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Mixture - Concrete - Solution/Explanation

 
 
Randy Dandy
 
  1  
Reply Sat 25 Apr, 2015 12:52 pm
How is the problem solved ? I don't know.
timur
 
  1  
Reply Sat 25 Apr, 2015 01:39 pm
@Randy Dandy,
It has been shown to you how the problem is solved.

You got the solution too.

I'm sorry it's beyond your current capabilities.
Randy Dandy
 
  1  
Reply Sat 25 Apr, 2015 01:48 pm
@timur,
I have been out of school over 30 years and am trying to re-learn on my own. I guess I am too rusty. I just don't get it.
0 Replies
 
Randy Dandy
 
  1  
Reply Sat 25 Apr, 2015 04:55 pm
Would someone kindly give more information on ratios in reference to mixtures? I am trying to understand.
0 Replies
 
Randy Dandy
 
  1  
Reply Sun 26 Apr, 2015 10:58 am
A follow-up question:
I just a related statement about another 1:2:4 mixture of concrete. The statement indicates for a cubic FOOT of concrete, .22 cu. ft. of cement, .44 cu. ft. of sand, and .88 cu ft. would be used. Would those be the correct answers ? The statement did provide the calculations. Just curious. Thanks.
Randy Dandy
 
  1  
Reply Sun 26 Apr, 2015 10:59 am
The statement should be: I just read a related statement.
0 Replies
 
timur
 
  1  
Reply Sun 26 Apr, 2015 11:14 am
@Randy Dandy,
We cannot tell, just with those bits of statements.

The answers COULD be correct depending on the enouncement of the problem.

They do not fit your problem as stated.
Randy Dandy
 
  1  
Reply Sun 26 Apr, 2015 12:37 pm
@timur,
Here is the statement:
"Concrete is made by mixing cement, sand, gravel, and water. A 1:2:4 mixture is made up of one volume of cement, twice that volume of sand, and 4 times that volume of stone. The volume of the mixed cement is less than the sum of the volume of the parts, because the open spaces between the stones which must be filled in making the concrete. One cubic foot of concrete contains: for 1:2:4 concrete - .22 cu. ft. cement, .44 cu. ft. sand, .88 cu. ft. gravel."

Maybe that will help.
timur
 
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Reply Sun 26 Apr, 2015 01:37 pm
@Randy Dandy,
Yes, that helps.

Now, what's the question?
Randy Dandy
 
  1  
Reply Sun 26 Apr, 2015 02:17 pm
@timur,
I know the mixture would be 7 parts total. Would the mixture be calculated as 1/7 cu. ft. cement, 2/7 cu. ft. sand, 4/7 cu. ft. gravel to get the .22, .44, and .88 ? I am trying to work out the solution.
timur
 
  1  
Reply Sun 26 Apr, 2015 02:38 pm
@Randy Dandy,
Those are indeed the volumes used to make a cubic foot of the mixture.

If you add them up, you'll have a total volume of 1.54 cu. ft. but you are looking for a 1 cu ft.

So where is the difference?

It's because when you mix the parts, the smaller granules fill the place taken by the air, which is expelled, diminishing the total volume.

Then you take your previous values to exclude the air:

x= .22

y= .44*.66 =.290

z= .88*.55 = .484

Then x+y+z=1 cu. ft.
Randy Dandy
 
  1  
Reply Sun 26 Apr, 2015 03:38 pm
@timur,
Thanks.
0 Replies
 
Randy Dandy
 
  1  
Reply Sun 26 Apr, 2015 05:34 pm
One more question:

Concrete weighs approx. 150 lbs. per cu. ft. Would the parts for the 1:2:4 mixture be 150 x 1/7 = 21.42 = 21 lbs. of cement, 150 x 2/7 = 42.85 = 43 lbs. of sand, and 150 x 4/7 = 85.71 = 86 lbs. of gravel/rocks ? Just curious. Thanks again.
0 Replies
 
Randy Dandy
 
  1  
Reply Mon 27 Apr, 2015 09:45 am
Please reply. Thanks.
timur
 
  1  
Reply Mon 27 Apr, 2015 09:57 am
@Randy Dandy,
No, you cannot use that ratio as the relative density of the mixture's components is different.

You can always make the calculations using the relative density of cement, sand and gravel taken from this table:

Density of building materials
0 Replies
 
 

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