Ársrit Verkfræðingafjelags Íslands - 01.01.1914, Blaðsíða 33

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for eoncrete. Would it not be possible to make some
satisfactory provisions as to the quality required of
cement fit for use?
Those foreign building regulations which I have
seen, have not contained any provisions regarding
the substances used for concrete, with exception of
the building acts of New-York City. There it is so
ordered, that the biggest pebbles of the grovel majr
have a diameter not surpassing 5 cm, and that only
such a cement may be called Portland cement, as
— unmixed — is able to sustain the weight of 8,5
kg/cm2, without being crushed, and liaving been ex-
posed to the air for one day; after one day in the
air and six days in water, it should be able to bear
21 kg/cm2, still witliout being quite crushed. Other
sorts of cement should be able to bear proportion-
ally 4,2 kg/cm2 and 8,5 kg/'cm2. — In the building reg-
ulalions now in force it is allowed to mix the con-
crete for house walls up to 1:5: 10. I find this con-
crete far too poor, and think that in this country it
could never be made from such materials or with
snch a care, as would be necessary to prevent it
from being soaked with water, and it is unsafe to
rely on the plastering of the walls as the sole pro-
tection against damage by water. To get good walls,
we must use a stronger concrete. Of course there
can hardly be question of making the wliole walls
of a house watertight jusl by concreting them, for
that purpose they had to be made from a concrete
of 1:2:4, or not much poorer. Neither is this neces-
sary. I have observed that walls made from a con-
crete of 1:4:7, are nearly waterproof, if carefully
prepared. It is probably more common to mix 1:4:8,
and that will do very well, only the other concrete is
safer and comparatively hardly more expensive. I do
not think it is advisible lo permit a poorer concrete
than 1:4:8, — (1:4:7), for the bulding of usual
dwellinghouses or other buildings of equal importance.
During the last years people have beginned to mix
the concrete with stone — for economical reasons.
Tlie Germans allow this lo the extent of 40°/o of the
voluine of the concrete. This is of course economical,
but must be limited, otherwise it will turn out badly.
The permission of using stone in this way should
depend on a certain thickness of the walls, not less
than 40 cm should be required — and on the brealh
of the piers between doors and windows, which
should be considerable and could be more closely
defined in the building regulátions. AIso should the
size of the stones be limited, it should not exceed
the lialf of the thickness of the walls and tliere
should never be a less interval between the single
slones or the stones and the surface than lx/2—2
limes the size of the biggest chips in the concrete.
Stones might be mixed in concreted walls, which
only had a certain pressure for instance 7 kg/cm2,
but it would probably be too complicated. When the
question is of dwellingliouses, I think it is doubtful,
whether it is prudent or not to save the concrete by
mixing it with stone. Very likely the thermal conduct-
ivity of the walls would be increased by this.
The thickness of the walls of onestoried houses,
and of the walls of the highest stories in manystoried
houses, need not be more than 23—24 cm. This
would be sufficient as strength regards, if the houses
were not extraordinary big. This thickness is appoin-
ted in our building regulations, but no difference is
made between small and big houses.
In most foreign towns, as far as I know, the
minimum thickness of outer walls must not pass
below l1/2 time the length of a brick or 35—38
cm. Rut then not only tlie durability is considered,
but the possible shelter against storm and rain as
well, as water alvaj's may be expected to force its
way through a wall which only is one brick thick,
or is cut across with transverse ligaments of brick.
But, to my knowledge, in foreign towns wooden walls
are not allowed as sheltering linings of the outer
walls, except in special cases, for instance in houses,
where only a single family lives.
Therefore, in my opinion, the provisions of the
building regulations, should be adapted to the strength
and density of tlie concrete which would be allowed
and chiefly used — I suppose, that would be con-
crete of 1 : 4 : 8 (— 1:4:7) — the size of the houses
being duely considered.
I11 foreign building regulations the thickness of
the walls is governed by the size of the brick and
running in V2 brick sizes (= width of a briek).
This is natural in countries, where people almost
exclusively build from bricks. Here it is dilferent,
where it is an easy matter to proportionate the thick-
ness of the concrete walls to the strength required,
which in ordinary cases is determinated with refer-
ence to the height and the breath of the building.
Therefore it seems to me most natural, that the pro-
visions of the build. reg. should adjust the thickness
of the walls to the size of the liouse.
Fortunately there are some rules to be found,
pointing towards this and approved of by learned
professionals. I mean the rules of Rondelet, which
he made afler having carefully measured all kinds
of houses. Snmmed up his rules run as follows: The
sidewalls of houses, which have internal supporting
walls, should have the thickness of V48 out of the
sum of the brealh of the house (measured inside)
and the height up to the roof. I11 houses, which have
not such supporting walls, the thickness ofthewalls
sliould be 1/2J of the breath of the house V« of
the height up to the roof. In both cases we speak