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Dense Graded Aggregate vs. Crushed Stone for Sidewalk ConstructionHelpful Member!(2) 

ropotto (Civil/Environmental)
18 Dec 11 13:30
What granular sub-base material placed on top of the prepared subgrade is the best cushion for uniform support by bridging over minor subgrade defects for sidewalk construction? 3/4" Dense Graded Aggregate or 3/4" Crushed Stone?

Is the use of crushed stone a better way to diminish the development of suction that leads to tensile-shrinkage failures?
 
Helpful Member!  cvg (Civil/Environmental)
18 Dec 11 15:26
remove the subgrade defects first
use dense graded, crushed, compacted material not open graded.
use joints to control the location of cracks.  
Ron (Structural)
18 Dec 11 16:36
what cvg said!

Also suction is not what leads to shrinkage cracks.  Autogenous shrinkage is not a function of suction but a result of chemical and physical volume change through hydration.
concretemasonry (Structural)
18 Dec 11 17:29
Much depends on the local aggregates that are available. Here we have have high quality glacial aggregates everywhere underlain with limestone outcroppings delow and surrounding. Many areas have great very dense glacial graded aggregates (generally rounded) and good crushed aggregates (angular dense limestone and igneous) readily available.

The cost and performance differences are minimal. So blending may be done, but for a sidewalk either choices perform well.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

ropotto (Civil/Environmental)
20 Dec 11 14:20
I should maybe explain the differences between crushed stone and dense grade aggregate.

Crushed stone is sedimentary rock that has been crushed and graded by screens to certain size classes. Crushed stone may also be made from granite and other rocks.
 
Dense grade aggregate, or DGA, also known as crusher run, this is a mixed grade of mostly small crushed stone in a matrix of crushed stone powder, graded to produce low void content and maximum weight when compacted.

 
Helpful Member!  cvg (Civil/Environmental)
20 Dec 11 14:55
doesn't really change the recommendation. a good base material should be well graded, granular material, composed of mostly crushed, sound aggregate, minimum of fines, able to be compacted to a dense mixture. I would stay away from too much "stone powder" and recommend less than 10% fines. Also, recommend maximum size of about 3/4 inch rock.

Either one or both of your material sources might work, especially since this is just a sidewalk, you have not given enough information to make a selection.

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