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Self Hardening Sandbags (W Cement?)


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Hi

The high rains have made the river gush cutting into the small road outside my property.

The OrBaTor have put a load of sandbags into the cut away section and I am told they will repair it when the level goes down.

however, it occurred to me:

After a year or two the woven polyester which makes up the sandbags will deteriorate in the sun. Then the sand will just wash away down the river.

Why not make up a weak dry mix of sand with cement?

One could mix up in a cement mixer dry, fill the bags, and let any river or rain water soak in and harden things up when it comes.

Sandbags form themsleves very nicely to the existing shape. No formwork or foundations. You could line the outside bends and have a permanent riverbank protection.

My questions:

What's the weakest/cheapest mixture which would be hard enough to do the job (my guess is not very hard by concrete standards)

I'm aware that a lean concrete mix has 10% cement. As price is critical, could one go lower? Much lower?

Would it be possible to just use fill soil with cement added?

What do the ingredients cost?

All comments welcome!

ps:

It's also occurred to me that this system could make a great cheap retaining abuttment to hold in a raised fill level I have to put on my land about 5 feet high. Cheap and saves any hassle with the fill sloping off onto the neighbour's land.

pps:

yes, the bags should be dark green or brown not white or orange to look ugly for years! But if necessary they could be made up very cheap.

pps:

more thoughts coming.

short lengths of thin re

bar could be stuck into a layer of bags before the next layer gets laid....and stabbed.....on top. Reinforcement.

Edited by cheeryble
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I'm a little surprised to see you using the accepted term (self-hardening sandbags) when you suggest that you do not understand the concept. Are you sure you don't know anything about this?

I was a British Royal Engineer for 22 years, and we had to use this principle in many projects around the world. A prime example was in Belize where we had to use this process to create the base for a temporary landing jetty.

Take a basic rice sack, and fill it with a pre-mix of 25% aggregate (grit to small stone level) 70% sand and 5% cement. Place them in a flemish bond (that's the typical Western bond which has bricks criss-crossed to create an appropriate bond), and then ensure that there is sufficient water added ro create the 'concrete' process. There has to be a drying process (i.e., a period withoutr rain), otherwise you will see salt leaching and the collapse of the integrity of the wall in a very short period of time.

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I'm a little surprised to see you using the accepted term (self-hardening sandbags) when you suggest that you do not understand the concept. Are you sure you don't know anything about this?

Hello George

I think I came up with the term myself this morning and looked it up and surprisingly found just one not very good reference via Google.

books.google.co.th/books?isbn=1597261432...

So maybe great minds think alike.

Strangely also I whilst I knew a lean mix was 10% cement I mentioned to a friend today that perhaps half would be enough as it is being hit by something soft not hard (my girlfriend sometimes complains about the same thing).

Seems to me a bag of cement is about 50 litres so if you said a sandbag contained the same as a cement bag you would get 20 self hardening bags for a bag of cement at about 150 baht so 7 or 8 baht each. Then sand/gravel I'm guessing 15 baht each, and a bag another few baht maybe totalling 20 to 30 baht each all in including my idea of stabbed-in thin rebar pieces.

My guesstimation is 7 bags to a sq metre so 14 for a 2 meter high run, something in the order of 500 baht per metre run including labour and my stabbed-in rebar idea and so on. Not too foul....and importantly it would be quick and simple to get on with compared to a "proper" concrete embankment.

In fact the orbator might provide at least the sandbagging and labour and I could pay for the cement and rebar (minimal) or perhaps they might realise they'll save money doing a permanent job themselves and offer me a knighthood.

I hadn't thought about salt leaching, knowing that if you leave a bag of concrete open even under shelter it will go off eventually, but take your point and a good spray would probably be appropriate.

Dark green or brown bags maybe difficult but really it would be worth ordering specially or having them made to avoid years of eyesore.

Thanks for the input....it certainly seems this is a generally unused idea and I'm also sure it would be appropriate for my earth retaining wall at the back side of my land especially as it will be invisible to anyone. Fill up the bags from a dry cement mixer I guess and some big snips for the rebar.

cheers Cheeryble

Edited by cheeryble
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This is getting better.

Thinking further every ouside bend where the banks are vulnerable has a matching inside bend where the material is deposited. So the sand costs (the highest) are labour only. In fact they were dredging or tidying the banks with a JCB recently nearby and selling the dirt on the side.

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"or perhaps they might realise they'll save money doing a permanent job themselves"

You are kidding right? Well at least you gave me a laugh. cool.gif

Now now think positive it's not much sweat.

They seem quite civilized at the office they may be all for it who knows stranger things have happened they must be bored stiff with complaints of this type and hardly any money in it.

If not manipulating them into doing this work will be a pleasure to formulate......and I think quite possible..

...and of course there's the standard Thai last resort.

I shall be taking samples of deposit from an "inside bend" tomorrow and checking various cement concentrations for hardness also compare using regular soft sand.

Edited by cheeryble
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  • 2 weeks later...

Fascinating news!

The riverbank in a very countrified section half a mile away from my land had collapsed right into the track section on it. I therefore took a closer look at the cut away section in front of my land. It seemed the river had bitten deeply into 5 metres but next to it looked strong. I climbed down. The edge felt hard. As I pulled away grass and so on I noticed a familiar shape, and here and there were the very small remains of white woven plastic. They had in fact shored up the riverbank some years ago using the very method I just "invented".....self hardening sandbags. (or maybe had filled the bags with wet mix). They had built up two steps each about three feet high of the "mortarbags". They were hard and strong and fit tightly together. This is great news for me as about 15 or 20m of the bend is already done. At worst another 15 or 20m needs doing and right now only 5 or 6. It didn't look ugly at all it was like old rock, blackened off but was half covered in vegetation anyway and the bags really had 99.9% gone. It amazes me this is not mentioned on the internet.

There goes my knighthood!

My question to concrete experts:

I know that lean concrete is 10% cement and George the Royal Engineer said, as I had hoped, 5% would do it. Now if I take the course sand from the inside bank buildup nearby it won't have aggregate in it. Is it the proportion of cement to sand that counts with the aggregate merely being a filler? In other words a 10% cement mix would actually have maybe 20% cement in ratio to the sand.....and unless i pay i will have only sand with the cement.

So......how much cement do i need if I have no aggregate?

Edited by cheeryble
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