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Specialize in Cutting Doorways and Windows in Concrete Foundations”
Are You in Waterboro Maine? Do You Need Concrete Cutting?
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Concrete Cutter
Call 207-284-0788
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ME and all surrounding Cities & Towns
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Turn
the dry said over and over with a shovel until it is thoroughly mixed and of a
uniform color. See that there are no hard lumps or cement "pockets"
remaining. Spread out the concrete mixture and empty on it the mixing box
filled even full of gravel. Mix this thoroughly. Add three-quarters of the
required amount of water—say, about gallon to each cubic foot of concrete.
Apply the water with a sprinkling can or hose with a spray nozzle, slowly and
evenly, mixing the whole mass at the same time. Illus. 4 and 5 show the method
of applying the water and Illus. 6 the method of mixing. As the center of
pressure continues to move away from the center of the joint, the unit-pressure
on one side becomes greater, and on the other side less, until the center of
pressure is at a point j of the width of the joint away from the center. In
this case (c), the center of pressure is at the extreme edge of the middle
third of the joint.
The group of pressures illustrated in diagram c becomes a
triangle, which means that the pressure at one side of the joint has become
just equal to zero, and that the maximum pressure at the other side of the
joint is twice the average pressure. If the line of pressure varies still
further from the center of the joint, the diagram of pressures will always be a
triangle whose base is always three times the distance of the center of
pressure from the nearest edge of the joint. If the total pressure on that
joint remains constant, then the intensity of pressure on one side of the joint
becomes extreme, and may be sufficient to crush the stone. Also, since the
elasticity of the stone (or of the mortar between the stones) will cause the
stone (or mortar) to yield, the yielding being proportional to the pressure,
the joint will open at the other side, where there is no pressure. in
accordance with this principle of the distribution of pressure, it is always
specified that a design for an concrete arch cannot be considered safe unless
it is possible to draw a line of pressure (an equilibrium concrete polygon)
which shall at every joint pass through the middle third of that joint.
If the
line of pressure at any joint does not pass through the middle third, it means
that such a joint will inevitably open, and make a bad appearance, even though
the unit-pressure on the other end of that joint is not so great that the
masonry is actually crushed. Since the actual crushing strength of stone is a
rather uncertain and variable quantity, a larger factor of safety is usually
employed with stone than with other materials of construction. This factor is
usually made ten; and therefore, whenever the line of pressures passes through
the edge of the middle third, the average unit-pressure on the joint should not
be greater than-r of the crushing strength of the stone. A table of these
ultimate values has been given in Table I, Part I (page 10). They vary from
about 3,000 pounds per square inch, for sandstone found in Colorado, up to
28,000 pounds per square inch for granite found in Minnesota.Add more water when dry spots appear until the
whole mass has been turned over at least three or four times. The concrete
mixture should now be shoveled into a compact mass to wheel away. It is
extremely bad practice to apply water with a hose which has not a spray
attachment as the heavy stream will cause the cement to wash away and be
deposited unevenly throughout the concrete mixture. After the concrete has been
mixed, it is in plastic form and must be placed in forms or moulds to shape it
in the required form. The subject of forms for concrete will be taken up later
on.
Are You in Waterboro Maine? Do You Need Concrete Cutting?
