In Italy the best sands come from the Brenta and the Adige, and nearly all the sands from crushers.
The advantages of sand as the bedding are essentially the following.
• greater overall elasticity which allows the paving to uniformly absorb the load of traffic (without forming micro-fractures), possible settling and extreme changes in temperature;
• possibility of using the elements of paving again if excavation is necessary or other work which involves removing the paved surface;
• total permeability of the surface, with evident advantages for dealing with rain etc., erosion and the refilling of underground water bearing strata.
b. SAND AND CEMENT: cement is added to good quality sand in the ratio of 2 liters/m^2. The mixing process, which is carried out dry to allow the laying of the cubes, should be done carefully so as to produce a uniform, well-amalgamated mixture in every part of the bedding, otherwise points of differential resistance and permeability could result in depressions.
It is advised, when possible, to mix the components by machine as this ensures improved mixing and blending, and, especially for large areas, a financial saving. The measurements and quantities are the same as those described above for just sand.
C. CEMENTED MORTAR: many paving elements of porphyry (slabs, tiles, “binderi” blocks, etc ) are bedded on an at least 4-5 on layer of cemented mortar. This is a bedding material made up of common mortar of sand and cement with the doses 250 kg of R325 cement per cubic meter of sand It s advisable, in the case of the foundation not being completely reliable, to add a 20 x 20 cm knit electro-saldered grid. The bed of mortar, at the moment at laying the individual elements, should be dusted superficially with cement in the ratio of a minimum 6kg/m^2.
