Type of Concrete Mix


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Old 04-20-07, 04:08 PM
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Type of Concrete Mix

My sidewalk was poured with a mix consisting of flat pieces of black stone. The stone ranges in size of about 1/4 inch to 3/4 inch by about 1/16 to 1/8 thick. Is this mix better then the gravel mix that consists of round stones?
 
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Old 04-20-07, 06:46 PM
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As a general rule elongated stone is not recommended for concrete. They are more easily broken and do not lend themselves to interlocking like a standard coarse/fine mix. I have never seen what you are talking about. It may be some sort of decorative concrete. In my area they use alot of granite which can be pretty dark in color but it is crushed and closely resembles tradition limestone.
 
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Old 04-21-07, 05:49 AM
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The stone that was used for our sidewalks over 50 years ago is the type that is hardened and is rounded at various sizes from 3/8 to about 3/4 inch in size.
Its the same stone that one see's popping up through the ground in one's garden. I don't think you can drill through this stone.
The stone in my sidewalk reminds me of slate. I can break it easily with a hammer.
I am going to visit a concrete distributor and ask if they supply concrete mixes using differant stone and the benefits and quality of each.
 
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Old 04-21-07, 07:35 AM
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rjordan392, did they mix the side walk material on your site?

Is that material found on your property?

Just trying to learn.

Dale
Indy
 
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Old 04-21-07, 09:07 AM
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Type of Concrete Mix

rjordan -

Are you trying to match the appearance of your old concrete or place good durable concrete?

Generally, darker aggregates are stronger if they are not elongated or contain laminations. Shale is an exception because of its expansion.

Natural rounded aggregates are generally very strong and durable, since the process of weathering from physical abrasion and climate have destroyed the less durable materials. Some glacial deposits MAY (not will) contain some undesireable materials such as shale, iron, etc. Crushed limestone is weaker then quarried granite, but the harder varieties make excellant aggregates.

Crushed igneous or granitic aggregates are usually very strong and cubic in shape. They are usually free of softer deleterious materials. Some crushed aggregates (trap rock) can be very angular, but they are also very hard and durable and not laminated like slate.

When you order concrete you should not be concerned with the aggregate appearance unless you are trying to acheive an architectural finish like washed exposed aggregate, sandblasted, ground or hammered appearances.

Good concrete will have a uniform surface without exposing individual particles. This is acheived by having the right gradation of aggregates from sand through the maximum size rock desired. An excess of sand and fines or angular aggregates may require more cement and water and will shrink more.

If you order concrete, the best thing to do is specify the same mix that is used for the city sidewalks and make sure it is air entrained for the required freeze-thaw durability. For additional durability, you may want a higher strength, but increased strength does not always provide more durability. Improper placement and finishing can ruin good concrete.

I really love the Philadelphia term concrete "distributor" - it brings back memories. My wife's father in Levittown could only buy beer from a beer "DISTRIBUTOR". Here, we have to deal with ready-mix companies and liquor stores.
 
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Old 04-21-07, 10:07 AM
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Smith Brother,
In most all cases, concrete is mixed at the distributor when a large batch is needed such as sidewalks.
 
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Old 04-21-07, 10:18 AM
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Concretemasonry,
I just did some repair work around my front steps and there was some concrete work performed there also and I found a angular shape piece that looks exactly as I described earlier, but this piece is about 1/4 inch thick and about 5/8 inch in diameter. This might be shale as you suggest.
The pieces in the sidewalk were probally broken away when I chipped away at all the loose concrete which explains the small thickness.
I think I better wait another two seasons to see if the spalling continues.
I might be looking at getting it done over. I was hoping to patch it but now I am convinced that it will look worse then it is.
 
 

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