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Cast Block Wall System (CASTECO) - Page 1

author: Robert Shannon

Design, Development, and Deployment of a Cast Wall System of high R value and fire resistance for bearing wall construction.

Preliminary Sketch

Preliminary Sketch

Criteria for cast wall system

Average R value of 40
Maximize recycled material
Minimize energy in production (embedded)
Maximize mass to interior
Allow for steel and concrete infill structure
Potential for multistory bearing walls
Maximize longevity
High fire rating
Waterproof
Channels for wiring
Easing of assembly
Facilitate attachment of other components

Purpose

A more sustainable substitute for reinforced concrete block is needed for the construction industry, one that includes insulation of the highest R-value per inch, on delivery to the site. It must provided for reinforcing, for adaptability to various configurations of the plans and elevations, and be easy to install without complicated equipment or procedures. It must be waterproof for long term duration, vermin-proof, fireproof, and earthquake resistant where needed. It must be able to accommodate electrical and small-scale mechanical runs inside the wall near the interface. It must have the option for various internal thermal mass on the inside layer to meet the thermal design systems of each specific building. Further, the block should be made of as much recycled and renewable materials as possible while satisfying the overall purpose.

Description of the parts

The insulative core is to be made of a matrix of perlite or pumice, bonded together and to the outer and inner wall substrates with a bonding agent (acrylic?) and fibres as reinforcing. This matrix should be capable of transferring some shear, compressive, and tensile loads between and along the edges (inn all directions.) Void trenches cast in this matrix can accommodate reinforced concrete superstructure and small wires and pipes for mechanical purposes. This material, along with the substrates should be cutable with a diamond blade saw. 
The outer and inner wall substrates should be made of a waterproof and fire-resistant composite board, currently available on the market. Its thickness could vary in response to desires for thermal mass, strength, weight, etc. The board should be of a high recycled content, and provide a good surface for bonding a stucco finish or allow attachments such as brick or veneer ties by screws without splitting.

Void Locations and Sizes

As these are determined by the configuration of the mold, which can vary to accommodate different requirements within a project. Special voids should be able to be cut with a diamond hole saw or extended speed bore. Of course the less matrix, the less insulation. At present our plan is to add reinforcing voids diagonally opposite each other in the block to use the maximum thickness of the wall for structure, creating the maximum moment arm for compression and tension resistance.

Assembly

It is assumed that the first course would be laid in cementous mortar in order to establish a level beginning for the layout. Above that, the block would be secured with a bead of adhesive on each side of the wall, and tapped down with a rubber mallet. Connective framing can be fastened to the openings by long screws into the matrix either on the surface or inserted between the substrates. Horizontal poured reinforcing in block construction as bond beams is usually spaced every four feet, so if the block were 2'8" long by 1'4" high, the horizontals poured ties could be every other course at 2'-8" increments. or every third course at 4' increments. A bond beam at the roof level could extend the width of the wall, if it is above the insulated space. Beam pockets at floor levels could extend halfway into the wall on a smaller horizontal pad.

The concrete frame shown separately. The spacing of the horizontal elements can be in any increments of 1'-4" o.c. The thickness of the concrete can vary; for example, at the base of the building where the loads are greater.

The concrete frame shown with bearing pads for floor structure. Loads are carried to both inner and outer vertical columns. Various configuration of the pad portion can respond to load requirements such a beam carrying significant load or a deeper beam.

Block sizes

A solid block 8x8x16 inches would weigh 19.8 lbs, and one 12x12x16 would weigh 60 lbs. The size of the block should be determined by the ability of one person being able to lift it into place. The modular sizes of standard concrete block may not be relevant in considering the sizes of these components, but bar spacing and insulation levels desired may influence the configuration, and thus the various sizes. In terms of compatibility with other systems, some increment of 8" ( 8-16-24 ) is probably wise. Additionally the manufactured available sizes of fiberboard fit this modular.

Tests performed in Winter' 07

Larger blocks of now refined mixtures were cast, but none of the tests proved capable of bonding to the fibre board which had been primed with a bonding agent. It would seem simpler to spray a harder coat of material to the front and back surfaces to create the hard surface for attachment or finishing.
The introduction of cellulose fibre and the elimination of the portland cement in one test casting have proved to be a progressive step forward. While slightly fragile to scratching at the surface, the block holds together well under compression. One additional idea to speed curing of the acrylic bonding agent would be to have metal forms coated with a surface to which the bonding agent does not readily adhere, with small holes over the entire surface to allow air to pass through the forms until the casting is adequately cured to un mold it.

Ideally a differential mix from edge to center would solve several problems, although the machinery to test this would be more complicated and expensive; however, such a method could be tested by approximation, by making 2 different mixes, and combining the differentially from edge to center and back to the other edge. This will be the basis for the next tests, along with forms that include voids for reinforced concrete fills, and at the scale of actual potential product

Block configuration 8x8x16 inches. R21.6, Weight 20 lbs.

Block configuration 8x10x24 inches. R27, Weight 37 lbs.

Block configuration 8x8x24 inches. R21.6, Weight 30 lbs.

Block configuration 8x12x24 inches. R32, Weight 45 lbs.