ES2891699B2 - High-resistance steelmaking self-compacting concrete and its production procedure - Google Patents

Description

DESCRIPTION

HIGH RESISTANCE STEEL SELF-COMPACTING CONCRETE AND ITS

PRODUCTION PROCEDURE

TECHNICAL FIELD OF THE INVENTION

The present invention is encompassed in the field of construction materials, specifically self-compacting concrete with steel slag and high resistance, that is, suitable for structural elements subjected to very high loads.

BACKGROUND OF THE INVENTION

Self-compacting concrete is a type of concrete with high workability in its fresh state, which means that it can be placed on site without any type of vibration, thus providing greater safety for the operator and lower energy consumption. However, for this it is necessary that the self-compactability of the concrete be optimally preserved over time.

Electric arc furnace slag is a residue from the steelmaking process in an electric furnace from scrap. It is a residue with a dark black color, high density and surface hardness, porosity and water absorption higher than that of natural limestone or siliceous aggregate. After crushing, the electric furnace slag has particle sizes suitable for use. Its characteristics make it ideal for making high-resistance concrete, due to its high density and resistance and its optimal adherence to the cement paste, and fundamentally to its microporosity, providing a concrete with great weight and inertia capable of resisting very high loads. . A correct mix design allows even more resistant concrete to be obtained than that obtained through the use of limestone or siliceous aggregate extracted from quarries or gravel pits.

On the other hand, ground granulated iron and steel slag is a by-product of the steel industry obtained by sudden cooling of the residue of the blast furnaces, known as slag, followed by crushing until reaching a grain size of the order of microns. This material is characterized by presenting pozzolanic and conglomerating properties, being capable of hardening when mixed with water and providing resistance. These aspects make it a product that can be used as a substitute for cement clinker, so as to reduce the high emission of CO ² into the atmosphere that is produced during the manufacture of clinker (approximately the manufacture of one ton of clinker causes the emission of 0.9 tons of CO ² into the atmosphere).

The addition of fibers is a technique developed in recent years. The presence of fibers in the concrete is beneficial because it allows "sewing" the cracks that originate in it, increasing resistance both before and after cracking. Both metal fibers, steel, and plastic fibers, generally polyethylene or polypropylene, have shown their validity. Their length is usually up to 50 mm, with a diameter between 0.2 mm and 1 mm. However, the fibers reduce the workability of the concrete, making it difficult to obtain highly workable concretes (such as self-compacting concrete) when they are added.

The existing state of the art describes the composition and recommendations for behavior in the fresh state of self-compacting concrete made with natural aggregates in all fractions (EFNARC, 2002. Specification Guidelines for Self-compacting Concrete, European Federation of National Associations Representing producers and applicators of specialist building products for Concrete (EFNARC). The requirements that self-compacting concrete must meet are included, among others, in the Spanish Instruction on Structural Concrete EHE-08 (EHE-08, 2010. Instruction on Structural Concrete EHE-08. Ministry of Development, Government of Spain).

In relation to self-compacting concrete made with electric arc furnace slag, there are few studies in which self-compacting concrete has been made with electric furnace slag in the coarse fraction (Sosa, I., Thomas, C., Polanco, JA, Setién, J., Tamayo, P., 2020. High performance self- compacting concrete with electric arc fumarate slag aggregate and cupola slag powder. App. Sci. 10 (3), 773. DOI: 10.3390/app10030773) and there are even fewer that include it in the fine fraction (Manjunath, R., Narasimhan, MC, Umesh, KM, Shivam, K., Bala Bharathi, UK, 2019. Studies on development of high performance, self-compacting alkali activated slag concrete mixes using industrial wastes. Constr. Build. Mater. 198, 133-147. DOI: 10.1016/j.conbuildmat.2018.11.242). The simultaneous use of electric furnace slag in the coarse and fine fractions without combination with any type of natural aggregate is highly novel.

Ground granulated steel slag has traditionally been used for soil stabilization (Du, YJ, Wu, J., Bo, YL, Jiang, NJ, 2020. Effects of acid rain on physical, mechanical and chemical properties of GGBS-MgO- solidified/stabilized Pb-contaminated clayey soil Acta Geotechnica 15 (4), 923-932 DOI: 10.1007/s11440-019-00793-y Wu HL Jin F Bo YL Du YJ Zheng, JX, 2018. Leaching and microstructural properties of lead contaminated kaolin stabilized by GGBS-MgO in semi-dynamic leaching tests. Constr. Build. Mater. 172, 626-634. DOI: 10.1016/j.conbuildmat. 2018.03.164) or the manufacture of road bases and sub-bases (Abdollahnejad, Z., Luukkonen, T., Mastali, M., Giosue, C., Favoni, O., Ruello, ML, Kinnunen, P., Illikainen, M., 2020 . Microstructural Analysis and Strength Development of One-Part Alkali-Activated Slag/Ceramic Binders Under Different Curing Regimes. Waste Biomass Valoris. 11 (6), 3081-3096. DOI: 10.1007/s12649-019-00626-9). The use of this residue for the production of concrete is very unusual (Bondar, D., Basheer, M., Nanukuttan, S., 2019. Suitability of alkali activated slag/fly ash ( AA-GGBS/FA) concretes for chloride environments: Characterization based on mix design and compliance testing.Constr.Build.Mater.

216, 612-621. DOI: 10.1016/j.conbuildmat. 2019.05.043; Yang, KH, Hwang, YH, Lee, Y., Mun, JH, 2019. Feasibility test and evaluation models to develop sustainable insulation concrete using foam and bottom ash aggregates. build Build. Mother. 225, 620-632. DOI: 10.1016/j.conbuildmat.2019.07.130), even more so when it comes to self-compacting concrete (Reddy, AS, Kumar, PR, Raj, PA, 2020. Development of Sustainable Performance Index ( SPI) for Self-Compacting Concretes J. Build . Eng. 27, 100974. DOI: 10.1016/j.jobe.2019.100974). There is no known study in which electric furnace slag has been combined with ground granulated iron and steel slag to produce self-compacting concrete.

In relation to the addition of fibers to concrete, there are several studies that show the behavior of traditional concretes vibrated with metal and/or plastic fibers made with natural aggregate (Akcay, B., Ozsar, DS, 2019. Do polymer fibers affect the distribution of steel fibers in hybrid fiber reinforced concretes? Constr. Build. Mater. 228, 116732. DOI: 10.1016/j.conbuildmat.2019.116732; Chen, X., Wan, DW, Jin, LZ, Qian, K., Fu, F ., 2019. Experimental studies and microstructure analysis for ultra high-performance reactive powder concrete.Constr.Build.Mater.

229, 116924. DOI: 10.1016/j.conbuildmat.2019.116924). There are studies of vibrated steel concrete made with electric arc furnace slag and fibers (Fuente-Alonso, JA, Ortega-López, V., Skaf, M., Aragón, Á., San-José, JT, 2017. Performance of fiber-reinforced EAF slag concrete for use in pavements. Constr. Build. Mater. 149, 629-638. DOI: 10.1016/j.conbuildmat.2017.05.174.). The studies that address the use of fibers in self-compacting concrete are much less numerous (Altalabani, D., Bzeni, DKH, Linsel, S., 2020. Mechanical properties and load deflection relationship of polypropylene fiber reinforced self-compacting lightweight concrete. Constr. Build. Mater 252, 119084. DOI: 10.1016/j.conbuildmat.2020.119084; S. Ghorbani, S. Sharifi, H. Rokhsarpour, S. Shoja, M. Gholizadeh, Rahmatabad, MAD, J. de Brito. , 2020. Effect of magnetized mixing water on the fresh and hardened state properties of steel fiber reinforced self-compacting concrete. Constr. Build. Mater. 248, 118660. DOI: 10.1016/j.conbuildmat.2020.118660). No study is known in which a self-compacting concrete made simultaneously with electric furnace slag and metal and/or plastic fibers has been developed.

DESCRIPTION OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other features thereof.

The object of the invention is a high-resistance self-compacting steelmaking concrete and its production process. The technical problem to be solved is to constitute the components of the concrete and to establish the stages of elaboration of so that a valid concrete is obtained for its use in structural elements according to the applicable regulations, with a manufacturing procedure that allows its implementation in an economic and sustainable way, that is, with low energy consumption.

In view of the foregoing, the present invention relates to a high-strength self-compacting iron and steel concrete comprising Portland cement as the first binder, aggregates, water and additives, as is known in the state of the art. Concrete is characterized by that which comprises metallic and/or plastic fibers, ground granulated iron and steel slag as the second binder, the aggregates comprise electric arc furnace slag, the entire coarse fraction and the entire fine fraction of the concrete being said slag. electric arc furnace. That is, the entire coarse fraction and the fine fraction is electric arc furnace slag, there is no coarse or fine fraction of another type of aggregate, that is, no natural aggregate is incorporated, be it siliceous or limestone. , to the coarse and fine fractions of aggregate.

One advantage of concrete is that the sustainability of self-compacting concrete is maximized both in terms of the aggregates used and the hydraulic binder.

Other advantages of concrete are that waste discharge is reduced, by using a relatively high amount of recycled aggregate in the form of electric arc furnace slag, and clinker consumption, by adding ground granulated iron and steel slag.

Another advantage of concrete is its real applicability on site thanks to its good workability, since it is easily pumpable, due to its self-compactability, which also allows easy concreting in areas of difficult access.

Another advantage is that, due to the inclusion of metallic and/or plastic fibers and its good interaction with the electric arc furnace slag and with the cementitious matrix, which incorporates ground granulated iron and steel slag, it provides a high resistance to cracking, even said resistance before and after the aforementioned cracking, which allows its application in elements structures (for example beams, columns, floors or walls) subjected to very high loads, both in reinforced and prestressed concrete applications, both in situ and prefabricated, as well as greater safety after a possible failure or breakage, as it allows for a increased time for the evacuation of the building or structure.

Likewise, the invention refers to a process for preparing the aforementioned self-compacting concrete, characterized in that it comprises the following stages in sequence: addition of 95% by volume of the water and all of the aggregates, including furnace slag electric arc, and binders, Portland cement being a first binder and ground granulated iron and steel slag a second binder; mixed; repose; addition of 5% by volume of the water and additives; mixed; and rest.

Some advantages of the procedure is its implementation with a minimum consumption of energy and time due to a process with few stages, which is relatively fast. Not having vibrated reduces fuel consumption and the consequent CO ² emissions, with the consequent reduction of the carbon footprint and preservation of the natural environment, facing climate change and contributing to a circular economy. This in turn makes it possible to further increase the sustainability of the concrete. It supposes, in addition to the aforementioned energy savings, a notable economic and performance advantage for the company, since it allows costs to be saved and the commissioning to be carried out more quickly.

DETAILED DISCLOSURE OF THE INVENTION

The invention is a self-compacting high-strength iron and steel concrete comprising Portland cement as the first binder, aggregates, water and additives, metallic fibers (these, for example, steel) and/or plastic fibers (these, for example, polyethylene or polypropylene), ground granulated iron and steel slag as the second binder, the aggregates comprising electric arc furnace slag, the entire coarse fraction and the entire fine fraction of the concrete being said electric arc furnace slag.

Optionally, it includes electric arc furnace slag dust fraction.

A dosage that is shown to be advantageous is that Portland cement as the first binder is between 60%-70% by volume of the total binders, ground granulated iron and steel slag as the second binder is between 30%-40% by volume of the total of conglomerates. That is, one binder is complemented by the other to reach all the binders in the concrete. The sum of both conglomerates, first and second, can reach between 10% and 10.5% of the total volume of concrete.

Another advantageous option in the dosage of the fractions is that the fine fraction is between 20% and 25% of the total volume of concrete, the coarse fraction is between 15% and 20% of the total volume of concrete. Furthermore, the dust fraction, when present, is between 35% and 40% of the total volume of concrete.

Another advantageous option is that the metallic and/or plastic fibers are between 0.25% and 1.0% of the total volume of the concrete.

Another advantageous option is that the water is between 15% and 20% of the total volume of concrete, the additives comprise a plasticizing additive and it accounts for between 0.5% and 0.8% of the total volume of concrete.

A detail of concrete is that the dust fraction is particles of size less than or equal to 0.5 mm, the fine fraction are particles of size greater than 0.5 mm and less than or equal to 4 mm, the coarse fraction are particles of size greater than 4 mm and less than or equal to 12 mm.

Another detail of the concrete is that the ground granulated iron and steel slag are particles of size up to 0.01 mm.

Another detail of the concrete is that the metallic and/or plastic fibers are particles of size between 0.1 mm and 30 mm.

The invention is also the process for making self-compacting concrete as described in its most general manner, comprising the following steps in sequence:

- addition of 95% by volume of the water and all the aggregates, among which are electric arc furnace slag, and binders, Portland cement being a first binder and ground granulated iron and steel slag a second binder;

- mixed;

- rest;

- addition of 5% by volume of water and additives;

- mixed;

- rest.

An advantageous option on the mixing and standing times is that each mixing stage has a duration between 1 minute and 3 minutes, each resting stage has a duration between 1 minute and 2 minutes. Specifically, each mixing stage lasts 2 minutes, each resting stage lasts 1 minute.

Following the proportions mentioned according to the aforementioned procedure, various mixtures for the self-compacting concrete object of the invention can be obtained. According to the international specifications for the characterization of self-compacting concrete (EN 206 and EFNARC recommendations), these mixtures presented a creepage class of SF1 (runoff between 550 mm and 650 mm) or SF2 (runoff between 650 mm and 750 mm) after the kneading process, a fresh density between 2.6 and 2.75 Mg/m3, an occluded air content between 1.9 and 2.2% and a drying shrinkage between 0.9 and 1.1 mm/m . Regarding the properties in the hardened state, the compressive strength at 28 days was between 55 and 80 MPa, the modulus of elasticity at 90 days between 30 and 45 GPa, the flexural strength at 90 days between 5 and 8 MPa, the indirect tensile strength at 90 days between 4 and 5.5 MPa, direct tensile strength at 160 days between 3.5 and 4.5 MPa, tensile modulus of elasticity at 160 days between 35 and 40 GPa, height mean water penetration at 90 days between 10 and 12 mm and maximum water penetration height at 90 days between 15 and 20 mm. All these properties were in accordance, according to current regulations, with a high-resistance concrete before the cracking

The properties of the post-cracking mixtures at 160 days were the following: according to the four-point bending test, the fracture toughness was between 10 and 25 Nm, the first crack resistance between 4 and 8 MPa and fracture energy between 0.7 and 1.2 N/mm; according to the three-point bending test with a notched specimen, the proportionality limit was between 3.5 and 5.5 MPa, the residual resistance for a notch opening of 3.5 mm between 1 and 3 MPa, the fracture energy between 0.5 and 2.5 N/mm and the fracture energy depending on the opening of the notch between 0.7 and 3 N/mm.

Example

Three mixtures are presented as an example, called T (metal fibers in 0.25% of the volume of concrete), M (metal fibers in 0.5% of the volume of concrete) and P (plastic fibers in a content of 0.5 % of concrete volume).

The chemical composition of the ground granulated iron and steel slag is shown in Table 1 (expressed in %):

table 1.Chemical composition of ground granulated iron and steel slag

The characteristics of the metallic and plastic fibers used are shown in Table 2:

Table 2. Characteristics of the fibers used

The dosage of the mixtures is shown in Table 3:

Table 3. Dosage of the mixtures (kg/m3)

The properties in the fresh state are shown in Table 4 (runoff class in parentheses):

Table 4. Properties in fresh state

The properties in the hardened state that describe the pre-cracking behavior are described in Table 5 (in parentheses the standard deviation):

Table 5. Properties in pre-cracking hardened state

The properties in the hardened state of the different post-cracking mixtures are shown in Table 6 (standard deviation in parentheses).

Table 6. Post-crack hardened state properties

Claims (14)

1. - High-strength iron and steel self-compacting concrete comprising Portland cement as the first binder, aggregates, water and additives, characterized in that it comprises metal and/or plastic fibers, ground granulated iron and steel slag as the second binder, the aggregates comprising arc furnace slag being the entire coarse fraction and the entire fine fraction of the concrete of said electric arc furnace slag. 2. -Concrete according to claim 1 comprising electric arc furnace slag powder fraction. 3. -Concrete according to claim 1 in which the Portland cement as the first binder is between 60%-70% by volume of the total binders, the ground granulated iron and steel slag as the second binder is between 30%-40% by volume of the total conglomerates. 4. -Concrete according to claim 3 in which the sum of both binders, first and second, accounts for between 10% and 10.5% of the total volume of concrete. 5. -Concrete according to claim 1 in which the fine fraction is between 20% and 25% of the total volume of concrete, the coarse fraction is between 15% and 20% of the total volume of concrete. 6. -Concrete according to claim 2 in which the powder fraction is between 35% and 40% of the total volume of concrete. 7. -Concrete according to claim 1 in which the metallic and/or plastic fibers are between 0.25% and 1.0% of the total volume of the concrete. 8. -Concrete according to claim 1 in which the water is between 15% and 20% of the total volume of concrete, the additives comprise a plasticizer additive and represents between 0.5% and 0.8% of the volume total concrete. 9. -Concrete according to claim 2 in which the powder fraction is particles of size less than or equal to 0.5 mm, the fine fraction is particles of size greater than 0.5 mm and less than or equal to 4 mm, the fraction coarse are particles with a size greater than 4 mm and less than or equal to 12 mm. 10. -Concrete according to claim 1 in which the ground granulated iron and steel slag are particles of size up to 0.01 mm. 11. -Concrete according to claim 1 in which the metallic and/or plastic fibers are particles of size between 0.1 mm and 30 mm. 12. -Procedure for the production of high-strength steel self-compacting concrete according to claim 1, characterized in that it comprises the following stages in sequence: - addition of 95% by volume of the water and all the aggregates, among which are electric arc furnace slag, and binders, Portland cement being a first binder and ground granulated iron and steel slag a second binder; - mixed; - rest; - addition of 5% by volume of water and additives; - mixed; - rest. 13. -Procedure according to claim 12, wherein each mixing stage lasts between 1 minute and 3 minutes, each resting stage lasts between 1 minute and 2 minutes. 14. -Procedure according to claim 13 in which each mixing stage lasts 2 minutes, each rest stage lasts 1 minute.