WO2016145301A1 - Modified particles for building and construction applications - Google Patents

Abstract

The invention encompasses concrete formulations and cementitious composites formed therefrom, where the concrete formulation includes modified composite particles that are formed from a particulate substrate, such as sand, and a polymeric coating, such as a hydrogel, that localizes on the surface of the particulate substrate to form the modified composite particles. The invention also encompasses methods of producing such formulations and cementitious composites.

Description

MODIFIED PARTICLES FOR BUILDING AND CONSTRUCTION APPLICATIONS

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No.

62/131,926, filed March 12, 2015, U.S. Provisional Application Serial No. 62/263,525, filed December 4, 2015, and U.S. Provisional Application Serial No. 62/271,448, filed December 28, 2015. The entire contents of the above-referenced applications are incorporated herein by reference. FIELD OF APPLICATION

[0002] This application relates generally to modified composite particles useful for various building and construction applications, including polymer-coated sand in cementitious composites.

BACKGROUND

[0003] Sand is used in a variety of building and construction applications. For example, sand forms an integral part of concrete mixtures that are used in building and construction. Sand mixtures are also used for specialized applications like playground construction.

Modifications in a sand product can allow improvements in strength, durability, and other desirable attributes of those materials using sand as a component.

[0004] Bare sand alone or mixed with other components can be used as an adjunctive material for specialized construction. For example, the specialized shock absorbing material used in playgrounds is typically a mixture of sand particles and finely crushed rubber.

However, these dissimilar materials tend to segregate, with the fine rubber particles migrating to the surface where it can get blown away by the wind. There remains a need in the art for improved specialty construction materials using bare sand and other, similar, fine particulate matter.

[0005] A major construction material employing sand is concrete. Concrete, formed from cement, water, and aggregate particles is a cementitious composite. In a cementitious composite, the cement and water combine to form a paste that coats the surface of the aggregate particles, binding them into an agglomeration. Mortar, grout, and stucco are other examples of cementitious composites. Aggregates used with cement in forming

cementitious composites may be fine particles (like sand) or coarse particles (like gravel or crushed stone); the aggregates typically account for 60-75% of the volume of the cementitious composite. As the chemical components of the cement hydrate, the interstitial substrate binding the aggregates will harden and gain strength, in a process called curing.

[0006] Cement, the binding agent that holds together the fine or coarse aggregates in concrete, is made primarily from limestone (calcium carbonate) and silica. Heated to a high temperature in a large rotating kiln, these ingredients fuse to form pellets termed "clinker," which is then pulverized into fine cement powder. For example, for Portland cement, calcium carbonate is heated with silicate minerals in a kiln at over 1400 degrees C to produce Portland cement clinker. Reaction between calcium oxide and silica results in dicalcium silicate and tricalcium silicate, the primary components in Portland cement.

Tricalcium aluminate and tetracalcium aluminoferrite are also formed when aluminum and iron compounds are present in the feed. Other impurities can lead to much more complex cement chemistry and variations. Sometimes, industrial waste, such as fly ash, is intentionally added.

[0007] The cement industry is called the most energy -intensive of all manufacturing industries, and energy consumption for cement manufacturing is predicted to increase by 75% between 2010 and 2040 according to the U.S. Energy Information Administration's 2013 Annual Energy Outlook report (http://www. eia. gov/forecasts/ aeo/). Cement production also has a major impact on gaseous and particulate emissions, including CO2, nitrogen oxides, and sulfur dioxide. All of this highlights the need for improved methods for the efficient use of cement, and there remains a need for improved methods of maximizing the amount of concrete produced from a given amount of cement.

[0008] Portland cement is the most common type of cement. Over four billion tons of cement are produced per year globally, much of which is Portland cement. Portland cement is composed of five major chemical ingredients in decreasing order of presence: tricalcium silicate (about 50% by weight), dicalcium silicate (about 25%), tricalcium aluminate (about 10%), tetracalcium aluminoferrite (about 10%) and gypsum (about 5%). When concrete mixtures are prepared by blending the dry Portland cement powder and particulate fillers with water, hydration occurs with the various cement ingredients. The growing hydration crystals cause the entire system to bind into a strong composite as it cures.

[0009] The behavior of tricalcium silicate in cement illustrates the intricate and evolving chemical-physical processes termed cement cure. Immediately upon the addition of water, tricalcium silicate rapidly reacts, forming calcium silicate hydrate, simultaneously generating calcium ions, hydroxide ions, and a large amount of heat (Stage I). The pH of the slurry (or paste) quickly rises to over 12 as a result of the release of alkaline hydroxide (OH^") ions. This initial hydrolysis burst slows down shortly after it starts, typically within minutes, resulting in a decrease in heat released. The hydration reaction nevertheless proceeds, albeit slowly, during this "dormant" period lasting several hours (Stage II), constantly generating calcium and hydroxide ions until the ions become saturated. Once this occurs, solid calcium hydroxide starts to crystallize. Simultaneously, calcium silicate hydrate begins to form. Ions fall out of solution due to precipitation, accelerating the reaction of tricalcium silicate to form even more calcium and hydroxide ions. The rate of heat release again rises, with a period of maximum heat production occurring between 10 and 20 hours after mixing (Stage III). The emerging calcium hydroxide and calcium silicate hydrate crystals provide nucleating "seeds," to which more crystals adhere. The crystals form a thick shell, making it difficult for water molecules to diffuse through and reach protected pockets of unhydrated tricalcium silicate. At this stage, further cement cure is controlled by the rate at which water molecules diffuse through the calcium silicate hydrate shell. The solid shell thickens over time, further slowing the production of calcium silicate hydrate.

[0010] This complicated curing process is influenced by many factors, including hydration kinetics, salt solubility, temperature, humidity, initial water content, mixture dispersion, and rate of water migration through crystal shells, microscopic cracks and imperfections. The strength of concrete depends critically on the microscopic structural alterations that occur during this hydration (curing) reaction. Concrete is known to continue the curing process over a long period of time, for years or even decades. The end result is often a porous morphology where calcium hydroxide solution fills voids between calcium silicate hydrate shells (with or without residual interior unhydrated cement core).

[0011] In a typical concrete mixture, cement is the most expensive material in the formulation, comprising about 13 to aboutl5%. Sand comprises about 30% of a concrete formulation, while coarse components comprise about 40%. Sand particles, although a smaller component of a concrete formulation, have a larger surface area to interact with the crystalline matrix of the cement composite. Thus, sand is an ideal substrate to be exploited for delivering chemicals from its surface into the concrete, and for tailoring the

physical/chemical properties of cement. Strengthening of concrete, for example, can be achieved by improving adhesion between cement and sand. [0012] Apart from cement and particulate materials, the remainder of the concrete formulation is water and air. Most concrete has a certain amount of air entrainment, typically in the range of a few percent by volume. In a typical concrete formulation, water is used to enable flow, i.e., workability, and it causes hydration of the oxides. Water typically comprises about 15 to about 20% of the concrete formulation; excessive amounts of water often lead to weaker final structures.

[0013] It is understood that the amount of water used to prepare the concrete mixture is a major factor influencing both the ease of processing and the final morphology. In general, the strength of concrete increases when less water is added. Concrete is actually mixed with more water than is needed for all the hydration reactions stoichiometrically, as the hydration reaction itself only consumes a limited amount. The extra water is necessary to give concrete sufficient workability and flowability. These features are important in order to allow proper mold/form filling and to release gross air bubbles upon vibration or compaction. High quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability of fresh concrete. The industry has been searching for ways to improve fluidity in the concrete formulation without increased use of water.

[0014] The extra water not consumed by the hydration reactions ends up being trapped in microstructural pore spaces; some pores, with trapped water, will remain despite

compaction. These pores greatly weaken the resulting composite, because they lack strength- forming calcium silicate hydrate bonds. As the composite weakens, it is susceptible to cracking and pitting. The pores in the composite impair its strength, in particular tensile properties, so that reinforcements (e.g., rebar) are necessary for many structural applications. There remains a need in the art, therefore, to minimize the impact of residual water on the strength of the cementitious composite.

[0015] As a further need in the art, it would be advantageous to improve the workability and/or flowability of a concrete mixture. Concrete setting or cement cure is an exothermic process that typically takes place in three stages, as described above. Cementitious composites are generally workable through the first half of Phase II, following which the mixture becomes too stiff to be manipulated or formed. In current use, admixture materials are used to accelerate or retard the setting of concrete. However, some of these agents have known disadvantages in the art. Furthermore, since only minute amounts of such admixture materials are added, efficient mixing and even distribution is difficult to achieve. Thus, workability and fiowability remain challenges, if one wishes to avoid excess water in the mixture, with its attendant effect on strength reduction of the cured composite.

[0016] A key category of chemical additives for improving cement handling properties includes plasticizers and superplasticizers, such as polymers having ethylene-oxide and carboxylic-acid functional groups. These polymers are used as dispersants to minimize particle aggregation and to improve the rheology of suspensions by lubricating the system and promoting flow, so that less water is required for these purposes. Other chemical additives can be useful as well. Chemical admixtures can be classified according to five major functions they deliver: air-entraining, water-reducing, retarding, accelerating and plasticizing (super-plasticizing). Other specialty functions include corrosion inhibition, shrinkage reduction, alkali-silica reactivity reduction, workability enhancement, bonding, damp proofing, and coloring.

[0017] Presently, chemical additives are simply mixed into the concrete formulation during processing. However, the heterogeneous nature of the concrete mixture interferes with the effective dissolution and uniform distribution of these additives throughout the formulation. There remains a need in the art, therefore, for chemical additives that can be immediately, directly and efficaciously dispersed in the concrete formulation, and their intended functionality becoming effective upon contact with water.

[0018] In conclusion, there remain unmet needs in the art for consistent, predictable, energy-conserving, and cost-effective technologies to create a workable, flowable, even malleable concrete mixture that is suitable for a wide range of construction uses. There remains a further need in the art to enhance the flowability and workability of the cementitious mixtures, without impacting the strength of the cured composite. In addition, there is an ongoing need in the art to produce a self-leveling, crack-resistant, strong, and smooth-textured concrete mixture, where these properties stem from the flowability of the mixture.

SUMMARY

[0019] Disclosed herein, in embodiments, are concrete formulations comprising modified composite particles, wherein the modified composite particles comprise a particulate substrate and a polymeric coating, and wherein the polymeric coating localizes on the surface of the particulate substrate to form the modified composite particles. In

embodiments, the particulate substrate comprises sand. In embodiments, the polymeric coating comprises a performance-enhancing or a processing-enhancing additive. In embodiments, the polymeric coating comprises a hydrogel. In embodiments, the polymeric coating comprises a functional group that forms precipitates with Ca++ ions. In

embodiments, the polymeric coating can further comprise a cationic/anionic polymer pair comprising a cationic polymer and a high molecular weight anionic polymer. The cationic polymer can be selected from the group consisting of polydiallyldimethylammonium chloride (poly-DADMAC), linear polyethylenimine (LPEI), branched polyethylenimine (BPEI), chitosan, and cationic polyacrylamide. In embodiments, the hydrogel can be selected from the group consisting of polyacrylamide, acrylamide copolymer, poly(acrylic acid), carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, and latex polymers. In embodiments, the hydrogel comprises an acrylamide copolymer, and the acrylamide copolymer is formulated as an inverse emulsion.

[0020] Also disclosed herein, in embodiments, are modified sand-based composite particles, wherein the particles comprise a sand substrate and a first polymeric coating, and wherein the first polymeric coating localizes on the surface of the sand substrate to form the modified sand-based composite particles. In embodiments, the first polymeric coating comprises urethane foam. In embodiments, the particle further comprises a second polymeric coating external to the first polymeric coating. The second polymeric coating can comprise an elastomeric polymer or an abrasion-resistant polymer, and the second polymeric coating can be crosslinked. Further disclosed herein are shock-absorbing particulate compositions comprising particles as described above. In embodiments, the particulate composition can comprise a plurality of elastomeric particles mixed with the particles as described above.

[0021] Further disclosed herein, in embodiments, are methods forming a cementitious composite, comprising providing a particulate substrate, coating the particulate substrate with a coating polymer to form a coated particulate substrate, and combining the coated particulate substrate with a cement and water, thereby forming the cementitious composite. In embodiments, the particulate substrate is a sand substrate. In embodiments, the coating polymer comprises a hydrogel. In embodiments, wherein the step of coating the sand substrate with the coating polymer is preceded by a step of coating the sand substrate with a primer polymer, upon which the coating polymer is deposited. In embodiments, the primer polymer comprises a cationic polymer and the coating polymer comprises an anionic polymer. In embodiments, the steps of providing, coating, and combining are performed at a point of use. Also disclosed herein are methods of forming a cement mixture at a point of use, comprising providing a sand substrate at the point of use, providing a coating polymer at the point of use, providing a cement at the point of use; coating the sand substrate with the coating polymer at the point of use to form a coated sand composite, and mixing the coated sand composite and the cement at the point of use to form the cement mixture. In embodiments, a method of forming a cementitious composite at a point of use comprises forming the cement mixture as disclosed above at the point of use, adding water to the cement mixture at the point of use, and mixing the cement mixture and the water at the point of use, thereby forming the cementitious composite.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The FIGURE is a flow diagram of a manufacturing process for coated fine aggregate particles.

DETAILED DESCRIPTION

[0023] The present invention relates to modified sand-based composite particles having particular use for construction-related applications.

[0024] In embodiments, the compositions and methods disclosed herein relate to high- performance cementitious composite materials. In embodiments, the cementitious composite material can be a concrete, a mortar, a grout, a stucco, or any other composite where an aggregate is bonded together with a fluid cement. In embodiments, the cement can be a Portland cement or any other hydraulic cement. In embodiments, the aggregate used in forming a cementitious composite material comprises coarse particles and fine particles or simply just fine particles. The fine particles are generally natural sand particles or pulverized stone, with most particles passing through a 0.375 inch sieve; coarse particles are greater in size than 0.19 inch, but generally range between 0.375 and 1.5 inches in diameter. Such fine aggregate materials useful for concrete composites shall be termed "fine aggregates" herein.

[0025] In one aspect, the modified sand-based composite particles are treated with formulations that are suitable for use in concrete formulations. In contrast to those technologies in conventional use, the unconventional modified sand-based composite particles as disclosed herein allow controlled and thus more complete cure of cement. Thus, with surface-modified sand as disclosed herein, concrete strength can be maintained, even enhanced, with higher water inclusion in the initial concrete mixture. In another aspect, the modified sand-based composite particles are treated with formulations that are suitable for use as a shock-absorbing particulate layer as might be used in playground construction. Other construction-related uses of the modified sand-based composite particles disclosed herein can be envisioned by artisans of ordinary skill.

[0026] In embodiments, the modified sand-based composite particles are capable of delivering additive formulations into a concrete mixture, where the composite particles comprise a sand substrate with a polymeric coating that can act as carriers for the additives. As a consequence of the large interfacial area, modified sand is a medium that has potential to deliver a variety of differently functioning additives into a concrete mixture. The polymeric coating around the sand can be engineered to have inherent additive properties, or it can be engineered to be complexed with chemical additives. In a given concrete mixture, one can employ a single type of modified sand-based composite particles, where all of the treated sand delivers a single additive; alternatively, one can also employ a mixture of modified sand-based composite particles, with some of the particles pretreated with one additive, and the rest with a different one. In other embodiments, modified sand-based composite particles can be prepared so that they comprise multiple layers of additives or combinations of additives. When modified sand-based composite particles are prepared as disclosed herein, sand clumping is no longer a problem and the additives can be effectively deployed within the mixture due to their presence on the large surface area offered by the particulate matter.

[0027] In embodiments, modified sand-based composite particles can be formed from a particulate sand substrate and a hydrogel coating, wherein the hydrogel coating localizes on the surface of the sand particle. The hydrogel-coated sand can then provide intrinsic lubricity, fluidity and dispersibility, without the need to add traditional plasticizers or superplasticizers.

[0028] In embodiments, the aggregate used in the cementitious composite comprises fine aggregates having one or more polymeric coating layers, wherein at least one of the polymeric coating layers comprises a hydrogel. Fine aggregates useful for these purposes can include fine-grained inorganic materials, for example, sand. Fine aggregates selected as substrates for polymeric treatment as described herein can be of any shape, although it is understood that particle shape and surface texture can affect the physical behavior of freshly mixed concrete. For example, rough-textured, angular or elongated materials are less prone to flowability than a smooth, rounded compact aggregate. In embodiments, a flat or elongated particle substrate can be limited to less than 15% by weight of the total aggregate used. In embodiments, a compact particle such as sand is desirable.

[0029] In embodiments, the hydrogel coating for the particulate substrate, e.g., the sand, comprises a water-swellable polymer. In embodiments, the hydrogel coating comprises a polymer selected from the group consisting of polyacrylamide, acrylamide-acrylate copolymers (e.g., in inverse emulsion form), poly (aery lie acid) salts, carboxy methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, and latex polymers. In embodiments, the hydrogel coating further comprises a cationic/anionic polymer pair comprising a cationic polymer and a high molecular weight anionic polymer. In embodiments, the cationic polymer is selected from the group consisting of poly-DADMAC, LPEI, BPEI, chitosan, and cationic polyacrylamide. In embodiments, the hydrogel coating further comprises a crosslinking agent. The crosslinking agent can comprise a covalent crosslinker. The covalent crosslinker can comprise a functional group selected from the group consisting of an epoxide, an anhydride, an aldehyde, a diisocyanate, and a carbodiimide. The covalent crosslinker can be selected from the group consisting of polyethylene glycol, diglycidyl ethers, epichlorohydrin, maleic anhydride, formaldehyde, glyoxal, glutaraldehyde, toluene diisocyanate, and methylene diphenyl diisocyanate, 1-ethyl- 3-(3-dimethylaminopropyl) carbodiimide. In embodiments, the hydrogel coating further comprises a delayed hydration additive. The delayed hydration additive can be selected from the group consisting of a low hydrophilic-lipophilic balance surfactant, an exclusion agent capable of excluding a finishing surfactant, a light ionic crosslinking agent, a light covalent crosslinking agent and a monovalent salt charge shielder.

[0030] 1. Coated Fine Aggregate Particulate Materials

[0031] Coated fine aggregate particles in accordance with these systems and methods can be formed using a wide variety of fine aggregate materials. Fine aggregate materials include graded sand, bauxite, crushed stone, silicate minerals, ceramic materials, glass materials, walnut hulls, polymeric materials, resinous materials, rubber materials, and the like. The fine aggregate particles are generally nonporous, but porous fine aggregate particles can be used in certain instances. Desirably, the fine aggregate particles will be comprised of materials (whether individual substances or aggregates of two or more substances) having a size in the order of mesh size 4 to 100 (US Standard Sieve numbers). As used herein, the term "particulate" includes all known shapes of materials without limitation, such as spherical materials, elongated materials, polygonal materials, fibrous materials, irregular materials, and any mixture thereof.

[0032] In an embodiment, the coated fine aggregate materials can be sand, where composite sand-based additive particles are formed by modification of a sand substrate with a water swellable polymer coating such as a hydrogel. These particles can be referred to as polymer coated sand. In embodiments, the sand substrate can be modified with the polymer coating before the sand substrate is introduced into the concrete mixture. In embodiments, performance-enhancing or processing-enhancing additives can be premixed with the swellable hydrogel prior to coating, so that the polymer deposited on the sand already contains an effective admixture functionality.

[0033] In embodiments, the amount of hydrogel polymer coating can be in the range of about 0.1 to about 10% based on the weight of the sand. In embodiments, the hydrogel layer applied onto the surface of the sand substrate can be a coating thickness of about 0.01% to about 20% of the average diameter of the sand substrate. Upon hydration and swelling of the hydrogel layer in the cement mixture, the hydrogel layer can become expanded with water, such that the hydrogel layer thickness can become about 10% to about 1000% of the average diameter of the sand substrate.

[0034] Many hydrophilic or colloidal polymers may be employed to coat sand for use in concrete mixtures. Many polymers are swellable in fresh water and yet responsive to environmental stimuli (e.g., experiencing chain conformational collapse when the temperature or pH rises drastically). Acrylic, methacrylic, or maleic containing polymers/co- polymers or emulsions can be used to coat sand. In embodiments, somewhat hydrophobic polymers can be used on sand surface such as styrene maleic anhydrides or their imidized version. Sulfonated polystyrene or lignin sulfonates (slightly sulfonated version) can be used to coat sand as well. All such polymers can be first blended with reactive components before sand coating. Once varnished on the sand surface, the reactive components are cured or crosslinked, further anchoring the entire coating on sand.

[0035] In embodiments, a hydrogel layer as described herein can be designed so that it collapses when calcium ions, as are found in concrete mixtures, are present. For example, carboxylates in the hydrogel can bind to calcium ions, forming precipitates. The mixed organic/inorganic layer formed thereby can promote adhesion between sand and cement, improving concrete tensile strength and compressive strength. [0036] Additional methods for modification of sand include spraying, varnishing or saturation of a liquid polymer formulation onto the sand substrate, followed by drying to remove water or other carrier fluids. The drying process can be accelerated by application of heat or vacuum, and by tumbling or agitation of the modified sand, such as a fluidized bed, during the drying process. The heating can be applied by forced hot air, convection, friction, conduction, combustion, exothermic reaction, microwave heating, or infrared radiation. Agitation during the sand modification process has a further advantage of providing a more uniform coating.

[0037] In other embodiments, the sand substrate can be modified with a polymer formulation, without the need for a drying step. This can be accomplished by the use of a solvent-free polymer formulation, or a curable formulation. In certain simplified methods, a dry or liquid polymer formulation can be applied onto the sand substrate via inline mixing, and the modified material thus prepared can be used without further processing. The moisture content of the sand substrate can be modified by addition or removal of water, or addition of other liquids. The modified sand-based composite particles of the invention can advantageously use a localized polymer concentration on the sand surface, in contrast to the traditional approach of making the entire fluid medium viscous. This localized hydrogel layer can permit a more efficient use of polymer.

[0038] In embodiments, the surface of modified sand-based composite particles can be coated with a selected polymer, either as a single layer or as a series of multiple coating layers, as described below in more detail. In embodiments, there can be one, two, or multiple (i.e., more than two) coating layers forming the composite sand particles disclosed herein, with the each of the multiple coating layers possessing some or all of the attributes of the coating layers described above, or with one or more of the multiple coating layers providing additional properties or features.

[0039] 2. Single-layer polymeric coating systems

[0040] In embodiments, a hydrogel coating can be applied to fine aggregate particles as a single layer. In embodiments, these coated fine aggregate particles can be formed by modification of the particulate substrate with a water swellable polymer coating such as a hydrogel. In embodiments, the fine aggregate particles can be modified with the polymer coating before the aggregates are introduced into the concrete mixture. In embodiments, the amount of hydrogel polymer coating can be in the range of about 0.1 to about 10% based on the weight of the fine aggregate particles. In embodiments, the hydrogel layer applied onto the surface of the fine aggregate particles can provide a coating thickness of about 0.01% to about 20% of the average diameter of the substrate. Upon hydration and swelling of the hydrogel layer in the concrete mixture, the hydrogel layer can become expanded with water, such that the hydrogel layer thickness can become about 10% to about 1000% of the average diameter of the substrate particles.

[0041] Methods for modifying the fine aggregate particles include spraying or saturation of a liquid polymer formulation such as an inverse emulsion of a hydrogel-forming polymer onto a substrate, followed by drying to remove water or other carrier fluids. The drying process can be accelerated by application of heat or vacuum, and by tumbling or agitation of the coated fine aggregate particles during the drying process. The heating can be applied by forced hot air, convection, friction, conduction, combustion, exothermic reaction, microwave heating, or infrared radiation. Agitation during the coating process has a further advantage of providing a more uniform coating on the fine aggregate particles.

[0042] The Figure shows an embodiment of a manufacturing process for the coated fine aggregate particles using dried sand and a liquid polymer. In the depicted embodiment, sand is conveyed into a mixing vessel, and a liquid polymer composition is sprayed via pump and spray nozzles onto the sand along the conveyor belt. The sand and liquid polymer report to a low shear mixing vessel, where the ingredients are further blended. After mixing, the modified sand containing the liquid polymer is sent to a dryer to remove water and/or organic carrier fluids associated with the liquid polymer. After the drying step, the modified aggregate particles are passed through size classification equipment, such as a sieve, to remove over-sized agglomerates. Mechanical mixers, shear devices, grinders, or crushers can be used to break up aggregates to allow the material to pass through the appropriate sized sieve. The finished material is then stored for shipment or use.

[0043] In embodiments, the sand that is used to produce fine aggregate particles can be pre- dried to a moisture content of <\ %, and preferably <0.1 % before being modified with a hydrogel polymer. In embodiments, the sand temperature at the time of mixing with the liquid polymer is in the range of about 10 to about 200° C, and preferably in the range of about 15 to about 60° C.

[0044] In embodiments, the sand is contacted with the liquid polymer composition by means of spraying or injecting. The amount of liquid polymer composition added is in the range of about 0.1 to about 20%, and preferably about 0.5 to about 10% by weight of the fine aggregate. The aggregate and liquid polymer are blended for a period of about 0.1 to about 10 minutes. In a preferred embodiment, the mixing equipment is a relatively low shear type of mixer, such as a tumbler, vertical cone screw blender, v-cone blender, double cone blender, or ribbon blender. In embodiments, the mixing equipment can be equipped with forced air, forced hot air, vacuum, external heating, or other means to cause evaporation of the carrier fluids.

[0045] In embodiments, the modified aggregate containing the liquid polymer is dried to remove water and/or organic carrier fluids associated with the liquid polymer. The dryer equipment can be a conveyor oven, microwave, or rotary kiln type. In an embodiment the drying step is carried out in such a way that the dried, modified aggregate contains less than 1% by weight of residual liquids, including water and any organic carrier fluids associated with the liquid polymer composition.

[0046] In embodiments, the same equipment can be used to blend the aggregate with the liquid polymer and to dry the blended product in a single processing stage, or in a continuous production line.

[0047] In other embodiments, methods for modifying the fine aggregate particles include synthesis of a hydrogel coating in situ, or in the presence of the fine aggregate particles, resulting in a hydrogel layer encapsulating the surface of the fine aggregate particles. As an example, the in situ synthesis of the hydrogel can be accomplished by combining fine aggregate particles with coating precursor monomers and/or macromonomers (macromers) followed by a polymerization step. In other exemplary instances a water-soluble polymer can be dissolved in monomers, with or without solvent, followed by polymerization in the presence of the fine aggregate particles, resulting in the formation of interpenetrating polymer networks as a coating on the fine aggregate particles. In other exemplary instances, the water-soluble polymer is dispersed in the monomers, with or without solvent, and the subsequent polymerization will result in fine aggregate particles encapsulated by a hydrogel consisting of water-soluble polymer particles locked up by the newly formed polymer. The monomers or macromers used can be selected from monomers that result in water-soluble polymers. In other exemplary instances, the particles can be encapsulated by non-water soluble polymer that will then be modified or hydrolyzed to yield the water-soluble hydrogel coating. As would be understood by those of ordinary skill in the art, the encapsulating layer can be formed by different polymerization techniques, with or without solvents. The in situ polymerization of polymer on the surface of fine aggregate particles can have the advantage of reducing or eliminating drying steps. [0048] By way of example, a water-soluble monomer(s) can be chosen from the following monomers or salts thereof: acrylic acid, methacrylic acid, acrylamide, methacrylamide, and their derivatives, carboxy ethyl acrylate, hydroxy ethylmethacrylate (HEMA),

hydroxy ethylacrylate (HEA), polyethylene glycol (PEG) acrylates, N-isopropylacrylamide (NiPAm), 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPS), sodium salt of styrene sulfonate, vinylsulphonic acid, (meth)allylsulphonic acid, vinylphosphonic acid, N- vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl-N- vinylformamide, N-vinylpyrrolidone, N-butyrolactam or N-vinylcaprolactam, maleic anhydride, itaconic acid, vinyl acetate, dimethyldiallylammonium chloride; quatemized dimethylaminoethyl methacrylate (DMAEMA),

(meth)acrylamidopropyltrimethylammonium chloride, methylvinylimidazolium chloride; 2- vinylpyridine; 4-vinylpyridine, and the like. The ratio of ionic to nonionic monomers can be selected to yield hydrogels with different charge density. In some instances, for example, it is desirable to have hydrogels with higher charge in order to yield coatings with faster hydration or swelling properties. In other instances, the ionizable monomers can be selected to have higher or lower ionization constants to yield hydrogels more or less stable in brine environments. Other advantageous properties can be imparted by selection of appropriate charge densities.

[0049] In embodiments, coating precursors can include polyfunctional monomers that contain more than one polymerizable group and that will introduce the crosslinking or branching points in the hydrogel. Examples of these monomers are: pentaerythritol triallyl ether, PEG-diacrylates and methacrylates, Ν,Ν'-methylenebisacrylamide, epichlorohydrin, divinyl sulfone, and glycidyl methacrylate. When such monomers are used, the crosslinking monomer will be in the range of about 0.001 to about 0.5 % of the total monomer content.

[0050] In embodiments the monomers/macromonomers used are selected from coating precursor monomers that that will form a non-water soluble coating. After the coating is applied, its further modification will result in the water swellable polymer. As an example, a polymeric coating containing hydrolysable groups can be formed, and subsequent hydrolysis will yield the hydrogel. Examples of monomers that fall in this category are esters, anhydrides, nitriles, and amides; for example, the ester monomers methyl acrylate, t-butyl acrylate can be used. As another example, a monomer containing vinyl functionalities can form the hydrogel by different polymerization techniques with or without solvents. The polymerization techniques include bulk, suspension, admicellar, and solution polymerization.

[0051] In other embodiments, coating monomers or precursors can be selected to form fine aggregate particles with a hydrogel comprising a polyurethane or polyurea. A list of suitable monomers to form polymers with polyurethane and/or polyurea functionalities are: polyols such as ethylene glycol, propylene glycol, glycerin, trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol, sorbitol, sucrose, a-methylglycoside, polyoxyalkylenes, such as PEG, copolymers of PEG-PPG, Pluronics, Tetronics, polyamines such as JEFF AMINE® polyetheramines. Among the isocyanates there may be mentioned toluene-diisocyanate, naphthalenediisocyanate, xylene-diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylene diisocyanate, trimethyl hexamethylene diisocyanate, cyclohexyl- 1,2-diisocyanate, cyclohexylene-l,4-diisocyanate and the like. Other appropriate polymers can include HYPOL® hydrophilic polyurethane prepolymers from Dow, DESMODUR® and MONDUR® resins from Bayer (2,4'- diphenylmethanediisocyanate, 4,4'- diphenylmethanediisocyanate, and their mixtures), and CONATHANE® (polyisocyanate functionalized prepolymers of toluene diisocyanate and poly(tetramethylene glycols)) from Cytec, and the like.

[0052] The coating of fine aggregate particles with a polyurethane (PU) hydrogel can be carried out by conventional methods. In an embodiment, the coating can be performed in bulk without the use of solvents. For example, a typical formulation for a crosslinked PU hydrogel can be prepared in a one-step bulk polymerization process using a diisocyanate, a polyoxyalkylene glycol, and a multifunctional crosslinking agent. In an embodiment, the formulation will contain 10 to 80% of a polyoxyalkylene glycol having the polyoxyalkylene molecular weight between 200 and 25,000.

[0053] 3. Alternative methods of making hydrogel-coated fine aggregates

[0054] Another method to form the hydrogel layer in situ can be carried out by dissolving or suspending a water-soluble polymer in a monomer formulation followed by

polymerization of the monomer. The monomers can be selected form the previous list of water soluble monomers. In the case that the water-soluble polymer is dissolved in the monomer mixture, the resulting coating will consist in interpenetrating hydrogel network of the initial water-soluble polymer and the polymer formed in situ. In the case where the water-soluble polymer is suspended in the monomer mixture, the resulting coating will consist of a hydrogel coating in which the water soluble particles are locked up or entrapped. For example, these particles can be trapped inside the newly formed hydrogel coating or they can be bonded to the newly formed polymer. The water-soluble polymer can be dissolved or suspended in the monomer formulation in the presence or absence of a solvent and the polymerization can be carried out by different techniques.

[0055] Suitable water soluble polymers to be mixed with monomers can be selected from the group consisting of polyacrylamide, polyacrylic acid, copolymers of acrylamide with acrylic acid salts, polyethyleneglycol, polyvinylpyrrolidone, polyvinylalcohol,

carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, starches, latex polymers, and the like.

[0056] Another method for modification of fine aggregate particles includes grafting hydrophilic polymers onto the particles. The grafting of polymer chains onto the surface of the particle can be done by reactions such as Huisgen cycloaddition and other coupling or addition reactions that can immobilize the polymers onto the particle surface.

[0057] The fine aggregate particles used for these purposes can be selected to have surface functional groups such as epoxy, vinyl, amine, hydroxyl, etc. Those groups can then react with polymers having groups capable of reacting with the functional groups on the particle surface. For example, fine aggregate particles comprising silica can be surface modified by silanes such as aminosilanes, vinylsilanes, epoxysilanes, etc.

[0058] In embodiments, the polymers that will react with the functionalized particle are hydrophilic linear or branched polymers or copolymers. The polymer can have one or more grafting moiety. In embodiments, the polymers can have functional groups such as amino, carboxyl or salts thereof, hydroxyl, thiol, acid anhydride, acid chloride and/or isocyanate groups which enable covalent binding to the functional groups of the particle. Examples of polymers that can be used to react with the functionalized particle are: epoxide

functionalized PEG, amine functionalized PEG, azide functionalized PEG,

polyethyleneimine, polyacrylic acid, polyvinyl alcohol, etc.

[0059] In embodiments the resulting hydrogel, in addition to having swellable properties, can have temperature responsive or pH-responsive properties. The resulting swellable properties of the fine aggregate particles can thus be tuned. This is an added benefit for enhancing flowability while preserving composite strength, since temperatures are lower at the early stages in which the coated aggregate particles are transported and full swelling behavior is desirable; higher temperatures are expected later in the curing process, where lower swelling of the hydrogel layer is desirable for packing improvement. The monomers used to make the temperature-responsive hydrogel-coated fine aggregate particles can be selected from N-isopropylacrylamide (NiPAm) (LCST=35 degrees C), ethylene oxide, propylene oxide, or other macromonomers/polymers that display a lower critical solution temperature (LCST). Methylcellulose is a readily available polymer with an LSCT of -50- 60 °C, making it suitable for this application. Chitosan is insoluble at higher pH, and soluble in acid, and is suitable for a pH responsive polymer coating approach.

[0060] Thermoresponsive polymers, such as polymers exhibiting LCST behavior, can be particularly advantageous for coating fine aggregate particles such as sand, to be used in preparing cementitious composites. Not to be bound by theory, it is understood that a thermoresponsive polymer can swell and absorb/retain water at temperatures below its trigger point or threshold temperature; above this temperature, the thermoresponsive polymer coils would collapse, releasing water. Polymers exhibiting thermoresponsive polymers can include this LCST behavior can include polymers comprising N- isopropylacrylamide, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose, and the like. Poly-N-isopropylacrylamide (NiPAm) is especially suitable for these applications. It can be used alone or in combination with other polymers to make coated fine aggregate particles such as sand, to be used in preparing cementitious composites.

[0061] In an embodiment, the process of converting a substrate such as sand into coated fine aggregate particles can be conducted at or near the point of use. This method has the advantage of converting a commodity material with high material handling costs, such as sand, into a specialized material that has added features. The sand can be acquired from local sources or shipped directly from a sand mining site or warehouse, for modification at the point of use. As used herein, the term "point of use" refers to any site where the concrete mixture is actually to be used, for example, a construction site, a building site, a site for repairing structural components, a highway site, an infrastructure site, an architectural site, an ornamental site, and the like. The concrete components may be mixed at the point of use, or they may be mixed at a different location, termed the point of mixture. Producing modified sand at or near the point of use (also known as in-situ preparation or preparation "on the fly") avoids having to ship sand first into a blending plant and then ship a second time from the blending plant to the point of use. In the case of sand, the shipping costs can be higher than the material costs, so avoidance of extra shipping is desirable for controlling costs.

[0062] As disclosed herein, the modified composite particles, e.g., modified sand-based composite particles, lead to tremendous utility in making advanced concrete formulations with either pre-coated sand, or sand coated at or near the point of use (in-situ, or "on the fly"), for example, just immediately prior to addition into the final blend vessels.

[0063] In embodiments, the process of manufacturing coated fine aggregate particles at or near the point of use can be called an "on-the-fly" process. In embodiments, the fine aggregate particles can be coated with a double coating, and optionally partially dried, at the point of use. The double coating can include a first coating that acts as a primer coating, and a second coating of the hydrogel forming polymer. The partial drying step may be just room temperature annealing to allow the high molecular weight hydrogel polymer to

entangle/intermingle and thus remain on the sand surface even during subsequent blending with cement and aggregate.

[0064] In embodiments, the fine aggregate, such as sand, can be modified with hydrogel polymer coating in a continuous process at or near the point of use. To accomplish this, the sand can be conveyed in slurry or dry form via pipe, conveyor, auger, or mill, and the sand can be mixed in a first injection point with a tether polymer to impart a cationic charge; examples of tether polymers are polyethylenimine, polydiallyldimethylammonium chloride, polyvinylamine, polyallylamine, chitosan, and epichlorohydrin/dimethylamine polymer.

After the sand and tether polymer have been combined, a second injection point can provide the hydrogel forming polymer, where the hydrogel polymer can be an anionic polymer such as a hydrolyzed polyacrylamide, a copolymer of acrylamide with anionic comonomers, a carboxymethylcellulose, and the like. The hydrogel forming polymer can also incorporate crosslinkers. The polymer layer can incorporate a polymer, block copolymer, or oligomer containing ethylene oxide or propylene oxide units, such as the Huntsman Jeffamine products, to enhance plasticity of the uncured cement mixture. In the process of combining polymer coated sand with the other cement slurry ingredients, the polymer coated sand can be pre-blended with a dry cement/sand mixture, or the polymer coated sand can be pre- wetted before blending with the other ingredients of the cement/sand mixture.

[0065] Hydrogel polymers that can be used to modify fine aggregate particles in accordance with the systems and methods disclosed herein can be introduced, in

embodiments, as oil-based emulsions, dispersions, water-based emulsions, latexes, solutions, and dispersions. In embodiments, the hydrogel polymer can be an alkali-swellable emulsion, wherein the hydrogel properties of the polymer are not fully developed until the polymer is contacted with alkali. In this embodiment, the alkali-swellable emulsion can be coated onto the fine aggregate particles to form coated fine aggregate particles, and these coated particles can respond proportionately as the pH of the concrete mixture rises.

[0066] In embodiments, an additive such as an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol, and ethanol can be added during or before the step of mixing the fine aggregate particles and the liquid polymer coating composition. In embodiments, inversion promoters useful as additives in the polymer coating formulations for fine aggregate particles can include high HLB surfactants, such as polyethylene oxide lauryl alcohol surfactant, (ETHAL LA- 12/80% from ETHOX), ethylene glycol, propylene glycol, water, sodium carbonate, sodium bicarbonate, ammonium chloride, urea, barium chloride, and mixtures thereof. In embodiments, inversion promoters can serve the function of facilitating the release of active polymer ingredients from the internal phase of an oil based emulsion polymer into the (typically aqueous) process fluid to be treated.

Since this process converts an oil continuous polymer into a water continuous environment, can be characterized as a phase inversion.

[0067] In other embodiments, the fine aggregate particles can be modified with a polymer formulation without the need for a drying step. This can be accomplished by the use of a solvent-free polymer formulation, or a curable formulation. In certain simplified methods, a dry or liquid polymer formulation can be applied onto the fine aggregate particles via inline mixing, and the modified material thus prepared can be used without further processing. The moisture content of the fine aggregate particles can be modified by addition or removal of water, or addition of other liquids, to allow the substrate to be effectively coated, handled, and delivered into the concrete mixture.

[0068] The coated fine aggregate particles can be further modified with a wetting agent such as a surfactant or other hydrophilic material to allow for effective dispersion into a concrete mixture. The coated fine aggregate particles can be further modified with an anticaking agent such as calcium silicate, calcium carbonate, talc, kaolin, bentonite, diatomaceous earth, silica, colloidal silica, or microcrystalline cellulose to improve the flowability and handling properties of the material before it is added to the cement mixture. The fine aggregate particles with the anticaking agent can have improved handling properties, such as free-flowing properties, resistance to clumping, ease of conveying, ease of metering, and ease of discharging from a storage vessel, hopper, truck, silo, conveyor, railcar, or transport vessel. In embodiments, the fine aggregate particles with the anticaking agents can have reduced drying requirements, so that the finished product can be produced with a reduced amount of energy, time, and equipment.

[0069] The fine aggregate particles as disclosed herein can have the advantage of delivering friction-reducing polymer into the concrete mixture fluid to improve the flowability, workability, and handling properties. Localizing the polymer around the aggregate surface as described herein can result in a more effective use of polymer and can improve the mixing of the fine aggregate particles within the concrete mixture. In embodiments, some of the hydrogel polymer can desorb from the surface of the fine aggregate particles to deliver friction reducing benefits or viscosity features to the mixture, thus lessening the need for free water addition.

[0070] The hydrogel polymer used for preparation of hydrogel-modified aggregates (e.g., sand) can, in embodiments, comprise polymers such as a polyacrylamide, copolymers of acrylamide with anionic and cationic comonomers, copolymers of acrylamide with hydrophobic comonomers, poly(acrylic acid), poly(acrylic acid) salts, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, alginate, carrageenan, locust bean gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion (HASE) polymers, latex polymers, starches, and the like. In embodiments, the hydrogel polymer can be crosslinked to enhance the water absorbing and swelling properties of the polymer. The crosslinkers can be introduced as an element of the hydrogel base polymer, or they can be introduced as chemical modifiers for pre-formed polymers.

[0071] In embodiments, polymer pairing or ionic crosslinking can be used to improve the hydrogel polymer retention on the surface of the fine aggregate particles, e.g., sand. For example, a cationic affixation polymer can be deposited onto the fine aggregate particles as a first layer to "lock in place" a second layer containing a hydrogel such as a high molecular weight anionic polymer. In embodiments, the cationic affixation polymer can be polydiallyldimethylammonium chloride (poly-(DADMAC)), linear polyethylenimine (LPEI), branched polyethylenimine (BPEI), chitosan, epichlorohydrin/dimethylamine polymer, ethylene dichloride dimethylamine polymer, or cationic polyacrylamide. The cationic affixation polymer layer can be placed on the fine aggregate particles either before or after surface modification with the anionic hydrogel layer. The ionic interaction can act as a crosslink mechanism to help prevent the anionic polymer from desorbing in high shear environments such as going through a pump or during transport and handling. The cationic affixation polymer can also improve polymer retention by causing a delay in the hydration and extension of the anionic polymer chains. It is believed that less polymer chain extension during the pumping process will yield higher polymer retention on the fine aggregate particles (i.e. less desorption). The two-layer approach can lead to the development of in- situ creation of coated sand at or near the point of use (i.e., on-the-fly manufacture of this engineered sand as a key ingredient of the novel concrete formulation). This has the advantage of not having first to dry the coated sand as a separate process step, leading to energy savings.

[0072] Covalent crosslinking of the hydrogel polymer layer on fine aggregate particle surfaces (e.g., the sand) can improve the swelling properties of the polymer and the shear tolerance to prevent premature release of the hydrogel from the fine aggregate particles during concrete mixing. Covalent crosslinkers can include the following functional groups: epoxides, anhydrides, aldehydes, diisocyanates, carbodiimides, divinyl, or diallyl groups. Examples of these covalent crosslinkers include: PEG diglycidyl ether, epichlorohydrin, maleic anhydride, formaldehyde, glyoxal, glutaraldehyde, toluene diisocyanate, methylene diphenyl diisocyanate, l-ethyl-3-(3-dimethylaminopropyl) carbodiimide, Ν,Ν'- methylenebisacrylamide. Covalent crosslinking of the hydrogel polymer layer on the fine aggregate particle surfaces can effectively create a swellable "polymer cage" around the particles. The covalent bonds prevent the polymer from completely desorbing into solution. The slightly insoluble polymer layer is able to swell and produce a hydrated polymer layer.

[0073] To further prevent the possible detachment of the hydrogel from the surface of the particle, the fine aggregate particles can be treated to impart functionalities that will also take part in the polymerization process. For example, sand particles can be treated with silanes to yield particles with vinyl functionalities, hydroxyl, epoxy, etc.

[0074] Delayed/controlled hydration of polymer layer may be desirable, in order to delay the hydration of the polymer surface modification during handling of the fine aggregate particles and combining them with other components of the concrete mixture.

Environmental factors such as humidity and rain could cause premature hydration of the polymeric coating, which would make it difficult to effectively meter the amount of coated fine aggregate particles added to the cement mixture. It is also believed that a fully hydrated polymer layer can be more prone to desorption under high shear conditions. For these reasons, it may be advantageous to engineer a coated fine aggregate particle having slower or delayed hydration properties. In embodiments, delayed hydration can be achieved by addition of a low hydrophilic-lipophilic balance (HLB) surfactant, exclusion of a high HLB finishing surfactant, ionic crosslinking, covalent crosslinking, charge shielding using a monovalent salt, or by incorporation of a hydrophobic layer such as a fatty acid, or a fatty alcohol.

[0075] In embodiments, hydrophobic groups can be incorporated into the hydrogel polymer to allow for hydrophobic interactions. This method can improve the salt tolerance of the hydrogel layer, such that the hydrogel layer remains swellable even in an aqueous fluid that contains elevated salt concentrations.

[0076] In embodiments, the compositions and methods of manufacture provided herein offer an advantageous solution to the traditional trade-off between strength and flowability for concrete mixtures, as set forth in the art. Hydrogel-coated fine aggregate particles, such as hydrogel-coated sand, for use in concrete mixtures provide built-in flowability properties, resulting in easy -to-work preparations that yield high-strength cured products.

[0077] 4. Multilayer polymer coating system

[0078] In embodiments, a fine aggregate particle can be coated with at least two layers of coating. For general use, fine aggregate particles can be coated at a remote location with at least two layers of coating, to yield coated aggregates that can later be incorporated into cementitious composites. First, for example, a pressure-activated fixative polymer can be used to coat the fine aggregate particle. This coating layer can be elastomeric, thereby providing resiliency and elasticity to the concrete. Second, a block copolymer can be adsorbed or otherwise disposed onto the first layer of coating. The copolymer can have a section with high affinity for the first polymeric layer, allowing strong interaction

(hydrophobic interaction), and can have another section that is hydrophilic, allowing for desirable interaction with the water in the concrete mixture.

[0079] In certain embodiments, a stronger interaction between the first and second coating layers may be useful. To accomplish this, a swelling-deswelling technique can be implemented. For example, the block copolymer can be adsorbed onto the surface of the coated particle. Then, the first coating layer can be swelled with small amounts of an organic solvent that allow the hydrophobic block of the copolymer to penetrate deeper into the first coating layer and to become entangled in the elastomeric coating. By removing the organic solvent, the layered polymeric composite will deswell, resulting in a stronger interaction of copolymer with the elastomeric particle. A method for swelling-deswelling technique is set forth in "Swelling-Based Method for Preparing Stable, Functionalized Polymer Colloids," A. Kim et al, J. Am. Chem. Soc. (2005) 127: 1592-1593, the contents of which are

incorporated by reference herein.

[0080] In other embodiments, certain of these coating systems can be employed to prepare coated aggregates at the point of use, e.g., at a job site where the coated aggregates are to be incorporated into the cementitious composite material, as will be described below in more detail.

[0081] While the embodiments described below refer to a two-layer coating system, it is understood that there may be multiple coating layers forming the coated aggregate particle, with the each of the multiple coating layers possessing some or all of the attributes of the two coating layers described in the exemplary embodiments.

[0082] a. Inner Polymeric Layer

[0083] In designing the polymers for the inner polymeric layer, a variety of pressure- sensitive adhesive polymers can be used, having different functionalities and molecular weights. This is the first coating layer that is applied to the fine aggregate particle.

Polymeric design for this inner polymeric layer can be directed by such variables as chemical resistance, ultimate adhesion, service temperature, and the like, so that a coating material can be selected that is targeted to the projected properties to obtain in the concrete.

[0084] In embodiments, coating thickness can be varied, which can have specific effects on the strength of adhesion of the fine aggregate particles with each other as they interact with the cement binder. Appropriate coating methods can include solution coating or in-situ coating where the polymer is synthesized in the presence of the fine aggregate particles.

[0085] In embodiments, the inner polymeric layer can be made from phenolic resins, epoxy resins, furan resins, phenolic formaldehyde resins, melamine formaldehyde resins, urethane resins and phenolic, furan resin mixtures, a urea-aldehyde resin, a urethane resin, a furan/furfuryl alcohol resin, a phenolic/latex resin, a polyester resin, an acrylate resin, or combinations thereof. In another embodiment of the invention, the inner polymeric layer with adhesive material can be a thermoplastic resin. Examples are: styrene block copolymers such as: SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene), SEBS (styrene- ethylene/butylene-styrene), and SEP (styrene-ethylene/propylene), ABS copolymers (i.e., acrylonitrile-butadiene-styrene). Other examples include EVA (ethylene vinyl acetate) copolymers, acrylic polymers, vinyl ethers, and silicone rubbers. A commercial thermoplastic, for example the ENABLE family of products available from ExxonMobil Chemical Co, can be used: these materials are a family of n-butyl acrylate copolymers (e.g., ENABLE EN 33900 and 60 ENABLE 33330).

[0086] In embodiments, these materials can be mixed with other resins as tackifiers that will increase their stickiness. Examples of tackifiers are: rosins and their derivatives, terpenes and their derivatives, shellac resin, small molecular weight aliphatic, cycloaliphatic and aromatic resins (less than 10 carbons), terpene-phenol resin, saturated hydrocarbon resin. An example of composition will be 30 - 70 % of total mass of tackifier agent to thermoplastic resin.

[0087] In embodiments, the inner polymeric layer can be applied to the particulate substrate by methods familiar to artisans of ordinary skill. For example, the application of the inner layer can be performed by solution coating, melt coating, or by 100% solid coating (no solvent needed). In embodiments, the inner layer can be applied in an amount of 0.05 to 10 weight percent of the fine aggregate particle, for example, in an amount of 0.5 to 5 percent.

[0088] b. Outer Coating Layer

[0089] It is desirable to impart hydrophilic features to the coated particle. In the aqueous environment of the concrete mixture, a hydrophilic coating can create a thin, water-like layer on the surface of the particle, making it slippery and reducing the friction between particles. This can facilitate the transport of the particles in the fluid.

[0090] By adding a hydrophilic coating to a fine aggregate particle for use in a

cementitious composition, a number of performance advantages can be achieved. When the hydrogel contacts the water in the mixture, there is an immediate water uptake into the swelling hydrogel layer, so that hydration burst is minimized. The presence of the hydrogel layer permits the slow and controlled release of water, to meet the hydration needs and to control the hydration rate as desired. The built-in lubrication of the hydrogel also permits a superplasticity when needed. When the fine aggregate particle is pre-coated with the hydrogel, as disclosed herein, there is a rapid and efficient distribution of the polymer upon mixing, since each grain carries the polymer. In addition, the dry components of the concrete mixture can be pre-mixed before water is added, and the sequence of water addition can be modulated to suit the particular job. In certain situations, the coated fine aggregate particles may be added into water before combining them with cement; other situations may involve dry-blending coated fine aggregate particles with dry cement solids before exposure to water. [0091] Finally, and most importantly, the hydrogel polymer possesses inherent

precipitation (also known as complexation) properties, where the rate or extent of precipitation can be controlled by virtue of choosing the right copolymer composition used to manufacture the coated fine aggregate particles. The hydrogel polymer is capable of interacting with calcium ions to form an insoluble complex, creating multiple molecular linkages between the filler and the binder. This polymeric calcium salt precipitate acts as a stress buffer and adhesion promoter between the filler and the binder, greatly increasing toughening the final composite.

[0092] In embodiments, a second coating layer can be applied as an outside layer to provide the desirable hydrophilic features to the overall fine aggregate particle. In other embodiments, intermediate layers can be applied to the fine aggregate particle, then the outermost hydrophilic layer can be provided. In the description that follows, the second coating layer forms the outer coating of the particle. It is understood, though, that the outer hydrophilic coating may be applied to any number of inner, intermediate layers, while still maintaining the advantageous properties of the particles in accordance with the present disclosure.

[0093] In embodiments, the outer layer can be partially or wholly formed from a polymer. For example, a suitable block copolymer can be designed having hydrophobic and hydrophilic sections. Variables involved in copolymer design include the molecular weight of polymer, ratio of hydrophobic to hydrophilic section, and the functionalities of the copolymer. The outer layer, for example a second coating layer, can be adsorbed onto the first layer using conventional methods of polymer adsorption, as would be known in the art, and/or swelling-deswelling using organic solvents.

[0094] In embodiments where a polymer layer is used as the outer coating layer, the polymer coating can be made from hydrophilic polymers like ethylene oxide/propylene oxide (EO/PO) copolymers, polyvinyl acetate, polyethylene-co-vinyl acetate, polyvinyl alcohol, polysaccharides, and the like. In embodiments, the outer layer can be fabricated from block copolymers having hydrophilic and hydrophobic segments. Such materials can be diblock, triblock or multiblock copolymers. For example, an ethylene oxide/propylene oxide block copolymer can be used, for example the Pluronic family of copolymers (BASF). As another example, Guerbet alcohol ethoxylates, lauryl alcohol- tridecyl alcohol- stearyl alcohol- nonylphenol- or octylphenol- ethoxylates, for example the Lutensol family of products (BASF). In embodiments, the selected materials will have a high hydrophilic- lipophilic balance, so that the product is substantially more hydrophilic than hydrophobic. Examples of such materials include certain stearyl alcohol and nonylphenol ethoxylates.

[0095] In embodiments, the second layer can be applied to the first layer using a swelling- based method. According to such a method, the first layer can be exposed to a solvent that can swell this layer without dissolving it. The polymer for the second layer, having both hydrophilic and hydrophobic segments, can be dissolved in the same solvent. When the solution bearing the second layer polymer is put into contact with the particles bearing the swollen first layer, the hydrophobic segments of the polymer will tend to interact with the hydrophobic first layer, resulting in entanglement of the two hydrophobic entities. When the solvent is removed, the first layer will deswell, locking the hydrophobic attachments of the second-layer polymer in place.

[0096] In other embodiments, the outer layer can be formed by chemical reaction or modification of the inner polymer layer. For example, the outer surface of the inner polymer layer can be oxidized, etched, epoxidized, ethoxylated, hydrolyzed, or otherwise coated to protect the inner polymer layer from the fluid environment in the cement.

[0097] c. Point-of-Use Preparation of Multilayer Coated Fine Aggregate Particles

[0098] In embodiments, a multilayer polymer coating can be applied to fine aggregate particles at the site where the cementitious composite is being prepared. For example, hydrogel-coated sand can be produced "on-the-fly" at the point of mixture to make concrete or other cementitious products. In an exemplary embodiment to prepare hydrogel-coated sand suitable for these purposes, sand can be subjected to two successive treatments just before the material is introduced into the mixing vessel as a component of the cementitious composite. In this embodiment, the bare sand particles can be first exposed (e.g., by spraying or in-line mixing) to a poly cation solution. The polymer attaches to the sand immediately, forming a "foundation" primer. Suitable polycationic polymers can include chitosan, polyvinylamines, polyallylamines, polydiallyldimethylammonium salts (e.g., polydiallyldimethylammonium chloride poly(DADMAC)), poly(dimethylaminoethyl acrylate methyl chloride quaternary) polymers, branched or linear polyethyleneimine, crosslinked amines, epichlorohydrin/dimethylamine (epi/DMA),

epichlorohydrin/alkylenediamines, quaternary ammonium substituted polymers, such as (aciylamide/dimethylaminoethylacrylate methyl chloride quat) copolymers and

trimethylammoniummethylene-substituted polystyrene, styrene maleic anhydride imide (SMAI), polyethylenimine (PEI), amine-aldehyde condensates, and the like. Following this exposure, the sand bearing the poly cation can be exposed to a second polymer comprising a polyanion, such as a solution, a dispersion, an emulsion, or an inverse emulsion. Suitable anionic polymers can include, for example, olefinic polymers, such as polymers made from polyacrylate, polymethacrylate, partially hydrolyzed polyacrylamide, and salts, esters and copolymers thereof (such as (sodium acrylate/acrylamide) copolymers), sulfonated polymers, such as sulfonated polystyrene, and salts, esters and copolymers thereof. For example, the second coating layer can be a hydrogel polymer such as polyacrylamide, copolymers of acrylamide with anionic and cationic comonomers, hydrolyzed

polyacrylamide, copolymers of acrylamide with hydrophobic comonomers, poly(acrylic acid), poly(acrylic acid) salts, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, alginate, carrageenan, locust bean gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion (HASE) polymers, latex polymers, starches, and the like. In embodiments, the polymers for the second layer can be covalently crosslinked. Covalent crosslinkers can include the following functional groups: epoxides, anhydrides, aldehydes, diisocyanates, carbodiimides, divinyl, or diallyl groups. Examples of these covalent crosslinkers include: PEG diglycidyl ether, epichlorohydrin, maleic anhydride, formaldehyde, glyoxal, glutaraldehyde, toluene diisocyanate, methylene diphenyl diisocyanate, l-ethyl-3-(3- dimethylaminopropyl) carbodiimide, N,N'-methylenebisacrylamide, and the like.

[0099] Using the formulations and methods described herein, coated fine aggregate particles, e.g., hydrogel-coated sand, can be prepared at or near the point of use ("on the fly") instead of at a remote factory site or sand quarry. This simplifies logistics, because only the appropriate polymers need to be shipped to production sites for application to bare sand, and one need not ship pre-coated sand prepared at a remote location.

5. Construction applications using modified sand-based composite particles a. Concrete mixtures

[00100] Cement hydration is exothermic. It also generates copious amounts of calcium hydroxide, making the interstitial and inter-particle water highly alkaline. Calcium is divalent, capable of bonding adjacent carboxylic or sulfonate groups, causing polymer precipitation and electrostatic crosslinking. Such calcium-induced

precipitation/crosslinking/anchoring on sand surface can greatly increase the interfacial adhesion between the hydrating cement and dispersed sand, enhancing concrete strength. Before the water turns highly alkaline, the polymer (e.g., hydrogel) on the modified sand- based composite particles swells, promoting sand dispersion and suspension in the mixture thus greatly improving fresh concrete workability and reducing water demand. In fact, the swollen gel layer around sand on the modified sand-based composite particles imparts viscoelasticity to the concrete mixture, and the resulting material can be extruded to fill cavities without slumping or sagging significantly. Often the overall mixture can retain a higher level of water (initially trapped in the swollen hydrogel) which is subsequently controllably released into the cement phase, causing more complete cure and significantly larger volume of cured concrete, without sacrificing the mechanical properties of the finished product. Further, the cured product embodying coated sand even exhibits enhanced performance compared to incompletely cured and water-starved conventional systems.

[00101] In an embodiment, modified sand-based composite particles as disclosed herein can be added into a concrete slurry along with dried sand in a conventional mixing vessel, e.g., in a ready-mix vessel. First, the polymeric coating around the modified sand-based composite particles swells in water, causing effective particle dispersion. As the hydration reaction of the oxides in cement progresses, the intervening water becomes highly alkaline and calcium ions abound in the environment. Properly chosen polymers on sand surface will collapse and precipitate due to calcium ion induced complexation. The organic-inorganic precipitate deposited on sand surface promotes cement-sand adhesion. Voids and capillaries are minimized.

[00102] For example, to enhance the effectiveness of traditional plasticizers and

superplasticizers in concrete, modified sand-based composite particles as disclosed herein can be used with pre-adsorbed polycations (e.g., PDAC and/or any of a number of poly- amines, both natural and synthetic). Here, cationically modified sand attracts these negatively charged polymeric admixtures such as the aforesaid plasticizers and

superplasticizers, polyacrylamide emulsions or acrylic latex on its surface, where their intended functions are exploited locally with performance exaggerated.

[00103] In embodiments, for example, a moldable system can be provided for cementitious composites. Using a coated fine particulate as described herein, a cement mixture can be prepared that will have moldable properties. A cement formulation comprising such coated fine particulates, e.g., a hydrogel-coated sand, can be mixed with water and placed at the desired location. Unless the polymer coating layer on the fine particles is very thin, the water absorption capacity of the coated sand can be so high as to lead to a cementitious mixture that is not "fluid-like" in appearance. Instead, the mixture can resemble a moldable "semi- solid" that assumes a doughy consistency. A cement mixture having this consistency can offer tremendous operational advantages, as the water is trapped in the swollen hydrogel layer around the sand can release slowly through diffusion. The hydration reaction in the concrete delivers the driving force to consistently and measurably shift water distribution equilibrium out of the gel layer into the hydrated crystal. Not to be bound by theory, it is envisioned that this shift can be caused to accelerate by an imposed hydrostatic pressure, squeezing the water from the gel layer to become available for cement cure.

[00104] Moreover, hydrogel-coated sand offers great flexibility in so far as mixture

"appearance" is concerned. Ultra-thin coatings can lead to more fluid-like (thus more conventional) mixtures. As another approach, mixed use of bare and coated sand can reduce the overall water absorption capacity of the gel-forming polymer layers. Thicker polymer layering on the sand can produce a thicker, more moldable consistency that allows shaping of the mixture for aesthetic or functional purposes.

[00105] Another approach for producing a moldable cementitious composite involves the use of thermoresponsive or pH-responsive polymers to form the water-trapping polymeric layer around the fine composites. For example, LCST polymers can be used to coat sand to form a coated sand useful for "tuning" the moldability of the cementitious composite. In such an embodiment, LCST-polymer-coated sand can be added to a cement mixture dry or pre-combined with water. The resulting mixture, comprising the LCST-polymer-coated sand, can be used to fill a framework or a mold, or can be troweled over a level surface such as a floor or a sidewalk. When local heating is introduced, cement cure is initiated. The heat that is released due to cure can self-sustain continued cure as the transition temperature of the LCST polymer is attained and its entrained water is released.

[00106] Once initiated, cure propagates temporally and spatially. By adjusting the thickness of the LCST polymers on the sand, the rate of water release and thus curing can be modified. Similarly, by mixing the LCST-polymer-coated sand with uncoated sand, curing rate can be manipulated. These formulations also allow spatial tuning of curing rate. For example, if a long pre-cast beam or column is desired, one can provide a cement mixture comprising the LCST-polymer-coated sand, and initiate cure from one end, while optionally imposing the hydrostatic pressure continuously throughout the beam or column). This pre-cast structure will have a dense final morphology because it has been controllably cured, as any potential creation of voids is suppressed by the applied pressure. b. Specialized applications

[00107] De novo functionalities may also be delivered over and above those contemplated by traditional admixtures. As an example, urethane chemistry can be incorporated into modified sand-based composite particles. As is understood in the art, an immense variety of formulations can be derived from creating urethanes, both rigid and soft. The key ingredients are an isocyanate compound (such as methylene diphenyl diisocyanate (MDI) and/or its oligomeric/polymeric forms), polyols (linear or branched), and catalysts. The urethane formulation may be melt- or solvent-coated on sand to form modified sand-based composite particles. For use in a concrete mixture, curing of the urethane formulation may be delayed until concrete slurry is prepared. Alternatively, the urethane precursors may be caused to react in the presence of controlled amounts of water (to achieve in situ foaming). In either case, the modified sand-based composite particles are comprised of sand particles shrouded by a layer of foam. This approach has the inherent advantage of geometrical precision, as the "voids" in the final concrete are small, numerous and evenly distributed, resulting in a low- density concrete with optimized mechanical performance. The polyols may be further chosen to deliver liquid water repellency to the urethane foam, preventing water intrusion even for a low-density structure.

[00108] Modified sand-based composite particles prepared as urethane foam-coated sand can have any range of coating thickness and core average diameter. Depending upon the relative ratio of the core and the shell using foam coating, the effective density of the modified sand-based composite particles can be lower than the density of sand alone. The lower density composite particles can be advantageous as a concrete additive.

[00109] There are other situations where an integrated composite particle comprising sand and a foam coating can be useful. For playground sand, as an example, a composite particle can be constructed using sand as a base, but adding a urethane foam coating. These particles can have less density than bare sand, so they will not segregate out from the rubber particles if used as a mixture; the uniform distribution of modified sand-based composite particles with rubber particles in such a mixture can contribute to more effective shock absorption and longer lifespan for the protective layer. As another approach, elastomeric modified sand- based composite particles can be formed, using sand as the substrate and coating it with two different shells. The first shell can be a foam substance, for example the urethane foam as described above. The top coat can be a rubbery or elastomeric material to provide abrasion resistance and resilience. Rubbery materials like Kraton, EPM, EPDM, natural and synthetic rubber, polybutylene, polyisobutylene, polyisoprene, polychloroprene, acrylic rubber, latex, EVA, ECO, silicone rubber, and the like can be used for the outer layer. In embodiments, the first coating on sand can impart strong adhesion properties to firmly anchor the elastomeric or shock-absorbing particles to the sand, preventing their eventual segregation.

[00110] In certain applications, the curing of cement, grout, stucco, or mortar takes place under non-ideal conditions. For example, these cementitious composites are used to repair cracks in structures, and to block the influx of water. Curing of the cementitious composites in the presence of water can lead to problems with curing and sealing. In embodiments, the coated fine aggregate particles of the invention can be incorporated into a cementitious composite that is used to seal or repair a structure against water intrusion, or to cure in the presence of excess water. The coated fine aggregate particles can offer some protection against the effects of the excess water.

[00111] Other combinations of layering materials can be used in modified sand-based composite particles for other specialized applications. For example, various polyesters and polyamides can be used as abrasion-resistant top coats over foams in making modified sand- based composite particles. As another example, crosslinkable formulations amenable to in situ crosslinking (e.g., urethane acrylates and epoxyacrylates) can be used as top coats over foams. Particles designed to have greater or lesser amounts of elasticity, water repellency, resiliency, abrasion resistance, etc., can be used in various specialized construction applications.

EXAMPLES

• Materials:

• Rubinate M (Huntsman, Woodlands, TX)

• Glycerol Propoxylate-block-ethoxylate (Sigma-Aldrich, St. Louis, MO)

· Triethanolamine (Sigma-Aldrich, St. Louis, MO)

• Castor Oil (Sigma-Aldrich, St. Louis, MO)

• Poly cat 8 (Air Products, Allentown, PA)

• Sand, -50/+70 (Sigma-Aldrich, St. Louis, MO)

• FLOP AM EM 533 (SNF)

· Sand, 30/50 mesh

• Sakrete Sand Mix, from True Value Hardware [00112] Example 1 : Preparation of modified sand-based composite particles

[00113] Outer polymer layers were applied to sand samples by mixing sand with liquid Flopam EM 533 emulsion polymer under different conditions. In one coating method, the liquid polymer product was added neat. In another coating method the polymer product was extended by diluting with hexane. For hexane dilution 10 g polymer was added to 10 g hexane in a 40 mL glass vial and vortex mixed until homogenous. Polymer was then added to 30/70 mesh frac sand samples of 30 g in FlackTek Max 100 jars. Samples were placed in a FlackTek DAC150 SpeedMixer at 2600 rpm for about 25 seconds. Samples were removed from SpeedMixer and allowed to dry in an oven at 80°C overnight.

[00114] Example 2: Better Suspension of Hydrogel Coated Sand

[00115] Bare sand and hydrogel coated sand can be compared in terms of their ease of dispersion with cement powder when water is added to form fresh paste/slurry. The hydrogel in this experiment can be a high molecular weight slightly hydrolyzed

polyacrylamide at a coating level of approximately 1% by weight sand basis. The coating procedure on sand can be performed as set forth in Example 1. One part of cement is dry- mixed with either two parts of sand (the control) or two parts of coated sand. About one part of water is added to either dry mixture, while a stirrer is used to make as smooth a paste/slurry as possible. The coated sand behaves differently from bare sand in that the coated sand particles rapidly absorb water initially, forming a gel-like substance similar to dough. This viscoelastic mixture does not sag or slump and can be extruded into cavities, offering significant placement advantages, possibly even eliminating the need for formwork, certainly sturdy /buttressed formwork. The water initially bound by the hydrogel slowly releases to the cement phase, causing controlled hydration and collapse of the swollen polymer. The end result is a cohesive integral object. The overall cured concrete has a larger volume in the case of coated sand as compared to bare sand (the control). In the bare sand case, some of the water is never integrated into the cured composite; floats to the top of the cured concrete and evaporates (thus lost).

[00116] Example 3: Foam-Coated Sand

[00117] A polyol formulation can be prepared by adding 80 parts glycerol propoxylate- block-ethoxylate, 20 parts triethanolamine, 5 parts deionized water, and 1 part Poly cat 8.

Then about 62 pphp (parts per hundred polyol) Rubinate M, a polymeric methylene diphenyl diisocyanate species, is mixed with the polyol formulation to achieve an isocyanate index of about 102. The resulting reactive mixture is immediately added to about 80 g of sand in a FlackTek Max 100 jar to achieve a 10 wt% coating, and is mixed in a FlackTek SpeedMixer for 10 seconds at about 850 rpm. After mixing the sand is immediately placed in a laboratory oven at about 80 degrees Celsius for about 10 minutes to finish curing. The resulting product is sand with a foamed polyurethane surface coating. The foamed polyurethane coating is "closed-cell" foam.

[00118] Example 4: Foam-Coated Sand

[00119] Sand can be surface treated with a foamed polyurethane by the following procedure. A polyol formulation is prepared by adding 80 parts glycerol propoxylate-block- ethoxylate, 20 parts triethanolamine, 5 parts deionized water, and 1 part Poly cat 8. About 2.5 mL of the resulting polyol formulation is added to about 80 g of sand in a FlackTek Max 100 jar and is mixed in a FlackTek SpeedMixer at about 850 rpm for about 15 seconds. To the sand treated with polyol is added about 1.3 mL Rubinate M to achieve an isocyanate index of about 102. Immediately after adding Rubinate M the sample is mixed in a

FlackTek SpeedMixer at about 850 rpm for about 15 seconds. After mixing the sand is immediately placed in a laboratory oven at about 80 degrees Celsius for about 10 minutes to finish curing. The resulting product is sand with about a 5 wt% foamed polyurethane surface coating. The foamed polyurethane coating is "closed-cell" foam.

[00120] Example 5: Foam-Coated Sand

[00121] Sand is surface treated with a delayed foamed polyurethane formulation by the following procedure. To about 80 g of sand in a FlackTek Max 100 jar is added about 2.8 mL castor oil and about 1 mL Rubinate M. The system is immediately mixed in a FlackTek SpeedMixer at about 850 rpm for about 30 seconds. The resulting product is sand with about a 5 wt% surface coating of a foamed polyurethane formulation that can be activated some time later by adding a blend of water and optionally a gelling catalyst. The coated sand is somewhat wet and tacky though still able to be transferred mechanically. The sand coating is then activated sometime after the coating process by adding about 0.2 g of a 5 part deionized water/1 part Poly cat 8 solution to the treated sand and mixing in a FlackTek SpeedMixer at about 850 rpm for about 10 seconds. The sand is then immediately place in a laboratory oven at 100 degrees Celsius for about 10 minutes to finish curing.

[00122] Example 6: Preparation of polymer coated sand

[00123] A coating composition was made by combining 10 g glycerol and 90 g SNF EM533 in a glass vial and mixing for 30 seconds with a vortex mixer. Next, 400 g of 30/50 mesh sand was added to a KitchenAid mixer bowl. 16 g of the coating composition was added to the KitchenAid mixer bowl. The mixer was then turned on to the lowest setting and left to mix for 7 minutes. After mixing, the sand/polymer mixture was split into 50 g samples and placed in a forced air oven at 80°C for 1 hr. After drying, the polymer coated sand was screened through a 25 mesh sieve to break up any clumps.

[00124] Example 7: Cementitious composite blends with polymer coated sand

[00125] Sakrete "Sand Mix" product was blended with additives as shown in Table I below. The "Sand Mix" product is a blend of sand and Portland cement, has a setting time of 6 hours, and uses a recommended 13% addition of water by weight (2.4 liters per 40 lb. bag) according to the manufacturer label information. Sand was 30/50 mesh size sand and polymer coated sand (PCS) was the material of Example 6. In certain test blends the PCS was blended with the dry Sand Mix before hydrating with water; in other test blends the PCS was combined with the water to hydrate the hydrogel polymer before blending the PCS with the dry Sand Mix. Each sample shown below was prepared by combining the ingredients in a plastic container and manually shaking the container to blend. The initial appearance of the blend was recorded and the presence of any free, unabsorbed water was noted. In cases where excess water was seen, the water was decanted and the mass of water recorded. After removing excess water, if any, the mass of the total samples was recorded.

[00126] The optimal water content of a cementitious composite blend was determined by the observation of a dry crumbly (DC) appearance when insufficient water was present, a slightly crumbly (SC) appearance when almost enough water was present, a paste (P) appearance when sufficient water was present, and a wet paste (WP) when too much water was present. The ideal combination was a paste (P), for example, 100 g of Sand Mix (Tests # 7.1 through 7.4) required 13 g of water to make a paste, resulting in 113 g of cementitious composite. In the presence of 6 g added sand, 100 g of Sand Mix (Tests #7.5 through 7.8) required 15 g of water to make a paste, resulting in 121 g of cementitious composite. In the presence of 6 g added Polymer Coated Sand (PCS), where the PCS was preswelled in water ("Wet" method) before blending with Sand Mix, 100 g of Sand Mix (Tests #7.9 through 7.12a) required 22 g of water to make a paste, resulting in 128 g of cementitious composite. In the presence of 6 g added Polymer Coated Sand (PCS), where the dry PCS was blended with Sand Mix before water was introduced ("Dry" method), 100 g of Sand Mix (Tests #7.13 through 7.17) required 22 g of water to make a paste, resulting in 128 g of cementitious composite. TABLE I

PCS = polymer coated sand, DC = dry, crumbly, SC = slightly crumbly, P = paste, WP = wet paste, n a = not applicable

[00127] These tests show that 100 g Sand Mix + 6 g sand made 121 g of cementitious composite, while 100 g Sand Mix + 6 g PCS made 128 g of cementitious composite. The polymer coating on the sand had a dramatic and unexpected effect of yielding 5.8% more cementitious composite (128 g vs. 121 g) for a given amount of Sand Mix, or a given amount of Portland cement. The extra 5.8% yield of cementitious composite represented a significant savings in cost, energy, and greenhouse gas emissions. [00128] Example 8: Preparation of polymer coated sand "on-the-fly"

[00129] This example demonstrates the process of coating particles with a polymer in a manner that might be suitable for use at the site where the cementitious composite is blended and cured. In this process, sand can be coated with a hydrogel forming polymer by blending the liquid polymer with the sand. For example, 100 grams of sand can be coated with 3.0 grams of SNF EM533 emulsion polymer. After blending, the carrier liquids in the emulsion polymer are allowed to dry and this produces a polymer coated sand. The polymer coated sand can then be blended with Portland cement, sand, and water to form a concrete mixture which then cures. The resulting cured mixture is a cementitious composite that includes the polymer coated sand.

EQUIVALENTS

[00130] While specific embodiments of the subject invention have been disclosed herein, the above specification is illustrative and not restrictive. While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. Many variations of the invention will become apparent to those of skilled art upon review of this specification. Unless otherwise indicated, all numbers expressing reaction conditions, quantities of ingredients, and so forth, as used in this specification and the claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that can vary depending upon the desired properties sought to be obtained by the present invention.

Claims

CLAIMS We claim:

1. A concrete formulation comprising modified composite particles, wherein the modified composite particles comprise a particulate substrate and a polymeric coating, and wherein the polymeric coating localizes on the surface of the particulate substrate to form the modified composite particles.

2. The formulation of claim 1, wherein the particulate substrate comprises sand.

3. The formulation of claim 1, wherein the polymeric coating comprises a performance- enhancing or a processing-enhancing additive.

4. The formulation of claim 1, wherein the polymeric coating comprises a hydrogel.

5. The formulation of claim 4, wherein the polymeric coating comprises a functional group that forms precipitates with Ca++ ions.

6. The formulation of claim 4, further comprising a cationic/anionic polymer pair comprising a cationic polymer and a high molecular weight anionic polymer.

7. The formulation of claim 6, wherein the cationic polymer is selected from the group consisting of poly-DADMAC, LPEI, BPEI, chitosan, and cationic polyacrylamide.

8. The formulation of claim 4, wherein the hydrogel comprises a polymer selected from the group consisting of polyacrylamide, acrylamide copolymers, poly(acrylic acid),

carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, and latex polymers.

9. The formulation of claim 8 wherein the hydrogel comprises an acrylamide copolymer, and the acrylamide copolymer is formulated as an inverse emulsion.

10. A modified sand-based composite particle, wherein the particle comprises a sand substrate and a first polymeric coating, and wherein the first polymeric coating localizes on the surface of the sand substrate to form the modified sand-based composite particles.

11. The particle of claim 10, wherein the first polymeric coating comprises urethane foam.

12. The particle of claim 10, wherein the first polymeric coating comprises a hydrogel.

13. The particle of claim 10, further comprising a second polymeric coating external to the first polymeric coating.

14. The particle of claim 13, wherein the second polymeric coating comprises an elastomeric polymer.

15. The particle of claim 13, wherein the second polymeric coating comprises an abrasion- resistant polymer.

16. The particle of claim 13, wherein the second polymeric coating is crosslinked.

17. A shock-absorbing particulate composition comprising the particle of claim 10.

18. The composition of claim 17, comprising a plurality of elastomeric particles mixed with the particle of claim 10.

19. A method of forming a cementitious composite, comprising:

providing a particulate substrate;

coating the particulate substrate with a coating polymer, to form a coated particulate substrate; and

combining the coated particulate substrate with a cement and water, thereby forming the cementitious composite.

20. The method of claim 19, wherein the particulate substrate is a sand substrate.

21. The method of claim 19, wherein the coating polymer comprises a hydrogel.

22. The method of claim 20, wherein the step of coating the sand substrate with the coating polymer is preceded by a step of coating the sand substrate with a primer polymer, upon which the coating polymer is deposited.

23. The method of claim 22, wherein the primer polymer comprises a cationic polymer and the coating polymer comprises an anionic polymer.

24. The method of claim 22, wherein the steps of providing, coating, and combining are performed at a point of use.

25. A method of forming a cement mixture at a point of use, comprising:

providing a sand substrate at the point of use;

providing a coating polymer at the point of use;

providing a cement at the point of use;

coating the sand substrate with the coating polymer at the point of use to form a coated sand composite; and

mixing the coated sand composite and the cement at the point of use, thereby forming the cement mixture.

26. A method of forming a cementitious composite at a point of use, comprising:

forming the cement mixture of claim 25 at the point of use;

adding water to the cement mixture at the point of use; and

mixing the cement mixture and the water at the point of use, thereby forming the cementitious composite.