Patent Application
20180007191
Concrete is a composite construction material composed primarily of aggregate, cement and water. There are many formulations that have varied properties. The aggregate is generally coarse gravel or crushed rocks such as limestone, or granite, along with a fine aggregate such as sand. The cement, commonly Portland cement, and other cementitious materials such as fly ash and slag cement, serve as a binder for the aggregate. Various chemical admixtures may also added to achieve varied properties. Water is then mixed with this dry composite which enables it to be shaped (typically poured) and then solidified and hardened into rock-hard strength through a chemical process known as hydration. The water reacts with the cement which bonds the other components together, eventually creating a robust stone-like material. Concrete has relatively high compressive strength, but much lower tensile strength. For this reason, is usually reinforced with materials that are strong in tension (often steel).
Concrete is widely used for making architectural structures, foundations, brick/block walls, pavements, bridges/overpasses, motorways/roads, runways, parking structures, dams, pools/reservoirs, pipes, footings for gates, fences and poles and even boats.
Construction aggregate, or simply “aggregate”, is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are a component of composite materials such as concrete and asphalt concrete; the aggregate serves as reinforcement to add strength to the overall composite material. Due to the relatively high hydraulic conductivity value as compared to most soils, aggregates are widely used in drainage applications such as foundation and French drains, septic drain fields, retaining wall drains, and road side edge drains. Aggregates are also used as base material under foundations, roads, and railroads. In other words, aggregates are used as a stable foundation or road/rail base with predictable, uniform properties (e.g., to help prevent differential settling under the road or building), or as a low-cost extender that binds with more expensive cement or asphalt to form concrete.
Pozzolans are commonly used as an addition (the technical term is “cement extender”) to concrete mixtures to increase the long-term strength and other material properties, and in some cases reduce the material cost of concrete. A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. Pozzolans are primarily vitreous siliceous materials which react with calcium hydroxide to form calcium silicates; other cementitious materials may also be formed depending on the constituents of the pozzolan.
The pozzolanic reaction may be slower than the rest of the reactions that occur during cement hydration, and thus the short-term strength of concrete made with pozzolans may not be as high as concrete made with purely cementitious materials; conversely, highly reactive pozzolans, such as silica fume and high reactivity metakaolin can produce “high early strength” concrete that increase the rate at which concrete gains strength.
Many pozzolans available for use in construction today were previously seen as waste products, often ending up in landfills. Use of pozzolans can permit a decrease in the use of Portland cement when producing concrete; this is more environmentally friendly than limiting cementitious materials to Portland cement.
One common pozzolan used in modern concrete is fly ash. Fly ash is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases. In an industrial context, fly ash usually refers to ash produced during combustion of coal. Fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys of coal-fired power plants, and together with bottom ash removed from the bottom of the furnace is in this case jointly known as coal ash. Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO), both being endemic ingredients in many coal-bearing rock strata.
Owing to its pozzolanic properties, fly ash is used as a replacement for some of the cement content of concrete. It can replace up to 30% by mass of Portland cement, and can add to the concrete's final strength and increase its chemical resistance and durability. Recently concrete mix design for partial cement replacement with High Volume Fly Ash (50% cement replacement) has been developed.
Silica fume, is another commonly used pozzolanic material, also known as microsilica, is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of the silicon and ferro-silicon alloy production and consists of spherical particles with an average particle diameter of 150 nm. Because of its extreme fineness and high silica content, silica fume is a very effective pozzolanic material.
Silica fume is added to 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.
Polystyrene is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry. Polystyrene is one of the most widely used plastics, the scale being several billion kilograms per year. Polystyrene can either be a thermoset or a thermoplastic. A thermoplastic polystyrene is in a solid (glassy) state at room temperature, but flows if heated above its glass transition temperature of about 100 ° C. (for molding or extrusion), and becomes solid again when cooled. Pure solid polystyrene is a colorless, hard plastic with limited flexibility. It can be cast into molds with fine detail. Polystyrene can be transparent or can be made to take on various colors.
Polystyrene can be recycled, and has the number “6” as its recycling symbol. The increasing oil prices have increased the value of polystyrene for recycling. No known microorganism has yet been shown to biodegrade polystyrene, and it is often abundant as a form of pollution in the outdoor environment, particularly along shores and waterways especially in its low density cellular form.
Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam. It is usually white and made of pre-expanded polystyrene beads. Familiar uses include molded sheets for building insulation and packing material (“peanuts”) for cushioning fragile items inside boxes. Sheets are commonly packaged as rigid panels which are also known as “bead-board”.
The invention described herein is a light weight synthetic particle (“particle”) which may replace all or a portion of the aggregate content in any given mixture. In one embodiment, the particle is comprised of at least a core coated with a wetting agent. In another embodiment, the aggregate is comprised of at least a core coated with a wetting agent; the wetting agent is then coated with a coating agent.
The core maybe be expanded polystyrene, styrene, or other lightweight material such as perlite, pumice, vermiculite, bamboo, wood chips or pellets, husks or shells from rice, coffee, cocoa, wheat or other plants, plant seeds, cores, stalks, strands or fibers, sea shell fragments, paper fragments or pellets, rubber fragments or particles, amongst other materials. The wetting agent may be a soluble, glass forming silicate salt, amongst others. The coating agent maybe an acrylic (virgin, or recycled, such as acrylic paint), biochar or other nutrient soil enhancers, cementitious and pozzolanic materials, Portland cement (all forms, including masonry, plastic, high-early, slag cement, etc.), fly ash, silica fume, perlite, metakaolin, pigments, iron oxide, gypsum, and/or fibers (including PVA, nylon, steel, fiberglass, organics), amongst others. The coating agent may be comprised of either a single material or a combination of materials.
The particle offers several benefits over traditional aggregates. It is an ultra-lightweight particle which can be used as an aggregate in concrete that is static-free and user-friendly for handling, blending, and application. Reducing the weight of concrete reduces worker fatigue, thereby reducing labor costs. Additionally, the particle is a green, sustainable building product that replaces natural minerals or other aggregate materials which must be mined, processed and transported to cement product manufacturing centers. The particle helps reduce transportation, handling, shipping costs and energy both to and from the factory. Also, the particle offers improved impact, fire, crack, and freeze-thaw resistance to concrete products.
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.
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.
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.
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.
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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.
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.
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.
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.
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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.
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.
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.
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.
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.
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.
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.
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.
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%.
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.
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.
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.
Referring to
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.
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.
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.
This application is a 371 of international application PCT/US2016/014463, filed on Jan. 22, 2016 takes priority from U.S. patent application Ser. No. 14,603780 filed on Jan. 23, 2015 which is a continuation-in-part of U.S. patent application Ser. No. 13/447,146, filed on April 13, 2012, which claims priority from U.S. provisional patent application Ser. No. 61/475,008, filed on Apr. 13, 2011, and U.S. provisional patent application Ser. No. 61/564,689, filed on Nov. 29, 2011, and incorporates each of the abovementioned applications by reference as if fully set forth herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/014463 | 1/22/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14603760 | Jan 2015 | US |
| Child | 15544771 | US |
