ES2394979B1 - PROCEDURE FOR THE MANUFACTURE OF ALKALINE CEMENTS FROM URBAN AND INDUSTRIAL VITREOUS WASTE. - Google Patents

Abstract

Process for the manufacture of alkaline cements from urban and industrial vitreous waste # The present invention relates to a 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 among a solution of NaOH and a solution of NaOH and Na {sub, 2} CO {sub, 3}, with at least one silico-aluminous material capable of being activated alkaline and at least one vitreous residue selected between urban vitreous waste and vitreous waste industrial, or any of their mixtures, where the percentage by weight of vitreous residue in the alkaline cement is between 20% and 80%. Another object of the invention is the cement obtained from said process and its use in obtaining concrete and / or prefabricated.

Description

Procedure for the manufacture of alkaline cements from urban and industrial vitreous waste.

Field of the invention

The present invention relates to the field of construction, and more specifically, to the sector of manufacture of cements, concretes and prefabricated. 5

BACKGROUND OF THE INVENTION

In the last year (2010) the world production of Portland cement 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; besides 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 10th century.

The manufacture of Portland cement involves a significant consumption of thermal and electrical energy, since very high temperatures (~ 1500 ° C) are required for all the chemical reactions that lead to the formation of the Portland cement clinker to be completed; as well as the grinding processes of the raw materials and the final cement components. Due to the improvements introduced in the factories, the specific energy required has been significantly reduced 15 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, since it exploits natural resources (quarries) and emits a large amount of polluting gases into the atmosphere (CO2, SO2, NOx). CO2 emissions are associated, fundamentally, with decarbonation of limestone, which is the main constituent of cement 20 (exceeding 60% of total emission). The remaining polluting gases are emitted during the combustion of fossil fuels used in cement plants. Globally, between 5-7% of CO2 emissions are due to the cement sector. If the growth of global cement production is maintained at the current rates, it is estimated that in the first quarter of the 21st century CO2 emissions from the cement industry could reach 3,500 million tons, a value similar to the total amount that it is currently broadcast in Europe (including transport, 25 energy industry, etc.).

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

However, the alkaline activators that favor the formation of materials with greater mechanical resistance and better lasting behavior are the hydrated alkali silicates (Me2O • mSiO2 • nH2O, Me = Na or K), called "waterglass", which are synthetic materials, obtained through costly 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 that line the present invention is framed, in which it is demonstrated that urban and industrial vitreous waste can be substitutes Valid of these alkaline solutions of "waterglass" 40 as activators in the preparation of alkaline cements. This is due to the fact that vitreous waste, due to its chemical composition based mainly on SiO2 (65-75%) and Na2O (12-15%), are potential alkaline activators of the "waterglass" family.

The urban vitreous waste collected in Spanish and European cities is not 100% recycled. It is not reused between 40-60% of the waste, either because these appear coated with other materials of ceramic and / or metallic type; well 45 because they are very fine granulometric fractions; by an inadequate chemical composition, or by problems associated with the color of the glass, etc. These rejections occur because these anomalies can alter conventional glass manufacturing processes. However, these residues 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 an increasing implementation in the 50 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% was recycled. However, although there is a tendency to collect and classify the urban and industrial vitreous waste according to its type, the truth is that these residues contain glasses with different chemical compositions (flat glass, with and without color, with ceramic or metallic coatings, etc.) , which makes it difficult to reuse them, when they are mixed, in the 55

conventional technological processes. In the European Union between 2-6% of vitreous waste is in this form of mixing, and in Russia it amounts to 6-10%.

All existing recycling technologies for mixed glass waste include a shredding operation. The fragments obtained (fraction 1-8 mm) can be used as additional components (aggregates) in the preparation of mortars and concretes. However, this practice is limited since in the opinion of some authors (CD Johnston 5 (2000), Journal of Testing and Evaluation, 2 (85), pp. 344-350) can occur alkali-silica reaction processes that can decrease the dimensional stability of concrete, affecting very negatively its strength and durability. 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 by vitreous waste in the preparation of concrete induces improvements in the mechanical properties and in the durability of concrete 10 (permeability to chlorides 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 aggregate is due to the formation of a Calcium-sodium hydrated silicate (NCSH) expansive around the glass particles, coming 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 alkalis of the cement. fifteen

 Mixed vitreous waste, in the form of powder (hardly reusable in glass manufacturing processes) can be reused in the construction sector, through the following applications:

1. Pozzolanic additions in Portland cement preparation (C. Shi, et al. (2005), Cement and Concrete Research, 35 (5), pp. 987-993);

2. Preparation of glass-ceramic composites together with other waste or industrial by-products, such as fly ash and slags, 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) (W.H. Chester (1992), Utilization of Waste Materials in Civil Engineering Construction, pp. 296-307);

4. Main component for the production of foamed glass in the manufacture of thermo-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 for synthesizing 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 when introducing new raw materials, and sometimes these changes are not positively valued (applications 1 and 3). Applications 2 and 4 involve high energy consumption, which increases production costs. In addition, the process of manufacturing the foamed glass leads to an important emission of CO2 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 manufacture implies lower energy consumption and lower emissions of polluting gases into the atmosphere (mainly CO2), than the manufacture of Portland cement. conventional. One of the 40 lines of research is to obtain new cements that lack clinker. These cements are obtained by the mixture of amorphous silico-aluminates such as high furnace slag, fly ash, metakaolin or volcanic rocks, or binary and ternary mixtures of these, with strongly alkaline solutions (NaOH, Na2CO3 or hydrated alkali silicates) (F. Puertas (1995), Construction 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 45 durables (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 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 which may consist of NaOH, where the mixture is subsequently subjected to a curing process. Likewise, GB 2362643 describes a "green" cement formed from a mixture of pulp ash from paper waste (60-70% by weight) and from glass waste (30-40% by weight).

The studies carried out on these cements and alkaline concretes (A. Fernández-Jiménez, F. Puertas, J.G. Palomo

(1999), Cement and Concrete Research, vol. 29, pp. 593-604) have shown that the most determining factor, from the resistant point of view, is the nature of the alkaline activator; being the solutions of hydrated sodium silicate ("waterglass") those that confer to the cementante material the greater mechanical resistances. Taking into account that urban vitreous waste is amorphous material with a chemical composition based on SiO2 (65-75%), CaO (6-12%), Na2O (12-15%), Al2O3 (0.5-5%) and Fe2O3 (0.1-3%), one might think that these materials could be potential alkaline activators (from the "waterglass" family) of high-kiln vitreous 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 may consist of high kiln vitreous slag, fly ash or other silico-aluminous materials capable of being activated alkaline. In addition, alkaline solutions of the NaOH and / or NaOH + Na2CO3 type are also to be used.

Also, it is a further object of the invention the use of 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 waste). Likewise, said method has the advantage, compared to other processes of the state of the art, of being carried out from a system of activation not only chemical, but also mechano-chemical. This mechano-chemical activation system is especially advantageous, as it is a much more effective system from the point of view of the resistant development of the pastes of cements and concretes.

Therefore, as a result of the use of the glassy residues as raw material of the process, it is possible to replace the solutions of hydrated sodium silicate (so-called "waterglass") commonly used in the art; solutions that give the cements and alkaline concretes the greatest resistance, but that are obtained through costly energy and ecology processes. Thus, 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. 25

Brief description of the figures

FIG. 1a shows the results of compressive strength as a function of the ratio vitreous residue / vitreous slag of high furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 7 days;

  FIG. 1b shows the results of flexural strength as a function of the vitreous residue / vitreous slag ratio of the high furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 7 days; 30

FIG. 1c shows the results of compressive strength as a function of the ratio vitreous residue / vitreous slag of high furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 90 days;

 FIG. 1d shows the results of resistance to bending as a function of the vitreous residue / vitreous slag ratio of the high furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 90 days;

FIG. 2a shows the results of compressive strength as a function of the vitreous residue / vitreous slag ratio of a high furnace subjected to mechanical-chemical activation with a NaOH / Na2CO3 solution for 7 days;

  FIG. 2b shows the results of resistance to bending as a function of the vitreous residue / vitreous slag ratio of the high furnace subjected to mechanical-chemical activation with a NaOH / Na2CO3 solution for 7 days;

FIG. 2c shows the results of the compressive strength as a function of the vitreous residue / vitreous slag ratio of the high furnace subjected to mechanical-chemical activation with a NaOH / Na2CO3 solution for 90 days; 40

 FIG. 2d shows the results of resistance to bending as a function of the vitreous residue / vitreous slag ratio of the high furnace subjected to mechanical-chemical activation with a NaOH / Na2CO3 solution for 90 days.

Detailed description of the invention

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

The conditions of preparation of the cements are described below:

It is called M: Material or mixture of materials susceptible to be activated alkaline (preferably selected from slag of high furnace, fly ash, metakaolin, or any other natural or artificial material of silico-aluminous composition), D: Alkaline solution (preferably selected from NaOH or NaOH and Na 2 CO 3); V:

Vitreous waste and A: Aggregates.

Although the composition of these vitreous residues can vary according to the origin and type of vitreous waste selected, in general, the composition of the vitreous waste can include SiO2 (65-75%), CaO (6-12%), Na2O ( 12-15%), Al2O3 (0.5-5%) and Fe2O3 (0.1-3%).

In a particular embodiment, said composition may comprise SiO2 (72.04%), Al2O3 (1.62%), Fe2O3 (0.27%), MgO5 (3.39%), CaO (8.19%), Na2O (12.11%), K2O (2.32%). ), TiO2 (0.04%), P2O5 (0.02%), Cr (179 ppm), Ba (67 ppm) and Pb (6 ppm).

In this way, the process object of the invention is characterized in that it comprises mixing at least one silico-aluminous material capable of being activated alkaline and at least one alkaline activator consisting of at least one vitreous waste selected from urban vitreous waste and vitreous waste. industrial, or any of their mixtures, where the weight percentage 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 Na 2 CO 3.

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

Also, in a particular embodiment of the invention, once the mixture is homogenized, chemical activation thereof can proceed. This chemical activation can be carried out by directly adding to the mixture the alkali-activated alumino-silico-alumina material (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 of pH = 13.19) and a NaOH / Na2CO3 solution (in the same manner, with a pH preferably greater than 13, and more preferably pH = 13.29) in an equivalent concentration preferably comprised between 3% and 20% Na2O over 100% of the silico-aluminous material capable of being activated alkaline (M). In each case, it will be necessary to determine the optimum liquid / solid ratio to achieve proper runoff or consistency. 25

After the chemical activation of the mixture, it can be cured. The temperature at which said curing step is carried out depends on the nature of the material capable of being activated alkaline, and can vary between room temperature (20 ° C-25 ° C) or a higher temperature, preferably comprised between 65 ° C and 85 ° C. The first case is preferably carried out when the silico-aluminous material comprises calcium-rich silico-aluminates (such as high-kiln vitreous slags) and the second case when it comprises calcium-poor silico-aluminates (as, for example, Fly ash). The preparation of the mortars 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 activated alkaline (M) and of the vitreous residue (V), the vitreous residue (V) can be subjected to a process of grinding, preferably in a ball mill. Said grinding can be carried out in such a way that for each gram of vitreous residue (V) there is added between 5 ml and 20 ml of at least one alkaline solution (D), preferably selected from a solution of NaOH (preferably of higher pH to 13, and more preferably of pH = 13.19) and a NaOH / Na2CO3 solution (preferably of pH above 13, and more preferably of pH = 13.29) in an equivalent concentration preferably comprised between 3% and 20% Na2O on the 100% silico-aluminous material capable of being activated alkaline (M). The grinding times may preferably vary between 2 and 6 h, until reaching a final average particle size preferably less than 90 μm. In this case, therefore, the activation of the mixture consists of a mechanical-chemical activation (unlike the chemical activation of the previous embodiment).

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

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

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, it is additional object of the invention the use of the cements described for the preparation of the corresponding concretes. 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 the EHE-08. 55

In all the processes described above, special care should be taken with the handling of vitreous waste, as well as that of strongly alkaline solutions.

  Examples

Following are a series of examples by way of illustration and non-limiting nature of the present invention:

Example 1 5

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

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

 Table 1. Chemical composition of high furnace vitreous slag (BFS (% by weight) 10

 SiO2

 35.34 Na2O 0.01

 Al2O3

 13.65 SO3- 0.06

 Fe2O3

 0.39 S2- 1.91

 MgO

 4.11 L.O.I. 2.72

 CaO

 41.00 I.R. 0.64

Table 2. Vitreous residue chemical composition (% by weight)

 SiO2

 72.04 K2O 2.32

 Al2O3

 1.62 TiO2 0.04

 Fe2O3

 0.27 P2O5 0.02

 MgO

 3.39 Cr (ppm)

 CaO

 8.19 Ba (ppm)

 Na2O

 12.11 Pb (ppm)

 Subsequently, an alkaline solution NaOH / Na2CO3 of pH = 13.29 was added directly to said mixtures in a concentration equivalent to 5% of Na2O over 100% of slag in the mixture. The liquid / solid ratio remained constant at 0.4. The preparation of the pastes was done manually and the obtained paste was poured in molds of 1x1x6 cm. The samples were cured in a humidity chamber at 22 ± 2ºC 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 high furnace vitreous slag (without ceramic residue) activated with the same activating solution at the same concentration was used, and with the same conditions of preparation and curing of the pastes. twenty

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

Example 2

 In this second example, prior to preparing the vitreous waste / glass slag from the high furnace, this residue was subjected to a milling process in a ball mill. This milling was carried out in such a way that for every 25 grams of residue there was in the milling 100 g of balls, with differentiated granulometry. In addition, for each gram of vitreous residue, 10 ml of the alkaline solution (NaOH / Na2CO3 pH = 13.29, 5% Na2O 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 μm. The milling times were: 10 min, 2h, 4h and 6h.

 With the resultant alkaline glass-solution suspensions, at each milling time, he added the slag from the furnace 30 to form the mixtures with the corresponding proportions (30/70 to 100/0). The liquid / solid ratio is

kept constant at 0.4. Subsequently, the process of kneading, compaction and curing of the test pieces was carried out in equal conditions to those described in the chemical activation.

 In all cases, the mechanical resistance to bending and compression was determined after 7 and 90 days of curing.

 The results show that 50/50 mixtures develop higher compressive strengths than those that lack vitreous residues (0/100 mixtures). 5

Claims

Process for the manufacture of alkaline cements, characterized in that it comprises mixing an alkaline solution with a pH higher than 13, where said solution is selected from a solution of NaOH and a solution of NaOH and Na2CO3, with at least one material silico-aluminoso susceptible of being activated alkaline and at least one vitreous waste selected between urban vitreous waste and industrial vitreous waste, or any of its mixtures, where the percentage by weight of vitreous residue in the alkaline cement is between 20% and 80%. 2. Process, according to claim 1, wherein the alkaline solution of pH higher than 13 is added directly to a homogeneous mixture of the silico-aluminous material and the vitreous residue, giving rise to a chemical activation of the mixture. 3. Process, according to claim 1 or 2, wherein after the chemical activation, a step of curing the mixture is carried out. 4. Process, according to claim 3, wherein said curing is carried out at room temperature comprised between 20 ° C and 25 ° C, or at a temperature comprised between 65 ° C and 85 ° C. 5. Process, according to claim 1, wherein prior to the mixing of the alkali-activated silico-aluminous material and the vitreous residue, a step of grinding the vitreous residue with the alkaline solution is carried out. pH higher than 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 activated alkaline, giving rise to a mechanical-chemical activation of the mixture. 6. Process, according to claim 5, wherein for each gram of vitreous residue between 5 ml and 20 ml of the alkaline solution of pH higher than 13 is added. 7. Process according to claim 5 or 6, wherein the grinding is carried out for a time between 2 h and 6 h, until reaching a final average particle size of the vitreous residue below 90 μm. 8. Process, according to any one of the preceding claims, wherein the alkaline solution is used in an equivalent concentration between 3% and 20% Na2O on 100% of the silico-aluminous material capable of being activated alkaline. 25 9. Process, according to any one of the preceding claims, wherein the vitreous waste comprises, in percentage by weight, between 65% and 75% of SiO2, between 6% and 12% of CaO, between 12% and 15% of Na2O, between 0.5% and 5% of Al2O3 and between 0.1% and 3% of Fe2O3. 10. Process according to any one of the preceding claims, wherein the silico-aluminous material is selected from a group consisting of tall furnace, fly ash and metakaolin vitreous slags, as well as any of its combinations. 11. Process, according to any one of the preceding claims, characterized in that it comprises a subsequent stage of aggregate addition. 12. Process, according to claim 11, wherein said aggregates are selected from siliceous aggregates and calcareous aggregates and where said aggregates are added in an arid / silico-aluminous material ratio capable of being activated alkaline comprised between 1/1 and 4 /one. 13. Alkaline cement obtainable from a process according to any one of the preceding claims. 14. Use of an alkaline cement according to claim 13 for the manufacture of concrete and / or prefabricated.      