Local builders mix their own concrete on site for floors and foundations. They are all working with the same weather, the same portland cement, the same additives and the same aggregate mix. We have no problem with frost. The builders know what they are doing.
My foundation mix was perfect and ready to walk on the next day. Another mix on another site is still soft in places after ten days. A couple of other pours are performing equally badly.
The concensus of opinion is that it must be the aggregate but the quarry say they add nothing to it.
What other variable might be causing this effect?
Replies
poorly mixed..
formula ratios are off...
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Yeah, when they are all using the same aggregate, it gets hard to blame it on the quarry. The only real variable from one pour to the next is the guys who mixed it on site.
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wonder if the portland was held back some or the aggrigrate was upper for a stretcher...
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''upper for a stretcher'' ??
Does this mean the aggregate was stockpiled for too long? How would that affect it?
I'm grateful for all the comments. I wonder if the quarry had a fuel spillage on to the aggregate, that seems the most likely to me. I know the various builders and they should know what they are doing.
I have heard of bad batches of Portland cement. Once a Polish ship had to sell off a cargo in a hurry. It was snatched up at a dollar a bag and landed in all sorts of places, the trouble was it cured to a bright white colour.
In the Outer Hebrides life was, and still is, a far slower pace. One group of islanders were presented with bagged cement for a new pier but ''it miraculously turned to stone'' before they could use it.
Puting cement bags in a hessian sack, building them up the side of a stream and soaking them was once an accepted way of building small bridge abuttments.
I think he meant "upped for a stretcher," meaning they added more aggregate at the last minute to increase volume. Unfortunately that would also decrease the portland ratio.
Edited 12/3/2007 4:57 pm ET by Mike_Maines
Fuel spill sounds like a possibility. I know where a hydraulic line burst on the loader and contaminated the pile.Bad portland is a first by me but you know how things are on that side of the pond better than I do...So next Q - is there a way to test? Probably if you want the expense for purpose of laying the cost of replacement on the right party...
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The mixes will have been done the old fashioned way, mixing aggragate and Portland cement on site to a standard mix in a big rotary mixer. Entrainment additives may have been used.
The Portland is so fresh from the local depot it is still warm, I can check if they have had any returns.
The point about salt is worthy, we have had a cold snap and traces of salt could have been left in the loading shovel or even in the truck bed.
What I will do in the morning is check with the quarry and if there is doubt about their aggregate I will get it from another quarry.
meant to type upped...
it's a way to add volume to batch...
but it lessens the portland ratio...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
Things have worked out. It seems that the batches of aggregate had a higher content of fine silt, perhaps because they came from the bottom of a pile. The silt would have been washed down there with all the rain we have been having.
All the pourings are now solid, they just took a lot of time to get there.
mixed on site makes me ask how. What size mixer? Or by hand? How were things measured? by whom?
It sounds like the portland cement was unevenly distributed through the mix. It should be thoroughly mixed through the aggregate before adding water..
My guess would be that they added it late and did not get it throughout the mix. The areas not kicking probably will not kick because there is a great lack of portland there.
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Another possiblity that comes to mind for mixed on site is that the water was not clean potable water. Oils or organic material interfered with the bonding action
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I've heard of situations like that where the cement was the problem. A pour with soft spots after ten days is probably going to have to be removed completely.
We poured a slab for a branch bank, came from an established redi-mix plant, they forgot to add enough cement. Left out most of it actually. Seven day break strength was something like 300 psi. Two weeks later the whole slab was removed (pretty easy) and replaced. Lost all the in-slab stuff, inlcuding rebar.
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Does the aggregate have salt on it/in it?