The right color of concrete?

[youngins]

We are in the process of adding a gate to an existing fence.

Saturday, we dug the hole for the new post and then added Quickrete.  Today, the post is rigid, but the concrete does not look like what I expected:



Is this brownish look OK for being set for 4 days?

Please note, this is the first time we have messed with the stuff - so it is possible we messed it up.

Thanks.

[Amanda_931]

One possible set of directions on the bag has you basically making soil cement--Mix the stuff in the bag with the dirt from the hole, stick it back into the hole, and add water.  

That would give you more dirt-colored concrete.  I set a mailbox post that way, no problems for over ten years.

[youngins]

That makes sense to me - we just mixed it in the hole.  Once we poured in the water it became mud-krete.

Thanks

[glenn-k]

You can also put it in the hole around the post with no water or throw a cup or two in as you pack the dry concrete mix around the post.  Ever leave a bag of concrete in a damp location?  It will set up in the bag.  There is usually enough moisture in the soil or if not the added bit will set it up.  The post will not fall over with the dry mix like it will with wet concrete and the resulting concrete will be even stronger.

Side note - concrete colors can vary from dark gray to white - white is usually special.  A bit of soil - especially with iron content will change the color quite a bit.

[MountainDon]

When I was building and installing playground equipment I used a lot of the dry quikrete. We tamped it into place using a 6 foot steel pry bar to ensure it filled the hole to the bottom. Then as Glenn said, we added a little water on top to be sure the top would set and not blow away or whatever.

If I recall my strength of materials class correctly it takes 28 days for concrete to develop max strength, IF it is kept moist to allow the cure to continue. (Remember, concrete doesn't dry (or it shouldn't), it cures... a chemical reaction dependent upon water.

Too much water weakens the concrete.

For a fence post though almost anything should do.

[Daddymem]

For the purposes of a fence post you are probably fine with a dry mix.  But you will not meet maximum strength if there isn't enough water in a concrete mix-that's why they do slump tests to determine the correct mix.  If there isn't enough water it dries out instead of chemically reacting like it is supposed to, it may be hard but it won't be as strong as when it is cured properly.

It looks to me from the picture that you have a lot of fines in your soil-silts and possibly clays.  Those most likely washed into your mix in the hole (because the particles are so small and light) and colored your concret, you should be fine.

[Erin]

I can't help but wonder...
Why are we setting a plain old fence post in concrete anyway?  

[PEG688]

It's a pretty common practice , I'd think by the looks of it that it is a Pressure treated 4x4 post.

In some areas , mostly areas with deep / lots of frost / freezing ground , folks will set fence posts using crushed stone , the stone binds together but drains better and is less likely to "frost heave " the post up out of the ground.


 But like I said it is very common to set the post in redimix / Quikcret, bagged redi mix so the post is less likely to blow over in a wind storm.

I wouldn't be worried about the color of that redi mix and for a fence post a compression test for concrete strength is sort of silly. Seldom is a test plug poured on a "normal" job  a Govt. contract , big civil job yes but a common residential job , never seen one poured, in 30 years of building. YMMV.

[glenn kangiser]

The bigger house project I'm working on - utility tunnel/basement  requires crushed cylinder test w/reports back to the engineer.  We left 3 on the jobsite and they froze so only 1 went to 3800 lbs -- other 2 went about 1900 due to freeze damage.  The concrete was fine - I'll get him some more from the next pour.  2500 was passing.

[desdawg]

I can't help but wonder...
Why are we setting a plain old fence post in concrete anyway?  

I believe youngins said this post needs to support the weight of a gate. I would think being surrouded by undisturbed soil it should be fine. Typically post mix costs less that regular concrete mix and is not as rich a mixture of portland and gravel. They skimp a bit on the amount of portland in post mix.