“We Specialize
in Cutting Doorways and Windows in Concrete Foundations”
Are You in Buxton Maine? Do You Need Concrete Cutting?
We Are Your Local
Concrete Cutter
Call 207-284-0788
We Service Buxton, ME
and all surrounding Cities & Towns
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Core Drilling Buxton Maine
Whenever
it is possible, apply the mortar surfacing or wearing surface as in sidewalks, concrete
floors, etc., at the same time as the base or main mass of concrete. This gives
far more satisfactory results and the proper depth of keystone for a concrete
arch should theoretically depend on the total pressure on the keystone of the concrete
arch as developed from the force diagram; and the depth should be such that the
unit pressure shall not be greater than a safe working load on that stone. But
since we cannot compute the stresses in the concrete arch, we know, at least
approximately, the dimensions of the concrete arch and its thickness, from
which we may compute the dead weight of the concrete arch, it is necessary to
make at least a trial determination of the thickness. The mechanics of such a concrete
arch may then be computed, and a correction may subsequently be made, if
necessary. Usually the only correction which would be made would be to increase
the thickness of the concrete arch, in case it was found that the unit-pressure
on any concrete would become dangerously high. The handbook quotes a rule which
he declares to be based on a very large number of cases that were actually
worked out by him, the cases including a very large range of spans and of
ratios of span to rise.
The rule is easily applied, and is sufficiently
accurate to obtain a trial depth of the keystone. It will probably be seldom,
if ever, that the depth of the keystone, as determined by this rule, would need
to be altered. The rule is as follows: For concrete architectural reasons, the
actual keystone of a concrete arch is usually made considerably deeper than the
concrete on each side of it, as illustrated in Fig. 218. When computing the
maximum permissible pressure at the crown, the actual depth of the concrete on
each side of the keystone is used as the depth of the keystone; or perhaps it
would be more accurate to say that the extrados is drawn as a regular curve
over the keystone (as illustrated in Fig. 223), and then any extra depth which
may subsequently be given to the keystone should be considered as mere
ornamentation and as not affecting the mechanics of the problem makes a
perfectly solid mass, like one huge stone, therefore causing no difficulties in
bonding. One of the best methods of removing the plaster from the forms is as
follows: After removing the forms concrete should he brushed while green with a
steel brush or one made of stiff fiber bristles. If the concrete hardens so
that the mortar cannot be brushed away from the coarse aggregate, the mortar
may be softened by a solution of muriatic acid. After brushing, the work should
be treated with an acid solution and for this purpose the solution should be 1
part of commercial muriatic acid to 3 parts of water. After the use of an acid
solution the work should be washed immediately, and thoroughly, with clean
water, as any acid remaining on the surface of the work will ultimately cause
streaks and discolorations.
The following materials are recommended as suitable
aggregates for the production of desirable brush surfaces, it being understood
in using any of them for aggregates that the concrete mixture is to be 1 sack
of Portland cement to 21/2 cu. ft. of aggregate. Yellow marble screenings up to
14 in.; red granite screenings up to 14 in.; black marble graded from 3/ to 1/2
in.; river or lake gravel graded from 14 to 1/2 in. To secure economy,
limestone may be substituted for white marble and either black granite or
trap-rock may be substituted for black marble. The above materials are merely
suggestions of the possibilities of concrete surfaces. Infinite variations may
be made by substitutions in combining materials, while if one takes trap-rock,
red granite or limestone, for instance, by merely increasing or diminishing the
size of one or two of the ingredients it readily will be seen that a great many
combinations may be effected, all of which will produce desirable surfaces for
brushing.
Are You in Buxton Maine? Do You Need Concrete Cutting?
We Are Your Local
Concrete Cutter
Call 207-284-0788
We Service Buxton, ME
and all surrounding Cities & Towns
