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Stone Under Footings and Slabs
- Thread starter TJAMBS
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Here
it is stated that the reason for inclusion of the crushed or rolling stone layer under slabs on grade is prevention of capilar soaking of the concrete (or in its day, masonry structural) components.
It is a good reason, and the romans had slabs on grade built on closely parallel vertical amphorae, quite likely in the same intent. Humid rooms, aesthetic effects apart, are concomitant with a number of illnesses, mainly rheumatic, and quite likely also allergic due to fungal and bacterial activity.
The advent of the sanitary floors and the better membranes to prevent capillarity, plus the cost of the layer of stone, have signified some decline in its usage, for membranes are relied upon to curtail capillar ascension of water, and no doubt an (above ground) sanitary space is a sounder humidity and flood barrier than the on the ground stone layer. By the way, always ventilate a minimum to forfeit the radon concentration risk.
Mechanically, crushed stone is also understood to provide an effect of cleavage on weak soils; probably our predecessors saw some buildings to slip; I have seen some usages such way under structural slab on the ground foundations to the impressive thickness of about 60 cm crushed stone layer for an akin thickness structural slab and only 6 floors above. So anywhere slippage is of concern, one can help the thing with some cleavage from a crushed stone layer (this will help to exact the shear strength available from the ground). You have then a multitude of stone size shear keys.
Through interlock and friction, it has also been used to reduce the amount of concrete in the SOG, a strategy that may work for some cases.
A downloadable study
it is stated that the reason for inclusion of the crushed or rolling stone layer under slabs on grade is prevention of capilar soaking of the concrete (or in its day, masonry structural) components.
It is a good reason, and the romans had slabs on grade built on closely parallel vertical amphorae, quite likely in the same intent. Humid rooms, aesthetic effects apart, are concomitant with a number of illnesses, mainly rheumatic, and quite likely also allergic due to fungal and bacterial activity.
The advent of the sanitary floors and the better membranes to prevent capillarity, plus the cost of the layer of stone, have signified some decline in its usage, for membranes are relied upon to curtail capillar ascension of water, and no doubt an (above ground) sanitary space is a sounder humidity and flood barrier than the on the ground stone layer. By the way, always ventilate a minimum to forfeit the radon concentration risk.
Mechanically, crushed stone is also understood to provide an effect of cleavage on weak soils; probably our predecessors saw some buildings to slip; I have seen some usages such way under structural slab on the ground foundations to the impressive thickness of about 60 cm crushed stone layer for an akin thickness structural slab and only 6 floors above. So anywhere slippage is of concern, one can help the thing with some cleavage from a crushed stone layer (this will help to exact the shear strength available from the ground). You have then a multitude of stone size shear keys.
Through interlock and friction, it has also been used to reduce the amount of concrete in the SOG, a strategy that may work for some cases.
A downloadable study
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