Estimating Concrete Question (strength)
OK all you concrete Goo roo’s……… I need some help estimating and some strength advice. I am in the middle of pouring columns for a suspended floor. I figured an estimation for one, and then we poured it and I found out that I was far off.
I’m attaching a (lame) drawing.
This is all in metric (everything here is) So I figured it in centimeters, then converted to meters. 240 x 20 x 300 = 1440,000cm cubed That plus 60x30x300 = 540,000
That is 1,980,000 cubic centimeters, divided into 1,000,000 cm cubed (1 cubic meter)
And I get 1.98 cubic meters of crete. We are mixing ourselves with mixer, so I figure we will lose some, plus the forms aren’t that hot (1×10 planks==plywood doesn’t exist here), so I think we will lose some there too. Here they tell me that 8 bags of portland mixed = roughly 1 cubic meter.
So I figure 18 bags will roughly fill it. It took 28 bags!
Our engineer tells us we are making 4000 lb mix, (1 bag portland, 10 gallons rock, 10 gallons sand, and 5 gallons water)
So where did I screw up? Also an architect here tells me that we are putting way too much cement in our mix, and that it is going to be too brittle. But we call the engineer, and he says NO Way! Less water is good (I know this) and theoretically we could pour straight cement and with that and all the Steel we’de be fine.
I thought cement strengthened by curing (over a period of days) and crystalizing around the aggregate?
Tommorrow we are pouring and the tell me to mix 1 bag portland (80lb) 15 gallon rock, 10 gallon sand, and 4.5 gallon water. This seems like it will be super dry to me—as the last batch )with the recipe above) yielded some DRy mud that wouldn’t fall without quite a bit of persuasion from the vibrator.
Opinions?
Edited 10/6/2005 10:38 pm ET by custombuilt
Replies
help?
Your aggregate compositin and sizes will have some bearing on the finished product but a quick calculation of the water-cement ratio will get you in the ball park.
Divide the weight of your water by the weight of your portland to get the ratio.
Compressive strength at 28 days.........non-air-entrained.....air entrained
6000 psi 0.41 --
5000 0.48 0.40
4000 0.57 0.48
3000 0.68 0.59
2000 0.82 0.74
Or, 5.5 US gallons = 45.9lbs divided by 80 = 0.57 or 4000 psi
5.0 = 41.7lbs divided by 80 = 0.52 or 4500 psi
4.5 = 37.6lbs divided by 80 = 0.47 or 5000 psi
Hey, Brownbagg, check my figures, huh?
Thanks a ton----
That chart is a big help.
Also, if I am mixing a 4000 pound mix, then roughly how many bags will it take to make 1 cubic meter. Or 1 cubic yard if thats easier, and I can convert.
Thanks, Jason
Here's a pic of a chart you can use to make up your mixtures. It's only a guide but should be sufficient.
If you use the water/cement ratio it looks like you could get a 6000 psi mix.
For more info pick up a copy of "Concrete for Small Jobs", IS174T, Portland Cement Asociation, 1980.
kewl.......
When in doubt, get a bigger hammer!