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Fine sand: is the one that their grains happen through
a sieve of meshes of 1mm of diameter and are retained by another one of 0.25mm.
Average Sand: she is that whose grains happen through a sieve of 2.5mm of
diameter and are retained by another one of 1mm. heavy Sand: she is the one that
their grains happen through a sieve of 5mm of diameter and are retained by
another one of 2.5mm. Heavy grain sands give, generally, mortars more resistant
than the fine ones, although they have the disadvantage of needing much paste
conglomerated to fill up its hollows and to be adherent. In against game, mortar
is plastic, being this one very porous and little adherent. The kneaded one of
mortars is made removing and shaking the components of the mixture the times
necessary to obtain its uniformity. This operation is called to beat the
mixture. Preferably, the kneaded one takes place in kneaders or concrete mixers,
beating the mixture with a minimum of a minute. The kneaded one by hand must be
done on an impermeable and clean platform, being made like minimum three
dangerous. The conglomerate in dust mixes in dry with the sand, adding later the
water. The time of use, in the cement mortar must be used only within the two
hours immediate to kneaded his. During this time water can be added, if it is
necessary, to compensate the loss gives of kneaded water of. Passed the term of
two hours, leftover mortar must be rejected, without trying to return to make it
usable. The lime mortar can be used during a limitless time whenever it is
conserved in the due conditions. With plaster a simple mortar forms kneading it
only with water and, sometimes, something of sand. The amount of kneaded water
of varies with the job class to that mortar is destined. Like approximate
amounts of plaster and water to make 1m³ of mortar of normal consistency,
usually they consider the following ones:
• Black plaster mortar: 850 kg of plaster and 6001 of water.
• White plaster mortar: 810 kg of plaster and 6501 of water.
The kneaded one is made spilling plaster quickly on the water deposited in a
trough, beating the mixture and trying that does not form grooms or bubbles.
Gravel. They are considered as gravel the rock fragments with an inferior
diameter to 15 cm. Added heavy resultant of the natural disintegration and rock
abrasion or transformation of a weakly cemented conglomerate. They have
application in rubblework, preparation of concrete armed and for paving of lines
of railroads and highways. In addition to the rocks that are divided already in
the nature, gravel from rocks crushed in the quarries can be obtained. Like fine
barren sands or, the gravel are small fragments of rocks, but of greater size.
Generally, gravel are considered the barren ones that are retained in a sieve of
meshes of 5mm of diameter. They can be the product of the natural disintegration
of rocks or the crushing or machaqueo of the same ones. All the conditions that
we indicated that the sands had to reunite for mortars are applicable to gravel.
As far as the form, one prefers the barren rolling, that is to say, coming from
rivers and beaches. Barren the natural ones, of form more or less cleared, give
more docile concretes and of easier positioning than the obtained ones with
crushed stone. To the concrete one a series of conditions according to the type
of work is demanded to him the concrete one is manageable, easy to transport and
to place, without losing its homogeneity, says that this concrete one is docile. |
