How Strong is Lightweight Concrete? - Deflection Test Perlite, Vermiculite, Lava Rock, CSA Panels 

I now have molds ready-to-go here: manabouttools.com/product-category/abs-plastic-molds/

As a mechanical engineer I have some suggestions for your testing. You are not doing tensile testing. You are doing beam loading with a point load in the middle. With a 500 lb point load the center of the beam sees the full 500 lbs and each end sees 250 lbs (so the pins only see 1/2 the load). This is not a good simulation of the dirt or ice load in your garden bed. Try a distributed load by putting at least three layers of bricks across the full face of the the panel, offsetting the seams, and then add more load (bricks or bags or whatever) evenly across the top of that. You should get a failure at the pins and you may be able to reach the theoretical weight of your truck wheel. (If you do another truck test build two ramps so you actually get even loading, you had more than 1/2 the rear truck weight on that one elevated tire.) This will also eliminate the chance that tall pile of bricks might fall on your head when you bend down to look for cracks. Had me worried a couple of times. Thumbs up for an excellent and thorough series, who knew it would be this fascinating?

I can't tell you how much I appreciate the time and effort you've put into this series. You've saved hundreds or thousands of us from making inferior mixes, jumping to faulty conclusions, or spending hours re-creating your experiments when... now we can just appreciate your transparency and due diligence and learn with you. Frickin' liked and subbed. Thank you.

I incorrectly referred to this as a tensile test when it is actually a deflection test. Thanks to the engineers out there that caught my error.

There's a handful of RU-vidrs who's videos I enjoy watching because they are so well presented. You are definitely in that group. Great work! 👍👍

although you said its not scientific it still holds a lot of value to see the breaking points of each type of mixture. thanks for the hard work, I think you can skip the gym this week

We recently bought a house in an area with expansive soils and temperatures that drop below 0 (F). Your testing is very relevant to our situation and I am very grateful for the effort you are expending on this project. Thank you!

I appreciate how your mind works, Kent. I also appreciate you sharing your testing with us! I look forward to the aircrete panel tests.

Excellent work, thanks for taking all that time to do these tests, much appreciated.

I am fascinated with this series, so well presented, so fine and i love the fact that a how to video on concrete planters turn into a civil engineering class. super fan of all your work. thank you very much.

I really appreciate all the effort you went through to try and get some accurate measurements to all the tests. Great job! Loved the video.

That's a well thought out and presented video. And you had a great workout doing it!

A great test of the blocks, thanks for doing this. A lot of labor you endured doing this. It is appreciated, I was curious after reviewing your recipes and your process.

Kent, I've watched from part one through this one and you have given me many ideas on how to address a problem I have on my property. I'm pretty sure I will use a version of your design with a vermiculite mixture to rebuild a planter berm that I made years ago to minimize the occasional flooding from our creek. Thank you for sharing this.

Man you are amazing, keep with the good work, hughs from Brazil!

I liked all of your videos so far. Your narrations flow smoothly.

First and foremost - I love this series. It's going to be the basis for a big experimental project I'm starting. One point you might consider - you are deflecting with the steel on the inward side / radius where compression occurs. It would be stronger if the steel was place on the outward side where tension occurs. It might be interesting to take too similar panels and flip test them. I'd bet having the steel on the outward side will near double performance.

I am impressed with your creativity and dedication to this topic. You address a lot of the issues discussed in engineering literature regarding concrete mix design, placing, curing and testing. One thing in particular I would like to note is for your beam (simple point load) test the tension exists in the lower portion (exterior side) of the panel so the reinforcing would be more effective the if it was placed as close as possible to the exterior face. Additionally your pin locations didn't fail because there is very little tension there, mainly shear force.

Thank you for your hard working to get those results.

awesome man looking forward to the test with the aircrete hoping for at least half the weight great job with all of that lifting you just made me nervous when you stood up on those bags

Great video! Thank you for the great work you put into this

Thanks man. I learned a lot about lightweight concrete from your videos. The animations are really helpful.

I appreciate your efforts. Keep up the good works

First off - once again, GREAT information Kent! Love your passion about these panels and the amount of information you share about them. I would have loved to see you test one of the thin panels you made with the CSA Rapid Set Mortar Mix.

It looks greatly strong enough to endure power and time endlessly . Great test and result.

Man, this is exactly what I've been watching this series for! You Sir with your testing and scientific methodology is starting to encroach on Project Farm territory. Loving this channel. How about trying to make a drywall form?

Thanks for making this video again, I'm going to use your formula of concrete because I know it works ( TEST ) .please keep up the good work.

Watched til the end. Good stuff.

Great series of tests and info....I should add, you're an impressively strong dude.

Very well presented... The truck right in the beginning was definitely being optimistic, 🤪 but I love that you showed your whole process, including the parts that failed. I personally would've thought the shop press would be the best idea, but it turned out to be a complete bust. Keep up the great work, you saved me a ton of time not having to test these myself!

I don't know if you have an engineering background but your approach is right up there. I've made forms from your videos and I love them. I use the perlite mix and heavy gauge 4 in x 6 inch heavy gauge hog panel . I'm a retired general contractor and have poured in many different forms more than 7 million square feet of concrete in 20 yrs of work. Based on a 4 inch thickness. Love your videos and keep them coming. I have added tile mosaics and face brick for custom pieces to the face inserts. Well done! Rob

Very scrupulous work👏! Thank you

That was great I was very surprised at the strength of the panels. The press with a different gauge is the way to go. Many Thanks

I liked the content of your channel. I'm following from Brazil

THANK YOU FOR DOING ALL THAT WORK . i AM IMPRESSED .

Hi there. Okay, so first and foremost thank you for your service. You are not just a good person but a Healthcare worker during these trying times, and whilst dealing with all that you are still responsible and Diligent about not letting your YT peeps down. Thank You! Ok. So... I of course decided to use your form plans and use the CSA!! FML, of all the choices I chose the dumbest! 😂 Funny thing was I knew this was the lightest the other day when i finished my first batch and as I was showing my brother via FAceTime (keeping healthy social distancing) one is the 24 inch panels fell back and well... Cracked right in the center! 😂 It’s just me. Nothing I try from YT works out. 😉 Anyway. Thanks for the info and god bless man. Btw: you’re very handsome. Wifey is lucky!

Thank you for the post

Great man, so humble 🙏thx

Good work.

Found thie just in time, wood is crumbling on my raised beds and will be doing your forms, just deciding on the mix.

It's very interesting! Double like!

Top Notch. Thank you!

very well done!

Cool video - interesting. I've made various things with cement/perlite , which have come out variously good or not. I think the H2O/cement ratio was responsible for that. Aircrete panels next, that should be interesting.

Great video. I loved how you tested the samples. The only suggestion I would make is that you test each of them to the point of failure to determine the tensile strength of each sample. That way you know which is strongest, which is weakest, and can place them in order of strength. Great work by the way. I was going to use treated pine or hardwood sleepers but will be adopting your method for my garden beds instead. I can buy concrete sleepers here but they are square-ended and cannot be joined they way yours do with the stepped end and hole for reo bar. Brilliant mate, just brilliant.

Saw your recent video with the new molds. Very impressive. I would be interested to see you try modifying the placement of the reinforcement inside the mold. Positioning the reinforcement closer to the outside edge would increase the strength since that is the point of greatest tensile stress. Maybe two sticks of rebar on on opposite sides of your decorative inlay?

I plan on trying this for my garden, tired of wood rotting out. May try it for flower borders but may try half rounded molding for a fluted look. May try making curves by using shorter sections, 2 feet or less using understatement plywood fastened to a curved form. Would start filling in middle then covering with curved plywood to hold in place. Good presentation.

very useful info...thanks for sharing

My back hurts after watching! I live In Puerto Rico and these panels would be a hit for fencing.

I have thought, reinforce it with post-tensioning, but thinking about that now, that would be overkill. They are garden box panels, not bridge decks.

Horizontal concrete slabs will be subjected to pull from 2 ends, not pressure. So it needs a steel core for bearing. You put a lot of steel at the ends of concrete slabs, so the two ends have very good bearing while the middle is less steel and disjointed with the two ends, so the middle will be weak. But I think they can withstand nearly 200 kilograms of pressure, which is good enough for making pots. Thanks for sharing your good ideas. :)

Keep experimenting. We got massive cylinder crush pressure by adding perlite to our portland sand cement. Our goal was less is more as we didn't want any of the perlite touching other perlite granules (very subjective). Lawson Texas

The crack on the first test with bricks was caused by the uneven support of the wood at the bottom. The right one was shorter, which caused pressure to accumulate on its far edge where the crack formed.

Very cool. I thought for sure the light concrete would be weaker, but now I see that the fibers and steel add much needed toughness to the material. Jumping over to aircrete... surely that stuff will crumble!

Love finding out great content is Canadian when I see a Mastercraft of Powerfist tool in the video!

I like the panels wish I had time to make my own

Would you ever consider making a counter top out of one of these lightweight mixes? I especially like the csa and perlite mix and think that'd make a great coubtertop

Kent, you're doing great work. How long did you allow the panels to cure before running these tests? I believe that 28 days is the normal period for concrete to achieve its engineered strength.

An ounce of prevention is worth a pound of cure. To minimize the effect of frost pressure, line the inside of the planter to the top of the dirt level with a material that will compress when pushed against. This will act as an expansion joint to absorb the dirt’s expansion. Good drainage under the planter will cause less water and then less expansion.

You are awesome!

So, a couple things I'd be curious about, would be a variety of tests using fiberglass. Perhaps a test with continuous fiberglass rebar of various sizes, as well as a test using fiberglass insulation as a filler material, if such might be possible? Also, perhaps tests between aerocrete and standard concrete, also maybe using traditional methods vs using an ultrasonic vibration cleaner to try to even out the mold. Performance with a variety of aggregate grain sizes might also be an interesting test.

To enhance the resistance the wire mesh should be place closer to the face subject to tensile stress (placing the reinforce closer to the outside face give additional protection against corrosion). Also a third light weight material could be expanded polysterene particles. It will be interesting to have a table that shows the strenght related to the thickness and lenght of the panels. Excellent job so far.

So... they are plenty strong for most applications. Now you should do a beam strength test. That one you should be able to use your press for. I copied and modified your design and I have my first batch done and getting ready to cast second round today. They are a nice panel design!

Have you done any analysis on what is the outward pressure from moist freezing earth on the aircrete garden panels?

Would have been nice to see at the end of the video, or maybe after the aircrete one, a table of all the types of mixtures, with and without reinforcement grids / types, so it's easy to tell at the end of the video which one was better or at what levels they broke. Either way thanks for the info, love the videos.

thanks for the tests - was really hoping to see aircrete test

Your method of testing reminded me of my first physics class at college nearly 50 years ago. The professor used real world examples of the various principles-wedges, pendulums, etc. and was mesmerizing in his presentation. Thank you for showing these tests. While not "scientific" in the current modern sense they are practical and show the durability of these panels. And you saved yourself a gym membership! Two observations: 1. The size of the reinforcing and the density of the grid will affect the tensile stress the panel will handle. If there were for example 4 longitudinal rods versus 2 you will see higher loads. 2. The distance of the reinforcing from the neutral axis towards the tension surface will also increase the tensile loading possible. If the inset were half as deep and the reinforcing were closer to the inset you would see an increase in loading before failure, but the panel would not look as good. Ultimately I believe the failure of the panels will be from the freeze/thaw cycles and absorbed moisture and that will take years. Thank you for your videos. Take care, stay well and keep having a good time.

These have been very good videos - Thanks for sharing them. They are Scientific tests though, and you have certainly put some effort into them. If you are aware of a term "Point Loading", then this is really what you have been testing. Michael & Haidee below was correct about tension and compression, but that is why reinforcing is introduced into concrete. Point Loading (surface area of load) is where your experiments have differed from the surface contact of the car tyre, to using one timber with the press and then increasing the point load with two timbers and your bricks. With full surface contact load when used to retain soil and I think that these will stand up to much larger forces. Well done!!

Thank you for your videos! The testing is great and way over the top! Any of these planter box panels seem to be far superior to any commercial version. Even at a tenth of the demonstrated strength, they should last a millennium, unless you intend to make bridges with them in the future.

Thank you for these helpful videos. Do you have all the formulas and tests written down that you have performed. I am going to be building some dome concrete structures out in Arizona Im going to make the aircrete bricks myself and build the domes out of the blocks. They will be approximately be 16x4x4 blocks that im going to be making and it seems your compressions strength test for each block was about 500 which is well over what i need for the domes as it will get a mesh screen over the entire dome and plastered. Im now wondering if I should put two sticks of rebar into each block or if that will be too much, Definitely in the header windows for sure tho!! Any feedback would be great!! Thank you - Konstantin

Like your videos! Could you tell me where to get perlite material? Thank you!

It would be useful to know if fence posts made in a similar manner would be sufficiently resilient

Great channel! Thank you! Hot/Cold expansion and contraction in geographic locations must also be a factor? Without frost ground heaves concrete is very stable. Also damp soil is fine down south around your project. But up north, it's big trouble when it freezes (as we all know) Thank you for a great channel!

I would still love to see tensioned panels made. It would be the most expensive probably, but long-term peace of mind in extreme uses would be worth it.

Could you test a couple panels with the face facing up instead of down. It seems as if the reinforced wire mesh its a little more towards the back side, I think it will be stronger with the face up

A scale on one side of test system with a press or pulley would allow you to increase the load in s controlled manor while still allowing you to get a good estimation on the weight at which they failed.

This is probably obvious and intuitive, but the load calculation is about (b*(h^3))/12, where b=base and h=height. You'll notice that the strength is a LOT greater if you tested those beams in the standing up direction. It'd be a lot harder to do the test, but I guess it depends on what kinds of loads you expect the garden boxes to "see" during their lifetime. For example: if they're 2" x 8", laying down they'd have an area moment of (8 x (2^3))/12 or 5.33 if you stood them up, it'd be (2 x (8^3))/12 or 85.333 - note that this means that they could carry 16x the load in the standing up direction. If you were worried about loading in that direction, I'll bet you could maintain the same weight, but gain a lot of strength if you made "ribs" that ran the length of the form on the inside "soil side". You'd have to play around with the dimensions.

I would think that by adding even 2 - 3/8” rebar would be stronger than the he cattle panel. There is really not much steel even though it might hold the panel together better as a raised bed panel. Than a stress test. I really like your Chanel. I am thinking about lining a creek that flows through my twenty acres with some sort of a concrete panel that I can just add them as they are made sort of thing. I watching your tests closely to give me insight on how to build them and what mixes I might use. Thanks

"Well, thats a fail." You only learn through failure. Every "failed" test is a learning opportunity.

Cool video.👍 When you load the panels your greatest force, or moment, is at the middle of the beam, not at the pins (hence why they don't break there, as each pin is a split or ratio of the load). Also, your wire mesh is negligible or zero in contributing any kind of reinforcement bcuz of the tiny size AND placing it in the center of the panel, or the neutral axis. Reinforcement need to be placed in the bottom portion of the cross section for the steel to be in tension. So really you're just testing the concrete itself, and you're loading the panel sideways. 🙂 Yeah I am one of those engineers. But not the kind that drives trains. Lol.

You may find that dual reinforcing mesh separated as much as possible within the structure will give you the greatest strength. You might be able to use lighter gauge reinforcing mesh too.

Kent-- These are useful, interesting and fun videos. Thanks much-- My only objection was watching you climb on top of panels loaded a meter high with concrete bags. I was waiting for the panel to fail to watch you tumble off the pile. Would the load be terribly different if you were to sit on the bags instead of standing? Safety first, friend!

I would like see a test of one made without the steel reinforcement and maybe one using fibre glass additive

I am curious to how much more pressure they could take if you used actual rebar rather than the wire mesh, especially for the lighter panels.

Thanks for the thorough investigation of home made concrete garden bed / fence panels. The takeaway I got was, they are plenty strong enough as built and Portland cement is just fine for the job. If anyone needed more strength then a loop around the indent would greatly increase the force required to initiate a crack in the face. The unwanted side effect would be a greater risk of concrete cancer. So, all in all it ain't broken, so don't fix it. BTW, I like your simple modular design. When I made a concrete raised bed some years ago, I bolted my panels together. It works well, but your design is more versatile.

Weight of the truck tire was on the wood block as it passed over the pin, and as it rolled off the wood block and onto the concrete the load transitions from being a sheer load to being a bending moment that created the large tensile stress on the bottom surface, causing the panel to fail at the distance in from the end. Also of note, weight is not equal between the two rear wheels as it gets transferred once the suspension gets compressed by the difference in height, so closer to 2,000 lbs was applied, not 1275lbs. You could potentially measure the deflection of the truck suspension to get a more accurate measure of the applied load, and from the distance the concrete cracked at then be able to back calculate the tensile failure strength. The wire mesh in the middle of the panels should have little impact on this failure mode, but the addition of fiberglass to some of the panels will have a major impact on the ability to handle tensile loads on the bottom side of the panel.

Great videos. You are so thorough and succinct, you could be Data's (Star Trek Next Generation) brother. Too bad he wasn't. He would be able to give you all the stats and precisely exact strengths by mental calculation.

Possibly mixing in cut up high pound fishing line could be an easy way to improve tensile strength

Are you gong to test the thinner CSA panel you made? I modified your plans and am about to pour some that are 3’ inside dimension and 10” tall. I made them taller so I can line the bottom and make them self wicking.

if 1/4 of a ton is 500lbs you'd think that the pressure gauge would have registered at least a little bit. then again the point load vs distributed load of the concrete bags may have played a role? i've listened to/watched almost a dozen of your videos and i think they're great. the narration is really solid and suitable for any time of day/mood

been benging these things really really love them for sure the smaller single layer beds. how ever i want to go 24" tall (3 panels high) with my bed. Im worried these things would lean outwords because there only held upright by steal rods. so the bottom piece wont relocate but could flex outward. would you ever do a video into that since your moving a lot of dirt around your house and have the panels already? 36'' x 96'' x 24'' wall bowing/leaning and flexing test possible fix. 4x4 cement post that connects the pieces in the corners and between each panel. something that could be 1' /1' deep.

use a 2000 lbs hydraulic gauge from local parker dealer great video thanks you are a amzing

I wonder how much additional strength you would get if you did not have those panels put in for looks, also if it would make any difference if you tested the panels the other way with the indention up.

Your reinforcement grid, works on the other side of a pushing force. So, the reinforcement wire, should be closer to the bottom side, under the press. If your reinforcement is closer to the other side, you would get a very different result.

At what depth you position the steel wire / mesh determines how much weight the panels can hold, essentially you want the steel to take all the compressive load. the surface that you are putting the weights (loading surface) on is in compression, aka added reinforcement is only for stabilization. I can draw you a engineering free-body diagram if need be to clarify. P.S. yes i'm a mech engr & i bought your old original plans but modified them a bit..

I would like to see your result with a graphene additive to aircrete.

you should see if there strong enough for floor joist

Great videos and a lot of work, but I think you may have vastly underestimated the forces involved in ice formation in your tests. The upper limit if pressure required to prevent ice expansion completely is of the order of 1GPa (~10 atmospheres). Your truck parked on a couple of 2x4 segments may have hit 1MPa order of magnitude. The other limit - expansion - is about 1%. So you either have to expand by ~0.3% in each direction or survive ~1000 times your truck-test weight in pressure, or some compromise between the two extremes. In the real world, obviously lots of organic material in soil is compressible (as would be a stryrofoam lining to protect your plant's root from frost). So, it would be very interesting to see how they survive trough a winter when filled with soil and whether mulch etc, would be sufficient to prevent those catastrophic forces that ice can produce. New video in the spring?

Can you clarify if the "regular concrete" is standard bagged concrete or is it glass fiber-reinforced concrete? In the 2.0 video with the dimensional lumber forms I believe you used the fiber-reinforced concrete. I'd be curious to see if the GFR concrete was any stronger.

Enjoyed the video as well as the series, I plan on making quite a few of these and find this very informative. Not trying to be the safety nazi here, but please be careful when lifting like that. Lift with your legs, not your back and the twisting and lifting like that is a great way to hurt yourself. Just trying to make sure you can keep making vids like this one :-)