WO2015018952A1

WO2015018952A1 - Method for producing cinder concrete

Info

Publication number: WO2015018952A1
Application number: PCT/ES2014/000128
Authority: WO
Inventors: Miguel Angel PARRON VERA; Maria Dolores RUBIO CINTAS; Francisco CONTRERAS DE VILLAR
Original assignee: Universidad De Cádiz
Priority date: 2013-08-03
Filing date: 2014-07-24
Publication date: 2015-02-12
Also published as: ES2537256B2; ES2537256A1

Abstract

The invention relates to a method for producing cinder concrete, for the valorisation of industrial waste, the slag in this case originating in the electric arc furnace steel industry, by means of the encapsulation thereof in a ceramic matrix of a composite material such as concrete, using it as a hydraulic binder. The method consists in substituting part of the cement, which is applied as a binder, with stainless steel slag, given the cementing characteristics thereof, in a quantity of up to a total of 25% of the cement. Said slags are highly abrasive, which provides the resulting concrete with a high resistance to wear. This characteristic means that the concrete obtained by means of said method is optimum for producing structures such as accropodes, tetrapods and/or caissons for marine filling, arranged as ripraps for shelter from the sea.

Description

PROCEDURE FOR THE MANUFACTURE OF ESCORIA CONCRETE.

SECTOR OF THE TECHNIQUE

Application of an industrial waste, in this case the slag originated in the electric arc furnace steel industry, encapsulating it in a ceramic matrix of a composite material such as concrete, using it as a hydraulic binder.

Regarding the industrial sector, its application in the construction of structural containment and control systems is remarkable, especially in the coastal ecosystem due to its rapid and intense exchange of matter and energy.

Its main application lies in the manufacture of acropods, tetrapods and / or seafill drawers arranged as breakwaters in shelter from the sea.

Other possible applications are in the containment of the land in bridges and walkways, being subjected to loads coming from the structure and to pressures derived from the embankment. Likewise, it is possible to use it in stirrups or buttresses as a link between the board and the track, as well as slender foundation elements that allow the control and transfer of loads to a resistant stage of the ground. Finally, it is worth noting its application as piles or building its cavity before concreting, or as micropiles.

STATE OF THE TECHNIQUE

The use of waste products from the steel industry as components of the concrete formulation is widely documented in the state of the art. Especially as regards the application of slags as substitutes for aggregates. However, no references have been found regarding the application of such slags as cement substitutes. In other words, its use as a binder component of concrete.

Different references oriented to the use of slags and other wastes have been found in the patent literature as contributions to the mixture according to the apparent volume, without conditioning at any time their contribution coefficients to obtain the actual volume of the mixture. Among the most outstanding references we can review the following:

The ES2204046 patent presents techniques for the processing of blast furnace slag, different in composition from that of an electric arc furnace, in its solidification and subsequent destination as an aggregate.

ES2269295 refers to the Procedure for processing slag, this time of stainless steel, and identical qualities and use as the previous invention.

Regarding the use of a cement binder in the inertization or immobilization of waste, in the ES2180085 patent the final waste is encapsulated, that is to say materials to which it is not possible to apply any valuation process, in which it includes urban solid waste , non-ferrous slag from blast furnaces, and other waste.

On the other hand, there are different procedures where stainless steel slags are processed. Thus, in the ES2262484 patent, a process is described in which a slag crushing step is carried out, in order to make the properties of the particles more homogeneous. In this way a higher quality material is achieved to be applied, for example in concrete or similar materials. Optionally, said step can be performed once the larger slag fragments have been removed by sieving. The slags thus crushed are embedded in a hardenable matrix in order to produce asphalt containing the slag particles in an agglutinated state. The ES2353071 patent describes another procedure similar to the previous ones introducing the asphalt as a matrix in addition to the concrete and hydraulic mortar.

DESCRIPTION OF THE INVENTION

One of the concerns that steel companies have is the elimination of their slags, waste generated in the manufacture of steel, especially stainless steel.

This causes an environmental problem as a result of the accumulation of the waste generated, as well as the economic cost of its disposal through landfill.

In certain countries, this type of waste, once inertized and given its low harmfulness, is poured directly into the sea. However, if the encapsulation of said waste is carried out by concrete, any possible component that was harmful, however minimal its presence, will remain neutralized and its exit to the outside will be prevented.

The proposed invention consists of a process for the manufacture of concrete by adding stainless steel slags from an electric arc furnace, or replacing part of the cement with these slags, to obtain a concrete formulation specially indicated for construction containment and control structures, optimally sustainable and energy cheaper.

Through the use of slag to concrete, the recovery of this waste is achieved, which, being basic and abrasive, will cause minor problems when used in the manufacture of marine jets, as a result of the beating of the waves. Likewise, the appearance of diseases that can be generated in the concrete is eliminated, since said material acquires a very high basicity. The addition of slags, in relation to the cement used, is estimated at a maximum of 15%, according to the dosage necessary for the manufacture of a certain structural block. In the case of substitution, the optimum proportion is up to 25% cement that is replaced by slag. The product obtained by the present invention, consists of a concrete with optimal characteristics for the construction of acropods, tetrapods and / or drawers for marine fill used as breakwaters, its use in stirrups or buttresses, or as piles or micropiles.

EMBODIMENT OF THE INVENTION

The process for manufacturing concrete slag stainless steel electric arc furnace object of the present invention can have two modalities. In the first case the slag is used as an additive, being able to control the size of the diameter of the slags. In the second modality the slags are used as a substitute for a fraction of the cement in the manufacture of concrete, without any type of refining as far as the diameter of these slags is necessary.

1. Procedure for the preparation of concrete with slag addition.

The invention in its first form uses cement as a binder and up to 15% of the amount of cement used in the manufacture of concrete is added, according to the dosage necessary for the construction of a certain structure. These slags must be previously crushed, until a particle size range of less than 5mm is obtained to form a stabilization layer for inertization and obtaining the same granular base. In the same way it is possible to use a thicker fraction of the crushed slags in combination with different types of aggregates, crushed, crushed, rounded etc. The results obtained for a conventional concrete with a 28-day break consisted of average values of 55 MPa of mechanical compressive strength according to UNE-EN 12390-3.

The concrete manufacturing process with slag addition

a) Calculate the amount of material needed for kneading, based on the size of the kneader.

b) Preparation of a table with the necessary additions of cement, sand, gravel, intermediate aggregate and water. The mixture used will have a 1: 5 ratio between cement and aggregate, a proportion that will remain fixed in the study of the first test with proportions of the cement curve without conventional additives to have it as a reference.

c) Addition of slag as an additive of the final product, in a maximum proportion of 25% of the amount of cement used in the manufacture of concrete.

d) Kneading with the required proportions.

e) Verification of the docility of the concrete, its cohesion, consistency, compactness and homogeneity.

2. Procedure for the production of concrete by replacing cement with slag.

In the second modality, a part of the cement, which is applied as a binder, is directly replaced by stainless steel slag given its binding characteristics. In addition, the slags are very abrasive, which makes the resulting concrete very resistant to wear, which makes it optimal for the manufacture of structures mentioned above. In other words, these slags will be used as a substitute in an amount of up to 25% of the cement.

In this way the slags are encapsulated in the matrix that constitutes the cement, which makes this material especially attractive from the environmental point of view. This makes in leachate tests conducted with This type of material is not visible chromium, present in the slags, as a result of this encapsulation, which prevents the release of heavy metals into the environment.

The average values obtained for this case were 44.23 MPa. Although the resistance decreases, the recovery of a residual product, such as slag, is achieved by including it in a processed product such as concrete.

In this example, no refining is necessary in relation to the size of the slag diameter, but a part of the cement that is applied as a binder by stainless steel slag is directly replaced. That is, these slags are used as a substitute in an amount of up to 25% total cement.

The procedure for obtaining this type of concrete begins with the determination of the mortar content that provides the mixture with adequate docility (the lack of mortar in the mixture leads to porosity and failures in the concrete). To determine the ideal mortar content, the amount of coarse aggregate is fixed and the amount of mortar is increased until the concrete has adequate consistency and cohesion, which is verified with practical observations through a test and test process. The steps to follow are:

a) Calculate the amount of material needed for kneading, based on the amount of material to be produced.

b) Preparation of a table with the necessary additions of cement, sand, gravel, intermediate aggregate and water. The mixture used will have a 1: 5 ratio between cement and aggregate, a proportion that will remain fixed in the study of the first test, in which we will have a conventional concrete c) Replacement of up to 25% of the cement used, by slag furnace electric arc, keeping constant the existing proportion with respect to the aggregates used.

d) Kneading with the required proportions. e) Verification of the docility of the concrete, its cohesion, consistency, compactness and homogeneity. Of the new concrete compared to the first trial.

The different tests that have been carried out to characterize the resulting material are described below:

Determination of the Water / Cement A / C ratio for the consistency chosen

Using the same mixture for which the ideal mortar content has been defined, consistency is checked with the Abrams cone. In the case that it is not stipulated, the necessary adjustment is made and the appropriate A / C ratio is obtained.

Description of the specimens

Two different types of test specimens were used to perform the mechanical tests.

• For the substitutions of cement by slag, it is up to 25% of the cement, while for the comparison with conventional concrete according to regulations and a / c ratio, the geometry of the specimens used, according to UNE-EN 12390-1 , were cylindrical, diameter d and height 2d which in our case, correspond to 45 mm in diameter and 90 mm in height

• The cylindrical specimens were carved without altering the mortar and coarse aggregate. As the surface was flat, the refraining or smoothing of the surface was eliminated by sulfur.

• These concretes were manufactured in a vertical shaft mixer with rotating bowl and fixed vanes, with a capacity of 80 liters.

• The sequence that has been used in relation to the introduction of materials has been: cement, slag, sand, coarse aggregate, gravel. Once mixed for 3 minutes the water and the mineral additive added this slowly for a good mixture of the materials, observing said mixture was homogeneous. The total kneading time revolved around 10 minutes.

• Once the proposed concretes were kneaded, they were emptied into molds, vibrating on a table for compaction, at a frequency of 42 Hz (2400 cycles per minute) according to UNE 12390-2 regulations.

• The specimens were covered with a plastic for 24 hours and then they were demoulded and taken to a humid chamber for curing, this being an enclosure that allows to maintain a relative humidity of 95% or more and a temperature of 20 ± 2 ° C Finally, there is the extraction of control specimens with which the tests were performed.

• These specimens have been kept in the chamber, until they are used, 24 hours before the test.

• For the realization of compression tests, three specimens have been used for each of them, at 7 and 28 days, respectively.

Material density

The UNE 12390-7: 2000 standard has been used to determine the density of concrete. The devices that have been used to determine the density of the material according to these regulations have been:

• Calibrate to determine the dimensions of the specimen.

• Balance, equipped with a stirrup, to be able to weigh the specimen both in the air and in the water, with an accuracy of 0.1% of its mass.

• Water tank, equipped with a mechanism to keep the water level constant and of sufficient size to allow the specimen on the stirrup to be completely submerged at constant depth.

• Forced draft stove, capable of maintaining the temperature at (105 ± 5) ° C • To carry out this study, the minimum volume of the specimen must be 0.785 liters. The specimens studied will not exceed the maximum size of coarse aggregate (25mm), in our case said maximum size was 16 mm.

The standard indicates the following process under which the mass of a test piece can be determined:

• Under reception conditions. The results of the measurements at reception were weighed with an accuracy of 0.1% of the mass of the specimen.

• Saturated in water. In this case, the specimen should be immersed in water at (20 ± 2 ° C) until the variation in weight, after 24 hours of immersion, is less than 0.2%, having dried the specimen superficially with a damp cloth before each weighing .

• Stove dried. In this case, the specimen is dried in a forced draft oven at (105 ± 5) ° C until the weight change, after 24 hours, is less than 0.2%. Before each measurement, the specimen should be allowed to cool to room temperature in a dry airtight container or in a desiccator. The mass value of the dried test tube in the oven must be noted.

Once all the calculations were made, we obtained a material density value of 2650 kg / m3, the conventional concrete being 2600 kg / m3.

Based on the results obtained, it follows that the addition of slag increases the density of the material. This result is explained by particle granulometry resulting in a greater amount of mass with greater specific weight in the specimens with slag addition than in conventional specimens without addition. _{íi d} o _{(() i) L} D _L D _tt meseeecpcn _p m

Leaching tests.

The UNE-EN 12920: 2007 + A1 Methodology for the determination of the behavior in leaching under specified conditions was followed to perform the leaching tests. The results were as follows: The specimens were aged rapidly. This process takes place after 28 days of curing in a humid chamber, it was subjected to an oven drying at 60 ° C for 48 hours and then submerged in a 70 ° C water bath for another 32 days. They were then deposited in an aggressive environment exposed to the weather. Once aged, the same technique described below was developed.

For the leaching test The test tube has been immersed in 800ml of distilled water for 24 hours. After the test period, the sample has been extracted and the solution of the leachate has been transferred to a 1000 ml volumetric flask flush with distilled water. The test has been repeated by immersing the test tube 24 hours more in another 800ml of water repeating the described methodology.

The behavior of the stainless steel slags encapsulated in the concrete were as follows: Table I shows the results in ppm (mg 1) of the two leachates.

Table I

Test tube components Cementen- Gravel + Slag Conventional concrete

Leaching 1 * 2 »19 29 19 29

Test tube weight (gr) 360.15 352.1 353.26

0.034 As <LD <LD <LD <LD <LD <LD

0.1 Ca 1.88 1.48 1.72 1.25 1.56 1.76

0.002 Cd <LD <LD <LD <LD <LD <LD

0.004 Cr rom 0.006 0.013 0.008 0.046 0.007 0.023

0.001 Cr * 0.002 <LD 0.001 <LD <LD <LD

0.003 Cu <LD <LD <LD <LD <LD <LD

0.042 Fe <LD <LD 0.054 <LD <LD <LD _{/ ()} or _iii K _tgg esm eccnm

0.053 Mg <LD <LD <LD <LD <LD <LD

0.001 Mn <LD <LD <LD <LD <LD <LD

0.01 Ni <LD <LD <LD <LD <LD <LD

0.021 Pb <LD <LD <LD <LD <LD <LD

0.09 s or 9.00 5.98 11.13 5.29 17.90 14.15

0.021 Sn <LD <LD <LD <LD <LD <LD

0.003 Ti <LD <LD <LD <LD <LD <LD

0.002 Zn 0.010 0.003 0.010 0.013 0.014 <LD

1.9 Na 13.52 6.29 15.49 7.90 16.81 7.15

0.014 At 0.111 0.048 0.082 0.079 0.071 0.042

0.056 K 23.60 14.59 31.75 18.46 28.15 17.87

0.025 Yes 2.88 2.09 3.59 2.40 2.75 1.90

TDS (ppm) 72.05 44.57 82.99 52.21 82.59 54.09

Conductivity (uS / cm) 129.1 80.9 148.3 94.3 147.6 97.6 pH 8,960 8,220 9,180 8,530 8,990 8,160

Table II refers these results to the weight of the sample tested (mg / kg). Table II

Test tube components Cementen- Gravel + Slag Conventional concrete

Leaching the 29 the 2S 18 28

Test tube weight (gr) 360.15 352.1 353.26

0.093

As <LD <LD <LD <LD <LD <LD

0.280 Ca 5,226 4,112 4,876 3,553 4,408 4,977

0.006 <LD

Cd <LD <LD <LD <LD <LD

0.011 0.017 0.036 0.022 0.130 0.020 0.065

**

0.003

Cr 0.004 <LD 0.004 <LD <LD <LD

91

0.009 Cu <LD <LD <LD <LD <LD <LD

0.117

Fe <LD <LD 0.153 <LD <LD <LD

0.146 <LD

Mg <LD <LD <LD <LD <LD 0.003

Mn <LD <LD <LD <LD <LD <LD

0.029 <LD

Ni <LD <LD <LD <LD <LD

0.058

Pb <LD <LD <LD <LD <LD <LD

0.250 s or ₄ "24.990 16.613 31.610 15.016 50.671 40.055

0.058

Sn <LD <LD <LD <LD <LD <LD

0.009 Ti <LD <LD <LD <LD <LD <LD

0.006 Zn 0.026 0.007 0.030 0.036 0.039 <LD

5,280 37,540 17,462 43,993 22,423 47,585 20,243

Na

0.039 0.305 0.132 0.233 0.224 0.202 0.118

To the

1,560 K 65,528 40,511 90,173 52,428 79,686 50,586

0.070 Yes 7,983 5,800 10,185 6,808 7,796 5,364

TDS 200 124 236 148 234 153

From these tables, as expected, in the second leaching a decrease in the concentration of leaching species is observed. The fact that some elements such as Cr T _0ta i present slightly higher values when re-leaching, is due to the decrease in pH and the consequent partial dissolution of its hydroxides, with L / D detection limit and TDS referred to 1 ppm in a milligram of solid solvent for every kilogram of water.

In the Directive on "Criteria and procedures for the admission of waste in landfills", the Leaching Limit Values are set out, according to the criteria established for hazardous waste admissible in landfills for non-hazardous waste. The maximum limit for total chromium is 4 mg / kg of dry matter calculated in terms of total release, for proportions between liquid and solid (L / S) of 2 1 / kg. This value being the least permissive of the set of tables dictated in this European Directive. If we make the balance in mg / kg of dry matter of the total chromium in Table I above and with an easy proportion it is determined that in our samples the leaching is lower.

Comparing it with a liter of water, if we take it to the proportion formulated in the table of II 1 / kg this value reaches 0.369 mg / kg well below the maximum limit of 4 mg / kg imposed by the standard.

The variability of the remaining metal oxides is qualitatively large but quantitatively negligible due to the existing disproportion, the narrowest being the one previously marked in _Crota i which represents one tenth of the assigned limit. The average of these parameters is less than 5%.

In addition to the leaching limit values mentioned in Table 2.3.1 Official Journal of the European Communities OJ L 11, 16.1.2003, p. 27/48; Directive with the Council Decision of 19/12/2002 2003/33 / EC, which establishes the criteria and procedures for the admission of waste to landfills in accordance with Article 16 and Annex II of Directive 1999/31 / EEC, granular waste must meet the following additional criteria:

PH parameter Limit value> 6

The lowest value recorded in the analytical is 8.22, higher than the one indicated in the standard.

Stable non-reactive wastes are those whose leaching behavior will not adversely change in the long term under the design conditions of the landfill, or in case of foreseeable accidents:

• in the waste considered in isolation (for example, by biodegradation),

• under the influence of long-term environmental conditions (eg water, air, temperature and mechanical restrictions),

· Due to the effect of other waste (including waste products such as leachate and gas). The encapsulation of the stainless steel slags in the concrete as a substitute, overcomes these conditions since the useful life of the structural elements executed are long lasting.

INDUSTRIAL APPLICATION

One of the most important characteristics of this type of material is its ductility and manageability at the time of its implementation. Likewise, it is worth mentioning the resistance to abrasion and therefore the wear of the material.

These characteristics make the material obtained as described in this patent, suitable for use in the construction of acropods, tetrapods and filler drawers for the realization of jets for harbor shelters, or to prevent the banishing of beaches, by the use of these structures during storms, when creating artificial totems.

On the other hand, the mixture generated with this material could in turn be used for the settlement of land by means of piles or micropiles that stabilize the soil avoiding internal slippage as well as the erosion of the ground that could be caused by the effect of poor filtration or landslide .

Valuation of an industrial waste of enormous volume that is currently deposited in landfills, for reuse as a material for use in this type of application.

Claims

1.- Slag concrete, characterized in that it uses stainless steel slag from an electric arc furnace, as a substitute for up to 25% of the total cement used in its formulation.

2. Procedure for the manufacture of slag concrete, according to claim 1, characterized in that it comprises the following steps:

b) Preparation of a table with the necessary additions of cement, sand, gravel, intermediate aggregate and water. The mixture used will have a 1: 5 ratio between cement and aggregate, which will remain fixed in the study of the first trial. , in which we will have a conventional concrete c) Replacement of up to 25% of the cement used, by electric arc furnace slag, keeping constant the existing proportion with respect to the aggregates used.

d) Kneading with the required proportions.

3. Use of slag concrete according to claim 1, for the manufacture of structural containment systems, such as tetrapods, acropods, and filler drawers, for harbor shelters.

4.- Use of slag concrete according to 1 for the manufacture of piles and micropiles, used in landfill and land stabilization.