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Precasting and Costs

Estimating

To bring the scope of operation into focus, there are some simple rules of thumb.

For an interior ceiling height of 7 panels high equal to 9' 4" the panel square footage is about 3.3 times the floor plan area. For example a 2,000 square foot house would require about 6,600 square feet of panel.

The average panel weight is 15 pounds per square foot. One yard of concrete will make about 4,000 / 15 = 267 square feet of panel.

A flatbed truck capacity of 40,000 pounds can haul 2,670 square feet of panel.

20 pallets can be loaded to 2,000 pounds per pallet.

An average value of $8 per panel square foot is a 2,670 sq ft x $8 = $21,360 product value per truckload

Panel material costs
2.67 sf panel 40 pounds concrete
Concrete $150 per 4,000 pounds = 1 cubic yard
Panel concrete cost = (40 / 4000) x $150 = $1.50
Two expanded steels @ 0.50 each = $1.00
Panel volume = 0.44 cubic foot
40% styrofoam insert
0.44 x 0.4 = 0.18 cubic feet
Styrofoam $2 per cubic foot
Styrofoam = $0.36 per panel

Spline = 15.5" + 24" = 40" per panel = 3.33 feet
Spline $0.25 per foot
Spline = $0.84 per panel Panel cost = $1.50 concrete + $1.00 expanded steel + $0.36 styrofoam + $0.84 spline = $3.50 per panel

Panel 24" x 16" = 2.67 square feet

Panel cost = $3.50 / 2.67 = $1.31 per square foot

Estimatine Example

40' x 25' = 1,000 square feet per floor interior square footage
Two floors, three slabs 6" thick, post tensioned

Slab concrete 1,000 x 3 x 0.5' = 1,500 cubic feet = 1,500 / 27 cubic feet per cubic yard = 55.55 cubic yards Pumped concrete 56 yards at $30 / yard, concrete with helix fiber $30 per yard

Concrete total $210 per yard
56 yards x $210 = $11,760 all concrete for slabs

Three slabs, two stories, 2,000 sq ft = $5.88 per floor plan square foot

2,000 square foot example, rule of thumb, panel square footage = 3.3 x 2000 = 6,600 square feet of panel

Panel cost = 6,600 x $1.31 = $8,846

Panel cost per floor plan square footage = $8,846 / 2,000 = $4.43

Cost per square foot so far = $5.88 + $4.43 = $10.31

Add insulation and post tensioning

Exterior wall area = (42+42+27+27) x (2 stories, each 10' x 20)=42+42+27+27 = 138' perimeter x 20 ' high = 2,760 square feet exterior area

Exclude 20% for window and doors, net area = 2,760 x .8 = 2,208 sq ft

Wall insulation, poly iso $40 per 3.5" thick 8' x 4' sheet

Per square foot = $40 / 32 sq ft = $1.25

2,208 sq ft x $1.25 = $2,760

Per floor plan square foot = $2,760 / 2,000 sq ft = $1.38 for wall insulation

Approximate $3 per slab square foot for post tensioning

6,000 sq ft of slab = $18,000 for post tensioning materials

Per 2,000 floor plan sq ft = $9 per sq ft

Total construction materials cost this far = $10.31 + $1.38 + $9 = $20.69 per floor plan square foot

Roof insulation

1,000 sq ft, 6" of polyiso, $60 per 8' x 4' sheet, $60 / 32 sq ft = $1.88 per sq ft

Roof insulation floor plan square footage = $1,880 / 2,000 = $0.94 per sq ft

Synthetic foam cellular concrete roof topping, $15 per 10 cubic feet

4" Thick, cubic feet = 1000 x 0.33 = $330

Raise to $1,000 for pumping

Floor plan $1,000 / 2,000 = $0.50 per sq ft

Add another $1.44 per floor plan square foot, now at $20.69 + $1.44 = $22.13 per floor plan square foot

Footing

138 feet of footing perimeter, 10" deep, 24" wide

Concrete volume = 138 x 0.87 x 2 = 240 cubic feet = 9 cubic yards

Concrete @ $210 per yard = $1,890

Footing rebar = 5/8" #5, three in longitudinal in footing, one for cross pieces, 4 total for estimating = 138 x 4 = 552 feet

28 lengths at 20', $15 per length, $420 for footing rebar

$2,310 additional from footing, now $2,310 / 2,000 = $1.16 more

$22.13 + 1.16 = $23.29 per plan square foot

Molds

Precision of the molds in fabrication and assembly is the key factor in system performance. The little extra time in being mindful is the best investment to be made.

I am not a craftsman nor a fabricator. I'm much more a specifier and experimenter. Yet if I can't do something I can't expect anyone to be able to do it either especially something as generic and ubiquitous as house construction. There are subtleties I never expected but so important to be heeded.

I have been developing this since 1985. Many form evolutions came forth. To try and test them, I undertook a solitary effort to build and evaluate their performance. Each trial could cover a few years. I could review each stage, but for now will focus on the latest and hopefully the last, although revision is only an insight away.

I didn't think it was possible to form a perimeter slot in cast concrete and have it release cleanly. But to my surprise it was possible. This required the mold to separate horizontally to allow the mold spline to separate from the cast concrete product.

To fabricate the mold profile from assembling components seems unfeasible, so a custom die for an extrusion is necessary. The first trial used aluminum. To my dismay, the extrusion had varying dimensions to make the extrusions problematic for achieving consistent precision. There are ways to persevere but the added effort over the long run is too much. Another big problem was the repeated necessity to neutralize the aluminum surface from reacting with concrete in order to release cleanly. It eventually happens, but the cleaning and scraping to get to that point is exasperating to say the least. This problem persisted despite using the most potent alkaline sodium hydroxide solutions to hasten the neutralizing reaction. Many times simply enduring through countless failed remedies and a damn the torpedoes attitude was necessary. Persisting at any cost and effort has been the traction forward.

To ease the uniformity of the extrusion and eliminate the seasoning process to not stick to concrete, a heavy duty window trim grade industrial pvc was chosen next. I made a deal with a Chinese company and successfully imported my current generation of molds. They executed the order excellently. The only drawback to pvc is that it will warp when exposed to direct sun, even if ultra violet resistances are added to the formulation.

I had initially envisioned being able to cast panels onsite and go directly from the mold into the wall. But because concrete is sensitive to climatic conditions and consistency is paramount, an inside casting facility is critical. The job skills required to do the work are minimal and is some instances buyers could supply their own labor.

Getting Started

Design/Architect

Design

Designing with CBS can be simple, though tedious . One two and three feet long panels. Can use graph paper where one square equals one square foot. Easy CAD design. A little practice and one can create a complete design with pencil and paper.

This not a system where things proceed sequentially, but concurrently. Trades do not come in and boom, electrical is done, and plumbing. This must be carefully planned. The system provides a simple grid to locate all electric boxes, plumbing sleeves, etc. These specialized circumstances are installed as they are encountered, knowing where something comes from and where it's going.

The intent is for durable buildings to be fireproof, hurricane,earthquake and tornado proof, and provide energy efficiency for many generations. The concrete exterior wall is immune from ultra violet damage and will never require paint. Paid for quality housing can erase the onus of mortgage payments from future generation's lives.

Permits

The infancy of the system currently prefers the wall cavity to be filled with reinforced concrete. A helix steel fiber added to the concrete eliminates much of the tied reinforcement. The structure may last a thousand years or more, providing incredible return on investment.

Bids

The decision always loom, to do something one's self or bid it out. This is a precision system. Once a setup works, it's good to use it permanently. As CNC machines proliferate, that may be a no brainer short cut for fast and accurate fabrication. Many factors will come into consideration, such a space available and feasibility to take on capital investment. Each component of the overall operation will have solutions unique to it. Understanding fully what is required is paramount.

Payment

The most legitimate way to fund a business, in my opinion, is through deposits on product made by willing customers, those who are early adopters. By the business staying out of debt, better value benefits the customer. This depends on the ability of the business to follow through in transparency, be accurate in its requirements and performance. It's best when the business has been carried out of pocket by the founders, who have already endured the risk, learned from experience, and are committed to win win for all. A new business model is necessary, one that runs on cooperation, openness, and grass roots appeal.

Importing

There are some things that a cash strapped start up need to take advantage. Through getting bids and analyzing alternatives, I was able to secure about an 80% savings by having my mold components come from China. The "tooling" charge, to make the dies that produce extrusions, were $700 in China compared to 4 and 5 thousand dollars here. The extrusions were able to be produced at a 75% savings in China compared to North America. Before that decision was made, I engaged a Canadian extrusion company. Their product was poor, caused grave problems, and they offered no remedies. The leap across the ocean for value was forced upon me.

There are components that will be a value judgment as to having them made here, or importing them. These decisions will be influenced by economies of scale, the business's ability to find proper local sourcing.

Extrusions

The system is designed to have only one critical dimensional tolerance, and that is the extrusions. The chosen material is window trim grade extruded pvc. It may be bolstered by having UV inhibitors added to the pvc, but experience has shown this is mostly inadequate, especially the hot summer sun at 9,000 feet. Another option is to affix stainless steel or galvanized steel strips to the pvc surfaces in vulnerable locations to shield and greatly reinforce. That is a difficult non standard application for adhesives to work well. The obvious choice is a polyurethane adhesive. I have compared brands, and Loctite which is available in the United States is a much better product than LePage, available in Canada. My experience showed it was a lengthy, difficult, and expensive process to procure satisfactory materials. These fabrications are best made in the United States, and then deployed in Canada if a market is to be developed there.

There are four different extrusions required. Immediately one can deduce a $20,000 outlay for tooling in the United States compared to a $2,800 investment for China. These toolings are currently complete and were satisfactorily used for our first China import. A set of molds is currently located in Canada and the other here in York Gulch, Colorado, where they are being used for the "Beckel Studio Garage" project.

Extrusion cutting

Making very consistent precise cuts is critical. The right blade makes all the difference. That was learned the hard way. This is the blade as on Dec 2016. Saw blade for cutting extrusion . Being able to cut melamine with a triple ground saw tooth is a key requirement. They don't like to say if it's made for cutting pvc.

One wants to measure to the inside face of the extrusion for making the miter cuts. (45 degree). This eliminates small variances in the extrusion thickness that could alter the length just a little bit. A solid fence and stop is set up, being a little long, and then fine tuning it down until the measured length is perfect.

This is all about having a real good eye and precisely reading a tape.. Ideally, the saw is permanently mounted and replicable stops for various lengths are established. It's best to use no wood in the setup, it's too unstable.

This could all be subbed out to a cnc shop. It would be excellent to have one in house. Not many cnc tools have the necessary accuracy.

I have learned that it's almost impossible for a blade to travel through this thickness and hardness of pvc. The 45 miter cut is bound to pull or push the blade.

Mold bases

These are the mold faces for the exterior face of the wall panel, cast into a pan type mold. Imported, they are 6 mm and in the US they are 1/4". That is about a half mm more thick. They are made from gray industrial grade pvc. Since the extrusion slot slides into the base, there are no critical measurements.

To aid the fitting of the base into the extrusion, the base sides are beveled for a tapered fit. This done with a deburring tool or grinder wheel on all the edges. This could be considered a step to be done in China.

Mold base stiffeners

Keeping the mold bases perfectly flat is also critical. The pvc base cannot be allowed to twist, which it can do. Steel square tubing carefully welded into a flat rectangle is the solution. The steel tubing assembly is the polyurethaned to the bottom of the mold base. The surface of the steel to make contact and the area on the pvc base to contact the steel need to be gone over with a grinder wheel to roughen the surfaces for much better adhesion. That is no fun but is necessary, probably the least fun aspect.

A pneumatic dispenser for large tubes of Loctite Urethane will save a lot of trigger squeezing on regular dispensers.

Waffles

These are innovative devices and really make the system special. They may be made of wood or even better 3/4" steel tubing. Woods tendency to warp will cause slight errors, but may be easier to do. These "waffles" hold styrofoam in place to vibrate into the mold filled with concrete. This saves on concrete and weight, and adds insulation. The expanded steels are also locked into position for proper accurate embedment in the wall panel. These pieces are prepped before hand. After the mold is filled, these pieces are vibrated into the concrete. They are held in place by thin plastic strips that fit into a slot at the right height in the extrusion.

Molds

A mold ends up being the assembly of the extrusions tightened into place with a ratchet strap around the perimeter. They are tightened to a template that fits inside, and then lifts out. The friction of it lifting out is a good magnifier for the uniformity of size. Each size of mold has its specific template.

Rachet straps

These are a quick assembly and disassembly device. They need no hooks. They are positioned in the center of the mold to apply even pressure. The coming together of the corners as they are tightened are checked for proper joining. The lengths are printed on the straps to identify what molds they go with.

Curing

Good concrete is made by it retaining its moisture for as long as possible. The pvc mold is impervious so no moisture escape from the panel front nor sides. The styrofoam inserts help block it on the back side. Maintaining heat to the curing is a big challenge working outside in cold temperatures. Loading the full molds into carts with insulated sides, top, and bottom is one solution, and by adding incandescent light bulbs inside as a heat generating source.

Smoothness and density

Because the panel face hardens against a non porous surface, no "capillaries" are formed. They are little tunnels through the concrete for escaping water and vapor in the mix, a part of the curing process. If there is no exit for water, then no capillary is formed. All the escape is through the back side, which is ideal. The exposed front surface stays intact, water will just bead up on it and flow down. The beveled edges of the panel assure the water goes straight down, from panel to stacked panels. This water shedding feature endures for a very long time. Concrete being immune to ultra violet degradation, does not degrade.

Disassembly

Once the panels have hardened sufficiently, they are extracted from the molds. This amount of time is determined by temperature and any accelerating effect of admixtures. An admixture is an added chemical to alter and enhance chemical reactions in the concrete.

The molds are disassembled. The straps are all removed, with the quick cam action of a ratchet strap. The screws that locked the expanded steels into position are removed. The waffle assemblies are pulled out leaving the styrofoam embedded in the concrete. They go to the removal gadget where the "L"s are spread apart, releasing the panel. Ideally it can go directly into position in a wall, or stacked on pallets, or acid stained any combination of a myriad of colors.

Alternately, a paint can be formulated from oxide powdered pigments, combined with linseed oil and mold release oil. Artistically applying these different colors to the mold face before filling with concrete is another aesthetic option. The possibilities are endless.

Transport

Five standard 24" x 16" panels can be layered stacked on a standard 32" x 48" pallet. That is 10.67 square feet. Each panel weighs 42 pounds, 5 panels is 210 pounds per layer. A typical load for a flatbed trailer 40' long is 40 to 48,000 pounds. Ten pallets long, two pallets wide, twenty pallets total. Each pallet can weigh around 2,000 pounds. That can be contrasted with a pallet of portland cement which is 35 sacks at 94 pounds per sack. At over 3,000 pounds per pallet is a heavy pallet. One can stack 10 layers high, a total of 2,100 pounds. Ten layers is 106 square feet of product. Twenty pallets is 2,160 square feet of product. If wholesaled for 8 dollars per square foot, twenty pallets per trailer equals about 17,000 dollars of product per truckload.

Unload

Materials handling strategies need great attention. Magnitudes of work are at stake. Pallets are forklifted from trailer to closest point of installation in the wall, while maintaining walking paths.

Footing or slab base

This is the most critical step. It's unusually demanding, especially for amateurs and rookies. Flatness and level determine the ease of getting the first row of panels correctly installed. Using wood for forming is fraught with peril as it's likely to warp and become close to useless. Subsoil condition determines the best approach, from rocky and difficult to anchor anything in the ground to soft and possible yielding. Screed rails need to be precisely set, and rechecked right before the concrete. Having to tie in vertical rebars coming up from the footing makes a good screeding very difficult. Maybe not so much for experienced pros. The solution, if requred, is to "stab" in (http://www.concreteconstruction.net/how-to/vertical-rebar-placement-in-footings_o)

Installation

With a flat level well executed start, all can proceed quickly. Skill in geometry is necessary to lay out the floor plan precisely. The wall is 12" wide, the distance between the slots for each panel side is 10". Care must be taken to assure slots are cut into installation base so the wall is properly centered. Given a flat level installation base, either a footing or slab, one installs the exterior and interior corners. These give a true plumb vertically, setting the vertical for the wall panels to mate into. The splines will insure a snug fit, but there may still be play in the vertical plumb. The ten inch width between the slot on the exterior and interior panels must be checked for accuracy and vertical. The overlapping expanded steels are then clamped and welded. A 115 volt wire feed welder using gas shielding will make the best welds. Three welds per overlap should insure strength and rigidity of the panels.

Alternatively, a welding jig may be employed that sets the vertical and separation automatically. Welded panels are then removed and installed. Care and verification needs to be demonstrated in the beginning to make sure that indeed the jig is correct. The interior and exterior panel may then be handled as a unit and installed. It's twice as heavy than doing one panel at a time, but is still manageable, particularly if handled by two people.

It's good to install vertical components of window and door frames as soon as possible to have another vertical reference. Panels can be installed from the frames towards other frames or the corners. The final panel that links the two directions should fit snugly. If anything is off, adjustable molds are used to make the appropriate length panel so all the vertical seams remain tight.

As the walls grow in height, scaffolding is used to facilitate installation. A scaffold jack may be employed to lift jig welded panels into position.

Mold cleaning and Panel Extraction

Molds consist of two "L" s that are spread apart horizontally until the mold spline clears the imprinted panel slot. The spreading action is done with either rubber mallets or a pneumatic device. Holes in the bottom of the mold "L"s engage pins in the separator to spread the L's as a unit, minimizing stress on the L vertex.

There may be some light areas of concrete still in the mold after panel removal. They are gently scraped clean with a putty knife or wide wood chisel. There may be some seepage from concrete being vibrated between the mold base and chamfer part of the extrusion mold side. It's cleaned also. Removing the panels as early as their achieved strength allows makes the cleaning easier.

There may be some residue from the release on the mold base which is scrubbed off with a scouring pad. The debris from cleaning is swept out of the mold through the separated corners, or vacuumed out, or dumped by turning the mold upside down.

Mold Release and Tinting

After cleaning, while the mold is still separated, release is applied to the base and the extrusions. A release that can be quickly applied with a brush is preferred. There are many to choose from. Whatever is locally available and tested to work well can be used.

Color can be added to the release for absorption into the concrete for aesthetic options. This must be experimentally developed until satisfactory results are obtained. A "paint" release may have the quality to seal the seam between the mold base and side, thereby eliminating seepage. This is desirable as it speeds and simplifies the mold cleaning step.

Mold reassembly and Template closure

This action determines the precision of the next cast panel. Uniformity is critical. By fitting a correct sized template inside the mold as it's tightened by the perimeter ratchet strap. the fit is monitored and any deviation immediately becomes obvious. The tightness and smoothness of removing the template is a fine tuning gauge. Always, the greater the precision, the faster and easier is the installation.

Styrofoam

Inexpensive styrofoam is a good material to displace the weight and thereby cement content of CBS panels. On the average a 40% reduction is achieved. Concrete will cost between six and seven dollars per cubic foot, while styrofoam Styrofoam of itself is an environment hazard, but used with concrete is recycled in a most efficient synergetic manner. Pieces are cut so on the panel perimeter a full width of 2" is maintained on the top, bottom, and vertical ribs containing embedded expanded steel. The sides are 1" wide so two abutting sides maintain the two inch structural width.

Cutting

Sheets of 2' x 4' styrofoam are most easily handled. They are available from insulation supply distributors. The most standard height used in 12", obtained by cutting the 2' wide sheet down the middle. Then widths of 10" and 4" are cut for the most standard deployment. These pieces mount to the installation jig that includes the expanded steel for fast easy insertion into the concrete after the mold is filled.

Door and Window Frames

These are pieces that span from the exterior wall to the interior wall to simply enclose the wall cavity to contain concrete. Their two inch thickness decreases the wall and door openings four inches of width and height. They can facilitate immediate installation of doors and windows, micro adjusted for perfect fit. They can then be further braced to absorb the pressure of concrete being filled into the wall cavity. Lower sills can be formed an extra two inches width to provide an exterior drip edge and wall overhang. Insulation may be cast into the frames to lower thermal conductivity and bridging, and lessen their weight.

Window and door frames can be trimmed with stainless steel, brass, flat black or white for a juxtaposition of "elements" for a simple elegant aesthetic.

Sawing Frame Slots

Door and Window Mall are not conducive for having a slot formed into them during casting. Instead they are cut into the backside of the frame piece with a guide on a circular saw to have the matching width as the spline that joins them together .

Ties

Securing styrofoam insulation to the waffle jig for installation into concrete is not totally straightforward due to styrofoam's weakness. There are devices that work very well, but a little difficult to track down.

Waffle unit jig assembly

These are simple units that can be quickly made in a jig for orienting the embedded expanded steels and styrofoam into the cast panel. They can be made from wood 1 x 2's or steel tubing. If wood, they are best protected with paint to not warp too severely.

If steel, then galvanized would be best to resist rusting, although welding would need to be properly ventilated.

The assembly is pressed into the concrete after weighing and during the vibrating phase. The vibration facilitates sinking down the proper amount into the panel back.

Expanded Steels

Realizing expanded steel and one particular size is perfect for this application really makes the system work. There are six strands, each 1/10 th inch by 1/10th inch, net cross sectional area is 1/100th sq in. Six strands combine for 6/100ths of a square inch, and divide that by 144 for its area per square foot. These small dimensions over the four inch length of embedment give great strength, ductility, and minimal thermal bridging.

They can be further insulated and made corrosion proof by dipping them into a coating like Nansulate. Just another step that isn't very necessary as rust on steel forms its own protective coating.

Good quality concrete with effective vibration forms protection of long duration.

Cutting into strips

Expanded steel has a quality from its shaping that tends to make the "diamonds" or bonds, where the strands emanate from, to be curved. That prevents them from being able to be sheared length wise with a shear as razor sharp "stingers" are created. That is solved by using steel cutting abrasive blades and manually running a circular saw down the length. It's a bit tedious, but very doable.

A plasma cutter or water jet cutter can also be used, but are a bigger investment.

Cutting to individual pieces

Once the three diamond wide strips are cut length wise, a basic 14" steel cut off saw easily makes the individual pieces. The piece that goes through the insulation on the exterior panel uses a three diamond long steel, if an interior panel, then a two diamond long expanded steel. The point is to have them overlap in the center of the cast in place concrete fill thereby further strengthening the joinery by being embedded in concrete.

Move to pouring station

A sound materials handling plan saves untold work. Few things gain clarity without some experience. Depending on one's space availability, each solution may be unique to its environment. This step helps one visualize quite a bit. Mold components should be on carts designed for efficient stacking. Then large numbers of components can simply be wheeled into position. A clear path is needed to get molds into position for placement on the scale at the mixer discharge.

Concrete mixing

If mixing concrete one's self in lieu of ready mix delivery, the sequence of adding to the mixer is surprisingly important. One does want cement and fine aggregates sticking to the fins in the drum. It's best to add about 75% of the coarse aggregate (pea gravel), 75% of the cement, 80% of the water, and 20% of the sand in the initial charge. The coarse aggregate and water will help scrub the cement and sand to the inside of the mixer. Once all that is well mixed, the remainder of the materials can be added in a second charging. The concrete quality will be much better and in the end, cleaning the mixer will be easier.

Aggregates

An easy rule of thumb is 3 2 1 0.5. That adds up to 6.5 parts. The 1 is water, 2 is portland cement. This makes a 0.5 water cement ratio, the maximum for really good concrete. Next is 3, three parts of concrete sand, and 4 is four parts of pea gravel less than or equal to 3/8" in size. So for example, to make 500 pounds of concrete, one will divide 500 by 10 to get 50 pounds per single part. Then water will be 50 pounds, cement 100 pounds, sand 150 pounds, and gravel 200 pounds. If it takes more than 50 pounds of water to get a good flowing mix, then a water reducer or plasticizer can be used to achieve desired workability. Those are called admixtures and can be tricky to work with, requiring experimentation to get a proper result. In lieu of trying to do that, one can decrease the amounts of sand and gravel proportionately until a flowable mix is achieved. Trial mixes and records of what works best need to be kept to maintain a uniform mix design. Attention needs to be paid to the dryness or wetness of the sand and gravel and adjustments made accordingly. Keeping one's sand and gravel out of the weather can really help.

Fibers

Reinforcing steel and pva (poly vinyl acetate) fibers can impart greater toughness to concrete panels by simply adding them to the concrete mix. There is a steel fiber called "Helix" that is recognized by code and structural engineers. It would be a luxury to have effective means for testing the added tensile strength of concrete that these fibers would contribute.

Discharging

The method of discharge depends on the mixer uses. Relatively small amounts of concrete are used, so a slow discharge is helpful. Depositing concrete on a plate so it can be pulled off by experienced hands into the mold which is sitting on a scale. Precise weights per size of panel need to be maintained for uniformity of panel thickness. A platform scale with a conveniently mounted brightly lit weight indicator with a "tare" function is most helpful.

Move to vibrator

The correct weight of concrete is put into each mold. To keep things moving fast, upon filling, the mold is moved to the vibrating table. The vibrator needs to be plenty powerful enough and be controlled by a foot switch. The waffle assembly of styrofoam and the expanded steels is pushed into the concrete and secured on the sides of the mold.

Move filled mold

This seems basic but is actually a big deal. Filled molds are more heavy and should be handled by two people, although one can still do it. Stacking molds in racks can save space, but is more handling. It's a tradeoff depending on one's available space. The most ideal is keeping them on conveyors without needing to lift them at all. Rolling molds with concrete is child's play compared to carrying them.

Splines

Splines that fit into slots in the panel perimeter are a fundamental installation feature of CBS. They are a tight block against wind driven rain. They also align the panels for ease of installation. Horizontal splines can be laid in full lengths along the wall, while vertical splines are usually 15-1/2", fitting easily between the rows.

Installation

Installation is so dependent upon excellent preparation and execution. Flat level footing or slab is everything. Correcting that is a pain, but doable. Corner panels go in first to establish a plumb vertical surface to attach to. Every new panel is checked carefully to see the nature of what's going on. The learning curve can advance rapidly to the point of installing as fast as they can be handled. It's not easy at first, but with awareness and doing can quickly simplify.

Testing and Earthquake Performance

CBS has a main feature ductility greater than other building method. The relatively small wall panels are spline joined around the perimeter. This allows one panel to move independently of the others. The expanded steel joinery for each wall face is very ductile also. It can stretch, expand, and twist without damage. So each wall face can move independently also. A simple reinforced concrete column beam system being encased within the wall system will have lateral forces damped (absorbed) by the wall. The fact that the wall system works in concert with the interior cast in place structural system is synergetic for building survival. These are subjective insights and good enough reason to warrant a testing program to see if this could be a breakthrough technology for building longevity.

There are two system aspects addressed the the ACI 318 Concrete Building Code. One is for the compressive strength of the panels, the second for the shear strength of the embedded expanded steel. The wall panels can carry about 15,000 pounds per lineal foot. The calculations are available at concretebuildingsystem.com.

Main areas of investigation would be the performance difference between a minimal column beam cast in place compared with filling the entire cavity with concrete.

High Rise Application

High rise construction uses cast in place concrete columns and post tensioned slabs formed repeatedly. The walls are then attached to the framework. CBS could be a desirable backwards way of building. The walls could be installed first, and be used as stay in place forms for the column, slab, and beam pours. Deep spandrel beams would automatically be formed within the walls, adding stiffness to the structure and perhaps allowing thinner slabs. When multiplied over the entire building, significant savings could be realized.

Simplest system performance

Settlement of ground support over a long time can be virtually inevitable. Rigid masonry structures suffer significant cracking. The more ductility a building has, the more displacement it can effectively endure. The vertical and horizontal splined wall panel seams are a perfect absorbing mechanism to distribute movement over a dampening path of least resistance. This is ideal response.

Using onsite raw dirt, not needing any processing, can be fill for the wall cavity. Strategic columns and a top steel reinforced concrete cast in place bond beam (so many syllables, need to invent a word for that, more than a lintel). OSB board is dropped into the cavity vertically. It is automatically contained against the welded expanded steel, which are all on equal module. Six inches in from the vertical edge and 12" on center. Simple. The top of soil fill supports the bottom of the bond beam. Dry soil acts as both fireproof thermal mass and insulation. Whole earth insulation.

Wall paper print screen

Stencils are a powerful way to impart detailed design. Modular sizes facilitate stencil use anywhere. More detail in walls reminds one of the meticulous fine artwork of Persian and Islamic people. If art is applied to a wall panel while still horizontal, before assembly, adorning is easier without concern for "running" due to gravity.

Choices are between the simplest, utilizing the glass smooth surface to shine on its own. Then color is an option, followed by imparted design (stencils), from a mosaic approach to Mayan type details

Structural Engineer

Precasting

Concrete Contractor

Customer

Property

Owner Built

General Contractor


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Walter DeVore, Jr
970 663 0524
720 213 8044
Cell: 303 319 3764
concretebuildingsystem@gmail.com

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