excess of the capacity recommended by the manufacturer on the nameplate.
Excessive overmixing requiring additions of water will not be permitted.
The mixers shall be maintained in satisfactory operating condition, and
mixer drums shall be kept free of hardened concrete. Mixer blades or
paddles shall be replaced when worn down more than 10 percent of their
depth when compared with the manufacturer's dimension for new blades.
Should any mixer at any time produce unsatisfactory results, its use shall
be promptly discontinued until it is repaired or replaced.
3.1.3.1
[Truck Mixers
Truck mixers and the mixing of concrete therein shall conform to the
requirements of ASTM C 94/C 94M. A truck mixer may be used for
conventional concrete complete mixing (transit-mixed) or to finish the
partial mixing done in a stationary mixer (shrink-mixed). Each truck shall
be equipped with two counters from which it shall be possible to determine
the number of revolutions at mixing speed and the number of revolutions at
agitating speed. Truck mixers shall not be used to mix or agitate concrete
with greater than 37.5 mm 1-1/2 inches NMSA or concrete with a slump of 50
mm 2 inches or less. The acceptability of truck mixers for uniform mixing
shall be determined by uniformity tests in accordance with ASTM C 94/C 94M.]
3.1.3.2
Pugmill Mixers
A batch or continuous mixing twin-shaft pugmill mixer shall be capable of
producing RCC of the same quality and uniformity as would be produced in a
conventional plant that meets all the requirements of these specification.
All pugmill mixers shall meet the requirements of paragraph CONTINUOUS
MIXING PLANT(S).
3.1.3.3
Mixer Uniformity Requirements
All mixers, except for truck mixers, shall be tested by the Government in
accordance with this paragraph and in accordance with COE CRD-C 55. When
regular testing is performed, the conventional concrete shall meet the
limits of any five of the six applicable uniformity requirements, and the
RCC shall meet the limits of any three of the four applicable uniformity
requirements. When abbreviated testing is performed, the concrete shall
meet only those requirements listed for abbreviated testing. The initial
mixer evaluation test shall be a regular test and shall be performed prior
to the start of concrete placement. The concrete proportions used for the
evaluation shall contain the largest size aggregate on the project and
shall be as directed by the Contracting Officer. Regular testing shall
consist of performing all tests on three batches of concrete. The range
for regular testing shall be the average of the ranges of the three
batches. Abbreviated testing shall consist of performing the required
tests on a single batch of concrete. The range for abbreviated testing
shall be the range for one batch. If more than one mixer is used and all
are identical in terms of make, type, capacity, condition, speed of
rotation, etc., the results of tests on one of the mixers shall apply to
the others, subject to the approval of the Contracting Officer. Mixer
evaluations shall be performed by the Government. The Contractor shall
provide labor and equipment as directed by the Contracting Officer to
assist the Government in performing the tests.
SECTION 03701
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