CA2229589A1 - A dry-pack method of recycling organic fibre and other polymeric materials into building blocks - Google Patents

Abstract

Methods and apparatuses are disclosed by which "waste" organic fibre and other polymeric materials, chopped or shredded into strands, are oriented, packed together and tightly enclosed in strong mesh to form building blocks. The orientation of the strands and the friction between them creates a firm block structure which is particularly suited to serve as the stabilizing, shear-resisting, insulating core of stressed skin sandwich walls and other building components; methods of forming such components are disclosed. The process entails no chemical treatments or binders, and little energy, so offering a means of benign waste management and sustainable production of housing. The preferred or primary polymeric wastes are wood, cereal straw, bagasse, and other plentiful cellulose fibre materials mechanically prepared from construction wastes, tree canopy, mill wastes and agricultural wastes. A significant proportion of the block can, however, be comprised of shredded waste plastics without unduly degrading the block properties dependent upon friction between the strands.

Description

BACKGROUND OF THE INVENTION
The provision of affordable housing is increasingly limited by the supply of basic resources.
Material resources are becoming less plentiful and less accessible, and material extraction and final production is becoming more costly, energy consuming and polluting in the very efforts to produce more from less. Even wood frame construction, clearly the most successful system based on renewable fibre, is consuming its forest resources at a questionably sustainable rate. The forest product innovators have been responding for decades, striving for sustainability and "value-added" profitability, by getting much more house from each tree and indeed from what were deemed "weed trees" and worthless wastes not lomg ago. The innovations all have in common the production of "reconstituted" wood fibre composite components, always entailing refining, heat and resins, and all at a price in terms of capital, energy and pollution.
At the same time, disposing of material wastes is becoming an immense problem, while efforts to recycle the wastes entail further energy and pollution: even the recycling of paper is arguably more of an environmental burden than incinerating it and producing heat and electricity.
One hundred years ago, needing good houses quickly and lacking access to lumber, Nebraska pioneers conceived an alternative form of housing from an alternative cellulose fibre, cereal straw, a "waste" fibre in abundant supply and needing no refinement.
Handsome examples of "Nebraska Straw bale" houses are still in use from those first days.
The pioneers stacked bales of straw - no refining, no binding resins or other treatments -then let them settle, rendered them on the outside with sand-lime stucco and on the inside with that or gypsum plaster, to form exterior walls and sometimes spine walls too. Their followers still do, with few changes.
The thermal performance of such strawbale houses would have been welcomed the first and every winter; given good design and care, their permanence has been proven through the twentieth century. Ample fire resistance has been demonstrated in lab and field. The Nebraskans demonstrated an alternative to wood frame construction, based on what might be called "dry-pack" blocks of straw.

But there were and are considerable shortcomings: the Nebraska Strawbale system for all its simplicity is not clearly ready to produce housing affordably in great numbers. It depends upon long stem straw, good baling, and a rather slow construction and settling process especially demanding of careful bracing and sheltering from wind and rain. The spongy, side-shearing bales entail difficulties in providing construction stability and safety.
The bales produce needlessly thick walls, increasing costs for a given usable area. Certainly the baled straw is well oriented to stabilize the stucco "skins"against buckling, so the skins can serve as the main loadbearing elements; engineers today are finally beginning to explore that quintessential characteristic of strawbale wall performance. But the straw is poorly oriented to develop shear strength as needed to withstand seismic loads or to build roofs, and its orientation also offers mediocre thermal resistance per unit of thickness. (The otherwise wasteful thickness of the walls does help compensate for the latter weakness.) Finally, the uneven wall can take great amounts of stucco/plaster to form plane surfaces; it may not readily accept the impact of modern "shotcreting"; and the usual hand-stuccoing is very laborious.
Notwithsanding the shortcomings of the Nebraskan-pioneered stuccoed strawbale wall composition as described above, it comprises almost all of the useful prior art regarding efficient dry-pack fibre building structures. U.S. Pat. 312,375 to Orr, 1885, "Wall of Buildings and Other Structures", discloses the approach of stacking bales of material and immediately screw-compressing the stack, apparently anticipating but not informing the beginnings of strawbale wall construction (which, until recent decades, simply relied upon settling of the stacked bales under the weight of the roof for some weeks, before stuccoing).
Canadian patent 283718 to Tchayeff, 19216, discloses a method of binding straw into building panels by means of wires stitching transversely through the straw, which wires connect to longitudinal "trellises" of wires disposed at each face. The straw lies axially along the panel length and would contribute very little to shear resistance in bending. Other inventors (Clayton 1905, Hewlett & Buckminster Fuller, 1926, and Eichelkraut, 1993) respectively incorporated concrete box structure, added binders to create hollow cored straw blocks which were then concrete filled, or incorporated concrete post structures. Similarly, Vohra in the U.S.A is applying for patent on a method of filling sandbags with waste materials and stacking them as infill in post and beam structures and the like ("Sandbag wall system shows promise", Energy Design Update, November 1997).

Strangely, no inventors seem to have recognized, deemed adequate or suggested improving upon the transverse stabilizing nature of the strawbale itself, as perforce used by the Nebraskan pioneers to marry with strong stucco to form a load bearing stressed skin wall.
They all use the bales primarily as an insulating filler or form, and then call upon other costly components to act as the primary wall structure. None have attempted to emulate, let alone improve upon, the remarkable material efficiencies that the Nebraskans had already demonstrated.
It is the simple, environmentally friendly "dry pack" nature of the straw bale, and its demonstrated adequacy as the core of composite wall structures, that inspires the inventions here disclosed. The inventions, beginning with a "blockmaker" departure from traditional baling, can utilize most cellulosic fibre resources in short strand form (including short stem straw, a by-product of the "Green Revolution") and other polymeric materials, while ameliorating or correcting the noted shortcomings in the prior art. The inspiration for the dry-pack "blockmaker" invention itself springs in part from commercial "baggers" developed for rectilinear bagging of peat moss, cellulose fibre and the like.
SUMMARY OF THE INVENTION
Methods and apparatuses are disclosed by which "waste" organic fibre and other polymeric materials, chopped or shredded into strands, are placed in a form substantially transversely to its long axis and packed forcefully together and tightly enclosed in strong mesh to form building blocks.
The orientation of the strands and the friction between them creates a firm block structure which is particularly suited to serve as the stabilizing, shear-resisting, insulating core of stressed skin sandwich walls and other building components; methods of forming such components are disclosed.
The preferred polymeric wastes are wood, cereal straw, bagasse, and other plentiful cellulose fibre materials mechanically prepared from construction wastes, tree canopy, mill wastes and agricultural wastes. A significant proportion of the block can, however, be comprised of shredded waste plastics without unduly degrading the block properties dependent upon friction between the strands.

The advantages of the invention are clear: The material preparation and block making processes entail no chemical treatments or binders, and little energy, so offering a means of non-polluting waste management and sustainable production of housing all in one. The insulating, energy-conserving final qualities and the absence of off gassing and other threats to indoor air quality are also of great benefit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The dry-pack invention refers to the concept of compressing strands of material together into useful block form forcefully enough that the friction between strands and their orientation produces desired strength qualities without the need for binders or adhesives, and locking-in and maintaining that compression by means of a strong mesh wrapping tightly enclosing the block. While the term "dry-pack" is therefore almost synonomous with "baling", we use "dry-pack" here to denote unique block-making with short strands of material to produce certain building block qualities that transcend the shortcomings of bales such as straw bales, as will become clear. "Bioblock" is the name we have registered for the block itself.
Pilot work and testing referred to herein is an engineering project conceived and directed by R.E. Platts, P. Eng., and recorded by him, followed by construction of a 22 ft.x40ft.
"honey house" bottling plant in Lascalles, Quebec, in 1997.
The dry-pack method of forming or recycling organic fibre and other polymeric material into building blocks is designed to use sound, dry material comprised of stems, straws, or shredded pieces cut into short strands. The strand length may range from 30 to 100 mm., as in the pilot blocks produced and tested to date, while the width or diameter may typically range from 2 to 30 mm. Greater or lesser strand dimensions may prove to be practicable and perhaps desirable, depending on the type and source of fibre, the block geometry and size, the transfer method of charging the forms and achieving desired orientation of strands, and the thermal and strucural qualities desired.
The organic fibre material resources, the "feedstock" for the strands, may be wood, cereal straw, bagasse, and other plentiful cellulose fibre materials mechanically prepared from construction wastes, tree canopy, mill wastes and agricultural wastes. A
significant proportion of the block can, however, be comprised of shredded waste plastics without unduly degrading the critical block properties, which are dependent upon friction between the strands. In the pilot fabrication and testing, we have made good quality blocks from shredded wood from roadside clearing and lumber mill wastes (slabs and edgings), including the bark; others from chopped wheat and barley straw; and others of shredded wood with up to 5% by volume of shredded waste polyethylene film, as an exploration of the effect of adding such a slippery material into the friction-dependent dry-pack block.
The qualities of all the tested blocks - sufficient to act as the stabilizing, shear resisting, insulating core of stressed skin (structural sandwich) walls for houses and other low-rise buildings - suggest that a very wide variety of organic fibre, including synthetic polymer types, and a considerable content of shedded polymeric wastes, can be dedicated or recycled into producing permanent shelter by means of the present invention of dry-pack blockmaking.
Waste polymer fabrics and sheet - automobile wastes comprising a vast example -can be utilized.
The term "strong mesh" as used herein refers to any mesh or open-weave fabric which is sufficiently open to allow the applied "skin" material to penetrate through it and thence into the strands. The preferably polymeric mesh thus becomes embedded in the skins and reinforces them; its strength qualities are chosen for that purpose as well as to hold the block of strands sufficiently compressed for handling and construction purposes. The skins referred to herein are preferably of stucco or like cementitious composition or of polymeric resin composition, and of thickness and strength qualities chosen to suit the expected loads on the structure.
While the above and following description of the preferred embodiment of the invention stays rather narrowly within the confines of the pilot R&D and test projects, it does not limit the conceptual or practical scope of the invention.
Throughout the drawings, like numbers denote like elements. Reference is made first to FIG. l, which is partly cut away or rendered transparent for clarity: Short strands of fibre or shredded material 1 falling into a mould cavity 2 assume an orientation substantially biased into horizontal attitudes transverse to the mould cavity; the fibres further orient themselves randomly in all directions. (The action is sometimes termed the "falling leaf effect".) This substantially transverse, mufti-directional orientation, in conjunction with forceful compression of strand against strand and the resulting friction between them, tends to impart integrity of form to the block as is firstly required for transport and handling to construct building components. (FIG. 1 is also used to help illustrate the placement of strong mesh 7, a primary element in the block, around a temporary separator sleeve 8, both being discussed later.) The orientation and compaction does much more. In FIG. 2, wherein the contained mass of strands (hereinafter called the "charge") is shown turned on its side, in normal stance for wall building, it can be seen that shear/diagonal tension forces 3 in play within a wall under load must pass through the strands 1 rather than between layers of them; shear strength is therefore substantial. Further, heat flow across the wall is resisted efficiently in that the strands do not conduct heat directly across (heat conductivity is much greater along a cellulose fibre than across it), and the multitude of small air spaces do not form aligned pathways. So the strand orientation in the invention immediately presents two important advantages over the straw orientation in the common bale: in the latter, the lie of the straws tends to be directly across the wall, from interior to exterior, offering less resistance to heat flow for given fibre and density, while forming transverse "slip planes" which substantially limit the shear strength.
Transfer of the strands 1 to charge the mould 2 may be effected by a conveyor belt, screw, fingered rollers or other mechanism, aided by fluidized bed or vibrating devices, as are well established in the art of conveying fibres or strands; these can be designed and adjusted to the particylar type, size and shape of the strands to convey and dump them without undue clumping.
The falling action will accomplish orientation as noted above but will not generally assure that the charge fills in the corners of the mould. That deficiency may perhaps be overcome by mechanically vibrating or shaking the mould. In the pilot production, however, the packing of corners was accomplished by hand, with prods, teaching the inventors that a "hand" shown in FIG 3, 4, can be designed and adjusted to do the job of distributing and initially compacting the charge of strands into the mould cavity. The hand consists of a four or more "fingers" 5 having their upper ends hinge jointed to the lower end of an up-and-down reciprocating push rod 6, so that they splay outward at their free lower ends as the rod forces them downward into the accumulating charge of strands. The action pushes the strands downward and radially outward to fill into the corners and outer reaches of the cavity generally. As the rod moves upward to prepare for another stroke, the fingers spring back or fall back closer to axial alignement with it, providing free path for more strands to fall or be vibrated or otherwise conveyed into the mould cavity. This fresh charge is in turn distributed into the corners and compacted by the next stroke of the rod and its splaying fingers. The geometry of the fingers and their degree of retraction and splaying is designed and adjusted so that the given types of charge is packed into the corners while maintaining a sufficient degree of radial orientation (i.e., with many of the strands pointing endwards at the corner or other peripheral bounds of the mould cavity). The pilot work, albeit dependent on hand charging and corner, showed that this is achievable in such a manner.
In FIG 4, a blockmaker mould section 12 is shown to help describe essential points of the invention. A complete wrapping of strong mesh 7, preferably of a polymer of the group containing polyester, polyamide or polycarbonate, is placed in the mould cavity 2, with its upper end left open to receive the charge of strands as previously described.
Since the charging of the mould and particularly the strong compaction of the strands (next described) would cause them to distort or tear the mesh or be "hung up" or arched upon it, the strands 1 must be separated from the mesh 7 during the charging and compacting operations.
Accordingly, the mesh is fitted tightly around a sleeve 8 of metal or plastic (aluminum sheet, in the pilot work) before placing mesh and sleeve in the mould; the sleeve separates the strands from the mesh. Returning to FIG. 1, the sleeve 8 is preferably made of two or more pieces as shown, overlapping but not secured together, so that the compression of the charge can force the sleeve to expand and stretch the mesh tightly to the limiting periphery of the mould cavity 2. (In addition, it may be preferable to pull the mesh strongly in the vertical direction and lock its upper end under tension, although this was not done in the pilot work and the blocks were nevertheless strong enough.) In the alternative, or in addition, the mesh 7 may be of heat shrinkable polymer and be further tightened by applying heat as a final stage of blockmaking.
Since the charge must be compressed considerably, its initial placement must extend above its final compressed height in the mould. As shown in FIG 4, the sleeve 8 accordingly extends above the mould to a height A to receive the full charge. Open bars 9 extend upward past the solid sides of the mould, supporting the top area of the sleeve as the charge is built up above the mould; these bars are either removable or are spaced apart to allow the mesh closing devices to reach in over the top of the mould and close off the mesh, as will be seen.

The piston 10 in FIG 4 is brought into position at A and compresses the charge with the desired force to final dimension at B. The sleeve allows the strands to compress and move downward freely, unhindered by the mesh, just as it had done during the charging operation.
The preferred concave shape of the piston 10, "dished" down into the charge, produces slightly excessive compaction of the central area of the charge to compensate for springback, as discussed below. Similarly, the preferred shape of the mould bottom 12' produces a slightly upward concavity in the charge as shown.
The compression completed, it is necessary to retain the middle of the upper end of the charge in its overly compressed position as the piston itself is retracted out of the way. In FIGS 4 & 5, the preferred retainer is shown as in the pilot blockmaker: a rod 11 axially mounted within the piston assembly, sliding independently of it.
In FIG. 5, the piston 10 has been retracted with the end of the charge retained by the rod 11, and the sleeve pieces 8 have been pulled vertically out of the mould leaving the mesh 7 directly and tightly wrapping the compressed strands within the mould. The narrow rod 11 does not interfere with the folding over and securing of the folds of mesh 13 (with cutouts to allow for the rod) nor do the spaced or removable bars 9. The bagging art offers devices to fold over and fasten such mesh, using heat sealing, stitching, staples or ring clips, FIG 6, 14. Once the mesh is folded and secured, the retaining rod is retracted and the upper end of the charge "spings back" to the desired plane. The mould is swung open to release the block.
The pilot blocks were closed by hand, using staples through the mesh into small plywood plates. Whether by machine or by hand, ring-clipping the folds of mesh to each other, as suggested in FIG 6, 15, may well be the preferred method. For small operations such as in underdeveloped countries, the blockmaker, its operations and final blocks may be much as described for the pilot and as shown in PHOTOS 1 - 4, perhaps incorporating the mechanical hand 4.
The desirable mechanization for volume production, however, would likely incorporate several time-and-labour-saving arrangements within the principles of the invention. For example, the charging operation would preferably take place at two or more separate stations in parallel to the "production line", charging sleeve assemblies pre-wrapped in mesh, since this operation is intrinsically much slower than the pressing operation itself. Further, the discharging of the moulded block might better be accomplished by pushing it right through the mould and sleeves (the bottom of the mould being a separate piece that would move downward in step with the piston) rather than pulling out the sleeves; then the retaining and end wrapping would proceed at essentially a third station.
The size and shape of the blocks can be usefully varied as shown in FIG. 7.
The pilot work proved the usability of the square section 16 ( 12 x 12 inches in that case) and next, for the honey bottling plant, a rectangular section 17 that builds more wall per block ( 12 in. thick x 16 in. high x 24 in. long in that example, a preferred shape and size). The block integrity for handling and stacking was more of a concern in the latter, 17 (the square section 16, more approaching a circle, is the more inherently stable), but all proved adequately strong.
Both these sections are preferably formed with rounded corners as shown, of about 1.5 in.
radius in the pilot work, to make them easier to form and less easily damaged in handling, and to lock in the stucco more securely as will be shown. The blockmaker can be designed to produce the "squashed log" shape, 18, or with more or less square cornered or rounded shapes in between these examples. The applicability of the shapes will be examined below.
For a given choice of strand material, the amount of compression and resulting strength of the block can be varied by changing the force applied through the piston 10 and the strength and stiffness (elastic modulus in tension) of the mesh 7. The designer might need blocks of greater transverse shear strength for seismic regions, for example, or where building arched roofs as noted later. Further compression can be retained by incorporating an axial wire or wires running through the block from one end to the other, and secured to small washers or other small load spreaders at each end. This would work with the mesh to compress the block axially while helping to keep the ends flat despite the greater springback forces.
In FIG 8, a wall section is shown composed of stacked blocks of rectilinear section 16; the section 17 type of shape would be used in like fashion. Stucco or other cementitious or resinous structural "skins" 19 have been applied, bonding through the mesh and into the strands. The bonding is especially strong at the indented joint where the rounded-corner block sits atop block, as shown in FIG 10, 20. It can be seen that the flat sided blocks and their modestly indented joints are appropriate for use with strong, relatively costly skin materials where the amount of material should be kept to a minimum but the lock-in of skin to block must be sufficient.

In FIG. 9, on the other hand, the "squashed log" block section 18 is seen to be appropriate for low-strength, less costly skin materials which would include the adobes, soil cements and perhaps lime stuccoes. The deeper recess or indentation at the joints between blocks better secures the skins to the block mesh and strands to assure stressed skin stability, and the greater amount of material used is of little consequence.
All such walls can be remarkably strong. In the pilot testing, walls of 12 in.
block core of shredded roadside bush faced both sides with 0.75 in stucco demonstrated stiffnesses and strengths exceeding those of common "2x6" wood frame walls. The mesh in this case was of polyolefin, 0.5 in openings, tensile strength about 200 lbs. per inch breadth of mesh.
Where greater strength is desired, for seismic regions or tornado regions for example, a separate layer of mesh can be applied full height over both sides of the stacked blocks before stuccoing, fastened to sole plates or foundation and a top plate (and thence to the roof).
Construction stability must be provided as the blocks are dry-stacked and the wall building operations proceed, and preferably without requiring close-spaced bracing or formwork.
The pilot work demonstrated that adequate construction stability could be assured by simply mortaring-in the joint indentations, or at least the horizontal joints, after each course or two of blocks were laid. The stabilizing effect is immediate; no need to wait for the mortar to cure.
(No mortar is required between the block interfaces; it's not needed for initial or final strength, and it adds to costs while increasing risk of moisture entry and decreasing the wall's thermal resistance. However, where very good thermal resistance is desired, it may be necessary to stuff or foam-in an insulating gap-filler at the joints between block ends, if and where the block shape and lack of resilience leaves gaps through the wall big enough to allow connective heat transfer. The pilot work was not conclusive on this point.) A speedier and potentially stronger way of providing construction stability is shown in FIGS. 11 and 12, showing respectively a cross section and side elevation of a stacked block wall: "Clip" the mesh of each face of each block to that of the block beneath it as each course or two are laid. The clipping can be done by hand, pulling the upper block mesh firmly down and the lower block mesh upwards while inserting the clip 21, thus pre-tensioning the mesh (both vertically and, by a sort of Poisson effect, horizontally). The clipping might well be done mechanically by stitchers or "hog ring" tools, within the concept herein claimed. A probable minimum amount of clipping is indicated in FIG. 12:
one clip 21 per block per face.
FIGS. 13 and 14 respectively show a front elevation and corresponding side view of a suggested wire clip 21. Such a clip allows a further side-twist tightening in place, with pliers, to the maximum force that the mesh can withstand; some such may be generally desirable. Preferably, clips can be designed within the invention, in wire or injection moulded plastic, to allow tightening as "over dead centre" devices, perhaps best exemplified by the Mason Jar "breakthrough" of a century ago.
Although knowledge of the transverse shear and shear creep properties of such dry-pack blocks is not yet sufficient to proceed with structural roof design, it is envisaged that arched roofs can be built to material advantage and within the scope of the invention. Certainly arch roofs can be usefully and soundly engineered by taking dead load and all long term loads into the arched "skins", while employing the dry-pack blocks only to stabilize the skins against buckling and to withstand short-term shear forces, as is claimed.

Claims (12)

1. A building block comprised primarily of organic fibre or other polymeric materials chopped or shredded into fibrous or ribbon-like strands, which are packed tightly together and retained in block form by an enclosing wrap of strong mesh in conjunction with their orientation and the friction developed between them.

2. A building block according to Claim 1 in which the choice of materials, the shape and orientation of the strands, the force of compaction and amount of friction developed between the strands, and their arrangement at the block faces, provide structural and thermal insulating properties enabling the block to serve as the core of a stressed skin sandwich building component formed when strong skin materials are applied to stacked assemblies of said blocks.

3. A building block according to Claim 2 in which the enclosing mesh is chosen to provide transverse tensile strength sufficient to stabilize structural skins against buckling outwardly, i.e. away from the block faces, by itself or in conjunction with the strands, thus improving the ability of the block to serve as the core of a stressed skin sandwich building component while widening the choice of strand materials and arrangements by reducing the structural demands imposed upon them.

4. A building block according to claims 1 - 3 in which greater axial compression, lengthwise to the block, is achieved by incorporating a tension wire or wires axially through the centre of the cross-section, locked into washers or like load-spreading plates bearing against each end of the block and tightened to suit.

5. A building block according to Claims 1 - 4 in which the flat-sided rectilinear shape of the block is designed to minimize the amount of material that must be applied to stacked assemblies of said blocks to achieve desired, consistent thickness of structural skins.

6. A building block according to claims 1 - 4 in which a rounded cross-section is formed, e. g. more of an oval or "squashed log" form of block, the better to receive and stabilize thicker adobe-like skins which become especially well locked into the blocks by penetrating through the mesh and into the strands in the deep recesses formed at the joints where rounded block lies atop rounded block.

7. A method of producing a building block as in Claims 1 - 6 in which:
- the mesh is formed tightly around a segmented, open-ended sleeve of transverse cross-sectional dimensions less than those of the final block, so enclosing all but one end of said sleeve, leaving an excess of mesh or fabric extending, open, past that open end; the mesh preferably tensioned two ways;
- the whole is placed within a rigid female mould of final block form so that the sleeve's open end is positioned at the mould's open end;
- the sleeved mould is charged with strands, placed through the open end;
- a piston rod and piston assembly is then brought to bear against the charge of strands at the open end;
- the charge is then piston-compacted into final block form, the sleeve preventing the compressing strands from snagging and "hanging up" on or tearing the mesh, and the compacting operation expanding the sleeve pieces outwardly against the female mould to further pretension the enclosing mesh.

- the sleeve pieces are extracted through the open end, leaving the pretensioned mesh behind, tightly enclosing the compressed strands; or the compressed charge is pushed through the mould while its dimensions are held constant, while the pretensioned mesh is pulled through by and with the charge, encasing it, and the sleeve pieces are left behind in the mould;
- the piston assembly is retracted away from the open end while the charge of strands is retained adequately in block form and compression by means of a retaining rod remaining in place against a point on the now-exposed end of the block of strands, said rod preferably contained within and free to slide within the main piston rod and piston; or such retention is effected by inserting rods transversely or by other practical means in the art that do not unduly block access to the now-exposed end of the charge;
- the excess mesh is folded tightly over the exposed end of the charge of strands and is secured by heat sealing, mechanically stitching, ring-binding, stapling or other practical means in the art to complete the building block;
- the retaining rod or other restraint is retracted and the completed dry-packed building block is removed.

8. A method according to Claim 7, wherein the charging, orienting and initial compacting of strands into the mould cavity is effected by a device consisting of a plurality of "fingers"
having their upper ends hinge jointed to the lower end of an up-and-down reciprocating push rod, so that they splay outward at their free lower ends as the rod forces them downward into the accumulating charge of strands, thus pushing the strands down and radially out to fill the sleeve fully into the corners; the fingers spring back almost into axial alignement with the rod on its upward stroke, but still cocked slightly outward in their downward stance, providing free path for more strands to fall or be vibrated or otherwise conveyed into the mould cavity; these then being oriented and compacted by the next stroke of the rod and its splaying fingers.

9. A wall structure in which the building blocks as in Claims 2 - 6 are laid in courses atop each other, "brick wise," and firstly given construction stability by applying mortar to both vertical faces, at least and particularly at the horizontaljoints between successive courses of the blocks, and finally given structural skins by stuccoing or otherwise forming hard skins or coatings on both exposed faces to complete the composite structure, a stressed skin sandwich wall.

9. A wall structure as in Claim 9 in which construction stability is provided not by mortaring the joints but by inserting clips to secure the mesh or fabric on each vertical face of each block to the corresponding mesh or fabric on the block above and below as each successive course is laid, forcefully tensioning the mesh or fabric over the height of the block assembly so that the assembly is contained in effect with a continuous mesh mounted and prestressed over the whole of each face (**).

10. A wall structure in which building blocks as in Claims 1 - 6 are laid to form the core and the wall is completed by such additional mesh, skins, frames, posts, backup structures or reinforcements as are required to prevent air leakage and water or water vapour penetration and to withstand dead and live loads including concentrated loads.

11. An arched roof construction in which the blocks as in Claims 2, 3, 4 or 5 are used to form the core to separate, insulate and structurally stabilize an inner and an outer thin arch-formed plates (skins), the whole constructed sandwich-fashion so that:
- the inner arched skin is strongly formed from fibre-cement or fibre-resin composition reinforced to withstand all dead loads and long-term live loads by itself or by sharing some of that function with the outer arched skin, relying very little if at all upon shear resistance and shear transfer through the blocks between these two skins in withstanding such sustained loads;
- the skins are bonded to the mesh and strands of the blocks so that the blocks can transfer direct vertical loading from the outer skin to be shared by the inner skin, and the blocks provide short-term shear resistance and composite coupling between the two skins to increase the capacity of the whole to withstand dynamic loads such as seismic and wind gust loads.

12. A method of forming the arched roof according to Claim 11, in which the reinforcing rods of the first or inner (bottom) skin are formed into half hoops and erected as the formwork upon which the block core assembly is laid, so that said inner skin can be "shotcreted" or otherwise wet applied to penetrate and bond to the underside of the arched block core assembly, and, once that skin is cured sufficiently to provide strength and stiffness, the outer skin is similarly wet-applied to cover, waterproof and complete the whole.