ES2891677B2 - Self-compacting concrete with recycled concrete aggregate and its production procedure - Google Patents

Description

DESCRIPTION

SELF-COMPACTING CONCRETE WITH RECYCLED CONCRETE AGGREGATES AND ITS

PRODUCTION PROCEDURE

TECHNICAL FIELD OF THE INVENTION

The present invention is encompassed in the field of construction materials, specifically self-compacting type concrete with recycled concrete aggregate.

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.

Recycled concrete aggregate is a waste from the precast concrete industry. Many prefabricated elements, such as beams or columns, are frequently discarded due to geometric and/or aesthetic defects. The crushing or crushing of these elements allows obtaining an artificial aggregate formed by crushed concrete that is traditionally deposited in landfills. This material is characterized by its very high water absorption, which can be ten times higher than that of traditional limestone aggregate, which makes it difficult to develop highly workable concrete with this material and makes it difficult to temporarily preserve self-compactability over time. over time, due to the rapid absorption of the water added to the concrete during its manufacture by the recycled concrete aggregate.

On the other hand, ground granulated iron and steel slag is a by-product of the iron and steel industry obtained by quenching the residue from blast furnaces, known as slag, followed by crushing to a size of grain of the order of mieras. This material is characterized by presenting pozzolanic and conglomerating properties, being capable of hardening when mixed with water and providing resistance.

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). On the other hand, there are several studies of self-compacting concrete made with recycled concrete aggregate used only in the coarse fraction (Grdic, ZJ, Toplicic-Curcic, GA, Despotovic, IM, Ristic, NS, 2010. Properties of self-compacting concrete prepared with coarse recycled concrete aggregate Construction and Building Materials 24 (7), 1129-1133 DOI: 10.1016/j.conbuildmat.2009.12.029 Tang WC Ryan PC Cui HZ Liao W 2016 Properties of Self-Compacting Concrete with Recycled Coarse Aggregate. Advances in Materials Science and Engineering. 2016, 2761294. DOI: 10.1155/2016/2761294) and very few studies that use it in small proportions of the fine fraction (Santos, SA, da Silva, PR, de Brito, J., 2017. Mechanical performance evaluation of self-compacting concrete with fine and coarse recycled aggregates from the precast industry. Materials. 10 (8), 904. DOI: 10.3390/ma10080904). In no case has the use of recycled concrete aggregate in the powder fraction ("filler" according to its common name) been studied for self-compacting concrete and, even less, the integral use of recycled concrete aggregate in the three fractions (coarse /fine/powder) in total substitutions of the coarse fraction and powder, optionally in the fine fraction.

On the other hand, blast furnace slag has been commonly used in the manufacture of concrete to replace aggregate (González-Ortega, MA, Cavalaro, SHP, Rodríguez de Sensale, G., Aguado, A., 2019. Durability of concrete with electric arc furnace slag aggregate. Construction and Building Materials. 217, 543 556. DOI: 10.1016/j.conbuildmat.2019.05.082). There are studies in which the natural aggregate has been replaced by blast furnace slag, in coarse, medium and fine fractions (Roslan, NH, Ismail, M., Khalid, NHA, Muhammad, B., 2020. Properties of concrete containing electric arc smoke steel slag and steel sludge. Journal of Building Engineering 28, 101060. DOI: 10.1016/j.jobe.2019.101060). Fibre-reinforced vibrated concrete valid for pavements has been produced with this residue (Lee, JH, Sohn, YS, Lee, SH, 2012. Fire resistance of hybrid fibre-reinforced, ultra-highstrength concrete columns with compressive strength from 120 to 200MPa. Magazine of Concrete Research 64 (6), 539-550 DOI: 10.1680/macr.11.00034 Papachristoforou M, Papayianni I. 2018 Radiation shielding and mechanical properties of steel fiber reinforced concrete ( SFRC) produced with EAF slag aggregates. Radiation Physics and Chemistry. 149, 26-32. DOI: 10.1016/j.radphyschem.2018.03.010) and self-compacting concrete, combined in this case with the addition of large amounts of natural limestone sand (Sosa, I., Thomas, C., Polanco, JA, Setién, J., Tamayo, P., 2020. High performance selfcompacting concrete with electric arc furnace slag aggregate and cupola slag powder. Applied Sciences (Switzerland). 10 (3), 773. DOI : 10.3390/app10030773).

Ground granulated iron and steel slag is a different waste from the previous one (CEDEX, 2013. Catalog of waste that can be used in construction. Center for Studies and Experimentation in Public Works (CEDEX)), as it has conglomerating properties (hardening after mixing with water) and has been used for the manufacture of cements (Sanjuán, MA, Argiz, C., 2014. Blast furnace slag cements in Spain. Cemento Hormigón. 964, 10-22). There are few studies that use the combination of ground granulated iron and steel slag and recycled aggregate for the manufacture of vibrated concrete (Majhi, RK, Nayak, AN, 2019. Bond, durability and microstructural characteristics of ground granulated blast furnace slag based recycled aggregate concrete. Construction and Building Materials.212 578 595. DOI: 10.1016/j.conbuildmat.2019.04.017;J Xie, J Wang, B Zhang, C Fang, L Li, 2019. Physicochemical properties of alkali activated GGBS and fly ash geopolymeric recycled concrete. Construction and Building Materials. 204, 384-398. DOI: 10.1016/j.conbuildmat.2019.01.191), but in no case for the manufacture of self-compacting concrete, and even less so, with high percentages of substitution of the binder.

In relation to the manufacturing process of self-compacting concrete made with recycled concrete aggregate, the existence of procedures based on in the realization of the kneading in two stages with (González-Taboada, I., González-Fonteboa, B., Eiras-López, J., Rojo-López, G., 2017. Tools for the study of selfcompacting recycled concrete fresh behavior : Workability and rheology. Journal of Cleaner Production. 1561-18. DOI: 10.1016/j.jclepro.2017.04.045) or without (Güneyisi, E., Gesoglu, M., Algin, Z., Yazici, H., 2014 Effect of surface treatment methods on the properties of self-compacting concrete with recycled aggregates . The pre-saturation of the aggregate from the industrial point of view is not viable due to the great time required during the manufacture of the material.

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 highly self-compacting concrete with recycled concrete aggregate and its production process. The technical problem to be solved is to constitute the components of the concrete and establish the production stages in such a way as to obtain a valid concrete for its use in structural elements according to the applicable regulations, with a production procedure that allows it to be put into work with a economically and sustainably, i.e. with low energy consumption.

In view of the foregoing, the present invention refers to a self-compacting concrete with recycled concrete aggregate comprising Portland cement as the first binder, aggregates, water and additives, as is known in the state of the art. The concrete is characterized by the one that comprises ground granulated iron and steel slag as the second binder, the aggregates comprise recycled concrete aggregate, the entire coarse fraction and the entire powder fraction of the concrete being said recycled concrete aggregate. That is, the entire coarse fraction and the dust fraction is recycled concrete aggregate, there is no coarse fraction or dust of another type 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, reaching a content of recycled material that can be up to half the total volume of the concrete mix.

Other advantages of concrete is that waste dumping is reduced, by using a relatively high amount of recycled aggregate, and clinker consumption, by adding ground granulated iron and steel slag.

Another advantage of concrete is its real applicability on site thanks to the excellent physical and mechanical properties of the resulting concrete.

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 45% by volume of water and all of the coarse fractions and recycled aggregate powder of concrete; mixed; repose; addition of 45% by volume of water, Portland cement as the first binder and ground granulated iron and steel slag as the second binder; mixed; repose; addition of 10% by volume of water and additives; mixed; repose.

The proposed procedure consists of three main stages, considered as such the addition of components with their corresponding mixing, proposing the rest of the mixture after each one of them to maximize the absorption of water by the recycled aggregate of concrete during the kneading.

An advantage of the procedure is that there is no need for pre-saturation, eliminating the time required to pre-saturate the recycled concrete aggregate.

Another advantage of the procedure is that the absorption of water by the recycled concrete aggregate after the described procedure is minimized, which allows it to be transported from the concreting plant to the place of placement without losing its properties, optimally conserving its self-compacting.

Other advantages of the procedure is its implementation with a minimum consumption of energy and time due to a kneading process in three main stages of addition and mixing that gives the concrete high self-compactability. Not having vibrated reduces fuel consumption and the consequent CO2 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 concrete with recycled concrete aggregate comprising Portland cement as the first binder, ground granulated iron and steel slag as the second binder, aggregates, water and additives. The aggregates comprise recycled concrete aggregate, the entire coarse fraction and the entire concrete powder fraction being of said recycled concrete aggregate.

Optionally, it comprises a fine fraction of recycled concrete aggregate and/or a fine fraction of siliceous sand. In other words, the fine fraction of recycled concrete aggregate may appear only without the fine fraction of siliceous sand, the fine fractions of both aggregates coexist, or only the fine fraction of siliceous sand may appear without the fine fraction of recycled concrete aggregate, as can be seen in the example mixtures in Table 2 below.

A dosage that is shown to be advantageous is that Portland cement as the first binder is between 40%-60% by volume of the total binders, ground granulated iron and steel slag as the second binder is between 40%-60% by volume of the total of conglomerates. That is, one binder is complemented by the other to reach all the binders in the concrete. Specifically, a preferred value in those ranges is that the first binder is 50% by volume of the total binders, the ground granulated iron and steel slag as the second binder is 50% by volume of the total binders.

Another advantageous option in the dosage of the fractions is that the powder fraction is between 10% and 15% of the total volume of concrete, the coarse fraction is between 10% and 15% of the total volume of concrete; the fine fraction is between 30% and 35% 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.

The invention is also the process for making self-compacting concrete as described in its most general manner, with the coarse and powder fractions, comprising the following stages in sequence:

- addition of 45% by volume of the water and of all the coarse fractions and powder of recycled concrete aggregate;

- mixed;

- rest;

- addition of 45% by volume of water, Portland cement as the first binder and ground granulated iron and steel slag as the second binder;

- mixed;

- rest;

- addition of 10% by volume of the water with dissolved additives, such as a setting regulator and a plasticizer;

- mixed;

- rest.

When the concrete includes the fine fraction, it is added at the first addition stage, along with the coarse and powder fractions.

An advantageous option on the mixing and standing times is that each mixing stage has a duration between 2 minutes and 5 minutes, each resting stage has a duration between 2 minutes and 5 minutes. Specifically, each mixing stage lasts 3 minutes, each rest stage lasts 2 minutes.

Example

Three mixtures are proposed, with 100% recycled concrete aggregate in the coarse fraction and powder, with contents of recycled concrete aggregate in the fine fraction of 0% (MIX0), 50% (MIX50) and 100% (MIX100). . It must be taken into account that the manufacturing possibilities are very wide and depend on aspects such as the place where the original crushed concrete was made, the characteristics of the natural aggregate used or the proportion of cement.

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

Its dosage is shown in Table 2:

Table 2. Dosage of the mixtures (kg/m3)

The properties in the fresh state are shown in Table 3 according to the international specifications for the characterization of self-compacting concrete (EN 206 and EFNARC recommendations) (in parentheses the runoff class -SF-, runoff viscosity -VS-, viscosity in the funnel test in V -VF-, passing ability -PA- and segregation -SR-corresponding):

Table 3. Properties in fresh state

The properties in the hardened state are collected in Table 4.

* Mixture valid as lightweight concrete.

Table 4. Properties in hardened state

The proposed mixing procedure, as well as the self-compacting concrete used, would be valid for structural use in both reinforced and prestressed concrete applications, both in situ and precast. In addition, in complex structures in which a very low self-weight of the components is required, the MIX100 mixture presents great application possibilities due to its lightweight concrete consideration.

Claims (10)

1. -Self-compacting concrete with recycled concrete aggregate comprising Portland cement as the first binder, aggregates, water and additives, characterized in that it comprises ground granulated iron and steel slag as the second binder, the aggregates comprising recycled concrete aggregate, the entire fraction being thick and the totality of the concrete powder fraction of said recycled concrete aggregate and in which Portland cement as the first binder is between 40%-60% by volume of the total binders, the ground granulated iron and steel slag as the second binder is between 40%-60% by volume of the total binders. 2. -Concrete according to claim 1 in which the Portland cement as the first binder is 50% by volume of the total binders, the ground granulated iron and steel slag as the second binder is 50% by volume of the total binders. 3. -Concrete according to claim 1 in which the powder fraction is between 10% and 15% of the total volume of concrete, the coarse fraction is between 10% and 15% of the total volume of concrete. 4. -Concrete according to claim 1 comprising fine fraction of recycled concrete aggregates and/or fine fraction of siliceous sand and in which the fine fraction is between 30% and 35% of the total volume of concrete. 5. -Concrete according to claim 4 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. 6. -Concrete according to claim 1 in which the ground granulated iron and steel slag are particles of size up to 0.01 mm. 7. -Procedure for preparing self-compacting concrete with recycled concrete aggregate according to claim 1, characterized in that it comprises the following stages in sequence: - addition of 45% by volume of the water and of all the coarse fractions and powder of recycled concrete aggregate; - mixed; - rest; - addition of 45% by volume of water, Portland cement as the first binder and ground granulated iron and steel slag as the second binder; - mixed; - rest; - addition of 10% by volume of the water with dissolved additives; - mixed; - rest. 8. -Procedure according to claim 7 in which the fine fraction is added in the stage of the first addition, together with the coarse fractions and powder. 9. -Procedure according to claim 7, wherein each mixing stage lasts between 2 minutes and 5 minutes, each rest stage lasts between 2 minutes and 5 minutes. 10. -Procedure according to claim 9, wherein each mixing stage lasts 3 minutes, each rest stage lasts 2 minutes.