Replies

1. 
   Biloxiblues | Mar 17, 2006 04:05am | #1

   Way cool!! I wish I had the time to do something like that!

   I'm not a cement/mortar expert, but make sure you wash/rinse any "natural" aggregate before it's used in mix.  Especially if it's being used structurally.

   Post photos.  Would love to see how it evolves!

1. 
   user-125051 | Mar 17, 2006 04:36am | #6

   i understand organic matter in the mix is a no no, but how does one go about washing sand and gravel

1. 
   Biloxiblues | Mar 17, 2006 04:52am | #9

   This is out of my hood, But; Out on an island I'm venturing to guess you're in for a boat-load of manual labor.  Assuming you have well water, I'm picturing a portable mortar/cement mixer, a garden hose, and a pitcher of lime daqueries(sp).

    

   I still say you go for it!  I'll live vicariously through you my man!!

2. 
   brownbagg | Mar 17, 2006 04:06am | #2

   what psi do you want and how big are the rocks

   . 2+3=7
3. 
   dustinf | Mar 17, 2006 04:07am | #3

   I don't think you can use beach sand in concrete.

   I remember reading some where that they used to do that in Florida, and the concrete didn't cure properly. 

    

   Stop, drop, shut 'em down, open up shop. 

1. 
   user-125051 | Mar 17, 2006 04:32am | #5

   the sand and gravel is from up around the build site not the waterfront, the sand doesnt look too fine either

4. 
   zak | Mar 17, 2006 04:13am | #4

   1 part cement to 4 or 5 parts sand and gravel (roughly 50-50) is a good place to start.  When I've done this before in the backcountry it was quite a pain- often it looks like sand and gravel on top, and then once you start digging there are either big rocks or dirt.  Dirt/fine sand is no good for your mix.  As someone else mentioned, salt is another big no-no, so don't even think of using beach sand if your island is in the briny.

   zak

1. 
   user-125051 | Mar 17, 2006 04:38am | #7

   did you have sand and gravel seperate or was the 50/50 a guess while looking at the naturally ocurring mix?

1. 
   zak | Mar 17, 2006 04:46am | #8

   Just a guess, you'll have to assess how much strength and uniformity you need.  if you don't need too much, eyeballing it should be fine.  This is assuming you've mixed concrete quite a few times before and have a feel for what it should be like.

   zak

5. 
   DML | Mar 17, 2006 05:32am | #10

   Back in the early part of the century in San Francisco a lot of the concrete or morter used in foundations was made of sand that they bought in from the local beach  because it was local and easy to get.

   You can always tell which foundations they did this on because when we get to go and look at the stuff it crumbles and falls away in our hands. The other thing is when you see some part of the world that has had an earthquake and all the concrete buildings have fallen down - bad mix.

   I'm not a concrete expert but my gut tells me this would not be a good idea, and at very least you should make a batch up and have it properly tested by an independent inspector for strength before doing anything.

   I guess the island a little too far off shore for a boom pump?

    

1. 
   brownbagg | Mar 17, 2006 05:35am | #11

   the salt in the sand retards the concrete mix, so it never get its strength.. 2+3=7

2. 
   user-125051 | Mar 19, 2006 09:59pm | #18

   yeah unfortunatley the island is too far for a boom truck there have been a lot of good ideas posted on the board though

6. 
   junkhound | Mar 17, 2006 05:44am | #12

   You did not say how much experience you have had mixing in a small mixer.  If much experience at all, you probably hav a feel for what the sand grave mix should look and feel like. 

   If you have not done it before, I'd recommend you at least get one load of reclaim or graded sand gravel mix for concrete to have a basis for comparison. 

   BTW, poorly graded means rocks , gravel or sand with very uniform sizes, well graded means good for mixing concrete, somewhat different than the language commonly associated with 'grading' means.

   There are many texts with various mixes.  I'll assume you want to mix the sand and gravel just as you dig it up, which is called 'pit run'.  The only way you will know what you will get with this is to wash it (lotta water,  easiest wash cycle is a couple of tumble cycles thru the mixer and dump the 'dirty' water before any cement added, you definetely wnat to get rid of all clay)  Then cast yourself a cyclinder or block of tentative mix and let it cure, then see how wellit stands up to bashing with a sledge next to bashing a similar block made of sacrete mix.

   Depending on how it 'bashes' you may luck out or will want to either go with bigger sonsotubes or haul in graded mix.

7. 
   davidmeiland | Mar 17, 2006 06:19am | #13

   Is there no chance you can hire a landing barge and have readymix delivered, or maybe just proper sand and gravel? I think it's unlikely that the native material will made good concrete, and if you're going to put in all that work you're going to want good concrete.

8. 
   blue_eyed_devil | Mar 17, 2006 06:48am | #14

   I'd also be inclined to try to use the local materials. All sand and gravel comes from the earth and you may very well be sitting on perfect concrete materials.

   Take a bucket full to the local concrete supplier and ask their opinon of your mix.

   If you still have doubts, get a test done on some of your finished products.

   blue

    

9. 
   VAVince | Mar 17, 2006 02:58pm | #15

   Look up a local engineering testing company. Stop by and pick up a couple plastic test cylinders and do a sample mix washing the sand and gravel as stated by others. Fill the cylinders and leave on site till it cures. Have the eng. co. break test after 7 days and see what PSI you have. The cost to crack the cylinder for test is only $20 or so. The guys there will be able to give you lots of good advise!!

                             Good luck

10. 
    brownbagg | Mar 17, 2006 03:22pm | #16

    I repeat. If you tell what psi you want and how big the rocks are, I can give you the mix design.

    . 2+3=7
1. 
   user-125051 | Mar 19, 2006 09:41pm | #17

   the coarse aggregate is a mixture of sizes maybe 3/8ths to 3/4 i am going to oversize the sonotubes for cheap insurance too. i imagine 2000- 3000 should suffice. what is an average strength mix?

1. 
   PhilGam | Mar 19, 2006 10:18pm | #19

   I would also do some research on rammed earth. 12-18" thick walls done in lifts of 18-24" high using a slip form. The basic mix is a soil with (.3 clay & .7 sand) and 3-5 % portland cement by weight. The walls could be 2-4 ft. sections in place of sonotubes depending on your design. I would think sonotube construction would be tough, unless you're doing low to the ground work. 

2. 
   brownbagg | Mar 19, 2006 10:20pm | #20

   2000 lbs is a joke, that why house fall in3000lbs mix cement 338 lbs
   fly ash 85 lbs
   sand 1434 lbs
   stone 1650 lbs
   water 250 lbs entrained air 16.92 oz.for a pump mix cement 427 lbs
   fly ash 184 lbs
   sand 1721 lbs
   pea gravel 1200 lbs
   water 324 lbs entrained air 24.4 oz. 2+3=7

1. 
   user-125051 | Mar 21, 2006 03:49am | #24

   why the fly ash?  What about a smaller ratio like 1:2:3 or whatever the mix is.  Whats with 2+3=7?

1. 
   brownbagg | Mar 21, 2006 03:57am | #25

   fly ash is a by product of coal fire powerplant. It has the same cement property as portland cement. It also cools off the mix and makes the mix more workable. plus its free so it lower the cost of the mix. If you have no access to fly ash. replace with portland cement.. BOB thinks I,m an idiot

2. 
   user-125051 | Mar 21, 2006 04:18am | #26

   i dont think there are any coal powerplants in the area but thanks for the tip.

3. 
   Gabe | Mar 19, 2006 10:31pm | #21

   Before you do something that you will regret, take a pail full to your local soil testing company and have them test it for you. They will tell you the proper content and will give you a printout of the results for you.

   Bring it to a small ready mix plant and give the guy a couple of bucks and ask for his advice for a reasonable mix for your needs.

   No fuss no muss.

   If your sand is silty your mix will be ####.

   Gabe

11. 
    PhilGam | Mar 20, 2006 01:21am | #22

    Here's one link, google rammed earth walls.

    http://www.rammedearthworks.com/facts.html

    How tall are the sonotubes?

1. 
   user-125051 | Mar 21, 2006 03:35am | #23

   they only extend three or four feet above ground