MORTAR OR CONCRETE MATERIAL CONTAINING METALLIC MINERAL EXTRACTION RESIDUES AND METHOD FOR PRODUCING SAME

Abstract

The present invention relates to a mortar or concrete material comprising cement, water, fine aggregate and coarse aggregate, wherein the fine aggregate is partially replaced by metallic mineral extraction residues (MMERs) not subjected to thermal treatment, with a pH of less than 7, with a particle size of less than 4 mm, and partially stabilised with limestone material that comprises at least 60% calcite with a particle size of less than 63 μm. The present invention also relates to the method for preparing said material and the use thereof to prepare construction materials.

Claims

1. A mortar or concrete material comprising cement, water, fine aggregate and coarse aggregate, characterised by further comprising metallic mineral extraction residues (MMERs) not subjected to thermal treatment, with a pH of less than 7, with a particle size of less than 4 mm, and partially stabilised with limestone material that comprises at least 60% calcite with a particle size of less than 63 μm.

2. The mortar or concrete material according to claim 1, comprising: at least 150 kg/m.sup.3 of cement, the fine aggregate, the MMRES's in at least 20% by weight of the fine aggregate, 0-70% by weight of coarse aggregate, at least 90 kg/m.sup.3 of water.

3. A method for preparing mortar or concrete material starting from metallic mineral extraction residues MMERs not subjected to thermal treatment and with a particle size of less than 4 mm according to claim 1, comprising the following steps: a) partial stabilisation of the MMERs with limestone materials that comprise at least 60% calcite and a particle size of less than 63 μm, until reaching a pH comprised between 7-10, b) homogenisation of the mixture obtained in a) with water until the saturation point, c) addition of cement, water and aggregates, d) homogenisation of the mixture obtained in step c).

4. A construction material comprising or obtainable from the mortar or concrete material according to claim 1.

5. The construction material according to claim 4, selected from coatings, footpaths, curbs, bollards, planters, drains, sewer pipes, filler concretes, mass concrete walls, submerged blocks, harbour breakwaters, safety barriers on motorways and highways, wastewater ducts, and precast slabs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0048] The method for implementing the present invention was carried out as described below:

[0049] Once the preliminary study of characterisation and risk analysis of the contaminated location containing the MMERs was carried out, a number of representative samples were taken, depending on the volume of residues and the judgment of the expert, and they were taken to the laboratory.

[0050] With the residues in the laboratory, they were characterised chemically and mineralogically and, at the same time, a granulometric analysis was performed, grinding all particles retained in the UNE-EN 933-2 sieve with a 4 mm opening to a suitable size.

[0051] The partial stabilisation phase involves the use of a limestone material that contains more than 60% calcite and the particle size is less than 63 microns, with which the pH of the MMERs was stabilised to a neutral or slightly basic value, immobilising the soluble metals or preventing them from precipitating into insoluble forms.

[0052] To this end, the acid generation potential of the residues was determined, as described in the UNE-EN 15875 standard.

[0053] This method was performed with the mixture at the saturation point in water in order to force the reaction and to subsequently prevent the MMERs from attacking some other component and/or taking a portion of the water intended to react with the cement due to hygroscopic phenomena or structural changes during the different crystallisation phases.

[0054] If for any reason it is not possible to execute this phase satisfactorily, the residues will be discarded and properly managed.

[0055] Next, the doses were chosen for cement, water, coarse aggregate (if concrete is to be manufactured), partially stabilised MMERs and fine aggregate (if the replacement thereof is not complete). The proportion of each of these components, with respect to the cement, was a personal choice, except for the limestone material which, as cited above, will depend on the acid generation potential of the MMERs, and it will depend, to a greater or lesser extent, on the final features of the desired product.

[0056] As cited in Annex 18 of EHE-08, the only restriction for non-structural concretes is that the cement dose and the minimum strength must be 150 kg/m.sup.3 and 15 N/mm.sup.2, respectively.

[0057] The method for mixing the different components may be performed by using any method which ensures the homogeneity of the product. The addition of MMERs will be carried out after partial stabilisation, thus preventing them from reacting with any other component of the mixture.

[0058] After the manufacturing process, the product was subjected to mechanical tests, determining the compressive strength thereof according to the UNE-EN 12390-3 standard for concretes or the flexural and compressive strength thereof for mortars according to the UNE-EN 196-1 standard, physical/chemical tests such as density, pH, conductivity, etc., and a study on stabilisation of soluble metals, analysing the curing water, in order to corroborate the perfect stabilisation and encapsulation of the residues.

[0059] If the results obtained during the previous step are satisfactory, the stabilised/solidified product can have several industrial applications, mainly in the construction field, otherwise it will be discarded and the process will have to be started again from the stabilisation.

[0060] The product obtained has multiple applications in the construction sector, such as: coatings, footpaths, curbs, bollards, planters, drains, sewer pipes, filler concretes, mass concrete walls, harbour breakwaters, safety barriers on motorways and highways, wastewater ducts, unreinforced precast slabs, among others.

[0061] The promotion and development of these materials implies significant environmental, economic and social benefits, such as the protection of ecosystems and the regeneration of highly degraded areas, greater availability of raw materials by drastically reducing the exploitation of natural resources, reduction of CO.sub.2 emissions to the atmosphere, creation of new markets, promoting less dependence on the import of raw materials, etc.

Embodiment of the Invention

Example 1: Method for Manufacturing Six Cylindrical Concrete Specimens Measuring 30×15 cm, with Replacement of 50% of the Fine Aggregate by an Equivalent Mass of MMERs Plus Limestone Filler

[0062] The specimens were classified into two groups according to the manufacturing method thereof: [0063] Group A: Normal manufacturing method. Specimens wherein the mass of “MMERs+Limestone Filler” is added dry. [0064] Group B: Manufacturing method modified according to the method of the proposed invention. Specimens wherein the mass of “MMERs+

[0065] Limestone Filler” is added at the saturation point in water.

Group A and B:

[0066] The origin of the residues used for both group A and group B was “La Bahía de Portman”, one of the most polluted areas in the Iberian Peninsula. There, it is estimated that a total of 60 million tonnes of hazardous residues like the ones described above is present, product of the intense mining activity carried out by the Lavadero Roberto for much of the 20th century.

[0067] The sample found was encrusted and larger than 4 mm, so it was necessary to grind it to a size of less than 4 mm. The chemical, mineralogical and granulometric characterisation carried out in the laboratory on the selected samples yields the following particular values:

TABLE-US-00001 MMER CHARACTERISTICS VALUE MUNSELL COLOUR 2.5Y, 5/6 PARTICLE SIZE (after grinding) <4 mm USDA TEXTURAL CLASS loam/silt BET SPECIFIC SURFACE AREA 16 m.sup.2/g RELATIVE DENSITY 2.6 g/cm.sup.3 pH 2.5

TABLE-US-00002 MMER COMPOUNDS MOLECULAR FORMULA PERCENTAGE NATROJAROSITE NaFe.sub.3.sup.(3+)(SO.sub.4).sub.2(OH).sub.6 60%  SIDERITE FeCO.sub.3 15%  GYPSUM CaSO.sub.4•2H.sub.2O 4% MAGNETITE Fe.sup.2+(Fe.sup.3+).sub.2O.sub.4 5% PYRITE FeS.sub.2 10%  QUARTZ SiO.sub.2 3% OTHER — 3%

TABLE-US-00003 MMER ELEMENTS TOTAL SOLUBLE LEAD 3,304 mg/kg 15 mg/kg ZINC 3,205 mg/kg 306 mg/kg CADMIUM 56 mg/kg 3.8 mg/kg COPPER 160 mg/kg 82 mg/kg ARSENIC 632 mg/kg 4.1 mg/kg IRON   38% 25% SULPHUR 15.01% <LOD

[0068] Depending on the mineralogy of the residue and following the steps described in the UNE-EN 15875 standard, it was determined that in order to partially stabilise it, it had to be mixed with a mass of limestone material equivalent to 30% of the total mass of the residue.

[0069] The limestone material used to carry out this method was a filler coming from aggregate sorting plants. Since it is found in abundance, it is economical and has a high carbonate content and the characteristics of which are as follows:

TABLE-US-00004 FILLER CHARACTERISTICS VALUE MUNSELL COLOUR 7.5 YR 8/2 AVERAGE PARTICLE SIZE 55 μm USDA TEXTURAL CLASS loam BET SPECIFIC SURFACE AREA 9 m.sup.2/g RELATIVE DENSITY 2.3 g/cm.sup.3 pH 8.3

TABLE-US-00005 FILLER COMPOUNDS MOLECULAR FORMULA PERCENTAGE CALCITE CaCO.sub.3 84%  DOLOMITE CaMg(CO.sub.3).sub.2 6% PHYLLOSILICATES illite 3% QUARTZ SIO.sub.2 7%

TABLE-US-00006 FILLER ELEMENTS TOTAL SOLUBLE LEAD <LOD <LOD ZINC <LOD <LOD CADMIUM <LOD <LOD COPPER <LOD <LOD ARSENIC <LOD <LOD IRON <LOD <LOD SULPHUR <LOD <LOD

Group A:

[0070] The mixing of the residue with the limestone filler was done by the dry method, stirring both masses between 5 and 10 min, in order to ensure the homogeneity thereof.

Group B:

[0071] The mixing of the residue with the limestone filler was done by the wet method, bringing both masses almost to the saturation point in water, for which the necessary amount thereof was added directly from the urban network and constantly stirred, between 5 and 10 min, in order to ensure the homogeneity thereof.

Group A and B:

[0072] Once the MMERs were partially stabilised, the concrete was then manufactured which, eventually, entailed the complete stabilisation thereof.

[0073] To this end, and once again based on mineralogy, an I 32.5 N/SR UNE 80303-1 cement was used, which corresponds to a sulphate resisting Portland cement with a normal strength of 32.5 MPa.

[0074] The chosen dose was determined to prepare a common mass concrete with a 28-day compressive strength of 20 MPa, and it has: [0075] 250 kg/m.sup.3 of cement. [0076] 480 kg/m.sup.3 of fine aggregate with 50% replacement: [0077] 240 kg/m.sup.3 of conventional fine aggregate. [0078] 240 kg/m.sup.3 of homogeneous mixture and at the saturation point in water of MMERs and limestone filler. [0079] 1,600 kg/m.sup.3 of coarse aggregate. [0080] 175 kg/m.sup.3 of water.

[0081] The use of a rotating drum system to mix all these components ensures the homogeneity of the product. The mass to be taken from each of the materials will depend on the density thereof and on the volume of product to be manufactured.

Group A:

[0082] When the partially stabilised and unsaturated residues were added to water, it was observed that they started to swell when they captured the dosing water that should react with the cement.

[0083] As the mixing time progressed, instead of forming, as one might expect, a homogeneous cemented mass with a dense/semi-fluid appearance, solid non-cemented aggregates with a spherical shape started to form which made it very difficult, or almost impossible, to fill the moulds of the specimens evenly.

[0084] As such, it was necessary to add between 50 and 100% extra water compared to what was initially proposed in order to achieve a minimally workable paste and, despite this, the final appearance was not that of concrete for use.

[0085] 24 to 48 hours after the moulds were filled, demoulding was carried out.

[0086] The appearance was of a material in a solid state which had, at first glance, structural problems, since interstitial voids were seen on the surface of the specimens.

[0087] Once the demoulding phase had been carried out, the specimens were placed in individual containers and were completely covered with water, staying in these conditions for, at least, 28 days.

Group B:

[0088] When partially stabilised residues almost to the saturation point were added in water, it was observed that a homogeneous mass with a dense/semi-fluid appearance started to form, which made it possible to easily fill the moulds of the specimens.

[0089] 24 to 48 hours after the moulds were filled, the demoulding phase was carried out.

[0090] The appearance had by the specimens with the method proposed by this invention was a solid and structurally compact material.

[0091] Once the demoulding phase had been carried out, the specimens were placed in individual containers and were completely covered with water, staying in these conditions for, at least, 28 days.

Group A and B:

[0092] Every day, or if establishing another longer time interval is considered appropriate, a sample of these waters was taken and chemical parameters such as pH, electrical conductivity and the content of soluble metals were analysed, among others.

[0093] After 28 days of curing, the specimens were extracted and subjected to compressive strength tests.

[0094] The results detailed below represent the average value of the experiments performed in the laboratory for each group during the research period prior to the writing of this invention.

TABLE-US-00007 28-DAY PARAMETERS INITIAL GROUP A GROUP B pH of curing water (—) 6.95 10.10 11.97 Electric cond. of curing water 2.09 13.63 12.02 (mS/cm) Soluble Metals of curing water <LOD <LOD <LOD (ppm) Compressive Strength of specimens 3.8 17.5 (MPa) Density of specimens (kg/m.sup.3) X 2,244 Suspended particles (%) 0 14 0

Group A:

[0095] Specimens manufactured according to the normal method: [0096] retained soluble contaminants, but did not retain all the particulates. [0097] did not reach the minimum compressive strength required by EHE-08 to be used as non-structural concretes.

[0098] Consequently, they have no application in the construction field.

Group B:

[0099] The specimens manufactured according to the modified method proposed by this invention: [0100] retained soluble and particulate contaminants, preventing dispersion to the medium. [0101] clearly overcame the minimum compressive strength required by EHE-08 to be used as non-structural concretes.

[0102] Consequently, they can be used in various applications as non-structural concretes in the construction field.