Little more is better or not?


  #1  
Old 10-28-12, 08:42 PM
L
Member
Thread Starter
Join Date: Oct 2012
Location: usa
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Little more is better or not?

Hi,
I am going to be mixing concrete for a driveway. I heard it said: 1-2-3,cement-sand-gravel. What if it was 2-2-3, would that be better?
 
  #2  
Old 10-29-12, 12:42 AM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 2,838
Upvotes: 0
Received 1 Upvote on 1 Post
It all depends on a number of different factors, including such things as if you are proportioning by weight or volume, and how wet the sand is, or how dense the rock is. Back in the days when I hand-batched literally tons of concrete, I always found the 1:2:3 mix to be just about right, by volume. It was a learning experience, to be sure, but consistently gave me concrete that attained good strength and fairly rapid initial set. Using a flat-bottomed batching shovel, my 1:2:3 batches resulted in very close to 15% by weight of cement (I was anal enough to actually weigh full shovels with a scale in my learning stages). A typical 6-sack batch plant mix, with compressive strengths of more than 3500 PSI, has a cement content of 14%, by weight.

If you double the amount of cement in the mix, with all other things being equal, several things will probably happen. The concrete will set up much faster, quite possibly making it more difficult to properly finish if you are batching, placing and finishing all by yourself. A common mistake for correcting flash-set is to add more water, which compounds the next problem--that being it's also likely to develop more shrinkage cracking in the finished product (both from the added water, and the rich mix). Encouraging cracking is something not desirable for a number of obvious reasons.

You need to look at the big picture for your driveway. That being it could just about kill one person to batch, place and finish a typical driveway. Not easy, even with some help. A typical driveway, 60' x 15' x 4" thick, has close to 48,000 pounds of concrete in it (more than 150 batches). That's 24 tons, in round numbers. Breaking it down into smaller pours will help, but not by much. Much easier to watch the stuff slide down the chute of a ready-mix truck, and simply write the man a check.
 
  #3  
Old 10-29-12, 06:05 PM
L
Member
Thread Starter
Join Date: Oct 2012
Location: usa
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Itís going to be by volume and small sections at a time, thatis if I can take the echo from my wife.

If I donít use too much water in the mix, and make sure it stay wet throw the hardening 50- 80 degree temps, will the strength of the concrete not increase?
 
  #4  
Old 10-29-12, 07:20 PM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 2,838
Upvotes: 0
Received 1 Upvote on 1 Post
Is your wife a skilled concrete finisher? Can she accurately move a wheelbarrow with 300 lb. of wet concrete in it, without dumping it all over the place? Is she willing to get her pretty shoes all full of wet mud, walking in it while keeping a nice, even roll ahead of the strike-off? If you answered "yes" to all 3 questions, you've got a keeper of a wife, and shouldn't have any problems with the driveway pour!

Doubling the amount of cement in any concrete mix is never a good idea. Any gain in strength is negated by having too many fines at the surface, and not enough rock, actually resulting in a finished surface lacking in durability. You (or the wife) will be standing on the wet concrete, trying to finish it after the bleed water evaporates off. And don't even think about trying to give it some surface texture to prevent being too slick when wet, as it will be too hard for a finishing broom to make impressions in. Stick with a 6-sack mix I referenced earlier, which for the sample dimensions I used will require 70 sacks of Portland cement. Or at least $650 worth, plus the sand and gravel to the tune of another $300 plus. Bottom line being you will probably spend more for materials and the "privilege" of batching it yourself than you would buying ready-mix.
 
  #5  
Old 10-30-12, 05:26 PM
L
Member
Thread Starter
Join Date: Oct 2012
Location: usa
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yes you are right the big truck is the easiest and lessmoney way to go. Just write a check to the big truck, oh ya, also have to go find some useless helpers and write more checks and prey they donít sue me while they screw up things. Then when the whole job is done, I will sit downand think why I used the big truck!
Just kidding around do not blow a fuse. You see I donít build bridges and its going to be a learning experience for me. Color, stamps andrebar are in the plan, in small sections and lots of time.
Ok because you build bridges I believe you. Double is trouble! So then, what about fractions more of cement. 50%, 25%, or even 10%more of cement. I am asking because if I shelve it, I will keep it on the positive side. Or do I have to be exact 1-2-3
Thank you
logmode
 
  #6  
Old 10-31-12, 11:50 AM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 2,838
Upvotes: 0
Received 1 Upvote on 1 Post
Life is far too short for me to "blow a fuse" over anything. Especially over some guy I don't know who appears to be headed in the wrong direction on his driveway project.

Increasing the cement content will normally increase the strength of concrete. But why do you think you need more than 3500 PSI concrete? A typical passenger car or pickup truck weighs around 4000 lb., or roughly 1000 lb. per wheel/tire bearing on the driveway. If we assume a tire foot-print being about 6" x 6", that's 36 sq. in. Doing the arithmetic (1000 divided by 36) results in an applied stress under each tire of just slightly less than 28 PSI. Meaning a standard 1:2:3 concrete mix will be about 125 times stronger than it needs to be (3500 divided by 28), for supporting a typical vehicle.

I'm sure anxious to hear why you think that wouldn't be strong enough for your driveway.
 
  #7  
Old 10-31-12, 08:17 PM
L
Member
Thread Starter
Join Date: Oct 2012
Location: usa
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
1-2-3 is fine, thank you for your help
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: