Abstract:
Modular plastic structural composites having a web section disposed along a horizontal axis and at least one flange section disposed along a horizontal axis parallel thereto and integrally molded to engage the top or bottom surface of the web section, wherein said composite is formed from a mixture of (A) high density polyolefin and (B) a thermoplastic-coated fiber material, poly-styrene, or a combination thereof. Composites molded in the form of I-Beams and bridges constructed therefrom are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/870,277, filed Aug. 27, 2010, now U.S. Pat. No. 7,996,945, which is a divisional of U.S. patent application Ser. No. 10/563,883, filed on June 8, 2006, and issuing as U.S. Pat. No. 7,795,329, which is the National Stage Entry under 35 U.S.C. §371 of International Patent Application Serial No. PCT/US03/22893, filed on Jul. 21, 2003, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/486,205, filed on Jul. 8, 2003. The disclosures of all of these applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains to new building forms made of degradation-resistant composites; structures produced from such novel forms; and related methods of producing and using such forms and structures. 
     BACKGROUND OF THE INVENTION 
     There presently are over 500,000 wooden vehicular bridges in the United States assembled from chemically treated lumber. An estimated forty percent of them are in need of repair or replacement. 
     There are several types of chemically treated lumber such as creosoted lumber and pressure treated lumber. These materials are relatively inexpensive to make and use, and they are just as versatile as any other form of wood. They also have enhanced resistance to microbial and to fungal degradation and to water. 
     However, the increasing popularity of chemically treated lumber has some negative repercussions that are just now being realized. Chemically treating lumber takes a perfectly useable, recyclable, renewable resource and renders it toxic. For example “pressure treated” or “CCA” lumber is treated with very poisonous chromated copper arsenic and cannot be burned. While CCA lumber can be buried, the leaching of toxic chemicals makes such disposal strategies undesirable. The disposal of creosoted lumber requires the use of special incinerators. These materials are becoming far more difficult and expensive to dispose of than to use. However, because of the long useful life of these materials, the economic and environmental impact of chemically treated lumber is just beginning to be felt. 
     Structural recycled plastic lumber represents a possible alternative to chemically treated lumber. U.S. Pat. Nos. 6,191,228, 5,951,940, 5,916,932, 5,789,477, and 5,298,214 disclose structural recycled plastic lumber composites made from post-consumer and post-industrial plastics, in which polyolefins are blended with polystyrene or a thermoplastic coated fiber material such as fiberglass. These structural composites presently enjoy commercial success as replacements for creosoted railroad ties and other rectangular cross-sectioned materials. The market has otherwise been limited for structural recycled plastic lumber, because it is significantly more expensive than treated wooden beams on an installed cost basis, despite the use of recycled waste plastics. 
     This significant cost difference became more evident in the construction of bridge structures in which pressure-treated wooden beams were replaced with structural recycled plastic lumber composite beams. While as strong as CCA treated wood, the recycled plastic composite beams were not as stiff, and tended to sag, or “creep.” It was possible to compensate for this by increasing beam dimensions and using more beams of rectangular cross-section. However, this just added to the already increased cost for materials and construction in comparison to treated lumber. 
     Structural beams that do not “creep” can also be prepared from engineering resins such as polycarbonates or ABS. However, these are even more costly than the structural composites made from recycled plastics. There remains a need for structural materials based on recycled plastics that are more cost-competitive with treated lumber on an installed cost basis. 
     BRIEF SUMMARY OF THE INVENTION 
     It has now been discovered that the immiscible polymer blends of U.S. Pat. Nos. 6,191,228, 5,951,940, 5,916,932, 5,789,477, and 5,298,214 can be formed into structural shapes that are more cost-efficient than traditional recycled plastic structural beams with rectangular cross-sections. The structural shapes according to the present invention are molded as a single integrally-formed article and include modular forms such as I-Beams, T-Beams, C-Beams, and the like, in which one or more horizontal flanges engage an axially disposed body known in the art of I-Beams as a web. The reduced cross-sectional area of such forms represents a significant cost savings in terms of material usage without sacrificing mechanical properties. Additional cost saving are obtained through modular construction techniques permitted by the use of such forms. 
     Therefore, according to one aspect of the present invention, a modular plastic structural composite is provided having web section disposed along a horizontal axis and at least one flange section disposed along a horizontal axis parallel thereto and integrally molded to engage the top or bottom surface of the web section, wherein the composite is 5 formed from a mixture of (A) high density polyolefin and (B) a thermoplastic-coated fiber material, polystyrene, or a combination thereof. The high-density polyolefin is preferably high-density polyethylene (HDPE). The thermoplastic-coated fiber material is preferably a thermoplastic-coated carbon, or glass fibers such as fiberglass. 
     The flange dimensions relative to the dimensions of the web section cannot be so great to result in buckling of the flange sections upon the application of a load. Preferably, the vertical dimension (thickness) of the flange section is about one-tenth to about one-half the size of the vertical dimension of the web section without any flange section(s) and the width dimension of the entire flange section measured perpendicular to the horizontal axis of the flange section is about two to about ten times the size of the width dimension measured perpendicular to the horizontal axis of the web section. 
     Other efficient structural shapes according to the present invention include tongue-in-groove shaped boards that form interlocking assemblies. It has been discovered that interlocking assemblies reduce the required board thickness because of the manner in which the assembly distributes loads between the interlocked boards. This also represents a significant cost savings in terms of material usage without sacrificing mechanical properties, with additional cost savings also obtained through the modular construction techniques these forms permit. 
     Therefore, according to another aspect of the present invention, an essentially planar modular plastic structural composite is provided having a grooved side and an integrally molded tongue-forming side, each perpendicular to the plane of the composite, in which the composite is formed from a mixture of (A) high-density polyolefin and (B) a thermoplastic-coated fiber material, polystyrene, or a combination thereof, wherein the grooved side defines a groove and the tongue-forming side is dimensioned to interlockingly engage a groove having the dimensions of the groove defined by the grooved side, and the grooved side and tongue-forming side are dimensioned so that a plurality of the essentially planar modular plastic structural composites may be interlockingly assembled to distribute a load received by one assembly member among other assembly members. 
     Preferred planar modular plastic structural composites have at least one pair of parallel opposing grooved and tongue-forming sides, defining therebetween a width or length dimension of the composite. Preferred composites also have board-like dimensions in which the length dimension is a matter of design choice and the width dimension is between about two and about ten times the size of the height, or thickness, dimension of the composite. 
     The modular plastic structural composites have utility in the construction of load-bearing assemblies such as bridges. Therefore, according to yet another aspect of the present invention, a bridge is provided, constructed from the I-Beams of the present invention, having at least two pier-supported parallel rows of larger first I-beams, and a plurality of smaller second I-beams disposed parallel to one another and fastened perpendicular to and between two rows of the larger first I-Beams, wherein the top and bottom surfaces of the second I-Beam flanges are dimensioned to nest within the opening defined by the top and bottom flanges of the first I-Beams. 
     The distance between the rows of first I-Beams and the rows of second I-Beams will depend upon factors such as the flange and web dimensions, the plastic components of the composite and the load to be supported by the bridge. Furthermore, whether the horizontally disposed axes of the first or second I-Beams extend in the direction of travel on the bridge is a matter of design choice, which may in whole or in part depend upon the aforementioned factors. 
     Because the second I-Beams are nested within the opening defined by the top and bottom flanges of the first I-Beams, the top surfaces of the second I-Beams are recessed below the top surfaces of the first I-Beams by a distance that is at least the thickness dimension of the top flange of the first I-Beam. Bridges constructed according to this aspect of the present invention will therefore further include a deck surface fastened to the first or second I-Beams. Preferred deck surfaces are dimensioned to fit between the top flanges of the parallel rows of the first I-beams. Even more preferred deck surfaces have a thickness dimension selected to provide the deck surface with a top surface that is essentially flush with the top surfaces of the parallel rows of first I-Beams. Other preferred deck surfaces are formed from the essentially planar modular plastic structural composites of the present invention having interlocking grooved and tongue-forming sides. 
     The modular components of the present invention permit the construction of load-bearing assemblies with fewer required fasteners, reducing the initial bridge cost, as well as the long-term cost of maintaining and replacing these corrosion-prone components. The plastic composite material also outlasts treated wood and requires significantly less maintenance than wood over its lifetime, further contributing to cost savings. 
     The foregoing and other objects, features and advantages of the present invention are more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a cross-sectional view of an I-Beam according to the present invention; 
         FIG. 2  is a side-view of the I-Beam of  FIG. 1 , perpendicular to the cross-sectional view; 
         FIG. 3  depicts a cross-sectional view of a C-Beam according to the present invention; 
         FIG. 4  is a side view of the C-Beam of  FIG. 3 , perpendicular to the cross-sectional view; 
         FIG. 5  depicts a cross-sectional view of a T-Beam according to the present invention; 
         FIG. 6  is a bottom view of the T-Bean of  FIG. 5 ; 
         FIG. 7  depicts a cross-sectional view of tongue and groove decking panels according to the present invention; 
         FIG. 8  depicts a side view of a bridge according to the present invention assembled from the I-Beams of the present invention; 
         FIG. 9A  is a top cutaway view of the bridge of  FIG. 8 , and  FIG. 9B  is a top cutaway view of the bridge of  FIG. 8 ; and 
         FIG. 10  is a top cutaway view depicting the perpendicular fastening of a smaller I-Beam according to present invention to a larger I-Beam according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The modular plastic structural composites of the present invention are prepared using the co-continuous polymer blend technology disclosed by U.S. Pat. Nos. 5,298,214 and 6,191,228 for blends of a high-density polyolefin and polystyrene and by U.S. Pat. No. 5,916,932 for blends of a high-density polyolefin and thermoplastic-coated fiber materials. The disclosures of all three patents are incorporated herein by reference. 
     As disclosed in U.S. Pat. No. 6,191,228 composite materials may be employed containing from about 20 to about 50 wt % of a polystyrene component containing at least about 90 wt % polystyrene and from about 50 to about 80 wt % of a high-density polyolefin component containing at least about 75 wt % high-density polyethylene (HDPE). Composite materials containing about 25 to about 40 wt % of a polystyrene component are preferred, and composite materials containing about 30 to about wt % of a polystyrene component are even more preferred. Polyolefin components containing at least about 80 wt % HDPE are preferred, and an HDPE content of at least about 90 wt % is even more preferred. 
     According to the process disclosed by U.S. Pat. No. 5,916,932 this composite may be further blended with thermoplastic-coated fibers having a minimum length of 0.1 mm so that the finished product contains from about 10 to about 80 wt % of the thermoplastic-coated fibers. U.S. Pat. No. 5,916,932 discloses composite materials containing from about 20 to about 90 wt % of a polymer component that is at least 80 wt % HDPE and from about 10 to about 80 wt % of thermoplastic-coated fibers. 
     The polyolefin-polystyrene composite materials suitable for use with the present invention exhibit a compression modulus of at least 170,000 psi. and a compression strength of at least 2500 psi. Preferred polyolefin-polystyrene composite materials exhibit a compression modulus of at least 185,000 psi and a compression strength of at least 3000 psi. More preferred polyolefin-polystyrene composite materials exhibit a compression modulus of at least 200,000 psi and a compression strength of at least 3500 psi. 
     Composite materials containing thermoplastic-coated fibers according to the present invention exhibit a compression modulus of at least 350,000 psi. The compression modulus exhibited by preferred fiber-containing materials is at least 400,000 psi. The composite materials containing thermoplastic-coated fibers exhibit a compression strength of at least 4000 psi. The compression strength exhibited by preferred fiber-containing materials is at least 5000 psi. 
     A cross-sectional view of an I-Beam  10  according to the present invention is depicted in  FIG. 1 , with a side view of the same I-Beam shown in  FIG. 2 . The I-beam has a traditional structure consisting of middle “web” or “body” section  20 , an upper flange  30 , and a lower flange  40 . The flange sections include a protruding section  50  that extends beyond the width of the web  20 . The face of the web  60  forms a structure that can engage other structures (e.g., smaller beams), as described further below. The width A of the flange sections is significantly wider than the width B of the web section. The height C of the flange sections is smaller than the height of the web sections. Despite the thin height of the flange section and the narrow width of the web section, the I-Beam is capable of supporting heavy structures and can be used in load-bearing structures, such as bridges and the like. 
     A cross-sectional view of a C-Beam  12  according to the present invention is depicted in  FIG. 3 , with a side view of the same C-Beam shown in  FIG. 4 . The C-beam also has a middle web section  20 , an upper flange  30 , and a lower flange  40 . The flange sections also include a protruding section  50  that extends beyond the width of the web  20 . The face of the web  60  also forms a structure that can engage other structures (e.g., smaller beams), as described further below. 
     A cross-sectional view of a T-Beam  15  according to the present invention is depicted in  FIG. 5 , with a bottom view of the same T-Beam shown in  FIG. 6 . The T-beam has a structure consisting of middle web section  20  and an upper flange  30 , but no lower flange. The flange section also includes a protruding section  50  that extends beyond the width of the web  20 . The face of the web  60  also forms a structure that can engage other structures (e.g., smaller beams), as described further below. 
       FIG. 7  shows assembled tongue-and-groove decking panels  100  and  150 . Panel  100  includes an end  110  having a tongue-shaped member  120  and an opposite end  130  defining a groove  140 . Panel  150  includes an end  160  having a tongue-shaped member  170  and an opposite end  180  defining a groove  190 . Tongue-shaped member  120  of panel  100  is depicted interlockingly engaging the groove  190  of panel  150 . The groove  140  of panel  100  is also capable of interlockingly engaging a tongue-shaped member of another panel. Likewise, the tongue-shaped member  170  of panel  150  is capable of engaging a groove of another panel. Flat top  125  of panel  100  and flat top  175  of panel  150  can serve as a load-bearing surface or barrier when such panels are assembled into a structure. 
       FIG. 8  illustrates a side view and  FIG. 9  a top partial cutaway view of a portion of a vehicular bridge  200  assembled from the above-described building forms. In the bridge structure, ends  211  and  212  of respective larger I-beam rails  213  and  214  are secured to respective pilings  216  and  217  by fasteners (not shown). The opposite respective I-Beam ends  220  and  221  are similarly secured to respective pilings  223  and  224 . Ends  225 ,  226  and  227  of smaller joist I-beams  228 ,  229  and  230  are fastened to the face  260  of I-Beam  213 , with respective opposing ends  231 ,  232  and  233  of the three smaller I-Beams fastened to the face  261  of I-Beam  214 . Similarly, ends  234 ,  235  and  236  of smaller joist I-beams  237 ,  238  and  239  are fastened to the face  262  of I-Beam  214 . 
       FIG. 10  is a top cutaway view depicting the fastening of end  225  of smaller joist I-Beam  228  to the face  260  of larger I-Beam  213  using L-shaped brackets  243  and  244  and fasteners  245 ,  246 ,  247  and  248 . Bracket  243  and fasteners  245  and  246  fastening the end  225  of I-Beam  228  to face  260  of I-Beam  213  is also shown in  FIG. 8 .  FIG. 8  also shows bracket  247  and fasteners  248  and  249  fastening end  231  of I-Beam  228  to face  261  of I-Beam  214 . 
       FIGS. 8 and 9  also show bridge deck  270  formed from interlocking panels  271  and  272  in which tongue  274  of panel  271  interlockingly engages groove  275  of panel  272 . Tongue  276  of panel  272  interlockingly engages groove  277 , and so forth. The respective top surfaces  279  and  280  of panels  271  and  272  comprise the surface  290  of bridge deck  270 . 
     Suitable fasteners are essentially conventional and include, without limitation, nails, screws, spikes, bolts, and the like. 
     The molding processes disclosed in U.S. Pat. Nos. 5,298,214, 5,916,932 and 6,191,228 may be employed to form the modular plastic structural composite shapes of the present invention. However, because articles are being formed having an irregular cross section in comparison to the beams having rectangular cross-sections that were previously molded, the composite blends are preferably extruded into molds from the extruder under force, for example from about 900 to about 1200 psi, to solidly pack the molds and prevent void formation. Likewise, it may be necessary to apply force along the horizontal beam axis, for example using a hydraulic cylinder extending the length of the horizontal axis, to remove cooled modular shapes from their molds. 
     Composite I-Beams of polyolefin and polystyrene according to the present invention having a 61 square-inch cross-sectional area exhibit a Moment of Inertia of 900 in 4 . Poly-olefin-polystyrene composite I-Beams according to the present invention having a 119 square-inch cross-sectional area exhibit a Moment of Inertia of 4628 in 4 . This represents the largest Moment of Inertia ever produced by any thermoplastic material for any structure, and compares to Moments of Inertial measured between 257 and 425 in 4  for rectangular cross-section wooden beams having a 63 square-inch cross-sectional area and Moments of Inertial measured between 144 and 256 in 4  for rectangular cross-section wooden beams having a 48 square-inch cross-sectional area. The end result is that a polyolefin-polystyrene composite bridge that would have weighed 120,000 pounds for the required load rating if prepared from rectangular cross-section composite materials, weighs just 30,000 pounds instead when prepared from the I-Beams of the present invention. 
     The modular plastic structural composites of the present invention thus represent the most cost-effective non-degradable structural materials prepared to date having good mechanical properties. The present invention makes possible the preparation of sub-structures with given load ratings from quantities of materials reduced to levels heretofore unknown. 
     The foregoing description of the preferred embodiment should be taken as illustrating, rather than as limiting, the present invention as defined by the claims. As would be readily appreciated, numerous variations and combinations of the features set forth above can be utilized without departing from the present invention as set forth in the claims. Such variations are not regarded as a departure from the spirit and scope of the invention, and all such variations are intended to be included within the scope of the following claims.