LIGHTWEIGHT SYNTHETIC PARTICLE AND METHOD OF MANUFACTURING SAME

Abstract

Lightweight synthetic particles that replace traditional aggregates and methods of producing the same are disclosed herein.

Claims

1. A light weight synthetic particle consisting of a core and wetting agent where the wetting agent is a water soluble, glass forming silicate salt, where a coating of the water-soluble wetting agent is substantially applied on the surface of the core and is then essentially dried.

2. The light weight synthetic particle of claim 1 where the core is at least one material taken from the group consisting of: EPS, perlite, vermiculite, bamboo, wood chips, wood pellet fragments, rice, coffee, cocoa husks, cocoa shells, husks from wheat, shells from wheat, husks from other plants, shells from other plants, seeds, cores, stalks, plant strands, plant fibers, sea shell fragments, paper fragments paper pellets, rubber fragments and rubber particles.

3. (canceled)

4. The light weight synthetic particle of claim 1 where the water soluble, glass forming silicate salt is potassium silicate.

5. The light weight synthetic particle of claim 1 wherein said water soluble, glass forming silicate salt is sodium silicate.

6. The light weight synthetic particle of claim 1 further consisting of a coating agent applied on the surface of the wetting agent.

7. The light weight synthetic particle of claim 6 where the coating agent is at least one taken from the group consisting of: acrylic, bio-char, cementitious materials, pozzolanic materials, Portland cement, masonry cement, plastic, high-early slag cement, fly ash, silica fume, metakolin, pigments, iron oxide, gypsum, fibers, PVA fibers, nylon fibers, steel fibers, fiberglass and organic materials.

8. A light weight synthetic particle of claim 1, where the dry coating of the water-soluble wetting agent on the core is performed under ambient pressure and temperature.

Description

BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS

[0018] FIG. 1 depicts a flow chart indicating the preferred process for manufacturing a synthetic aggregate.

[0019] FIG. 2 depicts an abstract cross-sectional view of non-spherical EPS particles, shredded, ground, texturized, or otherwise reduced according to the methods described herein, suspended in a cementitious mixture.

[0020] FIG. 3 depicts a flow chart indicating the preferred process for manufacturing an alternative synthetic aggregate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments. However, those skilled in the art will understand that the present invention may be practiced without these specific details, that the present invention is not limited to the described embodiments, and that the present invention may be practiced in a variety of alternate embodiments. In other instances, well known methods, procedures, components, and systems have not been described in detail. One of skill in the art will appreciate various modifications to the process, to the ingredients, and to the proportions of ingredients that are possible. One skilled in the art will further appreciate that the following steps can be scaled to allow larger or smaller quantities of product to be made.

[0022] The following description teaches a lightweight synthetic particle (“particle”). In one embodiment, the particle is comprised of at least a core coated with a wetting agent. In another embodiment, the particle is comprised of at least a core coated with a wetting agent, and then coated with a coating agent. The coating agent (or agents) may completely or partially encapsulate the wetting agent.

[0023] One exemplary core is expanded polystyrene (EPS). However, one of ordinary skill in the art will recognize that any suitable form of styrene polymers can be used in place of the EPS content with similarly beneficial results. In particular, manufactured, expanded or partially expanded polystyrene beads or other prepared pieces of suitable size, shape or texture may be used without departing from the scope of the aggregate described herein. Similarly, either virgin or recycled EPS or other styrene polymers can be used as the raw material. Other exemplary cores include perlite, vermiculite, bamboo, wood chips, wood pellet fragments, rice, coffee, cocoa husks or shells, husk or shells from wheat or other plants, seeds, cores, stalks, plant strands or fibers, sea shell fragments, paper fragments or pellets, biochar and/or other plant nutrients, amongst others, or a combination thereof.

[0024] The particle described herein can be blended with dry mix stucco, mortars, grouts, concrete or other dry cementitious mixes or can be directly added to wet-mix stucco, mortars, grouts, ready-mix concrete, slurries or other wet cementitious mixes. The particle is suitable for use in a wide variety of both structural and non-structural cement-based mixes. Incorporation of these particles advantageously increases fire resistance, flexibility, impact resistance and freeze-thaw durability over conventional aggregates. The particles are uniquely non-static and provide bond strength to the cement paste within a concrete mixture, thereby improving mixability, aggregate dispersal uniformity and permanently securing the particles within the cured matrix. The particles also help reduce the speed with which moisture escapes from freshly formed mixes, thereby improving hydration, which creates stronger concrete and helps reduce both micro and macro cracking. The higher air-containing content of the particles decreases mixture weight and adds valuable insulative and sound-absorbing properties to the final product (e.g., stucco, mortar, grouts, or concrete). Also, while conventional raw, white, hydrostatic and non-binding EPS beads are often visibly exposed on a given mixture's surface and/or may otherwise adversely affect finish appearance and desirability by creating pits, bumps, lumps other surface irregularities, the darkened coated particles stay well-bonded and well-suspended with the mixture and are therefore much less prone to “float” to the surface. The particles also homogeneously incorporate within soil mixes to advantageously decrease unit weight and help reduce the speed with which moisture may escape.

[0025] Referring to FIG. 1, in an exemplary embodiment of a method of preparing an exemplary particle having an EPS core, the components of which are described in detail below, raw EPS material 4 is finely crushed, sliced, shredded, texturized, or otherwise reduced into preferably non-spherical EPS particles 32 and placed in a wetting station 40. A wetting agent 42 is introduced to the EPS particles 32. The wetting agent 42 is preferably water mixed with a thickening agent such as acrylic. The EPS particles 32 are then thoroughly combined with the wetting agent 42 using a mixing device, such as a paddle mixer, or other blending method, such that the EPS particles 32 are substantially and uniformly coated with the wetting agent 42. After the EPS particles 32 are coated with the wetting agent 42, coating agents 46 are added in a coating step 44. The coating agents may include fly ash or silica fume or some combination thereof. In a particular embodiment, the coating agent 46 consists of equal parts by volume of fly ash and silica fume, combined with polyvinyl acetate (“PVA”) fibers. Other pozzolanic materials may also serve as effective additives. In an exemplary embodiment of the aggregate, the proportion of ingredients are:

TABLE-US-00001 Ingredient Volume % by Volume Ground EPS Content 4 gallons 77.1% Wetting Agent 0.125 gallons 2.4% Fly ash 0.5 gallons 9.6% Silica Fume 0.5 gallons 9.6% PVA Fibers 0.0625 gallons 1.2%

[0026] Finally, the wetted, coated EPS particles are dried 48. This process creates particles 52 for aerating cement, stucco and other cementitious materials. The use of finely ground EPS maximizes the encapsulated air in the particle by reducing the interstitial volume surrounding fully formed foam beads or scrap fragments. Larger beads used as a filler in cement and cementitious products are typically able to decrease cement-based product weights up to a limit of approximately 20%, while embodiments of the particles 52 described herein can decrease the same product weights by up to 80% or more, for example as may be preferable in the case of certain cement stucco base coat or finish applications, floating concrete, geo-filled slurries, or other products or applications that may require or benefit from ultra-lightweight materials.

[0027] For certain specialized uses, such as stucco, a small amount of a surfactant may also be added to the mix at this point. After adding the coating agents and any other dry ingredients, the particles 52 are again mixed thoroughly with mechanical paddle mixer until coating ingredients and/or fibers are evenly distributed in mixture. Certain air entraining agents, fibers, surfactants, pumping aids and other additives common to the stucco industry may also be incorporated in dry or wet stucco mixes containing the invention. The fly ash, silica fume and PVA fiber ingredients should be thoroughly blended with the EPS and other ingredients using a mechanical mixer or similar mechanism to ensure uniform and homogenous mixing of all ingredients in the matrix.

[0028] After the EPS particles 32 are wetted with the wetting agent 42 and the fly ash, silica fume and PVA fibers have been thoroughly blended with the finely shredded EPS particles, the removal of excess moisture during the drying step 48 ensures that any potential future storage problems which might be caused by excess moisture are minimized while the aggregate is stored in a bulk or bagged state. The mixture can be dried using conventional methods (e.g., circulating air) or can be allowed to air dry through natural convection. The EPS particles 32 are preferably dried until it does not bind together when squeezed. Alternatively, sufficient moisture-absorbing coating agent 42 content may be applied to enable a speedier drying process that does not require secondary curing time or procedures.

[0029] Appropriately ground EPS particles 32 combined with appropriate wetting and coating 42 agents are used to incorporate a concentrated air-infused material into the cement-based matrix. EPS beads contain approximately 95% air by volume and, therefore, the finer the grind, the greater the concentration of air that can be added to any given mixture. Once the finely ground, or otherwise reduced, EPS material is properly wetted and surface-coated to inhibit static and add a stabilizing film of dead weight, then dried, the resulting additive can be quickly and uniformly integrated into the applicable stucco or concrete mixture. Using a preferred method of processing the raw EPS material 4, the preferred size of the finely ground EPS particles 32 may range from 20 to 120 mils (0.508 to 3.048 millimeters). The exemplary embodiment may advantageously utilize EPS material obtained from post-consumer or manufacturing waste products, whereby foam pieces of various sizes are received from store outlets and other commercial sources. Although EPS sources ranging from Type 1 EPS (1 lb/cu. ft.) to Type 2 EPS (2 lb/cu. ft.) are preferred and are described below, other polystyrene materials, including other densities of EPS material, or other materials based on styrene polymer variants, such as cups, trays, containers, and egg cartons may be also be used. Other recycled products such as pulverized rubber tire fragments and/or other miniaturized plastic components, as well as organic byproducts such as rice hulls or wood chips may also be incorporated into the mix design. As described above, other cores that may be used are perlite, vermiculite, bamboo, wood chips, wood pellet fragments, rice, coffee, cocoa husks or shells, husk or shells from wheat or other plants, seeds, cores, stalks, plant strands or fibers, sea shell fragments, paper fragments or pellets, biochar and/or other plant nutrients rubber fragments or particles, amongst others, or a combination thereof.

[0030] Referring again to FIG. 1, in an exemplary method of preparing the EPS material for use in the particle described herein, during the EPS processing step 6, the raw EPS material 4 is sorted 8 and any relatively large foam pieces are broken into smaller sizes preferably no larger than approximately 6″ in the longest dimension 12. During this process, the raw EPS pieces are inspected for foam of the wrong type or color and for any loose, foreign objects, such as screws, tape, paper, and other foreign objects incorporated into foam packaging and any such offending material is removed. High and low-density foam chunks are also mixed into rough proportion such that, after processing, the EPS particles 32 have an approximate final density of 1.0-1.5 pounds per cubic foot. The reduced foam is then put through a pre-break milling process 16, whereby the foam is ground, crushed, cut or otherwise reduced to pieces no more than roughly 2 inches across 20. The reduced foam is then put through a final milling step 24 whereby the EPS material further processed, texturized, shredded, granulated, beaded, or otherwise reduced until the pieces are able to pass through an appropriately sized screening mechanism to be acceptable for processing.

[0031] Referring to FIG. 2, once the ground, shredded, or otherwise textured or screened EPS material is coated, the resulting non-static and readily homogenized particles are advantageously more efficiently incorporated into a cementitious mixture than otherwise possible using conventional, statically-charged and hydrophobic EPS beads or EPS-containing aggregates. Additionally, reducing the EPS particles in the manner described above creates irregularly shaped and/or sized materials that are more easily mixed and resist settling or rising in the mixture (either wet or dry) under vibration. The air-containing particulate density also retards the mixture drying process, which helps create better hydration and increases mixture “pot life”, which extends applicator “working time.” In the case of the utilization of recycled EPS waste material in the mixture, the higher the concentration, the greater the “green” environmental benefit. The invention's particle shape, size, texture and cement-bond-enabling outer coating also combine to improve compressive strength as compared to conventional round, smooth, virgin, and hydrophobic EPS bead particles. The ultralight particles provide lighter, smoother and more easily transportable, mixable, trowelable and/or pumpable mixtures and these properties combine to cause much less physical strain on work-persons, machinery and equipment and advantageously reduces structure weight.

[0032] Referring again to FIG. 1, pre-coating the EPS particles 32 with a wetting agent 42 including a thickening agent 43 permanently encapsulates the EPS particles 32 with a thin layer of the thickening agent. This layer helps to ensure a uniform bonding of the EPS particles 32 with the later applied coating materials 46 and further allows for a greater percentage of aeration of the bulk mixture and a more uniform distribution of the particles than provided by the conventional method of adding EPS content directly to cement products.

[0033] The wetting agent 42 allows the EPS-coating additives, described below, to adhere to the surface of the EPS particles 32. The introduction of the moisture in this step also helps weigh down the EPS particles 32, making it easier to uniformly mix with the coating agent(s) 46 in a later step 46. Wetting and later coating the EPS particles also reduces static electricity, which results in a smoother, more readily integrated mixing process. The addition of a thickening agent, such as acrylic, increases the wetting agent's stickiness, which allows for a stronger adhesion of the coating agent 46 to the surface of the EPS particles 32.

[0034] In certain embodiments of the aggregate disclosed herein, PVA is used as part of the wetting agent, preferably in a ratio of 3 parts water to 1-part PVA. In other embodiments, such as for use in the creation of stucco products, the addition of a small amount of a surfactant or other common stucco performance enhancing additives may be added to the wetting agent to improve the viscosity and body of the mix and to help homogenize the mix. The surfactant emulsifies with the water when water is added at the time of mixing of the product. Addition of the surfactant improves the mixability and workability of the mixture. The surfactant improves water resistance, flame and fire resistance and compressive strength. It also reduces the surface PH of stucco materials. In the proportions described in Table 1, the addition of 0.17 oz. of surfactant has proven effective.

[0035] After wetting 40, a coating agent of fly ash, silica fume and/or, in some embodiments of the present aggregate, cement and/or PVA fibers is applied to the EPS particles 32. The coating agent 46 is mixed with the EPS particles 32 such that the coating agent 46 is uniformly distributed through the mass of EPS particles 32. The surface of the individual EPS particles are thereby coated and the coating agents bond with the individual EPS particles.

[0036] The addition of fly ash to the coating agent 46 improves the workability and flowability of the additive. Fly ash is extremely fine, adheres well and improves coverage to small grind EPS particulate surfaces. Fly ash acts as a water-reducer or super-plasticizer. Fly ash fines fill up interstitial spaces in and around the fine grind EPS beads, thereby helping to create a denser and less permeable mixture. Fly ash is a common extender of cement. On vertical applications, the addition of fly ash to cement or cementitious products provides for better adhesion, improves “slump” and helps to “hold” the wall better. The fly ash should be added to the mixture after the moisture is added and before the moisture begins to evaporate. Fly ash also serves to weigh down the foam. Fly ash also allows the material to dry slower (retards the cure rate) because it holds the moisture longer. This also lengthens applicator workability time and helps decrease shrinkage and cracking. Addition of the fly ash keeps the mixture sticky and pliable.

[0037] Silica fume, like fly ash, is another recycled waste product and is derived from the production of silicon metal or ferrosilicon alloys in electric arc furnaces. Because of its chemical and physical properties, silica fume is a very reactive pozzolan. Concrete containing silica fume can feature very high strength and can be very durable. Because of its extreme fineness and high silica content, silica fume is a very effective pozzolanic material. Silica fume is commonly added to Portland cement concrete to improve its properties, in particular its compressive strength, bond strength, and abrasion resistance. These improvements stem from both the mechanical improvements resulting from addition of a very fine powder to the cement paste mix, as well as from the pozzolanic reactions between the silica fume and free calcium hydroxide in the paste.

[0038] The addition of silica fume to the coating agent 46 also reduces the permeability of concrete to chloride ions, which protects the reinforcing steel of concrete from corrosion. With the addition of silica fume, the slump loss with time is directly proportional to increase in the silica fume content due to the introduction of large surface area in the concrete mix by its addition. Although the slump decreases, the mix remains highly cohesive.

[0039] Silica fume also reduces bleeding significantly because the free water is consumed in wetting of the large surface area of the silica fume and hence the free water left in the mix for bleeding also decreases. Silica fume also helps improve hydration because it blocks the pores in the fresh concrete so that water within the concrete is not allowed as readily to rise or migrate to the surface.

[0040] Silica fume's fine size and inherent stickiness also improves its ability to both coat and bond to the wetted EPS surfaces. It also enhances product hardness.

[0041] Although it is known to use fly ash and silica fume as ingredients in common cement based admixtures, particles created by the method described herein are unique because the reduced EPS content is first coated with the wetting agent and the fly ash and silica fume are used to adhere to the EPS content in order to minimize the interstitial spaces between the individual EPS particles and enhance the bond strength between both the coated EPS particles and the cement particles within the desired admixture. Once the resultant lightweight mixture has dried and all ingredients are fully bonded, the resultant lightweight aggregate product ultimately helps to allow greater aeration of the intended aggregate mixture, up to 80%.

[0042] Cement may be used as an exclusive or added ingredient to the coating agents in order to catalyze the hardening of the surface coating of the coated, reduced EPS content. This, in turn, increases the resultant compressive strength of the resultant product. Other pozzolanic materials may also be used as coating agents without departing from the scope of the particle described herein.

[0043] In additional embodiments of the present particle, PVA fibers may be added to the mixture to form a fine, interlocking mesh within the particle that helps suspend, stabilize and reinforce the coated EPS and other components in the mixture. The PVA fibers improve the tensile and compressive strength of the concrete manufactured using the present aggregate. The workability of the concrete is also improved while brittleness is reduced. The fibers may be treated with oil to keep the fiber from bonding to the matrix. The oiled and asbestos-like nature of the selected ultra-high performance fiber causes the fiber to react to stresses in the concrete as though the fiber is protected by and moving within a sleeve, which allows the material to essentially “tear” rather than snap or shatter under severe stress forces.

[0044] The addition of the PVA fibers at this point allows the fibers to bond directly to the coating agent, which are in turn directly bonded to the ground EPS content material. Thus, when then resulting dried lightweight particle is then added to a stucco, concrete, mortar or gypsum based mixture, the individual fiber infused lightweight product particles stay better suspended within the matrix. The bonding of the fibers to the EPS-coated content also helps hold the lightweight particles in uniform suspension throughout packaging shipping, handling and dry storage conditions. Polypropylene, nylon, fiberglass and other types of fibers may serve as appropriate alternatives to the PVA fibers for some uses or applications.

[0045] Referring to FIG. 3, in an alternative embodiment 68 of the present particle, the wetting agent disclosed above is replaced by a wetting agent 56 including water soluble, glass forming silicate salt (“liquid glass”) such as, preferably, potassium silicate, sodium silicate or lithium silicate. In such embodiments, the raw EPS material 4 may be ground, texturized, or otherwise reduced in the same manner described above to produce the EPS particles 32 having the same characteristics. The alternative wetting agent 56 is prepared by mixing approximately thirty pounds of, preferably liquid, potassium silicate with approximately one hundred pounds of water. In some embodiments, an optional step 61 adds citric acid, a catalyzing agent, and/or commercially available pigment agents, such as fly ash or iron oxide, (collectively indicated as 70) to the aggregate. Generally, seven gallons of the alternative wetting agent 56 is sufficient to coat approximately forty-five cubic feet of EPS particles 32. In a preferred method of manufacturing such embodiments of the present aggregate, the wetting agent is applied to the EPS particles 32 by spreading the EPS particles 32 over a relatively wide area, then misting the wetting agent 56 over the EPS particles while agitating the EPS particles for approximately two minutes to encourage complete coating 60. The alternative wetting agent 56 infuses and encapsulates the EPS particles 32 with a smooth, glass-like, fire-retardant coating, thereby increasing the weight of the particles, reducing the accumulation of static charges and generally improving the overall handling characteristics of both the aggregate and the wet concrete product made therefrom. The resulting concrete's structural integrity and water repellency are respectively improved due to the potassium silicate's natural acid resistance and tendency to bind with excess calcium in the concrete. Coating EPS particles in the manner described above has other beneficial attributes during handling of the materials, including lessening of static electricity, reducing the electric spark or flame potential, and decreasing dust. The liquid glass coating also enhances the overall compressive strength of the resulting concrete.

[0046] In another embodiment the particle 68 does not require any additional coating agents, such as fly ash, silica fume, or PVA fibers, although such agents may be used to adjust the properties of the resulting aggregate without departing from the scope of the aggregate disclosed herein. Coating agents may include acrylics, bio-char or other soil nutrients, cementitious and pozzolanic materials, Portland cement (all forms, including masonry, plastic, high-early, slag cement, etc.), fly ash, silica fume, metakaolin, pigments, iron oxide, gypsum, and/or fibers (including PVA, nylon, steel, fiberglass, organics), amongst others.

[0047] For example, in certain embodiments of the alternative particle 68, a pigment, such as black iron oxide, may be added in order to increase the cosmetic appeal of the particle as well as to act as a visual aid to ensure uniform coating of the wetting agent on the reduced EPS material. The pigment may also be common concrete performance-enhancing materials such as silica fume or fly ash, which can be mixed with the liquid glass in the wetting agent 56 or applied as a coating material to the wetted surface in dry powder form. In certain embodiments of the alternative aggregate 68, citric acid is added to the wetting agent in order to catalyze the curing of the selected silicate. The drying time of the aggregate is thereby reduced. The citric acid also advantageously reacts with calcium in the resulting concrete.

[0048] The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.