Concrete Roads
and Their Construction
År: 1920
Serie: Concrete Series
Forlag: Concrete Publications Limited
Sted: London
Sider: 197
UDK: 625.8 Con-gl.
Being a Description of the concrete Roads in the United Kingdom, together with a Summary of the Experience in this Form of Construction gained in Australia, Canada, New Zealand and the United States of America.
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180
CONCRETE ROADS
Concrete
9. Proportions.—The coarse material and sand shall bo used by
volume in such proportions, one to the other, as are found by
trial with several mixtures of the same total quantity measured
separately, but of varying proportions, to give the least volume
of concrete when mixed with the prescribed quantity of cement
and tamped into a mould of known capacity.
For one-course roads not more than 5 parts of coarse and fine
aggregate, mixed as provided, to one of cement shall be used.
Generally speaking, where severe traffic conditions are likely to be
met, the concrete for a one-course road should be in the proportions
of 1 part of cement to 11 parts of fine aggregate and 3 parts of coarse
aggregate. For two-course roads not more than 8 parts of coarse
and fine aggregate, mixed as provided, to one of cement shall
be used for the lower course, and not more than 3 parts of fine
aggregate to one of cement for the upper or surface course.
10. Measuring the Materials.—The method of measuring the
materials for the concrete, including water, shall be one which will
ensure uniform proportions at all times. The cement shall be
taken by weight on the basis that 90 lb. is equivalent to a volume
of one cu. ft.
11. Mixing.—The concrete shall be mixed in a batch concrete mixer
of an approved type. The mixing shall continue until the in-
gredients are homogeneous and plastic throughout. The drum
shall be completely emptied after mixing each batch.
12. Consistency.—The quantity of water to be added to the concrete
shall be such as to secure a plastic mixture which can be easily-
worked, and so that only light tamping shall be necessary to con-
solidate when placed in position. Care shall be taken to pre-
vent an excessive amount of water being used, and the concrete
shall not be so sloppy as to cause a separation of the coarse aggre-
gate from the mortar during handling and laying.
Any concrete which has partially set before being placed in
position shall not be used. To avoid waste from this cause, all
concrete which is mixed ready for placing in position imme-
diately before the dinner hour or other stoppage of the work shall
be placed and finished before stopping. Under all circumstances
as little time as possible shall elapse between the mixing of the
poncrete and placing and finishing.