Old concret still in bags, usable if mixed with new?

While rooting around in the shed I re-discovered a few bags of Portland cement . Even though the bags are still sealed and were stored up on wood off the floor. The powder is no longer fine and free flowing. Will it do any harm to the mix in a few shovel fulls of old mix is used with new mix? Eg. Three shovels of new mix, three shovels of old and ten shovels of gravel? Setting some wooden poles for a fence.

don't see why not if it's still shovelable (new word)...... I wouldn't build a bridge out of it or try to rebuild the WTC tho.....

Like Dave2 said, for anchor'n fence post I'd rock on with it. Don't know if I'd trust it to hold alot of weight very high off the ground.

Dave

Should be ok if you let it mix longer to get the lumps out.

Fine for a fence post and similar, not fine for a structural component, you won't know if the portland is still good unless you mix up a batch and test it for compressive strength. Concrete mixed for any structural components would never be mixed with old or questionable materials, batch plant would be liable, and you could create an unsafe condition if the material were used, loads imposed on it and premature failure occurred.

Don't you add crushed rock (like 3/4") to the mix? I would mix like this:
1. Rock.
2. Water.
3. Cement-slowly-let the rock/water mix break it up.
4. Then, slowly, sand.
That always works for me. For flat work it'll work fine. I'm assuming you're using a John Deere mixer. Putt, putt, putty. ? (;>))

Delivered concrete gravel here is mix of crushed stone and fines ready to mix with Portland and water. Same stuff actually as what the municipality covers the side roads with. Some gravel pits around here natural deposits ready to use. The mixer is the old family heirloom that was well used before mixing concrete for the stables when my Father was a wee lad.

Figured the old Portland would have the same strength as just gravel and water alone. Just wanted to make certain the old product didn't weaken the new Portland. And just use the old as if it was sand added to the mix.

If the bags are still in good condition, try dropping them squarely (from 1'-2' in the air) onto a smooth concrete floor. After a couple of drops it should be good as new. I've done this quite a few times with bags that had become solid. Once the mixture is loose, I treat it as a new bag and have never needed to mix it with 'fresh' stuff.

Good luck.

I had it so hard that droping would not do any good, used a sledge hammer to break in chinks. Then put in dry mixer and let it toumble till it fined up, quite a while. Seemed after that no problem and used it under poles on adition on house. Had just the cement, also morter mix and gravel mix that had to do that with all of it and then mixed it all together. Probably 70 year old mixer.

I think for what you're using it for... just use it as is and don't worry about new stuff. If you were pouring something more critical then I might use some new stuff.
Having 2 or 3 open bags on the go to get this stuff used up won't do a lot of good. Probably have the whole thing go hard on you if you get some humidity on the open bags...

Rod

Technically speaking, its hard to say what you will actually get, concrete is a composite mix of differing sieve size aggregate, binder(cementitious material=Portland), water and other admixtures depending on the actual mix design. To attain a certain compressive strength, the mix design must have the correct amount of these materials to reach a specified compressive strength. It has to be mixed uniformly and with the same materials. The same materials meaning each of those is tested, gradation, specific gravity, moisture and or what have you. Change sources, you have to test the mix design again to prove it out to meet the specifications called for. Given the sieve size of portland, which to me is fine dust,finer than sand and you replace say the smaller aggregate(sand)that the design mix calls for, with the questionable portland,it could go 2 ways. One would be it increases the strength, because the material still retains its qualities, (you already have the required portland) and it will hydrate. Add to much the water cement ratio is off, and it could effect it adversely (portland is still good) material could easily fail due to proportion, water/cement ratio. I can't say if excess portland would make it more like hydraulic cement and give you minutes to place before it starts to hydrate and is unworkable to place. If the questionable portland replaces a larger sieve size aggregate, say like sand, (and is now inert from age or moisture,does not bind etc.) which is called for, that mix being tested and proved, you would in fact have to test it with that(your questionable portland) material in measured quantities that is used in place or addition to what is being used to create the mix,different than was tested and proven, if that makes any sense. In summary, DO NOT fool with a proven mix design without testing it first, before placing in say a structural component or even a slab for that matter if in fact a load will be imposed on it.

The other point being that each amount of aggregate of a certain sieve size is usually required from the smallest to the largest in measured quantities, so in effect if you place a bunch of powder in that mix to represent/replace the sand and its much smaller in sieve size and you overwhelm the mix with it, (say it seems like a good way to get rid of it etc.) it would be my opinion that the results may or may not add up to what you need in compressive strength, without testing you will not know. ASTM reference standards on this are actually fairly easy to understand as it applies to a mix design. The safe thing is to test the mix and know it proves out.

I suppose the point of writing this here is to make sure anyone reading does not get the idea that its okay to randomly change, add or substitute materials to a concrete mix design, one that has been proven, and expect the altered or modified material to perform the same as what was tested and proven to be a specific compressive strength. Its also hard to say how it would mix in, if too much, does it concentrate in areas, violating the compressive strength, cause failure say on a slab surface where it prematurely fails, spalls and exposes larger aggregate below etc. There is a myriad of things to consider when doing this. However, if its really a concrete fill for something non critical, non load bearing, not a column, beam, load bearing slab/deck, precast structure/pipe even a pole base for like a traffic light with a moment arm, no cause for concern, but use that mix without testing you very well can create an unsafe condition, premature failure or poor performance. Might not be the clearest way to describe it here, also a bit redundant after re-reading but hopefully the point gets across about the potential problems with untested, altered or modified mix designs.

When the contractor replaced my pailing fence, they just mixed the cement with the dirt from the hole and rammed it down,ground moisture would activate cement.

Kinda like fibre-glass, the portland is the resin and hardner, the aggerate is the matt or cloth. Too thick resin and no cloth equals no strength. Around fence posts, mixed, probably no big deal[unless you are going to put a Coverall building on it]....Ron