Help Improve a Portable Cement Mixer for Haiti

Greetings everyone. You have to see this work to believe it. I have and it does.

Cretesheet.com

It doesn't get much cheaper or simpler.

Hope it helps.

I watched the video, and I have to say......................that concrete sure doesn't look like it's evenly mixed to me. It's a great idea for filling post holes and such. I don't think it's the answer for building structures though.

It takes fifty four (54) 60 pound bags or forty and a half (40.5) 80 pound bags of pre-mixed Sacrete to make one cubic yard which will cover 81 square feet at 4" thick.

It would be faster to take a kids tricycle, turn it upside down on it's seat and handlebars, lay a 50 gallon drum on the wheels and spin it using the pedals to mix cement in it.

You would have to dry mix it really well first. But yeah....would work at least as well as shovel and wheel barrow.

I would like to see one which uses eight men per side though.

90 rpm to mix concrete seems incredibly fast to me. The best one I ever used was only going 10 or 20 rpm. Wet concrete is thick like chunky molasses. It requires a lot less mixing than either brick mortar or the mortar for rock walls. (Just because of all the different sizes of material in concrete and how they grind against each other).

Garth - some HP investigation - as offered.

It seems it radically changes with method of mixing. I.e. the (green) batch machine in your link, opposed screw method, is 'up there' for hp/m³, whereas the angled drum is about as good (small) as it gets.

Your common angled drum mixer is 3.5 cft, or 0.1 m3 rated, and 10% below that 'delivered'.

"Industrial" (trades duty) 3.5 versions are ~1.2 HP = 1600 W, have broader paddles, so higher internal lift, so shorter mix times, all day duty.

"Domestic" of the same capacity, (slower rpm, narrower/less paddles) ~700 W

A practical hp base point would be say; 10% over 7000W/m3 = 7.7kW/m³ = 10.3 hp/m³ (or say 10 hp/yd³)

Taking a "we have time" and want 'low HP/m³' approach;

The angled drum 'scaled up' would seem the most 'tunable' to hp.

This one is 350 x 280 or ~ 1m³ rated x 0.8 delivered.

I'll let you guys mull on that a bit while I find some reasonable 'animal power' numbers.

I'm assuming all who saw the bicycle power link, that he was knackered despite it being 'slop'.

Continuing;

To avoid the usual 'super athlete' interjections, this links to a study of what I would consider a comparable 'work situation'.

For those not fond of reading, it relates food, to fuel, to work out.

For those only interested in the human 'bottom line' number;

"The human work capability is around 250Wh/day, so it takes four days' of hard labour to deliver only one kWh"

In the following animal, section (well worth the full read) 'bottom line';

A thing to remember, is work animals need both the disposition to work, and apparatus training investment, as well as higher calorie feed to make up for lost grazing time.

I'd more or less forget about common cows and horses and focus on buffalo

/oxen

They also have a more efficient digestive system than people or horses - and are less fussy.

I finally watched the bicycle video. I think the guy will overheat. But also he is going too quickly. As long is the mixer is turning, it is good enough. could he have a hub gear in the bike to slow it down as he gets tired? So maybe a hand crank on the direct line with a big gear on it, with 2 gears left and right of it will do it too. You put the hand crank on the direct line for top gear one, and on the one of the different sized gears beside it for half full and full. To go slower. You also have the option to adjust the angle of the mixer to make it easier or harder.

I want one for myself! I sometimes mix navvyjack in a wheelbarrow. It is pretty quick this way (a lot quicker than mixing on the ground because you are at the right height). I still think that mixing is not the problem. Batch ingredient control is the problem.

By the way electric mixers that do this are about 600 bux here. For decent long lasting ones. And you really have to have water under pressure to wash the insides properly. For 600 dollars you can get at least 6 barrows.

Another option is dirt homes. Here is an up to earthquake code one in Canada,

http://inhabitat.com/three-buildings-achieve-worlds-first-living-building-certification/certified-living-buildings-eco-sense-home-1/

signed off by all the engineers made from cob with pumice in the mix for insulation.

Lots of earth in Haiti. If it was sorted properly and ready-mix certified "cobdirt" was available in bulk, people could build directly. I see no reason why Cob, light clay (Straw and clay together) and reinforced concrete beams cannot be used in buildings.

Light clay is still used in Germany for some buildings and I believe it is coded.

http://www.networkearth.org/naturalbuilding/clay.html

I think people are continuing to ignore bigger factors. Cement is expensive, so if contractors can get away with using less, they will. There will always be human nature and side jobs.

Also, cement gets wet in the bag sometimes and goes off. How will that be dealt with?

Garth, wishing you well in your continued struggle.

On the farm, we had a manually operated mixer that was relatively small, but seemed very effective.

The bowl was similar to the 0.1cubic meter unit shown in post 34, but with no motor or drive at the rear. On the front of the bowl (where the concrete mix comes out) there was a 300mm handle that allowed a person to crank the bowl. The tilt of the bowl meant this was surprisingly easy.

The unit was built into a wheelbarrow frame. When the mix was finished it was tilted up and poured directly into the formwork.

With two operators working "tag team" one cranking the handle, one shovels the mix (and then rests in preparation to crank the handle for the next load). It's hard YAKA for a days work, but possible. (I'd rather mix 1 cubic m this way than to mix 0.1 cubic by shovels in a barrow.)

An arrangement with multiple teams could be matched to the size of the pour. Sampling and quality control would require an alternative strategy.

Greeting all,

I have to apologize for being so brief in the last post. I should have continued with a discussion about applications. A friend of mine has had good success with forming thin shell concrete domes using only fine aggregates in his mixes. I would hazard to say that this type of application may well be the most cost effective way of building hurricane proof single family homes in a hurry. It should certainly be worth further evaluation. Importing only the Portland cement should lend a significant cost advantage over most other conventional building methods. I have to confess that being a precast concrete producer may lend a certain bias to my thinking, but a rather objective evaluation process led me into the business. We all know the advantages of dome construction, and for building them I believe that concrete may be the cheapest non exotic material commonly available today.

Food for thought.

That introduces a different set of problems

this sort of dome would be considered a non-traditional design & be disqualified from funding [ & any real consideration] by both the government organizations & non government organizations. The final word is by USAid.

disaster relief is big business & dominated by a bunch of unelected bureaucrats, with no real oversight.

Perhaps we could harness the energy created by Mister Fuller's continuous rolling motion in his grave. That could help pay for the legion of lawyers and bureaucrats necessary to change the rules.

If you look up "binni shell" or similar, you should find similar methods have been used in Australia for some years to build school multipurpose halls and such, but they do require continuous supply of consistent quality concrete for construction which I believe would be the greater challenge.

I started to try to read all the postings but I just don't have the time now. Sorry if this is a repeat of another posting.

I have seen several shows where they try to duplicate how people moved large stones and did other things in the past that we are tempted to classify as impossible. One of the methods that sometimes works is to make a giant hamster cage style "treadmill drum". One or more people walk in it and rotate it. Since is is round they are climbing with every step. They are also only using their legs (most powerful muscle of their body). A bevel gear would be required to translate the rotary motion from horizontal to the mixer tub angle (about 45 deg). With a little bit of a gear ratio I would think a 2 or 3 man team could turn tubs of 1/2 a cubic meter of concrete.

Not very high tech, but that is the point.

I have seen pendulum designs used for water pumping that claim to be easier to use than a crank or lever design. Perhaps a pendulum could be used for cement mixing.

It could be as simple as a rotating cement drum with a ratchet attached to the center that has a long arm and a weight at the end that someone kicks.

It could also be more complex to make the swinging stroke more uniform, more just throwing the pendulum idea out there than the specific design.

If you can get hold of one of the cheap drum cement mixers from Harbor Freight like the one Kramarat has and take the motor off, weld on a handle from a boat trailer wench and go at it.

It doesn't matter how fast the drum turns, only how many times and if you put the water in first as you should, then add portland then the sand it will be easy enough for two guys to take turns and make a batch in 5-10 minutes.

http://www.newdawnengineering.com/website/brickandtile/mixer/

good one

I've mixed I don't know how many yards of good concrete in wheelbarrows over the years. It's the way fencemen do it.

Five shovel fulls of sand and gravel is laid down level in the wheel barrow. The same shovel is used to shake out over that evenly as possible a shovel full of portland cement. Another layer of sand and gravel, layer of cement. We filled it up to the top because we mixed our concrete for each hole and so we only mixed what was needed. We used a D handle shovel and there's a technique that has to be mastered to be able to do it all day long.

When I'm mixing full wheel barrows at a time I will only fill the the wheel barrow two thirds full. I still use a D handled shovel.

The biggest problem with this is too much water is often added. It's physically difficult to mix it properly and extra water makes it easier.

I have a nine cubic foot mixer. One of the terms to used to describe a nine cubic foot mixer is "sack mixer". That comes from the formula of putting in ten gallons of water, one sack of portland cement, and enough sand and gravel to make it right. Cut back on the water if the sand is wet, add a little if it's bone dry. This will give you a consistant three thousand psi mix. If I'm pouring a small slab or a foundation beam I will put in a sack and a half of cement.

The secret to a good consistant mix is the ratio of cement and water. It also makes it simpler on the poor souls feeding the sand and gravel into the mixer.

Another trick fencemen use is they order their material as "re-mix". If we're getting it from a batch plant we get it straight from the mixer without the water or cement. We pull the truck under the mixer at the batch plant where they fill the concrete mixer trucks. Only we get just the sand and gravel mixed and without the water or cment. If we get it at a materials yard they usually have it already for us. They take a front loader bucket of sand and a bucket of gravel and they mix it together with the tractor. The advantage of the re-mix is you eliminate some of the human element in putting even amounts of sand and gravel.

The most important ingredient in either method is the drill sergeant attitude when it comes to the finished product. They both involve hard work and that's something that has to be learned to be appreciated. I've found making someone responsible for the finished product and then either jumping on them like a hen on a bug when it's wrong or praising them when it's right works great.