ES2930798A1 - Geopolymer, obtaining procedure and uses given to it (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Geopolymer, obtaining procedure and uses given to it. The present invention falls within the technical field of construction and refers in particular to a geopolymer and to the mortars and concretes obtained from the geopolymer of the invention. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Geopolymer, obtaining procedure and uses given to it

OBJECT OF THE INVENTION

The present invention falls within the technical field of construction and refers in particular to a geopolymer and to the mortars and concretes obtained from the geopolymer of the invention.

BACKGROUND OF THE INVENTION

Concrete is the most used construction material in the world because its application is very versatile. The essential ingredient of concrete is portland cement (CP). The CP presents environmental problems. The key reaction involved in the manufacture of CP is the decomposition of calcium carbonate into calcium oxide and carbon dioxide (CO ² ). The production of CP not only consumes a considerable amount of energy, it also emits a substantial amount of CO ² and other greenhouse gases into the atmosphere.

Global warming is caused by the emission of greenhouse gases such as CO ² into the atmosphere. The global cement industry contributes around 4 billion tons of greenhouse gas emissions annually. The production of one ton of PC emits approximately one ton of CO ² into the atmosphere. In addition, a large amount of natural minerals is used during the cement manufacturing process.

For this reason, alternative materials are currently being sought to replace conventional portland cement.

In this sense, geopolymer technology is one of the key developments to replace PC, since it is an ecological and low-cost substitute. In recent years, geopolymers have attracted considerable attention due to their physical and chemical characteristics such as low permeability, good chemical resistance, and good fire behavior. Due to these advantageous properties, the geopolymer is a promising candidate as an alternative to ordinary Portland cement for the development of sustainable products in the manufacture of concrete or mortar building materials.

The advantages of geopolymers are that they create a cement that requires a minimum amount of natural materials, produces a minimum amount of industrial by-products, and generates a reduced amount of CO ² during production.

Geopolymers can be made from different materials and waste.

For example, the patent with application number WO2020056470 describes the procedure for obtaining geopolymers characterized by its sintering step, said process comprising the steps of: (1) forming a geopolymer composition that comprises at least one aluminosilicate precursor, an alkaline activating agent and water, wherein in the geopolymer article, the aluminosilicate precursor particles are at least partially coated by the alkaline activating agent; and (2) calcining the geopolymer to sinter it.

On the other hand, industrial slag can be used in construction elements to prevent it from being taken to the landfill and to provide good physical-chemical characteristics to the final product. For example, submerged arc welding slag has been used to develop building elements, but not geopolymers. These slags have been exclusively mixed with Portlan cement. In the Eiffage document "Development of construction materials with welding slag residue", published on the website https://www.eiffageinfraestructuras.es/es/desarrollo-de-materiales-de-construccion-con-residuoescoria- de-soldering/, Portlan cement mixtures with slag are described. In this publication they refer to the pozzolanic capacity of the slag, this capacity is measured in cements to which a compound that reacts with clinker, portland cement, is added.

In the present invention, a procedure has been developed to take advantage of these submerged arc welding slags in construction products avoiding portland cement.

DESCRIPTION OF THE INVENTION

Submerged arc welding is a process in which heat is supplied by an electric arc generated between one or more electrodes and the work piece. This electric arc is submerged in a granular flux layer that completely covers it, protecting the deposited metal during welding. Hence the name of the process. The flux is deposited in front of the arc as welding progresses. When it solidifies, the excess granulated flux for reuse and the melt is removed by pecking. In modern equipment there is a vacuum cleaner that absorbs excess flux and sends it back to the feeding hopper. The solidified material of the flux is what is called submerged arc welding slag (SAWS).

A large amount of flux is converted to slag during the soldering process and, as this must be disposed of, landfill space is required for its disposal, as it is not biodegradable and therefore does not decompose over time.

Nowadays, most of the times submerged arc welding slag is disposed of in landfills, which has a cost, so it is interesting to put this residue to use.

In the present invention, a geopolymer obtained from submerged arc welding slag has been developed.

The term geopolymers refers to inorganic synthetic polymers formed from aluminosilicates activated by a basic solution at room temperature.

In the present invention, a geopolymer has been developed from submerged arc welding slag, slag that provides the aluminosilicate compound.

In a first aspect, the invention refers to a process for obtaining geopolymers that comprises the steps of:

a) mix a slag with an activating aqueous solution of: R(OH), R ² OSD ² , where R is selected from among Na+, Li+, K+

where the slag is a submerged arc weld slag

b) curing the mixture obtained in stage a).

Likewise, the invention refers to the geopolymer obtained by the procedure referred to in the first aspect of the invention.

The use of submerged arc weld slag has not been studied for the development of alkaline activated materials or geopolymers. Therefore, the use of submerged arc weld slag for the synthesis of geopolymers is also an aspect of the invention.

The great difference in terms of composition of a concrete that comprises a geopolymer, compared to conventional concrete, is that the binder is completely replaced by an inorganic polymer, geopolymer. Therefore, the concrete obtained is better from an environmental point of view. Another big difference with respect to CP is that the geopolymers do not form calcium silicate hydrates for the formation and resistance of the matrix, for this they use the polycondensation of silica and alumina and a high alkali content to achieve structural resistance and thus having an adequate behavior despite the fact that the concrete does not have Portlan cement in its composition.

For this reason, other aspects of the invention refer to concretes and mortars that comprise the geopolymer of the invention.

PREFERRED EMBODIMENT OF THE INVENTION

As we have seen, the first aspect of the invention refers to a process for obtaining geopolymers that includes the steps of:

a) mix a slag with an activating aqueous solution of: R(OH), R ² OSD ² , where R is selected from among Na+, Li+, K+

where the slag is a submerged arc weld slag

b) curing the mixture obtained in stage a).

Preferably, the activator is Na(OH) or Na ² OSO. Preferably, the activator/slag aqueous solution weight ratio is between 0.3 and 0.5.

Preferably, the concentration by weight relative to the volume of Na ² O or Na(OH) in the activating aqueous solution is in a range between 1% and 15%, more preferably between 4% and 10%.

Preferably, the activating aqueous solution from step a) has a pH between 13 and 14.

Preferably, the temperature of stage a) is in a range between 10°C and 33°C.

Preferably the temperature during stage b) of curing is in a range between 10°C and 33°C. In another preferred embodiment, the curing temperature is in a range between 60°C and 80°C for a time between 24 hours and 60 hours. and later between 10°C and 33°C.

The geopolymer obtained by any materialization of the procedure described in the previous paragraphs is also part of the invention.

Finally, as has been said, the concrete and mortar comprising the geopolymer of the invention is an aspect of the invention. Preferably, the concrete comprises geopolymer and an aggregate in a weight ratio of between 1/2 and 1/4.

Examples of the invention

Example 1 Preparation of a mortar

A mortar was prepared from the geopolymer of the invention and an aggregate. Normalized silica sand was used as aggregate.

The geopolymer was obtained from an activating solution/submerged arc welding slag weight ratio of 0.4.

The selected activator was Na ² O SiO ² , the weight ratio between SiO ² /Na ² O was 1/1 and the Na ² O concentration in solution that was tested was 4%, 5% and 6%.

Table 1 shows the amounts used in the dosages.

Table 1. Amounts used in the mortar.

The mortars were prepared in a mixer following the UNE EN 196-1 standard. For each sample (Na ² O at 4%, 5% and 6%), a total of three prismatic specimens measuring 160x40x40 mm were made. Regardless of the type of alkaline activator and the concentration, all the specimens were demolded after 24 hours. After the time After curing, the flexural and compressive strength was measured in a hydraulic press following the EN 196-1 standard.

With these dosages, mortars with resistances of up to 50 Mpa are obtained.

Example 2. Preparation of concrete

In the manufacture of concrete, the geopolymer of the invention was used.

For the synthesis of the geopolymer, submerged arc welding slag, two types of alkaline activators, Na ² OSiO ² and sodium hydroxide (NaOH) were used.

Initially, for the activating solution with Na ² OSiO ² , it was decided to use a solution/slag weight ratio=0.5, SiO2/Na2O=1 and three different values of Na ² O; 6%, 8% and 10%.

Table 2 shows the quantities used for the dosages.

Table 2

The concretes were prepared in a laboratory mixer. For each sample, a total of three 15x30 cm cylindrical specimens were made. Regardless of the type of alkaline activator and the concentration, all the specimens were demolded after 24 hours. After the curing time, the compressive strength was measured in a hydraulic press according to the European reference standards.

With these dosages, concrete with resistance of up to 55 Mpa at 28 days is obtained.

This manufacture of concrete was carried out using a special mixing process for concrete, also valid for mortars:

The submerged arc welding slag is mixed with the activator and an amount between 70 and 80% of the mixing water obtained from the calculated dosage (hereinafter Mixing 1 or A1). Starting from the activator (Na ² OSiO ² and/or NaOH) in a solid state (in flakes or another format), previously said precursor is dissolved correctly in the indicated water (between 70 and 80%). Next, the slag to be used in its entirety is introduced into that water. It is mixed with successive turns with a rod manually or in the mixer itself for a period of between 2 and 10 minutes, depending on the fineness and porosity of the slag. The object of this previous or first mixing (A1) between the slag and the activator is to achieve maximum activation of the submerged arc welding slag so that finally the mechanical performance, mainly, is the maximum in the concretes and mortars that are made. .

Regardless, the aggregates were mixed dry (hereinafter Mixed 2 or A2).

At the optimum moment of A2, the mixture obtained from A1 was introduced. The rest of the water up to 100% was used to "clean" or drag the possible product that is adhered to the walls of the container where the A1 product has been. Said cleaning was considered optimal with a mechanical agitation of the rest of the water. or manually, with the help of a rod or similar element for a few seconds. This "cleaning" water was introduced into A2 and all the dosing elements were left together in the mixer for a period of between 8 and 10 minutes.

Claims (11)

1. Procedure for obtaining geopolymers that includes the stages of: a) mix a slag with an activating aqueous solution of: R(OH), R ² OSD ² , where R is selected from among Na+, Li+, K+ where the slag is a submerged arc weld slag b) curing the mixture obtained in stage a). 2. Process for obtaining according to claim 1, characterized in that the activator is Na(OH) or Na ² OSiO ² . 3. Process for obtaining according to any one of claims 1 to 2, characterized in that the activator aqueous solution/slag weight ratio is between 0.3 and 0.5. 4. Process for obtaining according to any one of claims 1 to 3, characterized in that the concentration of Na ² O or Na(OH) in the activating aqueous solution is in a range between 1% and 15%. 5. Process for obtaining according to claim 4, characterized in that the concentration of Na ² O or Na(OH) in the activating aqueous solution is in a range between 4% and 10%. 6. Geopolymer obtained by the procedure defined according to any of claims 1 to 5. 7. Use of submerged arc welding slag for the synthesis of geopolymers according to claim 6. 8. Concrete comprising the geopolymer defined in claim 6. 9. Concrete according to claim 8 comprising geopolymer and an aggregate in a weight ratio between 1/2 and 1/10. 10. Mortar comprising the geopolymer defined in claim 6. 11. Mortar according to claim 10 comprising geopolymer and an aggregate in a weight ratio between 1/2 and 1/6.