WO2000024688A1

WO2000024688A1 - Hydraulically reactive particles and methods for their manufacture

Info

Publication number: WO2000024688A1
Application number: PCT/US1999/019188
Authority: WO
Inventors: Simon K. Hodson; Per Just Andersen
Original assignee: E. Khashoggi Industries Llc.
Priority date: 1998-10-28
Filing date: 1999-08-24
Publication date: 2000-05-04
Also published as: AU1440000A

Abstract

Hydraulically reactive particles having a hydraulically reactive shell integrally formed over an inorganic nonreactive interior portion. The reactive shell is formed so that a chemical bond exists between the reactive shell and the surface of the aggregate particles. The reactive shell can be formed by heating aggregate substrate particles coated with a complementary reactant that includes a component of a hydraulically settable binder that, when fused with the components found in surface of the aggregate substrate particles, will yield a desired hydraulically settable binder. The complementary reactant can be in the form of a particulate, a liquid, or superheated plasma. This process results in the reactive shell being composed of, for example, a hydraulic cement material that can react with water.

Description

HYDRAULICALLY REACTIVE PARTICLES AND METHODS FOR THEIR MANUFACTURE

BACKGROUND 1. Field of the Invention

The invention relates generally to hydraulically reactive particles and methods for their manufacture. More particularly, the invention is directed to aggregate particles in which at least a portion of the surface has been chemically modified in order to be hydraulically reactive. 2. The Relevant Technology

Hydraulic cement is an inorganic mineral binder that is typically derived from clay and limestone, and has been used for many years as the binding agent in mortars concretes, and other cementitious mixtures. Besides hydraulic cement, cementitious mixtures usually include some type of inert aggregate that acts as a low cost filler and which may be selected to improve the rheology of the initially wet mixture and the strength of the final hardened cementitious material. Water is added for the dual purpose of creating a workable mixture and also reacting with the hydraulic cement binder to form a cement paste binding system.

There are various concerns associated with making and using conventional cementitious materials, including the strength and cost of cementitious materials, size and shape of the particles within the cementitious mixture, the rheology, and the set time and control thereof. In general, the type, size, shape, specific surface area, and packing density of the particles, as well as the initial water concentration within the cementitious material, substantially affect the rheology of the uncured or unhardened cementitious mixture as well as the strength of the final hardened concrete. The types of aggregates that are included, and especially the concentration of hydraulic cement, can also greatly affect the cost and strength of the resulting concrete materials.

First, the type or identity of the particles within concrete greatly affect the final strength of the concrete — stronger particles will generally yield stronger concrete, while weaker, more easily crushed particles will generally yield weaker concrete. Second, the size, shape, specific surface area, and packing density of the particles have a significant impact on both the rheology and final strength of the concrete. The size and shape of the particles, particularly the relative sizes of the different particles, can greatly affect both the specific surface area and packing density of the particle system. In general, decreasing the specific surface area and increasing the packing density of the particles will both improve mixture rheology at a given water concentration and yield concrete having higher strength. Specifically, decreasing the specific surface area and increasing the packing density of the particles allows for the inclusion of less water while maintaining a desired slump or rheology of the wet cementitious mixture. Increasing the particle packing density also has the effect of decreasing the porosity of the concrete, which is known to increase concrete strength. Finally, it is known that decreasing the amount of water that is initially added to the mixture will generally increase the strength of the final hardened concrete by also reducing the porosity that is left behind by the excess water (i.e. , that amount of water that is not needed for hydration but which is added merely to achieve a desired rheology).

The strength of concrete is also related to the bond between the various particles. Because concrete is a heterogeneous mixture of individual particles including, but not limited to, hydraulic cement particles and generally inert aggregate particles, the particles themselves must be adequately bonded together in order to achieve a substantial level of the theoretical strength of the concrete mixture. Aggregate particles that are inadequately coated with hydraulic cement paste may form poor bonds with other particles, while unwanted porosity can further interrupt the particle-to-particle interface within the structural matrix of the final concrete. Thus, care must be taken to include sufficient water to effectively mix the hydraulic cement binder and particles and also to form a sufficient amount of cement paste needed to adequately coat the aggregate particles. On the other hand, care must me taken to not include so much water that the final strength of the concrete is compromised. Finally, a certain amount of water must be added to yield a cementitious mixture having the desired slump.

Being able to optimally satisfy these and other competing goals has not been easy and has led to the use of extremely complicated charts, tables, graphs, and other aids to provide optimal mix designs of aggregate, cement and water that will, in theory at least, adequately satisfy the various competing goals. In reality, there is usually considerable tradeoff between the various goals with, for example, the interest of high strength being sacrificed in order to achieve the goal of having the desired slump, or the interest of high strength being sacrificed in order to achieve the goal of low cost. In general, the goals of desired strength and rheology can often be satisfied by increasing the concentration of hydraulic cement. Nevertheless, because the hydraulic cement component is typically by far the highest priced component within cementitious mixtures, there is often a cost parameter that will limit the amount of hydraulic cement that can be added. Moreover, while increasing the hydraulic cement content can increase the binding effect between the aggregate particles within a certain range, there is an upper limit beyond which adding further cement can actually decrease the strength of the concrete since hydraulic cement is generally weaker than most conventional aggregates.

The size and shape of the hydraulic cement particles themselves can greatly affect the rheology, strength, and cost of cementitious materials. Since hydration occurs at the surface, more finely ground hydraulic cement particles will typically hydrate much faster than larger hydraulic cement particles. Thus, within a given time period, smaller cement particles will form more of the desired cement paste necessary to bond the inert aggregate particles together compared to larger cement particles. Moreover, finely ground cement particles can be more rapidly and thoroughly mixed within the cementitious mixture, which further assists in the formation of good particle bonds. However, finely ground cement particles hydrate so quickly that flash setting can occur. Although flash setting may be desired in certain limited circumstances, in general it is necessary to add a set retarder, such as gypsum, which inhibits the hydration reaction in order to slow down the hydration of finely ground cement. Gypsum can, however, reduce the strength of the final concrete material. Moreover, because finely ground cement particles have a high specific surface area due to their extremely small size, excess water is generally required to achieve adequate rheology, which is known to also reduce the strength of the final concrete. Finally, more time, energy, and cost is required to grind cement clinker into more finely ground particles compared to larger particles.

Replacing more finely ground cement particles with more coarsely ground cement particles has its advantages and disadvantages as well. Some of the advantages of using more coarsely ground particles is that they require less grinding, they hydrate more slowly, thus possibly avoiding the problems associated with flash setting, and they require less water to achieve a desired rheology due to their decreased specific surface area compared to more finely ground particles. However, larger cement particles have many disadvantages, such as extremely uneven morphology, higher porosity, relatively low strength, and extremely high cost compared to similarly sized aggregate particles, which makes them far less suitable than ordinary aggregates as larger sized particles within concrete.

Since hydration of cement is a surface phenomenon, larger cement particles will typically only hydrate on the surface in the short run (i.e., within the time period required for hardening), while remaining largely unhydrated in the interior for larger periods of time. Thus, only the surface of larger cement particles will act as a binder while the interior will only act as a filler in the short run. As a filler, cement particles are generally less suited than ordinary aggregate particles, which are typically much stronger, have far better morphology, have lower specific surface area, and which are many orders of magnitude less expensive. Because coarsely ground cement particles will hydrate far less than finely ground cement during a given period of time, it is generally necessary to increase the concentration of coarsely ground cement to achieve the same level of particle binding within a given time period compared to a given quantity of more finely ground cement. Thus, while larger cement particles might theoretically eliminate some of the problems of more finely ground cement particles, their use results in other, sometimes even greater, problems. In conclusion, there appears to be an advantage of using more finely ground cement particles compared to larger cement particles in most applications. Although using larger cement particles can address some of the problems of smaller cement particles, their use results in other problems that are often worse than the advantages. Thus, it has heretofore been impossible to obtain the benefits of using both large and small hydraulic cement particles while avoiding the associated problems of each. Instead, there is always a trade-off between different benefits and detriments when selecting hydraulic cement particle sizes.

The reason that hydraulic cement is so expensive compared to aggregates is the time and energy that are required to form a given quantity of hydraulic cement. Hydraulic cement is formed by reacting various natural minerals together in a high temperature kiln.

The materials added to the kiln must be carefully controlled in order to yield a hydraulic cement binder having the desired chemical characteristics, reactivity, and strength. The production of hydraulic cement binders is also very energy intensive, which greatly adds to the cost of its production. Two or more different grinding steps of the resulting clinkers are generally required, which makes cement production time-intensive as well.

When cement particles have been formed by crushing and grinding larger cement clinker pieces, the individual cement particles will generally have fractured surfaces and rough edges and, thus, do not pack together very well. It is known that rounding the edges of cement particles enhances their ability to slide over each other, thereby improving the packing efficiency of cement particles. An additional heating step is required, however, in order to round the edges of conventional cement particles, further adding to the cost of manufacture. Some have even attempted to coat cement particles with silica fume, which further greatly increases the already high cost of hydraulic cement compared to aggregates. In contrast, rocks, gravel and sand may be extracted at relatively low cost from the earth and then graded using sieves to yield aggregates having a desired particle size or range of particle sizes. Natural geological forces have, over time, yielded a wide variety of aggregates having desired sizes, shapes, strengths and other mechanical properties. In some cases, some crushing may be necessary to yield aggregate particles having a desired size, although the cost of such milling is minimal compared to the cost of manufacturing an equal volume of hydraulic cement.

In view of the foregoing, it would be a tremendous advancement in the art to provide processes for manufacturing hydraulically reactive particles that eliminated at least some of the problems associated with both small and large hydraulic cement particles.

Further, there is a need for improved processes for manufacturing larger sized hydraulically reactive particles having improved properties compared to coarsely ground hydraulic cement particles.

It would indeed be an advancement in the art to provide processes for manufacturing hydraulically reactive particles that had more uniform shape and size, greatly increased strength, and greatly decreased cost compared to an equivalent volume of similarly sized conventional hydraulic cements.

It would yet be an improvement in the art to provide processes for manufacturing a large variety of differently sized and shaped hydraulically reactive particles without the need for subsequent grinding and grading following the manufacturing process as in the process of manufacturing conventional hydraulic cements.

Moreover, it would be an advancement to provide processes for manufacturing hydraulically reactive particles from a wide variety of naturally occurring geologic mineral materials. It would further be an advancement to provide processes for manufacturing relatively large-sized hydraulically reactive particles that could nevertheless substantially completely hydrate within a shorter period of time compared to similarly sized hydraulic cement particles.

It would yet be an advancement in the art to provide processes for manufacturing hydraulically reactive particles that yielded concrete having greatly improved bond strength between the various particles in order to yield concrete products having greatly increased strength and durability, and less shrinkage.

It would be an additional advancement in the art to provide processes for manufacturing hydraulically reactive particles that had a surface chemistry that was similar, or even identical, to that of conventional hydraulic cement particles. Finally, it would be an important advancement in the art to provide processes that yielded hydraulically reactive particles having varying sizes so as to yield more densely packed hydraulically reactive particles.

Such hydraulically reactive particles, their methods of manufacture, and hydraulically settable compositions made therefrom are disclosed and claimed herein.

SUMMARY OF THE INVENTION

The present invention is directed to novel hydraulically reactive particles which have a hydraulically reactive exterior shell integrally formed over a generally nonreactive interior portion. Such hydraulically reactive particles are, in essence, reactive aggregates and can take the place of at least a portion of conventional hydraulic cement binders and/or aggregates within concrete materials. The hydraulically reactive particles of the present invention have improved morphology, increased strength, more efficient particle packing densities, and decreased specific surface area compared to conventional hydraulic cement particles. Moreover, the hydraulically reactive particles of the present invention can be manufactured at a fraction of the cost of conventional hydraulic cement since a substantial portion of the hydraulically reactive particles of the present invention will comprises unreacted and inert natural mineral aggregate.

In forming the hydraulically reactive particles, a wide variety of either naturally occurring or synthetically produced inorganic aggregate particles may be surface reacted with an appropriate complementary reactant to form the hydraulically reactive shell or surface. The reactive shell is integrally bonded to part of the crystal structure of the aggregate interior, which yields particles having greatly increased bond strength compared to aggregates held together by conventional hydraulically settable binders.

Aggregates that may be surface reacted to form hydraulically reactive particles preferably comprise naturally occurring minerals that include one or more components found in conventional hydraulically settable binders. Such minerals include those that are high in one or more of silica, calcium, aluminum, iron, magnesium, manganese, phosphorous, Group I metals, and Group II metals, and which can surface react with a complementary reactant to form a hydraulically reactive surface. A large proportion of naturally occurring mineral deposits found in the earth comprise one or more of the foregoing types of minerals.

By way of example, if an aggregate that is naturally high in silica (SiO₂) and/or alumina (Al₂O₃) is surface reacted with lime (CaO) at elevated temperature, the outer surface of the aggregate will comprise calcium silicates and/or calcium aluminates and possibly other hydraulically reactive substances that, when exposed to water, will undergo hydration. Similarly, if an aggregate that is naturally high in limestone (CaCO₃) is surface reacted with silica and/or alumina at elevated temperature, the outer surface of this aggregate will likewise comprise calcium silicates and/or calcium aluminates that, when exposed to water, will undergo hydration. Thus, it is possible to manufacture hydraulically reactive particles that have a substantially nonreactive aggregate interior and a hydraulically reactive surface having a chemistry that is similar, if not identical, to conventional hydraulically settable binders. It will be appreciated that the present invention diverges from the practice of coating aggregates with hydraulic cement particles, which does not yield a reactive surface that is integrally bonded to the aggregate interior.

The hydraulically reactive shell or surface of the hydraulically reactive particles of the present invention may have a wide variety of thicknesses depending on the desired application. The distribution and depth of the hydraulically reactive shell will depend on a variety of factors, including the size and morphology of the aggregate substrates, the concentration and reactivity of the complementary reactant, the dwell time within the reaction chamber, and the temperature to which the particles are heated. In general, aggregates having a more uniform shape will yield a reactive shell having a more uniform distribution and depth; increasing the concentration and reactivity of the complementary reactant will increase the depth of the reactive shell; increasing the dwell time and reaction temperature will yield both a more evenly distributed and reactive shell.

In general, it will be preferable for the reactive shell to be distributed around the entirety of the aggregate surface and also at a relatively uniform depth in order to ensure a more uniform hydration time and bond strength within the resulting concrete material. The preferred reactive shell thickness as a fraction of the overall aggregate particle will largely be a function of the aggregate size. It will also depend on the desired concentration of hydraulically reactive binder within the final concrete material. In general, the larger the aggregate particle, the smaller will be the relative depth of the reactive shell. In order to obtain the cost savings, increased strength, and improved rheological properties associated with the hydraulically reactive particles of the present invention, the reactive shell will preferably have a thickness of less than about 1/3 of the diameter of the aggregate particles, more preferably less than about 1/10 of the particle diameter, and most preferably less than about 1/100 of the particle diameter. Nevertheless, it is certainly within the scope of the invention to manufacture hydraulically reactive particles having any distribution pattern and depth of the reactive shell. A general method for making the hydraulically reactive particles according to the present invention comprises the steps of obtaining a batch of aggregate particles having a desired chemical makeup, size, and shape and then exposing the aggregate surfaces to a complementary reactant at a temperature sufficient to cause the surface of the aggregate particle to react with the complementary reactant and thereby form an integral reactive shell comprising a hydraulically reactive substance. In one preferred method the aggregate particles are coated with a complementary reactant that has been finely ground, fumed, or otherwise processed to yield extremely small particulates of the complementary reactant, typically in the order of 0.01-10 microns. Simultaneous with, or subsequent to, the process of coating the aggregates with the complimentary reactant, the coated aggregate particles are heated at an appropriate temperature for a sufficient period of time in order for the complementary reactant to fuse or otherwise react with an appropriate quantity of the aggregate particle. This may be carried out, for example, using a rotary kiln used to manufacture conventional hydraulic cement binders. The coated aggregate particles are preferably heated using a superheated, short dwell time, reaction chamber.

The temperature and dwell time will preferably be controlled so as to ensure that only the surface of the aggregate particle reacts with the complementary reactant. It is generally not desirable for the interior of the aggregate to fuse or otherwise react with the complementary reactant. In the manufacture of conventional hydraulically settable materials, the concentration of the feed materials that are added to the kiln must be carefully controlled in order to yield a hydraulic cement having a desired chemical makeup. However, in the case of the present invention, the existence of excess quantities of the minerals found in the aggregate substrate might create a final hydraulically reactive material too low in the complementary reactant in the case where too much of the aggregate were caused to react. In other words, it may be desired in many cases for the complementary reactant to react with a controlled amount of the aggregate so as to yield a reactive shell having a desired ratio of lime, silica, and/or other reactive subcomponents. Thus, it may be advantageous to ensure that the complementary reactant only reacts with a limited amount of the aggregate particle in order to yield a reactive surface having the desired ratio of reactive subcomponents. This can usually be achieved by heating the kiln to a temperature, in combination with a selected dwell time, that only causes a surface reaction rather than complete fusion of the aggregate particles.

A wide variety of aggregates having varying chemistries can be surface treated with a complementary reactant to yield a reactive surface. If, for example, the aggregate is an argillaceous material, such as a silicious or aluminous material, the complementary lime reactant will comprise a finely divided calcium oxide powder that will react with an appropriate depth of the silicious aggregate surface so as to form hydratable calcium silicates and/or aluminates in a desired ratio. Conversely, if the aggregate is a calcareous material, the complementary argillaceous reactant will comprise finely divided silica and/or alumina that will react with an appropriate depth of the calcareous aggregate so as to form hydratable calcium silicates and/or aluminates in a desired ratio.

Alternatively, the complementary reactant can be applied as an aqueous solution. An example of a silicious reactant which may be applied to calcareous aggregates is aqueous sodium silicate. An example of an aqueous aluminous reactant that may be applied to calcareous aggregates is aqueous sodium aluminate. An example of an aqueous calcareous reactant which may be applied to silicious or aluminous aggregates is aqueous calcium hydroxide. The particles may be passed through a bath, may be sprayed with the aqueous solution, or may be coated with the liquid complementary reactant using any means known in the art. Thereafter, the coated aggregate particles are passed through a kiln and heated to an appropriate temperature and for an appropriate length of time in order for the complementary reactant-containing coating to react with an appropriate amount of the aggregate so as to thereby form the desired hydraulically reactive shell.

In forming the hydraulically reactive particles of the invention, whether coated with a solid powder or liquid reactant, the temperature at which the coated aggregate particles should be heated will depend in a variety of factors, including the temperature at which the various reactants optimally react, the time period at which the coated particles will be heated and the melting point of the particles. It is possible for the reaction temperature to be heated to a temperature far greater than what the particles will themselves be heated to so long as the dwell time is low enough. Coated particle will be preferably passed through a reaction chamber heated to a temperature in a range from about 500°C to about 3000°C, more preferably in a range from about 1000°C to about 2000°C, and most preferably in a range from about 1200°C to about 1800°C.

Preferred dwell times within the reaction chamber will be in a range from about 15 seconds to about 60 minutes, more preferably in a range from about 30 seconds to about 30 minutes, and most preferably in a range from about 1 minute to about 10 minutes This will preferably result in the high temperature reaction of the surface of the aggregate particles with the complementary reactant to produce the reactive shell, with accompanying melting of the reaction products and rounding of the edges of the aggregate particles. The aggregate particle interior will be largely left intact and unreacted.

In a more preferred embodiment of the present invention, the complementary reactant may be applied to and reacted with the aggregate surface in the form of a superheated plasma. In this embodiment, the energy necessary to react the complementary reactant with the aggregate surface can be largely supplied by the superheated plasma reactant. This allows for a more carefully controlled and evenly produced reaction between the reactant and the aggregate substrate. In order to form a plasma the complementary reactant will be heated to above the vaporization temperature of the reactant using plasma forming means known in the art. One preferred way is using electric energy. In some cases it may be necessary to preheat the aggregate particles in order to ensure a more complete reaction with the complementary reactant.

In order to form a plasm from the complementary reactant having sufficient energy to complete the reaction with the substrate particle, the complementary reactant will be superheated to at least its boiling point. For example, silica boils at 2230°C at atmospheric pressure while calcium oxide boils at 2850°C. However, the plasma can be heated far above the boiling point of the reactant so as to provide sufficient heat energy to complete the reaction with the substrate particle. Depending on the identities of the complementary reactant, substrate particle, and intended hydraulically settable reaction product, the reactive plasma will preferably be initially heated to a temperature in a range from about 1500°C to about 5000°C, more preferably in a range from about 2000°C to about 4000°C, and most preferably in a range from about 2500°C to about 3500°C.

In order for the aggregate particle surfaces to be more readily reactive with the complementary reactant, it may be preferable to pretreat the aggregates such as by heat sintering or calcination or by washing with an acid or base wash. In general, silicious or aluminous aggregates can be advantageously pretreated by sintering and/or washing with an aqueous base. Calcareous aggregates can be advantageously pretreated by calcining and/or washing with an aqueous acid. The hydraulically reactive aggregate particles can be used alone, can be blended with fillers and other additives, and/or can be blended with conventional hydraulically settable materials such as portland cement in order to form a variety of cementitious materials. In this way, concretes suitable for a wide variety of desired purposes can be manufactured. Suitable fillers and additives include nonreactive aggregates, fibers, rheology-modifying agents, dispersants, plasticizers, air entraining agents, set accelerators, and the like. The hydraulically reactive particles will hydrate in the presence of water in order to form an initially workable material having a desired rheology, which will then harden or cure to form a desired concrete material.

An advantage of the hydraulically reactive particles of the present invention is that they are far less expensive to produce compared to conventional hydraulic cements. Because only the surface is hydraulically reactive, only enough complementary reactant and heat must be introduced into the reaction chamber in order to form a hydraulically reactive surface. The remaining interior portion of the hydraulically reactive particles, which is not reacted at all, will comprise low cost aggregate material.

Another advantage is that the hydraulically reactive particles of the present invention have a smoother and much more regular surface compared to similarly-sized hydraulic cement particles. Aggregates typically have a much more uniform and smooth shape to begin with compared to hydraulic cement particles, especially more coarsely ground cements. Moreover, the already smoother and more uniformly shaped aggregate particles are made even more smooth, more regular, and more rounded as a result of the formation of the hydraulically reactive surface. The result is a remarkably smooth and uniform particle morphology, which means that the hydraulically reactive particles of the present invention have a far lower specific surface area compared to comparably sized hydraulic cement particles. They are also capable of being more efficiently packed, particularly since hydraulically reactive particles having specifically selected sizes can be mixed together in order to increase and optimize the particle packing density.

Yet another advantage is the possibility of having relatively uniform hydration times, even when using widely varying hydraulically reactive particle sizes. Because the hydration reaction occurs at the surface, the depth of the hydraulically reactive layer will determine the time it will take to fully hydrate the hydraulically reactive particles. Thus, so long as the thicknesses of the hydraulically reactive layers of the different hydraulically reactive particles are relatively the same, it will be possible to use a wide range of differently sized hydraulically reactive particles while maintaining more uniform hydration dynamics of the overall mixture. This is in sharp contrast to conventional hydraulic cements, whose hydration dynamics are closely related to particle size. Moreover, compared to coarsely ground hydraulic cement particles, which can take 50 years or more to completely hydrate, similarly sized hydraulically reactive particles according to the invention can be made to hydrate in a much shorter time period, such as in the order of days or weeks.

A further advantage of the hydraulically reactive particles of the invention is that the hydraulically reactive coating is integrally attached to the nonreactive interior. The result is a much stronger bond between the different hydraulically reactive particles compared to aggregates bonded together by conventional hydraulic cement paste, which is only able to mechanically adhere to the aggregate surfaces in most cases. In essence, it may be fair to draw an analogy between two freshly poured slabs of concrete, which are chemically interlinked, on the one hand, and a new layer of concrete poured over an already existing concrete substrate, which will form a cold joint, on the other. Conventional hydraulic cement binders may be viewed as forming a "cold joint" or "cold bond" with the nonreactive aggregates such that the aggregate particles are thereby adhered together in an imperfect manner using conventional hydraulic cement binders. In contrast, there is more of a chemical bond or crystalline linkage between the hydraulically reactive surface and the nonreactive interior within the hydraulically reactive particles of the present invention. This results in a chemical bond between the hydraulically reactive particles rather than the "cold bond" between the aggregate particles using conventional hydraulic cement binders.

These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

The disclosed invention relates to hydraulically reactive particles having a reactive exterior shell integrally formed around a generally nonreactive interior aggregate portion. The hydraulically reactive particles will themselves hydrate in water and are therefore self-binding. Such hydraulically reactive particles can be used in a manner similar to conventional hydraulically settable binders within concrete materials, and can replace a portion or even all of the hydraulic cement binder. In addition, because a substantial portion the hydraulically reactive particles includes a nonreactive aggregate interior, such particles can replace a portion or even all of the aggregates themselves.

The hydraulically reactive particles of the present invention are superior to conventional hydraulic cement binders because they have improved morphology (/^'. e. , have more regular shape), increased particle strength, can have widely varying particle sizes while maintaining similar hydration times, and have greatly decreased specific surface area compared to conventional hydraulic cement particles. Because the hydraulically reactive particles can be made to have a wide variety of different sizes, it is possible to use particle packing techniques in order to provide more highly packed hydraulically reactive particles compared to conventional hydraulic cement binders. Finally, the hydraulically reactive particles can be manufactured at a fraction of the cost of conventional hydraulic cement binders since a substantial portion of the hydraulically reactive particles will comprise unreacted and inert natural mineral aggregates.

The terms "hydraulically reactive particle", "hydraulically reactive material", "hydraulically settable material", "hydraulic cement", and hydraulically settable binder", as used in the specification and appended claims, are intended to include inorganic materials that are able to hydrate and develop strength properties by chemically reacting with water. An example of a hydraulically settable binder is portland cement, which is used in the manufacture of a wide variety of concretes and mortars.

The terms "nonhydraulically reactive", "nonreactive interior", "inert aggregate", and "nonhydraulically reactive aggregate", as used in the specification and appended claims, shall refer to materials that are largely inert and nonreactive when exposed to water. Nonhydraulically reactive materials act as passive, largely inert, fillers within, e.g., concrete, and are typically bound together using some kind of hydraulically reactive or hydraulically settable binder, such as portland cement. For example, aggregates commonly used in the concrete industry are "nonhydraulically reactive". The substantially nonreactive interior core of the hydraulically reactive particles according to the invention comprise the portion of the aggregate substrate that has not chemically reacted with a complementary reactant to form a hydraulically reactive material. Thus, the interior core preferably remains inert and is therefore "nonhydraulically reactive". The terms "hydraulically reactive shell" and "hydraulically reactive portion", as used in the specification and appended claims, shall refer to the portion of the overwise nonhydraulically reactive aggregate substrate that has become hydraulically reactive as a result of the aggregate substrate having been treated with a complementary reactant. Because the hydraulically reactive shell is formed by reacting at least a portion of the aggregate surface, the hydraulically reactive shell is "integrally" and "chemically" bonded to the remaining portion of the aggregate.

The terms "integrally" and "chemically" bonded, as used in the specification and appended claims, when referring to the bond or interface between the substantially nonreactive interior and the hydraulically reactive portion of the hydraulically reactive particles according to the present invention, shall be understood to mean that the hydraulically reactive portion has chemical, rather than merely mechanical bonds, between it and the nonreactive interior. These chemical bonds are much stronger than, for example, the largely mechanical bond between cement paste and nonreactive aggregate particles, or the bond between an aggregate particle and unreacted hydraulic cement particles applied to the surface of the aggregate particle.

The terms "hydrate" and "hydration", as used in the specification and appended claims, are intended to describe the chemical reactions that take place between hydraulically reactive materials and water, which cause such materials to solidify or cure. For simplicity, in describing the hydration of hydraulic cements, it is often assumed that the hydration of each compound takes place independently of the hydration of other compounds present in the hydraulically reactive mixture. In reality, the hydration of hydraulic cements involves complex interrelated reactions of each compound in the cementitious mixture. The chemistry of hydration is extremely complex and can only be approximated by studying the hydration of pure hydraulic cement compounds.

Nevertheless, it is known that the process of hydration is dependent upon various factors, including the surface area and reactivity of the hydraulically reactive particles, the water- to-cement ratio, the existence of set accelerators or set retarders, and the type and concentration of other admixtures that may affect cement hydration, such as superplasticizers.

When water is mixed with a hydraulic cement, the existing minerals in the surface of the hydraulically reactive material either decompose or combine with water, and a new phase of reaction products, such as a calcium-silicate-hydrate gel, grows throughout the volume. As more hydration reaction products are formed, the aqueous phase becomes supersaturated with such products, which results in the formation of solidified crystalline materials. As more solidification of the reaction products occurs, hardening or curing takes place. Upon curing of a cementitious mixture, the water-cement mixture, sometimes referred to as the cement paste phase, is able to bind the nonreactive aggregates together to form solidified concrete. The amount of water mixed with the cement and the intensity of mixing can be controlled to maximize the ultimate properties while at the same time imparting desirable rheological properties to the cement paste. Although higher strengths can theoretically be achieved by reducing the water-to-cement ratio, inadequate mixing and wetting of the components with cement paste can actually reduce the strength. Thus, conventional concrete mixtures nearly always include an excess of water. Conventional hydraulic cements such as portland cement are manufactured by processing and proportioning suitable raw materials, burning or clinkering at a suitable temperature in a kiln to form a dehydrated material, and then grinding the resulting hard nodules (called "clinkers") to the fineness required for an adequate rate of hardening by hydration with water. Typically, two types of raw materials are required to manufacture hydraulic cements. One type is known as the "calcareous material", which is rich in calcium, examples of which include limestone, chalk, and marl. The other type is known as the "argillaceous material", which is rich in silica and/or alumina, such as clay, shale, sand or feldspar. Appropriate quantities of calcareous and argillaceous raw materials are mixed together and heated in a kiln during a first heating phase to about 750 °C for a number of hours, which causes the calcium carbonate (CaCO₃) to partially decompose through the release of carbon dioxide (CO₂) and form calcium oxide (CaO or "C"). The raw materials are also dehydrated through the release of initially bound water in the form of water vapor. The raw materials are further heated during a second heating phase to about

1050°C, which causes dicalcium silicate (C₂S) to be formed. The partially reacted raw materials are then additionally heated in a third heating phase to about 1250°C, which produces, in addition to C₂S, tricalcium silicate (C₃S), tricalcium aluminate (C₃A), and tetracalcium aluminum ferrite (C₄AF). These reaction products are generally in the form of larger sized particles known as "clinkers", which are then ground to a desired size depending on the intended use to produce ready-mix hydraulic cement. The term "ready- mix" is used to mean a hydraulic cement material that is ready to use once water is added thereto. Additives such as set regulators (e.g., gypsum) are typically added to conventional hydraulic cement materials to prevent flash setting. With respect to portland cement, the principal hydraulically reactive components are dicalcium silicate and tricalcium silicate, with lesser amounts of tricalcium aluminate and tetracalcium aluminum ferrite. The hydration reactions of the principal components found in portland cements are abbreviated as follows:

2C₂S + 4H --► C₃S₂H₂ + CH dicalcium silicate 2C₃S + 6H C_{3 2}H₂ + 3CH tricalcium water C-S-H calcium silicate hydroxide

C₃A + 26H + 3CSH₂ — C₆AS₃H₃₂ tricalcium calcium ettringite aluminate sulfate dihydrate

C₆AS₃H₃₂ + 2C₃A + 4H 3C₄AsH₁₂ ettringite

C₄AF + 26H + 3CSH₂ — C₆AFS₃H₃₂ + C tetracalcium aluminum ferrite

C,AFS, ^τ,H^{l l}n + 2C₃AF + 4H 3C.AFSH,

where dicalcium silicate is 2CaO-SiO₂, tricalcium silicate is 3CaO-SiO₂, calcium hydroxide is Ca(OH)₂, water is H, S is sulfate, and C-S-H ("calcium silicate hydrate") is the principal hydration product. The formula C₃S₂H₂ for calcium silicate hydrate is only approximate because the composition of this hydrate is actually variable over a wide range (0.9 < C:S < 3.0). It is a poorly crystalline material which forms extremely small particles in the size of colloidal matter of less than 0J μm in any dimension. It will be appreciated that there are many other possible hydration reactions that occur with respect to other hydraulic cements and even with respect to portland cement.

On first contact with water, calcium and silicate ions dissolve from the surface of each tricalcium calcium silicate grain, and the concentration of calcium and hydroxide ions rapidly increases. The pH rises to over 12 in a few minutes. The rate of this hydrolysis slows down quickly but continues throughout a dormant period. After several hours under normal conditions, the hydration products of calcium silicate hydrates and calcium hydroxide start to form, and the reaction again proceeds rapidly. Dicalcium silicate hydrates in a similar manner, but is much slower because it is a less reactive compound than tricalcium silicate. For additional information about the hydration reactions, reference is made to F.M. Lee, Chemistry of Cement and Concrete, 3rd edition, pp. 177-310. In conventional concrete materials, it has been observed that the better the contact between individual hydraulic cement particles both before and during hydration, the better the hydration product and the better the strength of the bond between the particles. Hence, the positioning of cement particles in close proximity one to another before and during hydration plays an important role in the strength and quality of the final cement article. In the present invention, good particle-to-particle contact is greatly enhanced due to the use of larger hydraulically reactive particles and, optionally, due to the use of few intervening nonreactive aggregates. II. Formation of Hydraulically Reactive Particles In view of the problems set forth herein associated with the manufacture and use of conventional hydraulic cement binders, the present invention provides a way to produce a wide variety of hydraulically settable particles, including those that are chemically similar to conventional hydraulic cement binders but which are superior in the ways enumerated herein. In order to manufacture hydraulically reactive particles that will behave and be chemically similar to conventional portland cement, the aggregate substrate and complementary reactant should be selected in order to yield a reactive surface that includes the same components found in portland cement, namely dicalcium based silicate (C₂S), tricalcium silicate (C₃S), tricalcium aluminate (C₃A), and tetracalcium aluminum ferrite (C₄AF). Alternatively, there are a wide variety of other hydraulically settable binders not based on portland cement that can be formed in the surface of essentially nonreactive aggregates. These include but are not limited to gypsum cements, phosphate cements, high alumina cements, lime-based cements, silicate cements (including α-and β -calcium silicates, other calcium silicates, and mixtures thereof), calcium aluminate cements, phosphate cements, slag cements, pozzolanic lime cements, magnesium oxychloride cements, alumino-ferrite cements, silicates, aluminates, alumino-ferrites, and phosphates complexed with various Group I and Group II metals, and combinations of the foregoing. In fact, any known mineral-based hydraulic cement can be formed on the surface of an otherwise inert aggregate particle and be part of the present invention. For example, where it is known that larger gypsum dihydrate particles are inert inorganic aggregates and also that gypsum hemihydrate is a hydraulically settable material, it is certainly within the scope of the present invention to form gypsum hemihydrate on only the surface of an otherwise gypsum dihydrate particle to form a hydraulically reactive particle according to the present invention. Likewise, calcium chloride can be chemically adhered to the surface of limestone particles to form a lime-based cement. In forming the hydraulically reactive particles of the invention, naturally occurring inorganic mineral substrates are coated with a complementary reactant and processed so that a reactive exterior shell is formed and chemically bonded to the surface of the interior portion. The nonreactive interior portion of the hydraulically reactive aggregate particles of the invention includes the portion of the mineral substrate that has not reacted with the complementary reactant or otherwise become part of the integral reactive shell. In order to form the hydraulically reactive surface on the mineral aggregate particle, a complementary reactant is selected that, when heated in the presence of the minerals found within the aggregate substrate, will chemically react or otherwise become associated with the minerals found in the surface of the aggregate substrate in order to form a new material on the surface of the particle that will react in the presence of water and thereby adhere to other particles.

A. Raw Material Aggregate Substrates

Virtually any inorganic particle that has a chemical makeup that can be altered or reacted in a way so as to make it hydraulically reactive can be used as an aggregate substrate. The only criteria is that the particle should have a desired size, shape, and strength for a particular use, and also that it be capable of being treated in a manner that would make at least a portion of the particle surface hydraulically reactive. Preferred raw material aggregate substrates include naturally occurring minerals that are low cost and easily processed to have a hydraulically reactive surface. For example, a wide variety of aggregates commonly used in the concrete industry are preferred due to their ready availability, good strength properties, desirable particle size and morphology characteristics, and chemical compatibility with hydraulically settable binders.

Suitable inorganic raw material aggregates that can be used to form the hydraulically reactive particles according to the invention include naturally occurring minerals that include one or more of the following chemical constituents: silica, alumina, calcium, magnesium, phosphorous, iron, manganese, complexes of the foregoing such as aluminum silicates or alumino-ferrites, and complexes of silicates, aluminates, alumino-ferrites, or phosphates in combination with a wide variety of metals. Many naturally occurring minerals include a combination of the foregoing chemical constituents in varying proportions. Based on an understanding of hydraulically reactive materials in general, one of ordinary skill in the art can select an appropriate inorganic aggregate substrate that is capable of being processed in order to have an inorganically reactive shell formed thereon by reacting the substrate with an appropriate complementary reactant. For example, if a particular mineral deposit is rich in argillaceous materials such as silica, alumina, and/or alumino-ferrites, then such a mineral would be capable of forming a hydraulically reactive material when reacted at high temperatures with a calcareous material such as lime. The resulting calcium silicates, calcium aluminates, and/or calcium alumino-ferrites will hydrate in the presence of water to form calcium silicate hydrates, calcium aluminate hydrates, and/or calcium alumino-ferrite hydrates.

Conversely, materials that include mostly calcareous constituents, such as limestone and magnesium, will become hydraulically reactive if exposed to an argillaceous material such as silica, alumina, and/or an alumino-ferrite.

Examples of natural materials that are rich in argillaceous materials (i.e., in which the mineral could be reacted with, e.g., a calcareous material and become hydraulically reactive) include the following: all types of clays, shales and feldspars, natural pozzolans, granite, albite, allanite, alunite, amphibole, analcime, andalusite, andesine, apophyllite, augite, beryl, boehmite, zeolites, quartz, quartzite, biopyribole, bytownite, cancranite, chabazite, chrysoberyl, ceosite, corundum, diopside, dumortierite, epidote, feldspathoids, garnet, garnierite, glaucophane, idocrase, jadeite, kaliophilite, kalsilite, kyanite, labradorite, lawsonite, melilite, natrolite, onyx, pyroxenes, topaz, chalcedony, chlorite, illitite, montmorillonite, kaolinite, gibbsite, glauconite, microcline, mascorite, opal, orthoclase, and pyrophyllite.

Examples of mineral deposits that are rich in calcareous materials (i.e. , in which the mineral could be reacted with, e.g., an argillaceous material and become hydraulically reactive) include the following: limestone, chalk, marl, marble, anyhydrite, gypsum, ankerite, aragonite, calcite, pyroxene and fluorite.

Examples of minerals that include significant quantities of one or more Group I or Group II metals other than calcium (in addition to silicates, aluminates and other anions) include the following: anthophyllite, dolomite, magnesite, barite, celestite, biotite, brucite, carnotite, cordierite, cryolite, enstatite, epsomite, feldspathoids, humite, talc, lazurite, leucite, olivine, omphascite, phlogophite, pigeonits, pollucite, sepiolite, serpentine, sodalite, spodumene, nesquehonite, lansfordite, artimite, and strontianite.

Examples of minerals that include high percentages of phosphate or other phosphorous containing complexes include the following: amblygonite, apatite, natrophite, sterconite, phosphamite, biphasphammite, montebrasite, lewistonite, beryllonite, newberyite, bobbierite, struvite, hautefullite, gordonite, amphithalite, collinsite, and phosphoferrite.

Minerals that are rich in manganese include the following: psilomelane, pyrolusite, hausmannite, huebnerite, manganite, rhodonite, mangadolomite, kutnohonite, and manganankerite.

In addition to the foregoing naturally occurring minerals, there are plentiful sources of synthetically derived or man-altered minerals that can be made hydraulically reactive. One type includes synthetic or man-made pozzolans, such as fly ash and silica fume. Because such materials are generally finely divided particulates, it would be necessary in most cases to re-form such materials into larger sized particles, such as by fusing them together, in order to obtain particles of a desired size and order to be capable of being surface reactive. Another important synthetic substance is slag, which is a by product of the smelting of ores, primarily iron ore. Yet another is crushed brick made from clay. Pozzolan, slag and crushed brick particles contain substantial concentrations of silicates and aluminates, together with lesser quantities of calcium, magnesium and other metal oxides. Pozzolans, slags and crushed bricks are known to become hydraulically reactive if treated with an appropriate quantity of lime or other highly alkaline material. Preferred raw material aggregates include limestone, chalk, and marl, which are rich in calcium, and sand, clay, feldspar, and shale, which are rich in silica. The foregoing minerals are especially preferred due to their plentiful nature and extremely low cost.

Because there is a close correlation between particle size and shape of the original aggregate substrate with a final hydraulically reactive particle being produced, it will be possible to select the final hydraulically reactive particle size by selecting aggregate substrates having roughly the same desired particle size and shape as the resulting hydraulically reactive particles. In contrast to conventional hydraulic cement particles, which are formed by fusing together finely ground feed materials, which must thereafter be mechanically ground or crushed into desired hydraulic cement binder particles, the hydraulically reactive particles of the present invention may be selected simply according to the desired size of the final hydraulically reactive particles. One benefit of this is the elimination of multiple grinding steps, which greatly reduces the cost of equipment and manufacture. Moreover, superior particle size and morphology are possible compared to the limited range of possible particle sizes and morphologies of conventional hydraulic cement binders.

Nevertheless, because many of the complementary reactants that will be used to form the hydraulically reactive surface on the aggregate substrates will themselves tend to add to the mass of the aggregate particles as the reactive surface is formed, there will be a slight incremental increase in the size of the particles as more complementary reactant is used. Thus, the final hydraulically reactive particle size will often be somewhat larger than the original aggregate size, with the size increase being proportional to the depth of the reactive layer that is formed. The benefit of this is that the formation of the hydraulically reactive layer will tend to smooth out irregularities found in the aggregate substrate particles. Thus, whereas most naturally occurring aggregate particles will already have a morphology that is far superior compared to conventional hydraulic cement binders, the additional smoothing effect of reacting the surface of these particles will further yield more regularly shaped reactive particles. The result of having more regularly-shaped particles is that cementitious materials formed therefrom will have fewer unwanted voids and a greater particle packing density.

In order to further increase the particle packing density of the hydraulically reactive particles according to the present invention, it is preferable to select differently sized and graded particles that can more closely pack together. For example, larger particles within a particle size range can be mixed with smaller particles of a different particle size range in order for the smaller particles to occupy the spaces between the larger particles. In general, particle packing techniques of mixing together larger and smaller particles can be used for three or more different particle size ranges in order to further maximize the particle packing density. As a general rule, coarse aggregates are those that have a particle size in a range from about 5 mm to about 5 cm. Medium aggregates have a particle size in a range from about 1 mm to about 5 mm. Fine aggregates have a particle size in a range from about 0J mm to about 1 mm. Finally, ultra-fine aggregates such as man-made pozzolans, typically have a particle size less than about 100 microns. It is within the scope of the present invention to manufacture hydraulically reactive particles of any size, although such particles will typically have a size greater than about 0J mm.

A detailed discussion of particle packing techniques can be found in the following article co-authored by one of the inventors: Johansen, V. & Andersen, P.J. "Particle Packing and Concrete Properties," Materials of Concrete II, at 111-147, The American Ceramic Society (1991). Further information regarding particle packing techniques is available in the doctoral dissertation of Andersen, P.J., "Control and Monitoring of Concrete Production - a Study of Particle Packing and Rheology," The Danish Academy of Technical Sciences. For purposes of disclosing techniques for optimizing the packing density of particle systems, the foregoing articles are incorporated herein by specific reference. Finally, there are many aggregates that can be reacted to form a reactive surface thereon that have relatively low density and therefore are light-weight. These include, for example, perlite, vermiculite, glass beads, hollow glass spheres, porous ceramic spheres, tabular alumina, expanded clays, pumice, and other expanded geological materials. Such materials tend to be argillaceous and will become hydraulically reactive by treatment with a calcareous material.

B. Complementary Reactants

Any of a wide variety of naturally occurring or synthetic aggregate substrates can be made hydraulically reactive by treating the surface with a complementary reactant, generally in the presence of substantial heat, in order for the naturally occurring minerals in the substrate aggregate and the complementary reactant to form a desired substance on the surface of the aggregate particle that is hydraulically reactive. Knowing the chemical makeup of the aggregate substrate and also the desired hydraulically reactive surface will determine what substance or substances are deficient and need to be supplied by the complementary reactant. Thus, one or more complementary reactants should be selected in order to supply the substances in the aggregate that are deficient in order to yield a desired hydraulically reactive product.

For example, materials rich in silica can be treated with lime at elevated temperatures to form hydratable calcium silicates. Similarly, materials high in alumina can be treated with lime to form hydratable calcium aluminates. Moreover, both silicates and aluminates can be treated with highly basic oxides of virtually any Group I and Group II at elevated temperature in order to become hydraulically reactive. Magnesium containing substances can be treated with magnesium chloride and heated to form magnesium oxychloride cements. Limestone can be treated with a pozzolan or other silica-containing material at elevated temperatures in order to become hydraulically reactive. Slag and pozzolans, which are rich in silicates and aluminates, can be treated with lime in order to form a slag cement. Pozzolans can be treated with lime and gypsum and then heated to form supersulfated cements. The complementary reactants can be derived from minerals set forth in the preceding section relating to aggregate substrates and may themselves comprise natural substances, or they may be chemical derivatives of natural minerals.

As will be discussed more fully hereinafter, the complementary reactant may be applied in basically one of three forms. In the simplest method, the complementary reactant can be applied to the surface of the aggregate substrate as a finely divided particulate substance. In a second method, the complementary reactant can be applied in the form of a liquid, such as an aqueous solution or a colloidal suspension. In a third method, the complementary reactant can be applied in the form of a superheated and highly reactive plasma. In most cases it will be necessary to heat the complementary reactant and aggregate substrate in order to cause the substances found therein to more closely associate in order to form the new hydraulically reactive mineral substance. In some cases, however, mere contact between the complementary reactant and aggregate substrate will be sufficient to cause the two to react together in a matter that makes the resulting surface hydraulically reactive.

C. Methods For Reacting Aggregate Substrates With Complementary Reactant Coatings

In general, the method of forming the hydraulically reactive aggregate particles of the invention comprises obtaining a plurality of inorganic aggregate particles of a desired size and shape and then forming a hydraulically reactive exterior layer or shell on the particles in a manner so that a chemical bond is formed between the reactive shell and the particles. This can be accomplished by surface-treating the aggregate particle with an appropriate complementary reactant and then causing the two to react together in order to yield a hydraulically reactive surface. However, prior to reacting the aggregate substrates and complementary reactants, it may be desirable or necessary to pretreat the aggregate substrates to make their surfaces more reactive and receptive to the complementary reactant.

For example, the surface of the uncoated aggregate particles may be made more reactive by sintering. The pre-treatment step of sintering will generally occur as the first step of a two-step sintering process in which the complementary substrate is reacted with the aggregate substrate particles during a second sintering step. In the first step, the aggregate substrate particles are pre-heated by dropping them through a high temperature reaction chamber to calcine the surface of the particles. Sintering the aggregate particles in order to calcine the surfaces of the particles removes water, carbonates and/or other substances which, when removed, will increase the tendency of the surface to become hydraulically reactive when treated with the one or more complementary reactants. In many cases, calcining the surface can also make the aggregate substrates more reactive by creating a more porous surface having increased surface area.

An acid or base surface treatment can also be utilized to make the aggregate particles more reactive. In this process, aggregates such as limestone, chalk, marl, and other alkaline aggregates, which tend to be more basic, can be treated with an acid, while more acidic aggregates, such as those containing substantial quantities of phosphorus, alumina and silica, can be treated with a base. Treatment of a basic aggregate substrate with an acid will act to strip away at least a portion of the surface layer from the aggregate substrate surface in order to yield a cleaner, more reactive surface. Similarly, reacting more acidic aggregate particles with a base will act to do the same. The acid or basic washes will also tend to create microscopic pitting, which increases the surface area and reactivity of the aggregate substrate particles.

1. Application of Complementary Reactant as a Powder. Liquid or Plasma The complementary reactant can be applied to the aggregate substrate surface in any form that will ultimately yield a hydraulically reactive portion in at least part of the aggregate substrate surface. In one preferred method, aggregate particles can be coated or otherwise exposed to the complementary reactant in the form of a finely divided powder material. One or more of the components of a desired hydraulically reactive substance is supplied by the aggregate substrates and the complementary or necessary component or components required to yield a desired hydraulically reactive substance are provided by the powdered coating material. For example, in the manufacture of a portland-type cement coating, an argillaceous aggregate may be treated with finely divided lime, or a mixture of lime and another basic alkali or alkaline metal oxide, such as sodium oxide or magnesia. Similar, limestone or other calcareous aggregates can be treated with finely divided silica (such as silica fume), or a mixture of silica and alumina and/or an alumino-ferrite. The powdered complementary reactant will generally have a particle size in a range from about 0.01 micron to about 10 microns.

In applying the powdered complementary reactant to the aggregate substrate particles, the components can be mixed together in a tumbler or roller mill in predetermined proportions to yield a desired coating density of the powdered coating material over the aggregate particles. Adhesion between the aggregates and complementary reactant powder can be enhanced by moistening the aggregate particles before or during contact with the complementary reactant powder, such as with water, or by means of an adhesive or other adhesion-promoter. The powdered complementary reactant can also be applied in multiple stages, which are separated by intermediate steps of sintering the coated aggregate particles in order to cause the coating powder to fuse, or otherwise form a more secure bond, with the aggregate substrate particles between coating stages. Thereafter, further powdered reactant can be applied and reacted with the aggregate particles by further sintering. In an alternative method, the complementary reactant may be applied to the aggregate substrate particles in the form of a liquid coating. The liquid may. for example, be a solution or colloidal suspension that will precipitate or otherwise deposit out the complementary reactant upon heating to remove the solvent. A preferred solvent is water, since water is an excellent solvent for alkaline oxides and alkali silicates and is inexpensive, essentially inert at this stage of the process, and easily removed by evaporation. The liquid coating can be applied by spraying the aggregate substrate particles or by immersing the particles in the liquid.

Coating aggregates with an aqueous solution or colloidal suspension appears to allow for a greater coating density of complementary reactant, compared to coating with a powdered reactant, since there is greater adhesion of the subsequently dried reactant. One reason is because the reactant is drawn deeper into the pores of the aggregate particles compared to the application of powdered reactants. Also, liquid reactants, once dried, form a more durable crust compound to powder-to-particle adhesion. Adhesion between powder or liquid reactant coatings and the aggregate substrate particles can also be enhanced using the concept of zeta-potential. Zeta-potential is the potential difference or surface charge produced from a solid-liquid interface due to ions absorbed from the moving solution and can be controlled by addition of suitable ions so as to either produce or prevent flocculation. In using zeta-potential to coat the aggregate particles, one charge (e.g., negative) is put on the aggregate particles and an opposite charge (e.g., positive) is put on the complementary reactant material so that an attractive force exists to provide enhanced adhesion of the complementary reactant coating and the aggregate particles. In using zeta potential, it is generally preferable to maximize the zeta potential of each of the components in order to promote maximum flocculation between the aggregate particles and complementary reactant.

In a preferred liquid coating method, a calcareous aggregate such as calcium carbonate (e.g., ground limestone) is immersed in or sprayed with an aqueous sodium silicate solution. The surface of the calcium carbonate aggregate reacts with the sodium silicate coating to produce a reactive shell of calcium silicates on the surface of the particles upon sufficiently heating the coated particles. Alternatively, the limestone can be treated with colloidal silica or alumina gels in water.

In another preferred liquid coating method, silica-based aggregate particles are immersed in or sprayed with a liquid coating such as an aqueous calcium hydroxide solution. The calcium hydroxide reacts with silicates found in the surface of the aggregate particles upon heating sufficiently to produce a reactive shell of calcium silicates on the surface of the. In like manner, a variety of solutions of alkali silicates, colloids, gels, and other alkali or alkaline salts can be applied in desired quantities to appropriate aggregate substrates.

In the foregoing methods for applying the complementary reactant, including both using a powdered or liquid-phase reactant, the initial interaction between the aggregate substrate particles and the complementary reactant is largely mechanical. Whereas the mechanical adhesion can be enhanced by using zeta-potential techniques, adhesives, moistening, and penetration of the complementary reactant into pores of the aggregate substrates, true chemical adhesion is not achieved until the coated aggregate particles are sintered sufficiently to cause the complementary reactant constituents to fuse or otherwise become chemically associated with the substances found in the aggregate particle.

In another preferred embodiment for applying the complementary reactant to the aggregate substrate, the reactant is applied in the form of a superheated plasma-phase material. Plasma-phase materials are essentially vaporous materials that, upon cooling, can quickly resolidify to form a continuous fused shell of the complementary reactant around the aggregate particle. Not only is the complementary fused reactant better able to bond to the substrate compared to powders or deposited solutions or colloids, there is also the possibility of significant chemical interaction and/or fusing between the complementary reactant and the aggregate surface. This is due to the tremendous heat energy contained in the plasma-phase reactant. Depending on the identity and temperature of the aggregate particles and plasma-phase complementary reactant, the coating density of the reactant on the particle surface, and the reactivity between the reactant and substrate particle, it is possible for at least a portion of the deposited plasma reactant to form a hydraulically reactive substance without further heating of the coated aggregate particles. Nevertheless, it may be necessary to subject the aggregate particles coated with the plasma-phase reactant to a further sintering step in order to completely form the hydraulically reactive coating.

2. High Temperature Reaction

Although it is possible for highly reactive complementary reactants to immediately associate with the aggregate particle surface in order to form a hydraulically reactive material, in most cases it will be necessary to subject the coated aggregate particles to a further heating or sintering step. The purpose of the heating or sintering step is to cause the complementary reactant to fuse or otherwise become chemically associated with the outer portion of the aggregate particle. This sintering process is similar to the burning process that is used to form portland cement within a rotary kiln. Because of this, it is certainly within the scope of the present invention to pass coated aggregate particles through a hydraulic cement kiln in order to cause the formation of portland cement or other hydraulically reactive substances on the particle surfaces.

Nevertheless, due to the relatively small proportion of each aggregate particle that will actually react with the complementary reactant, due the fact that the reaction is mainly a surface reaction, it is generally possible and preferred to pass the coated aggregate particles through a quick dwell-time, high temperature reaction chamber. In a preferred embodiment, the coated aggregate substrate particles are vertically dropped through a high temperature, short dwell time reaction chamber. The dwell time of the particles can be adjusted by dropping the particles through the chamber in batches or by causing the particles to pass along a circuitous path through the reaction chamber.

The preferred temperature range of the reaction chamber will be dependant upon the chemical makeup of the aggregate substrate, the complementary reactant, the desired hydraulically reactive substance to be formed on the aggregate surface, and the associated dwell time of the particles within the reaction chamber. The temperature and dwell time should be selected in order to cause substantially complete interaction between the complementary reactant and the substrate particles using a minimum amount of heat energy in order to yield the most economically produced hydraulically reactive particles. Preferred reaction chamber temperatures will depend on the type of reactant, substrate, and dwell time and will be in a range from about 500°C to about 3000°C, more preferably in a range from about 1000°C to about 2000°C, and most preferably in a range from about 1200°C to about 1800°C.

The dwell time within the reaction chamber will likewise be determined by the chemical makeup of the aggregate particles and the complementary reactant, as well as the hydraulically reactive substance being formed on the aggregate substrate. In order to mass produce hydraulically reactive particles in an efficient manner, it will generally be preferable for the high temperature chamber to have a relatively short dwell time. Preferably, the dwell time within the reaction chamber will be in a range from about 15 seconds to about 60 minutes, more preferably in a range from about 30 seconds to about 30 minutes, and most preferably in a range from about 1 minute to about 10 minutes.

Besides causing the complementary reactant and surface of the aggregate substrate particles to fuse, react, or otherwise associate together to form the hydraulically reactive coating, another effect of the high temperature reaction step is to smooth out the rough edges of the hydraulically reactive particles. This yields particles having a more regular morphology than even naturally occurring aggregates, which themselves generally have a far superior morphology compared to conventional hydraulic cement particles, which tend be extremely irregular, jagged and porous.

By way of example, in a preferred method for forming portland cement on the surface of a limestone aggregate particle, such particles are coated with a powdered or colloidal silica material or a silicate solution to form initially coated particles. The coated particles are then dropped through a high temperature reaction chamber in order to cause the silica and calcium ions to fuse or otherwise interact together to form calcium silicates. The carbonate ions on the limestone aggregate surfaces will generally be caused to decompose into oxide ions, which are incorporated into the calcium silicates, and carbon dioxide, which is driven off in the form of a gas. In addition to silica materials, alumina materials and alumino-ferrite materials can also be included with the silica materials to form a hydraulically reactive shell that is even more chemically similar to portland cement.

In an alternative method, silica-based aggregates, such as clays, feldspars, granite, quartz, silica sand, and the like are coated with lime powder or an aqueous lime solution.

Thereafter, the coated silica-based aggregate particles are passed through a high temperature reaction chamber in order to cause the lime to fuse with the silica-based substances within the aggregate in order to form calcium silicates. Whereas some aggregates also will include alumino-silicates and alumino-ferrites, which can form calcium aluminates and calcium alumino-ferrites during sintering, it may be necessary to augment the lime reactant with one or more of alumina and alumino-ferrite in order to yield a reactive substance that more closely resembles and behaves like portland cement.

D. Properties. Applications and Advantages of Hydraulically Reactive Particles In many respects, the hydraulically reactive particles according to the present invention can be used in a manner similar to conventional hydraulically reactive materials. In various embodiments, the hydraulically reactive aggregate particles can be used alone, can be blended with fillers and other additives, and/or can be blended with conventional hydraulically settable materials such as portland cement in order to form a wide variety of cementitious materials. In this way, concretes suitable for a wide variety of desired purposes can be manufactured. Suitable fillers and additives that may be blended with the hydraulically reactive particles include non-reactive aggregates, fibers, rheology-modifying agents, dispersants, air entraining agents, set accelerators, and the like. The hydraulically reactive particles will hydrate in the presence of water in order to form an initially workable material having a desired rheology, which will then harden or cure to form a desired concrete material.

A major advantage of the hydraulically reactive particles of the present invention is that they are far less expensive to produce compared to conventional hydraulic cements. Because only the surface is hydraulically reactive, only enough complementary reactant and heat must be introduced into the reaction chamber in order to form a hydraulically reactive surface of a desired thickness, concentration, or depth. The remaining interior portion of the hydraulically reactive particle, which is not reactive at all, comprises low cost aggregate material. This results in particles with less than 100% of their composition comprising a hydraulically reactive material. This is different from prior hydraulic cement binder particles, which comprise 100% hydraulically reactive material.

Depending on the size of conventional hydraulically settable binders, much of the interior of the cement particles will remain unhydrated and will themselves comprise an aggregate filler to the extent that the interior portion only hydrates slowly or otherwise does not participate in the binding of other particles. Thus, much of the hydraulic cement material within conventional hydraulic cement binders is essentially wasted. Since filler materials are generally many orders of magnitude less expensive than hydraulic cement particles, any use of hydraulic cement materials as a filler rather than as a binder is, by definition, wasteful. In sharp contrast, a considerable portion, usually the dominant portion, of the hydraulically reactive particles of the present invention will comprise low cost, unreacted and inert aggregate material.

The hydraulically reactive shell or surface of the hydraulically reactive particles of the present invention may have a wide variety of thicknesses depending on the desired use or application. The distribution, depth and concentration of the hydraulically reactive shell will depend on a variety of factors, including the size and morphology of the aggregate substrates, the concentration and reactivity of the complementary reactant, the dwell time within the reaction chamber, and the temperature to which the particles are heated. In general, aggregates having a more uniform shape will yield a reactive shell having a more uniform distribution and depth; increasing the concentration and reactivity of the complementary reactant will increase the depth (and, hence, the concentration) of the reactive shell; increasing the dwell time and reaction temperature will yield both a more evenly distributed and reactive shell.

In general, it will be preferable for the reactive shell to be distributed around the entirety of the aggregate surface and also at a relatively uniform depth in order to ensure more uniform hydration times and bond strength within the resulting concrete material. The preferred hydraulically reactive shell thickness as a fraction of the overall aggregate particle will largely be a function of the aggregate size. It will also depend on the desired concentration of hydraulically reactive binder within the final concrete material. In general, the larger the aggregate particle, the smaller will be the relative depth, or fraction, of the reactive shell. In order to obtain the cost savings, increased strengths, and improved rheological properties associated with the hydraulically reactive particles of the present invention, the reactive shell will preferably have a thickness less than about 1/3 of the diameter of the aggregate particles, more preferably less than about 1/10 of the particle diameter, and most preferably less than about 1/100 of the particle diameter.

Nevertheless, it is certainly within the scope of the invention to manufacture hydraulically reactive particles having any distribution pattern and depth of the reactive shell.

The hydraulically reactive particles can have a wide variety of sizes in order to replace or otherwise behave like fine, medium and coarse aggregates used in the concrete industries. Therefore, there is no preferred size of hydraulically reactive particles according to the invention, since the size, or range of sizes, of the hydraulically reactive particles will depend on the desired rheological and strength properties, as well as the intended use, of the resulting cementitious materials. In general, however, the hydraulically reactive particles of the present invention will be many orders of magnitude larger than conventional hydraulic cement particles. Nevertheless, because hydraulic cement particles often comprise a fine particle in multi-particle systems, it may be desirable to use conventional hydraulic cement particles, pozzolans, or other fine particulate materials than can occupy the smaller spaces between the larger hydraulically reactive particles. As discussed above, it may be preferable in many cases to include differently sized and graded particles in order to increase the particle packing density of the resulting particulate system. Increasing the particle packing density improves the rheological properties of the wet mixture, as well as the final strength property of the final hardened cementitious material.

Another advantage is that the hydraulically reactive particles of the present invention will generally have a much more regular and smooth surface compared to similarly sized hydraulic cement particles. Aggregates typically have a much more uniform and smooth shape to begin with compared to hydraulic cement particles, especially more coarsely ground cements. Moreover, the already smoother and more uniformly shaped aggregate particles are made even more smooth, more regular, and more rounded as a result of the formation of the hydraulically reactive surface due to the fusing together of the aggregate surface and complementary reactant. The result is a remarkably smooth and uniform particle morphology, which means that the hydraulically reactive particles of the present invention have a far lower specific surface area compared to comparably sized hydraulic cement particles. They are also capable of being more efficiently packed, since it is known that particles having a more regular morphology can be more closely packed compared to more irregularly shaped particles.

In the case where it is desired to optimize the particle packing density of the hydraulically reactive particles of the present invention, or the packing density of the inventive particles combined with inert aggregate particles, conventional hydraulically reactive binders, or other particulate substances, it will generally be preferable to select and combine particles that will result in a particle packing density in a range from about 0.6 to about 0.95, more preferably in a range from about 0.65 to about 0.9, and most preferably in a range from about 0J to about 0.85. By way of comparison, particle systems having a packing density of 0.65 include seven times the interstitial space compared to particle systems having a packing density of 0.95. The result is that particle systems having a packing density of 0.65 will require roughly seven times the amount of water to obtain the same level of workability compared to particle systems having a packing density of 0.95. Thus, increasing the particle packing density can improve the flow properties while reducing the amount of required water to obtain such flow properties. In addition, it is known that reducing the amount of water added to cementitious materials will greatly increase the strength of the resulting hardened concrete material.

Yet another advantage of the hydraulically reactive particles of the invention is the greatly reduced hydration time compared to conventional hydraulic cement binders. Because typical hydraulic cement binders are entirely made of hydraulically reactive substances, but because hydration is generally a relatively slow surface phenomenon, it may take many years for larger-sized conventional hydraulic cement particles to become completely hydrated. Altering the size of the hydraulic cement particles greatly affects the time it will take to hydrate such particles, with larger particles taking many times longer to hydrate compared to smaller cement particles. In sharp contrast, the depth of the hydraulically reactive shell, rather than the size of the hydraulically reactive particle, will determine the time it will take to substantially hydrate the hydraulically reactive particles of the present invention. Thus, so long as the thickness of the hydraulically reactive shell is relatively small, the hydration time will also be relatively small. Thus, a wide range of differently sized and graded hydraulically reactive particles that nevertheless will completely hydrate in the same time frame can be used within the same cementitious mixture. Speeding up the hydration time is a tremendous advantage, both in terms of saving time when building a desired cementitious structure and also in terms of obtaining maximum strength in a shorter period of time. Because unhydrated hydraulic cement particles are generally very weak, substantial hydration of such particles is necessary in order to obtain maximum strength of concrete materials produced therefrom. In contrast, because the interiors of the hydraulically reactive particles are comprised mainly of high strength aggregate material, the hydraulically reactive particles of the present invention will yield concrete materials having maximum strength in a relatively short time period. There is no need for the particle interiors to hydrate in order to strengthen the particles. Thus, compared to coarsely ground hydraulic cement particles, which can take 50 years or more to be completely hydrated, similarly sized hydraulically reactive particles according to the invention can be made to hydrate in a much shorter time period, such as in the order of days or weeks. The result is hydraulically reactive particles that react quicker and achieve substantially higher strength in a given time period compared to conventional hydraulically reactive particles.

A further advantage of the hydraulically reactive particles is the greatly reduced cost of manufacture compared to the manufacture of conventional hydraulic cement materials. In order to produce a given quantity of conventional hydraulically reactive particles, it is necessary to heat together and fuse, or otherwise react, the entire batch of material used to form conventional hydraulic cements. In contrast, only that portion of the reactive particles that is intended to be hydraulically reactive will need to be heated in order to make it reactive. Thus, the procedures for making the hydraulically reactive particles of the present invention will utilize far less heat and time compared to conventional procedures for manufacturing hydraulic cements. Moreover, unlike conventional hydraulic cements, which generally yield clinkers that need to be further ground and graded using multiple grinding and grading steps, the hydraulically reactive particles according to the present invention will generally require no grinding or grading steps subsequent to formation. Hence, both energy and capital equipment costs can be greatly reduced in the manufacture of the inventive hydraulically reactive particles.

A further advantage of the hydraulically reactive particles of the invention is that the hydraulically reactive surface will be integrally attached to the non-reactive interior. The result is a much stronger bond between the different hydraulically reactive particles compared to aggregates bonded together by conventional hydraulic cement paste, which is only able to mechanically adhere to the aggregate surfaces. In essence, it may be fair to draw an analogy between two freshly poured slabs of concrete, which are chemically interlinked on the one hand, and a new layer of concrete poured over an already existing concrete substrate, which will form a cold joint, on the other. Conventional hydraulic cement binders may be viewed as forming a "cold joint" or "cold bond" with a nonreactive aggregate such that the aggregate particles are adhered together in an imperfect manner using conventional hydraulic cement binders. In contrast, there is more of a chemical bond or crystalline linkage between the hydraulically reactive surface and the non-reactive interior within the hydraulically reactive particles of the invention. This results in a chemical bond between the various hydraulically reactive particles rather than a "cold bond" between the aggregate particles and conventional hydraulic cement binders used in conventional concrete materials.

In summary, the hydraulically reactive particles of the present invention can be formed in a lower energy process, with fewer steps, in a shorter time period, and at lower cost than conventional hydraulic cement forming processes. The hydraulically reactive particles can also be manufactured from a wider range of starting raw materials compared to conventional cement materials, and have a faster set time with more controllability and faster total reaction time. The hydraulically reactive particles have an increased natural packing density, increased strength, increased chemical/physical stability, less shrinkage, reduced final porosity or microporosity, which is the porosity of the gel, and more efficient total reaction product distribution compared to conventional cementitious materials. III. Examples of the Preferred Embodiments

The following examples set forth various compositions, methods, and reaction conditions that can be used in the preparation of hydraulically reactive aggregate particles according to the invention. While the examples are hypothetical in nature they are based upon actual laboratory studies and an extensive knowledge of the manufacture of hydraulic cement binders.

Example 1 Hydraulically reactive particles are manufactured from crushed granite as the aggregate substrate and powdered lime as the complementary reactant. The granite particles are graded to have an average particle size of approximately 5 mm. The lime powder has an average particle size of about 1 micron.

100 kg of granite particles are introduced into a preliminary mixing chamber and mixed with 10 kg of the lime powder. The granite and lime are blended together using a tumbling action, which results in the granite particles becoming coated with the fine powdered lime. Thereafter, the lime-coated granite particles are fed through a reaction chamber and heated to 1250°C for a period of 5 minutes in order to cause the lime to fuse with the surface of the granite particles. The high temperature reaction results in the formation of calcium silicates and calcium aluminates, which are formed as a hydraulically reactive coating on the surface of the otherwise inert granite particles. The hydraulically reactive granite particles, after formation of the hydraulically reactive surface, have a smoother morphology compared to the unreacted particles and are only slightly larger in size. When blended with water, the particles will hydrate and harden in order to yield a hardened concrete material of relatively high strength.

Example 2 The procedures of Example 1 are repeated in every respect, except that the granite particles are pre-treated by washing them in a strong alkali solution comprising potassium hydroxide. Thereafter, the slightly moistened granite particles are blended with the lime powder, with the residual moisture improving adhesion between the granite particles and lime powder. The resulting hydraulically reactive granite particles have a slightly greater concentration of hydraulically reactive substances due to the alkali wash and greater adhesion of lime powder to the granite particles.

Example 3 100 kg of granite particles are coated with 10 kg of lime that has been dissolved in water to form a saturated calcium hydroxide solution. The lime solution is repeatedly sprayed over the surface of pre-heated granite particles in order to form successive layers of dried lime crust over the granite particles.

The lime crust-coated granite particles are passed through a high temperature reaction chamber and heated to a temperature of 1400°C for 4 minutes in order to cause the lime to fuse with the surface of the granite particles and thereby form a hydraulically reactive surface around the granite particles. The resulting hydraulically reactive particles are similar to those obtained in Examples 1 and 2, except that the distribution of the hydraulically reactive surfaces are more uniform compared to where dry particulate lime is used.

Example 4 100 kg of granite particles are reacted with 10 kg of lime that has been superheated to 3500°C in order to form a highly reactive plasma. The granite particles are themselves pre-heated to a temperature of 500°C in order to remove extraneous water, open up the pores and improve the reactivity of the granite surface particles, and in order to promote the fusion of the superheated lime plasma with the silica and alumina substances found in the granite substrate particles. The plasma deposition is carried out using a plasma deposition chamber. The heat from the superheated lime plasma is sufficient to create a hydraulically reactive surface on the granite particles.

Example 5 The procedures of Example 4 are repeated in every respect, except that the plasma lime coated granite particles are passed through a secondary reaction chamber at a temperature of 1500° C for 1 minute in order to further fuse and react the deposited lime over the granite particle surfaces. The result is a more uniformly distributed and reactive hydraulically settable coating on the granite particle surfaces.

Example 6 100 kg of limestone particles are coated with 10 kg of sodium silicate that has been dissolved in water to form a saturated sodium silicate solution. The limestone particles are pre-calcined at temperature of 750°C for 5 minutes in order to cause the surface of the limestone particles to release CO₂ from a portion of the surface to thereby yield a lime surface. The sodium silicate solution is repeatedly sprayed over the surface of pre-heated limestone particles in order to form successive layers of dried sodium silicate crust over the limestone particles.

The sodium silicate coated limestone particles are passed through a high temperature reaction chamber and heated to a temperature of 1500°C for 3 minutes in order to cause the silicate ions to react with the lime on the surface of the limestone particles to form a hydraulically reactive surface around the limestone particles. The resulting hydraulically reactive limestone particles are able to hydrate in the presence of water and form a relatively strong hardened cementitious material. IV. Summary

The present invention provides processes for manufacturing hydraulically reactive particles that eliminate at least some of the problems associated with both small and large hydraulic cement particles.

The present invention further provides improved processes for manufacturing larger sized hydraulically reactive particles having greatly improved properties compared to coarsely ground hydraulic cement particles. The present invention also provides processes for manufacturing hydraulically reactive particles that have more uniform shape and size, greatly increased strength, and greatly decreased cost compared to similarly sized conventional hydraulic cement particles of equivalent volume.

Furthermore, the present invention provides processes for manufacturing a large variety of differently sized and shaped hydraulically reactive particles without the need for subsequent grinding and grading following the manufacturing process as in the process of manufacturing conventional hydraulic cements.

In addition, the present invention provides processes for manufacturing hydraulically reactive particles from a wide variety of naturally occurring geologic mineral materials.

Further, the present invention provides processes for manufacturing relatively large-sized hydraulically reactive particles that can nevertheless substantially completely hydrate within a short period of time compared to similarly sized hydraulic cement particles. The present invention yet provides processes for manufacturing hydraulically reactive particles that yield concrete having greatly improved bond strength between the various particles in order to yield concrete products having greatly increased strength and durability, and less shrinkage.

Finally, the present invention provides processes for manufacturing hydraulically reactive particles that have a surface chemistry that is similar, or even identical, to that of conventional hydraulic cement binders.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. What is claimed is:

Claims

1. A hydraulically reactive particle comprising: a substantially nonhydraulically reactive interior portion; and a hydraulically reactive outer portion disposed over at least a portion of the substantially nonhydraulically reactive interior portion, wherein the hydraulically reactive outer portion is chemically bonded to the substantially nonhydraulically reactive interior portion.

2. A hydraulically reactive particle as defined in claim 1 , wherein the particle has a diameter in a range from about 5 mm to about 5 cm.

3. A hydraulically reactive particle as defined in claim 1 , wherein the particle has a diameter in a range from about 1 mm to about 5 mm.

4. A hydraulically reactive particle as defined in claim 1 , wherein the particle has a diameter in a range from about 0.1 mm to about 1 mm.

5. A hydraulically reactive particle as defined in claim 1. wherein the particle has a diameter of less than about 0J mm.

6. A hydraulically reactive particle as defined in claim 1, wherein the substantially nonhydraulically reactive interior portion comprises a naturally occurring mineral that, when treated with a complementary reactant, is capable of forming a hydraulically reactive material.

7. A hydraulically reactive particle as defined in claim 6, wherein the naturally occurring mineral includes one or more elements selected from the group consisting of silicon, calcium, aluminum, iron, magnesium, phosphorus, sodium, potassium, manganese, sulfur, oxygen, mixtures thereof, and compounds thereof.

8. A hydraulically reactive particle as defined in claim 1, wherein the substantially nonhydraulically reactive interior portion comprises a calcareous material.

9. A hydraulically reactive particle as defined in claim 8, wherein the calcareous material is selected from the group consisting of limestone, chalk, marl, calcium carbonate, gypsum, and mixtures thereof.

10. A hydraulically reactive particle as defined in claim 8, wherein the hydraulically reactive outer portion is formed by reacting the calcareous material with an argillaceous material.

11. A hydraulically reactive particle as defined in claim 10, wherein the argillaceous material comprises fumed silica.

12. A hydraulically reactive particle as defined in claim 1, wherein the substantially nonhydraulically reactive interior portion comprises an argillaceous material.

13. A hydraulically reactive particle as defined in claim 12, wherein the argillaceous material is selected from the group consisting of sand, clay, granite, shale, silica, alumina, and mixtures thereof.

14. A hydraulically reactive particle as defined in claim 12, wherein the hydraulically reactive outer portion is formed by reacting the argillaceous material with a calcareous material.

15. A hydraulically reactive particle as defined in claim 14, wherein the calcareous material comprises lime.

16. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive outer portion comprises a portland cement.

17. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive outer portion includes at least one hydraulically reactive material selected from the group consisting of dicalcium silicate, tricalcium silicate, tricalcium aluminate, and tetracalcium aluminum ferrite.

18. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive outer portion comprises a hydraulically settable binder selected from the group consisting of gypsum cements, supersulfated cements, phosphate cements, magnesium oxychloride cements, calcium aluminate cements, slag cements, pozzolanic lime cements, alumino-ferrite cements, silicate cements, high alumina cements, lime- based cements, and mixtures thereof.

19. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive outer portion has a thickness of less than about 1/3 the diameter of the hydraulically reactive particle.

20. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive outer portion has a thickness of less than about 1/10 the diameter of the hydraulically reactive particle.

21. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive outer portion has a thickness of less than about 1/100 the diameter of the hydraulically reactive particle.

22. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive particle has a substantially smoother morphology compared to a similarly-sized hydraulic cement particle.

23. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive particle has a substantially higher compressive strength compared to a similarly-sized hydraulic cement particle.

24. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive particle will hydrate in a substantially faster time frame compared to a similarly-sized hydraulic cement particle.

25. A hydraulically reactive particle as defined in claim 1, wherein the hydraulically reactive outer portion completely encapsulates the substantially nonhydraulically reactive interior portion.

26. A composition of matter comprising a plurality of hydraulically reactive particles, each of the hydraulically reactive particles including: a substantially nonhydraulically reactive interior portion; and a hydraulically reactive outer portion disposed over at least a portion of the substantially nonhydraulically reactive interior portion, wherein the hydraulically reactive outer portion is chemically bonded to the substantially nonhydraulically reactive interior portion.

27. A composition of matter as defined in claim 26, wherein the hydraulically reactive particles have a natural particle packing density in a range from about 0.6 to about 0.95.

28. A composition of matter as defined in claim 26, wherein the hydraulically reactive particles have a natural particle packing density in a range from about 0.65 to about 0.9.

29. A composition of matter as defined in claim 26, wherein the hydraulically reactive particles have a natural particle packing density in a range from about 0J to about 0.85.

30. A composition of matter as defined in claim 26, wherein the hydraulically reactive outer portion completely encapsulates the substantially nonhydraulically reactive interior portion of the hydraulically reactive particles.

31. A composition of matter as defined in claim 26, wherein the hydraulically reactive outer portion of the hydraulically reactive particles comprises a portland cement.

32. A composition of matter as defined in claim 26, wherein the hydraulically reactive outer portion of the hydraulically reactive particles includes at least one hydraulically reactive material selected from the group consisting of dicalcium silicate, tricalcium silicate, tricalcium aluminate, and tetracalcium aluminum ferrite.

33. A composition of matter as defined in claim 26, wherein the hydraulically reactive outer portion of the hydraulically reactive particles comprises a hydraulically settable binder selected from the group consisting of gypsum cements, supersulfated cements, phosphate cements, magnesium oxychloride cements, calcium aluminate cements, slag cements, pozzolanic lime cements, alumino-ferrite cements, silicate cements, high alumina cements, lime-based cements, and mixtures thereof.

34. A composition of matter as defined in claim 26, further comprising at least one additional component selected from the group consisting of nonhydraulically reactive aggregate particles, fibers, rheology-modifying agents, dispersants, plasticizers, air- entraining agents, hydraulically settable binders, and set accelerators.

35. A composition of matter as defined in claim 26, further comprising water that has not resulted in substantial hydration of the hydraulically reactive particles such that the composition of matter is substantially flowable.

36. A composition of matter as defined in claim 26, further comprising water that has resulted in partial hydration of the hydraulically reactive particles.

37. A substantially hardened composition of matter comprising initially hydraulically reactive particles that have been exposed to water such that the initially hydraulically reactive particle have been caused to hydrate and thereby form the substantially hardened composition of matter, wherein the initially hydraulically reactive particles, prior to hydration with water, include: a substantially nonhydraulically reactive interior portion; and a hydraulically reactive outer portion disposed over at least a portion of the substantially nonhydraulically reactive interior portion, wherein the hydraulically reactive outer portion is chemically bonded to the substantially nonhydraulically reactive interior portion.

38. A substantially hardened composition of matter as defined in claim 37, wherein the initially hydraulically reactive particles, upon hydration, yield hydrated particles, each of which is chemically bonded to at least one other of the hydrated particles.

39. A substantially hardened composition of matter as defined in claim 37, wherein the hydraulically reactive outer portion of the initially hydraulically reactive particles comprises a portland cement.

40. A substantially hardened composition of matter as defined in claim 37, wherein the hydraulically reactive outer portion of the initially hydraulically reactive particles includes at least one hydraulically reactive material selected from the group consisting of dicalcium silicate, tricalcium silicate, tricalcium aluminate, and tetracalcium aluminum ferrite.

41. A substantially hardened composition of matter as defined in claim 37, wherein the hydraulically reactive outer portion of the initially hydraulically reactive particles comprises a hydraulically settable binder selected from the group consisting of gypsum cements, supersulfated cements, phosphate cements, magnesium oxychloride cements, calcium aluminate cements, slag cements, pozzolanic lime cements, alumino- ferrite cements, silicate cements, high alumina cements, lime-based cements, and mixtures thereof.

42. A substantially hardened composition of matter as defined in claim 37, further comprising at least one additional component selected from the group consisting of nonhydraulically reactive aggregate particles, fibers, rheology-modifying agents, dispersants, plasticizers, air-entraining agents, hydraulically settable binders, and set accelerators.

43. A substantially hardened composition of matter as defined in claim 37, wherein the initially hydraulically reactive particles have a natural particle packing density in a range from about 0.6 to about 0.95.

44. A substantially hardened composition of matter as defined in claim 37, wherein the initially hydraulically reactive particles have a natural particle packing density in a range from about 0.65 to about 0.9.

45. A substantially hardened composition of matter as defined in claim 37, wherein the initially hydraulically reactive particles have a natural particle packing density in a range from about 0J to about 0.85.

46. A method of manufacturing a hydraulically reactive particle comprising:

(a) providing an aggregate substrate and a complementary reactant that, when caused to react with at least a portion of the surface of the aggregate substrate, will form a hydraulically reactive material on at least a portion of the surface of the aggregate substrate; and (b) reacting the complementary reactant with at least a portion of the surface of the aggregate substrate in order to form the hydraulically reactive material that is chemically bonded to at least a portion of aggregate substrate.

47. A method as defined in claim 46, wherein the hydraulically reactive material is formed by heating the aggregate substrate and complementary reactant at a temperature and for a time sufficient to yield the hydraulically reactive material.

48. A method as defined in claim 46, wherein the complementary reactant is applied to the surface of the aggregate substrate in the form of a finely-divided powder.

49. A method as defined in claim 46, wherein the complementary reactant is applied to the surface of the aggregate substrate in the form of a liquid.

50. A method as defined in claim 49, wherein the liquid comprises an aqueous solution of the complementary reactant in water.

51. A method as defined in claim 49, wherein the liquid comprises a colloidal suspension of the complementary reactant in water.

52. A method as defined in claim 46, wherein the reacting step is carried out within a reaction chamber that is heated to a temperature in a range from about 500°C to about 3000°C.

53. A method as defined in claim 46, wherein the reacting step is carried out within a reaction chamber that is heated to a temperature in a range from about 1000°C to about 2000°C.

54. A method as defined in claim 46, wherein the reacting step is carried out within a reaction chamber that is heated to a temperature in a range from about 1200°C to about 1800°C.

55. A method as defined in claim 46, wherein the complementary reactant is applied to the surface of the aggregate substrate in the form of a superheated plasma.

56. A method as defined in claim 55, wherein the superheated plasma is initially heated to a temperature of about 1500°C to about 5000°C.

57. A method as defined in claim 55, wherein the superheated plasma is initially heated to a temperature of about 2000°C to about 4000°C.

58. A method as defined in claim 55, wherein the superheated plasma is initially heated to a temperature of about 2500°C to about 3500°C.

59. A method as defined in claim 46, wherein the aggregate substrate comprises a naturally occurring mineral.

60. A method as defined in claim 59, wherein the naturally occurring mineral includes one or more elements selected from the group consisting of silicon, calcium, aluminum, iron, magnesium, phosphorus, sodium, potassium, manganese, sulfur, oxygen, mixtures thereof, and compounds thereof.

61. A method as defined in claim 46, wherein the aggregate substrate comprises a calcareous material.

62. A method as defined in claim 61, wherein the calcareous material is selected from the group consisting of limestone, chalk, marl, calcium carbonate, gypsum, and mixtures thereof.

63. A method as defined in claim 61, wherein the hydraulically reactive material is formed by reacting the calcareous material with an argillaceous material.

64. A method as defined in claim 63, wherein the argillaceous material comprises fumed silica.

65. A method as defined in claim 46, wherein the aggregate substrate comprises an argillaceous material.

66. A method as defined in claim 65, wherein the argillaceous material is selected from the group consisting of sand, clay, granite, shale, silica, alumina, and mixtures thereof.

67. A method as defined in claim 65, wherein the hydraulically reactive material is formed by reacting the argillaceous material with a calcareous material.

68. A method as defined in claim 67, wherein the calcareous material comprises lime.

69. A method as defined in claim 46, wherein the hydraulically reactive material comprises portland cement.

70. A method as defined in claim 46, wherein the hydraulically reactive material includes at least one hydraulically reactive material selected from the group consisting of dicalcium silicate, tricalcium silicate, tricalcium aluminate, and tetracalcium aluminum ferrite.

71. A method as defined in claim 46, wherein the hydraulically reactive material comprises a hydraulically settable binder selected from the group consisting of gypsum cements, supersulfated cements, phosphate cements, magnesium oxychloride cements, calcium aluminate cements, slag cements, pozzolanic lime cements, alumino- ferrite cements, silicate cements, high alumina cements, lime-based cements, and mixtures thereof.

72. A method as defined in claim 46, wherein the hydraulically reactive particle has a diameter in a range from about 5 mm to about 5 cm.

73. A method as defined in claim 46, wherein the hydraulically reactive particle has a diameter in a range from about 1 mm to about 5 mm.

74. A method as defined in claim 46, wherein the hydraulically reactive particle has a diameter in a range from about 0J mm to about 1 mm.

75. A method as defined in claim 46, further including pre-treating the surface of the aggregate substrate, prior to reacting the aggregate substrate with the complementary reactant, by means of at least one process selected from the group consisting of calcining, sintering, acid washing, and base washing.

76. A method as defined in claim 46, wherein the reacting step results in the hydraulically reactive material completely encapsulating the aggregate substrate.

77. A method as defined in claim 46, wherein the reacting process is carried out by means of the complementary reactant forming the hydraulically settable material without further heating of the aggregate substrate.

78. A method of manufacturing a hydraulically reactive particle comprising:

(a) providing an aggregate substrate and a complementary reactant that, when caused to react with at least a portion of the surface of the aggregate substrate, will form a hydraulically reactive material on at least a portion of the surface of the aggregate substrate;

(b) applying the complementary reactant to at least a portion of the surface of the aggregate substrate in order to form a coated aggregate substrate;

(c) heating the coated aggregate substrate at a temperature and for a sufficient period of time in order to form a hydraulically reactive material on at least a portion of the surface of the aggregate substrate.

79. A method as defined in claim 78, wherein the complementary reactant is applied to the aggregate substrate in the form of a particulate.

80. A method as defined in claim 78, wherein the complementary reactant is applied to the aggregate substrate in the form of an aqueous solution.

81. A method as defined in claim 78, wherein the complementary reactant is applied to the aggregate substrate in the form of a superheated plasma.

82. A method of manufacturing a hydraulically reactive particle comprising:

(a) providing an aggregate substrate and a complementary reactant in the form of a superheated plasma that, when caused to react with at least a portion of the surface of the aggregate substrate, will form a hydraulically reactive material on at least a portion of the surface of the aggregate substrate; and

(b) reacting the complementary reactant in the form of a superheated plasma with at least a portion of the surface of the aggregate substrate in order to form a hydraulically reactive material on at least a portion of the surface of the aggregate substrate.

83. A method as defined in claim 82, further including the step of heating the hydraulically reactive particle to a temperature of at least about 1000° C in order to further fuse the complementary reactant with the surface of the aggregate substrate.