I agree, but the problem with someone watching is the attempt to entertain while testing is really tuff to listen to. It would be much easier to digest if it was a heck of a lot simpler in delivery.
Finally someone does the test that I wanted to see and I wasn't surprised by the results since I was responsible for concrete pours in the commercial construction industry. I would never dry pour concrete for a home project.
Here in the UK, we have a product called "Ready To Use Postcrete" by Blue Circle, targeted at fencers. You dig the hole, pack the dry pre-mix around the fence post, and then add water. This method works well because it holds the post pre-set, allowing you to move on quickly. However, I'm guessing Blue Circle has formulated this mix specifically for this application, and I think some people mistakenly believe this is how you can lay concrete using standard cement. People often don't read labels. On the techical sheet its states "POSTCRETE may not be used for general concreting, screeds, mortar, grout or render. If a specified compressive strength is required, POSTCRETE should not be used." Maybe in the US, you have a similar product you can try as an experiment. Keep up the great work on your channel; it's fantastic !
We do have this in the states as well. I think it works because it just needs to compact itself densely enough to hold the post in. Denser than the dirt around it essentially. It doesn’t need wear resistance on the surface or a high amount of compressive strength as a unit. I would use it for fence posts, but always steer people away from “dry pouring” and concrete for anything exposed and especially anything structural. Its a lame diy trend aimed at people that dont know any better. I always tell people its easier to just mix it anyway, and it costs the same either way. And try to explain the benefits of using the concrete the way it is meant to be used.
Folks report excellent, lasting result using only packed gravel or crushed stone around fence posts. I wouldn't try that with a foundation wall, or even a curb for that matter. If the reason doesn't seem obvious, please try it. Make sure you post a video of the results for us.
We have the same stuff down here in Australia and it's definitely not meant for load-bearing/structural applications. I've pulled out some posts in the last year that were set in it and also some set in proper concrete. The concrete around the post mix posts just crumbled away as I pulled them out of the ground, while the proper concrete posts required the use of a demolition saw and sledge hammer+wedge to get off the posts after I'd pulled them out.
Absolutely great content! The volume of this video ranges between about 35 decibels to about 100 decibels. I feel sorry for any one trying to watch this wearing earbuds. Once again absolutely top notch content.
Wow, very comprehensive testing of a somewhat fringe practice! There is another reason dry pour is always going to be inferior: Cement powder loses MOST of its volume when you wet it. This means that dry pour will have very extensive voids just for that reason, as well as voids because you didn't vibrate it either.
@@TylerLey Alright!! More science! From fuzzy memory: If you take 2 cups of cement powder and mix it with 3/4 cup of water, it all fits into one cup. So this would be in the range of an 8x reduction in volume of cement dry-to-wet. That is a huge deal. Had this issue with the local batch plant, where they would reduce a yard of concrete by a cu ft when adding an extra sack of cement - but it really doesn't add any volume (just takes up voids), so that yard now becomes 26 cu ft (and costs more).
I watched a large amount of videos about dry pour concrete and noticed a major difference in method of pour. I think that their might be one more sample that you might want to test regarding strength of the concrete. 1 - People dry pour the concrete and level it without any compacting. 2 - The dry pour mix are compacted in layers in order to make sure that there are as little air molecules as possible. *** I think that this could potentially prove to be a much stronger sample during testing than what you have. My gut feel is that it would most probably still not be as strong as wet pour, but significantly higher strength than the dry pour sample you had.
Very good video, although the one flaw that makes this less than totally convincing: Your test cell is completely sealed at the bottom, which is very unrealistic. A real slab pour has all sorts of porous substances around it to allow air to escape without having to force upwards through the water. If someone could repeat this exact methodology but with some sort of porous stopper at the bottom of the acrylic, then we'd have an open and shut case.
I like that you showed a practical use case for dry pour. I wish you would have tested a few samples with a freeze/thaw cycles for the dry pour. I have used dry pour on fence posts more than ten years ago and the posts are still solid.
I do a lot of freeze thaw testing and I don't think the dry pour would do well in the "standard" freeze thaw test. If concrete stays dry then it is not damaged by freezing and thawing. If you went out and kept water on your fence post and then let it freeze then I think it would start to be damaged. If water does not pond around the fence post then that might be why you don't see any damage. We are doing a massive study on freeze thaw environments around the US. We have learned a ton about why concrete fails rapidly in some areas and not in others. We are writing the papers now. Videos should follow after that.
I recently reset some fence posts that had been pushed up by freezing thaw over many decades. They each had a small amount of concrete around them, maybe a 50lb bag at most, with the post protruding out the bottom. I left the concrete on the post since it was holding on to the post very well. I cleaned off all the dirt very well and where necessarily brushed to clean pockets androids in the surface. I then redug the holes making them about 8" larger than the existing concrete post slug and about 12" deeper as well. I did a modified dry pour in that I spray water as I pour it in the hole and then used a #5 rear to tamp the mix and get out air pockets as well as compress the mix. I added about 160lbs of concrete at each post. The last 6" gets a proper mix concrete with minimal water used. This has been my "method" for years including protective bollards. In the case of the bollards couple got tested and faired well. But I sure as hell would never dry pour a slab.
Have done dry pour a couple of times not on fence posts. Works for posts. Add an inch and wet it with a hose until about 4 or 5 inches thick then wet it hard and let it sit until it is soaked in. Then, run a plate compactor over it until it gets soupy top and finish it. Seems to work fairly well. But was just a quick fix sort of thing. Wet much better.
Here's something you could add on to your dry pour tests ! Add colloidal silicates, let it cure Add sodium, silicates, let it cure Measure again! I am very interest in that!
I am so glad you did this work, as I have been arguing this over an over again with my friends and neighbors. Now I can finally send them data to back up my assertion.
Loved your video, however I really want to know if you have any results for the misted or saturated dry mix concrete compressive strength as it ages? I can imagine that with the equal water content to wet mix, much of the water is lost to transpiration/evaporation, so there is not enough left to saturate the cement in the mix to allow for crystalline growth over time, but the saturated mix may differ. I also had a thought experiment - what if we used a hybrid method for a reasonable thickness slab of 2-3 inches: 1) Lay and level the premix concrete dry for ease (most people’s issue) 2) Fully saturate with water with misting without waiting for the top to form a crust (if we wait for a crust to form before saturation we define the volume of end product and rule out additional compaction or agitation) 3) Vibrate and tamp the formwork (using something like a sander attached to a 2x4) to compact the concrete, remove air gaps and encourage closer bonding between the aggregate and itself, as well as any rebar present. 4) Add more premix if needed if the casting compacts enough to be lower than the formwork. I think this would probably combine the ease of set up with the dry mix, and offset some of the bonding and hydration issues due to lack of agitation of the paste to ensure better coverage/coating of the aggregate than by capillary action alone.
Been waiting for you to weigh in on this topic. Good to see an ASTM C 39 test run on the dry pour. You confirmed my suspicions on poor bonding, poor paste quality, and poor durability. Would be interesting to do a follow up on Alite and Blite formation with dry pour. Thoroughly enjoy your videos.
In the South sometimes "readymix" concrete bags are placed in deep ruts on dirt driveways in the bag. Then with rains they solidify to be giant pavers so your vehicle does not bottom out. You try not to drive over them until hard. This crude hack actually works OK. If you make the bag conform to the valley of the rut then the cured bag has less unsupported voids below so they they last longer. ie concrete has about zero strength in tension. ;) If you have as source of water you can poke holes in the top so the bags keep moist longer so they cure better. With 3 expensive rapid set 25 buck bags I had left over(from a job) they cured to be insanely great. With the basic lost cost concrete Mix bags the results have a wide scatter.; great to broken since another drove up a private driveway thru the flagged area of bags When I have a water source I wet the rut if dry beforehand. Then place the bags to fill the ruts. Poke holes in the tops of the bags only and dump water on the bags and "TRY: :) to mix the water in the bag. Do this on a road to a rural cabin in the woods. Then rewet the bags with water hours later and keep the cure going. If you have the time and water supply you can add rebar and uses the rut as a concrete form and just properly mix it with a shovel and use part of the bags at the top to delay the crust curing too fast. ie do not offend the concrete curing Gods wrath!
I see people use bags of concrete in similar ways here in California, too. Typically farmers or people living in rural areas. Stacked concrete bag construction can be useful for a lot of things. I have seen a lot of people build up a driveway over a culvert using this technique. Also sometimes they build low retaining walls this way. Seems to work well.
When I first saw a couple of these dry pour videos, my thought was "Is this as strong as mixed concrete?" My guess was probably not because I figured there was no way to ensure that all the cement got evenly wet out. Some parts would get too much water and other parts wouldn't get enough. This was a great video that confirmed my suspicion.
I think the core reasoning behind dry pour is to avoid using a mixer. What about something like a "Mix in place" method? Something like where you pour the dry mix into the mould, add water, and then maybe agitate and stir with a metal rake or something equivalent? How would that compare to something like a traditional wet mix?
Good luck. It's hard enough to mix in place like in a wheelbarrow. After doing 2 dry pours at my house, there's no way I'd wet mix in place in the form itself, that would be more work that people are trying to avoid. I actually have walkway slabs next to each other both dry and wet poured that's been thru 2 years of freezing. Both have held up great. For walkways or low load projects, dry pour works fine. The only difference at my place is appearance basically.
Doing that works fine in a post hole but doesn't really work in most applications. It still leaves dry pockets and it pulls dirt/mud/debris into the concrete mix.
Fence posts only...somtimes. Not having a way of mixing is the only advantage of this drymix over wet. You can get superior finishes and compaction with wet mix. I've watched off gridders in stunned amazement making more work for themselves with dry mix and feeling so great about it at sunset, still spraying, when they could have finished the same job by morning tea with wet mix and had the rest of the day off to do something else.
Setting fence posts in concrete is setting them in a cup to hold water and rot them out later. Set fence posts by tamping the rocks and dirt that came out of the hole back in, that is all it takes. No water or imported materials needed.
@@nspro931 yes, tamping in the fence post is perfectly fine if done correctly. Concrete provides a reasonably predictable outcome. When concrete is used to set posts, the bottom of the post sits on a permeable layer first and the concrete poured over tat and around the post provides stability. The top of the concrete should be crowned for drainage too. Not all soils are suited to tamping alone. Not all poles are fence posts. Directly driving posts is preferred in rural settings where soil type allows. Anyway, this is about dry mix V wet mix concrete not a fence post setting tutorial. I hear you on the rotten fence posts.
On wood privacy fences, where the posts last 10-15 years before rotting out, you might not want high-strength concrete that will be difficult to remove.
Great content. Because the air is going UP, it stands to reason that the more shallow the mold, there would be a slight increase in strength as you step downward
The further the air has to travel to get out of the mix, the more pronounced the air pockets have to be to release the air. The shorter the travel, the air pockets can and will be more constricted. If you did a compressive test of a 2-4 inch pour I guarantee the strength profile would NOT hit the PSI of WET MIX, but it should be closer than the 8 inch deep sample
Have you tried dry pour with adding water while adding the mix? Like dumping bags while water is spraying to minimize air channeling and hydrate the mix better without the need to mix?
Thank you so much for doing this. I have a lot more confidence in dry pour (for small projects) now after seeing this. I have a feeling there will be some movement in Big Bagged Concrete to incorporate additives to make dry pour more mainstream.
Another way I've seen dry-pour concrete used is around posts dug into the ground. When you dig the hole, put the post in the ground and fill the hole with dry concrete mix. This presumes there is enough water in the surrounding soil to hydrate the cement. I've seen this done often and have always wondered how strong that concrete mix gets.
I think this application works because the concrete isn't subjected to particularly high stresses, acting largely as a mass ballast and to increase the friction as the post is torqued out of the ground. The primary load is still transferred from the post to the soil since the post is placed in direct contact with the ground prior to packing dry concrete mix around it.
I have seen a fair bit of videos about dry pour and always understood it to be meant for low-load applications. Like the examples you mentioned and maybe fenceposts or floor for a shed, etc. I'm sure there are some people out there trying to make a driveway with dry pour and based on this video that seems like a bad idea. The "saturated" idea of the dry pour seemed to be 3x as strong as the "same water" dry pour you used for the majority of the tests. I would like to see the saturated method tested to see if it strengthens over time and if it bonds at all to the rebar. Thanks again for taking the time to make this video it was very educational and you do a great job keeping attention.
It worked great for my shed base. 3 years and no cracks. I live in a cold climate too. Would I use it for my house foundation? No, but for most little projects it makes a lot of sense. I wet the soil before I poured the concrete bags into the form.
Despite the... concrete info... put out in this video, there are people who will still argue that dry pour is just as good as wet pour. I actually didn't need this video to tell me dry pour was garbage, but now when i am doing a project and the customer or my friend asks why we can't do dry pour, i can just point them to this video. The why is much easier to explain now, thank you. I always knew, but now i know!
Makes sense, but got me curious: What if you'd flood *and* vibrate the crap out of the dry pour? Should help reduce the air channels to the absolute minimum. Also, could the poor bonding to the rebar be partially that the dry pour was so weak the rebar was gouging out a channel due to the lateral force pulling it along, and not only poor packing? (I'd imagine vibrating would help either way.)
I had to pour a 6' x 3.5' slab for a small garden shed by myself, with only a shovel and a small wobbly old wheelbarrow, and I was not looking forward to all that rushed stress mixing work pain. So I tried this sort of hybrid method I guess you could say, where I wet the aggregate base, then dumped the bags into the form dry, and added water as normal, and mixed it in place, as best as I could. I thought it would save time before the cure started. I don't know if it did. It was a real pain in the ass dealing with the wire mesh, I think I might have deided to take it out to mix the bottom, and then tried my best to put it back in at proper depth. Overall I know I didn't get the same level of mixing I would normally get, and I'm not sure if I broke any bonds that were starting to form due to the kinda drawn-out process. After 7 days in shade with very irregular misting (oops) when the forms were removed, the sides had some visible signs of needing more vibration or maybe my mix was a little dry, but so far 2 years on, it has been totally fine, through two freeze-thaw cycles and tons of rain and saturated soil. This summer I did a "normal" wet mix method for some front steps and about 5' of pathway. I don't know how long that is going to last because again it was a small rickety wheelbarrow that could take 2 bags at a time max, and a shovel to mix a lot of concrete in a short amount of time...I guess we will see how it holds up! This stuff was in full afternoon sun although it was kept wet and covered for 4-5 days. Anyway, I'm rambling to no one who cares LOL cool story bro.
Great video and something to keep in mind - dry ppur is still pretty damn strong. 600-800 PSI, 800 pounds per inch is still pretty strong! Even dry pour may be 5-10X as strong as the soil it's sitting on or in. If you need maximum strength, you need to measure and mix properly. If you DON'T need 3,500 pounds per inch strength, dry pour may be fine for that project. Fence posts are the canonical example - the soil around the concrete will move before the concrete breaks. Another example - my air conditioners are on pads made of FOAM. Dry pour is 20X stronger than you need for an air conditioner pad.
It would be intriguing to investigate how raising the Portland cement content in the mixture influences the binding properties and overall strength. Since dry pour concrete is easy to use for those living in remote locations, incorporating Portland cement adds only a small expense for greater convenience.
I see what you are saying. That is an interesting idea and could help. I don't think it is that hard to get a mixer and make the material with that. Another option is hoe and water. Concrete has been poured in remote locations for decades.
By far the best video I have seen on this topic. It left only one question that I had wondered about unanswered. Dry mix in a bag usually is not well mixed. The aggregate and sand seem to settle out of the mix during transport. I'm curious if mixing it well while dry to redistribute the components `evenly would make a difference. I think dry mix is garbage, but as someone who has fumbled his way through finishing concrete I can see the allure. So if you're desperate for content you could do a supplement to this video and try it.
Great video and VERY interesting! What would happen if after wetting the dry pour you hit it with a plate vibratory compactor? This is a tool many small contractors have or a DIYer could rent. Also, concrete pavers are made this way, although I know they use a higher pressure than could be achieved with a portable vibrator. Could that significantly boost the compressive strength?
That is an interesting idea! I agree that the surfactant will lower the surface tension and cause the channels to be smaller after the air leaves. This could be another idea to try in future testing.
Great video! I don't care which side wins, I'm just enjoying the process! The surfactants idea would be interesting to see. About your set up specifically, the thing I was wondering - could there be another way to let out the air? You used a non-permeable barrier on the sides and bottom (which isn't normal for wet pour or dry pour - and you proved dry pour can't be done that way!) And it didn't stick to rebar, so would it stick to fiber reinforcement? Is it cheating to wet the rebar in some way before placement? Are the problems you're finding solvable with different techniques, cement mixes, or additives? The youtube algo wants to know!
I have had great success with dry pour but I do it differently, first I only add about an inch of dry concrete at a time, wetting the layer down until the water is absorbed then adding another inch or so of dry concrete, wetting that layer and so on until the form is filled, I also add a little bit of soap to the water and it really helps the water absorption,
one of my biggest issues with the dry pour is the lack of mixing of ingredients. While its safe to say a bag of concrete has all the ingredients, in the right proportions, there is no telling where those ingredients are in the bag. Those bags ride who knows how far on trucks & then get moved all around the store....ingrediants settle. If you dont mix it, theres no way to ensure proper distribution of cement & aggregates.
After watching (thumbs up) I'd suggest a different approach to dry pour: Pour half. Add rebar in a grid pattern, nestled in so it is covered. Lay pieces of plastic in the center of each grid square. Mist. The air will escape from the middles, away from the rebar. Remove the plastic bits, pour the rest of the dry mix, replace the plastic bits, and mist. Remove the bits and keep the surface oversaturated 😊
Even ACI requires rodding cylinders when testing to consolidate them and thats been mixing in the truck with midrange and the proper water to cement ratio. I knew this was basically compacted sub grade that can take the rain . But to each their own.
This is really good information. Did you test the 20+ day strength of the dry pour that got the maximum amount of water? It appear that it was the strongest of the dry pour methods, so I'm curious about how it ended up after the full cure time?
Another thing I'd like to see is mixing in leca balls into the concrete mix. I'd expect it to get weaker, but how much and with which percentage will it be significant. Leca balls will reduce the weight and improve the insulation, so that's the case I consider for using that in the mix.
Thanks! This is like low quality light weight aggregate. We are doing work on light weight aggregate now. I will post a video once it is finished. The strength loss is tied to the density of the concrete and the strength of the light weight aggregate. I don't think the leca balls are very strong but we could check.
This might be the best use case Ive heard. It would compact like abc and be at least as strong, most likely quite a but stronger. Surface density doesnt matter. Its common in my area where pavers are desired for the look for concrete to be used under the pavers in a high load application. This might be an upgrade over abc. My only problem is that with this application i can pump standard concrete, bull float, and leave. Id pay the extra money to not mess with the bags lol. In my area the readymix price equals the bag price at right around 1 yard. So might not even be a cost incentive. I could see it in certain areas though for sure
Thanks for the comment. This is a cool idea. People commonly use cement treated base for this application. You mix cement in with soil at a pretty low percentage and it can be compacted and smoothed. This would be less expensive then dry pour but you would save some labor by directly placing the dry pour.
I like that idea! Someone else asked about vacuuming the water in from the bottom. I think it should do much better. That would be a fun experiment to try.
@@TylerLey Similarly, I wonder what happens if you replicate a real world fence post scenario: * Dry mix surrounded by a porous material. (dirt) * Flooded with water. * That porous material is misted continually. * One to three times a day that porous material is flooded with water. This replicates someone setting up a sprinkler and it being in an area where it rains constantly. I know it still won't be as strong as mixed concrete, but for that situation does it really need to be?
People think they've figured out some novel way to do something that has literally been developed over the last 150 years with countless millions having been spent on researching and perfecting mix designs. Thank you for putting this out there.
I'm curious how this relates to the findings researchers had when they analyzed the ancient roman/greek concrete structures. If I recall, they theorized that their wet concrete was mixed somewhat clumpy (not well mixed with clumps of dry cement) when poured. The dry cement (lime?) would eventually activate when small cracks occurred over time and thus become "self-healing". The result was concrete that would last thousands of years. Based on this video, I would guess that the ancient concrete probably had poor load strength.
Great info. The dry pour advocate I know is claiming it allows self healing. I believe it stems from a misunderstanding of the news articles that refer to the papers from the research on Roman concrete. In particular “Hot mixing: Mechanistic insights into the durability of ancient Roman concrete” The claim was made that crack formation would allow better water penetration over time. There’s some flaws in this argument and it’s also still limited to the ultimate strength of wet mix concrete.
ouch, with that PSI there goes my thinking about making a dry pour car pad, I think jack stands might punch right through the concrete. I want more safe, not less haha
Great video. What if you added the water to the cylinder first? Also, do you think mixing the dry-pour in the dry state would be beneficial? Is it possible that the components get stratified in the bag and need to be mixed back up?
Interesting video Id be interested to see if doing something like tamping or some other way of manipulateing the concrete while in the form after you wet concrete would effect the strength. I mean its still not going do be as good as wet mixed concrete but it would be interesting to see if it improves strength by 10-20%.
It'd be neat to develop a recipe that does work well as a dry pour. I wonder if superplasticizer would improve the permeation. I wonder if hammered cellulose would improve it.
I'm planning a dry pour to level a sloped floor. Wet mixing might not give me enough time to work out the level as I'll be working alone. One particular thing we do here in india is we stamp on the dry pour during misting to remove air pockets; second thing is I'm planning to mist it with water & SBR in 1:1 ratio. Hope it works...
Did you try a dry pour sample in a vacuum chamber? It might be a way to test the hypothesis that air returning to the surface is she causes the weakness as you could theoretically achieve complete saturation. If still performs less well then there may also be other factors at play.
Thanks so much for this video! It would be great if you or your students could do a video where you give instructions for maximizing the strength of a dry pour concrete slab given your expertise. In essence, is there a way to get to 2000-3000 psi with dry pour (the recommended psi for concrete patios)? For example, if you started with high-strength concrete that's rated for 4000 psi, did a dry pour, and continuously added water for X days would it consistently reach 2000 psi, making it a reasonable substitute for wet mixing for a DIYer who wants to do a simple patio?
My initial guess before watching the video is it will depend on the thickness or depth of the concrete. I would think moisture can only penetrate so far, so would not fully cure the concrete if it's too thick.
Our work showed that it penetrated all the way through. There was some additional work where we measured the water content of the fresh concrete using the Phoenix at the top of the 4x8 cylinder and at the bottom and the water content was exactly the same. This showed that there was equal water at the bottom and the top of the cylinder. I didn't include it because the video was already really long. Maybe I will make a follow up and include it.
Tyler could you test a machine called the Mud Mixer to see if there is enough mixing to properly hydrate and form a good quality paste as the mixed concrete leaves the chute? I like the idea that the MM save time in mixing, but if the concrete is not as strong as concrete mixed in a rotary drum, then the time savings is not worth it.
Good idea! I would have to get one. I have done a lot of testing on volumetric mixers. They use augers to mix the concrete and they do a good job of mixing in a short period of time and so I think there is a chance that this machine would work well.
@@TylerLey Volumetric mixers are incredible machines, the ability to easily adjust the slump, strength, or 'recipe' on the fly, no worries of how far a jobsite is from the concrete plant, ability to do complex/ time consuming pours that are in backyards with limited access and having to use wheelbarrows or jump form silo construction with a skip bucket on a donkey winch. One difference the volumetric mixers have an auger that is 8 - 9 feet long with different shaped flights at certain locations in the mixer. If you could do some compression testing videos with the Mud Mixer that would be amazing.
I can see the obvious problem with dry mixing here is as the water penetrates the mixture, it'll create a gradient of moisture, creating uneven hydration. It also drag along the cement particles, again creating an uneven distribution of cement. You need to mix the cement to create a homogeneous structure.
I wonder how the dry placed concrete would perform if the water was slowly added at the bottom of the mold? Still looks like you'd have lots of voids, but at least you'd get all the air out.
Very interesting. Alot of theories that popped into my head when i started seeing dry pour videos pop up online turned out to be true. The air was interesting and not something i had originally thought about. What are your thoughts on surface performance of dry pour vs a hard troweled or troweled and then broomed standard concrete surface? My kneejerk reaction would be to think the unfinished surface would be much less dense, more open, more permeable to stuff that would hurt it, more prone to issues like spalling and scaling from freeze thaw and deicing in cold climates, and much less wear resistant over time. Im a finisher, not an engineer, but try to understand the inner working of concrete as well as i can in order to produce work at the highest possible level. Would definitely be interested to hear your thoughts on this.
Thanks! I think the surface would not be as stong as well finished concrete. The best way to get dry pour is to leave the water on the surface. This will cause a very high water to cement ratio at the surface. Also, the dry pour does not contain entrained air and so it will have freeze thaw and scaling issues if ice is applied to it and it freezes.
@@TylerLeyThanks for the reply, glad to know i was on the right track. Love the videos, you and Intelligent concrete have taught me a lot about the technical side of concrete. Its crazy that all this great info is free, and we appreciate it.
So the next question is: how strong does concrete get if you remove all that air with a vacuum pump? Does dry mix get still stronger? I know removing air from a slab, form, or hole is hard, but try capping the test cylinder and connecting a vacuum pump. Have plenty of standing water above the mix, so it invades the pores where air escapes.
I think it is both. The pictures are the failed concrete and so the concrete was damaged when it pulled out. I do think the dry pour didn't pack as well around the bar and that is why there is such a big difference between the two.
How well does the cylinder test result apply to the horizontal and shallow pad, do you think? There are much higher ratio of surface area for water absorption and more area for air to escape.
That is a good point. We did a 4x8 cylinder because that is the standard way to test the compressive strength of concrete. We could build modify molds for future testing. I agree that if the cylinder is not as tall then the air channel effect may not be as detrimental to the dry pour but I still think it is there because the air needs to escape as the water is added.
Great video! What I haven’t seen though, is someone that follows the Cajun country livin instructions to the letter. And I wonder if they end up filling more of those air gaps doing it their way? The explanation here suggests it’ll still be weaker, but I wonder if the factor can get reduced from 2.2x and if so, how much?
Awesome Video..... Q Wonder when they're bagging the cement. it's Not fully mixed together, but it's more in parts (Quality control) or after it's bagged then it's haled hundreds of miles away, the mix settles and separates. So I'd Love to see If you can/would pour full bag of dry cement into a mixer/lrg bowl then mix contents fully, then put in your clear tube & add the water and see if that will increase strength. I'm betting it would.
I’m not a fan of dry pour, but have you considered that dry pour is usually done atop a dirt/gravel base? Could the test results differ if the dry pour was atop a gravel base that allowed the excess water to go below the mix?
I don't think there is excess water. We found that the more water you added, the better the performance is. If you are going to dry pour concrete then I would add all the water you can to it.
@@TylerLey I was suggesting that it’s possible the results might have been better if above a base that could “store” some of the water and keep the moisture level high.
HI Tyler, I love your videos, they are very informative and interesting .. I used to do construction for most of my life all over the world, but now I am retired and do hobby investing to "kill the time" and keep my brain occupied, so I don;t get Alzheimers :) :) I wonder, if it would be possible to create video analyzing concrete industry in US/Americas like who are biggest producers, what causes booms and bust in concrete business, etc. Thank you
This is fantastic information, thank you Tyler. I do not think anybody that thinks rationally and has common sense thinks that dry pour is superior to wet mix concrete. People that dry pour concrete are just lazy and do not want to put in the work to mix concrete. I will only use wet pour concreted
I wonder if tamping the dry mix in layers of 3”-4” would help reduce voids. All the same, seems like a larger amount of effort just to make a viral method compare to the tried and tested
Interesting! i guess that the dry pour would cope with freeze/thaw cycles in the long run either. Atleast not in my area. To me it seems like dry pour = save a little time, initially when doing the project. But get a much weaker result and risc a shorter life-cycle of the finished product.
So can you (completely) fix the dry pour simply by adding the water from beneath? Slowly rising water level inside the container should push the air out of mix so there should be no dry channels left behind?
I would be interested in the results after 28 days. And maybe even a year. Maybe it takes longer to reach full strength and/or has other benefits that only manifest later on?
We did 28 d testing in the video. We saw no increase in strength over time. That was shown in a graph. We have some long term samples to see how they perform. Maybe we can do an update video.
@@TylerLey Sorry, my bad. I somehow missed that - I guess I wasn't enough attention for some reason. Would love to see a video on the long term samples.
A link to this video needs to be put in the comments of every dry pour concrete video.
Agreed. At least the people doing dry pour videos (the ones I’m watching at least) recognize they aren’t making anything of structural substance.
I agree, but the problem with someone watching is the attempt to entertain while testing is really tuff to listen to. It would be much easier to digest if it was a heck of a lot simpler in delivery.
Finally someone does the test that I wanted to see and I wasn't surprised by the results since I was responsible for concrete pours in the commercial construction industry. I would never dry pour concrete for a home project.
Here in the UK, we have a product called "Ready To Use Postcrete" by Blue Circle, targeted at fencers. You dig the hole, pack the dry pre-mix around the fence post, and then add water. This method works well because it holds the post pre-set, allowing you to move on quickly. However, I'm guessing Blue Circle has formulated this mix specifically for this application, and I think some people mistakenly believe this is how you can lay concrete using standard cement. People often don't read labels. On the techical sheet its states "POSTCRETE may not be used for general concreting,
screeds, mortar, grout or render. If a specified compressive strength is required, POSTCRETE should not be used." Maybe in the US, you have a similar product you can try as an experiment. Keep up the great work on your channel; it's fantastic !
That’s exactly what I was thinking. Although I thought you out the water in the hole first which would help with the air issues.
We do have this in the states as well. I think it works because it just needs to compact itself densely enough to hold the post in. Denser than the dirt around it essentially. It doesn’t need wear resistance on the surface or a high amount of compressive strength as a unit. I would use it for fence posts, but always steer people away from “dry pouring” and concrete for anything exposed and especially anything structural. Its a lame diy trend aimed at people that dont know any better. I always tell people its easier to just mix it anyway, and it costs the same either way. And try to explain the benefits of using the concrete the way it is meant to be used.
I agree with @markdourmert
I think this is find for fence posts but I would mix the material if I was making anything important.
Folks report excellent, lasting result using only packed gravel or crushed stone around fence posts. I wouldn't try that with a foundation wall, or even a curb for that matter. If the reason doesn't seem obvious, please try it. Make sure you post a video of the results for us.
We have the same stuff down here in Australia and it's definitely not meant for load-bearing/structural applications. I've pulled out some posts in the last year that were set in it and also some set in proper concrete. The concrete around the post mix posts just crumbled away as I pulled them out of the ground, while the proper concrete posts required the use of a demolition saw and sledge hammer+wedge to get off the posts after I'd pulled them out.
Absolutely great content! The volume of this video ranges between about 35 decibels to about 100 decibels. I feel sorry for any one trying to watch this wearing earbuds. Once again absolutely top notch content.
Wow, very comprehensive testing of a somewhat fringe practice! There is another reason dry pour is always going to be inferior: Cement powder loses MOST of its volume when you wet it. This means that dry pour will have very extensive voids just for that reason, as well as voids because you didn't vibrate it either.
huge voids because on extraordinarily high air entrapment.
Thanks for the comment. That is a good point. Let me do some calculations on how big of a deal that is. Take care!
@@TylerLey Alright!! More science! From fuzzy memory: If you take 2 cups of cement powder and mix it with 3/4 cup of water, it all fits into one cup. So this would be in the range of an 8x reduction in volume of cement dry-to-wet. That is a huge deal.
Had this issue with the local batch plant, where they would reduce a yard of concrete by a cu ft when adding an extra sack of cement - but it really doesn't add any volume (just takes up voids), so that yard now becomes 26 cu ft (and costs more).
@@happy2b4 that's why i do weight batching instead of volumetric batching.
what about when vibrating the dry pour when using a complete form? would have been easy to test in the examples in the video
Awesome video. Clears up myths I had heard about dry pour. Your energy is contagious. This made my day!
Thank you for bringing clarity to this subject
Thanks for watching!
Yet, as is often the case with real science. We now have more questions.
@@TylerLey Thanks for this info, Tyler! You are an authoritative source.
I watched a large amount of videos about dry pour concrete and noticed a major difference in method of pour. I think that their might be one more sample that you might want to test regarding strength of the concrete. 1 - People dry pour the concrete and level it without any compacting. 2 - The dry pour mix are compacted in layers in order to make sure that there are as little air molecules as possible. *** I think that this could potentially prove to be a much stronger sample during testing than what you have. My gut feel is that it would most probably still not be as strong as wet pour, but significantly higher strength than the dry pour sample you had.
I had my suspicions this was the case glad it was confirmed.
Fantastic information!! Very well explained and the photos were very helpful.
Thanks for watching!
Hopefully, this video will put an end to the dry pour you tubes that play over and over in my mind and keep me up at night.
Very good video, although the one flaw that makes this less than totally convincing: Your test cell is completely sealed at the bottom, which is very unrealistic. A real slab pour has all sorts of porous substances around it to allow air to escape without having to force upwards through the water. If someone could repeat this exact methodology but with some sort of porous stopper at the bottom of the acrylic, then we'd have an open and shut case.
I like that you showed a practical use case for dry pour. I wish you would have tested a few samples with a freeze/thaw cycles for the dry pour. I have used dry pour on fence posts more than ten years ago and the posts are still solid.
I do a lot of freeze thaw testing and I don't think the dry pour would do well in the "standard" freeze thaw test. If concrete stays dry then it is not damaged by freezing and thawing. If you went out and kept water on your fence post and then let it freeze then I think it would start to be damaged. If water does not pond around the fence post then that might be why you don't see any damage.
We are doing a massive study on freeze thaw environments around the US. We have learned a ton about why concrete fails rapidly in some areas and not in others. We are writing the papers now. Videos should follow after that.
I recently reset some fence posts that had been pushed up by freezing thaw over many decades. They each had a small amount of concrete around them, maybe a 50lb bag at most, with the post protruding out the bottom. I left the concrete on the post since it was holding on to the post very well. I cleaned off all the dirt very well and where necessarily brushed to clean pockets androids in the surface. I then redug the holes making them about 8" larger than the existing concrete post slug and about 12" deeper as well. I did a modified dry pour in that I spray water as I pour it in the hole and then used a #5 rear to tamp the mix and get out air pockets as well as compress the mix. I added about 160lbs of concrete at each post. The last 6" gets a proper mix concrete with minimal water used. This has been my "method" for years including protective bollards. In the case of the bollards couple got tested and faired well. But I sure as hell would never dry pour a slab.
@@TylerLey As someone in the northern US, im lolking forward to those freeze/thaw videos!
Have done dry pour a couple of times not on fence posts. Works for posts. Add an inch and wet it with a hose until about 4 or 5 inches thick then wet it hard and let it sit until it is soaked in. Then, run a plate compactor over it until it gets soupy top and finish it. Seems to work fairly well. But was just a quick fix sort of thing. Wet much better.
Here's something you could add on to your dry pour tests !
Add colloidal silicates, let it cure
Add sodium, silicates, let it cure
Measure again! I am very interest in that!
I am so glad you did this work, as I have been arguing this over an over again with my friends and neighbors. Now I can finally send them data to back up my assertion.
I'm glad someone is finally giving us some concrete numbers to the standard knowledge that wet pour is better than dry pour for strength.
It's cemented in my brain now, that's for sure.
Waiting for someone to do this and I expected these same results. Excellent work and thanks for doing this. 👏👏
Love the enthusiasm for your profession
A milion thanks from Transilvania! You answer so many questions and i learned sooooo much from you! Love your videos!
Hello ✌️
Loved your video, however I really want to know if you have any results for the misted or saturated dry mix concrete compressive strength as it ages?
I can imagine that with the equal water content to wet mix, much of the water is lost to transpiration/evaporation, so there is not enough left to saturate the cement in the mix to allow for crystalline growth over time, but the saturated mix may differ.
I also had a thought experiment - what if we used a hybrid method for a reasonable thickness slab of 2-3 inches:
1) Lay and level the premix concrete dry for ease (most people’s issue)
2) Fully saturate with water with misting without waiting for the top to form a crust (if we wait for a crust to form before saturation we define the volume of end product and rule out additional compaction or agitation)
3) Vibrate and tamp the formwork (using something like a sander attached to a 2x4) to compact the concrete, remove air gaps and encourage closer bonding between the aggregate and itself, as well as any rebar present.
4) Add more premix if needed if the casting compacts enough to be lower than the formwork.
I think this would probably combine the ease of set up with the dry mix, and offset some of the bonding and hydration issues due to lack of agitation of the paste to ensure better coverage/coating of the aggregate than by capillary action alone.
Been waiting for you to weigh in on this topic. Good to see an ASTM C 39 test run on the dry pour. You confirmed my suspicions on poor bonding, poor paste quality, and poor durability. Would be interesting to do a follow up on Alite and Blite formation with dry pour. Thoroughly enjoy your videos.
Thanks so much!
I agree that hydration product investigation would be cool. Take care!
In the South sometimes "readymix" concrete bags are placed in deep ruts on dirt driveways in the bag. Then with rains they solidify to be giant pavers so your vehicle does not bottom out.
You try not to drive over them until hard. This crude hack actually works OK.
If you make the bag conform to the valley of the rut then the cured bag has less unsupported voids below so they they last longer. ie concrete has about zero strength in tension. ;)
If you have as source of water you can poke holes in the top so the bags keep moist longer so they cure better.
With 3 expensive rapid set 25 buck bags I had left over(from a job) they cured to be insanely great.
With the basic lost cost concrete Mix bags the results have a wide scatter.;
great to broken since another drove up a private driveway thru the flagged area of bags
When I have a water source I wet the rut if dry beforehand. Then place the bags to fill the ruts. Poke holes in the tops of the bags only and dump water on the bags and "TRY: :) to mix the water in the bag. Do this on a road to a rural cabin in the woods. Then rewet the bags with water hours later and keep the cure going.
If you have the time and water supply you can add rebar and uses the rut as a concrete form and just properly mix it with a shovel and use part of the bags at the top to delay the crust curing too fast.
ie do not offend the concrete curing Gods wrath!
This sounds like a good application. I think mixing the concrete up may do even better.
I see people use bags of concrete in similar ways here in California, too. Typically farmers or people living in rural areas. Stacked concrete bag construction can be useful for a lot of things. I have seen a lot of people build up a driveway over a culvert using this technique. Also sometimes they build low retaining walls this way. Seems to work well.
When I first saw a couple of these dry pour videos, my thought was "Is this as strong as mixed concrete?" My guess was probably not because I figured there was no way to ensure that all the cement got evenly wet out. Some parts would get too much water and other parts wouldn't get enough. This was a great video that confirmed my suspicion.
I think the core reasoning behind dry pour is to avoid using a mixer. What about something like a "Mix in place" method? Something like where you pour the dry mix into the mould, add water, and then maybe agitate and stir with a metal rake or something equivalent? How would that compare to something like a traditional wet mix?
Good luck. It's hard enough to mix in place like in a wheelbarrow. After doing 2 dry pours at my house, there's no way I'd wet mix in place in the form itself, that would be more work that people are trying to avoid. I actually have walkway slabs next to each other both dry and wet poured that's been thru 2 years of freezing. Both have held up great. For walkways or low load projects, dry pour works fine. The only difference at my place is appearance basically.
Doing that works fine in a post hole but doesn't really work in most applications. It still leaves dry pockets and it pulls dirt/mud/debris into the concrete mix.
Fence posts only...somtimes.
Not having a way of mixing is the only advantage of this drymix over wet. You can get superior finishes and compaction with wet mix.
I've watched off gridders in stunned amazement making more work for themselves with dry mix and feeling so great about it at sunset, still spraying, when they could have finished the same job by morning tea with wet mix and had the rest of the day off to do something else.
And they pour right on the grass.
Setting fence posts in concrete is setting them in a cup to hold water and rot them out later. Set fence posts by tamping the rocks and dirt that came out of the hole back in, that is all it takes. No water or imported materials needed.
@@nspro931 yes, tamping in the fence post is perfectly fine if done correctly. Concrete provides a reasonably predictable outcome. When concrete is used to set posts, the bottom of the post sits on a permeable layer first and the concrete poured over tat and around the post provides stability. The top of the concrete should be crowned for drainage too. Not all soils are suited to tamping alone. Not all poles are fence posts.
Directly driving posts is preferred in rural settings where soil type allows.
Anyway, this is about dry mix V wet mix concrete not a fence post setting tutorial.
I hear you on the rotten fence posts.
not having a way to mix? shovel & wheel barrel ? hell, I've seen people make a mound on the ground & mix it with their feet....always a way.
Can you test a dry pour with concrete reinforcing fibers? 🤔 Nice video btw!
On wood privacy fences, where the posts last 10-15 years before rotting out, you might not want high-strength concrete that will be difficult to remove.
Great content. Because the air is going UP, it stands to reason that the more shallow the mold, there would be a slight increase in strength as you step downward
The further the air has to travel to get out of the mix, the more pronounced the air pockets have to be to release the air. The shorter the travel, the air pockets can and will be more constricted. If you did a compressive test of a 2-4 inch pour I guarantee the strength profile would NOT hit the PSI of WET MIX, but it should be closer than the 8 inch deep sample
Have you tried dry pour with adding water while adding the mix? Like dumping bags while water is spraying to minimize air channeling and hydrate the mix better without the need to mix?
Thank you so much for doing this. I have a lot more confidence in dry pour (for small projects) now after seeing this. I have a feeling there will be some movement in Big Bagged Concrete to incorporate additives to make dry pour more mainstream.
Thx! Interesting! Concrete needs proper vibration and mixture then!
Another way I've seen dry-pour concrete used is around posts dug into the ground. When you dig the hole, put the post in the ground and fill the hole with dry concrete mix. This presumes there is enough water in the surrounding soil to hydrate the cement. I've seen this done often and have always wondered how strong that concrete mix gets.
I think this application works because the concrete isn't subjected to particularly high stresses, acting largely as a mass ballast and to increase the friction as the post is torqued out of the ground. The primary load is still transferred from the post to the soil since the post is placed in direct contact with the ground prior to packing dry concrete mix around it.
I agree with Maud!
Professor Ley, you never fail to impress.
Great Job, you are a credit to your school.
Thank you!
I have seen a fair bit of videos about dry pour and always understood it to be meant for low-load applications. Like the examples you mentioned and maybe fenceposts or floor for a shed, etc. I'm sure there are some people out there trying to make a driveway with dry pour and based on this video that seems like a bad idea. The "saturated" idea of the dry pour seemed to be 3x as strong as the "same water" dry pour you used for the majority of the tests. I would like to see the saturated method tested to see if it strengthens over time and if it bonds at all to the rebar. Thanks again for taking the time to make this video it was very educational and you do a great job keeping attention.
It worked great for my shed base. 3 years and no cracks. I live in a cold climate too. Would I use it for my house foundation? No, but for most little projects it makes a lot of sense.
I wet the soil before I poured the concrete bags into the form.
Conclusion: even the WORST MIXED concrete is better than dry pour concrete. Just mix it.
Despite the... concrete info... put out in this video, there are people who will still argue that dry pour is just as good as wet pour. I actually didn't need this video to tell me dry pour was garbage, but now when i am doing a project and the customer or my friend asks why we can't do dry pour, i can just point them to this video. The why is much easier to explain now, thank you. I always knew, but now i know!
Are you and your freaks…team publishing these results? Always love to follow up in more detail. Thanks!
Makes sense, but got me curious:
What if you'd flood *and* vibrate the crap out of the dry pour?
Should help reduce the air channels to the absolute minimum.
Also, could the poor bonding to the rebar be partially that the dry pour was so weak the rebar was gouging out a channel due to the lateral force pulling it along, and not only poor packing?
(I'd imagine vibrating would help either way.)
Great video, very accessible for the regular person.
I had to pour a 6' x 3.5' slab for a small garden shed by myself, with only a shovel and a small wobbly old wheelbarrow, and I was not looking forward to all that rushed stress mixing work pain. So I tried this sort of hybrid method I guess you could say, where I wet the aggregate base, then dumped the bags into the form dry, and added water as normal, and mixed it in place, as best as I could. I thought it would save time before the cure started. I don't know if it did. It was a real pain in the ass dealing with the wire mesh, I think I might have deided to take it out to mix the bottom, and then tried my best to put it back in at proper depth. Overall I know I didn't get the same level of mixing I would normally get, and I'm not sure if I broke any bonds that were starting to form due to the kinda drawn-out process. After 7 days in shade with very irregular misting (oops) when the forms were removed, the sides had some visible signs of needing more vibration or maybe my mix was a little dry, but so far 2 years on, it has been totally fine, through two freeze-thaw cycles and tons of rain and saturated soil. This summer I did a "normal" wet mix method for some front steps and about 5' of pathway. I don't know how long that is going to last because again it was a small rickety wheelbarrow that could take 2 bags at a time max, and a shovel to mix a lot of concrete in a short amount of time...I guess we will see how it holds up! This stuff was in full afternoon sun although it was kept wet and covered for 4-5 days. Anyway, I'm rambling to no one who cares LOL cool story bro.
Great video and something to keep in mind - dry ppur is still pretty damn strong. 600-800 PSI, 800 pounds per inch is still pretty strong! Even dry pour may be 5-10X as strong as the soil it's sitting on or in. If you need maximum strength, you need to measure and mix properly. If you DON'T need 3,500 pounds per inch strength, dry pour may be fine for that project. Fence posts are the canonical example - the soil around the concrete will move before the concrete breaks.
Another example - my air conditioners are on pads made of FOAM. Dry pour is 20X stronger than you need for an air conditioner pad.
It would be intriguing to investigate how raising the Portland cement
content in the mixture influences the binding properties and overall
strength. Since dry pour concrete is easy to use for those living in
remote locations, incorporating Portland cement adds only a small
expense for greater convenience.
I see what you are saying. That is an interesting idea and could help.
I don't think it is that hard to get a mixer and make the material with that. Another option is hoe and water. Concrete has been poured in remote locations for decades.
By far the best video I have seen on this topic. It left only one question that I had wondered about unanswered. Dry mix in a bag usually is not well mixed. The aggregate and sand seem to settle out of the mix during transport. I'm curious if mixing it well while dry to redistribute the components `evenly would make a difference. I think dry mix is garbage, but as someone who has fumbled his way through finishing concrete I can see the allure. So if you're desperate for content you could do a supplement to this video and try it.
Great video and VERY interesting! What would happen if after wetting the dry pour you hit it with a plate vibratory compactor? This is a tool many small contractors have or a DIYer could rent. Also, concrete pavers are made this way, although I know they use a higher pressure than could be achieved with a portable vibrator. Could that significantly boost the compressive strength?
The dust would be insane
No, you wet it first. No dust. I've done it.
Really awesome explanation!
Sounds like a bit of surfactant might make a big difference in the way air gets out of the concrete and change the air channel structure
That is an interesting idea! I agree that the surfactant will lower the surface tension and cause the channels to be smaller after the air leaves. This could be another idea to try in future testing.
@@TylerLey Wouldn't a concrete vibrator remove all of the air channels as well?
Great video! I don't care which side wins, I'm just enjoying the process! The surfactants idea would be interesting to see. About your set up specifically, the thing I was wondering - could there be another way to let out the air? You used a non-permeable barrier on the sides and bottom (which isn't normal for wet pour or dry pour - and you proved dry pour can't be done that way!) And it didn't stick to rebar, so would it stick to fiber reinforcement? Is it cheating to wet the rebar in some way before placement? Are the problems you're finding solvable with different techniques, cement mixes, or additives? The youtube algo wants to know!
Try adding water gel beads in between layers when laying down the concrete mix. That way it will release water to create a tighter bond.
I have had great success with dry pour but I do it differently, first I only add about an inch of dry concrete at a time, wetting the layer down until the water is absorbed then adding another inch or so of dry concrete, wetting that layer and so on until the form is filled, I also add a little bit of soap to the water and it really helps the water absorption,
I was thinking about doing every two inches. How long have you had your slab completed for? I was also going to tamp between lifts
one of my biggest issues with the dry pour is the lack of mixing of ingredients. While its safe to say a bag of concrete has all the ingredients, in the right proportions, there is no telling where those ingredients are in the bag. Those bags ride who knows how far on trucks & then get moved all around the store....ingrediants settle. If you dont mix it, theres no way to ensure proper distribution of cement & aggregates.
After watching (thumbs up) I'd suggest a different approach to dry pour:
Pour half. Add rebar in a grid pattern, nestled in so it is covered. Lay pieces of plastic in the center of each grid square. Mist.
The air will escape from the middles, away from the rebar.
Remove the plastic bits, pour the rest of the dry mix, replace the plastic bits, and mist. Remove the bits and keep the surface oversaturated
😊
Even ACI requires rodding cylinders when testing to consolidate them and thats been mixing in the truck with midrange and the proper water to cement ratio. I knew this was basically compacted sub grade that can take the rain . But to each their own.
This is really good information. Did you test the 20+ day strength of the dry pour that got the maximum amount of water? It appear that it was the strongest of the dry pour methods, so I'm curious about how it ended up after the full cure time?
Other tests I saw it say to use as little water as possible to make the wet mix for the strongest results. Just enough to make it workable
Another thing I'd like to see is mixing in leca balls into the concrete mix. I'd expect it to get weaker, but how much and with which percentage will it be significant.
Leca balls will reduce the weight and improve the insulation, so that's the case I consider for using that in the mix.
Thanks! This is like low quality light weight aggregate. We are doing work on light weight aggregate now. I will post a video once it is finished. The strength loss is tied to the density of the concrete and the strength of the light weight aggregate. I don't think the leca balls are very strong but we could check.
Thank you for reporting!
Thanks!
Dry pour might make a good base for DIY pavers or any low load temporary pad - it would be easy to bust up and re-use as fill.
This might be the best use case Ive heard. It would compact like abc and be at least as strong, most likely quite a but stronger. Surface density doesnt matter. Its common in my area where pavers are desired for the look for concrete to be used under the pavers in a high load application. This might be an upgrade over abc. My only problem is that with this application i can pump standard concrete, bull float, and leave. Id pay the extra money to not mess with the bags lol. In my area the readymix price equals the bag price at right around 1 yard. So might not even be a cost incentive. I could see it in certain areas though for sure
Thanks for the comment. This is a cool idea.
People commonly use cement treated base for this application. You mix cement in with soil at a pretty low percentage and it can be compacted and smoothed. This would be less expensive then dry pour but you would save some labor by directly placing the dry pour.
Now a question for curiosity alone , does the dry mix gets stronger if it is hydrated from the bottom? (no air channel created)
I like that idea! Someone else asked about vacuuming the water in from the bottom. I think it should do much better. That would be a fun experiment to try.
@@TylerLey Similarly, I wonder what happens if you replicate a real world fence post scenario:
* Dry mix surrounded by a porous material. (dirt)
* Flooded with water.
* That porous material is misted continually.
* One to three times a day that porous material is flooded with water.
This replicates someone setting up a sprinkler and it being in an area where it rains constantly.
I know it still won't be as strong as mixed concrete, but for that situation does it really need to be?
Also try splitting the concrete mix into fourths and the water into fifths, and pouring it into the cylinder like a multi layer sandwich.
People think they've figured out some novel way to do something that has literally been developed over the last 150 years with countless millions having been spent on researching and perfecting mix designs. Thank you for putting this out there.
I'm curious how this relates to the findings researchers had when they analyzed the ancient roman/greek concrete structures. If I recall, they theorized that their wet concrete was mixed somewhat clumpy (not well mixed with clumps of dry cement) when poured. The dry cement (lime?) would eventually activate when small cracks occurred over time and thus become "self-healing". The result was concrete that would last thousands of years. Based on this video, I would guess that the ancient concrete probably had poor load strength.
Great info.
The dry pour advocate I know is claiming it allows self healing. I believe it stems from a misunderstanding of the news articles that refer to the papers from the research on Roman concrete. In particular “Hot mixing: Mechanistic insights into the durability of ancient Roman concrete”
The claim was made that crack formation would allow better water penetration over time. There’s some flaws in this argument and it’s also still limited to the ultimate strength of wet mix concrete.
Hank you very much professor. Fantastic and useful video, thank you very much.
Thanks!
ouch, with that PSI there goes my thinking about making a dry pour car pad, I think jack stands might punch right through the concrete. I want more safe, not less haha
I agree that jack stands would put a lot of stress on the pad. Thanks for watching.
Great video. What if you added the water to the cylinder first? Also, do you think mixing the dry-pour in the dry state would be beneficial? Is it possible that the components get stratified in the bag and need to be mixed back up?
Interesting video Id be interested to see if doing something like tamping or some other way of manipulateing the concrete while in the form after you wet concrete would effect the strength. I mean its still not going do be as good as wet mixed concrete but it would be interesting to see if it improves strength by 10-20%.
Can you do a in depth video on air pour additives in concrete?
And the diffrens in ordinary cement and construction cement.
It'd be neat to develop a recipe that does work well as a dry pour. I wonder if superplasticizer would improve the permeation. I wonder if hammered cellulose would improve it.
I'm planning a dry pour to level a sloped floor. Wet mixing might not give me enough time to work out the level as I'll be working alone. One particular thing we do here in india is we stamp on the dry pour during misting to remove air pockets; second thing is I'm planning to mist it with water & SBR in 1:1 ratio. Hope it works...
Did you try a dry pour sample in a vacuum chamber? It might be a way to test the hypothesis that air returning to the surface is she causes the weakness as you could theoretically achieve complete saturation. If still performs less well then there may also be other factors at play.
Thanks so much for this video! It would be great if you or your students could do a video where you give instructions for maximizing the strength of a dry pour concrete slab given your expertise. In essence, is there a way to get to 2000-3000 psi with dry pour (the recommended psi for concrete patios)? For example, if you started with high-strength concrete that's rated for 4000 psi, did a dry pour, and continuously added water for X days would it consistently reach 2000 psi, making it a reasonable substitute for wet mixing for a DIYer who wants to do a simple patio?
I would like to see the wet-mix sample testing with and without vibration / de-gassification to see what % strength increase can be gained.
I'm going to do a wet dry pour. It would be good to do a test on it as a comparison.
My initial guess before watching the video is it will depend on the thickness or depth of the concrete. I would think moisture can only penetrate so far, so would not fully cure the concrete if it's too thick.
Our work showed that it penetrated all the way through.
There was some additional work where we measured the water content of the fresh concrete using the Phoenix at the top of the 4x8 cylinder and at the bottom and the water content was exactly the same. This showed that there was equal water at the bottom and the top of the cylinder.
I didn't include it because the video was already really long. Maybe I will make a follow up and include it.
Awesome information, I have been wondering about this. Question: What if you fill it from the bottom?
Cool video. I kinda hated all the water sound effects, but it is a good video anyway.
Tyler could you test a machine called the Mud Mixer to see if there is enough mixing to properly hydrate and form a good quality paste as the mixed concrete leaves the chute? I like the idea that the MM save time in mixing, but if the concrete is not as strong as concrete mixed in a rotary drum, then the time savings is not worth it.
Good idea!
I would have to get one.
I have done a lot of testing on volumetric mixers. They use augers to mix the concrete and they do a good job of mixing in a short period of time and so I think there is a chance that this machine would work well.
@@TylerLey Volumetric mixers are incredible machines, the ability to easily adjust the slump, strength, or 'recipe' on the fly, no worries of how far a jobsite is from the concrete plant, ability to do complex/ time consuming pours that are in backyards with limited access and having to use wheelbarrows or jump form silo construction with a skip bucket on a donkey winch. One difference the volumetric mixers have an auger that is 8 - 9 feet long with different shaped flights at certain locations in the mixer. If you could do some compression testing videos with the Mud Mixer that would be amazing.
I can see the obvious problem with dry mixing here is as the water penetrates the mixture, it'll create a gradient of moisture, creating uneven hydration. It also drag along the cement particles, again creating an uneven distribution of cement. You need to mix the cement to create a homogeneous structure.
I wonder how the dry placed concrete would perform if the water was slowly added at the bottom of the mold? Still looks like you'd have lots of voids, but at least you'd get all the air out.
Very interesting. Alot of theories that popped into my head when i started seeing dry pour videos pop up online turned out to be true. The air was interesting and not something i had originally thought about. What are your thoughts on surface performance of dry pour vs a hard troweled or troweled and then broomed standard concrete surface? My kneejerk reaction would be to think the unfinished surface would be much less dense, more open, more permeable to stuff that would hurt it, more prone to issues like spalling and scaling from freeze thaw and deicing in cold climates, and much less wear resistant over time. Im a finisher, not an engineer, but try to understand the inner working of concrete as well as i can in order to produce work at the highest possible level. Would definitely be interested to hear your thoughts on this.
Thanks!
I think the surface would not be as stong as well finished concrete. The best way to get dry pour is to leave the water on the surface. This will cause a very high water to cement ratio at the surface. Also, the dry pour does not contain entrained air and so it will have freeze thaw and scaling issues if ice is applied to it and it freezes.
@@TylerLeyThanks for the reply, glad to know i was on the right track. Love the videos, you and Intelligent concrete have taught me a lot about the technical side of concrete. Its crazy that all this great info is free, and we appreciate it.
🙏👷👍 Respected Professor Ley , as usual great content. Would like to listen more on split beam test.
More split beam test coming soon
@@TylerLey thanks 👍👷🙏
So the next question is: how strong does concrete get if you remove all that air with a vacuum pump? Does dry mix get still stronger?
I know removing air from a slab, form, or hole is hard, but try capping the test cylinder and connecting a vacuum pump. Have plenty of standing water above the mix, so it invades the pores where air escapes.
Did the dry pour not get aroud the rebar or did it pull through making it smooth? Because it looks like a wider channel to me.
I think it is both. The pictures are the failed concrete and so the concrete was damaged when it pulled out. I do think the dry pour didn't pack as well around the bar and that is why there is such a big difference between the two.
How well does the cylinder test result apply to the horizontal and shallow pad, do you think? There are much higher ratio of surface area for water absorption and more area for air to escape.
That is a good point. We did a 4x8 cylinder because that is the standard way to test the compressive strength of concrete. We could build modify molds for future testing.
I agree that if the cylinder is not as tall then the air channel effect may not be as detrimental to the dry pour but I still think it is there because the air needs to escape as the water is added.
Great video! What I haven’t seen though, is someone that follows the Cajun country livin instructions to the letter. And I wonder if they end up filling more of those air gaps doing it their way? The explanation here suggests it’ll still be weaker, but I wonder if the factor can get reduced from 2.2x and if so, how much?
Awesome Video..... Q Wonder when they're bagging the cement. it's Not fully mixed together, but it's more in parts (Quality control) or after it's bagged then it's haled hundreds of miles away, the mix settles and separates.
So I'd Love to see If you can/would pour full bag of dry cement into a mixer/lrg bowl then mix contents fully, then put in your clear tube & add the water and see if that will increase strength. I'm betting it would.
Great video. Edited it yourself, didn't you.
I’m not a fan of dry pour, but have you considered that dry pour is usually done atop a dirt/gravel base? Could the test results differ if the dry pour was atop a gravel base that allowed the excess water to go below the mix?
I don't think there is excess water. We found that the more water you added, the better the performance is. If you are going to dry pour concrete then I would add all the water you can to it.
@@TylerLey I was suggesting that it’s possible the results might have been better if above a base that could “store” some of the water and keep the moisture level high.
Your testing is cool, but i still wonder how the container changed it. i think it might be different if you used a cardboard tube on top of gravel
HI Tyler, I love your videos, they are very informative and interesting .. I used to do construction for most of my life all over the world, but now I am retired and do hobby investing to "kill the time" and keep my brain occupied, so I don;t get Alzheimers :) :) I wonder, if it would be possible to create video analyzing concrete industry in US/Americas like who are biggest producers, what causes booms and bust in concrete business, etc. Thank you
This is fantastic information, thank you Tyler. I do not think anybody that thinks rationally and has common sense thinks that dry pour is superior to wet mix concrete. People that dry pour concrete are just lazy and do not want to put in the work to mix concrete. I will only use wet pour concreted
Thanks for the note. I do think that dry pour could have its place in some applications but I would be careful where I used it.
U still down to talk on a podcast
Imagine how bad the dry pour would look in northern areas with lots of freeze/thaw cycles in a typical year.
I wonder if tamping the dry mix in layers of 3”-4” would help reduce voids. All the same, seems like a larger amount of effort just to make a viral method compare to the tried and tested
Interesting! i guess that the dry pour would cope with freeze/thaw cycles in the long run either. Atleast not in my area.
To me it seems like dry pour = save a little time, initially when doing the project. But get a much weaker result and risc a shorter life-cycle of the finished product.
So, what if you vacuumed the water in from the bottom? If what you say is true, that would solve the air channel issue. Right?
Good idea!
That should work and would be a good thing to try to prove the theory.
So can you (completely) fix the dry pour simply by adding the water from beneath? Slowly rising water level inside the container should push the air out of mix so there should be no dry channels left behind?
Can you do a video talking about basilisk healing agent additive?
I would be interested in the results after 28 days. And maybe even a year. Maybe it takes longer to reach full strength and/or has other benefits that only manifest later on?
We did 28 d testing in the video. We saw no increase in strength over time. That was shown in a graph. We have some long term samples to see how they perform. Maybe we can do an update video.
@@TylerLey Sorry, my bad. I somehow missed that - I guess I wasn't enough attention for some reason. Would love to see a video on the long term samples.
As a professor and engineer how many water sound effects do you use in your teachings??