Abstract:
An aircraft runway safety area for slowing an aircraft that has overrun a runway, including a brittle, nondeformable material for arresting the travel of an aircraft without catastrophically damaging the aircraft, the nondeformable material being configured to crush upon being contacted by the aircraft to effect arrest, and comprising incompressible material in the form of one or more foamed glass bodies, each respective body having a top surface, a bottom surface and oppositely disposed side surfaces, and a frangible matrix encasing the one or more foamed glass bodies, the frangible matrix fabricated to protect the incompressible material and having a breaking strength sufficient to readily break without subverting the arrestment characteristics of the incompressible material. The frangible matrix is different from the incompressible material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This continuation-in-part patent application claims priority to co-pending U.S. patent application Ser. No. 11/276,193 filed on Feb. 17, 2006. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to the field of ceramic composite materials and, specifically, to an incompressible ceramic material and/or composite ceramic material having a tailored failure mode for use as a runway safety area construction material, and method of making and using such a runway safety area. 
       BACKGROUND 
       [0003]    Foamed glass is an established lightweight ceramic material. Typically, foamed glass is made in one of two ways. The first way involves preparing a stable foam from water and foaming agent, preparing a wet mixture or slurry of solid components (where cement is the main substance), quick mixing the foam and the slurry, filling molds with prepared the mixed foam/slurry, and firing the same. The second way to make foamed glass involves making use of the property of some materials to evolve a gas when heated. A foamed glass material may be prepared by mixing crushed vitreous particles and a foaming agent (such as CaCO 3  or CaSO 4 ), placing the mixture in a mold, heating the mold (such as by passing the mold through a furnace) to a foaming temperature, and cooling the mold to produce foamed glass bodies. 
         [0004]    Slag is a nonmetallic byproduct of metallurgical operations. Slags typically consist of calcium, magnesium, and aluminum silicates in various combinations. Iron and steel slags are byproducts of iron and steel production. For example, an iron blast furnace is typically charged with iron ore, fluxing agents (such as limestone or dolomite) and coke (as fuel and reducing agent). Iron ore is typically a mixture of iron oxides, silica, and alumina. When sufficiently heated, molten slag and iron are produced. Upon separation of the iron, the slag is left over. The slag occurs as a molten liquid melt and is a complex solution of silicates and oxides that solidifies upon cooling. 
         [0005]    The physical properties of the slag, such as its density, porosity, mean particle size, particle size distribution, and the like are affected by both its chemical composition and the rate at which it was cooled. The types of slag produced may thus conveniently be classified according to the cooling method used to produce them—air cooled, expanded, and granulated. Each type of slag has different properties and, thus, different applications. 
         [0006]    While useful as insulation and as abrasive materials, foamed glass bodies (made with or without foamed slag), are typically unsuitable for use as lightweight filler and/or in composite materials due to factors including cost and the propensity for foamed glass to hydrate and expand. 
         [0007]    Thus, there remains a need for an easily produced foamed glass material that is more resistant to expansion from hydration and/or more easily aged, and for composite materials incorporating the same. The present invention addresses this need. 
       SUMMARY 
       [0008]    The technology discussed below relates to manufactured composite materials, such as roadbed and airport runway safety areas (RSA&#39;s) incorporating lightweight foamed glass and cementitious or other ceramic materials to define structural composite materials having controlled failure mode properties, and the method for making the same. One object of the present invention is to provide an improved foamed glass-containing structural composite RSA material. Related objects and advantages of the present invention will be apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic view of a first embodiment of a process for making foamed glass composites. 
           [0010]      FIG. 2A  is a schematic view of a second embodiment of a process for making foamed glass bodies and composites and its uses. 
           [0011]      FIG. 2B  is a schematic view of a third embodiment of a process for making foamed glass bodies and composites and its uses. 
           [0012]      FIG. 3A  is a schematic view of a process for mixing a batch of precursors for a foamed glass article according to a fourth embodiment of the present novel technology. 
           [0013]      FIG. 3B  is a schematic view of a process for firing a foamed glass article mixed according to  FIG. 3A . 
           [0014]      FIG. 3C  is a perspective view of as milled glass powder according to the process of  FIG. 3B . 
           [0015]      FIG. 3D  is a perspective view of rows of milled glass powder mixture ready for firing. 
           [0016]      FIG. 3E  is a perspective view of  FIG. 3D  after firing into a substantially continuous foamed glass sheet. 
           [0017]      FIG. 4  is a process diagram of the process illustrated in  FIGS. 3A and 3B . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    For the purposes of promoting an understanding of the principles of the claimed technology and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the claimed technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the claimed technology relates. 
         [0019]    Vitreous materials, such as soda-lime-silica glasses and metallurgical byproduct slags, are typically foamed through a gasification processes to yield a typically predominately vitreous, typically silaceous incompressible cellular glass product. Typically, a foaming precursor is predominately vitreous or non-crystalline prior to the foaming process, since a glassy precursor slag material typically has a viscosity at temperature that is convenient to the foaming process. More typically, the vitreous starting material will have a traditional soda-lime-silica glass composition, but other compositions, such as aluminosilicate glasses, borosilicate glasses, vitreous peralkaline slag or other vitreous slag compositions may be foamed as well. For example, a peraluminous slag with significant alkali and alkaline earth oxides may also be utilized. After the vitreous precursor is foamed, the foamed glass is physically combined with cement to form a composite material suitable for building or structural applications or the like. 
         [0020]    In the case of slagaceous precursor materials, the slag is typically predominately vitreous in character, and more typically has a maximum 40% by volume crystalline material. The slag is typically initially crushed and sized to approximately 10 microns median particle size, more typically at least 90 percent of all particles are less than 75 microns. 
         [0021]    If the crushed and/or powdered slag is dry, water is added to the powdered slag to about 0.1 to about 0.5% (by mass). Alternately, if no water is added, limestone or other solid foaming agent may be added (typically about 4 percent or less by mass, more typically about 2 percent or less by mass). The mixture is then formed into pellets (between 0.05 and 1 cubic centimeter), preheated (to no more than within 25° C. of the dilatometric softening point) and then passed through a high temperature zone, such as one generated by a rotary kiln or a flame (contained in a ceramic or refractory metal tube). The residence time in the zone is short, typically about 0.5 to about 10 seconds, and the temperature is high (adiabatic flame temperature in excess of 1300° C.). In the case of a flame, the thermal energy provided to the material by the direct flame enables a change of state reaction in the foaming agent and the resulting gas will force the now viscous matter to foam. The foamed pellets or foamed media are air quenched below the dilatometric softening point of the material, and then allowed to dry by slow cooling. 
         [0022]    The foamed glass or ceramic media are incompressible and typically have a relative volume expansion in excess of three fold, and more typically the volume expansion is as high as 10 fold or greater. This process results in individual, low-density (specific gravity less than 0.3) foamed media with a median pore size in the range of 0.1 to 2 mm. 
         [0023]    Composite materials may be prepared by mixing the foamed slag with Portland cement; at least two types of composite materials may be made according to this technique. A first composite material may be prepared by mixing a thin mixture of cement with foamed media, wherein the foamed media comprises at least 85 volume percent of the total cement/other aggregate. The foamed media are typically incorporated into the cement (and aggregates, if needed) after the water has been added. The resulting mixture acts as a very viscous material and is pressure or gravity formed into a slab (or other coherent shape) or direct cast into a prefabricated form. The shape or form is then allowed to set. The resulting composite material sets up to be a rigid, relatively lightweight (specific gravity &lt;0.75) incompressible material with surface properties typical of Portland cements. Chemicals and finishing systems compatible with Portland cement can be used in conjunction with this material. The resultant composite material has a brittle fracture or failure mode, with successive cells fracturing under applied compression. The energy imparted by a compressive load is thus dissipated through the fracture of successive glass cells. The composite material is for all practical purposed substantially or completely rigid and substantially or completely incompressible and non-deformable, as a compressive load is supported by a body formed from the composite material without deformation or compression of the body, until the load exceeds the compressive strength of the body, whereupon cells begin to catastrophically fail through a crushing mechanism. At no point does the body compress or deform such that removal of the applied force results in a decompression or recoil of the body into its original uncompressed, undeformed shape. 
         [0024]    A second composite material is formed as a mixture of cement with typically less than 50 volume percent foamed slag media. The media is typically dry mixed with cement prior to water additions. The mixture is then prepared as common cement. Additional aggregates may be incorporated as per common practice. This second composite material is likewise incompressible and has a very high strength; the composite compressive strength is typically at least 25% higher per unit mass than is that of the identical cement prepared without the foamed slag addition. It can be used in any application compatible with Portland cement. 
         [0025]    A third incompressible composite material is formed as aqueous slurry mixture comprised of gypsum with typically less than 50 percent by volume foamed glass or slag. The media are typically added to the gypsum after the material is slurried. Additional binders, fillers and setting agents may be added per common practice. The resulting material has a very low density and high acoustic absorption. There are no chemical compatibility limitations on the extent of foamed glass additions. Any limitations typically arise from strength considerations and other physical properties. 
         [0026]    In another example, the vitreous precursors  210  to the foaming process are waste glasses. Waste glasses typically have a soda-lime-silica composition, and are generally first crushed or ground  220 , and then typically sized  230 , to produce a particulate frit  235  suitable for pelletizing  250  or otherwise forming into regular shapes for foaming. 
         [0027]    As with slagaceous precursors as described above, if the particulate waste glass  210  is dry, water may be added to the in small amounts to promote handling and to better adhere the foaming agent uniformly to the particles for more even distribution. Alternately, if no water is added, limestone or other solid foaming agent  240  may still be added, typically in small amounts (such as less than 2 percent by mass) and mixed to form a substantially heterogeneous foamable vitreous mixture. The mixture  245  is then typically formed  250  into pellets (between 0.05 and 1 cubic centimeter), loaves, or other regular green bodies  260  convenient for foaming and is next preheated  265 , typically to no more than within 25° C. of the dilatometric softening point. Preheating  265  readies the green bodies  260  for rapid heating  270  into the foaming temperature region. 
         [0028]    The preheated green bodies  260  are then passed through a high temperature zone  275 , such as one generated by a rotary kiln or a flame (contained in a ceramic or refractory metal tube). The residence time in the zone is short, typically about 0.5 to about 10 seconds, but may be longer for larger green bodies  260 . The temperature is substantially high (adiabatic flame temperature at least about 1200° C. and typically around 1300° C. or higher). The rapid influx of thermal energy provided to the material enables a change of state reaction in the foaming agent  240  and the resulting gas will force the now viscous matter to foam. 
         [0029]    The foamed bodies  275  are then rapidly quenched  280  to below the dilatometric softening point of the material, and then allowed to cool to room temperature at a second, typically slower, cooling rate. The cooling rate is typically rapid enough such that the foamed glass  275  does not anneal or only partially anneals, resulting in a harder foamed glass body  285  with built-in stresses that enhance its crushing strength and toughness, and also give rise to a crushing failure mode in compression and torsion. The cooling rate typically varies due to belt speed. The high end is typically about 15-25° C. per minute, while the low end is typically about 10-20° C. per minute for the temperature range from the foaming temperature to just below the dilatometric softening point; more typically, cooling from the foaming temperature to below the dilatometric softening pint temperature occurs at a rate of about 20 degrees Celsius per minute. The cooling rate typically diminishes as the body  285  approaches the softening point. 
         [0030]    After foaming, the bodies  275  leave the kiln and are quenched  280 , typically via exposure to air or forced water jacket cooling, and the cooling rate is increased to about 25-40° C. per minute during the rapid quench, more typically at least about 30 degrees Celsius per minute. After the rapid quench, the cooling rate is decreased to about 3-10° C. per minute. All cooling rate values are for the center of the foamed glass bodies  285 . 
         [0031]    For foamed media produced on a belt process, the pellets or green bodies  260  are typically configured such that the resultant foamed glass bodies  275 ,  285  have irregular oblong or ovoid shapes. More typically, the green bodies  260  are preformed or pressed pellets sized such that the resultant foamed bodies  275 ,  285  have major axis dimensions of between about 10 mm and 80 mm. Accordingly, these bodies  285  are typically sized and shaped to be engineered drop-in replacements for mined gravel aggregate and have superior water management, compressive strength, failure mode, erosion, stackability, chemical stability and toughness properties. Alternately, the foamed bodies  285  may be made to other convenient size and shape specifications, such as in larger orthorhombic parallelepiped or ‘brick’ shapes, still larger ‘cinder block’ dimensions, relatively thin plates, and the like. 
         [0032]    One advantage of this process is that the furnace residence time of vitreous bodies  275  during the foaming process is reduced a factor of 4-9 over most conventional glass foaming techniques. Moreover, the foamed glass bodies  285  can be produced with mean cell sizes of less than about 0.2 mm in diameter, and with typically individual cells sizes ranging down to about 0.1 mm in diameter or less. Bodies  285  having such small cell sizes are typically of the closed cell type, which gives rise to crushing strengths of at least about 50 psi, typically between about 50 and 150 psi, and more typically well over the typical 100 psi (for comparably dense open cell material) to well over 200 psi. Further, bodies  285  having substantially open cells sized in the less than 0.1-0.2 mm range exhibit enhanced capillary action and accordingly rapidly absorb and efficiently retain water. 
         [0033]    The natural break-up of the material under rapid cool down, due to thermally induced stresses, results in a more angular, jagged foamed glass body  285  as opposed to a foamed glass piece shaped by crushing a large body. The physical measure is that the so-produced foamed glass bodies  285  have a range of aspect ratios (largest to smallest diameter) about 50% higher than the 1 to 1.25 ratio average for smaller bodies formed via a crushing process. This gives rise to the 35 degree stacking angle and ensures the material breaks up before slip failure. 
         [0034]    In one example, oblong, irregularly shaped foamed bodies  285  produced as described above and having major axial dimensions of about 80 mm are used as fill material  290  behind rock retaining walls. As these fill material bodies are relatively light weight, relatively strong in compression, have a characteristic stacking angle of about 35 degrees and are characterized by an open pore structure, a substantially smaller volume of foamed glass aggregate fill is required as compared to traditional mined gravel. For a 6 foot retaining rock wall, the required foundation thickness is reduced from 54 inches to 24 inches, the required rock is reduced by 7.5 cubic feet per linear foot of wall, and the required concrete is reduced by 2.5 cubic feet per linear foot of wall. The amount of graded fill is reduced from 40 cubic feet per linear foot of wall to 24 cubic feet per linear foot of wall. This reduction is made possible by the high stacking angler (about 35 degrees) of the foamed glass aggregate material  290 , the physical manifestation of which is its tendency to fail by a crushing mechanism (shattering of the individual cells) instead of the individual aggregate pieces sliding over themselves. Additionally, the open pore structure of the foamed glass aggregate  285  gives rise to superior drainage and water management properties, reducing or eliminating the need for a separate inlaid drain pipe. In other words, by replacing mined gravel with engineered foamed glass aggregate  290  characterized by a high stacking angle, the amount of fill may be nearly halved and, consequently, the foundation depth and wall thickness may likewise be substantially reduced. 
         [0035]    Likewise, the foamed glass aggregate fill may replace traditional mined fill gravel  295  in road beds. Less volume of the foamed glass aggregate fill is required, as it has superior strength, porosity and failure mode characteristics, giving rise to shallower road beds, reduced construction time and expenses, less excavated dirt to be trucked away, reduced energy usage in road construction, simplified road drainage, and the like. Moreover, the roads themselves may be constructed of concrete including foamed glass aggregate made as described above, which likewise has enhanced strength and decreased weight characteristics. 
         [0036]    In another embodiment, the foamed glass bodies produced as described above may be incorporated into acoustic ceiling tiles  300 . The foamed glass material is chemically stable and inert, non-toxic, lightweight, and its porosity gives rise to sound-dampening. The tiles may be made entirely of shaped foamed glass (in the form of relatively thin panels), or may incorporate foamed glass particles or bodies in a structural matrix, such as a polymer based, fibrous, cementitious, or like matrix material. Of course, the foamed glass bodies  285  may also be used as aggregate  305  in traditional concrete. 
         [0037]    In another embodiment, incompressible foamed glass bodies  285  are produced, in some typical embodiments as described above, for incorporation into RSA&#39;s  350 . Typically, the incompressible foamed glass bodies  285  are produced having a closed cell or closed porosity structure to retard or prevent water infiltration and hydration. The foamed glass material is physically incompressible and chemically stable and inert. The RSA&#39;s  350  are typically formed from an incompressible foamed glass composite material  360  including foamed glass bodies  285  in a ceramic matrix  370 . Typically, the composite material includes at least about 50 volume percent foamed glass, more typically at least about 60 volume percent foamed glass, still more typically at least about 70 volume percent foamed glass, yet more typically at least about 80 volume percent foamed glass, and in some embodiments at least about 90 volume percent foamed glass. The foamed glass bodies  285  may be in the form of aggregate  305 , shaped foamed glass blocks, or a combination of sizes and shapes incorporated into a structural matrix  370 , such as a polymer based, fibrous, cementitious, or like matrix material. In some embodiments, the foamed glass bodies  285  may also be used as aggregate  305  in traditional concrete. For RSA&#39;s, a higher relative volume of the foamed glass aggregate  305  and/or bodies  285  fill is required, as the composite RSA  360  typically has lower crush strength to provide the desired predetermined failure mode characteristics, i.e., the RSA  360  will crush under the weight of an oncoming aircraft to bleed off its kinetic energy and slow its progress across the RSA  360  until it stops without incurring significant or catastrophic damage. Moreover, the RSAs  360  are typically constructed of incompressible foamed glass bodies  295  and/or aggregate  305  (more typically closed cell foamed glass aggregate  305  and/or bodies  295 ) in a thin ceramic or structural frangible matrix  370 , wherein the surface  375  of the RSA  360  is matrix material  370 . The matrix  370  may be concrete, asphalt, or the like. The RSA  360  typically has a solid surface  375 , and more typically has a ridged, textured or contoured surface  375  to further bleed kinetic energy from an oncoming aircraft. The frangible matrix  375  typically has a different composition than the enveloped bodies  295  and/or aggregate  305 , and is more typically sufficiently strong to provide protection and structural support to the bodies  285 , but no so strong as to not yield to the oncoming aircraft, so as to break readily without subverting the aircraft arrestment characteristics of the incompressible material  360 . 
         [0038]    For RSA&#39;s  360  featuring ridges  363 , the ridges  363  are typically sized to be about the height of a landing gear tire or less, such that when an oncoming tire encounters a ridge  363 , the tire both crushes the ridge  363  with both oncoming (forward directed) force and the supported weight (downward directed force) of the aircraft, to more directly bleed off forward momentum and thus more efficiently slow the aircraft. 
         [0039]    The foamed glass bodies  285  for the RSA composite  360  may generally be prepared as described above, albeit the bodies  285  are typically foamed at a higher temperature, typically between about 1600 degrees Celsius and about 1900 degrees Celsius, to yield a closed pore structure. In other embodiments, the foamed glass may be prepared by the techniques described in U.S. Pat. Nos. 5,821,184 and 5,983,671, or the like. In still other embodiments, the foamed glass is prepared so as to have a very low to substantially zero crystalline silica content. 
         [0040]    Typically, the foamed glass bodies make up at least 50 volume percent of the RSA composite  360 , more typically at least 75 volume percent, still more typically at least 85 volume percent, yet more typically at least 90 volume percent, and may make up as much as 95 volume percent or more. By varying the ratio of foamed glass bodies  295  to cementitious matrix material  375  in the composite  360 , and by varying the thickness of the top layer of matrix material  375  in the composite  360 , the crushing strength of the composite  360  bed may be ‘fine-tuned’ so as to allow maintenance and emergency vehicles to traverse the composite  360  beds without crushing them, but not so as to allow an oncoming aircraft free traverse without crushing the composite  360  beds. In all cases, the RSA composites  360  including foamed glass bodies  285  are inherently non-flammable. 
         [0041]      FIGS. 3A-4  illustrate another method of producing lightweight foamed glass matrix  110  defining a plurality of voluminous, closed off and/or interconnecting pores  115 . The pores  115  typically have diameters ranging from about 0.2 mm to about 2.0 mm. The pore walls  117  can be formed to exhibit a crazed or microcracked microstructure  119 . As illustrated schematically in  FIGS. 3A-4 , a ground, milled and/or powdered glass precursor  120 , such as recycled waste bottle and/or window glass, is mixed with a foaming agent  122  (typically a finely ground non-sulfur based gas evolving material, such as calcium carbonate) to define an admixture  127 . The foaming agent  122  is typically present in amounts between about 1 weight percent and about 3 weight percent and sized in the average range of about 80 to minus 325 mesh (i.e. any particles smaller than this will pass through—typically, the apertures in 80 mesh are between about 150 and about 200 micrometers across and the apertures in—352 mesh are between about 40 and about 60 micrometers across). More typically, the foaming agent has a particle size between about 5 and about 150 microns. Typically, a pH modifier such as dicalcium phosphate  124  is added to the admixture  27 , wherein the pH modifier  124  becomes effective when the foamed glass product  110  is used in an aqueous environment. The pH modifier  124  is typically present in amounts between about 0.5 and 5 weight percent, more typically between about 1 and about 2 weight percent. Additional plant growth nutrient material may be added to the starting mixture to vary or enhance the plant growth characteristic of the final product  110 . 
         [0042]    Foamed glass, like most ceramics, is naturally hydrophobic. As hydrophobic surfaces are not conducive to wetting and impede capillary action, treatment is typically done to make the pore walls  117  hydrophyllic. In one embodiment, the pore walls  117  are coated to form a plurality of microcracks  119  therein. The microcracks  119  supply increased surface area to support wicking. Alternately, or in addition, an agent may be added to further amend the surface properties to make the foamed glass more hydrophilic. Such an agent may be a large divalent cation contributor, such as ZnO, BaO, SrO or the like. The hydrophilic agent is typically added in small amounts, typically less than 1.5 weight percent and more typically in amounts of about 0.1 weight percent. 
         [0043]    The combination is mixed  126 , and the resulting dry mixture  127  may then be placed into a mold  128 , pressed into a green body and fired without the use of a mold, or, more typically, arrayed into rows  131  of powder mixture  127  for firing and foaming. Typically, whether placed  129  into the mold  128  or not, the mixture  127  is typically arrayed in the form of several rows  131 , such as in mounds or piles of mixture typically having a natural angle of repose of about 15 to 50 degrees, although even greater angles to the horizontal can be achieved by compressing the dry mixture  127 . This arraying of the rows  131  allows increased control, equilibration and optimization of the heating of the powder  127  during firing, reducing hot and cold spots in the furnace as the powder  127  is heated. This combing of the powder  127  into typically rows  131  of triangular cross-sections allows heat to be reflected and redirected to keep heating of the rows generally constant. 
         [0044]    The mold  128 , if used, is typically a refractory material, such as a steel or ceramic, and is more typically made in the shape of a frustum so as to facilitate easy release of the final foamed glass substrate  110 . Typically, the inside surfaces of the mold  128  are coated with a soft refractory release agent to further facilitate separation of the foam glass substrate  110  from the mold  128 . In a continuous process, the powder  127  is typically supported by a fiberglass mesh fleece or the like to prevent fines from spilling as the powder  127  is moved via conveyor through a tunnel kiln; the fleece is burned away as the powder  127  sinters. 
         [0045]    The so-loaded mold  128  is heated  130  in a furnace by either a batch or continuous foaming process. More typically, the mixture  127  is then heated  130  in order to first dry  132 , the sinter  134 , fuse  136 , soften  138 , and foam  140  the mixture  127  and thereby produce a foamed glass substrate  110  having a desired density, pore size and hardness. As the powdered mixture  127  is heated to above the softening point of glass (approximately 1050 degrees Fahrenheit) the mixture  127  begins to soften  138 , sinter  134 , and shrink. The division of the powdered mixture  127  into rows or mounds allows the glass to absorb heat more rapidly and to therefore foam faster by reducing the ability of the foaming glass to insulate itself. At approximately 1025 degrees Fahrenheit, the calcium carbonate, if calcium carbonate has been used as the foaming agent  122 , begins to react with some of the silicon dioxide in the glass  120  to produce calcium silicate and evolved carbon dioxide. Carbon dioxide is also evolved by decomposition of any remaining calcium carbonate once the mixture reaches about 1540 degrees Fahrenheit, above which calcium carbonate breaks down into calcium oxide and carbon dioxide gas. Once the temperature of the mixture  127  reaches about 1450 degrees Fahrenheit, the glass mixture  127  will have softened sufficiently for the released carbon dioxide to expand and escape through the softened, viscous glass; this escape of carbon dioxide through the softened glass mass is primarily responsible for the formation of cells and pores therein. The mixture  127  in the mold  128  is held for a period of time at a peak foaming temperature of, for example, between about 1275 and about 1900 degrees Fahrenheit, more typically between about 1550 and about 1800 degrees Fahrenheit, still more typically between about 1650 and about 1850 degrees Fahrenheit, or even higher, depending on the properties that are desired. By adjusting the firing temperatures and times, the density and hardness as well as other properties of the resultant substrate  110  may be closely controlled. 
         [0046]    As the mixture  127  reaches foaming temperatures, each mass of foaming  140  glass, originating from one of the discrete rows or mounds, expands until it comes into contact and fuses with its neighbors. The fused mass of foaming glass then expands to conform to the shape of the walls of the mold  128 , filling all of the corners. The shapes and sizes of the initial mounds of mixture are determined with the anticipation that the foaming  140  mixture  127  exactly fills the mold  128 . After the glass is foamed  140  to the desired density and pore structure, the temperature of the furnace is rapidly reduced to halt foaming  140  of the glass. When the exterior of the foamed glass in the mold has rigidified sufficiently, the resultant body  110  of foamed glass is removed from the mold  128  and is typically then air quenched to thermally shock the glass to produce a crazed microstructure  119 . Once cooled, any skin or crust is typically cut off of the foamed glass substrate  110 , which may then be cut or otherwise formed into a variety of desired shapes. Pore size can be carefully controlled within the range of about 5 mm to about 0.5 mm, more typically within the range of between about 2.0 mm and 0.2 mm. Substrate density can be controlled from about 0.4 g/cc to about 0.26 g/cc. Typically, the bulk density of the crushed foam may be as low as 50% of the polyhedral density. 
         [0047]    The substrate  110  may be either provided as a machined polyhedral shape  110  or, more typically, as a continuous sheet that may be impacted and/or crushed to yield aggregate or pebbles  150  (typically sized to be less than 1 inch in diameter). The crushed substrate material  150  may be used to retain water and increase air volume in given soil combinations. The polyhedrally shaped substrate bodies  110  are typically sized and shaped as aggregate for use in an RSA composite material. The foamed glass material  110  itself is typically resistant to aqueous corrosion and has minimal impact on solution pH. In order to provide better pH control, the foamed glass material  110  is typically doped (in batch stage, prior to foaming) with specific dicalcium phosphate or a like pH stabilizing material  124  which dissolves in water to help stabilize the pH. The foamed glass substrate  110  can typically hold between about 1.5 and about 5 times its own weight in water in the plurality of interconnected pores  117 . 
         [0048]    Crushed foam bodies  150  may be rapidly made by an alternate method. Using soda-lime glass frit or powder as the glass component  122 , the processing is similar to that described above but without the annealing step. The alternate method employs the same foaming temperature ranges as related above. The batch material  127  consists of up to 8 percent by mass limestone, magnesite, or other applicable foaming agent  122 , usually less than 2 percent by mass dicalcium phosphate  124 , with the balance being a borosilicate, silicate, borate or phosphate glass frit  122 . The batch  127  is then placed in a typically shallow mold  128 , more typically having a configuration of less than 2″ batch for every square yard of mold surface. The mold  128  is typically then heated to approximately 250° C. above the dilatometric softening point for soda-lime glass (or the equivalent viscosity for other glass compositions) and allowed to foam. The mold  128  is held at the foaming temperature for less than 30 minutes and then pan quenched, i.e. substantially no annealing is allowed to occur 
         [0049]    This method typically yields a material  110  of density less than 0.25 g/cc, and more typically as low as about 0.03 g/cc. This material  110  is then crushed into pebbles  150 , with a corresponding lower bulk density as per the above-described method. Material made by this alternate method has similar chemical properties as described above but has substantially lower strength. 
         [0050]    Still another alternate method of preparing foamed glass substrate material  110  is as follows. A batch  127  is prepared as discussed above and pressed into small (typically less than 5 mm diameter) pellets. The pellets are rapidly heated, such as by passage through a flame source, passage through a rotary furnace, or the like. Typically, the pellets are heated to about 1500 degrees Fahrenheit, such as to cause the pellet to expand as a foam particulate without the need for a mold. This material yields the weakest, but least dense foam particles. The typical density may be as low as 0.02 g/cc or as high as 0.2 g/cc, or higher. 
         [0051]    The foamed glass substrate  110  typically has a porosity in the range of between about sixty-five and about eighty-five percent. Air holding capacity is typically between about forty and about fifty-five percent. 
         [0052]    The pore size is typically between about 0.2 mm and about 2.0 mm in diameter, with a relatively tight pore size distribution. The finished substrate  110  is typically processed through a series of conveyors and crushing equipment to yield a desired size spread of pellets  150 . 
         [0053]    The precursor glass material is typically recycled or post-consumer waste glass, such as plate, window and/or bottle glass. The glass is ground or milled to a fine mesh profile of minus 107 microns. A typical sieve analysis of the precursor glass is given as Table 1, and a compositional analysis of the glass is given as Table 2. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Sieve Analysis 
               
             
          
           
               
                 Class up to (μm) 
                 Pass (%) 
                 Remaindser (%) 
                 Incidence (%) 
               
               
                   
               
             
          
           
               
                 0.7 
                 1.3 
                 98.7 
                 1.3 
               
               
                 0.9 
                 1.6 
                 98.4 
                 0.3 
               
               
                 1 
                 1.8 
                 98.2 
                 0.2 
               
               
                 1.4 
                 2.8 
                 97.2 
                 1.0 
               
               
                 1.7 
                 3.7 
                 96.3 
                 0.9 
               
               
                 2 
                 4.6 
                 95.4 
                 0.9 
               
               
                 2.6 
                 6.4 
                 93.6 
                 1.8 
               
               
                 3.2 
                 7.9 
                 92.1 
                 1.5 
               
               
                 4 
                 9.9 
                 90.1 
                 2.0 
               
               
                 5 
                 12.0 
                 88 
                 2.1 
               
               
                 6 
                 14.0 
                 86 
                 2.0 
               
               
                 8 
                 17.5 
                 82.5 
                 3.5 
               
               
                 10 
                 20.5 
                 79.5 
                 3.0 
               
               
                 12 
                 23.3 
                 76.7 
                 2.8 
               
               
                 15 
                 27.3 
                 72.7 
                 4.0 
               
               
                 18 
                 31.1 
                 68.9 
                 3.8 
               
               
                 23 
                 37.2 
                 62.8 
                 6.1 
               
               
                 30 
                 45.1 
                 54.9 
                 7.9 
               
               
                 36 
                 51.2 
                 48.8 
                 6.1 
               
               
                 45 
                 59.2 
                 40.8 
                 8.0 
               
               
                 56 
                 67.6 
                 32.4 
                 8.4 
               
               
                 63 
                 72.3 
                 27.7 
                 4.7 
               
               
                 70 
                 76.6 
                 23.4 
                 4.3 
               
               
                 90 
                 86.5 
                 13.5 
                 9.9 
               
               
                 110 
                 92.7 
                 7.3 
                 6.2 
               
               
                 135 
                 97.1 
                 2.9 
                 4.4 
               
               
                 165 
                 99.3 
                 0.7 
                 2.2 
               
               
                 210 
                 100.0 
                 0 
                 0.7 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Glass oxide 
                 Wt. % 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 SiO 2   
                 71.5 
               
               
                   
                 Na 2 O 
                 12.6 
               
               
                   
                 K 2 O 
                 0.81 
               
               
                   
                 Al 2 O 3   
                 2.13 
               
               
                   
                 CaO 
                 10.1 
               
               
                   
                 MgO 
                 2.3 
               
               
                   
                 TiO 2   
                 0.07 
               
               
                   
                 Fe 2 O 3   
                 0.34 
               
               
                   
                 BaO 
                 0.01 
               
               
                   
                 SO 3   
                 0.05 
               
               
                   
                 ZnO 
                 0.01 
               
               
                   
                   
               
             
          
         
       
     
         [0054]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the invention are desired to be protected.