concrete strength vs. hi strength vs. mortar vs. cement


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Old 08-01-06, 08:01 PM
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concrete strength vs. hi strength vs. mortar vs. cement

hey all,
i learned earlier on this site that high strength concrete has a greater percentage of cement in it which makes it easier to smooth out.

well, if high strength only has more cenent in it, does that mean mortar is stronger than high strength, and would pure cement be the strongest?

just curious.
m
 
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Old 08-01-06, 08:16 PM
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concrete strength vs. hi strength vs. mortar vs. cement

Too many people are concerned with compressive strength of concrete. Strength is not the critical factor in good concrete.

Pure cement is not the strongest. It takes aggregate to make concrete. Generally adding cement will increase the strength of concrete.

You must have the proper aggregate in the correct sizes and have the least water to place (not pour) it correctly.

You can make concrete in strengths from less than 1500 psi to over 8000 psi, depending on what you want and how you want to use it.

Interlocking concrete pavers have a minimum compressive strength of 8000 psi, but I have seen 12,000 psi. The extra strength is not necessary for load carrying.

Mortar serves a different purpose than concrete and it is tested differently, so you cannot compare the strengths. The general recommendation for mortar is that you use the LOWEST strength possible to carry the loads, since the are other more important properties to be concerned with.

Dick
 
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Old 08-01-06, 09:26 PM
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thanks concrete masonry,
i guess i'm more curious about tension strength with this question, not compresion strength. the compression strength of any of these materials will be sufficient for me.

using mortar is an option, so i would like to compare the respective tension strengths of these materials.


its concerning an issue that i brought up in this post: http://forum.doityourself.com/showthread.php?t=270042
about a bad concrete slab. i'll be making a new slab on top of it- half of it being an insulation layer made of a 1 part cement to 8 parts perlite mix and the top half being the mortar or concrete which will make up part of the brick oven mass after the brick layer. on top of the oven i am instructed to use regular brick mortar with some fire clay mixed in and add a 2 inch layer over the bricks - i was going to use the same for the top half of this slab in question, with some rebar in it.


anyhow, which one has better tension stregth?

thanks,
m
 
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Old 08-02-06, 06:39 AM
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concrete strength vs. hi strength vs. mortar vs. cement

Duplicate - See other post.

Dick
 
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Old 08-02-06, 06:41 AM
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concrete strength vs. hi strength vs. mortar vs. cement

I don't see where you will get appreciable tensile stresses, so tension should not be a problem. If I remember, your dimensions a so small that tension should not be a problem. Heat might be a problem, but there are high temperature cements (lumnite, fondu, etc.) that have been used for years, but not in your type of application.

You seem to have some sort of a plan and recommendations and are guessing at what to do to improve it.

You have no proportions or refernce to what kind of "brick mortar" you are using. Usually bond is a factor in mortar and not tensile strength. Because of the vagueness, it is hard to make any suggestion.

It is always dangerous to try to change a plan or recommendations by using guesses, since the originals are well proven. Combining two different methods (shotgun approach)can lead to problems

Dick
 
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Old 08-02-06, 08:32 AM
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i'm curious about tensile strengths because i'm worried about a table top slab, supported on three sides caving in or bending/cracking in the middle. the slab area is 3.5' by 3.5'


but, specifically about the material concrete:
you're saying that you can only get higher strength concrete by adding more cement up to a point, beyond that point (specifically the mix that makes up the high strength) adding more cement weakens the mix?

p.s.
the plan just calls for regular brick mortar, and i assume thats type S because type S is what they sell at home depot.
 
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Old 08-02-06, 10:07 AM
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Concrete

It would help if you had a drawing of what you have and what you are trying to do. Right now all anyone can find out about your project is a lot of bits and pieces from different postings.

I would have torn out the original slab you poured if only to get a fresh start and build according to the plans. Now you seem be trying to correct matters.

As bad as your original slab was, you probably do not have enough load to cause a problem with anything (based on the bits and pieces provided) since it is not large enough to develop any real stresses due to exterior loads. All I see is a brick oven sitting on your old slab, near the support below, and the only load would be the what you put inside the oven.

You seem to be adding layers (2") over your existing slab. Reinforcing the top layer of your new sandwich probably won't do anything because there will be no tension in that layer. Why are you worrying about the new top concrete slab when the perlite slab under it has virtually no strength? (especially if you over-mix the perlite) and you have no appreciable load?

This type of oven is very simple and could be built without a lot of detailed analysis, just as they have been built for centuries. It does not take any unusual materials.

This is not a strength problem. As an example, in South America, they have been building very sophisticated 20 story loadbearing block buildings out of 6" block walls with no steel or concrete columns for over 20 years. The floor slabs are only 3" to 7 1/2" inches thick.

A drawing or some details would help to avoid getting lost in the details.

Dick
 
 

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