Abstract:
A culm block and a method of manufacture are disclosed. The culm block comprises a plurality of straw stalks that are “vertically aligned”, i.e., perpendicular to the ground when the block is laid flat. The straw is treated with a moisture inhibitor and/or a binder. Throughholes, which may have tubes associated therewith, are formed into the top and bottom walls of the culm block. A lath or external strapping sleeve is wrapped about the front, rear, and side walls of the block for added structural support. The method of manufacture may include sorting the stalks according to length, checking the stalks for moisture content, and drying the stalks depending upon their moisture content prior to compression and formation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The field of the present invention relates to building materials and particularly to “green” building blocks made from culm such as residual rice straw, a by-product of the rice growing industry.  
           [0002]    Providing affordable housing while decreasing air pollution is an ideal worth fighting for. Housing is typically considered by most not to be affordable due, in part, to the high cost of the building materials. Conventional building materials, such as lumber, are costly because they are becoming more and more scarce as the demand for more and more housing increases to meet the needs of the world&#39;s burgeoning population. In addition, when the trees are cut down to make the lumber to build the house, the result is an adverse effect on our air quality as these natural resources are no longer able to turn carbon dioxide into oxygen.  
           [0003]    In an effort to find alternative building materials, people have been turning to recycled goods and/or the by-products of an industry. One such source has been culm, commonly referred to as straw, which is what is left over when grains, such as wheat, rice, barley, oats, and rye, are harvested. Straw is a viable building material because it is plentiful and inexpensive. Buildings built with straw bales have well-insulated walls, simple construction, and low costs. Moreover, in many areas, straw is still burned in fields, producing significant air pollution. For example, in California more than one million tons of rice straw were burned each fall in the early 1990&#39;s, generating an estimated 56,000 tons of carbon monoxide annually, which is approximately twice that produced from all of the state&#39;s power plants. By converting an agricultural by-product into a valued building material, another benefit to the community is therefore a reduction in air pollution.  
           [0004]    A number of drawbacks exist to the use of straw as a building material. Straw does not have the same structural integrity as wood, cement, or other conventional building materials. As a consequence, straw does not have the load bearing capacity that so many architects, engineers, and contractors require. Straw is also highly susceptible to moisture and can and will rot if there is too much exposure to moisture over time. Moreover, straw bales are of an inconsistent quality. They are also not sized to building industry standards.  
           [0005]    [0005]FIG. 5 is illustrative of some of these points. Shown there are two differently sized conventional straw bales, namely, a 3-tie straw bale on the left and a 2-tie straw bale on the right. The denomination of “3-tie” or “2-tie” is due to the number of ties T being wrapped about the straw stalks S, as seen in FIG. 5. The larger 3-tie bale is typically 32″ to 47″ long by 23″ to 24″ wide by 14″ to 17″ high. The dimensions of a 2-tie bale are similarly varied and are typically in the range of 35″ to 40″ long by 18″ wide by 14″ high. A conventional concrete or cinder building block, however, is typically 24″ long by 12″ wide by 12″ high. The weight of a 3-tie bale can be anywhere between 75 to 100 lbs., whereas a 2-tie bale is typically 50 lbs. OSHA product weight requirements, however, require less than 50 lbs. per block, with 40 lbs. typically being an acceptable weight that can be handled by one person.  
           [0006]    [0006]FIG. 5 illustrates that the straw stalks S of a conventional straw bale appear to be aligned parallel to a single axis of alignment, A w . The appearance of alignment occurs because of the cut, rake, and bale process of making the bale. There are no machines or modifications of machines that intentionally align the straw to make specific straw-aligned bales. The general alignment A w  of the straw S can be described as “horizontally aligned”, i.e., horizontal or parallel to the ground G when the bale is laid flat. The general alignment A w  can also be described as running parallel to the width W axis and perpendicular to the length L and height H axes or, alternatively, parallel to the plane defined by the top or bottom walls (the intersection of the L and W axes).  
           [0007]    It is the inventors&#39; understanding that those skilled in the art prefer “horizontal alignment” to increase the load bearing capacity of each bale. Gleaned from compression tests of individual bales, the prior art teaches that flat bales can carry far more load than bales stacked on edge. Flat bales failed at an average load of 10,000 lb/ft 2  (48,800 kg/m2); on edge, bales failed at an average of 2,770 lb/ft 2  (13,500 kg/m 2 ). To further increase the load bearing capacity of the bale other than laying it flat, the prior art also teaches the use of threaded rods that may be inserted through each bale or framed around each bale and then bolted through a wide top plate and tightened down after the roof is installed. Pre-compressing the walls in this manner minimizes further settling after the roof is installed.  
           [0008]    [0008]FIG. 5 also illustrates how conventional prior art straw bales do not have a smooth cut surface and the corners are rounded, i.e., the edges are not crisp and the corners are not square. What FIG. 5 does not illustrate is the high level of susceptibility to moisture damage that straw has or the inconsistent and often poor quality of the traditional straw bale itself.  
           [0009]    A “green” building material such as a culm or straw block that has an increased load bearing capacity over traditional straw bales, is of a consistent quality, is sized for building industry standards, and has an increased resistance to water damage is therefore desired.  
         SUMMARY OF THE INVENTION  
         [0010]    Having recognized these conditions, the present invention is directed to a culm block comprising a plurality of straw stalks that are “vertically aligned”, i.e., perpendicular to the ground when the block is laid flat. Vertically alignment, the inventors surprisingly discovered, advantageously provides for at least 25% greater load bearing capacity compared to conventional horizontally aligned bales. Vertical alignment also advantageously provides for increased insulating values, as well as a smooth cut surface. By vertically aligning the straw, the culm block of the present invention also advantageously has a consistent shape, with square corners and crisp edges.  
           [0011]    Another related aspect of the invention is to provide a culm block that is properly sized for building industry standards.  
           [0012]    The culm block may also be treated with a binder and a moisture inhibitor to further increase the block&#39;s quality, structural integrity, and resistance to moisture damage.  
           [0013]    The culm block may optionally include a pair of throughholes drilled through the top and bottom walls. The holes may be used to tie the blocks to the foundation and thereby ultimately increase the shear integrity of the wall system.  
           [0014]    In a similar manner, the culm block may include a lath or external strapping sleeve for added structural support. Prior to the addition of the lath, the culm block may be mill finished to further increase its quality and consistency.  
           [0015]    Another aspect of the present invention is a method for forming the novel culm block that may include sorting the stalks according to length, checking the stalks for moisture content, and drying the stalks depending upon their moisture content prior to compression and formation. Other and further objects and advantages will appear hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a perspective view of a culm block according to a preferred embodiment;  
         [0017]    [0017]FIG. 2 is another perspective view of the culm block shown in FIG. 1;  
         [0018]    [0018]FIG. 3 is a cross-sectional view taken along line  3 - 3  shown in FIG. 1;  
         [0019]    [0019]FIG. 4 is a flow chart illustrating a preferred method of manufacturing the culm block shown in FIG. 1; and  
         [0020]    [0020]FIG. 5 illustrates the prior art. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    Preferred embodiments will now be described with reference to the drawings. For clarity of description, any element numeral in one figure will represent the same element if used in any other figure.  
         [0022]    FIGS.  1 - 3  illustrate a culm block  10  comprised of a plurality of adjacent stalks  12  substantially aligned parallel to one another and formed to define the building block  10 . The stalks  12  may be wheat, rice, barley, oats, or rye straw. Rice straw is preferred due to its extremely high silica content and therefore inherent fire retardant properties. Moreover, rice straw is typically weed and pest free.  
         [0023]    The block  10  has a top wall  14  and an opposing bottom wall  16 , a front wall  18  and an opposing rear wall  20 , and first and second opposed sidewalls  22 . A lath  24  is seen disposed about the front and rear walls  18 ,  20  and sidewalls  22 . The lath  24  may be described as a sleeve that is wrapped about the block  10 .  
         [0024]    The lath  24  provides increased structural support to the block  10 . Such a feature is particularly advantageous when one considers that a traditional bale typically only has two or three ties usually made of twine for support, such as the ties T illustrated in FIG. 5. Because of such a lack of support, conventional bales can easily fall apart or bulge under their own weight. The lath or wire mesh banding  24  around block  10  girdles it and advantageously provides resistance to the straw stalks  12  from bulging. In addition, the lath  24  also provides an additional option for an anchoring system. In particular, the lath  24  acts as stucco wire and will make the construction process with the block  10  faster than conventional bales. Conventional bales require the stapling of stucco wire on the side of the straw bale wall in order to provide an adequate structural matrix for the stucco. This process is eliminated with the novel block  10 .  
         [0025]    The lath  24  may be comprised of completely recycled material such as recycled steel or plastic. If steel is used, it is preferably galvanized and more preferably galvanized and coated.  
         [0026]    Turning to FIGS. 1 and 2, the top wall  14  and bottom wall  16  define a pair of holes  25  therethrough. Tubing  26 , which may be made from recycled plastic, may be inserted into each hole  25 . The holes  25 , either with or without tubing  26 , may be included in block  10  to offer an optional alignment and anchoring system. If employed, the holes  25  are preferably 2½″ in diameter. Structural steel reinforcing may be inserted through each hole  25  and set with a concrete grout, for example. The pre-drilled holes  25 , when filled with concrete and steel, help to tie the blocks to the foundation, ultimately increasing the shear integrity of the wall system.  
         [0027]    [0027]FIGS. 1 and 2 illustrate a block  10  that is sized to a building industry standard, namely, 24″ long by 12″ wide by 12″ high. Accordingly, the block  10  illustrated in FIGS. 1 and 2 is rectangular in shape. Other dimensions may also be employed as long as they are standardized building sizes. Unlike traditional bales that are odd-sized, such as a 3-tie bale that may be 40″ long by 22″ wide by 16″ high, the block  10  is a size that a builder can utilize consistent with existing building techniques developed for concrete blocks. Consequently, block  10  is easily adapted to current construction techniques; it easily integrates with traditional 4′ by 8′ construction modules; and it requires less space in the floor plan when compared to the larger footprint of a traditional straw bale wall.  
         [0028]    As shown in FIGS. 1 and 2, the block  10  preferably weighs under 40 lbs. With this light weight, one person can handle the block  10 . This weight is also within the OSHA product weight requirements, unlike traditional bales that may weigh up to 75 to 100 lbs., which weight requires two or more persons for moving and constructing.  
         [0029]    As best seen in FIG. 3, the stalks  12  of the culm block  10  are “vertically aligned”, i.e., they are perpendicular to the ground G when the block  10  is laid flat. The axis of alignment A H  of the straws  12  is therefore preferably orthogonal to the plane defined by the top and bottom walls  14 ,  16  (the intersection of the L and W axes). As seen in FIG. 3, the axis of alignment AH runs orthogonal to the width W and length L axes and parallel to the height H axis or, alternatively, orthogonal to the plane defined by the ground G.  
         [0030]    Contrary to the teachings of the prior art, vertically alignment provides for at least 25% greater load bearing capacity compared to conventional non-aligned or potentially “horizontally aligned” bales. Vertical alignment also advantageously provides for increased insulating values, possibly R-28 or higher, because horizontally placed straw of traditional bales acts like a wick, thus increasing the conductance (U-value) of the material and undesirably allowing for greater thermal transmission. Vertical alignment also provides for a smooth cut surface. By vertically aligning the stalks  12 , the culm block  10  of the present invention has a consistent shape, with square corners and crisp edges. This makes the construction of buildings much more efficient when compared to traditional rounded corner straw bales.  
         [0031]    Turning to FIG. 4, a method of forming the novel block illustrated in FIGS.  1 - 3  is disclosed. As shown there, the first step is “Harvest straw from field” at step  28 . After harvesting, the straw then needs to be transported to the processing facility as shown at step  30 . Once at the processing facility, the straw is unloaded at step  32 , preferably via a hydraulic squeeze lift, and then loaded into an apparatus to remove the ties T (as shown in FIG. 5). The apparatus is preferably a Hunterwood 3-tie de-stacker. Once loaded into the de-stacker, the straw is moved down a conveying system to a twine saw. When the twine hits the twine saw, the bale ties are removed at step  34 . The next step, step  36 , is entitled “Treat straw with a non-toxic moisture inhibitor and/or binder.” 
         [0032]    At step  36 , a moisture inhibitor and/or a binder is disposed on or integrated into the straw  12 . Step  36  ensures that the block  10 , when delivered, has a consistent quality. Current bales, such as those illustrated in FIG. 5, have high fluctuations in sizes, typically up to five inches, and a wide range in moisture content, typically between 10 to 25%. High moisture is the weakness and largest concern for builders interested in integrating straw building materials into their work. Straw will not rot at a moisture content of 14% or less. For this reason, the block  10  preferably has a predetermined moisture content not to exceed 14%. To ensure this, a drier system is part of the manufacturing process, as illustrated in FIG. 4 at step  42 .  
         [0033]    The binder and moisture inhibitor are both preferably environmentally friendly and non-toxic. When treated with the binder, the structural integrity of the block  10  should be increased without decreasing the insulating properties of the block  10 . In a similar manner, when the stalks  12  are treated with the moisture inhibitor, the block&#39;s resistance to moisture is increased without decreasing the insulating properties of the block  10 . Accordingly, the binder may be selected from the group consisting of aluminum hydroxide, magnesium hydroxide, clay, kaolin, bitumen, and most preferably borax (a natural product composed of hydrated sodium borate, sometimes referred to as or including sodium borate decahydrate, sodium diborate, tincal, tincalconite, tincar, hydrated sodium boration, sodium tetraborate, rasorite, or Sporax®). The moisture inhibitor may be selected from the group consisting of paraffin wax, silica gel (a non-toxic, non-corrosive form of silicon dioxide synthesized from sodium silicate and sulfuric acid and processed into granular or beaded form), molecular sieve (a uniform network of crystalline pores and empty adsorption cavities derived from sodium, potassium or calcium crystalline hydrated aluminosilicates), activated clay (a layered structure of activated (bentonite) clay that is a naturally occurring, non-hazardous and salt-free substance), bitumen, and most preferably borax.  
         [0034]    Referring again to FIG. 4, the next step in the process is step  38  entitled “Align and sort straw.” Here, the stalks  12  are intentionally aligned substantially parallel and most preferably parallel to one another. The stalks  12  are also preferably sorted according to length, wherein stalks  12  of substantially identical length are grouped together. After the stalks  12  are aligned and sorted together and step  38 , the moisture content of the stalks  12  is then checked at step  40 . The stalks  12  are dried via a drier system dependent upon the moisture content at step  42 . The stalks  12  are preferably dried to a moisture content not to exceed 14%, as straw will not rot at a moisture content of 14% or less.  
         [0035]    After the stalks  12  are dried to the preferred moisture content of 14% or less, the stalks  12  are compressed and formed into standardized building blocks wherein the stalks  12  are vertically aligned or, stated otherwise, perpendicular to the ground when the block is laid flat, as shown in FIG. 4 at step  44  and, regarding the vertical alignment, as best seen in FIG. 3. For compressing and forming the stalks  12  into the block shape, the stalks  12  are preferably fed into a Hunter Wood fc8310 series forage compactor. Once compacted, the block  10  exits the compression chamber and is sleeved with a lath, preferably comprised of recyclable galvanized steel and coated at step  46 . The block  10  then exits the conveyor, is palletized, stretch-wrapped, pallet bar coded, and ready for shipping or storage.  
         [0036]    Prior to the addition of the lath, such as lath  24  illustrated in FIGS. 1 and 2, the culm block  10  may be mill finished to further increase its quality and consistency. Where the optional throughholes, such as holes  25  illustrated in FIGS. 1 and 2, are desired, the holes may be drilled before or after step  46 , but are preferably drilled before step  46 . Tubing  26  may also be inserted into each hole  25  at this time. The pre-drilled holes  25 , when filled with concrete and steel, help to tie the blocks  10  to the foundation, ultimately increasing the shear integrity of the wall system.  
         [0037]    Thus, while embodiments and applications of the novel culm block and method for making the culm block have been shown and described, it would be apparent to one skilled in the art that other modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the claims that follow.