the reason for.
the reason for.
(OP)
why? use gravel or 3/4" aggregate sub-base for concrete slabs?
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RE: the reason for.
Consolidating the fill also consolidates the sub-base and results in a more uniform base and sub-base stiffness.
Both help improve the quality of the slab.
Both the ACI and Portland Cement Association published material several years ago that indicated that the increase in the load carrying capacity of slab is only marginally improved by the addition of a granular base.
RE: the reason for.
Granular subbase prevents the buildup of pore pressure immediately beneath the slab and allows capillary drainage as well.
RE: the reason for.
So if the slab was placed directly on (compacted) soil, ground water would rise up to the top of the soil, through capillary action, and saturate the bottom of the slab and eventually migrate through the slab to the surface.
Thus the 4 to 6 " layer of 3/4" stone helps prevent water (in liquid state) from reaching the bottom of the slab.
Water in vapor state will still come up and either be stopped by a "vapor retarder" (plastic sheet) or if there is no vapor retarder, travel through the slab.
It will then evaporate into the air, or be stopped by a floor covering and condense (not good).
mdaskilewicz@cuh2a.com