WO2003059844A1

WO2003059844A1 - Method of producing lightweight aggregates at a low temperature

Info

Publication number: WO2003059844A1
Application number: PCT/IB2002/000798
Authority: WO
Inventors: Oscar Hernandez Osorio; Luis Manuel Vasquez Ardila
Original assignee: Oscar Hernandez Osorio; Luis Manuel Vasquez Ardila
Priority date: 2002-01-18
Filing date: 2002-01-18
Publication date: 2003-07-24
Also published as: AU2002237485A1

Abstract

The invention relates to a process or method of producing lightweight aggregates such as those used in the preparation of lightweight concretes. According to the invention, the lightweight aggregates are produced by mixing potassium or sodium silicates with powders, such as vegetable or mineral carbon ash, sand, clay, kaolin and other materials. For expansion and drying purposes, said mixture is subjected to a gradual temperature increase, from ambient temperature, no greater than 40 °C, to 250 °C at the end of the cycle, although a higher final temperature would not affect the properties of the end product. The mixing and heating operations involved in the inventive method can be carried out in standard equipment in accordance with the characteristics of the mixture and the end product desired.

Description

PROCESS TO MANUFACTURE LIGHTWEIGHT AGGREGATES A B JA

TEMPERATURE

1. INTRODUCTION

This invention consists of a method of manufacturing lightweight aggregates at low temperatures, which can be used to manufacture lightweight concrete, mixing liquid sodium or potassium silicates with powdered materials, such as sands, clays, kaolin, coal ash vegetable or mineral or others, and subjecting this mixture to a temperature heating process that increases slowly and continuously from room level to a maximum of 250 ° C at the end of the cycle.

2. HISTORICAL SUMMARY OF LIGHT AGGREGATE COUGH FOR CEMENT

In the construction industry, concrete is used that consists of cement and aggregates. These aggregates help shape the compressive strength and other characteristics of the concrete. The most common aggregates due to their hardness, low cost and easy achievement are river stones, crushed quarries and sands. But all these materials are high weight, in the order of 2 tons per cubic meter, which is why heavy concretes are obtained that need stronger and more expensive structures. The aggregates represent a high percentage of the total weight of the concrete and this percentage can be more than 50%. So, if you can make lightweight concrete, the design of the structure can change and lower the cost.

We are considering as lightweight aggregates any material that can be mixed with cement to form concrete of lower density than normal ϊ without significant loss of its hardness and strength properties and that if there is any loss the material can perform well in some specific use.

Light aggregates can be natural or artificial. In nature there are some such as vermiculite, shale, slate, bentonites and pumice, among others. But it became obvious that if light aggregates could be made using waste materials such as ash from energy processes based on the combustion of mineral coal, for example, it could help ecology and the construction industry.

On the other hand, some time ago, processes were developed to produce light aggregates by expanding clays, materials based on plastic resins and expanded slags. Generally these processes are of high temperatures, 1000 ° C or more, and therefore require high cost equipment.

3. TECHNICAL SUMMARY

Unlike the processes, currently in use, that use temperatures of the order of 120Q ° C, the system object of this patent obtains the same results with maximum temperatures of 250 ° C. No higher temperatures are needed but the final product does not suffer deterioration if it is done.

This is a process for the manufacture of light aggregates similar to those already known, but it follows a different method that uses liquid sodium or potassium silicates, used separately or mixed in any proportion, such as binders and foaming agents, which give the consistency to the initial mix and the characteristics or physical properties of the final product.

This invention does not attempt to register the idea of "artificial light aggregates" but a different method for their manufacture, even if the products thus manufactured may have the same or different characteristics, or physical properties, with those already known in the market and made by the methods traditional.

4. DESCRIPTION OF THE PROCESS 4.1.MATERIALS TO USE.-

4.1.1. BINDERS (liquids) .- The alkaline sodium and potassium silicates can be of the commercial qualities in liquid form that are on the market. The concentration of these materials does not fundamentally change the final results, but adjustments to the formulation are necessary depending on that concentration. Solid alkaline sodium and potassium silicates, or a mixture of the two in any proportion, can be used, but must be previously dissolved in water in order to make a homogeneous mixture with the filler material. Liquids or solutions with densities between 20 ° Bé and 60 ° Bé are appropriate but a more recommended range would be between 45 ° Bé and 55 ° Bé. The SiO2: Na2O or SiO2: K2O ratio in these binders is also important because the siliceous part gives the resistance properties while the sodium (as carbonate) or potassium (as carbonate) parts provide the gaseous part for the expansion of the mixture. This SiO2: Na2O or SÍO2.K2O ratio should be of the order of 1.5: 2.5 to 3: 3.5 and recommended 1.8: 2.5.

4.1.2. FILLING MATERIAL or SOLIDS.- These materials can be ash of any kind, kaolin, sand, cement, calcium carbonates, clays, bentonites, limes, ground rice husks, ground paper and, in short, any material that you want to bind , fine or thick, preferably with a mesh size greater than 50, depending on the material chosen and the desired properties. The formulation must be adjusted according to the type of filler and its mesh. The physical and chemical properties of the filler must also be taken into account because it can be of the water-absorbing or non-inert type, and this can change the properties of the mixture. With lighter materials, such as ash, lighter aggregates will be produced.

4.1.3. OTHER ADDITIVES.-It is advisable to check the compatibility of any additive with the binder to avoid undesirable reactions. Gas producing additives can be used if a greater foaming and expansion effect is desired but this is seldom necessary. Mineral or organic colors can also be used to obtain a specific desired appearance in the final product. A 2% by weight of cement called Sorel (magnesium oxychloride) will increase the compressive strength in the final product regardless of the type of filler used, be it clay, ashes, etc.

4.2. FORMULATION.-

The mixtures of sodium and potassium silicates can be of any proportion or can be used without mixing depending on the qualities desired in the final product. However, for concrete aggregates, sodium silicate works on its own and in many cases is less expensive. The proportions between AGLOMERANTE and SOLIDOS can go from 10%: 90%, for heavier final product to 90%: 10%, for very light final product. For an aggregate for concrete with physical properties similar to Expanded Clays found in the market, the best proportions range from 25%: 75% to 35%: or 5%.

4.3. THE PROCESS.-

4.3.1. First Step.- Mix the Binder with the Filling. This mixture is made with the appropriate equipment, which depends on the type of mixture desired, which in turn depends on the formulation. Mixing can be done in a simple paddle mixer, a double turn mixer or others, whichever gives the most homogeneous mix corresponding to a specific formulation.

4.3.2. "Second Step." Extrusion of the mixture.- The mixture is extruded to form pellets or granules ("pellets") of a convenient size and shape. It could even be a continuous tape to be crushed at the end of the drying cycle. The used machinery may also be the one normally found on the market.There is no special specification for the extruder or extender.

4.3.3. -Third step .. Expansion .- The expansion takes place when the temperature rises from room temperature (assumed to be no more than 50 ° C) to 100 ° C. This step should be done slowly to allow heat to spread through the mix evenly, and when the mix reaches a temperature between 60 ° C and 100 ° C the binder expands and the mix increases in size. This expansion occurs due to the chemical composition of the binder that produces gases, mainly carbon dioxide, due to heat. Some fillers can also produce gases when decomposed by heat. Depending on the size of the granules or "pellets", this expansion can take between 3 and 20 minutes. It is important to keep in mind that the temperature must rise gradually, since if it rises too quickly, the expansion can produce defects such as a vacuum bubble in the center of the expanded part, which translates into a decrease in pressure resistance as it has formed an empty shell.

This third expansion step can be done in any temperature controlled furnace, but a tunnel type furnace with endless conveyor belt is recommended because it can be most practical. The temperature throughout the oven must be controlled so that the amount of heat increases evenly as the mixture progresses. The conveyor belt must be made of, or covered with, a non-stick material, such as silicone rubber or tefϊon, since the mixture may stick to the belt. This expansion stage for a centimeter diameter pellet or pellet, for example, can take 10 minutes.

A microwave oven system can also be used as long as temperatures are well controlled. In this case, the times required for each step or stage of the process may decrease, but the cost of energy consumption must be taken into account compared to other energy sources such as natural gas, heat from other operations where hot gases are released. whose energy can be recovered, etc. But for relatively small operations, the microwave oven system may be ideal. A combination of different energy sources can also be considered convenient to lower costs, or time, in each step or stage of the process.

4.3.4. Step Four.- Final Drying.- Once the expansion of the mixture has completely occurred, the material must also be completely dried. From this point onward, the temperature can be rapidly increased to the 250 ° C level. At this stage, again, the drying time will depend on the size of the pieces and the quantity of the same, but a granule or "pellet" of 1 centimeter in diameter can dry in 10 minutes. A longer drying time or a higher temperature will not harm the final product, but it is important that the product is completely dry at the end of this stage.

Therefore, the total time of the baking process, for pieces of 1 centimeter in diameter, should not exceed 20 minutes. However, variations may occur due to different possible formulations. This is because the total amount of water in the mixture can be from 10% to 50% of the total weight and it is moisture that must be evaporated.

Claims

RETV1NTHCACIONES. Process for the production of lightweight aggregates for use in lightweight concrete used in the construction industry, which consists of mixing liquid Sodium Silicate or Liquid Potassium Silicate, individually, or both combined in any proportion as binders, with any powder, fine or coarse, but compatible, such as ashes, clays, kaolins, cements and limes, among others, to obtain a mass that when subjected to a heating process, raising the temperature gradually, but constantly and slowly , from room temperature, not exceeding 40 ° C, up to 100 ° C for an expansion stage and proceed to final drying at a temperature not exceeding 250 ° C. In this way the dough expands uniformly, increasing its total size and acquiring compressive strength, to a greater or lesser degree, depending on the initial formulation. Process for the production of light aggregates using the Alkaline Silicates mentioned in Claim # 1 which can be of the commercial liquid qualities normally found in the market, with proportions of SiO2: Na2O or SiO2: K2O between 1.5: 2.5 and 3: 3.5 and no other additives are necessary. Process for the production of light aggregates in which the liquid Silicates referred to in Claims # 1 and # 2, such as solutions made of solid Silicates, the density must be between 45 ° Bé and 55 ° Bé. Process for the production of light aggregates in which the material to be agglomerated mentioned in Claim # 1, called "fillers", can be any powder or crushed material such as ashes from charcoal or mineral residues of thermoelectric operations, residual kaolins ceramic operations, all types of limes, ground rice husks, dried clays and other materials. Process for the manufacture of lightweight aggregates with properties that are suitable for use as lightweight aggregates in concrete for the construction industry in which the proportions of materials, for the mixture mentioned in Claim # 1, of binder (liquid) and filler (solid), are between 25%: 75% and 35%: 65%, but other combinations are possible when special additives are used or specific densities are desired. Process for the manufacture of lightweight aggregates for which there are additives that can be part of the mixture described in Claims # 1 and # 4, even when they are not indispensable, and that can be used in order to change the characteristics of the final product , such as, color, moisture resistance, and compression resistance. These may be additives that produce gases if a greater foaming and expansion effect such as carbonates is desired. Mineral or organic colors to obtain a specific desired appearance in the final product. 2% by weight of cement called Sorel (mangnesic oxychloride) for example, increase the compressive strength in the final product regardless of the type of filler used, be it clay, ash, etc. Said additives may be incorporated into the mixture at any time during the mixing stage. Process for the production of lightweight aggregates having four stages, or steps, according to Claim # 1, which are: 1) MIXING of the liquid binder with the powder filling; 2) EXTRUSION to form granules, or "pellets"; 3) EXPANSION by heating of the dough, raising the temperature gradually, steadily and slowly; 4) DRYING at 250 ° C. For granules of 1 cm in diameter this drying time can be 10 minutes. Process for the manufacture of lightweight aggregates in which the sequence or order of incorporation of the ingredients into the mixture referred to in Claims # 1, # 4, # 5 and # 6 and in the mixing stage referred to in Claim # 7, It is not important as long as a homogeneous mixture is obtained in the end. Process for the manufacture of light aggregates in which the proportions of ingredients of the mixture described in Claims # 1, # 5 and # 6 may vary but thus the characteristics of the final product will vary. Process for the manufacture of lightweight aggregates in which a novel and important part is the stage of expansion of the mass mentioned in Claim # 7. Such expansion should be done by increasing the temperature of the dough gradually but steadily and slowly, from room temperature, not exceeding 40 ° C, to 100 ° C, according to the formulation of the mass and the size of the granules. For granules of 1 c in diameter this expansion time can be 10 minutes. Process for the manufacture of lightweight aggregates in which the total time required for the expansion and drying stages, according to Claim # 1, and expressed separately in Claims # 7 and # 10, will depend primarily on the initial moisture of the mixture and size of the parts submitted to the process. Manufacturing process of light aggregates in which, after the mixture has been expanded and when said mixture is found at 100 ° C, drying is carried out, as set forth in Claims # 1 and # 7. At this point in the process you can quickly raise the temperature to 250 ° C, Manufacturing process of lightweight aggregates whose invention has the advantage of using low temperatures (of the order of 250 ° C maximum) compared to some current processes, in which Alkali silicates and other binders are used but they need maximum temperatures of the order of 1000 ° C or more. Process for manufacturing lightweight aggregates in which increasing the drying temperature or drying time beyond that set forth in Claims # 1, # 7 and # 12 does not impair the properties of the final product, that is, it continues to serve for lightweight concrete in the construction industry. Process for manufacturing lightweight aggregates with which the material obtained according to Claims # 1, # 7, # 10 and # 12 can be used as a lightweight aggregate in the manufacture of concrete of lower weight than those normally manufactured with heavy aggregates such as stones of river or crushed quarries.