WO2012172138A1

WO2012172138A1 - Method for the production of alkali cements from industrial and urban waste glass

Info

Publication number: WO2012172138A1
Application number: PCT/ES2012/070408
Authority: WO
Inventors: Francisca PUERTAS MAROTO; Juan José TORRES CASTAÑÓN; Celia VARGA FERNÁNDEZ; Manuel Torres
Original assignee: Consejo Superior De Investigaciones Científicas (Csic)
Priority date: 2011-06-17
Filing date: 2012-05-31
Publication date: 2012-12-20
Also published as: ES2394979A1; ES2394979B1

Abstract

The invention relates to a method for the production of alkali cements, characterised in that it comprises mixing an alkaline solution having a pH greater than 13 and selected from an NaOH solution or an NaOH and Na2C03 solution, with at least one alumino-silicate material that can be alkali-activated and at least one waste glass selected from urban waste glass, industrial waste glass or any of the mixtures of same, in which the percentage by weight of waste glass in the alkali cement is between 20% and 80%. The invention also relates to the resulting cement and to the use thereof in the production of concrete and/or prefabricates.

Description

PROCEDURE FOR THE MANUFACTURE OF ALKALINE CEMENTS FROM URBAN AND INDUSTRIAL VITREOS WASTE

Field of the Invention

The present invention relates to the field of construction, and more specifically, to the manufacturing sector of cement, concrete and prefabricated.

Background of the invention

In the last year (2010) world cement production

Portland exceeded 2,000 million tons, which is more than 300 kg per inhabitant of the planet; being the second product, after water, more consumed by man; In addition to being the essential component of the concrete used in construction. The development of these Portland cement concretes has been one of the fundamental pillars in the progress achieved in Western countries during the twentieth century.

The manufacture of Portland cement implies an important consumption of thermal and electrical energy, since very high temperatures (~ 1500 ° C) are required to complete all the chemical reactions that lead to the formation of the Portland cement clinker; as well as the grinding processes of raw materials and final cement components. Due to the improvements introduced in the factories, the specific energy required has been significantly reduced in recent years. Between 1973 and 1988 the specific energy needed to produce clinker decreased from 4750 MJ / t of clinker to 3750 MJ / t. Since then, the specific energy has remained more or less constant. Additionally, the cement industry is also a highly polluting industry, as it exploits natural resources (quarries) and emits a large amount of polluting gases into the atmosphere (CO ₂ , SO ₂ , NO _x ). The CO ₂ emissions are associated mainly to the decarbonation of limestone, which is the major constituent of the cement raw material (exceeding 60% of the total emission). The remaining gases Pollutants are emitted during the combustion of fossil fuels used in cement plants. Globally, between 5-7% of CO ₂ are due to the cement sector. If the growth of world cement production remains at current rates, it is estimated that in the first quarter of the 21st century CO ₂ emissions from the cement industry could reach 3.5 billion tons, a value similar to the total amount which is currently broadcast in Europe (including transport, energy industry, etc.).

Therefore, the study and development of alternative construction materials to traditional Portland cements, in whose manufacture no polluting gases are emitted and an appreciable energy saving is obtained, constitutes a research line of great scientific and technological interest worldwide. Among these alternative materials are those that come from the alkaline activation of industrial by-products such as blast furnace slag and / or fly ash. These cements are obtained by mixing said residues and alkaline solutions. These new cements are characterized by low hydration heats, high mechanical performance, and good durability against different aggressive chemicals (acidic, sulphate, etc.), and do not require the high energy consumption that are inherent to the process of elaboration. Portland cement manufacturing.

However, the alkaline activators that favor the formation of materials with greater mechanical resistance and better durable behavior are hydrated alkali silicates (Me ₂ 0 ^« mS i0 ₂ · ηΗ ₂ θ; Me = Na or K), called" waterglass ", which are synthetic materials, obtained through economically expensive and highly polluting processes. One way to improve the economic and ecological balance of alkaline cements would be to find substitutes (total or partial) of these alkaline activators, and in this line the present invention is framed, in which it is demonstrated that urban and industrial vitreous residues can be valid substitutes for these alkaline solutions of "waterglass" as activators in the preparation of alkaline cements. This is because vitreous residues, due to their chemical composition based primarily on S1O ₂ (65-75%) and Na ₂ Ü (12-15%), are potential alkaline activators of the "waterglass" family.

Urban vitreous waste collected in Spanish and European cities is not 100% recycled. Between 40-60% of the waste is not reused, either because these are covered with other ceramic and / or metallic materials; well because they are very fine granulometric fractions; due to inadequate chemical composition, or due to problems associated with the color of the glass, etc. These rejections occur because these anomalies can alter the conventional glass manufacturing processes. However, these wastes would be suitable for incorporation into the final composition of the new alkaline cements; enabling its reuse.

The collection and management of glass waste is an environmental policy with a growing implementation in developed countries. In the United States, 12.5 million tons of vitreous waste are generated annually, of which only 20% is recycled. In 2008, around 1 million tons of glass were collected in Spain, of which 60% were recycled. However, although it tends to collect and classify urban and industrial vitreous waste according to its type, the truth is that these residues contain glass with various chemical compositions (flat glass, with and without color, with ceramic or metal coatings, etc.) , which hinders its reuse, when mixed, in conventional technological processes. In the European Union between 2-6% of vitreous residues are in this form of mixing, and in Russia it amounts to 6-10%.

All existing mixed glass waste recycling technologies include an operation of crushed The fragments obtained (fraction 1-8 rom) can be used as additional components (aggregates) in the preparation of mortars and concrete. However, this practice is limited because in the opinion of some authors (CD Johnston (2000), Journal of Testing and Evaluation, 2

(85), pp. 344-350) alkali-silica reaction processes can occur that can decrease the dimensional stability of concrete, affecting its strength and durability very negatively. However, some authors (M. Jin, et al. (2000), ACI Structural Journal, 97 (2), pp. 208-213) openly disagree with this interpretation; and even other researchers have shown that the replacement of 20% of the cement with vitreous residues in the preparation of concrete induces improvements in the mechanical properties and durability of the concrete (chloride permeability and ice-thaw cycles). In a very recent work C. Shi (C. Shi (2009), Journal of Materials in Civil Engineering, 21 (10), pp. 529-534) demonstrates that the expansion in concretes with vitreous aggregates is due to the formation of a Hydrated calcium-sodium silicate (NCSH) expansive around the glass particles, from the dissolution and precipitation in basic medium of the sodium-calcium glasses themselves, and not to the interaction between the glass particles and the cement alkalis.

Mixed vitreous waste, in powder form

(Hardly reusable in glass manufacturing processes) can be reused in the construction sector, through the following applications:

1. Pozzolanic additions in the preparation of Portland cements (C. Shi, et al. (2005), Cement and Concrete

Research, 35 (5), pp. 987-993);

2. Preparation of vitroceramic composites together with other industrial waste or by-products, such as fly ash and slag, ceramic waste, etc. In this case the sintering takes place between 850-1100 ° C (F.

Andreola, et al. (2008), Ceramics International 34, pp. 1289-1295);

3. Preparation of polymer matrix composites (pavements for vehicles and pedestrians) (WH Chester (1992), Utilization of Waste Materials in Civil Engineering Construction, pp. 296-307);

4. Main component for the production of foamed glass in the production of heat-insulating materials. This process requires temperatures between 630 and 850 ° C (A.V. Gorokhovski, et al. (2005), Waste Management 25, pp. 733-736);

5. Raw material to synthesize solid sodium silicates and / or purified silica.

In the patent literature, US 6344081 describes a concrete comprising cement and recycled glass particles. On the other hand, US2005 / 0055069 describes a process of producing concrete from recycled glass, where said concrete comprises 25-79% by weight of glass; 8-35% by weight of cement and up to 22% by weight of an inhibitor of the alkali-silicon dioxide reaction.

These applications have some important problems in practice. On the one hand, the industries involved (cement and concrete preparation) must change their conventional process by introducing new raw materials, and in some cases these changes are not valued positively (applications 1 and 3). Applications 2 and 4 involve high energy consumption, which increases production costs. In addition, the manufacturing process of foamed glass entails an important emission of CO ₂ into the atmosphere.

On the other hand, there is currently a great interest in the construction sector to develop new cements and construction materials, whose manufacturing implies lower energy consumption and lower emissions of pollutant gases into the atmosphere (mainly CO ₂ ), than cement manufacturing Conventional Portland One of the lines of research is to obtain new cements that lack clinker. These cements are obtained by mixing amorphous silico-aluminates such as blast furnace slags, fly ash, metacaolin or volcanic rocks, or binary and ternary mixtures of these, with strongly dissolved solutions. alkaline (NaOH, Na ₂ C03 or hydrated alkali silicates) (F. Puertas (1995), Building Materials, vol. 45 (239), pp. 53-66). Numerous works have confirmed the good mechanical properties (A. Fernández-Jiménez, F. Puertas, JG Palomo (1999), Cement and Concrete Research, vol. 29, pp. 593-604) and durable (F. Puertas, et al. (2009), Cement and Concrete Composites, vol. 31, pp. 277-

284) that present these cements, mortars and alkaline concretes, as well as their high thermal resistance (C. Shi (2003), Advances in Cement Research, vol. 15 (2), pp. 77-81), being in many cases superior to that of conventional Portland cement.

KR 2010037889 describes a cement manufacturing process comprising the use of recycled glass particles and fly ash, as well as an activating agent that can consist of NaOH, where the mixture is subsequently subjected to a curing process. Also, GB 2362643 describes a "green" cement formed from a mixture of pulp ash from paper waste (60-70% weight) and glass waste (30-40% weight).

Studies on these alkaline cements and concretes (A. Fernández-Jiménez, F. Puertas, JG Palomo (1999), Cement and Concrete Research, vol. 29, pp. 593-604) have shown that the most determining factor, since the resistant point of view is the nature of the alkaline activator; being the solutions of hydrated sodium silicate ("waterglass") those that give the cementitious material the greatest mechanical resistance. Taking into account that urban vitreous wastes are amorphous materials with a chemical composition based on Si0 ₂ (65-75%), CaO (6-12%), Na ₂ 0 (12-15%), A1 ₂ 0 ₃ (0.5 -5%) and Fe ₂ 0 ₃ (0.1-3%), one might think that these materials could be potential alkaline activators (of the "waterglass" family) of high furnace glass slag and / or fly ash or other aluminosilicates.

Description of the invention

It is a first object of the invention a process for the manufacture of alkaline cements from urban and industrial vitreous waste, among other components. These components can consist of slag vitreous blast furnace, fly ash or other silico-aluminous materials that can be activated alkaline. In addition, alkaline solutions of the NaOH and / or NaOH + Na ₂ C0 _{3 type will also be used} .

Likewise, it is a further object of the invention to use said alkaline cements to prepare the corresponding concretes.

Thus, the invention relates to a new process for the manufacture of alkaline cements based on the use of new raw materials (vitreous residues). Likewise, said procedure has the advantage, compared to other processes of the state of the art, of being carried out from an activation system not only chemical, but also mechanical-chemical. Said mechanochemical activation system is especially advantageous, since it is a much more effective system from the point of view of the resistant development of cement and concrete pastes.

Therefore, as a consequence of the use of vitreous residues as the raw material of the process, it is possible to replace the solutions of hydrated sodium silicate (called "waterglass") commonly used in the art; solutions that give cements and alkaline concrete the greatest resistance, but are obtained through costly and ecologically costly processes. In this way, the present invention is capable of providing obvious economic and ecological advantages associated with the final product, but also related to the recovery or recovery of a waste (urban or industrial vitreous waste) not reusable in conventional glass manufacturing processes.

Brief description of the figures

FIG. the sample the results of compressive strength as a function of the vitreous / slag residue ratio blast furnace glass under chemical activation with a NaOH / Na ₂ C0 ₃ solution for 7 days;

FIG. Ib shows the results of flexural strength as a function of the vitreous residue / slag vitreous blast furnace ratio subjected to chemical activation with a NaOH / Na ₂ C0 ₃ solution for 7 days;

FIG. shows the results of compressive strength as a function of the vitreous residue / slag vitreous blast furnace ratio subjected to chemical activation with a solution of NaOH / Na ₂ CC> 3 for 90 days;

FIG. Id shows the results of flexural strength as a function of the vitreous residue / slag vitreous blast furnace ratio subjected to chemical activation with a solution of NaOH / Na ₂ CC> 3 for 90 days;

FIG. 2a shows the results of compressive strength as a function of the vitreous residue / slag vitreous blast furnace ratio subjected to mechanochemical activation with a solution of NaOH / Na ₂ CC> 3 for 7 days;

FIG. 2b shows the results of flexural strength as a function of the vitreous residue / slag vitreous blast furnace ratio subjected to mechanochemical activation with a solution of NaOH / Na ₂ CC> 3 for 7 days;

FIG. 2c shows the results of compression resistance as a function of the vitreous residue / slag vitreous blast furnace ratio subjected to mechanochemical activation with a solution of NaOH / Na ₂ CC> 3 for 90 days;

FIG. 2d shows the results of flexural strength as a function of the vitreous residue / slag vitreous blast furnace ratio subjected to mechanochemical activation with a solution of NaOH / Na ₂ CC> 3 for 90 days;

FIG. 3 shows the solubility of S1O ₂ in White glass water and the effect of the particle size of the glass;

FIG. 4 shows the results of chemical activation at T ^at room. Specifically, it shows the solubility of S1O ₂ of the four glasses in the three media (¾0, NaOH and NaOH / Na ₂ C0 ₃ );

FIG. 5 shows the solubilities in the low glass the conditions of chemical activation with temperature (80 ± 2 ° C) and chemical activation at room temperature (22 ± 2 ° C): FIG 5a in NaOH solution and FIG. 5b in NaOH / Na ₂ C0 ₃ solution.

FIG. 6 shows the differences in solubility between the three activation processes for the Topaz and Mixture glasses in the NaOH / Na ₂ C0 ₃ solution.

Detailed description of the invention

It is therefore a first object of the invention a process for the manufacture of alkaline cements by reusing urban and / or industrial vitreous waste in its composition.

Cement preparation conditions are described below:

It is called M: Material or mixture of materials capable of being activated alkaline (preferably selected from blast furnace slags, fly ash, metacaolin, or any other natural or artificial material of silico-aluminous composition), D: Alkaline solution (preferably selected from NaOH or NaOH and Na ₂ COs); V: Vitreous residue and A: Aggregates.

Although the composition of these vitreous residues may vary according to the origin and type of vitreous residue selected, in general, the composition of the vitreous residues may comprise Si0 ₂ (65-75%), CaO (6- 12%), Na ₂ 0 (12-15%), A1 ₂ 0 ₃ (0.5-5%) and Fe ₂ 0 ₃ (0.1-3%).

In a particular embodiment, said composition may comprise Si0 ₂ (72.04%), A1 ₂ 0 ₃ (1.62%), Fe ₂ 0 ₃ (0.27%), MgO (3.39%), CaO (8.19%), Na ₂ 0 ( 12.11%), K ₂ 0 (2.32%), Ti0 ₂

(0.04%), P ₂ 0 ₅ (0.02%), Cr (179 ppm), Ba (67 ppm) and Pb (6 ppm).

Thus, the process object of the invention is characterized in that it comprises mixing at least one silico-aluminous material capable of being alkaline activated and at least one alkaline activator consisting of at least one vitreous residue selected from urban vitreous residues and vitreous residues industrial, or any of its mixtures, where the percentage by weight of vitreous residue in the alkaline cement is between 20% and 80%, and more preferably between 50% and 80%. Additionally, at least one alkaline solution of pH greater than 13 is added to the mixture, wherein said solution is preferably selected from a solution of NaOH and a solution of NaOH and Na2C03.

In a particular embodiment of the invention, the mixing and homogenization of the silico-aluminous material capable of being alkalinely activated (M) and of the vitreous residue (V) can be carried out mechanically (for example, by turbo), for at least 2 hours .

In another particular embodiment of the invention, the process may comprise a previous additional step of treating the vitreous residue (V) with the alkaline solution of pH> 13 at a temperature preferably between 78 and 82 ° C. In this case, after 2 h of interaction, you can proceed to filter and collect the liquids, which can be used as a kneading liquid with the silico-aluminous material capable of being activated alkaline (M). In this case, the best results have been obtained in those embodiments in which the alkaline solution consists of a solution of NaOH and Na ₂ CÜ3 and the size of the glass particles is less than 45 um.

In a further particular embodiment of the invention, once the mixture of the alkaline solution is homogenized, with the material capable of being alkaline activated and at least one vitreous residue, chemical activation thereof can be carried out. This chemical activation can be carried out by direct addition to the mixture of the silico-aluminous material capable of being alkalinely activated (M) and the vitreous residue (V) of at least one alkaline solution (D), preferably selected from a solution of NaOH (preferably a strongly basic solution with a pH greater than 13, and more preferably pH = 13.19) and a NaOH / Na ₂ C03 solution (in the same way, with a pH preferably greater than 13, and more preferably pH = 13.29) in an equivalent concentration preferably comprised between 3% and 20% Na ₂ Ü over 100% of the silico-aluminous material capable of being alkaline activated (M). In each case, it will be necessary to determine the optimal liquid / solid ratio to achieve adequate runoff or consistency.

After the chemical activation of the mixture, it can proceed to cure it. The temperature at which said curing stage is carried out depends on the nature of the material capable of being alkaline activated, and may vary between room temperature (between 20 ° C and 25 ° C, and more preferably between 20 and 22 ° C) or a higher temperature, preferably between 65 ° C and 85 ° C, and more preferably between 78 ° C and 82 ° C. The first case is preferably carried out when the silico-aluminous material comprises calcium-rich silico-aluminates (for example, blast furnace vitreous slags) and the second, when it comprises calcium-poor silico-aluminates (such as ashes flyers). The mortar preparation of these cements can be carried out, preferably, under equal conditions to those described in the European cement standard EN 197-1.

In another particular embodiment of the invention, prior to the preparation of the mixture of the silico-aluminous material capable of being alkaline activated (M) and the vitreous residue (V), the vitreous residue (V) can be subjected to a process grinding, preferably in ball mill. Said milling can be carried out in such a way that for each gram of vitreous residue (V) between 5 ml and 20 ml of at least one alkaline solution (D) is added, preferably selected from a NaOH solution (preferably of pH higher than 13, and more preferably of pH = 13.19) and a solution of NaOH / Na ₂ C0 ₃ (preferably of pH greater than 13, and more preferably of pH = 13.29) in an equivalent concentration preferably comprised between 3% and 20% of Na ₂ 0 over 100% of the silico-aluminous material capable of being alkaline activated (M). Grinding times can preferably vary between 2 and 6 h, until reaching an average final particle size preferably less than 90 um. In this case, therefore, the activation of the mixture consists of a mechanochemical activation (as opposed to the chemical activation of the previous embodiment).

In this particular embodiment of mechanochemical activation, once a vitreous residue suspension (V) - alkaline solution (D) is obtained, the material capable of being alkaline activated (M) is added (preferably, a mixture of silico- aluminates) to form mixtures with the corresponding proportions. As in the case of chemical activation, the ratio of silico-aluminous material / vitreous residue in said mixtures is between 80/20 and 20/80, and more preferably between 70/30 and 30/70.

It has been shown that mechanochemical activation at room temperature (between 20 ° C and 24 ° C) is slightly more effective than chemical activation at room temperature for long stirring times (above 6 hours). The highest Si solubility of the glasses, under these activation conditions, is obtained when the alkaline solution is NaOH / Na ₂ C03. It has also been shown that, when the particle size of the glass is less than 45 μπι, it is when the greatest solubilities of S1O _{2 are obtained} . It has also been proven that the chemical activation of vitreous residues with temperature (80 ± 2 ° C) is the one that induces the most solubility of the glass.

Subsequently, the process of kneading, compacting and curing the specimens can be carried out under equal conditions to those described in the chemical activation, that is, under equal conditions to those described for the European cement standard EN 197-1.

In a further particular embodiment of the invention, the process may also comprise the addition of siliceous or calcareous aggregates (A), preferably in an A / M ratio between 1/1 and 4/1. Thus, the use of the cements described for the preparation of the corresponding concretes is a further object of the invention. The Manufacture of these concretes can be carried out following the recommendations of the regulations and prescriptions of each country; in the case of Spain, following EHE-08.

In all the processes described above, special care must be taken with the management of vitreous residues, as well as with strongly alkaline solutions. Examples

A series of examples are given below by way of illustration and with no limitation of the present invention:

Example 1

In this first example, an alkaline cement was prepared according to the process object of the invention, as previously described.

For this, different vitreous residue / vitreous slag mixtures from high kiln (BFS) (from 30/70 to 100/0) were prepared, with the following chemical composition (in percentage by weight):

Table 1. Chemical composition of vitreous slag from blast furnace (BFS

(% in weigh)

Table 2. Chemical composition vitreous residue (% by weight)

Then, to these mixtures was added in a manner direct an alkaline solution NaOH / Na2CC> 3 of pH = 13.29, in a concentration equivalent to 5% Na2Ü over 100% slag in the mixture. The liquid / solid ratio remained constant at 0.4. The preparation of the pastes was done manually and the paste obtained was poured into 1x1x6 cm molds. The samples were cured in a humidity chamber at 22 ± 2 ° C and a relative humidity of 99%. The mechanical behavior of the mixtures at 7 and 90 days of curing is shown in Fig. 1. As a reference medium, a mixture of glass furnace slag (without ceramic residue) activated with the same activating solution at the same concentration was used, and with equal conditions of preparation and curing of pasta.

In Fig. 1, the 0/100 mixture is the paste without vitreous residue. As can be seen, comparable resistance is obtained when the slag content is 60 or 80%.

Example 2

In this second example, prior to preparing the vitreous residue / vitreous slag mixtures of blast furnace, this residue was subjected to a milling process in a ball mill. This grinding was carried out in such a way that for each gram of waste there were 100 g of balls in the ground, with differentiated granulometry. In addition, for each gram of vitreous residue, 10 ml of the alkaline solution (NaOH / Na ₂ C03 pH = 13.29, 5% Na2Ü per slag mass) was added, with the same concentration as described above. In all cases the particle size of the vitreous residue was always less than 45 um. The grinding times were: 10 min, 2h, 4h and 6h.

With the resulting alkaline glass-solution suspensions, at each grinding time, the blast furnace slag was added to form the mixtures with the corresponding proportions (30/70 to 100/0). The liquid / solid ratio remained constant at 0.4. Subsequently, the process of kneading, compacting and curing the specimens was carried out under equal conditions to those described in the chemical activation. In all cases, the mechanical resistance to bending and compression was determined at 7 and 90 days of curing.

The results show that 50/50 mixtures develop greater compressive strengths than those without vitreous residues (0/100 mixtures).

Example 3

In this example, four different types of vitreous residues were selected: white, green, topaz and unmanaged mixture. These materials were characterized through the FRX technique. Table 3 shows the chemical composition of these glasses when their particle size is less than 45 um.

Table 3. Chemical composition of the four glasses used for a size less than 45 um (% by weight)

To assess the mechanism and the kinetics of solubility of the glasses in strongly basic media, three different activation methods have been used:

a) Chemical activation ^{at room} temperature (22 ± 2 ° C);

b) Chemical activation at high T ^at (80 ± 2 ° C);

c) Mechanochemical activation (in the ball mill ^{at room} temperature, 22 ± 2 ° C).

For each of the activation processes they have Considering the following variables or conditions:

Nature of the glass: 4 different, nature of the activating solution: water (pH = 7, as a reference), a solution of NaOH (pH = 13.6) and a mixed solution of NaOH / Na ₂ CC> 3 (pH = 13.8), the concentration of both solutions being 4 M; glass particle size: 45, 90 and 125 um, and stirring time: 10 min, 2, 4 and 6 h.

The chemical activation process at T ^{at room} temperature (22 ± 2 ° C) consisted of magnetic stirring by means of a magnet at a constant and equal stirring speed for all cases. The solid: liquid ratio was 1: 100.

In the process of chemical activation at high T ^at (80 ± 2 ° C) the system used was identical to the previous one, with the difference that a water bath was applied to the chemical agitation so that it could reach and maintain the desired temperature during the process.

The mechanical-chemical activation process was carried out in a steel ball mill, where the ratio of the size and number of balls to the amount of solid and liquid added is important in the dissolution of the glass. The best results were obtained with 5g of solid in 500mL of solution and with a quantity of lkg balls (with balls of different sizes).

After each of the processes and times, the Si content was filtered and analyzed by ICP, in the liquids obtained, in order to determine the percentage of S1O ₂ dissolved in the glasses. The equipment used was an inductively coupled plasma atomic emission spectrometer (ICP) of the VARIAN 725-ES brand.

Results and Discussion

Chemical activation at T ^at room (22 ± 2 ° C)

All glasses react with water, so consider a mechanism for interaction with water. In contact with the aqueous medium, what happens is an exchange of sodium ions for hydronium ions. Hydronium ions are present in water in equilibrium with OH- ions, so This exchange is what causes the material to dissolve. As can be seen in Figure 3, as the agitation time increases, the solubility of the silicon oxide in the glass increases, regardless of the size of its particles. However, when the size of the glass particles is less than 45 um, it is when the greatest solubility is obtained.

On the contrary, when the glass is in contact with a strongly alkaline solution, the mechanism is different and is governed by the OH- groups of the base. The reaction of the glass with the OH- groups always causes the rupture of the Si-O bonds, with the consequent partial destruction of the network. It can be said that the attack of glass in basic medium is a depolymerization process, where the total destruction of the network and the slow dissolution of the glass occurs [J.M. Fernandez Navarro "Glass". Superior Council of Scientific Investigations. Spanish Society of Ceramics and glass. Madrid, 2003]. This process induces a greater solubility of the glass than in aqueous media.

Figure 4 shows the solubility of the four glasses in the three media (H20, NaOH and NaOH / Na ₂ C03) for a size less than 45 um. Table 4 compares the% of dissolved S1O ₂ , for the four glasses, after treatment for 6 hours in water and with the NaOH and NaOH / Na ₂ C0 ₃ solutions.

The results obtained confirm the greater solubility of Si in alkaline media. With the NaOH solution, this solubility is, depending on the nature of the glass, between 16 and 43% higher than in water. When the pH of the solution is slightly increased (as in the case of the NaOH / Na ₂ C03 mixture solution with respect to that of NaOH), the amount of S1O ₂ extracted increases markedly due to the destruction of the network due to the breakage of the the Si-O-Si links. The difference between both alkaline solutions is significant, obtaining a solubility between 12-53% higher when the solution used is that of NaOH / Na ₂ C03. The Higher solubility of the glass was obtained with the Topaz colored glass (Table 4).

Table 4. Solubility of Si0 ₂ (%) after 6 hours of stirring in the three media (H ₂ 0, NaOH and NaOH / Na ₂ C0 ₃ ) for a size <45 um (B = White;

V = Green; T = Topaz; M = Mix)

From the results obtained in the chemical activation process, the Topaz and Mixture vitreous residues were selected for subsequent studies of high temperature chemical activation and mechanochemical activation.

Chemical activation at high T ^at (80 ± 2 ° C)

As in the previous process ^at room T, the particle size of the glass is also a relevant factor, the higher solubilities and glass are obtained when the particle size thereof is less than 45 μπι. However, the effect of the nature of the alkaline solution does not appear to be as relevant as in the T solubility tests ^at ambient. At 80 ± 2 ° C, very similar dissolved S1O ₂ values are obtained for both glasses and with the two alkaline solutions (Figure 5). However, the NaOH / Na ₂ CC> 3 mixture solution is the one that behaves somewhat better, dissolving between 5 and 14% more S1O ₂ in the Topaz and Mixture glasses, respectively. In this test under temperature values of dissolution percentages around 60% of total S1O _{2 were obtained.} the glasses. These results show that temperature is a very important variable in the process of dissolving glasses (see Figure 5). Comparing for the Mixture glass, the solubility of S1O ₂ at T ^{at room} temperature with the NaOH / Na ₂ C03 solution was 1.7%, while at 80 ± 2 ° C it was 56%.

Mechanochemical activation (22 ± 2 ° C)

Mechanochemical activation is slightly more effective than chemical activation at room temperature for long stirring times (above 6 hours) (see Figure 6). The highest Si solubility of the glasses, under these activation conditions, was obtained when the alkaline solution was NaOH / Na ₂ C03. As in the other tests, when the particle size of the glass was less than 45 um, it is when the highest solubilities of SIO ₂ were obtained. The results obtained through this test allowed to know the amount of silicon that can be dissolved when preparing pasta specimens (ash / slag / kaolin + glass + alkaline activating solution), since these tests are done under a mixer , which is still a mechanochemical activation.

The above tests show that the best results are obtained when the activation is carried out with NaOH / NaC03 and the activated mixture is subjected to a heat treatment at a temperature between 78 and 82 ° C.

Claims

1. Process for the manufacture of alkaline cements characterized in that it comprises mixing an alkaline solution of pH greater than 13, where said solution is selected from a solution of NaOH and a solution of NaOH and Na ₂ CC> 3, with at least one material silico-aluminous susceptible to be activated alkaline and at least one vitreous residue selected from urban vitreous and industrial vitreous wastes, or any of their mixtures, where the percentage by weight of vitreous residue in alkaline cement is between 20% and 80 %.

2. Method according to claim 1, wherein the alkaline solution of pH greater than 13 is added directly on a homogeneous mixture of the silico-aluminous material and the vitreous residue, resulting in a chemical activation of the mixture.

3. Method according to claim 1, characterized in that it comprises a previous additional step of treating the vitreous residue with the alkaline solution at a temperature preferably between 78 and 82 ° C.

4. Method according to claim 3, wherein after 2 h of interaction between the vitreous residue and the alkaline solution, the filtrate is filtered and collected, said liquids being used as a kneading liquid with a silico-aluminous material selected from slag and / or fly ash.

5. Method according to any one of the preceding claims, wherein after the chemical activation, a curing step of the mixture is carried out.

6. Method according to claim 5, wherein said curing is carried out at room temperature between 20 ° C and 25 ° C, or at a temperature between 65 ° C and 85 ° C.

7. A method according to claim 1, wherein prior to the mixing of the silico-aluminous material capable of being alkaline activated and of the vitreous residue, a milling step of the vitreous residue with the higher pH alkaline solution is carried out at 13, followed by the subsequent mixing of the vitreous residue and the alkaline solution of pH higher than 13 with the silico-aluminous material capable of being alkaline activated, resulting in a mechanochemical activation of the mixture.

8. The method according to claim 7, wherein for each gram of vitreous residue, between 5 ml and 20 ml of the alkaline solution of pH greater than 13 is added.

9. A method according to claim 7 or 8, wherein the grinding is carried out for a time between 2 h and 6 h, until an average final particle size of the vitreous residue of less than 90 um is reached.

10. Method according to any one of the preceding claims, wherein the alkaline solution is used in an equivalent concentration between 3% and 20% Na ₂ Ü over 100% of the silico-aluminous material capable of being alkaline activated.

11. Method according to any one of the preceding claims, wherein the vitreous residue comprises, in percentage by weight, between 65% and 75% of S1O ₂ , between 6% and 12% of CaO, between 12% and 15% of Na ₂ 0, between 0.5% and 5% of AI2O3 and between 0.1% and 3% of Fe ₂ 0 ₃ .

12. Method according to any one of the preceding claims, wherein the silico-aluminous material is selected from a group consisting of vitreous slag from blast furnace, fly ash and metacaolin, as well as any combination thereof.

13. Method according to any one of the preceding claims, characterized in that it comprises a subsequent step of aggregate addition.

14. Method, according to claim 13, wherein said aggregates are selected from siliceous aggregates and calcareous aggregates and wherein said aggregates are added in an aggregate / silico-aluminous material ratio capable of being alkaline activated between 1/1 and 4 / one.

15. Alkaline cement obtainable from a process according to any one of the preceding claims.

16. Use of an alkaline cement according to claim 15 for the manufacture of concrete and / or prefabricated.