC2, S3, Dmax16 mm in kg/m ³ was mixed for 1 m ³ :

CEM I 42.5 R An admixture of slag from the power plant Aggregate fraction 0/4 mm Aggregate fraction 8/16 mm Water Superplasticizer 225 kg 80 kg (weight ratio 36% to CEM I) 895 kg 944 kg 176 kg 2.4 kg

Example 5

The following formula of concrete C25/30, XC2, S3, Dmax16 mm in kg/m ³ was mixed for 1 m ³ :

CEM I 42.5 R An admixture of slag from the power plant Admixture from brick demolition waste Aggregate fraction 0/4 mm Aggregate fraction 8/16 mm Water Superplasticizer 225 kg 40 kg (weight ratio 18% to CEM I) 40 kg (weight ratio 18% to CEM I) 890 kg 944 kg 179 kg 2.4 kg

Example 6

The following formula of concrete C25/30, XC2, S3, Dmax16 mm in kg/m ³ was mixed for 1 m ³ :

CEM ll/A-S 42.5 R An admixture of slag from the power plant Admixture from brick demolition waste Aggregate fraction 0/4 mm Aggregate fraction 8/16 mm Water Superplasticizer 230 kg 40 kg (weight ratio 17% to CEM II) 40 kg (weight ratio 17% to CEM II) 895 kg 944 kg 179 kg 2.4 kg

Example 7

The following formula of concrete C25/30, XC2, S3, Dmax16 mm in kg/m ³ was mixed for 1 m ³ :

CEM ll/A-S 42.5 R An admixture of slag from the power plant Aggregate fraction 0/4 mm Aggregate fraction 8/16 mm Water Superplasticizer 228 kg 80 kg (weight ratio 35%) to CEM II) 898 kg 944 kg 176 kg 2.4 kg

The solutions in examples 1 to 7 always met the requirements of the original reference formula (given before the examples), in terms of fresh properties, i.e. j. consistency, as well as in terms of hardened properties, i.e. j. compressive strength values for strength class C25/30.

Active admixtures, as described, will be transported to the concrete plants in dry powder form in cement tankers or in large bags. In this case, they are added to concrete in mixtures with CEM I, II, III or V cements in doses verified in advance during proof tests. Doses of active admixtures vary according to the required consistency, strength class of concrete, degree of influence of the environment in which the concrete will be used, type of cement used, granulometry and efficiency index of individual types of these active admixtures.

In general, the mixing ratios of defined admixtures with cements range from 10 to 90% of the weight of the type of cement used.

In particular, this will enable:

a) reduction of cement doses,

b) increasing the strength of concrete,

c) improving the durability of concrete,

d) improving the pumpability and compactibility of concrete,

e) modification of the rheological properties of fresh concrete,

f) a combination of all the mentioned benefits,

g) economic savings a

h) reducing the carbon footprint.

Industrial applicability

The technical solution is intended for the use of new types of industrially produced active admixtures from secondary raw materials intended for the production of concrete in partial replacement of various types of cement. These admixtures will fulfill both an active function (partial replacement of all commonly used cements, improvement of the physical and mechanical properties of concrete - higher strength, resistance to chemically aggressive environments, the action of pressurized water, etc.) thanks to their fineness, the pore structure will be thickened, which will again contribute to the improvement of the mechanical properties and durability of concrete and, in the fresh state, to the improvement of workability, pumpability and self-compaction of concrete. The scope of their use is for all types of concrete of strength classes and degrees of environmental impact listed according to STN EN 206+A2 and STN P 73 2404 in the valid versions and for all used consistencies of fresh concrete. Thanks to low material costs, a lower carbon footprint and a lower price, concretes modified in this way find wide use in the field of ready-mixed concrete, as well as in the production of concrete prefabs, concrete products or in dry silicate mixtures.

The technical solution will make it possible to efficiently process waste raw materials that have not yet been used for further refining, and to create new materials with high added value and significant economic, ecological and raw material savings.

The use of admixtures according to the technical solution will make it possible to reduce doses of all types of cement and/or increase the strength of concrete, and/or improve the durability of concrete, and/or improve the pumpability and compactibility of concrete, or a combination of all the above benefits.

Claims (1)

1. Low-carbon active concrete admixture from secondary raw materials, characterized by the fact that it is in the form of a fine-grained powder from waste from the group of brick demolition waste, concrete demolition waste 5, slag resulting from power plant or heating plant operations or raw materials previously stored in landfills containing pozzolanic or latent hydraulic character, individually or in a mixture from the mentioned sources, while the admixtures from the mentioned crushed raw materials have a defined granulometry in the range from 1 to 150 micrometers with a specific surface according to Blain in the range from 250 to 700 kg/m ² and an efficiency index according to EN 450-1 in the range from 60 to 95%. 10 2. Concrete, characterized by the fact that it contains a low-carbon active admixture according to claim 1, in the range from 10% to 90% by weight of the used weight dose of cement for each partial concrete recipe.