Concrete Building System is transformative for quality, durability, economy, and simplicity for construction anything from small cabins to high rise office towers.
It is user friendly, with all the demands of precision being provided by a simple molding technique a virtual lifetime of development by me, Walt DeVore. I have had the rare combination of a college degree in Engineering, no responsibility of family, and a minimal overhead lifestyle that allowed me to serve this idea that grew and took me over. I have lived next to Continental Divide, when the granite quartz “spine” of the continent has “whispered” to me the need to do this.
Perimeter slot “splines” tiles together similar to tongue and groove.
No Paper Wrap
No Batt Insulation
No Drywall, hanging, taping, mudding, sanding, texturing, painting
No trim carpentry
Manual handling at only 14 pounds per square foot
Exterior tiles installed from interior eliminating scaffolding on outside
Hay bale, rammed earth, cob, and many “soil” based options from antiquity are greatly strengthened by leaving space between wall sections. These spaces can define a vertical concrete column from floor to ceiling that support a horizontal bond beam around the wall perimeter.
The partitionable interior wall cavity makes a simple process of adding plain dirt, sand, or gravel or whatever as a bulk fill. Dirt works fine as insulation and thermal mass. The main concern for an energy efficient wall is preventing air infiltration. This one factor is huge compared to R values. There’s no better way to stop infiltration than filling a volume on the inside.
Between the soil partitions that space is filled with cast in place concrete with a vertical rebar or two. The dirt fill is stopped how ever many inches from the top to support a cast in place horizontal bond beam.
The most high powered use is a stay in place form for cast in place concrete with rigid insulation (polyiso) against the exterior tile (on the inside of it). This wall is designed for maximum seismic (California Code) along with extra safety factor for the structural engineer of record. The reinforcement that will satisfy and give the most stringent performance are #5 (5/8″ diameter) rebar on 16″ centers, both horizontally and vertically.
Concrete is the heavy industrial solution to mega projects that need to serve for a long long time. The heaviest trucks on the road are concrete mixer trucks. They often need to deploy an extra axle to take weight at the limit of capacity and have one more place to support it. When one thinks of a concrete wall it may be seeing a “tilt up” slab cast on the ground and lifted upright with a crane. Big machinery being used at its capacity. That sure keeps the idea far away from the common mind.
I have had a concrete mixer that makes a lot of concrete compared to regular consumer mixers. I had no equipment to move it with, so it all fell upon my own muscle. I’m just a string bean skinny guy and the weight I needed to handle was and continues to be formidable. For survival, of course I’m going to obsess on how to make my life easier.
The easy all too obvious idea is lightweight concrete made with an “expanded pumice” that like popcorn it is more lightweight. But it’s a special energy intensive product and substantially more expensive. If it’s the only thing to do then one is stuck with it.
I next discovered what was called “cellular concrete”. That’s adding a foam, like shave cream” into the mix to poof it out so air is more of the volume and thus more lightweight. Once one is set up to make it, it’s inexpensive and seemingly a good way to go. But, and big but, actually two, the foam has a detergent quality that dissolves form release oil. The product won’t come out of the mold. What a hassle. I went all the up to chain saw bar oil and it worked some although it left dark stains.
And then finally, I got struck by an overdue “Eureka”! If I can’t work with concrete that weighs 40% less, use 40% less concrete. The first immediate advantage is the savings in the portland cement, the dry powdered glue that with water added becomes a bulk paste for gluing sand and gravel together. And, with the aggregate particles more smoothly round compared to the large surface area of poofy lightweight aggregate, one can use about half the amount of cement. That I can go with. But how to use less concrete?
Most building systems are a form of “post and beam” with minimal filler in between. Our oh so familiar “framing” with wood is classic. Vertical sticks on 16″ centers. When I see it I’m chilled by the fact it’s an optimal arrangement of kindling that when ignited will burn at a maximum rate. I’m too impressionable to be comfortable with that. It’s still fundamental.
So with the panel or tile, whatever you want to call it, being 2″ thick I felt a 2″ high beam felt nice and symmetrical. Add to that 2″ wide columns with a concrete web 1/2″ thick being monolithic with them. There is some very strong “composite” action going on.
You can see that going on here:
For a dry stack system the flatness and level of the slab or footing is critical of speed and ease of building. Concrete finishing is most important. For an amateur like myself. poor execution equals a rough start of shimming and grinding to get that first layer correct. It is avoided by having an experienced crew with proper equipment to complete a quality slab.
A great training boost and familiarization for concrete finishing can be found on Youtube.
The molds must be fast, easy, and above all, precise and uniform. I have had eight evolutions of mold construction. One thinks one is sure in the design stage, but use over time is the only way to know for sure. That hurdle has finally been cleared. This is why I’m now able to offer production with clear conscience and complete confidence. Many “eureka” insights have accumulated over 35 years.
The final piece of the puzzle is knowing what their containment strength is. How high or deep can a concrete pour be without exceeding the bursting strength of the tiles? That’s in process right now, constructing bladders to inflate within the wall cavity to simulate concrete pressure. That tensile strength stress will exceed any other future force. The goal is to pour ten feet of concrete and have containment of 1500 pounds per square foot.
A ten feet height of concrete weighing a most dense of 150 pounds per cubic foot will exert 1,500 pounds of force at its bottom. Divide that by 144 square inches in a square foot and the psi force equals 10.4. An inflated tire may be 30 psi. It’s an important perspective to embrace. Pounds per square inch are common in steel and concrete units. Pounds per square foot is common in wood framing.
A concrete blowout during placement is the worst that can happen. Ascertaining the capability of something new requires testing. The testing means so much. Finding the best concrete mix with all the available resources is not straight forward. Reinforcing fibers and now “mini rebars” of Helix steel fiber offer enhanced tensile strengths. Just how much needs to have destructive testing that the bladder expansion test will do.
Above is a spreadsheet image of the current inventory of molds.
On the live Google spreadsheet, all the numbers adjust according to the entered quantity.
Column A shows the panel (tile) dimensions in inches.
Column B is the quantity of molds per size.
Column C is the weight of concrete per tile. New technology may reduce this weight around 15%.
Column D is the weight of concrete each mold size consumes.
Column E is the square footage of each tile.
Column F shows the total square feet of tiles produced given the quantity for the size.
Column G is the number of expanded steels per tile size.
Column H is my perceived sales price per square foot for that size. This is subject to modification.
Column I is the projected revenue per tile size at that quantity.
Column J is the number of minutes per mold to fully process the tile.
Column K is the time in minutes to do all the tiles of that size.
Column N is how much floor space is needed for each tile size per total quantity.
N23 (1,041) is the square footage of floor space to store all the molds for curing.
By placing the filled molds on carts with casters, about 400 pounds of concrete plus mold weight per cart, they can easily be rolled and placed tight against each other for zero wasted space. At disassembly, they be rolled into the area for fast handling.
Lintels are used over door and window openings to span the opening by one foot on each side to maintain uniform spacing. They can also be used in walls to lend some patterning for a degree of mosaic effect.
The illustrations below show the front view, the blocking out with styrofoam, and the expanded steel on the back side, followed by the actual dimensions.
Dimensions have been slightly altered and will be covered elsewhere.
These tiles could be considered optional. The wall ends need to be enclosed to contain whatever goes into the cavity. These pieces continue the beveled edges and thickness for a whole system performance.
If one chooses not to reduce the opening by the two inch per side thickness, one can block off the wall ends with braced plywood and finish the opening with any technique of one’s choosing.
Using different elements can create stunning contrasts.
Stainless steel, thin exotic wood veneers, sheets of copper, strips of black and white wood can contribute to elegant juxtapositions.
For direct, straight forward, and economical completion, these frame tiles serve well.
They all have either #3 or #4 rebar top and bottom spanning the length. Even with that they need to be handled vertically to not bend the piece.
The expanded steels become embedded and locked while pouring the cast in place phase .
Assuring perfectly square keeps installation fast and smooth.
With those steels sticking out the back, how does one store and ship the tiles?
The bonus of expanded steel is its ductility. They are simply bent down by foot leverage, and they stack nicely. Pieces of two inch polyiso provide spacing.
When time to use, the steels are simply bent back to vertical.
Concrete quality and consistency is critical. The system “tiles” will perform indefinitely through climate extremes. The employed concrete will have the longest return on investment of any construction option.
This is the first “wet cast” concrete modular system. Traditional blocks and mortar with its dry cast surface roughness and skilled block laying necessity now have an alternative. My system, at only 15 pounds per square foot, is unskilled user friendly.
A simple 3 : 2 : 1 mix design is used. That is 3 parts quarter inch pea gravel, 2 parts sand, and 1 part cement. The strength determining water cement ratio is under 0.5.
The first look is at the tensile or shear (punching) strength. The most conservative equation is 2 x sqrt f’c x perimeter(bo) x depth. Looking at one square inch to match the standard strength unit psi, one has a 4″ perimeter and depth of 1/2″. So that term is 2. Use a conservative strength reduction factor of 0.85. Although we will use a 4,000 psi concrete, let’s assume a 3,000 psi concrete. The square root of 3,000 is 54.77. One square inch of 3,000 psi concrete has a punching shear strength of 0.85 x 2 x 54.77 x 4 x 0.5 inch thickness = 186.22 psi.
The force of ten feet head of concrete at 1,500 pounds per square foot is 1,500 / 144 = 10.42 pounds per square inch.
A most important characteristic for precast concrete is the consistency in the casting environment, especially regarding temperature and humidity. Structural strength is only as strong as the weakest member.
What about the compressive strength? I believe ACI 318 equation 22-14 for non reinforced precast concrete is pertinent.
There is a uniform structural geometry to all the tiles. You see from the tile illustrations above that this it:
There are 12 square inches in the cross section, which is Ag, use 4,000 psi for f’c, the concrete strength, lc the length is 12 inches, and h, the tile height, is 16″.
The formula becomes:
0.45 x 4,000 x 12 x [1 – (12/(32 x 16)^2] = 21,600 x (1 – 0.0005) = 21,600 x .9995 = 16,200 pounds. The 0.85 phi factor of equation (22-3) reduces it to 13,770 pounds per foot. So that is what ACI 318 says is the load carry capability per foot of this wall system. That is one face, not counting the opposite face.
The above equation reduces the prescribed concrete strength (0.45) for a safety factor. Another safety factor is added by stating Pu is “factored” axial force. Factored usually means taking the “dead load”, the actual weight of the structure, and multiplying it by 1.4, increasing that weight 40%. Also added is the “live load”, added weight produced by people, furnishings, wind, and snow. To be “factored” those weights are multiplied by 1.7, increasing them 70%. To find perspective on the wall tile capability, let’s put this together.
Our code formula says we can support 16,200 pounds. This means that theoretically from calculations one could go 4.4 stories (13,770 / 3,083).
This is straight unbiased arithmetic. A structural engineer would say but this is a system and the interaction of the tiles being a 7 tile tall story may introduce other deflections to invalidate all of this. At least a perspective is introduced that shows this is a very stout system.
So far no structural engineer has felt confident to attribute even one pound of strength to the system. Fear of liability and litigation is paralyzing for innovation. It would be an easy task to introduce “destructive” testing to ascertain the real world performance.
Upon review, I see an error that would attribute even more strength. Just for the heck of it, let’s see what comes from it. The shown cross section is actually for 12 of the 16 inch panel height, because of the two 2″ “beams” at the top and bottom of the tile. So in the equation the term (32 x 16) becomes (32×12). Working that through we get 0.45 x 4,000 x 12 x [1 – (12/(32 x 12)]^2 = 18,562.5 pounds per foot. Apply the 0.85 strength reduction factor of phi Pn of (22-13) Code equation number and we end up with 15,778 pounds per foot length of tile. Our floor height ability is increased from 4.4 to 5.1.
This module is common throughout all the wall tiles and is the most conservative look at the wall tiles.
These numbers are without supplemental cast in place concrete within the wall cavity.
Insulated concrete forms are a prevalent alternative to wood. They are a reason that I neglected feeling the imperative for testing. It’s comparing styrofoam to concrete. If styrofoam works for containment, it’s obvious that concrete would work. The differences are huge.
ICF requires standard materials to attach to the styrofoam bracing. Siding or stucco or whatever are still necessary for the exterior, along with their vulnerabilities. Drywalling the interior is still big work to be done.
Concrete between sytrofoam is stifled from performing. It’s fireproof nature is compromised, thermal mass performance hindered, and radiant emanation is lost. ICF has left the status quo construction industry fairly intact.
Why squander money and performance when it’s not necessary?
Putting floor to ceiling windows in all the vertices assures the occupant of not seeing any closed corners. One's view of the wall can continue to the horizon.
It’s about time housing gets a new perspective. The norm is for neighbors to be virtually anonymous. With societal and climatic changes accelerating, neighbors should depend on each other like never before. Our current subdivision layout scheme certainly supports division. Lawns are a chemical repository, which, in the name of green, are toxic particularly to children and animals.
I have learned a fundamental truth from my life, and that is my life is no better than the life of my dog. Dog virtually sounds like a degrading word, except for the fact it is god backwards. The gold standard of a “fenced” backyard is woefully inadequate. The main source of problems with dogs is the fact they don’t get sufficient exercise. A happy dog is a tired and socialized dog. There needs to be ample space for people to meet and dogs to romp. I feel that space needs to be at a minimum the size of a football field.
There is a wonderful solution for this. Currently, the standard home / lot ratio is 0.4 . For example, say a football field is 120 yards long and 60 yards wide. That is 360 feet by 180 feet which equates to 64,800 square feet. If an average two story house has a footprint of 1,500 square feet the lot size minus the house would be 2,250 square feet. A block then would consist of 29 houses.These 29 houses would encircle the football field. Decisions to manage the space would be shared responsibility. There would be no “side yards” which is usually wasted space. The houses would share common walls for a complete enclosure. Concrete construction with total soundproofing will guarantee complete privacy and safety. Are there still people who yearn for a cooperative village lifestyle?
In true Columbo fashion, there is still one more thing. Natural energy systems are a vortex. That is a rotating circular motion. Maybe a reason why things have become so discordant is the orthogonal prevalence that we take as normal. Maybe natural energy gets thrown into chaos in a rectangular structure and that gradually permeates our psyche.
Perhaps the two most Nature attuned cultures are the Tibetans and Native Americans. They had round abodes. Round isn’t an attribute at this point of my system, but octagonal is very easy to do. Octagons offer great versatility in contiguous housing.
Contiguous housing may be a synonym for “townhomes” but in my opinion there is a big leap beyond that. I am a dog lover. My personal creed is that my life is no better than the life of my dog, my created external soul. A happy dog is a tired dog. Running and playing carefree is essential. Sadly, that is virtually impossible in most circumstances. A fenced yard is woefully inadequate. Dogs need at least the size of a football field to have decent environment. That is where contiguous housing comes in.
The key to friendly relations with neighbors is to have a common denominator that drew you in the first place. In my experience, dog parks are where one will find the nicest people who really care about their dogs, and their own exposure to fresh air and vitamin D.
When I’m visiting my partner in the “city” from my mountain sanctuary, it’s a fifteen mile drive to a dinky dog park. There is no other option despite massive acreage of agricultural land.
How to solve that.
It doesn’t need to be octagons, but just for an example, these are 36′ diameter octagons enclosing a football field area. In regular subdivisions, side yards and pretty much the entire “yard” are chemical laden minimal utility spaces facing streets that really only give separation. If the side yards were removed and all the space concentrated in the center, everyone would have plenty of safe space. People would know and be friendly for the common denominator of wanting this. The space could be everyone’s idea and responsibility to create a Nature preserve with gardening, labyrinths, picnic areas, one’s own consensual private space. Sports could flourish again. The former analog world can be somewhat reclaimed. Carl Jung in his autobiography stressed the need for “Reform by Retrogression”. We have outpaced our connection with our ancestral roots and need to reconnect. Relief from digital will aid our balance.
Ongoing Construction, More to Come. Call me at 303 949 5947 with any questions or desire to get engaged.