Walter DeVore, Jr
970 663 0524
720 213 8044
Cell: 303 319 3764
Precast panels use only 15 pounds of concrete per square foot of wall face. Panels are easily handled manually. Styrofoam is embedded between structural ribs to displace concrete. They may be reinforced with mini rebar Helix steel fiber , a code approved product, and or, pva fibers. The option of using integral color dyes is more affordable with less concrete to tint.
Expanded steel is a perfect material to embed into the panel backside. Each strand is 1/10" x 1/10" equal to 1/100 square inch. Six strands are commonly used, a total cross section of 6/100 square inch. Steel has a typical "U" heat transmission value of 50 per square foot. Since 0.06/144 is very small, thermal bridging is minimal. CBS is the only building material that has an embedded projection to create a third dimension (width of wall). The ductility of expanded steel helps force dissipation and survivability in catastrophic conditions. A wall cavity of any width may be formed by choosing the appropriate length of expanded steel.Two wall faces are simply welded for a "container wall" of continuous internal "cavity". Within the wall cavity, design versatility abounds.
A continuous slot cast into the perimeter of the panel receives a spline to align, seal, and reinforce panel abutment seams. The spline has a chevron cross section making for easy mating of panels.
Standard panel sizes of one, two, and three feet long by sixteen inches high, aid symmetry in design and are conducive to standard material sizes of four feet by eight feet.
In the old days, panels were bolted together. Rubber washers provided a thermal break. The force of filling the cavity with concrete would push the panels a little bit out.
A piece of scrap thin steel bar may be placed between the expanded steels to give more meat to weld to if necessary.
Even 36" x 16" panels, 4 square feet, 60 pounds, are easily handled by fit women. Age is little barrier.
The embedded steels are easily bent over for stacking on pallets. Pallet weight can average 2,000 pounds. At 40 pounds (18 kilograms)per panel, fifty panels comprise a pallet. At 2-2/3 (24" x 16") square feet per panel, 133 sq ft of panel are on one pallet.
Depending on one's insulation strategy, both panels can be insulated like ICF's.
While the panels are horizontal, mixing acid stains in a water film can create interesting effects.
Gallon milk jugs full of water can triple the thermal mass of a wall since water's specific heat is 62.4 btu's per cubic foot compared to concrete's 18. Laying sand around the jugs can cushion and protect them for the long haul.
Panels are slotted around their perimeter. Splines align and seal the assembly.
Another application is to attach to steel studs to gain a wall cladding and added space for insulation and/or conduit installation. Regular drywall may be installed to the inside face of the steel studding.
Having to tie vertical rebar stubs to footing rebar makes pouring and leveling concrete much more difficult. If wall panels are designed to begin on the footing, then getting the necessary flatness to set the panels on is not easy. Maybe because I have little experience with this I don't know how well it can be performed. Since vertical rebar can go from the bottom of the first row of panels directly to the roof, I don't understand why the little bit more embedment into the footing is necessary.
The following excerpt from Concrete Construction Magazine addresses this situation:
PROBLEM CLINIC VERTICAL REBAR PLACEMENT IN FOOTINGS
By Concrete Construction Staff
Q: When placing vertical rebar in a residential footing, is it necessary to tie them in place before the concrete pour, or can workers just "stab" them in after the concrete has been placed and struck off?
A: As part of a larger research program ("How Clean Must Rebar Be?"), we did some research on the comparative bond strength of rebar held in place during concrete placement and rebar pushed into position after the concrete had been placed. For the held-in-place condition, we constructed three bond pull-out specimens with a 6-inch rebar embedment depth by using the bottom halves of 6x12-inch plastic cylinder molds with 1/2-inch-diameter holes drilled through the bottom of each.
We placed the molds on 2x6-inch boards that had been predrilled with 1/2-inch-diameter, 1/2-inch-deep holes. We inserted #4, Grade 60 deformed black-steel rebar in a vertical position with 1/2 inch of the rebar protruding from the bottom of the cylinder mold into the hole in the 2x6. This helped keep the rebar vertical during placement of 3 1/2-inch-slump concrete around it.
For the pushed-in-place rebar, we placed the concrete into the 6x6-inch cylinder molds and then stabbed #4, Grade 60 deformed rebar into the concrete and through the hole in the bottom of the mold. We made three bond pull-out specimens by this method. Concrete strength was about 5500 psi when the bars were pulled out.
Technicians measured slip of the 1/2-inch-long free end of the rebar while applying load to the longer end of the bar in each specimen. They recorded slip when the bar yielded and when the bar broke. Neither of the two bars-held-in-place or stabbed-pulled out of the concrete.
The results are summarized in the table. Local building codes may not permit stabbing the bars. However, our test results indicate that the performance will be the same whether the rebar are stabbed into place in consolidated concrete or held in place while concrete is placed around them. Bond pull-out test results (average of three tests).
Rebar is easily secured to the expanded steels. A conduit fed electric box is seen in the lower left.
Inside and outside corner pieces are difficult because of needing to be precise in the x, y, and z planes. Mold assembly is key and right angles need welded braces in the mold to lock in the angle. These corner molds were a challenging later development in order to give the aesthetic impression of full wall width blocks. Seeing abutting two inch thick corner pieces was eliminated. For low cost housing, regular straight pieces can be abutted at right angles and glued with polyurethane construction adhesive. They can be clamped overnight for a strong rigid connection and then additionally secured by adjacent rows.
Electric boxes fastened to mold face with silicone and cast into panel. They are then connected with conduit. Conduit connection in box must be greater than two inches from face of box to clear the two inch panel thickness for connection fit.
Molds on cart for easy handling and compact storage.
Expensive lumber used one time. Forming expense very high.
A bit of idle time while I load the mixer for the next batch.
Hard scapes and living walls can be made by casting holes into panels and filling cavity with soil. Plants can grow out of the wall. Grey and black water can be introduced with perforated pipe to be purified by root microbial action. Walking paths and labyrinths can be constructed. Can be part of structure for continuous demarcation.
Columns, spandrel beam supporting slab simply formed within wall cavity. Beam depth and column can be custom set within the cavity using welded expanded steels as back braces. Increasing the depth increases the structural stiffness cubed, an easy economical way to have more strength. Columns can be formed as a rectangle, a "+", a "T", or an "L". These shapes have enhanced stiffness. Less concrete, a lighter building. Forming expense is eliminated.
Forming for beams and columns is inherent in the panels. One has a stay in place form and an architectural finish glass smooth concrete surface on the outside.
Zipping back to Colorado for a project by the Continental Divide. Fun for all getting out of the house. Easy jobs anyone can do. People enjoy the immediate sense of accomplishment, investing one's time for a return on investment over subsequent centuries. Concrete is maintenance free and with increasing drought offers piece of mind of fireproof construction.
While importing mold components from China I tried their expanded steel. It wasn't really expanded and proved to be brittle when bending over for compact pallet stacking. The best by far to use is known as "inch and a half number 9 expanded steel. It's about $40 per sheet. It's easily cut to whatever size is required for any size wall cavity. Different cavity widths only require an adjustment in the exterior corner size to maintain uniform consistent spacing of panels both interior and exterior. Visualizing this isn't real straight forward but drawing it out makes it clear.
Voids can be created by embedding styrofoam at vibration while casting. The conrete rib embedding the expanded steel retains its two inch thickness for overall strength.
This is a 16" wide wall with a 12" wide cavity. Two 2" thicknesses of polyiso against the exterior panel provides ample insulation. (4" x R6 per inch = R24) When one does energy calculations the largest by far heat loss is from air infiltration. Concrete poured into the cavity stops infiltration. The sealing detail around window and door frames needs to be carefully considered. One sees the grooves around each panel perimeter that accepts a precision custom tapered "strip" to align and seal panel seams. Panels are installed as fast as they can be delivered if precise accuracy is achieved with slab or footing flatness. Embedded expanded steels overlap for simple, fast, economical tack welds.
A 115 Volt wire feed welder easily makes spot welds. Complete rigidity of connections is assured. However, ductility in the steels themselves help insure survivability should a catastrophic force act. One side of the wall can move independently of the other to absorb and dissipate earthquake forces.
To make welding easier, a strip of thin bar steel can be a backer. Any degree of "stiffness" can be imparted to connections.
If one chooses system type window frames, then extra forming to seal off wall ends can be eliminated. The back side of frame pieces also have embedded expanded steels that extend into the cast in place area. When walls are filled with concrete they become locked and embedded.
Testing to know the precise capabilities of the system is paramount. However, the most extreme stresses will occur when the wall panels are resisting formwork pressure from being filled with concrete. Whatever the maximum fill height would be, most likely around 10 feet per floor, a demonstration wall can be constructed to a height to simulate ultimate pressure. Panel consistency is a huge factor. If a wall is built high enough be filled to failure, great confidence can be derived to know that any blowouts can be completely avoided. Ultimate strength from testing to failure illustrates the full capability of what the joined molds can endure. Eliminating bracing keeps the area clear and reduces materials and labor.
Since concrete aggregate and cement properties may vary by location, verifying performance with local materials is prudent. Another strength factor of adding Code approved Helix steel fibers can be investigated. A maximum amount of 13 pounds per cubic yard is a demonstrated upper limit.
The structural engineer may be able to extrapolate the results of form height and pressures to ascertain panel strength for wind, earthquake, and load bearing capabilities. Concrete failure ultimately is a failure in tension as compressive forces generate internal tensile forces.
For the greatest economy quality control is a wise investment. The less variability in concrete mixes and curing, the less portland cement is needed. This requires a stable climate that's not likely to be found or an indoor temperature humidity controlled environment. A "volumetric" (mixes concrete continuously as opposed to single batch loads) mixer may be the best choice as fresh concrete is easier to maintain.
There is a lot of material handling that needs to be carefully planned. Carts can hold about five molds using 5" casters for easy rolling, have proven to be very helpful. Full molds on carts can be stored with maximum density and then easily separated for processing.
The trick for panels to be lightweight using high strength pea gravel concrete. Tapered blocks are pressed during vibration into the panel back, eliminating 40% of cement content and weight. Displacement blocks are removed for reuse at a precise time after casting.
Another option for concrete displacement is to add styrofoam pieces. They have the advantage of not needing to be removed and cleaned. Roofing supply companies may sell it inexpensively. Prepping (cutting) the pieces can be done with a hot wire (preferred), a sharp blade, circular knife, or running through a table saw. If space permits, this can be done in house.
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Walter DeVore, Jr
970 663 0524
720 213 8044
Cell: 303 319 3764
Walter DeVore, Jr